THIRD TOPICAL WORKSHOP ON PROTON-ANTIPROTON …

C E R N 83-04 10 M a y 1983

O R G A N I S A T I O N E U R O P É E N N E P O U R LA R E C H E R C H E N U C L É A I R E

CERN E U R O P E A N O R G A N I Z A T I O N F O R N U C L E A R R E S E A R C H

THIRD TOPICAL WORKSHOP ON PROTON-ANTIPROTON COLLIDER PHYSICS

Rome, 12-14 January 1983

Organized under the joint sponsorship of Istituto Nazionale di Fisica Nucleare, Rome, and the University of Rome, Italy

PROCEEDINGS Editors: C.Bacci

G. Salvini

G E N E V A

1983

© Copyright C E R N , Genève, 1983

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UNIVERSITÀ DEGL1 STUDi Di R O M A UNIVERSITY O F R O M E

ISTITUTO N A Z I O N A L E Di FÍSICA N U C L E A R E N A T I O N A L INSTITUTE O F N U C L E A R P H Y S I C S

3rd T O P I C A L W O R K S H O P O N P R O T O N A N T I P R O T O N C O L L I D E R P H Y S I C S •

R O M E J A N U A R Y 12-14 1983

R E V I E W A N D P E R S P E C T I V E S A F T E R O N E Y E A R O F P R O T O N - A N T I P R O T O N PHYSICS. R E C E N T D A T A F R O M P R O T O N - A N T I P R O T O N C O L L I D E R S . I N T E R M E D I A T E B O S O N S : T H E O R E T I C A L A N D E X P E R I M E N T A L P R O G R E S S . N E W F L A V O U R S : E X P E R I M E N T A N D T H E O R Y . R E C E N T A D V A N C E S IN T E C H N I Q U E S F O R H I G H E N E R G Y E X P E R I M E N T S . F U T U R E C O L L I D E R S .

• n. cAaieeo • P. DARftfULAT • o cum » §. ÛA8ATHULER • M. L. LEDERMAN • C RUBilA • G SALVINI • A. ZlCmCHI

« C 8ACCI • 8. BORGIA • S CUNSOLO (Bimotor of th» m-tttum of Pñyston -Chairman)

• S. CT ANGELO • L, PAOLUZt

Address request tor information and invitations to: Prof C 8ACCI 3-rd Topical Workshop on proton antiproton collider Physics istitulodi m m *Q. Marconi. PI« Atoo Moco. 2-00185 Rom» - Italia

Previous Wats/topa mm held at Coltaga d» Franc« (1$W) and al Macti$0n(1981)

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ABSTRACT

The Third Topical Workshop on Proton-Antiproton Collider Physics — after the first at College de France, in 1979, and the second at Madison, W i s e , in 1981 — was held in Rome from 12 to 14 January 1983. The proceedings of this last meeting are reported here.

The workshop was devoted to a discussion of the experimental results at 540 GeV (CERN SPS Collider) and 60 GeV (CERN ISR) centre-of-mass energy. A number of events were observed in two experiments, UA1 and UA2, which could be interpreted as the first evidence for the existence of the intermediate vector boson W*. The jet structure of events with high transverse energy was fully confirmed. A number of theoretical reports explored the present agreement with QCD and the future steps beyond the present standard theories. A review of present and future high-energy machines, and a comparison between e + e ~ and pp colliders, was made through a round-table discussion and a number of reports by experts directly involved.

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F O R E W O R D

These are the Proceedings of the 3rd Topical Workshop on Proton-Antiproton Collider Physics.

The previous Workshops were held at Paris, Collège de France, in 1979, and at Madison (USA), in 1981. This Workshop in Rome, the third, covered the experimental results obtained up to December 1982, with the CERN Intersecting Storage Rings (ISR) and the Super Proton Synchrotron (SPS) used as proton-antiproton colliders. It was expected, and it was very clear both during the Workshop and after, that this Rome meeting would be very important; and in fact it will take a significant place in the history of elementary particles for at least two reasons. The first is that the total luminosity of the SPS collider during 1982 has allowed the exploration of events in the 100-1000 picobarn region ( 1 0 ~ 3 3 to 10~ 3 I + c m 2 ) . This means that for the first time we could explore "Electroweakland", and go directly on to verify whether these Intermediate Vector Bosons, foreseen in 1967, really exist.

The second reason is the discovery of some basic simple structure in the proton-antiproton collisions at high transverse energy.

Events with isolated electrons of large p T were presented at this meeting, for the first time, by the two experiments, UA1 and UA2. These same events are now accepted as evidence for W + production and subsequent lepton decay. This conclusion was not firmly stated at the Rome meeting because of an understandable caution on the part of the groups, and because a complete analysis (in particular on the W mass) was not yet available.

For possible future interest we consider it convenient to publish, together with the papers connected with the W + and submitted by the rapporteurs of UA1 and UA2 after the end of the Conference, the copy of the transparencies presented in their talk.

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As is well known, two papers on the observation of the W have been submitted to an international Journal. One can see that all the experimental data were presented at the Rome Workshop: it is really worth noticing the speed with which the data were analysed and the physics interpreted considering the complexity of the collisions and the sophistication of the detectors.

Finally, let us say that the three unforgettable days of this Rome Workshop have increased our confidence in the capacity of the European countries to work together efficiently in the most advanced fields of science and technology.

* * *

We gratefully acknowledge the financial support of the Scientific Institutions and other Authorities that made this Workshop possible.

Special thanks are due to Mrs. Gigliola Gori, to Mrs. Mirella Keller and to Mr. Bruno Pellizzoni for the very efficient assistance and secretarial work before, during, and after the conference.

The Advisory and the Organizing Committees

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CONTENTS

Foreword vii Wednesday, 12 January 1983:

Chairmen L. Van Hove and L.Ii. Lederman 1 G. Salvini3

Introduction 3 M. Calvetti3

Physics at CERN collider using a "minimum bias" trigger 10 C. Conta3

Inclusive charged and neutral particle production and search for relativistic particles with fractional electric charge at the CERN pp collider 50

D.E. Ward, Review of results from the UA5 experiment 75

G. Ekspong3

Multiplicity correlations in pp collisions at 540 GeV 112 C. Rubbia3

Experimental observation of isolated large transverse energy electrons with associated missing energy 123

P. Darriulatj Preliminary searches for hadron jets and for large transverse momentum electrons at the SPS pp collider 190

G. Matthiae3

Elastic scattering and total cross-section at the CERN collider 237

G. Cavboni, Measurements of cr t o t, da e^/dt and event distributions in pp and pp collisions at /s = 31, 53, and 63 GeV 251

D. Favart3

Measurement of small angle pp and pp elastic scattering at the CERN intersecting storage rings 270

L. Camïl1evL3

Recent large transverse momentum results from the ISR 282

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Thursday, 13 January 1983: Chairmen S. Van der Meer and E. Gabatkuler 291

F. Ceradinij Small angle elastic scattering at the CERN proton-antiproton collider 293

A.V. Tollestrupj Fermilab pp collider 313

A. Martin, Elastic scattering and total cross-section 351

G. Altarelli, QCD and pp collider physics 372

J. Sass3

Observation and study of jets at high pj with UA1 central calorimetry 393

Round-table discussion on "Hadron colliders versus e + e -

colliders": Chairman N. Cabïbbo 405

E. Picasso, A contribution to the discussion 407

A. Ziohidhi Hadron colliders versus e + e ~ colliders 409

Friday, 14 January 1983: Chairmen E. Amaldi3 A. Astbury3 G. Brianti 433

A. Z-iohi-ohij New flavours: experiment versus theory. From charm to the 4th family 435

M. Consoliy Precision prediction for the intermediate vector boson parameters 478

M. Veltman3

Physics above 100 MeV 489 M. Greco3

Production of transverse energy ( E x ) in hadron collisions 496 G. Panoheri,

QCD radiation and the multiplicity distribution at the collider 503

L. Van Hove3

Hot hadronic matter and pp collider 514 R. Barbierï,

Weak interactions in the region of the Fermi scale 518 G. Preparatas

"Reasonable" expectations for hadroproduction at collider energies 525

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M. Jacob, Hadronic jets 538

G. Brianti, Introduction to "Practical and foreseeable limitations in usable luminosity for colliders" 553

S. van der Meert

Practical and foreseeable limitations in usable luminosity for the collider 555

C. Rubbia, Future of pp colliders 562

N. CabibbOt What next? 567

L.M. Lederman,

Conclusions and future perspectives 575

List of participants 581

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I N T R O D U C T I O N

by G. Salvini

We are here to get the first significant fruits of an enterprise which might have looked too difficult or i m p o s sible six years a g o . Our p r e s e n t day p r o t o n - a n t i p r o t o n physics is the second act in the p h y s i c s of matter colliding with a n t i m a t t e r , which has always had Europe among the p r o t a g o n i s t s . The first act was the physics of e + e ~ c o l l i d e r s . Let me go through some main h i s t o r i c a l steps and forgive me for recalling the role of this Institute and of Italy in p a r t i c u l a r .

- It is in this p l a c e , not exactly the walls but the Institute of Physics in the U n i v e r s i t y of R o m e , that E n r i c o Fermi in 1933 (half a century ago) wrote an h i s t o r i c a l work of a few p a g e s : "The first theory of weak i n t e r a c t i o n s " . ^ * '

In March 1960 Bruno T o u s c h e k , professor in this I n s t i t u t e , proposed at F r a s c a t i ^ ^ ' the first e + e~ ring ADA (Anello di A c c u m u l a z ione ) . (I was then director of F r a s c a t i , and I am proud for having favoured and e n c o u r a g e d as much as possible the starting of this d e v e l o p m e n t ) . Physicists and technicians of the L a b o r a t o r i e s of Frascati started immediately for a r e a l i z a t i o n which is one of the fastest in the history of m a c h i n e s : ADA was ready in F e b r u a r y 1961.

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1961-1963 are the b e a u t i f u l years with ADA in Orsay and the intense Italo-French c o l l a b o r a t i o n ' ^ ^ .

Preparation of ACO starts in 1964. In 1966 the h i s t o r i c a l physics of ACO and the companion Russian VEP b e g i n s . The j> , uo i f V e c t o r M e s o n s , on the theoretical line of the still partially true Vector D o m i n a n c e , were thoroughly studied (it is the occasion here to remember

i ( 4 our unforgettable i n s p i r e r J. S a k u r a i ) v

Construction of A D O N E , e + e ~ 3 GeV colliding ring, starts in 1963. ADONE is ready in 1969.

- 1970: the physics of ADONE b e g i n s . The expected e l e c t r o magnetic desert is filled with hadronic t r e e s . It is the multihadronic p r o d u c t i o n , in part expected after the results from S L A C ^ ^ ^. U n f o r t u n a t e l y nature was not generous to us: our maximum energy was 3 GeV c.m., but

has a mass of 3070 + .1 M e V / c 2 and the r meson has a mass of 1784 + 3 M e V / c 2 •

1973 and after: it is the glorious physics of SPEAR, DORIS, PETRA, PEP. It is the beginning of the r e v o l u t i o n of our times and I have not to recall it here . Let me only recall that December 1974 issue of P h y s . Rev. L e t t e r s , announcing J ^ from more than two s o u r c e s , with the Editorial hailing the n e w c o m e r ' ^ ' .

But the second act of m a t t e r - a n t i m a t t e r (from e + e~ to pp ) had already started during the s i x t i e s .

In 1966 G.I.Budker' " p r o p o s e s electron cooling, a method to collimate a n t i p r o t o n s in order to realize p r o t o n -antiproton c o l l i s i o n s . I remember the interest for his proposal (I first heard it at Saclay, on Sept. 1 9 6 6 ) , in the eyes of the ADA builders and in m e . In the same

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period Budker exposed his very advanced ideas during a visit in F r a s c a t i .

1966-68: the stochastic cooling is proposed by S.Van der M e e r ' ® ^ . Both methods for cooling antiprotons became successful in these last ten y e a r s , as we know.

1976: We arrive at the recent times of p r o t o n - a n t i p r o t o n with the proposal of C . R u b b i a , D . C l i n e , P . M c I n t y r e ' ^ ' to use big SPS machines as c o l l i d e r s .

In 1977 a complete project started at CERN to use CERN SPS as a collider. This has been an operation of many e n g i n e e r s , p h y s i c i s t s and t e c h n i c i a n s , with C.Rubbia and S.Van der Meer as p r o t a g o n i s t s . We know that Carlo R u b b i a was the main link between the m a c h i n e and the e x p e r i m e n t s .

Preparation of four e x p e r i m e n t s , UA1 , U A 2 , U A 4 , U A 5 , started in 1978, and their basic structure and role shall be recalled at this m e e t i n g , together with the recent r e s u l t s .

In the middle of 1981 we had the first indication that proton antiproton was not a dream: the p-p i n t e r a c t i o n s were clearly coming and well separated from the beam gas i n t e r a c t i o n s .

In the last part of 1981 we had the first p r o t o n - a n t i -9 6 — 2

proton events, with a still low luminosity (»10 cm s ) ; but this was already enough to get some h u n d r e d thousands events, and to p u b l i s h altogether more than 10 original scientific p a p e r s , between U A 1 , UA2 , U A 4 , U A 5 . Some people sitting in this room honestly thought that we were mad in hoping to enter "picoland" , that is to

_ O -3 O

succeed in m e a s u r i n g c r o s s - s e c t i o n s less than 10 J J c m ,

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w i t h t h i s " a r r a n g e d " p p a c c u m u l a t o r , d e r i v e d f r o m t h e

S P S .

A n d n o w w e a r e h e r e at t h e b e g i n n i n g of 1 9 8 3 . T h i s

m e e t i n g c o m e s j u s t a f t e r a s u c c e s s f u l y e a r 1 9 8 2 : in f a c t _ i

w e h a d a t o t a l l u m i n o s i t y of 26 n b a n d y o u w x l l h e a r

t h e r e s u l t s w i t h i n t h i s e v e n i n g .

A s a l w a y s in t h e s e e n t e r p r i s e s w h i c h o p e n a n e w w o r l d ,

s c i e n t i f i c or g e o g r a p h i c in n a t u r e , w h a t is i m p o r t a n t is

d e t e r m i n a t i o n , c h a r a c t e r , a n d w h a t I s h a l l c a l l s p l e n d i d

f o r s e e i n g v i s i o n , e v e n b e y o n d o r d i n a r y l o g i c a n d

e x p e c t a t i o n . T h i s w a s t h e c a s e of t h e f i r s t t e a m p r o p o s i n g

p p . B u t it is a l s o t r u e t h a t w e s t a r t e d (or h a d t o s t a r t )

p e r h a p s w i t h t o o m o d e s t or i n s u f f i c i e n t p r e t e n s e s , a n d w e

i n c r e a s e d g r a d u a l l y o u r r e q u e s t s : a m e t h o d w h i c h d o e s n o t

a l w a y s m a x i m i z e l o v e a n d c o n f i d e n c e f r o m d i r e c t o r s a n d

c o m p e t i t o r s .

T h e f i r s t s k e t c h e d p r o j e c t f o r t h e s t u d y of p p

i n t e r a c t i o n s a n d f o r t h e p r o d u c t i o n of W , Z w a s c o n s i d e r i n g

t h e p o s s i b i l i t y of k e e p i n g t h e e x p e r i m e n t w i t h i n t h e m a x i m u m

d i m e n s i o n s of t h e a l r e a d y e x i s t i n g t u n n e l of t h e S P S , b y

u s i n g a d e n s e h i g h s u p e r c o n d u c t i n g m a g n e t , a n d a c o n d e n s e d

T u n g s t e n o r U r a n i u m c a l o r i m e t e r .

T h e n e x t w a s an e n l a r g e m e n t of t h e t u n n e l u p t o a w i d t h

of 8 m e t e r s , b u t it w a s c l e a r l y t o o s m a l l . T h e n G i o r g i o

B r i a n t i o f f e r e d u s 12 m e t e r s , a n d w e f o u n d it s l i g h t l y

i n s u f f i c i e n t . T h e n B r i a n t i a r r i v e d a t 20 m , n o t o n e cm m o r e !

O . K . , G i o r g i o ! W e s h a l l w a l l o w in i t ! G o a n d s e e , n o w ! N o t

m a n y c e n t i m e t e r s a r e l e f t . Of c o u r s e , I am r e f e r r i n g t o U A 1 .

I t m a y b e t h a t o t h e r e x p e r i m e n t s h a d n o t so m a n y p r o b l e m s as

w e h a d , t a k i n g a l s o t h e a d v a n t a g e of c o m i n g a l i t t l e l a t e r

a n d h a v i n g m o r e s p e c i f i c g o a l s .

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Brianti asked us about the c a b l e s . When we made our first too modest requests he laughed at them. Look now, he was right. Many persons thought in 1977-78 that we were u n d e r e s t i m a t i n g our own a p p e t i t e , and that to satisfy it was a bit d a n g e r o u s . But I wish to say (this is a p e r s o n a l view) that as a matter of fact CERN accepted the c h a l l e n g e . I wish to appreciate this fact very much, p e r s o n a l l y , as I did three years ago.

We shall know now within one day what we really grasped. It may be that people will go home without k n o w i n g yet if they, the two g i a n t s , W- and Z° , are in sight, ready to welcome our e x p e r i m e n t a l visit. But we know one thing, already: in this 1982 we have entered E l e c t r o w e a k land. We know this for our e x p e r i m e n t s are clear enough to m e a s u r e neatly cross sections below one nanobarn , and this is the main point. We can now put clear questions to N a t u r e in this domain.

We know also that we are just starting a long road. We can be more ambitious than to have a simple yes or no on the existence of the Intermediate Vector B o s o n s : we'll have in future to verify the existence or not of Higgs and heavy f l a v o u r s , and to find agreement or not with Q C D . N o t h i n g will be obvious or easy. We know that p h y s i c a l reality, even when expectations are confirmed, jumps over us in u n e x p e c t e d ways .

As you see in the program, we are going to have a round table on e + e~ versus p p . This should be very i n t e r e s t i n g . This comparison is a point of reference of our future, but it could even become a turning p o i n t . We hope to have discussions and comments from the floor, and criticism. At the basis of these comparisons and of what we are doing, there is the p r e c i s i o n of our m e a s u r e m e n t s (Fig. 1 ) and the quality of the SPS C o l l i d e r . The fact is that the formula of our progress is very simple.

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/ s s

/

u F ( * * < o

> /O CAK S

S h o u l d t h e r e s o l u t i o n of e a c h of t h e q u a n t i t i e s l i s t e d

in t h i s f i g u r e b e w o r s e b y a f a c t o r t w o or t h r e e , n o n e w

r e s u l t s c o u l d be p o s s i b l e . A n d I c a n s a y t h a t a l s o t h e s o m e

t i m e f e r o c i o u s o b s t i n a c y of e a c h of t h e f o u r h o u n d r e d

p e r s o n s i n v o l v e d in g r a s p i n g e v e r y l i t t l e b i t of p r e c i s i o n

a n d r e s o l u t i o n in a n y d e t a i l , f r o m l e n g t h of c a b l e t o d r i f t

v e l o c i t y , w a s t h e h a r d a n d r i g h t w a y to p r o c e e d .

I w a s n e v e r so i n t e r e s t e d a n d c u r i o u s . A n d I c o n s i d e r

m e l u c k y f o r b e i n g h e r e . S o m a n y p e r s o n s u n d e r s t a n d a n d s e e

b e t t e r a n d m o r e t h a n m e in t h i s r o o m . B u t t h e f u t u r e of

t h e s e t h i n g s , s u r p r i s e s , e x p e r i m e n t a l d e v e l o p m e n t s , is

b e y o n d t h e c a p a c i t y of a s i n g l e m a n , w h a t e v e r m a y be h i s

v a l u e . P h y s i c s is a r a g i n g a n d g e n e r o u s t i g e r , a n d it is

d i f f i c u l t t o r i d e o n i t .

My TO success: ptxeanoA/

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p o s i t r o n S t o r a g e R i n g s . S a c l a y , S e p t e m b e r 2 6 - 3 0 ( 1 9 6 6 ) .

(8) S t a f f o f t h e CERN p p p r o j e c t ; P h y s . L e t t . 1 0 7 B , ( 1 9 8 1 ) , 3 0 6 .

(9) C.Rubbia, P.McIntyre and D.Cline, Proceedings International Neutrino Conference, Aachen (1976) (Vieweg, Braunshweig, 1 9 7 7 ) , p . 6 8 3 .

A n d t h e n l e t m e e x p r e s s a w i s h : m a y it be t h a t w e a r e

e n t e r i n g a l a n d m u c h w i d e r t h a n e x p e c t e d , a n d w h i c h c a n n o t

b e c o v e r e d b y e a c h of us . E u r o p e a n f o r c e s a n d t h e f o r c e s of

a l l o t h e r C o n t i n e n t s m u s t t h e r e f o r e j o i n o n t h e i r e f f o r t s ;

e v e n so it c o u l d be t h a t w e a r e n o t e n o u g h .

W h o c a n d a r e s a y t o d a y w h e r e w e w i l l h a v e a r r i v e d i n

1 9 8 6 , e v e n t w o y e a r s b e f o r e L E P s h a l l be r e a d y ?

- 10 -

PHYSICS AT THE CERN COLLIDER USING A "MINIMUM BIAS" TRIGGER

Aachen 1 -Annecy (LAPP ) 2 -B i rmingham 3 -CERN ** -He 1 s inki 5 -QMC, London 6 -Par i s (Coll. de France) 7-Riverside 8-Roma 9-Rutherford Appleton L a b . 1 0 -

Saclay (CEN) 1^Vienna 1 2 Collaboration

U A 1 Collaboration

Presented by M. Calvetti

10 10 2 .9 ** % G. Armson , A. Astbury , B. Aubert , C. Bacci , G. Bauer , A. Bézaguet ,

R. Bock1*, T . J . V . Bowcock', M. Calvett i" , T . Carrol l" , P. Catz*, P. Cennini",

S. Centro", F. Ceradini", S. C i t t o l i n " , D. Cline**, C. Cochet 1 1 , J . Colas 2 ,

M. Corden', D. Dallman 1 2 , M. DeBeer 1 1, M. Deila Negra*, M. Demoulin",

Denegri 1 1 , A. Di Ciaccio', D. DiBitonto", L. Dobrzynski7, J . D . Dowell', M. Edwards, 1 6 t 1 . 1 . 7

K. Eggert , E. Eisenhandler , N. E l l i s , P. Erhard , H. Faissner , G. Fontaine , R. Frey", R. Frühwirth 1 2 , J . Garvey*, S. Geer ?, C. Ghesquière?,

2 1 S 7 . 1 1 P. Ghez , K.L. Gibom , W.R. Gibson , Y. Giraud-Héraud , A. Givernaud ,

A. Gonidec2, G. Grayer 1 0 , P. Gutierrez*, T . Hansl-Kozanecka1, 10 * o i •> W.J. Haynes , L.O. Hertzberger , C. Hodges , D. Hoffmann , H. Hoffmann , ic 3 S H H 6

D.J. Holthuizen , R.J. Homer , A. Honma , W. Jank , G. Jorat , P . I .P. Kalmus , S S 3 0 S . t

V. Karimäki , R. Keeler , I . Kenyon , A. Kernan , R. Kmnunen , H. Kowalski , W. Kozanecki', D. Kryn", F. Lacava", J . - P . Laugier 1 1 , J . - P . Lees 2, H. Lehmann1,

1 11 . . 2 .11 11 , 1 1 K. Leuchs , A. Lévêque , D. Linglin , E. Locci , M. Loret , J . - J . Malosse ,

T . Markiewicz", G. Maurin", T . McMahon', J . - P . Mendiburu', M.-N. Minard 2, S . H " I .10 i %

M. Moricca , H. Muirhead , F. Muller , A.K. Nandi , L. Naumann , A. Norton ,

A. O r k i n - L e c o u r t o i s L . Paoluzi ' , G. Petrucci", G. Piano Mortari ' , M. Pimiä*,

A. Placci", E. Radermacher1, J . Ransdell', H. Reithler 1 , J . - P . Revol", J . R i c h 1 1 ,

M. Rijssenbeek", C. Roberts 1 ' , J . Rohlf", P. Rossi", C. Rubbia", B. Sadoulet", 7 .c . .S 11 . 1 1 11 G. Sajot , G. Salvi , G. Salvim , J . Sass , J . Saudraix , A. Savoy-Navarro ,

D. Schinzel", W. Scott 1 ", T .P. Shah 1 ' , M. Sp i ro 1 1 , J . Strauss 1 2 , K. Sumorok*,

F. Szoncso 1 2, D. Smith', C. Tao", G. Thompson', J . Timmer", E. Tscheslog 1,

J . Tuominiemi*, S. Van der Meer", J . - P . Vial le" , J . Vrana', V. Vuillemin",

H.D. Wahl 1 2 , P. Watkins', J . Wilson', G.Y. Xie", M. Yvert*, E. Zurfluh" * NIKHEF, Amsterdam, The Netherlands ** University of Wisconsin, Madison, Wisconsin, USA

- 1 1 -


T h e r e s u l t s o b t a i n e d b y t h e U A 1 c o l l a b o r a t i o n a t t h e C E k N

p r o t o n - a n t i p r o t o n c o l l i d e r h a v e b e e n p r e s e n t e d i n m a n y c o n f e r e n c e s ( R e f . 1 ) .

T h a t g i v e s me t h e o p p o r t u n i t y t o d e s c r i b e o u r r e s u l t s w i t h o u t e n t e r i n g t o o

m u c h i n t h e d e t a i l s o f t h e e x p e r i m e n t a l a p p a r a t u s o r t h e t e c h n i c a l i t i e s o f t h e

d a t a a n a l y s i s .

T h e d a t a h a v e b e e n c o l l e c t e d i n O c t o b e r - N o v e m b e r 1 9 8 1 w i t h a t y p i c a l 2 7 _ 2 _ i

l u m i n o s i t y o f A, 10 cm s f o r a t o t a l i n t e g r a t e d l u m i n o s i t y _ i

o t 2 0 ub . T h e t r i g g e r w a s p r o v i d e d b y t w o s e t o f s c i n t i l l a t o r c o u n t e r s

l o c a t e d a t 3 m a n d 6 . 2 m f r o m t h e i n t e r a c t i o n r e g i o n , c o v e r i n g a n a n g u l a r

r a n g e i r o m 5 m r a d t o 3 0 0 m r a d ( . F i g . 1 ) ( 2 < l nl < 5 n = p s e u d o r a p i d i t y ) .

P a r t i c l e s p r o d u c e d i n a p p c o l l i s i o n c r o s s t h e t r i g g e r c o u n t e r s a t t h e s a m e

t i m e , w h i l e p a r t i c l e s p r o d u c e d u p s t r e a m o f t h e d e t e c t o r ( b e a m - g a s ,

b e a m - l o s s e s ) h i t t h e c o u n t e r s a t d i f f e r e n t t i m e s .

T h e t i m e - o f - f l i g h t w a s h e n c e u s e d t o s e l e c t r e a l i n t e r a c t i o n s t o g e t h e r

w i t h t h e c o n d i t i o n t o h a v e t h e p r o t o n a n d a n t i p r o t o n b u n c h e s c r o s s i n g e a c h

o t h e r i n t h e c e n t r e o f t h e d e t e c t o r ( b e a m p i c k - u p ) , toe e s t i m a t e o n t h e b a s i s

o í t h e o b t a i n e d p s e u d o r a p i d i t y d i s t r i b u t i o n t h a t w e w e r e c o l l e c t i n g a b o u t 9 5 %

o f t h e t o t a l i n e l a s t i c c r o s s - s e c t i o n w h i l e t h e s i n g l e d i f f r a c t i o n p r o c e s s e s , * )

w e r e n o t a e t e c t e a .

I n t h i s p a p e r t h e p h y s i c s o f t h e e v e n t s c o l l e c t e d u s i n g t h i s " m i n i m u m b i a s

t r i g g e r " i s d e s c r i b e d . A f t e r a b r i e f d e s c r i p t i o n o f t h e d e t e c t o r , I w i l l

p r e s e n t r e s u l t s c o n c e r n i n g p a r t i c l e p r o d u c t i o n ( p s e u d o r a p i d i t y d i s t r i b u t i o n s ,

m u l t i p l i c i t y a n d K N O s c a l i n g ) . T r a n s v e r s e e n e r g y d i s t r i b u t i o n s , l o n g a n d s h o r t

r a n g e c o r r e l a t i o n s , a n d f i n a l l y h i g h p t p h y s i c s a n d j e t s .

T H E b F / l E C T O R

A s c h e m a t i c o f t h e UA1 d e t e c t o r i s s h o w n i n F i g . 2 . T h e p r o t o n b u n c h e s c o m e i n

f r o m l e f t a n d t h e a n t i p r o t o n b u n c h e s f r o m t h e r i g h t . T h e y c r o s s e a c h o t h e r i n

t h e c e n t r e o f t h e d e t e c t o r . C h a r g e d t r a c k s a r e m e a s u r e d w i t h t h e c e n t r a l d r i f t

* ) ( T h i s i s n o t c o m p l e t e l y t r u e b e c a u s e t h e d i f f r a c t i o n p r o d u c t i o n o f h i g h

m a s s e s , a s i n d i c a t e d b y t h e UA4 e x p e r i m e n t , c o u l d p r o d u c e p a r t i c l e s i n t h e

b a c k w a r d d i r e c t i o n t r i g g e r i n g t h e d e t e c t o r . T h i s h a s t o b e b e t t e r

u n d e r s t o o d , b u t c l e a r l y s i n g l e d i f f r a c t i o n e v e n t s a r e s t r o n g l y s u p p r e s s e d ) .

- 1 2 -

c h a m b e r s w h i c h a r e i n s i d e a u n i f o r m h o r i z o n t a l d i p o l e f i e l d o f 0 . 7 T e s l a . T h e

r e a d o u t e l e c t r o n i c s p r o v i d e a c o m p l e t e d i g i t a l i m a g e o f e a c h e v e n t .

A n a v e r a g e o f 1 0 0 p o i n t s i n s p a c e a r e m e a s u r e d a l o n g e a c h t r a c k ( d r i f t

t i m e c o o r d i n a t e a = 3 0 0 u , c h a r g e d i v i s i o n a = 3 c m ) , a n d t h e s p e c i f i c

e n e r g y l o s s i n t h e g a s i s a l s o m e a s u r e d p r o v i d i n g p a r t i c l e i d e n t i f i c a t i o n

c a p a b i l i t y . I h e c e n t r a l d e t e c t o r i s s u r r o u n d e d b y e l e c t r o m a g n e t i c

c a l o r i m e t e r s . T h e s e a r e f o r m e d b y P b - s c i n t i l l a t o r s a n d w i c h e s ( 2 5 r . J J w h i c h

a r e r e a d o u t f r o m f o u r l o n g i t u d i n a l s a m p l e s e n a b l i n g t h e s h a p e o f t h e

l o n g i t u d i n a l d e v e l o p m e n t o f a s h o w e r t o b e m e a s u r e d . T h e e x t e r n a l h a d r o n

c a l o r i m e t e r ( 5 X) i s b u i l t f r o m s c i n t i l l a t o r p l a t e s i n s e r t e d i n t o t h e

l a m i n a t e d y o k e o f t h e m a g n e t ( t w o s a m p l e s i n d e p t h ) . F i n a l l y t h e h a d r o n

c a l o r i m e t e r s a r e s u r r o u n d e d b y u - c h a m b e r s ( 8 l a y e r s o f d r i f t t u b e s ) .

I n t h e f o r w a r d d i r e c t i o n b o t h d r i f t c h a m b e r s a n d c a l o r i m e t r y e x t e n d d o w n o

t o l e s s t h a n 1 w i t h r e s p e c t t o t h e b e a m d i r e c t i o n . T h e U A 1 d e t e c t o r i s

c h a r a c t e r i s e d b y t h e e x c e l l e n t d e t e c t i o n a n d m e a s u r e m e n t o f c h a r g e d

t r a c k s , 4 i r c a l o r i m e t r y a n d y d e t e c t i o n i n t h e c e n t r a l r e g i o n . A g e n e r a l

d e s c r i p t i o n o f t h e c a l o r i m e t r y i s g i v e n i n F i g . 3 .

A N G U L A R D I S T R I B U T I O N

T h e a n g u l a r d i s t r i b u t i o n a n d t h e m u l t i p l i c i t y o í t h e c h a r g e d t r a c k s h a v e

b e e n m e a s u r e d u s i n g t h e c e n t r a l d r i f t c h a m b e r s . T h e y a r e o b t a i n e d f r o m a

s a m p l e o f <\, 8 0 0 0 e v e n t s c o l l e c t e d w i t h o u t m a g n e t i c f i e l d i n o r d e r t o

s i m p l i f y a c c e p t a n c e c o r r e c t i o n s . I n t h e p l a n e o r t h o g o n a l t o t h e m a g n e t i c f i e l d

( x - y p l a n e ) , w h e r e t h e t r a c k f i n d i n g i s p e r f o r m e d ( F i g . 4 ) , t h e p o i n t s a l o n g a

t r a c k a r e m e a s u r e d w i t h v e r y g o o d a c c u r a c y ( a x >\, 2 0 0 u i o r t h e w i r e

p o s i t i o n s , a y ^ 3 0 0 u f o r t h e d r i f t t i m e c o o r d i n a t e ) .

T h e p r e c i s i o n o f t h e d e t e c t o r , c o m p a r e d w i t h i t s d i m e n s i o n , i s s o g o o d

t h a t t h e t r a c k f i n d i n g e f f i c i e n c y i s c o n s t a n t a t 9 6 ± 1% i n d e p e n d e n t o f t h e

c o m p l e x i t y ( m u l t i p l i c i t y ) o f t h e e v e n t s . T h e p s e u d o r a p i d i t y o f a p a r t i c l e i s

d e f i n e d a s :

n = - fcnUg e/2)

w h e r e 6 i s t h e a n g l e b e t w e e n t h e o u t g o i n g t r a c k a n d t h e b e a m d i r e c t i o n .

A n g u l a r d e p e n d e n t c o r r e c t i o n s f o r y c o n v e r s i o n i n t h e b e a m - p i p e

( 3 X | n l < 1 . 2 5 u p t o 15% f o r 3 . 2 5 < l n | < 3 . 5 ) a n d n u c l e a r i n t e r a c t i o n

( 1 % t o 97a) h a v e b e e n a p p l i e d . T h e c o n t r i b u t i o n f o r s t r a n g e p a r t i c l e s d e c a y s

- 13 -

i s f a i r l y u n i f o r m i n p s e u d o - r a p i d i t y a t a b o u t 4 % . T h e l o w m o m e n t u m c u t - o f f

c a u s e d b y p a r t i c l e s s t o p p i n g i n t h e v a c u u m p i p e w a l l s r e m o v e l e s s t h a n 1% o f

t h e t r a c k s . T h e o b t a i n e d p s e u d o - r a p i d i t y d e n s i t y d i s t r i b u t i o n i s s h o w n i n F i g .

5 . T h e h e i g h t o f t h e p l a t e a u a t n—0 i s

I t r e p r e s e n t s a n 80% i n c r e a s e f r o m I S R e n e r g i e s ( / s = 63 G e V ) . T h e r i s e o f

t h e r a p i d i t y p l a t e a u v s t h e t o t a l e n e r g y i n t h e c m . s y s t e m ( F i g . 6 ) i s

c o n s i s t e n t w i t h a l i n e a r d e p e n d e n c e f r o m l o g s . T h e p s e u d o - r a p i d i t y r a n g e i s

n o t f i l l e d u n i f o r m l y . T h e p l a t e a u i n c r e a s e o n l y 2 u n i t s o í n o u t o f t h e 4 . 6

e x t r a u n i t s a v a i l a b l e ( c o m p a r e d w i t h I S R ) . A t t h e c o l l i d e r e n e r g y a n e n h a n c e d

p a r t i c l e s p r o d u c t i o n i n t h e c e n t r a l r e g i o n i s o b s e r v e d . T h e i n t e n s i t y o f t h e

e f f e c t i s a l s o m u l t i p l i c i t y d e p e n d e n t ( a s a l r e a d y o b s e r v e d a t t h e I S R ) . F i g . 7

s h o w s t h e p s e u d o - r a p i d i t y d i s t r i b u t i o n s f o r d i f f e r e n t m u l t i p l i c i t i e s .

B o t h t h e I S R a n d t h e c o l l i d e r d a t a s h o w t h e s a m e q u a l i t a t i v e f e a t u r e s ,

n a m e l y a c e n t r a l d i p a t l o w m u l t i p l i c i t y w h i c h d i s a p p e a r s i n g o i n g t o h i g h

m u l t i p l i c i t i e s a n d a s h r i n k i n g o r t h e d i s t r i b u t i o n w i t h i n c r e a s i n g

m u l t i p l i c i t y .

M U L T I P L I C I T Y A N D K.N0 S C A L I N G

A n o t h e r i m p o r t a n t i n f o r m a t i o n w h i c h m a y b e e x t r a c t e d f r o m " m i n i m u m b i a s

e v e n t s " i s t h e f l u c t u a t i o n o f t h e n u m b e r o f c h a r g e d t r a c k s p r o d u c e d i n a p p

i n t e r a c t i o n . I t i s i n t e r e s t i n g t o c o m p a r e w i t h t h e r e s u l t s o b t a i n e d a t l o w e r

e n e r g i e s t o s e e w h e t h e r o r n o t a n e w m e c h a n i s m i s r e s p o n s i b l e f o r t h e p a r t i c l e

p r o d u c t i o n .

D a t a a r e p r e s e n t e d u s i n g t h e K N O v a r i a b l e n / < n > w h e r e < n > i s t h e

a v e r a g e n u m b e r o f c h a r g e d t r a c k s p r o d u c e d . K N O s c a l i n g c l a i m s t h a t t h e

t o p o l o g i c a l c r o s s - s e c t i o n s a a r e s u c h t h a t :

a i n < n > — — = u; (

° T 0 1 \ < n >

w h e r e i s e n e r g y i n d e p e n d e n t

- 1 4 -

< n > < n > 2 1 / 2

D l < n ( n - l ) > - < n > ] '

2 < ( n - < n > ) >

Y 2 - 2 < n >

i _ < ( n - < n > ) >

Y j S < n >

•l 2 2 < ( n - < n > ) - 3 < ( n - < n > ) > >

k

< n >

t h e y m e a s u r e t h e d i s p e r s i o n ( Y J ) , t h e s y m m e t r y ( 7 2 ) t h e s k e w n e w s s ( y , )

a n d t h e e x t e n s i o n o f t h e t a i l ( y H ) o f t h e d i s t r i b u t i o n . We h a v e c a l c u l a t e d t h e

m o m e n t s u s i n g t h e o b s e r v e d m u l t i p l i c i t y d i s t r i b u t i o n f o r I n l < 3 . 5 t h e r e s u l t s a r e

s h o w n i n F i g . 9 w h e r e t h e y a r e c o m p a r e d w i t h t h e I S R d a t a .

I n s p i t e o f t h e f a c t t h a t K N O s c a l i n g s h o u l d b e v a l i d t o r t h e t o t a l

m u l t i p l i c i t y a n d n o t i n t h e r e s t r i c t e d r a p i d i t y r a n g e ( I n l < 3 . 5 ) u s e d i n

t h i s a n a l y s i s , n o c h a n g e o f t h e Y ~ M O M E N T S f r o m t h e I S R t o t h e c o l l i d e r i s

o b s e r v e d K N O . S c a l i n g i s s a t i s f i e d .

C O R R E L A T I O N S

A n o t h e r i n t e r e s t i n g f e a t u r e o f t h e m i n i m u m b i a s e v e n t s i n t h e p r e s e n c e o f

s h o r t a n d l o n g r a n g e c o r r e l a t i o n s . I f N _ a n d N + a r e t h e n u m b e r o f

I n F i g . 8 a r e s h o w n t h e o b s e r v e d m u l t i p l i c i t y d i s t r i b u t i o n s f o r t h e t w o

r a p i d i t y r a n g e s . T h e d o t t e d l i n e i n F i g . 8 b ) i s t h e S l a t t e r y ( R e t . 2 ) f i t t o

t h e F N A L d a t a ( e n e r g y ) w h i l e t h e d e G r o o t f o r m u l a , d e r i v e d t h e o r e t i c a l l y f r o m

a n u n c o r r e l a t e d c l u s t e r m o d e l , i s a g o o d r e p r e s e n t a t i o n o f t h e I S R r e s u l t s .

B o t h a r e c o m p a r e d w i t h o u r d i s t r i b u t i o n . T h e d e G r o o t f o r m u l a i s a b e t t e r

d e s c r i p t i o n f o r l a r g e m u l t i p l i c i t i e s w h e n t h e r e s u l t s a r e l e a s t s e n s i t i v e t o

a c c e p t a n c e e f f e c t s . N o t e t h a t f o r I n l < 1 . 5 ( F i g . 8 a ) t h e d i s t r i b u t i o n

a p p e a r s t o b e f l a t t e r t h a n f o r I n l < 3 . 5 .

T h i s i s a g a i n a c o n s e q u e n c e o f t h e f a c t t h a t e v e n t s w i t h h i g h e r m u l t i p l i c i t y

t e n d t o h a v e m a n y p a r t i c l e s e m i t t e d i n t h e c e n t r a l r e g i o n . A m o r e q u a n t i t a t i v e

w a y t o c o m p a r e t h e s h a p e o f t h e d i s t r i b u t i o n s a t d i f f e r e n t e n e r g i e s i s t o u s e

t h e m o m e n t o f t h e \Ji f u n c t i o n . We u s e t h e Y ~ n l o m e n t s d e f i n e d a s :

- 15 -

p a r t i c l e s o b s e r v e d i n o n e e v e n t in two s y m m e t r i c i n t e r v a l s of p s e u d o - r a p i d i t y

(Fig. 10) t h e n w e o b s e r v e t h a t :

< N _ > = A + B N +

w h e r e B is the c o r r e l a t i o n s t r e n g t h , B=0 m e a n s no c o r r e l a t i o n a t all ( F i g .

1 1 ) . In F i g . 12 the m e a s u r e d slope p a r a m e t e r s a r e c o m p a r e d w i t h the r e s u l t s at

the IbK. A s w e c a n s e e b o t h long a n d s h o r t r a n g e c o r r e l a t i o n s i n c r e a s e w i t h

e n e r g y .

T R A N S V E R S A kN.EK.GY D I S T R I B U T I O N

C A L O R I M E T R Y

A s c h e m a t i c of the UA1 c e n t r a l c a l o r i m e t r y c o v e r i n g the a n g u l a r r e g i o n o o

5 < 6 < 175 , is s h o w n in F i g . 13. T h e b a r r e l e.m. c a l o r i m e t e r

is m a d e o f 24 s e m i c y l i n d r i c a l c o u n t e r s o n e a c h side of the b e a m s . E a c h of t h e 0 0

e n d - c a p e.m. c a l o r i m e t e r s (5 < 6 < 25 ) c o m p r i s e s 32 r a d i a l

s e c t o r s . T h e d e t e c t o r m e a s u r e s t r a n s v e r s e e n e r g y d i r e c t l y s i n c e the r e a d o u t is o

a t 6=25 a n d t h e a t t e n u a t i o n l e n g t h of the s c i n t i l l a t o r has b e e n c h o s e n o o

t o m a t c h the v a r i a t i o n of s i n e b e t w e e n 5 a n d 25 . A p o s i t i o n

d e t e c t o r , 11 r. A d e e p in the e n d - c a p c a l o r i m e t e r p e r m i t s the r e c o n s t r u c t i o n

of the e n e r g y o f f - l i n e . T h e h a d r o n c a l o r i m e t e r is a l s o s e g m e n t e d in 232

i n d e p e n d e n t c e l l s , the g r a n u l a r i t y d e p e n d i n g o n the d i s t a n c e f r o m the b e a m as

s h o w n in F i g . 13. F o r any e v e n t a total of 1184 i n d e p e n d e n t e n e r g y d e p o s i t i o n s

a r e m e a s u r e d . F o r e a c h cell w e d e f i n e a n e n e r g y v e c t o r w i t h its o r i g i n at the

i n t e r a c t i o n v e r t e x , p o i n t i n g to the c e n t r e of the c e l l and w i t h a n a m p l i t u d e

e q u a l to the m e a s u r e d e n e r g y . T h e total t r a n s v e r s e e n e r g y is d e f i n e d as :

£ „ s I E , sine. T i l i

w h e r e 6^ i s the a n g l e b e t w e e n the e n e r g y v e c t o r a n d t h e b e a m a x i s .

T h e a b s o l u t e e n e r g y c a l i b r a t i o n of o u r c a l o r i m e t e r s (± 3% e . m . , ± 5%

h a d r o n i c ) h a s b e e n o b t a i n e d in e x t e n d e d m e a s u r e m e n t s in a test b e a m u s i n g ji,

ir, p a n d e a t d i f f e r e n t e n e r g i e s . T h e e n e r g y r e s p o n s e is m o n i t o r e d w i t h a 4

C u r i e C o s o s o u r c e for the e.m. c a l o r i m e t e r s . T h e r e s p o n s e of the h a d r o n

c a l o r i m e t e r is m o n i t o r e d u s i n g c o s m i c ray m u o n s a n d 3 s o u r c e w h i c h c a n b e

p l a c e d in r e p r o d u c i b l e p o s i t i o n s . D e s p i t e the h i g h c e n t r e - o t - m a s s e n e r g y a t

http://kN.EK.GY

- 16 -

t h e c o l l i d e r , t h e l l A l c e n t r a l c a l o r i m e t e r s m e a s u r e m o s t l y l o w e n e r g e t i c

p a r t i c l e s ( < 1 G e V ) . T h e m i n i m u m b i a s e v e n t s a r e i n d e e d c h a r a c t e r i s e d b y

m a n y p a r t i c l e s o f l o w m o m e n t u m . L o w e n e r g e t i c p i o n s l o s e a n e n e r g y d e p e n d e n t

f r a c t i o n o f t h e i r e n e r g y i n t h e e l e c t r o m a g n e t i c s e c t o r . T o g e t t h e t o t a l

e n e r g y w e u s e a c o r r e c t i o n f a c t o r t o t h e m e a s u r e d " e l e c t r o m a g n e t i c e n e r g y "

b e f o r e a d d i n g u p t h e m e a s u r e d h a d r o n i c e n e r g y : E = „R + R W E

IUI em H*

h a v e u s e d a n a v e r a g e c o r r e c t i o n o n t h e b a s i s o f t h e m e a s u r e m e n t w i t h t h e

t e s t - b e a m , b u t t h i s e f f e c t t o g e t h e r w i t h t h e n o n - l i n e a r r e s p o n s e o f t h e h a d r o n

c a l o r i m e t e r a t l o w e n e r g y , i n t r o d u c e a s c a l e u n c e r t a i n t y i n s u m m e d t r a n s v e r s e

e n e r g y E^, o f ^ 3.5%.

R E S U L T S

D a t a w e r e t a k e n w i t h o u t m a g n e t i c f i e l d . T h e o b t a i n e d t r a n s v e r s e e n e r g y

d i s t r i b u t i o n s a r e s h o w n i n F i g . 14 t o r d i f f e r e n t p s e u d o - r a p i d i t y r a n g e s . T h e

a v e r a g e v a l u e o f t h e t r a n s v e r s e e n e r g y s c a l e w i t h t h e |nI r a n g e c o n s i d e r e d .

T h e t r a n s v e r s e e n e r g y i s d e p o s i t e d u n i f o r m l y i n t h e a v a i l a b l e n r a n g e I til

< 3 . T h e e x p o n e n t i a l t a i l e x t e n d i n g u p t o v e r y h i g h e n e r g i e s i s d u e t o t h e

p r e s e n c e o f v e r y h i g h m u l t i p l i c i t y e v e n t s a s s h o w n i n F i g . 15 w h e r e t h e m e a n

t r a n s v e r s e e n e r g y i s p l o t t e d v s t h e o b s e r v e d c h a r g e d m u l t i p l i c i t y . T h e t a i l o f

t h e E^ d i s t r i b u t i o n i s a c o n s e q u e n c e o f t h e m u l t i p l i c i t y f l u c t u a t i o n r e l a t e d

t o t h e K N O s c a l i n g , t h e l a r g e E T a r e b u i l t u p b y m a n y p a r t i c l e s w i t h l o w

e n e r g y . I f w e p l o t E^ a s a f u n c t i o n o f t h e K N O t y p e v a r i a b l e E T / < E T >

w e o b t a i n a d i s t r i b u t i o n s i m i l a r t o t h e i|i f u n c t i o n . ( F i g . 1 6 ) .

T h e m e a n t r a n s v e r s e e n e r g y p e r o b s e r v e d c h a r g e d t r a c k i n c r e a s e s w i t h

m u l t i p l i c i t y . C o n s i d e r i n g t h e f a c t t h a t a l s o n e u t r a l s a r e p r o d u c e d w e c a n s a y

t h a t t h e a v e r a g e t r a n s v e r s e e n e r g y p e r p a r t i c l e i s s m a l l e r t h a n 1 G e V ( F i g .

1 6 b ) . T h e m u l t i p l i c i t y d e p e n d e n c e o f t h e a v e r a g e E^, p e r t r a c k h a s b e e n a l s o

d i r e c t l y m e a s u r e d f o r c h a r g e d t r a c k s u s i n g t h e m a g n e t i c f i e l d a s d e s c r i b e d i n

t h e n e x t c h a p t e r .

P_t D I S T R I B U T I O N

T h e i n c l u s i v e p^ i n v a r i a n t c r o s s - s e c t i o n h a s b e e n m e a s u r e d f o r c h a r g e d

t r a c k s i n t h e r a p i d i t y r a n g e I y I < 2 . 5 , a n d f o r n e u t r a l s ( I T , y , y )

f o r 1 . 6 < y < 2 . 5 . T h e d i s t r i b u t i o n ( F i g . 1 7 ) , h a s b e e n n o r m a l i s e d t o a

t o t a l n o n - d i f t r a c t i v e i n e l a s t i c c r o s s - s e c t i o n o f 4 0 mb a n d h a s b e e n c o r r e c t e d

f o r t h e f i n i t e e x p e r i m e n t a l r e s o l u t i o n .

- 17 -

W e o b s e r v e a n i n c r e a s e o f 3 o r d e r o f m a g n i t u d e a t 10 G e V / c w i t h r e s p e c t t o

t h e I S R i n a g r e e m e n t w i t h Q C D p r e d i c t i o n s ( R e f . 3 ) . T h e m e a n i s <\,

4 2 4 M e V / c t o b e c o m p a r e d w i t h t h e I S R v a l u e o f 3 5 7 M e V / c . F i g . 18 s h o w s a n

e m p i r i c a l f i t t o o u r d a t a , u s i n g t h e f o r m u l a :

d cr A p , E — =

d p ( p t+ P t ° ) n

t h e s a m e e x p r e s s i o n c a n f i t a l s o t h e I S R d a t a , s e e T a b l e . 1 .

T h e p t s p e c t r u m i s s h o w n i n F i g . 19 f o r d i f f e r e n t m u l t i p l i c i t y d e n s i t i e s

a n d i t g i v e s d i r e c t e v i d e n c e f o r s t r o n g c o r r e l a t i o n b e t w e e n m u l t i p l i c i t y a n d

P t , a s s u g g e s t e d b y c a l o r i m e t r i c m e a s u r e m e n t . T h e m e a n , a s

d e t e r m i n e d f r o m t h e i n v a r i a n t c r o s s - s e c t i o n , i n c r e a s e s l i n e a r t y w i t h

i n c r e a s i n g m u l t i p l i c i t y u n t i l a t <\, 4 6 0 M e V / c i t a p p e a r s t o s a t u r a t e ( F i g .

2 0 ) .

T h e i n c l u s i v e p t s p e c t r u m f o r n e u t r a l p a r t i c l e s ( n , n> y) i n t h e

r a p i d i t y r a n g e 1 . 6 < l y l < 2 . 5 i s s h o w n i n F i g . 2 1 . T h e m e a s u r e m e n t h a s

b e e n m a d e u s i n g t h e e n d - c a p e l e c t r o m a g n e t i c c a l o r i m e t e r , l o o k i n g f o r e . m .

e n e r g y d e p o s i t i o n n o t a s s o c i a t e d t o c h a r g e t r a c k s m e a s u r e d i n t h e c e n t r a l

d e t e c t o r ( F i g . 2 2 ) . T h e r e s u l t i n g n e u t r a l e l e c t r o m a g n e t i c p t s p e c t r u m i s i n

c o m p l e t e a g r e e m e n t w i t h t h e c h a r g e d p a r t i c l e p t s p e c t r u m . T h e v a l u e o f t h e

c r o s s - s e c t i o n a n d t h e s h a p e o f t h e d i s t r i b u t i o n a r e i n a g r e e m e n t w i t h Q C D

e x p e c t a t i o n s .

C O R R E L A T I O N S

C o r r e l a t i o n s b e t w e e n p a r t i c l e s w i t h l a r g e t r a n s v e r s e m o m e n t u m h a v e b e e n

o b s e r v e d a t t h e I S R a s w e l l a s a t t h e c o l l i d e r e n e r g y w h e r e t h e F e y n m a n x^,

i s q u i t e s m a l l e r :

X T = 2 P t / ' / s < 0 , 0 4

We d e f i n e t h e " t r i g g e r " p a r t i c l e i n o n e e v e n t a s t h e p a r t i c l e w i t h t h e l a r g e s t

t r a n s v e r s e m o m e n t u m . We r e q u i r e p t m a x > 4 G e V / c . T h e p l a n e o r t h o g o n a l t o

t h e t r i g g e r d e f i n e s t w o h e m i s p h e r e s ; t h e t o w a r d h e m i s p h e r e , w h e r e t h e t r i g g e r

i s , a n d t h e a w a y h e m i s p h e r e . F i g . 2 3 s h o w s t h e d i s t r i b u t i o n o f t h e r a p i d i t y

- 1 8 -

d i f f e r e n c e b e t w e e n t h e t r i g g e r p a r t i c l e , a n d t h e s e c o n d a r i e s i n t h e t o w a r d

s i d e f o r d i f f e r e n t p £ c u t s . T h e h i g h e r t h e p t o f t h e s e c o n d a r i e s t h e

s m a l l e r i s t h e r a p i d i t y d i s t a n c e f r o m t h e t r i g g e r . I n o n e e v e n t t h e p a r t i c l e s

i n t h e s a m e h e m i s p h e r e w i t h t h e l a r g e s t p t h a v e a l s o s i m i l a r r a p i d i t i e s . T h e

c l u s t e r i n g o f p a r t i c l e s w i t h l a r g e p t i s a i s o e v i d e n t f r o m F i g . 24 w h e r e t h e

a z i m u t h a l d i s t a n c e o f a l l t h e s e c o n d a r i e s f r o m t h e t r i g g e r p a r t i c l e i s p l o t t e d .

S e c o n d a r i e s w i t h l a r g e p t a r e c o p l a n a r w i t h t h e t r i g g e r a n d t h e b e a m

d i r e c t i o n ( p a r a l l e l o r a n t i p a r a l l e l t o t h e t r i g g e r ) . T h e y a n d 9 c o r r e l a t i o n s

a r e s h o w n i n F i g . 2 5 . I t i s i m p o r t a n t t o n o t e t h a t p a r t i c l e s i n t h e a w a y s i d e

a r e c o r r e l a t e d ( o p p o s i t e ) t o t h e t r i g g e r i n <p ( a z i m u t h ) , b u t n o t i n 0

r a p i d i t y . A t 1 8 0 f r o m t h e t r i g g e r t h e s h a p e o f t h e Ay d i s t r i b u t i o n d o e s

n o t c h a n g e i f t h e p t C u t i s i n c r e a s e d . O n t h e o t h e r h a n d , i f w e d e f i n e a

s e c o n d t r i g g e r p a r t i c l e i n t h e a w a y s i d e , t h e n w e d i s c o v e r t h e s a m e k i n d o f

r a p i d i t y c o r r e l a t i o n s b e t w e e n t h e a w a y t r i g g e r a n d t h e a w a y s e c o n d a r i e s ( F i g .

2 6 ) . T h i s i s a l l i n q u a l i t a t i v e a g r e e m e n t w i t h t h e p i c t u r e o f h a r d s c a t t e r i n g

a m o n g t w o c o n s t i t u e n t s ( c o p l a n a r i t y ) , f o l l o w e d b y t h e i n d e p e n d e n t

f r a g m e n t a t i o n o f t h e t w o p a r t o n s ( s a m e s i d e y - c o r r e l a t i o n s ) .

JETS

T h e i n v a r i a n t c r o s s - s e c t i o n a t h i g h p f c a n d t n e p r e s e n c e o f h i g h p f c

c o r r e l a t i o n i s a f i r s t i n d i c a t i o n o f t h e h a r d p a r t o n s c a t t e r i n g t h a t s h o u l d

l e a d t o t h e o b s e r v a t i o n o f e v e n t s w i t h j e t s i n t h e f i n a l s t a t e . T h e b e s t w a y

t o l o o k f o r j e t s i s t o u s e t h e c a l o r i m e t r y b e c a u s e t h e e n e r g y f l o w i s s o m e w h a t

l e s s d e p e n d e n t f r o m t h e f r a g m e n t a t i o n p r o c e s s t h a n t h e o b s e r v a t i o n o f c h a r g e d

t r a c k s o n l y .

We l o o k e d t o r e v e n t s w i t h l o c a l i s e d t r a n s v e r s e e n e r g y d e p o s i t i o n , a n d w e

f o u n d a r a t e t h a t i s n o t c o m p a t i b l e w i t h s t a t i s t i c a l f l u c t u a t i o n o f t h e u s u a l

m i n i m u m b i a s p a r t i c l e s p r o d u c t i o n . T h i s s t u d y i s p o s s i b l e b e c a u s e o f t h e

c o m p l e t e s o l i d a n g l e c o v e r a g e o f t h e L A I d e t e c t o r ( t r a c k i n g a n d c a l o r i m e t r y ) .

T h e s e a r c h t o r j e t s h a s b e e n p e r f o r m e d u s i n g t h e c e n t r a l c a l o r i m e t r y

( e l e c t r o m a g n e t i c + h a d r o n i c 2 5 < 6 < 1 6 5 , A«p = 2 I R ) F i g . 2 7 .

We i n t r o d u c e a n o p e r a t i o n a l d e f i n i t i o n o f a j e t i n t e r m s o f e n e r g y

d e p o s i t i o n i n t h e c a l o r i m e t e r c e l l s . T h i s i n t r o d u c e s a n a r b i t r a r i n e s s w h i c h

w i l l a f f e c t a n y q u a n t i t a t i v e s t a t e m e n t o n t h e j e t p r o p e r t i e s , b u t w e d o n o t

c a r e n o w b e c a u s e w e w a n t t o s e e s i m p l y i f j e t s e x i s t o r n o t . We u s e t h e w i n d o w

a l g o r i t h m . I n e a c h h a l f s h e l l o f t h e c e n t r a l c a l o r i m e t e r s ( s e e F i g . 2 7 ) a n y

- 19 -

g r o u p o f 8 a d j a c e n t e . m . c e l l s , t o g e t h e r w i t h t h e h a d r o n i c o n e s m a t c h i n g t h e m

i n t h e p r o j e c t i o n d e f i n e s a " w i n d o w " (An ^ 1 ) . We " m o v e t h e w i n d o w " a l o n g

t h e b e a m d i r e c t i o n l o o k i n g f o r t h e w i n d o w w i t h t h e l a r g e s t t r a n s v e r s e e n e r g y

d e p o s i t i o n (E^,^ o n e s i d e YL^2 t h e o t h e r o n e ) .

I f t h e t r a n s v e r s e e n e r g y i n t h e w i n d o w e x c e e d s t w o t h i r d s o f t h e t o t a l

t r a n s v e r s e e n e r g y d e p o s i t e d i n t h a t h a l f - s h e l l , t h e w i n d o w i s s a i d t o c o n t a i n

a j e t . We h a v e e v e n t s w i t h 0 - j e t , o n e - j e t , t w o - j e t s . F i g . 2 8 s h o w s t h e

f r a c t i o n R o f t w o - j e t e v e n t s a s a f u n c t i o n o f t h e t o t a l t r a n s v e r s e e n e r g y . A t

l o w E , j , ( k T < 4 0 G e V ) m o s t o f t h e e v e n t s a r e t h e u s u a l m i n i m u m b i a s

e v e n t s . L o w E^ m e a n s a l s o s m a l l m u l t i p l i c i t y . N o w i f t h e r e a r e f e w p a r t i c l e s

p r o d u c e d i t i s e a s y t o h a v e l o c a l i s e d e n e r g y d e p o s i t i o n ( f o r o n e t r a c k o n l y

t h e e n e r g y i s a l w a y s l o c a l i s e d ) . I n c r e a s i n g E^ a n d h e n c e t h e m u l t i p l i c i t y i t

i s h a r d e r t o h a v e a f l u c t u a t i o n t h a t d e p o s i t s m o s t o f t h e e n e r g y i n o n e

w i n d o w , a n d t h a t i s t h e r e a s o n w h y t h e f r a c t i o n R o f t h e " j e t t y " e v e n t s

d e c r e a s e s f r o m 0 G e V t o < 4 0 G e V E^.. l n a b s e n c e o f j e t s R s h o u l d c o n v e r g e

t o z e r o t o r l a r g e E^,. O n t h e c o n t r a r y t h e f r a c t i o n o f j e t t y e v e n t s i n c r e a s e s

u p t o 80% f o r E T ^ 1 0 0 G e V g i v i n g a c l e a r e v i d e n c e o f t h e f a c t t h a t t h e

l a r g e t r a n s v e r s e e n e r g y e v e n t s a r e d o m i n a t e d b y j e t - p r o d u c t i o n . F i g . 2 9 s h o w s

5 e v e n t s w i t h E^ > i Q O G e V . T h e t w o j e t s s t r u c t u r e i s a l s o s h o w n b y t h e

c o p l a n a r i t y p l o t ( F i g . 3 0 ) .

C O N C L U S I O N S

T h e b a s i c f e a t u r e s o f p a r t i c l e p r o d u c t i o n a t t h e c o l l i d e r e n e r g y a r e t h e

s a m e a s o b s e r v e d a t t h e I S R i n s p i t e o f t h e f a c t o r 10 i n c r e a s e i n t h e t o t a l

e n e r g y . T h e h e i g h t o f t h e r a p i d i t y p l a t e a u i n c r e a s e s l i n e a r l y i n l g s a n d i s a

s i m p l e e x t r a p o l a t i o n o f t h e I S R r e s u l t s ; t h e w i d t h o f t h e r a p i d i t y p l a t e a u

a l s o i n c r e a s e s l i k e l g s . E n h a n c e d c e n t r a l p r o d u c t i o n i s o b s e r v e d i n e v e n t s

w i t h h i g h m u l t i p l i c i t y . T h e l o n g a n d s h o r t r a n g e c o r r e l a t i o n i n c r e a s e s

l i n e a r l y i n l g s b u t b e c a u s e o f t h e d i f f e r e n c e i n s l o p e t h e d i f f e r e n c e b e t w e e n

l o n g a n d s h o r t r a n g e c o r r e l a t i o n i s s m a l l e r . K N O s c a l i n g i s s a t i s f i e d .

A l l t h e s e f a c t s , a n d i n p a r t i c u l a r t h e KNO s c a l i n g , l e a d t o t h e

o b s e r v a t i o n o f s p e c t a c u l a r e v e n t s w i t h m o r e t h a n 1 0 0 c h a r g e d t r a c k s . I n a

s m a l l f r a c t i o n o f t h e e v e n t s , < 1%, t h e h a r d s c a t t e r i n g a m o n g t h e p a n d p

c o n s t i t u e n t s i s m a n i f e s t . C o p l a n a r i t y a n d s a m e - s i d e y c o r r e l a t i o n s a r e

- 20 -

*) The invariant p f c cross-section is in agreement with QCL> prediction as well as the invariant jet cross-section. (Invariant jet cross-section have been presented by J. bass in another talk at this workshop).

observed for high p t particles • The use of the minimum bias trigger together with the 4ir calorimetry proves the existence of jets. The events with large transverse energy are indeed dominated by jet production.

R e f e r e n c e s

- 21 -

R e f . 1. A a c h e n - A n n e c y ( L A P P ) - B i r m i n g h a m - C E R N - L o n d o n ( Q u e e n M a r y C o l l e g e ) - P a r i s

( C o l l è g e d e F r a n c e ) - R i v e r s i d e - R u t h e r f o r d - S a c l a y ( C E N ) - V i e n n a C o l l a b .

" A 4ir S o l i d A n g l e D e t e c t o r f o r t h e S P S u s e d a s a P r o t o n - A n t i p r o t o n

C o l l i d e r a t t h e C e n t r e - o f - M a s s E n e r g y o f 5 4 0 G e V " , p r o p o s a l C E R N / S P S C / 7 8 - 0 6 /

P 9 2 ( 1 9 7 8 ) ;

M . B a r r a n c o L u q u e e t a l . , N u c l . I n s t r u m . M e t h o d s 1 7 6 ( 1 9 8 0 ) 1 7 5 ;

M. C a l v e t t i e t a l . , N u c l . I n s t r u m . M e t h o d s 176 ( 1 9 8 0 ) 2 5 5 ;

K . E g g e r t e t a l . , N u c l . I n s t r u m . M e t h o d s _176 ( 1 9 8 0 ) 2 1 7 , 2 2 3 ;

A . A s t b u r y , P h y s . S c r . 2 3 ( 1 9 8 1 ) 3 9 7 ;

S . C i t t o l i n , " T h e D A 1 D a t a A c q u i s i t i o n S y s t e m " , T a l k I n t e r n . C o n f . o n

I n s t r u m e n t a t i o n f o r C o l l i d i n g B e a m P h y s i c s , ( S L A C , S t a n f o r d , F e b r u a r y ( 1 9 8 2 ) ;

B . S a d o u l e t , " F i r s t R e s u l t s f r o m t h e UA1 D e t e c t o r a t t h e S P S C o l l i d e r " ,

p r e s e n t e d a t X V I I t h R e n c o n t r e d e M o r i o n d ( M a r c h 1 9 8 2 ) ;

P . I . P . K a l m u s , " T h e C E R N P r o t o n - A n t i p r o t o n C o l l i d e r P r o g r a m m e " , p r e s e n t e d a t

I n t . W o r k s h o p o n V e r y H i g h E n e r g y I n t e r a c t i o n s i n C o s m i c R a y s ( U n i v e r s i t y o f

P e n n s y l v a n i a , A p r i l 1 9 8 2 ) C E k N / E P / 8 2 - 5 8 ;

M . C a l v e t t i , " T h e U A 1 C e n t r a l D e t e c t o r " , t a l k a t I n t e r n . C o n f . o n

I n s t r u m e n t a t i o n f o r C o l l i d i n g B e a m P h y s i c s , ( S L A C , S t a n f o r d , F e b r u a r y 1 9 8 2 )

C E k N E P / 8 2 - 4 4 ;

G . A r n i s o n e t a l . , P h y s . L e t t . 1 0 7 B ( 1 9 8 1 ) 3 2 0 ;

G . A r n i s o n e t a l . , " T r a n s v e r s e M o m e n t u m S p e c t r u m o f N e u t r a l E l e c t r o m a g n e t i c

P a r t i c l e s P r o d u c e d a t t h e C E R N P r o t o n - A n t i p r o t o n C o l l i d e r " , C E R N - E P / 8 2 - 1 2 0

P r e s e n t e d t o t h e X X I I n t e r n a t i o n a l C o n f e r e n c e o n H i g h E n e r g y P h y s i c s , P a r i s

2 6 - 3 1 J u l y 1 9 8 2 ;

G . A r n i s o n e t a l . , " S e a r c h f o r C e n t a u r o L i k e E v e n t s a t t h e C E R N P r o t o n -

A n t i p r o t o n C o l l i d e r " , C E R N - E P / 8 2 - 1 2 1 , S u b m i t t e d t o P h y s . L e t t . B .

G . A r n i s o n e t a l . , " T r a n s v e r s e E n e r g y D i s t r i b u t i o n s i n t h e C e n t r a l C a l o r i m e t e r s "

C E R N - E P / 8 2 - 1 2 2 ;

G . A r n i s o n e t a l . , " C h a r g e d P a r t i c l e M u l t i p l i c i t y D i s t r i b u t i o n s i n P r o t o n -

A n t i p r o t o n C o l l i s i o n s a t 5 4 0 G e V C e n t r e o f M a s s E n e r g y " , S u b m i t t e d

t o P h y s . L e t t B ;

D . D i B i t o n t o , " R e s u l t s f r o m E x p e r i m e n t L A I a t t h e C E R N p p C o l l i d e r " ,

C E R N / E P / 8 2 - 1 7 4 , p r e s e n t e d a t t h e 1 0 t h A n n u a l S L A C S u m m e r I n s t i t u t e T o p i c a l

S t a n f o r d , 1 6 - 2 7 A u g u s t 1 9 8 2 ;

- 2 2 -

G . A r n i s o n e t al., P h y s . L e t t . 1 1 8 B ( 1 9 8 2 ) 167 ;

G . A r n i s o n e t a l . , P h y s . L e t t . 1 1 8 B ( 1 9 8 2 ) 173 ;

G . A r n i s o n e t a l . , P h y s . L e t t . 1 2 1 B ( 1 9 8 3 ) 77 ;

G . A r n i s o n e t a l . , " O b s e r v a t i o n o f J e t s i n H i g h T r a n s v e r s e E n e r g y E v e n t s

a t t h e C E k N P r o t o n - A n t i p r o t o n C o l l i d e r " , s u b m i t t e d t o P h y s . L e t t B ;

G . A r n i s o n e t a l . , P h y s i c s L e t t . B 1 2 2 ( 1 9 8 3 ) 1 0 3 .

K e f . 2 . P . S l a t t e r y , P h y s . R e v . L e t t . 29_ ( 1 9 7 2 ) 1 6 2 4 .

E . h . d e G r o o t , P h y s . L e t t . 5 7 B ( 1 9 7 5 ) 1 5 9 .

R e f . 3 . R . O d o r i c o , p a p e r X X I I n t e r n . C o n f . o n H i g h E n e r g y P h y s i c s ( P a r i s , J u l y 1 9 8 2 ) ;

R . P . F e y n m a n , R . D . F i e l d a n d G . C . F o x , P h y s . R e v . D 1 8 ( 1 9 7 8 ) 3 3 2 0 ;

K . H o r g a n a n d M. J a c o b , N u c l . P h y s . B 1 2 9 ( 1 9 8 1 ) ;

G . C . F o x a n d R . L . K e l l y , C a l t e c h r e p o r t C A L T - 6 8 - 8 9 0 ( 1 9 8 2 ) ;

W. T h o m é e t a l . , N u c l . P h y s . B 1 2 9 ( 1 9 7 7 ) 3 6 5 ;

T . K a f k a e t a l . , P h y s . R e v . D 1 6 ( 1 9 7 7 ) 1 2 6 1 ;

C . M . G . L a t t e s e t al., P h y s . R e p . 65_ ( 1 9 8 0 ) 1 5 1 .

- 23 -

Table 1

Data Pt interval used (GeV/e)

A ( 1 0 - 2 4 c m 2 G e V - V )

p t0 n <Pt> (GeV/e)

x2 Degrees of freedom

this work 0.3 - 10 0.47 ± 0.01 1.30 ± 0.20 9.14 ± 0.90 0.424 ± 0.001 51 52 0.3 - 2 0.46 ± 0.01 1.30 fixed 9.14 ± 0.02 0.424 ± 0.001 29 32 2 - 10 0.37 ± 0.06 1.30 fixed 8.99 + 0.15 0.435 ± 0.012 20 19

Alper et al. (s/s = 63 0.1 - 2.0 0.28 ±0.01 1.30 fixed 10.7 ± 0.03 0.340 ± 0.002 59 18 GeV) .0.22 ± 0.01 1.83 ± 1.24 13.3 ± 6 0.356 ± 0.002 11 17

QCD 2 - 4 0 1.30 fixed 8.33 calculation 0.80 8.02

Fit parameters of Ed3o¡d?p = AptoUpt + Pt 0 )" at y/s = 540 GeV for different bands of charged track multiplicity. The fits were made for the region 0 < Pt < 6 GeV/c, with p T 0 fixed at 1.30.

n/Ay in/Ay A ( 1 0 - 2 4 c m 2 G e V - 2 c 3 )

n (pt> (GeV/c)

x 2 Degrees of freedom

0.6 - 1 0.8 0.009 ± 0.001 11.02 ± 0.20 0.325 44 32

1 - 2 1.5 0.042 ± 0.001 10.41 ± 0.08 0.352 61 42

2 - 3 2.5 0.063 ± 0.001 10.17 ± 0.05 0.363 77 44

4 - 5 4.9 0.066 ± 0.001 9.45 ± 0.05 0.404 49 45

7 - 8 7.5 0.040 ± 0.001 8.87 ± 0.05 0.444 45 45 9 - 10 9.5 0.024 ± 0.001 8.64 ± 0.06 0.462 42 44

12 - 14 12.8 0.011 ±0.0004 8.48 ± 0.08 0.476 38 45 14 - 16 14.9 0.004 ± 0.0002 8.67 ± 0.14 0.459 54 43

Fit parameters of Ed3a/d3p = Ap"ol(Pt + Pto)": (a) For UA1 data at Vs = 540 GeV, (b) For ISR data at ^ = 63 GeV [ 4 ] . (c) For QCD prediction M y/s = 540 GeV [ 6 ] . Quoted errors are purely statistical. Projected (marginal) errors are given for p° and n since they are highly correlated

- 24 -

M i n i m u m B i a s t r i 6 & e r

~ 3 * « «ir/ orí- / Ö ^ - V 4t* 3 W 4 a r A J L

\ ~ 7

i

O R . Y

F,<¡2

- 26 -

C A L O R I JA E T R Y

v a l o r

F0RWA«.O

X

1c« Fe

• 29 X 0 -

fcir*n Se -

C A L C O A S

12.2 X

M cm Fe

3 0 X 0

2mm Pt 2mm Sc

I ' *

5"e,m. Fe.

23- X 0

MmmPfc G mm Sc

5.8 X

5 C M FE.

2 ¿ X 0 -1.2 mm Pb. 1.5mm Sc -

o.2° o.r ' B o u c h o n ' ' G o n d o l a .

c | o 0

E.m. 0.15 VF

0.1S V I F

0 . 1 2 .

7 1 7 0 1 S V E 1

VT

- 27 -

i • Th i s Expt

O UA5 (A)

tt I S R (11)

U BaLLoani Data (2 Î A P P l

FNiAL C l 4 í

ù.

JO 100

Ti" G e V

u v a *

I I IM5-

1000

111***

20

10

* ! • *

d n

4

t 4

t

t t t t t

n ?50 í * + t • • • I ¿ t l < n $ S O T

• • •

• t T t 21<¿n<30

M M n<n< 2 0

t t t t 6 < n ¿10

t

T T

1 1 > 0 <n<5

1.0 2 - 0

i l l

3 - 0

• t f

- 29 -

H 10-

10"

de Croot Slottery

1.0 2.0 fl/<n> Î o

1 0 - 1 '

(b) 7) <ï 3.5

1.0

<*>;m "/<»>

F i a 8

III

3 0

i ' r

0 5 -

0 4 -

0 3 -

0-4 -

0 2 -

0 0 -

04

0 2 h

00

• • •

ISR (11) UA1

S

© --I 1 L

10 20 50 100 200 500 s/s GeV

.28

.24

.20

.14

.10

.06

.08

.04

0

41 M *

t . t<

ß> .

Yl T Serpukhovl A„ -X FNAL *' 1 • I S R J • U A l | N | < 3 . 5 ^ (b)

H t ©

V

- I — i,.

F .g3

10 20 50 100 200 500 vT GeV

- 30 -

S H O R T

M.

/—!^ / £ -*-3 -2. -i f i l l rm

> 1 Z 3 « t 3*+

8 s CoRRÉLATi©*» STftfA/ôTtf

L Ö H 6

- 31 -

- 32 -

In-T TTTII'I ill 111 TTTTT

+

— =F + + — + —

A -A B-B C - C

Barret hadron+EM End-Cap EM End-Cap hàdron

The UA1 central calorimeters

Central calorimeter characteristics

Calorimeter Sampling step Thickness3^ Depth segments in read-outa)

Solid angle coverage Cell size Resolution

e.m.

barrel

1.2 mm lead

1.5 mm scintillator

26 X„ 3.3:6.6:9.9:6.6 X 0 25° < 8 < 155°

$ ^ 2TT

A8 -v- 5°

-V, TT

0.1SAÎ

e.m.

end-cap

4.0 mm lead

6.0 mm scintillator

27 X 0 4:7:9:7 X 0 5° < 8 < 25"

t> 2TI

A8 -v. 20 s

A* -v- 11*

0.12/ZEj.

Hadron

barrel

S m iron

1 cm scintillator

4.9 X 2.5:2.5 X 25° < 8 < 155'

$ "v- 2ir

Hadron end-cap

5 m iron 1 cm scintillator

7.1 X 3.5:3.5 X 5' < 8 < 25" $ -x. 2ir

0.8//Î

a) X 0 • radiation length, X - absorption length.

F , , 1 5

- 33 -

E T D I & T M S U T I Q N

JL2L < 3 A<£ = 2TT

J i

-m a

10

p Fox a Kelly 2 t = ( Q C D < E T > = 2 4 , 4 G e V

no hodronization)

-O

E

LU

b

9 ° g < E T > = 11.3 GeV

G « 9 8 c t < E T > = l 3 , I G e V » lT7l < 1.5» o 1.5 <|77| < 3

' • 8 A<£ = 27T

I O O P i O if

IQ"2 = -

< E T > = 7,2 GeV J77J = 5 . 4 G e V ln l<0.75 B ~ \ Ad3 = 27T T

j r \ \ • •

- 1 \ N A 5 • VS = 2 4 GeV T T è * -Ï

X - it t * , 1 100

- 34 -

kOQ

Í > O

LU V

10 20 30 40 50 60 Observed Mult fckftv^tJ^

F'3 1 5

2

O 1 2 3 4 5

z = E T / < E T >

- 36 -

: D \ EdV/d 3 p [cm 2c 3Gev" 2] |~d

d\ + (h H - fh - )/2 |y|<2.5 UA1

0 2 4 6 8 P T G e V / c

Fij.tt

F . j . 1 8

- 38 -

Ed 3 c r /d 3 p I c m V G e v " 2 ]

a a a

Vi

- 9 -

• H + + + + + +1+

1 i

'TT-A <n/Ay>=10.2

• <n/Ay>=5.7

• <n/Ay>=2.4

T

P T G e V / c

f., 19

- 39 -

 G e v / c

0 . 5 2

0 . + 8

i " 1 U i " 1 U

i—

0 . 4 +

c » c c . f ? T > : < « j i « V c

OA i

0 . 3 6 -è Global A v e r a g e s : •

0 This e x p e r i m e n t : 5 4 0 G e v

^ p p ISR : 6 3 G e v R e f s 3 a / 8

• p p F N A L : 19.6 G e v + v e s Ref 9

0 . 3 2 4

o p p F N A L : 19.6 G e v

I I i i i

- v e s Ref 9

0 . 2 . 5 5 . 7 . 5 1 0 . 1 2 . 5 1 5 . 1 7 . 5 2 0 .

N u m b e r of C h a r g e d Particles / Unit of Rapidity

F ¡ 3 2 0

- 40 -

f= A ' -

4 *

E d 3 c r / d 3 p

. 5 6 T e s l a

++.

+

4*

+ (h++h")/2 !y|<2.5 UA1 a 7 ^ + 7 7 + 7 1.6<|y|<2.5 UA1 A (h++h")/2 90° 53GeV BS o TT0 90° 63GeV CCOR • 7T° 90° 63GeV OCRS • (h++h")/2 50° 63GeV CDHW

P T

8

G e V / c 10 12 14

F . j 2 i

U A 1 C o l l a b o r a t i o n P B A R - P a t 5 4 0 G e V

3 2 « e c * ttf

X + 10%

tot*

POSITION SC.TZCTÛH.

F . q . 2 2

- 42 -

T R I G G E R p t A B O V E 4- G e V / c

( T O W A £ ß S H E M I S P H E R E )

S E C O N D A R Y p, A B O V E 0 Tftictf ft

S E C O N D A R Y p t A B O V E 1 G e V / c

S E C O N D A R Y p t A B O V E 2 G e V / c

T R i t t e * CXCU/OED

F . 8 . 2 3

- 43 -

TRIGGER p, A 3 OVE + GeV/c

SECONDARY p t ABOVE 0

O 40 SO 12Q 160 A4»

SECONDARY p t ABOVE 1 GeV/c

80 120 160 A4»

SECONDARY p t ABOVE 2 GeV/c

80 120 160 A4>

- 44 -

- 4 5 -

J I I I L - + - 2 0 2 I

- 46 -

7 A 7 ? - o . ? s r

o n Pr , r K . s l J e . (£>Ç*=~tr)

lilt*-*

Ao X vT \ ! 2 -1 J J i k il t-f

24- / \ -Í 24- / \ -Í 24- / \ -Í 24- / \ -Í 1111V J il-C w WFViT msiiifi

Ao /.¡.\i U

2l\ ELH CELLS

Ao m£> CELLS

6 ELM C s a S - f 3 HR2>CSUS

ft'pc/ aíwOíj S 3. c h a f e s lO / K iTVcríC ET-> 5

F . , . 2 *

- 47 -

10" -27

> <u O * 10'

~ I0" 3 0

^ i o - 3 2

0.8

c

0.6

o

_ 0.4 o c o

o út 0.2

i 1 1 1 1 r— a) TOTAL TRANSVERSE ENERGY DISTRIBUTION

b )

2 0 4 0 6 0 80 l E T (GeV)

ICO 120

- 48 -

Transverse energy flow of the 5 events with ZET>IOOGeV

Et max 8.6 GeV

CM O

»i id

Number of events r <

P

I M

- 50 -

A b s t r a c t - W e p r e s e n t r e s u l t s on the p r o d u c t i o n of c h a r g e and n e u t r a l particles at large angle at an energy ^s* = 540 G e V . N o e v i d e n c e h a s b e e n found for the e x i s t e n c e of light r e l a t i v i s t i c q u a r k s .

M e m b e r s of the UA2 C o l l a b o r a t i o n : M. B a n n e r , P h . B l o c h , F. B o n a u d i , K. B o r e r , M. B o r g h i n i , J.-C. C h o l l e t , A . G . C l a r k , C. C o n t a , P. D a r r i u l a t , L. Di L e i l a , J. D i n e s - H a n s e n , P.-A. D o r s a z , L. F a y a r d , M. F r a t e r n a l i , D. F o i d e v e -a u x , J.-M. G a i l l a r d , D. G i l d e m e i s t e r , V . G . G o g g i , H. G r o t e , B. H a h n , H. H a n n i , J.R. H a n s e n , P. H a n s e n , T. H i m e l , V. H u n g e r b u h -l e r , P. J e n n i , O. K o f o e d - H a n s e n , M. L i v a n , S. L o u c a t o s , B. M a d -s e n , P. M a n i , B. M a n s o u l i ë , G . C . M a n t o v a n i , L. M a p e l l i , B. M e r k e l , M. M e r m i k i d e s , R. M o l l e r u d , B. N i l s s o n , C. O n i o n s , G. P a r -r o u r , F. P a s t o r e , H. P l o t h o w - B e s c h , N . P r e v o t , J.-P. R e p e l l i n , A. R o t h e r n b e r g , A. R o u s s a r i e , G. S a u v a g e , J. S c h a c h e r , J.L. Sie g r i s t , F. S t o c k e r , J. T e i g e r , V. V e r c e s i , H.H. W i l l i a m s , H. Zac c o n e , W . Zeller and A. Z y l b e r s t e j n .

I N C L U S I V E C H A R G E D A N D N E U T R A L P A R T I C L E P R O D U C T I O N A N D S E A R C H F O R R E L A T I V I S T I C

P A R T I C L E S W I T H F R A C T I O N A L E L E C T R I C C H A R G E A T T H E C E R N p p C O L L I D E R

The UA2 C o l l a b o r a t i o n * ^ (Univ. B e r n , C E R N , N B I C o p e n h a g e n ,

L A L O r s a y , Univ. and INFN P a v i a , CEN Saclay)

Presented by: C. Conta

INFN and U n i v e r s i t y of P a v i a , Italy

1.- I N T R O D U C T I O N

T h e U A 2 e x p e r i m e n t ( 1 ) , i n s t a l l e d at t h e C E R N p p c o l l i

d e r ( 2 ) , t o o k t h e first d a t a at t h e end of t h e 1 9 8 1 .

The m a i n g o a l o f t h e e x p e r i m e n t is to d e t e c t the w e a k interme

d i a t e b o s o n s Z ° and W ~ in their e l e c t r o n i c d e c a y m o d e s :

- o o o + -p p + Z + X Z e + e

- + - + + p p -»• W - + X + W - -* e- + v(v)

For t h i s r e a s o n e l e c t r o n i d e n t i f i c a t i o n is instrumented o v e r

8 0 % of t h e t o t a l solid a n g l e by l e a d - s c i n t i l l a t o r s a n d w i c h c o

u n t e r s , p r o v i d i n g an acceptenceof = 7 0 % . H a d r o n d e t e c t i o n is al

so i n s t r u m e n t e d in t h e c e n t r a l r e g i o n by iron-scintillator sand

w i c h c o u n t e r s in o r d e r to study high-r^ h a d r o n j e t s .

T h e o r y (3) p r e d i c t s an e l e c t r o n - p o s i t r o n asymmetry in t h e o o

W d e c a y , w i t h a s i g n i f i c a n t signal b e t w e e n 20 and 30 . The U A 2

f o r w a r d - b a c k w a r d (F/B) s p e c t r o m e t e r s c o v e r the polar a n g u l a r re

g i o n s from 2 0 ° to 37.5° and from 14 2.5° to 1 6 0 ° w h e r e a t o r o i

dal m a g n e t is i n s t r u m e n t e d : t o g e t h e r w i t h a h i g h a c c u r a c y v e r

tex d e t e c t o r , t h e F/B d r i f t c h a m b e r s a l l o w c h a r g e m e a s u r e m e n t s

on e l e c t r o n s u p t o 60 GeV/c m o m e n t u m .

A n a z i m u t h a l w e d g e of 3 0 ° , o p e n e d in t h e central c a l o r i m e

t e r , is e q u i p p e d as a m a g n e t i c s p e c t r o m e t e r w i c h is very u s e

ful to i n v e s t i g a t e p h e n o m e n a of r e l a t i v e l y h i g h cross s e c t i o n

such as i n c l u s i v e charged and n e u t r a l p a r t i c l e p r o d u c t i o n at

r e l a t i v e l y h i g h p ^ and new stable c h a r g e d p a r t i c l e s w i t h or

w i t h o u t f r a c t i o n a l c h a r g e .

2. E X P E R I M E N T A L A P P A R A T U S

A n p l a n v i e w of t h e U A 2 d e t e c t o r is shown in F i g . 1 .

- 52 -

T h e m e a s u r e m e n t of t h e i n t e r a c t i o n p o i n t and of t h e p a r t i c l e

t r a j e c t o r i e s in a b s e n c e of m a g n e t i c field is a c h i e v e d b y m e a n s

o f the v e r t e x d e t e c t o r which consists of four m u l t i w i r e p r o p o r

t i o n a l c h a m b e r s (MWPC) w i t h h e l i c o i d a l c a t h o d e strip r e a d - o u t ,

two J a d e - t y p e d r i f t s c h a m b e r s w i t h 24 cells e a c h , for a t o t a l

of 288 w i r e s e q u i p p e d w i t h m u l t i h i t r e a d - o u t a n d c h a r g e d i v i s i o n ,

24 s c i n t i l l a t i o n c o u n t e r s , a r r a n g e d as a c y l i n d r i c a l h o d o s c o p e ;

a fifth M W P C , p r e c e d e d b y 1.5 r a d i a t i o n lenghts o f t u n g s t e n .. is

u s e d for shower l o c a l i z a t i o n in front of the e l e c t r o m a g n e t i c

c e n t r a l c a l o r i m e t e r . F o r t h e r e s u l t s p r e s e n t e d h e r e t h e i n f o r

m a t i o n s from the v e r t e x d e t e c t o r is used to s e p a r a t e pp e v e n t s

from b a c k g r o u n d and to d e t e r m i n e t h e c o l l i s i o n p o i n t w i t h a

p r e c i s i o n of ± 1 m m a l o n g t h e b e a m l i n e .

T h e v e r t e x d e t e c t o r is s u r r o n d e d b y a c e n t r a l c a l o r i m e t e r w i t h

consists of l e a d - s c i n t i l l a t o r e l e c t r o m a g n e t i c and iron-scintil.

lator h a d r o n c o u n t e r s c o v e r i n g polar a n g l e 6 f r o m 4 0 ° to 1 4 0 °

and a z i m u t h a l a n g l e cf> from 3 0 ° to 3 3 0 ° . In t h e p r e s e n t stage

of the e x p e r i m e n t t h e r e m a i n i n g a z i m u t h a l a n g l e (± 1 5 ° a r o u n d

the h o r i z o n t h a l p l a n e ) is c o v e r e d by a s i n g l e s p e c t r o m e t e r which allow

for the m e a s u r e m e n t o f c h a r g e d and n e u t r a l p a r t i c l e at 9 0 ° d e g r e e s .

A d e t a i l e d d e s c r i p t i o n of t h e p e r f o r m a n c e s of the c e n t r a l c a l o

r i m e t e r w i l l be o b j e c t of a n o t h e r r e p o r t at t h i s c o n f e r e n c e ( 4 ) .

The forward and b a c k w a r d r e g i o n s (polar angle 20° < 6 < 3 7 . 5 ° and

14 2.5° f 9 < 1 6 0 ° , r e s p e c t i v e l y ) are i n s t r u m e n t e d by 12 t o r o i d a l

m a g n e t sectors (B.l = .38 T.m) followed by 3x3 d r i f t c h a m b e r

p l a n e s for t h e c h a r g e d t r a c k s m o m e n t u m m e a s u r e m e n t . In t h e

- 53 -

d i r e c t i o n : their space r e s o l u t i o n of 250 ym w i l l a l l o w a

A p / P = «006 p that is a d e g u a t e to m e a s u r e t h e p a r t i c l e c h a r g e s

for t h e d e t e r m i n a t i o n of the W -> e v ( v ) c h a r g e a s y m m e t r y .The

d r i f t c h a m b e r s are t h e n f o l l o w e d b y a 1.4 r a d i a t i o n l e n g t h t h i c k

i r o n - l e a d c o n v e r t e r and four l a y e r s of m u l t i t u b e p r o p o r t i o n a l

c h a m b e r s (MTPC) w h o s e p u r p o s e is t o l o c a l i z e e l e c t r o m a g n e t i c

s h o w e r s . E l e c t r o m a g n e t i c c a l o r i m e t e r sectois finally c o m p l e t e

t h e F/B d e t e c t o r s . A l s o t h e F/B c a l o r i m e t e r s w i l l b e d e s c r i b e d

in m o r e d e t a i l in a n o t h e r r e p o r t at this c o n f e r e n c e ( 4 ) .

F i n a l l y , the w e d g e d e t e c t o r (Fig. 2) is a s i n g l e arm s p e c t r o m e

t e r c o v e r i n g 22° in a z i m u t h and 6 8 ° in p o l a r a n g l e a r o u n d

0 = 9 0 ° . Two coils p r o d u c e a field w h o s e i n t e g r a l is 1.1 T.m

and u s e s the c a l o r i m e t e r i r o n as r e t u r n y o k e . T h e s p e c t r o m e t e r

c o n s i s t s o f 12 d r i f t c h a m b e r s p l a n e s , w i t h w i r e s a t + 7 ° , 0 ° ,

- 7 ° r e s p e c t to t h e v e r t i c a l d i r e c t i o n , for t h e m e a s u r e m e n t s of

t h e c h a r g e d p a r t i c l e t r a j e c t o r i e s . C o m b i n i n g the m e a s u r e m e n t

of t h e i n t e r a c t i o n p o i n t c o m i n g f r o m the v e r t e x d e t e c t o r and

t h e d e t e r m i n a t i o n of t h e p a r t i c l e t r a j e c t o r i e s c o m i n g f r o m t h e

c h a m b e r s , the charged p a r t i c l e m o m e n t u m c a n b e m e a s u r e d w i t h

a r e s o l u t i o n of

T h e c h a m b e r s a r e then f o l l o w e d b y a s c i n t i l l a t o r - i r o n - s c i n t i l l a

tor s a n d w i c h . Both s c i n t i l l a t o r h o d o s c o p e consists o f 28 v e r t i

c a l c o u n t e r s . Each c o u n t e r of t h e front h o d o s c o p e is e q u i p p e d

w i t h sense w i r e at 0 ° , + 7 ° r e s p e c t to the m a g n e t i c f i e l d

(p in G e V / c )

s e c t o r three t r a p e z o i d a l c h a m b e r s h a v e 3 s e n s i t i v e p l a n e s e a c h

- 54 -

w i t h two P M ' s , for t i m e - o f - f l i g h t (TOF) m e a s u r e m e n t s over a

d i s t a n c e of 2.5 m w i t h a r e s o l u t i o n of .48 ifisec . T h e c o u n t e r s

after t h e 2 cm t h i c k iron p l a t e act as a p r e s h o w e r c o u n t e r s

for the l e a d - g l a s s w a l l w i c h c o m p l e t e s t h e s p e c t r o m e t e r . T h e

l e a d - g l a s s w a l l (Fig. 3) c o n s i s t s of 28 v e r t i c a l c o l u m n s of

10 c e l l s , s t a g g e r e d as shown in F i g . 3 , each c e l l b e i n g a 2

l e a d - g l a s s b l o c k 14.5 r a d i a t i o n l e n g t h d e e p r 1 5 x 1 5 cm in

c r o s s s e c t i o n . A t t h i s stage of t h e e x p e r i m e n t 2 c o l u m n s of

t h e l e a d - g l a s s a r r a y h a v e b e e n r e p l a c e d by a set of five sein

t i l l a t i o n s c o u n t e r s for d E / d x m e a s u r e m e n t s . The energy r e s o

l u t i o n of t h e lead g l a s s w a l l h a s b e e n m e a s u r e d to be a_/E = (11 . 6 + 3 2 . 5 / E ) 1 / 2 % (E in GeV) E

Each b l o c k h a s b e e n c a l i b r a t e d u s i n g 10 G e V e l e c t r o n s , and is

m o n i t o r e d w i t h a X e l i g h t flasher s y s t e m ; t h e c a l i b r a t i o n r e

m a i n e d s t a b l e t o w i t h i n Í 2% d u r i n g t h e p p r u n n i n g p e r i o d .

T h e d E / d x c o u n t e r m e n t i o n e d a b o v e is u s e d t o s e a r c h for fractio

nally c h a r g e d p a r t i c l e s (quarks) A s s h o w n i n F i g . 4, it c o n

sists of 5 plex;jipop p l a t e s 100 cm h i g h , 30 c m w i d e and 4 c m

t h i c k ; t h e l i g h t is c o l l e c t e d at t h e t o p and b o t t o m ends of

each p l a t e . V e t o c o u n t e r s c o v e r i n g t h e l i g h t g u i d e s a r e used

to r e j e c t e v e n t s w i t h p a r t i c l e s c r o s s i n g t h e light guides and

faking a s m a l l i o n i z a t i o n in the c o u n t e r s . T h i s d E / d x c o u n t e r

h a s b e e n c a l i b r a t e d at the C E R N PS and its r e s p o n s e to M I P has

b e e n studied as a f u n c t i o n of t h e i m p a c t p o i n t .

Two s c i n t i l l a t o r a r r a y s d e t e c t i n g s m a l l a n g l e s e c o n d a r i e s are

u s e d t o d i s c r i m i n a t e a g a i n s t e v e n t s from s o u r c e s other t h a n

- 55 -

b e a m b e a m c o l l i s i o n s . E a c h a r r a y , c o v e r i n g o n e u n i t o f r a p i d i t y

a r o u n d y = ± 4 . 7 , i s s i t u a t e d ± 1 0 . î m a w a y f r o m t h e i n t e r a c t i o n

p o i n t . A l l t r i g g e r s r e q u i r e a c o i n c i d e n c e o f s i g n a l s f r o m t h e

t w o h o d o s c o p e s , , w i c h a r e a l s o u s e d f o r t h e l u m i n o s i t y e v a l u a t i o n .

T h e t o t a l i n t e g r a t e d l u m i n o s i t y f o r w h i c h w e p r e s e n t r e s u l t s i s

- 1

7 5 y b , c a l c u l a t e d u n d e r t h e a s s u m p t i o n t h a t t h e n o n d i f f r a c t i v e

p p c r o s s s e c t i o n a t / s = 5 4 0 G e V i s 3 8 m b ; t h e s y s t e m a t i c e r r o r

i n t h e l u m i n o s i t y m e a s u r e m e n t h a s b e e n e s t i m a t e d t o b e t 1 7 % .

3 . I N C L U S I V E T T ° P R O D U C T I O N ( 5 )

T h e p r o d u c e d 7 T ° 1 s a r e i d e n t i f i e d f r o m 2 p h o t o n d e c a y s , w i t h

t h e p h o t o n s s e p a r a t e l y m e a s u r e d ; t h e m e a n p r o d u c t i o n a n g l e i s

0 = 9 0 ° a n d t h e T T ° t r a n s v e r s e m o m e n t u m c o v e r s t h e r a n g e 1 . 5 < p < 4 . 5

G e V / c .

T h e t r i g g e r f o r T T ° d e t e c t i o n r e q u i r e d a c o i n c i d e n c e b e t w e e n a s i

g n a l f r o m e a c h o f t h e t w o l u m i n o s i t y c o u n t e r s a n d a t o t a l e n e r g y

d e p o s i t i o n i n t h e l e a d - g l a s s w a l l e x c e e d i n g a p r e d e f i n e d t h r e s h o l d

o f 1 . 1 G e V . T h e e n e r g y d e p o s i t i o n i s r e d u c e d t o a n u m b e r o f c l u

s t e r d e f i n e d a s a s e t o f a d j a c e n t c e l l s w i t h e n e r g y g r e a t e r t h a n

1 0 0 M e V ; t h e m i n i m u m s ^ j a t i a l s e p a r a t i o n o f t w o r e s o l v e d c l u s t e r

i s a b o u t 2 5 c m . O n l y e v e n t s h a v i n g a t l e a s t 2 c l u s t e r s o f m o r e

t h a n 2 0 0 M e V i n t h e l e a d - g l a s s w a l l a r e s e l e c t e d ; i f a t r a c k , a s

m e a s u r e d i n t h e d r i f t c h a m b e r s , c r o s s e s t h e l e a d - g l a s s w a l l a t a

d i s t a n c e l e s s t h a n 1 2 c m f r o m t h e c l u s t e r c e n t e r , t h e e v e n t i s

r e j e c t e d s i n c e t h e c l u s t e r i s a t t r i b u t e d t o a c h a r g e d h a d r o n ,

i m p l y i n g a l o s s o f 2 i 1 % o f r e a l T T ° d e c a y s .

T h e i n v a r i a n t m a s s d i s t r i b u t i o n o f t h e Y Y s a m p l e i s s h o w n i n F i g .

5 w h e r e a T T ° p e a k i s c l e a r l y v i s i b l e o v e r a c o m b i n a t o r i a l b a c k -

- 56 -

g r o u n d of 20 to 3 0 % d e p e n d i n g o n t h e t r a n s v e r s e m o m e n t u m .

F r o m t h e M o n t e C a r l o c a l c u l a t i o n (solid line in F i g . 5 ) , a 4%

r e a d j u s t e m e n t of the e n e r g y s c a l e w a s needed to get a g r e e m e n t

w i t h t h e i d a t a : this d e v i a t i o n c o u l d b e a t t r i b u t e d to t h e e x t r a

p o l a t i o n of 10 GeV e l e c t r o n c a l i b r a t i o n of l e a d - g l a s s to p h o t o n s

in t h e G e V r a n g e .

T h e a c c e p t a n c e is limited at low p T by solid a n g l e and a h i g h p T

b y t h e p r o b a b i l i t y of b o t h p h o t o n s of m e r g i n g into a s i n g l e

c l u s t e r : it is c a l c u l a t e d f r o m t h e M o n t e C a r l o s i m u l a t i o n and

v a r i e s f r o m .15 to .27 h a v i n g a m a x i m u m at p T = 2.7 G e V / c . T h e

l u m i n o s i t y , m e a s u r e d from t h e l e f t - r i g h t c o i n c i d e n c e s of t h e lu

m i n o s i t y c o u n t e r s , h a s a 1 6 % u n c e r t a i n t y c o m i n g from t h e r e l i a b i

lity of t h e s e c o u n t e r s .

T h e p T d e p e n d e n c e of the i n v a r i a n t c r o s s s e c t i o n for i n c l u s i v e

TT° p r o d u c t i o n is s h o w n in F i g . 6. T h e solid line of F i g ; 6 s h o w s

t h e m e a s u r e d p i o n p r o d u c t i o n in t h e / s = 53 G e V p p c o l l i s i o n s at

ISR (6) in the p T r a n g e of t h i s e x p e r i m e n t . A t h i g h t r a n s v e r s e

m o m e n t u m w e o b s e r v e a large i n c r e a s e of t h e ir° cross s e c t i o n w h e n

the e n e r g y r i s e s from 53 t o 540 G e V .

In t h e inset of F i g . 6, an e n h a n c e m e n t in t h e r e g i o n of t h e n

m a s s is c l e a r l y v i s i b l e ; t h i s \ y y m a s s d i s t r i b u t i o n is o b t a i n e d

w h e n m o r e severe s e l e c t i o n c r i t e r i a a r e a p p l i e d . A n a m o u n t o f

53 Í 15 e v e n t s a b o v e b a c k g r o u n d is o b s e r v e d : this is c o n s i s t e n t

w i t h a n e s t i m a t e of 48 e v e n t s o b t a i n e d from a M o n t e C a r l o c a l c u

l a t i o n u n d e r t h e a s s u m p t i o n t h a t t h e i n c l u s i v e c r o s s s e c t i o n f o r

n and TT° p r o d u c t i o n are in t h e r a t i o .55 as m e a s u r e d in t h e ISR

e n e r g y r a n g e ( 7 ) .

- 57 -

T h e i n c l u s i v e s i n g l e p h o t o n s p r o d u c t i o n h a s b e e n i n v e s t i g a t e d

c o m p a r i n g t h e t r a n s v e r s e momentum d i s t r i b u t i o n o f a r e s t r i c t e d

p h o t o n s a m p l e w i t h t h e p r e d i c t i o n o f a M o n t e C a r l o s i m u l a t i o n

u s i n g a s i n p u t t h e m e a s u r e d i r ° c r o s s s e c t i o n , and a s s u m i n g a p^

i n d e p e n d e n t n / u 0 r a t i o e q u a l t o . 5 5 . I n t h e p T r a n g e b e t w e e n

1.5 a n d 3 G e V , a r a w e x c e s s o f 24 ± 58 p h o t o n s h a s b e e n o b s e r v e d .

A f t e r c o r r e c t i o n s f o r a p o s s i b l e n o n l i n e a r i t y i n t h e e n e r g y

r e s p o n s e o f t h e l e a d g l a s s a n d f o r a p o s s i b l e c o n t a m i n a t i o n o n

n e u t r a l h a d r o n s , m o s t l y a n t i n e u t r o n s , a d e f i c i t o f 4 6 ± 90

p h o t o n s i s o b t a i n e d ; a 95% c o n f i d e n c e l e v e l u p p e r l i m i t i s s e t

f o r t h e s i n g l e p h o t o n s p r o d u c t i o n y / " n 0 < 7.5% i n t h e p T r a n g e b e

t w e e n 1.5 a n d 3 G e V .

T h e t e c h n i q u e u s e d i n t h e l e a d - g l a s s a r r a y t o m e a s u r e TT° h a s al^

s o b e e n a p p l i e d t o t h e f o r w a r d - b a c k w a r d e l e c t r o m a g n e t i c c a l o r i

m e t e r s . T h e i n c l u s i v e c r o s s - s e c t i o n o b t a i n e d f r o m t h e s e d a t a c o

v e r s a p T r a n g e o f .5 t o 2 . 2 GeV/c a n d a r a p i d i t y b e t w e e n 1.1 a n d

1 . 7 . T h e m e a s u r e m e n t ( n o t shown) i s i n g o o d a g r e e m e n t w i t h t h e

f i t p e r f o r m e d o n t h e T T +,TT , T T ° c r o s s s e c t i o n a t 90° ( s e e s e c

t i o n 4 ) .

4 . I N C L U S I V E CHARGED P A R T I C L E PRODUCTION

C h a r g e d p a r t i c l e p r o d u c t i o n a t 90° h a s b e e n i n v e s t i g a t e d i n

t h e w e d g e d e t e c t o r .

T h e t r i g g e r r e q u i r e d a b e a m - b e a m c o l l i s i o n s i g n e d b y t h e l e f t - r i g h t

c o i n c i d e n c e o f t h e l u m i n o s i t y c o u n t e r s a n d a c o i n c i d e n c e o f W

a n d W ß h o d o s c o p e d e f i n i n g t h e p r e s e n c e o f a c h a r g e d t r a c k i n t h e

s p e c t r o m e t e r . T h e m a t c h i n g o f t h e t r a c k d i r e c t i o n a f t e r b e n d i n g ,

- 58 -

as d e f i n e d by t h e set of 12 d r i f t c h a m b e r s p l a n e s , a n d of the in

t e r a c t i o n p o i n t , as d e f i n e d b y the v e r t e x d e t e c t o r , a l l o w s for

t h e m o m e n t u m and c h a r g e d e t e r m i n a t i o n of a p a r t i c l e . In a d d i t i o n

t i m e - o f - f l i g h t m e a s u r e m e n t s in t h e W h o d o s c o p e p r o v i d e t h e par r —

t i c l e i d e n t i f i c a t i o n : K a r e s e p a r a t e d from IT u p t o m o m e n t a of

1.1 GeV/c and p f r o m TT and K u p to 1.8 G e V / c .

T h e d e t e c t o r a c c e p t a n c e as a f u n c t i o n of t r a n s v e r s e m o m e n t u m is

computed u s i n g a M o n t e - C a r l o p r o g r a m for the 3 p a r t i c l e t y p e s

(iT,K,p). P a r t i c l e s are g e n e r a t e d w i t h flat r a p i d i t y y and azimu

t h a i angle < d i s t r i b u t i o n s . T h e t r a c k i n g of each p a r t i c l e through

the s p e c t r o m e t e r t a k e s into a c c o u n t t h e d e t e c t o r g e o m e t r y and

field m a p , as w e l l as m u l t i p l e s c a t t e r i n g and p a r t i c l e d e c a y

e f f e c t s . C o r r e c t i o n s h a v e b e e n applied for the loss of t r a c k s

due to n u c l e a r i n t e r a c t i o n s , w h i c h o c c u r m a i n l y in the v a c u u m

p i p e and in the v e r t e x d e t e c t o r c h a m b e r w a l l s . T h e w e d g e chambers

e f f i c i e n c i e s h a v e b e e n m e a s u r e d , r e s u l t i n g in a m e a n t r a c k r e

c o n s t r u c t i o n e f f i c i e n c y of 9 8 % .

T h e q u a l i t y and e f f i c i e n c y of the v e r t e x finding in the v e r t e x

d e t e c t o r h a v e b e e n m o n i t o r e d u s i n g the t r a c k s of the w e d g e or the

F/B s p e c t r o m e t e r s in s p e c i a l runs w h e r e the m a g n e t i c f i e l d s w e r e

o f f . T h e v e r t e x finding e f f i c i e n c y is at least 9 7 % .

T h e integrated l u m i n o s i t y is 5 yb ; . a t 1 7 % s y s t e m a t i c error

r e f l e c t s t h e run t o r u n f l u c t u a t i o n s ( 5 ) .

T h e i n v a r i a n t cross s e c t i o n of i n c l u s i v e h a d r o n p r o d u c t i o n (char

ge averaged) is d i s p l a y e d as f u n c t i o n of p T o n F i g . 7a in the p T

range 0.4 to 2 G e V / c . T h e p o s i t i v e to negative r a t i o is m e a s u r e d

t o b e 1.008 ± 0 . 0 2 1 . It is p T i n d e p e n d e n t and c o n s i s t e n t w i t h u -

nity as expected (Fig. 7 b ) .

- 59 -

E r = A 3~ . . 1 - 2 - ) * d p T

- 2 3

w i t h A = 1.43 m b GeV c , n = 8 . 3 + 0 . 2 and p in G e V / c .

In c o n t r a s t to t h e ISR r e s u l t s ( 1 1 ) , t h e d a t a c a n n o t b e fitted

b y a n e x p o n e n t i a l law in the p T r a n g e b e l o w 1 G e V / c .

R a t i o s of p a r t i c l e p r o d u c t i o n s e v a l u a t e d at the s a m e t r a n s v e r s e m a s s ( M T = / p T

2 + M 2 , w h e r e M is the p a r t i c l e m a s s ) have b e e n ob

served to be M T i n d e p e n d e n t at ISR e n e r g i e s . F i g . 8b gives the

ratio K / Ï Ï and p/ïï as f u n c t i o n of . No M T d e p e n d e n c e is f o u n d .

A v e r a g i n g o v e r the measured r a n g e w e g e t :

^ = 0.39 ± 0.02 (stat.) ± 0.03 (syst.)

and

F o r e a c h p a r t i c l e t y p e , t h e p o s i t i v e to n e g a t i v e r a t i o is a l s o

P T i n d e p e n d e n t and c o n s i s t e n t w i t h 1, namely

+ + ^ = 1.006 ± 0 . 0 2 5 , ^ 3 = 0.94 ± 0.06, Ç = 1.01 ± 0.09 Tf K p

T h e i n v a r i a n t c r o s s s e c t i o n s for ÏÏ, K, p, shown o n F i g . 8a a r e

t h e r e f o r e c h a r g e a v e r a g e d .

T h e c h a r g e d k a o n p r o d u c t i o n is in good a g r e e m e n t w i t h a K s m e a

s û r e m e n t ( 9 ) . ± o

In F i g . 9, ÏÏ and ÏÏ c r o s s s e c t i o n s m e a s u r e d in t h i s e x p e r i m e n t

(5) and at t h e ISR (10) are d i s p l a y e d . W e o b s e r v e a good a g r e e m e n t

b e t w e e n o u r charged and n e u t r a l p i o n c r o s s s e c t i o n s . C o m p a r e d

to ISR d a t a , w e note an i n c r e a s e of the p i o n c r o s s s e c t i o n b y a

f a c t o r of 2 at 0.4 G e V / c , r e a c h i n g a factor of 4 at 1.4 G e V / c .

C h a r g e d and neutral p i o n d a t a c a n be fitted to t h e e m p i r i c a l from:

- 6 0 -

E = 1.02 ± 0.05 ( s t a t . ) ± 0.05 ( s y s t . ) TT

While the p/fr r a t i o appears to be s imi lar to the p/ir r a t i o

measured at the ISR, the K / T T r a t i o has increased from ISR to SPS

c o l l i d e r enrgies by 40%. This is possibly due to a more copious

production of heavy f l a v o r s .

Charged p a r t i c l e production has been investigated also i n the F/B

sepctrometer s t a r t i n g from events selected with the minimum bias

t r i g g e r wich requires a beam-beam c o l l i s i o n signed by the l e f t -

- r i g h t coincidence of the luminosity counters.

Using the same rechnique as in the wedge detector, but without

p a r t i c l e i d e n t i f i c a t i o n , preliminary results based on meagre

s t a t i s t i c s have been obtained as far as the inc lus ive cross sec

t i o n is concerned: the charged p a r t i c l e p^ spectrum, ranging from

.5 to 2.2 GeV/c, averaged on the r a p i d i t y i n t e r v a l from i 1 to

t 1.8, is shown in F i g . 7a; the posit ive to negative r a t i o is

consistent with 1 and p T independent, as shown i n F i g . 7b.

5. SEARCH FOR FRACTIONALLY CHARGED P A R T I C L E S ( 1 2 )

As mentioned before, i n the data col lected so far , the ap

paratus was such that two columns of the lead glass array have

been replaced by a set of f i v e s c i n t i l l a t o r counters to Q 5

used for dE/dx measurements (F ig . 4 ) . In t h i s configuration a

t r i g g e r sensit ive to charged part ic les with f r a c t i o n a l e l e c t r i c

charge was constructed by l i n e a r l y adding the amplified signals

from the top and bottom phototubes of each counter Q1 to Q and

- 6 1 -

r e q u i r i n g that at least t h r e e o u t of the five s i g n a l s so o b t a i n e d

e x c e e d a t h r e s h o l d c o r r e s p o n d i n g to an i o n i s a t i o n of 0 . 0 5 , if w e

d e f i n e as unity t h e m o s t p r o b a b l e p u l s e h e i g h t of m i n i m u m i o n i z i n g

p a r t i c l e s ( M I P s ) . A f u r t h e r c o i n c i d e n c e r e q u i r e m e n t w a s t h a t b o t h

p h o t o t u b e s from e i t h e r o n e of t h e two W p c o u n t e r s in front of t h e

Q-telescope give o u t p u t s a b o v e a t h r e s h o l d c o r r e s p o n d i n g to a n

i o n i z a t i o n of 0 . 0 3 .

In o r d e r to s u p p r e s s b a c k g r o u n d from s o u r c e s o t h e r t h a n p p c o l l i

s i o n s , the t r i g g e r a l s o r e q u i r e d a c o i n c i d e n c e w i t h a m i n i m u m

b i a s e v e n t . - 1

D u r i n g d a t a taking t h e t y p i c a l t r i g g e r r a t e w a s 0.02 s at a lu 26 — 2 —1

m i n o s i t y of 10 cm s . A total n u m b e r of 1 5 0 6 2 t r a i g g e r s w a s - 1

r e c o r d e d , c o r r e s p o n d i n g to an i n t e g r a t e d l u m i n o s i t y of 75 yb

In the d a t a a n a l y s i s , e v e n t s are selected r e q u i r i n g 6 i o n i s a t i o n

m e a s u r e m e n t s from W p and t o Qj. c o u n t e r s c o r r e c t e d for the p o s

s ible impact p o i n t p o s i t i o n ; t h e n the m o s t p r o b a b l e i o n i z a t i o n

I h a s b e e n e s t i m a t e d by m e a n s of the l i k e l y l o o d m e t h o d a l l o w i n g

for t h e r e j e c t i o n of e v e n t s i n c o n s i s t e n t w i t h a s i n g l e I v a l u e .

Events w i t h s i g n a l s f r o m v e t o c o u n t e r s are a l s o r e j e c t e d . F u r t h e r

s e l e c t i o n c r i t e r i a h a v e b e e n a p p l i e d to r e j e c t b a c k g r o u n d e v e n t s

d u e to p a r t i c l e s p a s s i n g nearby t h e d E / d x c o u n t e r s o r t r a v e r s i n g

it only p a r t i a l l y . T h e I d i s t r i b u t i o n of t h e r e m a i n i n g e v e n t s is

shown in F i g . 1 0 a ; t h e r e a r e 23 e v e n t s , shown in Fig; 1 0 b , w h i c h h a v e

a b n o r m a l l y low i o n i z a t i o n , I <.7. A c a r e f u l e x a m i n a t i o n of t h e s e

events shows t h a t 15 of t h e m c a n b e e x p l a i n e d as i n t e r a c t i o n s in

the i r o n p l a t e or in t h e last two c o u n t e r s Q. and Q r ; the r e m a i -4 O

ning 8 e v e n t s are s h o w n as shaded area in the d i s t r i b u t i o n of

F i g . 1 0 b .

- 62 -

T h e r e q u i r e m e n t t h a t , f o r e v e n t s w i t h I >.5, at least 6 out of

12 d r i f t c h a m b e r p l a n e s h a v e a h i t in front of the Q c o u n t e r s and

t h e a d d i t i o n a l r e q u e s t t h a t n o e n e r g y d e p o s i t i o n b e p r e s e n t

in e i t h e r of the t w o c o l u m n s of lead g l a s s c o u n t e r s a d j a c e n t to

t h e Q - t e l e s c o p e , leaves no e v e n t s in t h e sample of e v e n t s w i t h

I < . 7 . o

T h i s n u l l r e s u l t c a n b e e x p r e s s e d as an u p p e r limit for t h e r a t i o

R Q of t h e q u a r k y i e l d around 90° t o t h a t of p a r t i c l e s w i t h u n i t

e l e c t r i c c h a r g e . T h e 9 0 % c o n f i c e n c e level u p p e r limit is g i v e n

b y t h e r e l a t i o n 2.3 = N a i ) R ^ M B Q Q

w h e r e is the d e t e c t i o n e f f i c i e n t y and is the t o t a l n u m b e r

of m i n i m u m b i a s e v e n t s r e c o r d e d d u r i n g t h e e x p e r i m e n t .

T h e d e t e c t i o n e f f i c i e n c y is c a l c u l a t e d u s i n g a M o n t e - C a r l o simu

latiori p r o g r a m . l t d e p e n d on t h e g e o m e t r y of t h e d e t e c t o r , o n t h e

q u a r k m a s s and m o m e n t u m s p e c t r u m b e c a u s e of t h e d e t e c t o r t h i c k n e s s -2

of ^ 40 gr cm b e t w e e n t h e p p c o l l i s i o n p o i n t and c o u n t e r Q^,

and o n t h e d e f l e c t i o n of t h e p a r t i c l e t r a j e c t o r i e s d u e to the m a

g n e t i c field of t h e s p e c t r o m e t e r . Q u a r k s of v a r i o u s m a s s e s m ^ and

e l e c t r i c c h a r g e equal t o Í 1/3 and ± 2/3 are g e n e r a t e d in the M o n

te C a r l o s i m u l a t i o n w i t h a flat r a p i d i t y d i s t r i b u t i o n a r o u n d 9 0 ° ,

and w i t h a t r a n s v e r s e m o m e n t u m d i s t r i b u t i o n of t h e form p e x p 2 2 1 2 - 1 ( - B m T ) , w h e r e m T = (p^ + m ^ ) 2 and B = 5 (GeV/c ) as s u g g e s t e d

by t h e r m o d y n a m i c a 1 m o d e l s for p a r t i c l e p r o d u c t i o n (13) . T h e b e

h a v i o u r of <XQ is reflected in F i g . 1 1 , w h i c h shows t h e 9 0 % c o n f i

d e n c e l e v e l u p p e r l i m i t for t h e r a t i o R ^ as a f u n c t i o n of t h e

q u a r k m a s s m ^ , for b o t h 1/3 and 2/3 q u a r k c h a r g e s .

http://program.lt

- 63 -

I n c o n c l u s i o n , n o e v i d e n c e f o r p a r t i c l e s w i t h f r a c t i o n a l e l e

c t r i c c h a r g e h a s b e e n f o u n d a t t h e CERN p p c o l l i d e r ( / s = 5 4 0

G e V ) . T h e y i e l d o f l i g h t q u a r k s w i t h c h a r g e 1 / 3 o r 2 / 3 i s a t

m o s t 1 / 5 0 0 0 o f t h a t o f p a r t i c l e s w i t h u n i t c h a r g e . T h e s e n s i

t i v i t y o f t h e m e a s u r e m e n t d e c r e a s e s w i t h i n c r e a s i n g q u a r k mas 2

s e s a n d a t m = 2 G e V / c t h e u p p e r l i m i t o f t h e r a t i o o f q u a r k - 3

y i e l d t o t h a t o f p a r t i c l e s w i t h u n i t c h a r g e b e c o m e s 2 . 5 x 1 0 f o r - 3

q u a r k s w i t h c h a r g e 2 / 3 a n d 1 0 f o r q u a r k s w i t h c h a r g e 1 / 3 .

6 . CONCLUSIONS

T h e i n c l u s i v e i r 0 p r o d u c t i o n f r o m p p c o l l i s i o n s a t / s = 5 4 0

GeV h a s b e e n m e a s u r e d i n t h e p T r a n g e 1 . 5 t o 4 . 5 G e V / c : i t i s l a r

g e r t h a n t h a t m e a s u r e d i n p p c o l l i s i o n s a t I S R e n e r g y . An n s i g n a l

h a s b e e n m e a s u r e d , c o n s i s t e n t w i t h n A ° = . 5 5 a s m e a s u r e d a t t h e

I S R . No e v i d e n c e h a s b e e n f o u n d f o r p h o t o n s o u r c e s o t h e r t h a n T T °

a n d n p r o d u c t i o n .

T h e i n c l u s i v e c h a r g e d h a d r o n p r o d u c t i o n h a s a l s o b e e n m e a s u r e d

w i t h p a r t i c l e i d e n t i f i c a t i o n b e l o w 1 . 4 G e V / c f o r p r o t o n s a n d 1 . 1

G e V / c f o r k a o n s : i n t h i s r a n g e t h e p a r t i c l e r a t i o s a r e t r a n s v e r s e

m a s s i d e n p e n d e n t a n d , w h i l e t h e p / ir r a t i o s h o w s l i t t l e c h a n g e

c o m p a r e d t o t h e I S R , t h e K / T T r a t i o h a s i n c r e a s e d b y 40%.

C h a r g e d a n d n e u t r a l p i o n i n c l u s i v e c r o s s s e c t i o n c a n b e f i t t e d

t o t h e e m p i r i c a l f o r m :

w i t h A = 1 . 4 3 mb GeV c , n = 8 . 3 ± 0 . 2 a n d p T i n G e V / c .

C o n c e r n i n g t h e s e a r c h f o r r e l a t i v i s t i c p a r t i c l e s w i t h f r a c t i o n a l

e l e c t r i c c h a r g e , n o e v i d e n c e h a s b e e n f o u n d f o r s u c h p a r t i c l e s :

- 64 -

t h e y i e l d o f l i g h t q u a r k s w i t h c h a r g e 1 / 3 o r 2 / 3 i s a t m o s t

1 / 5 0 0 0 o f t h a t o f p a r t i c l e s w i t h u n i t c h a r g e .

ACKNOWLEDGEMENTS

We d e e p l y a c k n o w l e d g e t h e h e l p o f t h e t e c h n i c a l s t a f f s o f

t h e I n s t i t u t e s C o l l a b o r a t i n g i n U A 2 .

T h e a u t h o r w o u l d a l s o l i k e t o t h a n k t h e o r g a n i s e r s f o r a n e n j o y a

b l e c o n f e r e n c e . I a l s o t h a n k M r s . R . M a r c h i n i a n d A . M o n t a g n a f o r

t h e i r h e l ¿ ) i n p r o d u c i n g a w r i t t e n v e r s i o n o f t h i s t a l k .

- 65 -

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t e r n a t i o n a l C o n f e r e n c e o n E x p e r i m e n t a t i o n a t LEP, U p p s a l a ,

1 5 - 2 0 J u n e 1 9 8 0 .

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P o l a n d , 2 4 - 2 8 May 1 9 8 2 , p g . 7 .

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F . W . B ü s s e r e t a l . , N u c l . P h y s . B 1 0 6 ( 1 9 7 6 ) 1 .

A . G . C l a r k e t a l . , N u c l . P h y s . B 1 4 2 ( 1 9 7 8 ) 1 8 9 .

7 ) F .W. B ü s s e r e t a l . , P h y s . L e t t . 5 5 B ( 1 9 7 5 ) 2 3 2 .

K. E g g e r t e t a l . , N u c l . P h y s . B 9 8 ( 1 9 7 5 ) 4 9 .

C . K o u r k o u m e l i s e t a l - , P h y s . L e t t . 84B ( 1 9 7 9 ) 2 7 7 .

8 ) UA2 C o l l a b o r a t i o n , M. B a n n e r e t a l . , I n c l u s i v e C h a r g e d P a r t i

e l e P r o d u c t i o n a t t h e CERN p p C o l l i d e r ( t o b e p u b l i s h e d i n

P h y s i c s L e t t e r s ) .

9) K. A l p g a r d e t a l . , P h y s . L e t t . 1 1 5 B ( 1 9 8 2 ) 6 5 .

1 0 ) M. B a n n e r e t a l . , P h y s . L e t t . 4 1 B ( 1 9 7 2 ) 5 4 7 .

B . A l p e r e t a l . , N u c l . P h y s . B87 (1975) 19 a n d N u c l . P h y s .

B100 (1975) 2 3 7 . 11) T . A k e s s o n e t a l . , P h y s . L e t t . 1 0 8 B (1982) 5 8 .

- 66 -

1 2 ) UA2 C o l l a b o r a t i o n , M. B a n n e r e t a l . , A S e a r c h f o r R e l a t i v i -

s t i c P a r t i c l e s w i t h F r a c t i o n a l E l e c t r i c C h a r g e a t t h e CERN

p p c o l l i d e r ( t o b e p u b l i s h e d i n P h y s i c s L e t t e r s ) .

1 3 ) R. H a g e d o r n a n d J . R a n f t , S u p p l . N u o v o C i m . i6 ( 1 9 6 8 ) 1 6 9 ; R.

H a g e d o r n , S u p p l . N u o v o C i m . 6 ( 1 9 6 8 ) 3 1 1 .

- 67 -

F I G U R E C A P T I O N S

F i g . 1: P l a n v i e w o f t h e U A 2 d e t e c t o r .

F i g . 2: S i d e v i e w o f c e n t r a l p a r t o f t h e U A 2 d e t e c t o r s h o v i n g

t h e s i n g l e a r m l a r g e a n g l e s p e c t r o m e t e r ( w e d g e d e t e c

t o r ) .

F i g . 3: E x p l o d e d v i e w o f t h e w e d g e d e t e c t o r .

F i g . 4 : S i d e (a) a n d t o p ( b ) v i e w o f t h e d E / d x c o u n t e r i m p l e

m e n t e d i n t h e w e d g e d e t e c t o r .

F i g . 5 : I n v a r i a n t m a s s d i s t r i b u t i o n o f t h e t w o - p h o t o n s s a m p l e

( f u l l d o t s ) . T h e d i s t r i b u t i o n i n t h e i n s e r t a r o u n d t h e

n m a s s i s f o r s t r i c t e r c u t s ( s e e t e x t ) . T h e r e s u l t o f

t h e M o n t e C a r l o s i m u l a t i o n ( s o l i d l i n e s ) h a s b e e n a d d e d

t o a h a n d - d r a w n b a c k g r o u n d ( d a s h e d l i n e s ) .

F i g . 6 : T h e m e a s u r e d i n v a r i a n t c r o s s - s e c t i o n f o r p p - TT° + ... ( f u l l d o t s ) a t / ï ï = 5 4 0 G e V i s c o m p a r e d t o t h a t f o r pp-*-

TT° + . . . a t /'s - 5 3 G e V ( s o l i d l i n e ) . T h e p p d a t a a r e

f r o m R e f . ( 6 ) ; i n t h e l o w e r P T r a n g e t h e m e a n o f TT a n d

T f c r o s s - s e c t i o n s h a s b e e n u s e d . T h e d a s h e d l i n e i s a n

e x t r a p o l a t i o n o f t h e d a t a o f R e f . ( 6 ) t o C o l l i d e r e n e r g y _o 9

u s i n g t h e f o r m p T ° ( 1 - x T ) . F i g . 7 : a ) I n v a r i a n t c r o s s s e c t i o n f o r h a d r o n p r o d u c t i o n ( c h a r

g e a v e r a g e d ) ( h = TT+K+P ) •

b ) P o s i t i v e t o n e g a t i v e r a t i o a s f u n c t i o n o f p t -

F i g . 8 : a ) I n v a r i a n t c r o s s s e c t i o n f o r IT ( t r i a n g l e s ) , K ( f u l l

d o t s ) a n d p ( s q u a r e s ) p r o d u c t i o n ( c h a r g e a v e r a g e ) a s f u n

c t i o n o f p t .

b ) T h e r a t i o s K/TT ( c r o s s e s ) a n d P/TT ( o p e n c i r c l e s ) e v a

l u a t e d a t t h e s a m e t r a n s v e r s e m a s s ( M t ) a s f u n c t i o n o f M.

F i g . 9: I n v a r i a n t c r o s s s e c t i o n f o r TT ( t r i a n g l e s ) a n d TT° ( R e f .

5 ) ( s q u a r e s ) m e a s u r e d i n t h i s e x p e r i m e n t c o m p a r e d t o I S R

d a t a f r o m A l p e r e t a l . ( s e e R e f . 1 0 ) . T h e s o l i d l i n e i s t h e f i t t o o u r d a t a ( s e e t e x t ) .

- 68 -

F i g . 1 0 : a ) D i s t r i b u t i o n o f t h e m o s t p r o b a b l e i o n i s a t i o n I Q .

b ) E x p a n d e d v i e w o f t h e I d i s t r i b u t i o n i n t h e r e g i o n

o f a b n o r m a l l y l o w i o n i s a t i o n . T h e s h a d e d a r e a r e p r e

s e n t s t h e d i s t r i b u t i o n f o r t h e e i g h t e v e n t s w h i c h c a n

n o t b e e x p l a i n e d a s i n t e r a c t i o n s i n t h e i r o n p l a t e o r

i n t h e l a s t t w o p l a n e s o f t h e Q - t e l e s c o p e .

F i g . 1 1 : T h e 90% c o n f i d e n c e l e v e l u p p e r l i m i t f o r t h e r a t d o

d e f i n e d a s t h e r a t i o o f q u a r k y i e l d t o t h e y i e l d o f

p a r t i c l e s w i t h u n i t e l e c t r i c c h a r g e , a s a f u n c t i o n o f

t h e q u a r k m a s s m^. T h e c u r v e s l a b e l l e d 2 / 3 a n d 1 / 3 r e

f e r t o t h e a b s o l u t e v a l u e s o f t h e q u a r k c h a r g e s , r e s p e

c t i v e l y .

F i g . 2

- 7 0 -

12 Drift Chamber planes

Front Hodoscope

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D r i f t c h a m b e r s

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- 7 1 -

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Particle ratios E d 3 a / d p 3 ( c m 2 G e V - 2 c 3 )

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- 75 -

REVIEW OF RESULTS FROM THE UA5 EXPERIMENT

UA5 Collaboration: Bonn-Brussels-Cambridge-CERN-Stockholm

Presented by D.R. Ward3

Cavendish Laboratory, Cambridge

1. Introduction

This paper presents a general review of the results obtained from the UA5

streamer chamber experiment in the first year or so of operation of the CERN

SPS-collider at /s = 540 GeV. Particular emphasis will be placed on recent

results on particle multiplicities (§§5,9) and on preliminary results from the

latest runs of UA5 in September 1982 (§§4,5).

The principal objective of the UA5 experiment was to perform a rapid and

detailed survey of the main features of hadronic interactions in the new energy

regime made available at the SPS-collider. It was necessary to be prepared for

possible unexpected phenomena, as hinted at in cosmic ray data El], and

therefore a versatile and readily understood detector covering a large solid

angle was designed.

The detector will be described in §2, and the trigger and data taking

reviewed in §3. Results on charged particle production will be considered in

§§4,5, followed by data on strange particles (§6) and photons ( § 7 ) . In §8 the

search for Centauro events will be outlined, and our results on particle

multiplicities summarized in §9. Future plans for UA5 will be discussed in

§10, and some concluding remarks appear in §11. Results from the UA5 experiment

on forward-backward correlations are presented in an accompanying paper by

G. Ekspong.

2 . T h e U A 5 d e t e c t o r

T h e U A 5 d e t e c t o r h a s b e e n d e s c r i b e d i n r e f . [ 2 ] . A s c h e m a t i c d r a w i n g o f

t h e d e t e c t o r , a s u s e d i n t h e r u n o f S e p t e m b e r 1 9 8 2 , i s s h o w n i n f i g . 1. T h e

m a i n t r a c k d e t e c t o r s a r e t w o v e r y l a r g e ( 6 m x 1 . 2 5 m x 0 . 5 m ) s t r e a m e r c h a m b e r s

p l a c e d a b o v e a n d b e l o w t h e S P S b e a m p i p e . E a c h c h a m b e r w a s v i e w e d b y t h r e e

c a m e r a s , e a c h o f w h i c h r e c o r d e d a s t e r e o p a i r o f v i e w s . T h e c a m e r a s w e r e

e q u i p p e d w i t h i m a g e i n t e n s i f i e r t u b e s . T h e t r i g g e r w a s p r o v i d e d b y l a r g e

m o d u l a r p l a n e s o f s c i n t i l l a t i o n c o u n t e r h a d o s c o p e s .

T w o s i g n i f i c a n t i m p r o v e m e n t s i n t h e d e t e c t o r w e r e m a d e i n 1 9 8 2 . F i r s t l y

t h e 0 . 4 m m c o r r u g a t e d s t e e l b e a m p i p e w a s r e p l a c e d b y a 2mm b e r y l l i u m v a c u u m

c h a m b e r . T h i s r e s u l t e d i n a f i v e f o l d r e d u c t i o n i n e l e c t r o m a g n e t i c b a c k g r o u n d ,

a n d n o t o n l y m a d e t h e p h o t o g r a p h s m u c h c l e a r e r a n d e a s i e r t o m e a s u r e , b u t

a l s o s i m p l i f i e s m a n y f e a t u r e s o f t h e d a t a a n a l y s i s . S e c o n d l y a " n e u t r a l

h a d r o n d e t e c t o r " ( N H D ) w a s p l a c e d a t 9 0 ° . T h i s d e t e c t o r c o n s i s t e d o f a 4m x l m

l e a d - i r o n - s c i n t i l l a t o r - s a n d w i c h c a l o r i m e t e r , a n d i t s m a i n p u r p o s e w a s t o i d e n t i f y

n e u t r a l h a d r o n s , t h o u g h i t c a n a l s o b e u s e d t o m e a s u r e e n e r g i e s o f o t h e r

p a r t i c l e s .

3 . T r i g g e r a n d d a t a t a k e n

A s i m p l i f i e d s c h e m a t i c o f t h e d e t e c t o r , s h o w i n g t h e c o m p o n e n t s r e l e v a n t f o r

t h e t r i g g e r , i s p r e s e n t e d i n f i g . 2 ( a ) . T h e t r i g g e r a r m s c o v e r t h e p s e u d o r a p i d i t y

r a n g e s 2 <|n | < 6 ( n = - l o g t a n 6 / 2 , w h e r e 6 i s t h e p o l a r p r o d u c t i o n a n g l e i n t h e

C M . ) . O u r b a s i c " m i n i m u m b i a s " t r i g g e r d e m a n d e d a t l e a s t o n e h i t i n e a c h

h o d o s c o p e a r m , i . e . A 1 . A 2 , i n c o i n c i d e n c e w i t h a b e a m c r o s s i n g . T h i s t r i g g e r

i s h i g h l y e f f i c i e n t , e x c e p t f o r e l a s t i c a n d s i n g l e d i f f r a c t i v e e v e n t s . I n

25 - 2 - 1

o u r r u n s o f 1981 t h e l u m i n o s i t y w a s s o l o w ( ¿ 10 c m s ) t h a t f o r s o m e o f

o u r d a t a w e n e e d e d f u r t h e r t o r e d u c e b a c k g r o u n d b y d e m a n d i n g > 2 h i t s i n A l .

I n t h e r u n s o f 1 9 8 2 t h e l u m i n o s i t y w a s c o n s i d e r a b l y h i g h e r ( £ 1 0 c m s ) .

I n a d d i t i o n t o t a k i n g a f u r t h e r l a r g e s a m p l e o f m i n i m u m b i a s t r i g g e r s w e w e r e

a b l e t o e m p l o y s o m e m o r e s o p h i s t i c a t e d t r i g g e r s , s u c h a s A l . A 2 ( s e n s i t i v e t o

e v e n t s w h e r e t h e p d i f f r a c t i v e l y d i s s o c i a t e s ) a n d A l . A 2 ( " p - d i f f r a c t i v e " ) .

A s m a l l a m o u n t o f t e s t d a t a w e r e a l s o t a k e n r e q u i r i n g > 3 G e V o f e n e r g y t o b e

d e p o s i t e d i n t h e c a l o r i m e t e r . T h e t r i g g e r s a n d d a t a t a k e n a r e s u m m a r i z e d i n

t h e t a b l e b e l o ? .

O c t o b e r / N o v e m b e r 1981 , , , „ 2 5 - 2 - 1 L < 10 cm s

T r i g g e r T y p e N o . p i c t u r e s % g o o d e v e n t s N o . m e a s u r e d b y D e c . 8 2

M i n i m u m B i a s A 1 . A 2 o r ( A l > 2 ) . A 2

6 0 K 2 0 - 8 0 % ^ 6 K

S e p t e m b e r 1 9 8 2 L < 1 0 2 7 c m ~ 2 s - 1

M i n i m u m B i a s

p - d i f f r a c t i v e

p - d i f t r a c t i v e

A l . A 2

A l . Ä 2

À l . A 2

A l . A 2 ( N H D > 3 G e V ;

3 0 K 95% t. 1 3 0 0

5 K 20% ^ 8 0 0

6 K 3% <\. 5 0 0

2 K 95% <\. 160

T h e r e l a t i o n s h i p b e t w e e n t h e d i f f e r e n t t r i g g e r s a n d v a r i o u s p h y s i c a l

p r o c e s s e s i s s k e t c h e d i n f i g . 2 ( b ) . F o r t h e p r e s e n t d i s c u s s i o n t h e i n c l u s i v e

i n e l a s t i c c r o s s s e c t i o n c a n b e d i v i d e d i n t o t w o c o m p o n e n t s , t h e s i n g l e

d i f t r a c t i v e ( " S . D . " ; a r o u n d 1 5 - 2 5 % o f ° ¿ n e ^ a t l o w e r e n e r g i e s ) a n d t h e n o n

s i n g l e - d i f t r a c t i v e ( " N . S . D . " ) . B y s i n g l e d i f f r a c t i o n w e m e a n t h e e x c i t a t i o n

o f o n e o f t h e i n c i d e n t p a r t i c l e s i n t o a m a s s i v e s t a t e , w h o s e m a s s i s f o u n d a t

2 2 - 1

l o w e r e n e r g i e s t o s c a l e a c c o r d i n g t o d a / d ( M / s ) <\< (M / S ) . O u r d e t e c t i o n

e f f i c i e n c y f o r s u c h e v e n t s d e p e n d s o n d e t a i l s o f t h e m o d e l a s s u m e d f o r t h e

- 78 -

p r o d u c t i o n a n d d e c a y o f t h e e x c i t e d s t a t e , a n d t h i s q u e s t i o n i s s t i l l u n d e r

i n v e s t i g a t i o n a t p r e s e n t . We c o r r e c t t h e N S D d a t a u s i n g a M o n t e - C a r l o p r o g r a m

c o n s t r a i n e d t o d e s c r i b e c o r r e c t l y a l l o u r e x p e r i m e n t a l r e s u l t s o n c h a r g e d

p a r t i c l e , s t r a n g e p a r t i c l e a n d p h o t o n p r o d u c t i o n a n d t h e i r c o r r e l a t i o n s .

U s i n g t h i s M o n t e - C a r l o w e f i n d t h a t ^ 95% o f N S D e v e n t s a r e a c c e p t e d b y t h e

m i n i m u m b i a s t r i g g e r , b u t t h a t t h i s t r i g g e r a c c e p t s n o e l a s t i c e v e n t s a n d a

v e r y s m a l l f r a c t i o n ( m o d e l d e p e n d e n t , b u t p r o b a b l y < 10%) o f SD e v e n t s . U n l e s s

o t h e r w i s e s t a t e d t h e r e s u l t s b e l o w r e f e r t o t h e N S D c o m p o n e n t o n l y , c o r r e c t e d

f o r t h e 5% t r i g g e r l o s s .

T h e d i f f r a c t i v e t r i g g e r a c c e p t s t h e r e m a i n i n g 5% o f N S D e v e n t s t o g e t h e r

w i t h a s u b s t a n t i a l f r a c t i o n ( ^ 5 0 ± 1 5 % a c c o r d i n g t o o u r p r e s e n t b e s t e s t i m a t e s )

o f t h e SD c r o s s - s e c t i o n . I n o r d e r t o e x t r a c t c o r r e c t e d r e s u l t s o n SD p r o c e s s e s

i t i s n e c e s s a r y t o s u b t r a c t t h e r e s i d u a l N S D e v e n t s f r o m t h e d i f f r a c t i v e

t r i g g e r s . T h i s p r o c e d u r e i n t r o d u c e s s i g n i f i c a n t s y s t e m a t i c u n c e r t a i n t i e s ,

w h i c h w e a r e a t p r e s e n t i n v e s t i g a t i n g . H o w e v e r , m a n y o f t h e s e u n c e r t a i n t i e s

c a n c e l o u t i f o n e c o m b i n e s t h e SD r e s u l t s w i t h t h e N S D c o m p o n e n t t o o b t a i n f u l l

i n c l u s i v e d a t a . S o m e p r e l i m i n a r y i n c l u s i v e m e a s u r e m e n t s , u s i n g t h e d i f f r a c t i v e

t r i g g e r s , w i l l b e p r e s e n t e d b e l o w . We b e l i e v e t h e s y s t e m a t i c e r r o r s i n t h e s e

r e s u l t s t o b e < 5 % .

4 . C h a r g e d p a r t i c l e p r o d u c t i o n

O u r m e a s u r e m e n t s o f t h e c h a r g e d p a r t i c l e p s e u d o r a p i d i t y d i s t r i b u t i o n h a v e

b e e n p u b l i s h e d i n r e f . [ 3 ] . I n f i g . 3 w e s h o w o u r l a t e s t m e a s u r e m e n t s f o r N S D

e v e n t s , b a s e d o n d a t a t a k e n w i t h t h e B e r y l l i u m b e a m p i p e . A g r e e m e n t w i t h t h e

o l d e r r e s u l t s ( r e f [ 3 ] , o r f i g . 1 4 ( a ) ) i s e x c e l l e n t , s h o w i n g t h a t t h e c o r r e c t i o n s

a r e w e l l u n d e r s t o o d . T h e r e s u l t s o f t h e UA1 e x p e r i m e n t i n t h e m o r e l i m i t e d

r a n g e | n | < 3 . 5 C 4 ] a r e a l s o c o m p a t i b l e w i t h o u r s . We a l s o s h o w i n f i g . 3 o u r

- 7 9 -

p r e l i m i n a r y d e t e r m i n a t i o n o f t h e f u l l i n c l u s i v e p s e u d o r a p i d i t y d i s t r i b u t i o n

( i . e . i n c l u d i n g t h e S . D . c o m p o n e n t ) .

I t i s o f i n t e r e s t t o c o n s i d e r t h e e n e r g y d e p e n d e n c e o f t h i s d i s t r i b u t i o n .

I n f i g . 4 w e p l o t t h e c h a r g e d p a r t i c l e d e n s i t y a t n = 0 a g a i n s t C M . e n e r g y ,

/ s . O u r m e a s u r e d v a l u e s a r e 3 . 1 ± 0 . 1 f o r N S D e v e n t s a n d 2 . 7 ± 0 . 1 5 f o r t h e

i n c l u s i v e s a m p l e . T h e l o w e r e n e r g y d a t a , w h i c h i n c l u d e s i n g l e d i f f r a c t i o n ,

s h o u l d b e c o m p a r e d w i t h o u r i n c l u s i v e m e a s u r e m e n t i n f i g . 4 . T h e d a t a a r e

c l e a r l y c o n s i s t e n t w i t h a l i n e a r d e p e n d e n c e o n l o g s . T h i s v i o l a t i o n o f

F e y n m a n s c a l i n g w a s f i r s t n o t e d a t t h e I S R , b u t o n l y a t t h e S P S c o l l i d e r h a s

t h e r a n g e o f C M . e n e r g i e s b e c o m e l a r g e e n o u g h t o e s t a b l i s h t h e f o r m o f e n e r g y

d e p e n d e n c e .

We c a n a l s o c o n s i d e r t h e q u e s t i o n o f F e y n m a n s c a l i n g i n t h e b e a m f r a g m e n t a t i o n

r e g i o n s . F o r t h i s p u r p o s e w e u s e d a t a t a k e n w i t h t h e U A 5 d e t e c t o r a t t h e I S R ,

a t / s = 5 3 G e V , a n d a n a l y s e d b y e s s e n t i a l l y t h e s a m e t e c h n i q u e s [ 5 ] . T o m a k e

* * t h i s t e s t w e n e e d t o c o m p a r e t h e d a t a a t e q u a l v a l u e s o f n - y ^ e a s a - T h e I S R

& is d a t a h a v e t h e r e f o r e b e e n s h i f t e d b y y , ( 5 4 0 G e V ) - y , ( 5 3 G e V ) = 2 . 3 u n i t s .

b e a m b e a m

We o b s e r v e r e a s o n a b l e s c a l i n g ( t o ± 10%) f o r | r) — y'| 3 e a ml < 3 . T h e r e i s p o s s i b l y

a s l i g h t d r o p i n t h e p a r t i c l e d e n s i t y i n t h e f r a g m e n t a t i o n r e g i o n g o i n g f r o m

5 3 G e V t o 5 4 0 G e V , b u t a d e f i n i t i v e a n s w e r w i l l h a v e t o w a i t u n t i l t h e d i f f r a c t i v e

t r i g g e r s a r e f i n a l l y a n a l y s e d .

T h e a v e r a g e c h a r g e d m u l t i p l i c i t y m a y b e o b t a i n e d b y i n t e g r a t i n g t h e d a t a

p o i n t s s h o w n i n f i g . 3 . T h e e x t r a p o l a t i o n t o t h e r e g i o n | y | > 5 i s m a d e u s i n g

o u r M o n t e - C a r l o p r o g r a m , a n d i s s m a l l ( 7 ± 3 % ) . T h e r e s u l t s a r e :

< n , > = 2 8 . 9 ± 0 . 4 N S D c h

< n c k > = 2 6 . 5 ± 1 . 0 I n c l u s i v e ( p r e l i m i n a r y )

I n f i g . 5 t h e s e v a l u e s a r e c o m p a r e d w i t h l o w e r e n e r g y d a t a . I n r e f [ 6] a

n u m b e r o f f i t s t o t h e e n e r g y d e p e n d e n c e o f < nc j 1

> w e r e p e r f o r m e d . T h e b e s t f i t ,

- 80 -

a q u a d r a t i c i n l o g s , i s s h o w n i n f i g . 5 , a n d i s c l e a r l y c o n s i s t e n t w i t h o u r I

i n c l u s i v e m e a s u r e m e n t . O t h e r f o r m s , s u c h a s s 4 , c a n b e c l e a r l y e x c l u d e d b y

t h e c o l l i d e r d a t a . S e v e r a l c o s m i c r a y m e a s u r e m e n t s [ 7 ] a r e a l s o s h o w n i n f i g .

5 , a n d a r e g e n e r a l l y c o n s i s t e n t w i t h t h e t r e n d o f a c c e l e r a t o r d a t a , g i v e n t h e

l a r g e e r r o r s i n t h e c o s m i c r a y d a t a .

I n f i g . 6 w e p r e s e n t c h a r g e d p a r t i c l e p s e u d o r a p i d i t y d i s t r i b u t i o n s f o r

v a r i o u s r a n g e s o f o b s e r v e d m u l t i p l i c i t y ( nc ^ S ^ 0 - 8 n ^ o n a v e r a g e ) . We

o b s e r v e t h a t a s t h e c h a r g e d m u l t i p l i c i t y i n c r e a s e s t h e m a i n r i s e i n p a r t i c l e

p r o d u c t i o n i s i n t h e c e n t r a l r e g i o n . A t l a r g e c m . r a p i d i t i e s t h e d a t a t e n d

t o c o n v e r g e , i n d e e d i n t h e v i c i n i t y o f |n | ^ 5 t h e p a r t i c l e d e n s i t y i s

c o n s i s t e n t w i t h b e i n g m u l t i p l i c i t y i n d e p e n d e n t .

5 . C h a r g e d m u l t i p l i c i t y d i s t r i b u t i o n

T h e o b s e r v e d ( u n c o r r e c t e d ) c h a r g e d m u l t i p l i c i t y d i s t r i b u t i o n f o r N S D

e v e n t s i s s h o w n i n f i g . 7 ( a ) . T h e t e c h n i q u e s b y w h i c h t h i s d i s t r i b u t i o n c a n

b e c o r r e c t e d f o r e x p e r i m e n t a l a c c e p t a n c e a r e o u t l i n e d i n r e f C8], a n d t h e

r e s u l t i n g c o r r e c t e d m u l t i p l i c i t y d i s t r i b u t i o n i s s h o w n i n f i g . 7 ( b ) . H o w e v e r ,

i t s h o u l d b e n o t e d t h a t t h e c o r r e c t i o n p r o c e d u r e i n t r o d u c e s s t r o n g c o r r e l a t i o n s

b e t w e e n n e i g h b o u r i n g d a t a p o i n t s . N e v e r t h e l e s s , i t i s s t r a i g h t f o r w a r d t o

t a k e t h e s e c o r r e l a t i o n s i n t o a c c o u n t i n c o m p u t i n g t h e m o m e n t s o f t h e c o r r e c t e d

d i s t r i b u t i o n , g i v e n i n t h e t a b l e b e l o w .

- 81 -

Charged multiplicity moments at /s = 540 GeV

<n> 28.9 ± 0.4

D 2 15.4 ± 0.3

D 3 15.5 ± 0.5

D 4 21.7 ± 0.6

<n>/D 2 1.88 ± 0.03

C 2 1.28 ± 0.01

C 3 2.00 ± 0.04

C 4 3.61 ± 0.13

Y 2 .282 ± .009

Y 3 .152 ± .015

Y 4 .075 ± .020

The dispersions are defined by = <(n-<n>)^>^^

The C-moments are defined by C = <n^>/<n>^. q

2

The Y^moments are defined by = (Ü2/<n>) ;

Y 3 = (D 3/<n>) 3; Y 4 - ( D ^ - D ^ ) / < n > \

We have used these results to examine the energy dependence of multiplicity

distributions. A useful phenomenological framework on which to base this

comparison is the KNO scaling hypothesis (derived from Feynman scaling L"9]),

which proposes that:

<n> n s-*°°

*• i|>(z = n/<n>) ,

- 8 2 -

i n o t h e r w o r d s t h a t t h e s h a p e o f t h e d i s t r i b u t i o n s h o u l d a s y m p t o t i c a l l y

b e c o m e i n d e p e n d e n t o f e n e r g y . T o c o m p a r e o u r d a t a i n f i g . 7 w i t h t h e K N O

h y p o t h e s i s w e u s e f i t s t o ^ ( z ) b a s e d o n l o w e r e n e r g y d a t a , t o g e t h e r w i t h o u r

o b s e r v e d < n > .

( i ) T h e d a s h e d c u r v e s u s e a f i t t o i K z ) f o r i n c l u s i v e d a t a , d u e t o S l a t t e r y

[ 1 0 ] . T h i s S l a t t e r y f u n c t i o n g i v e s a r e a s o n a b l e f i t t o t h e d a t a , t h o u g h

t h e r e d o s e e m t o b e r e g i o n s o f s y s t e m a t i c d i s a g r e e m e n t . T h e UA1

c o l l a b o r a t i o n h a s m a d e a s i m i l a r c o m p a r i s o n C 4 ] , w i t h c o n s i s t e n t r e s u l t s .

H o w e v e r , s i n c e t h e c o l l i d e r d a t a e x c l u d e t h e s i n g l e d i f t r a c t i v e c o m p o n e n t

t h e r e i s n o l o g i c a l b a s i s f o r t h i s c o m p a r i s o n , a n d t h e a p p r o x i m a t e s c a l i n g

s e e n i s p r o b a b l y f o r t u i t o u s .

( i i ) T h e s o l i d c u r v e s a r e b a s e d o n a f i t t o i|>(z) u s i n g p u b l i s h e d N S D d a t a

[ 8 ] , w h i c h s h o u l d b e m o r e n e a r l y c o m p a r a b l e w i t h o u r r e s u l t s . U s i n g t h e

o b s e r v e d < n > = 2 8 . 9 w e o b t a i n a b a d f i t t o t h e d a t a , b u t b y u s i n g

< n > ^ 26 w e c a n o b t a i n a n a d e q u a t e d e s c r i p t i o n o f t h e m a i n p e a k .

H o w e v e r , t h e d a t a t h e n s h o w a s u b s t a n t i a l e x c e s s f o r n > 4 0 . We t h u s

s e e a s i g n i f i c a n t v i o l a t i o n o f K N O s c a l i n g f o r t h e N S D c o m p o n e n t ,

p r o b a b l y a s s o c i a t e d w i t h a g r o w i n g t a i l o f t h e d i s t r i b u t i o n . C o n f i r m a t i o n

o f s u c h a n e f f e c t m a y b e g i v e n b y f i g . 8 , w h i c h s h o w s t h e p e r c e n t a g e o f

e v e n t s h a v i n g z > Z q , f o r N S D d a t a , a s a f u n c t i o n o f / s . I d e a l K N O

s c a l i n g w o u l d i m p l y t h a t t h i s f r a c t i o n b e c o n s t a n t . We o b s e r v e a

s i g n i f i c a n t i n c r e a s e i n t h e p r o p o r t i o n o f h i g h m u l t i p l i c i t y e v e n t s , a n

e f f e c t p r o b a b l y p r e s e n t i n t h e l o w e n e r g y d a t a , b u t p l a i n l y e s t a b l i s h e d

a t t h e m u c h h i g h e r e n e r g y o f t h e S P S c o l l i d e r . T h e e f f e c t c l e a r l y i n c r e a s e s

w i t h z . o

T h e m o m e n t s o f t h e m u l t i p l i c i t y d i s t r i b u t i o n m a y b e u s e d t o t e s t K N O

s c a l i n g o r t o c h a r a c t e r i z e i t s v i o l a t i o n . F o r e x a m p l e , f i g . 9 s h o w s a p l o t

2 i o f D_ = < ( n - < n > ) > 2 a g a i n s t < n > . I n t h e c a s e o f K N O s c a l i n g a t f i n i t e e n e r g i e s

- 8 3 -

t h e d a t a s h o u l d f o l l o w a s t r a i g h t l i n e p a s s i n g t h r o u g h t h e o r i g i n . I n f a c t

t h e l o w e n e r g y i n c l u s i v e d a t a f a l l o n a l i n e w i t h i n t e r c e p t n = 1 ( d a s h e d

c u r v e ) . T h e h i g h e r m o m e n t s b e h a v e s i m i l a r l y . T h i s i m p l i e s a v i o l a t i o n o f

K N O s c a l i n g a t f i n i t e e n e r g i e s , b u t w o u l d , i f s u c h a t r e n d c o n t i n u e d , l e a d t o

a s y m p t o t i c K N O s c a l i n g . A l t e r n a t i v e l y , o n e c o u l d i n t e r p r e t t h i s a s a

m o d i f i e d f o r m o f K N O s c a l i n g , i n t h e v a r i a b l e z ' = ( n - a ) / ( < n > - a ) w i t h a ^ 1.

O u r p r e l i m i n a r y i n c l u s i v e d a t a p o i n t d o e s n o t , h o w e v e r , s e e m t o b e c o n s i s t e n t

w i t h t h e l i n e a r f i t t o l o w e n e r g y d a t a .

P u b l i s h e d N S D d a t a a r e a l s o s h o w n i n f i g . 9 . We s e e t h a t t h e l o w e n e r g y

d a t a a r e c o n s i s t e n t w i t h i d e a l s c a l i n g , i . e . a s t r a i g h t l i n e t h r o u g h t h e

o r i g i n ( s o l i d c u r v e ) . H o w e v e r t h e U A 5 m e a s u r e m e n t i s p l a i n l y i n c o n s i s t e n t

w i t h t h i s . We c a n n o t h o w e v e r e x c l u d e t h e p o s s i b i l i t y t h a t K N O s c a l i n g m a y

h o l d a s y m p t o t i c a l l y f o r t h e N S D c o m p o n e n t , a n d t h a t a t f i n i t e e n e r g i e s

m o d i f i e d K N O s c a l i n g i n z 1 = ( n - a ) / ( < n > - o t ) w i t h a i> 2 m a y b e a r e a s o n a b l e

a p p r o x i m a t i o n t o t h e d a t a ( d o t t e d c u r v e ) .

6 . S t r a n g e p a r t i c l e p r o d u c t i o n [ 1 1 ]

I n f o r m a t i o n a b o u t s t r a n g e p a r t i c l e p r o d u c t i o n h a s b e e n o b t a i n e d b y o b s e r v i n g

t w o - p r o n g n e u t r a l d e c a y s ( V ' s ) a n d o n e - o r t h r e e - p r o n g c h a r g e d d e c a y s w i t h i n

t h e s e n s i t i v e v o l u m e o f t h e c h a m b e r . A l l t h e d e c a y s u s e d h a v e b e e n c h e c k e d

v i s u a l l y o n t h e p h o t o g r a p h s . T h e g o o d s p a t i a l r e s o l u t i o n o f t h e s t r e a m e r

c h a m b e r s y s t e m w a s i n v a l u a b l e i n p r o v i d i n g a n u n a m b i g u o u s s a m p l e o f s u c h d e c a y s .

A l l r e s u l t s r e f e r t o t h e r e g i o n | n | < 3 , s i n c e t h e p r o b a b i l i t y o f d e c a y i n t h e

c h a m b e r v o l u m e f e l l r a p i d l y b e y o n d t h i s r a n g e .

T h e t h r e e - p r o n g c h a r g e d d e c a y s c o u l d b e u n a m b i g u o u s l y i n t e r p r e t e d a s

± ± ± K g * T h e o n e - p r o n g d e c a y s c o u l d b e e i t h e r K o r I T , b u t M o n t e - C a r l o s t u d i e s

s h o w e d t h a t a d e c a y a n g l e c u t c o u l d b e u s e d t o r e j e c t m o s t o f t h e ir~ d e c a y s .

T h e V ' s w e r e a m i x t u r e o f y c o n v e r s i o n s a n d K ? , K ° , A a n d Ä d e c a y s . P h o t o n s

- 84 -

w e r e r e j e c t e d u s i n g a n o p e n i n g a n g l e c u t , a n d K ° w e r e i d e n t i f i e d a s V ' s n o t XJ

c o p l a n a r w i t h t h e p r i m a r y v e r t e x . E a c h r e m a i n i n g c o p l a n a r V c o u l d b e

i n t e r p r e t e d a s K ° o r A / A , a n d o n c e a h y p o t h e s i s f o r t h e m a s s e s o f t h e p a r t i c l e s S

* o w a s m a d e t h e i r m o m e n t a a n d c m . d e c a y a n g l e ( c o s o ) c o m p u t e d . H o w e v e r , a K g

w i t h c o s 9 n e a r z e r o y i e l d s a r a t h e r s y m m e t r i c V i n t h e l a b , a n d s u c h a V c a n

o n l y b e i n t e r p r e t e d a s a A b y g i v i n g i t a v e r y l o w m o m e n t u m , s o t h a t i t w o u l d

h a v e b e e n u n l i k e l y t o r e a c h t h e c h a m b e r v o l u m e .

E a c h V w a s t h e r e f o r e s o l v e d a s b o t h A o r K ° , a n d t h e r a t i o o f t h e d e c a y s '

p r o b a b i l i t i e s p l o t t e d a g a i n s t c o s o f o r t h e K ° h y p o t h e s i s ( f i g . 1 0 ( a ) ) . F o r is. S

1 * 1 o | c o s 9 [ < 0 . 5 t h e l i f e t i m e p r o b a b i l i t y c l e a r l y f a v o u r s t h e K s o l u t i o n , a n d w e K. S

t a k e t h e s e V ' s a s a s a m p l e o f c l e a n K ° . F i g . 1 0 ( c ) s h o w s t h a t t h e s e K ° h a v e

t h e e x p e c t e d l i f e t i m e d i s t r i b u t i o n . T h e r e g i o n c o s 6 | > 0 . 5 c o n t a i n s a m i x t u r e

o f K ° ( e q u a l i n n u m b e r t o t h o s e i n | c o s 6 ^ | < 0 . 5 ) a n d A / Ä ( w h o s e n u m b e r a n d

o t h e r p r o p e r t i e s m a y b e i n f e r r e d b y s u b t r a c t i o n ) . F i g . 1 0 ( b ) s h o w s t h a t a *

M o n t e - C a r l o c a l c u l a t i o n b a s e d o n t h i s i n t e r p r e t a t i o n f i t s t h e c o s 0 d i s t r i b u t i o n

w e l l .

T o c o r r e c t t h e K~ a n d d a t a k n o w l e d g e o f t h e i r m o m e n t u m d i s t r i b u t i o n

i s r e q u i r e d . I n f i g . 1 1 ( a ) w e s h o w t h e p^, d i s t r i b u t i o n s f o r K ° a n d A / X , f o r

w h i c h t h e m o m e n t a c.ni b e c a l c u l a t e d . I n b o t h c a s e s t h e d a t a a r e c o n s i s t e n t - b p T

w i t h t h e f o r m e , a n d a s s u m i n g t h i s h o l d s a t a l l p ^ w e c a n e s t i m a t e v a l u e s

o f , 0 . 7 0 ± 0 . 1 2 G e V / c f o r K ° a n d 0 . 6 5 ± 0 . 2 0 G e V / c f o r A / Â . We t h e n a s s u m e JL S

o ± o t h e s a m e v a l u e o f <Prp > f o r a n d K a s f o r K .

T h e t a b l e b e l o w g i v e s t h e o b s e r v e d n u m b e r o f d e c a y s , a n d t h e r e s u l t i n g

c o r r e c t e d y i e l d s :

- 85 -

S t r a n g e p a r t i c l e y i e l d s a t / s = 5 4 0 G e V

D e c a y t y p e U n c o r r e c t e d

N o . o f d e c a y s u s e d M e a n N o . p e r e v e n t i n |ri|<3

K s

9 2 1 . 0 ± 0 . 2

17 1 . 0 ± 0 . 3

+ r 1 - p r o n g 123 1 . 8 ± 0 . 2

** 3 - p r o n g 7

A / Ä 46 0 . 3 5 ± 0 . 1 0

T h e d a t a a r e c o n s i s t e n t w i t h t h e n a i v e e x p e c t a t i o n t h a t :

< K ° > = < K £ > = | < K ± > ,

a n d t h i s s e r v e s a s c o n f i r m a t i o n o f t h e v a l u e o f u s e d i n t h e a n a l y s i s ,

s i n c e t h e d e t e c t i o n p r o b a b i l i t y f o r K ° i n c r e a s e s w i t h , w h e r e a s t h a t f o r

o ±

a n d K d e c r e a s e s w i t h . I n f a c t i f w e a s s u m e e x a c t e q u a l i t y b e t w e e n

c h a r g e d a n d n e u t r a l k a o n s a l o w e r l i m i t o f 0 . 5 8 G e V m a y b e p l a c e d o n a t

90% c . l .

O u r d a t a a r e c o m p a r e d w i t h l o w e r e n e r g y r e s u l t s i n f i g . 1 2 . F i g 1 2 ( a )

s h o w s f o r k a o n s [ 1 2 ] , a n d f i g . 1 2 ( b ) t h e r a t i o I T / i r * o r QSL0+¥L°)/it*

[ 1 2 , 1 3 ] . I t a p p e a r s f r o m f i g . 1 2 ( b ) t h a t t h e K / i r r a t i o i s i n c r e a s i n g s l o w l y

w i t h e n e r g y , t h o u g h t h e s i t u a t i o n i n t h e I S R e n e r g y r e g i o n i s r a t h e r c o n f u s e d .

R e s u l t s o n K ~ p r o d u c t i o n f r o m t h e U A 2 e x p e r i m e n t [ 1 4 ] c o n f i r m t h i s c o n c l u s i o n .

A m o r e s t r i k i n g e f f e c t i s t h e i n c r e a s e o f , w h i c h c o u l d p o s s i b l y s u g g e s t

t h a t s o m e e f f e c t i v e t h r e s h o l d f o r a p r o c e s s g i v i n g h i g h e r p^, k a o n s m a y h a v e

b e e n c r o s s e d , s u c h a s c h a r m d e c a y .

T h e p s e u d o r a p i d i t y d i s t r i b u t i o n s o f b o t h n e u t r a l a n d c h a r g e d k a o n s a r e

c o n s i s t e n t w i t h b e i n g f l a t ( f i g . 1 1 ( b ) ) , a s w a s t h e o v e r a l l c h a r g e d p a r t i c l e

d i s t r i b u t i o n i n t h e r a n g e | n | < 3 . T h e t a b l e b e l o w g i v e s k a o n y i e l d s i n v a r i o u s

- 86 -

M u l t i p l i c i t y d e p e n d e n c e o n k a o n p r o d u c t i o n ( i n | n | < 3 ) a t / s = 5 4 0 G e V

O b s e r v e d m u l t i p l i c i t y ( n ° ^ S ) < n ( K s / K L ) >

< n ° ? S > c h

< n ( K ± ) > o b s

< n c h >

< 2 0 0 . 0 8 ± 0 . 0 2 0 . 0 7 ± 0 . 0 1

2 1 - 3 9 0 . 0 8 ± 0 . 0 2 0 . 0 8 ± 0 . 0 1

> 4 0 0 . 1 1 ± 0 . 0 3 0 . 0 7 ± 0 . 0 1

a l l 0 . 0 9 ± 0 . 0 2 0 . 0 8 ± 0 . 0 1

7 . P h o t o n p r o d u c t i o n [ 3 ]

I n f o r m a t i o n o n i n c l u s i v e p h o t o n p r o d u c t i o n h a s b e e n o b t a i n e d f r o m t h e

o b s e r v a t i o n o f s h o w e r s i n t h e s t e e l b e a m p i p e a n d t h e 9 0 ° l e a d g l a s s p l a t e s .

S h o w e r s i n t h e b e a m p i p e a r e i d e n t i f i e d i n t h e v e r t e x f i n d i n g p r o c e d u r e a s

e x p l a i n e d i n r e f . [ 3 ] . S u c h s h o w e r s a r e e x p e c t e d t o b e m a i n l y p h o t o n

i n d u c e d , b u t a l s o i n c l u d e h a d r o n i c s h o w e r s a n d c h a n c e s p u r i o u s a s s o c i a t i o n s

o f t r a c k s . A s t u d y o f M o n t e - C a r l o e v e n t s a l l o w e d c u t s t o b e d e v i s e d , b a s e d

o n t h e w e l l c o l l i m a t e d n a t u r e o f e l e c t r o m a g n e t i c s h o w e r s , w h i c h p r o d u c e d a

s a m p l e o f p h o t o n i n d u c e d s h o w e r s o f p u r i t y £ 8 0 % . F o r e x a m p l e , f i g . 13 s h o w s

t h e c u t o n s h o w e r o p e n i n g a n g l e a p p l i e d i n t h e r a n g e 2 < | n | < 3 .

T h e n u m b e r s o f p h o t o n s o b s e r v e d w e r e t h e n c o r r e c t e d u s i n g t h e M o n t e - C a r l o

i n m u c h t h e s a m e w a y a s f o r c h a r g e d p a r t i c l e s . T h e r e s u l t i n g p s e u d o r a p i d i t y

d i s t r i b u t i o n i s s h o w n i n f i g . 1 4 ( a ) , w i t h t h e c h a r g e d p a r t i c l e d a t a f o r

r a n g e s o f o b s e r v e d c h a r g e d m u l t i p l i c i t y . T h e p r o p o r t i o n o f k a o n s s h o w s n o

s i g n i f i c a n t v a r i a t i o n w i t h m u l t i p l i c i t y .

- 87 -

c o m p a r i s o n . T h e r e s u l t s f r o m t h e b e a m p i p e a n d t h e l e a d g l a s s p l a t e a r e

c o n s i s t e n t , g i v i n g a d d e d c o n f i d e n c e i n t h e r e s u l t s . We o b s e r v e a s i g n i f i c a n t

e x c e s s o f p h o t o n s ( 3 4 ± 2 i n | n | < 5 ) o v e r c h a r g e d p a r t i c l e s ( 2 6 . 5 ± 1 i n | n | < 5 ) .

T h e r a p i d i t y d i s t r i b u t i o n o f p h o t o n s i s s e e n t o b e n a r r o w e r t h a n f o r c h a r g e d

p a r t i c l e s .

We w o u l d e x p e c t m o s t p h o t o n s t o o r i g i n a t e f r o m i r° d e c a y s . T h e n a r r o w e r

p h o t o n d i s t r i b u t i o n t h e n a r i s e s n a t u r a l l y a s a c o n s e q u e n c e o f t h e TT° d e c a y

k i n e m a t i c s . T o i n t e r p r e t t h e p h o t o n e x c e s s w e f i r s t s u b s t r a c t t h e

K ° -*- 2TT° -»• 4 y c o n t r i b u t i o n f r o m t h e p h o t o n d i s t r i b u t i o n a n d t h e K - , p , p S

c o n t r i b u t i o n s f r o m t h e c h a r g e d p a r t i c l e d i s t r i b u t i o n , u s i n g t h e p a r t i c l e

y i e l d s t o b e s u m m a r i z e d i n § 9 . I n t e g r a t i n g t h e r e s u l t i n g d i s t r i b u t i o n s

( f i g . 1 4 ( b ) ) g i v e s 3 1 . 5 ± 2 p h o t o n s a n d 2 2 . 5 ± 1 T T * i n | n | < 5 .

T h e s e r e s u l t s a r e i n c o n s i s t e n t w i t h t h e n a i v e e x p e c t a t i o n t h a t o ± .

<ir > =¡ £<ir > . T w o p o s s i b l e i n f e r e n c e s m a y b e d r a w n :

e i t h e r <ir°> = 1 . 4 x 5 < T T ± >

o r t h e r e i s s o m e o t h e r s o u r c e o f p h o t o n s . F o r e x a m p l e

t h e d a t a a r e c o m p a t i b l e w i t h <ir°> = 2<T T ~ > t o g e t h e r

w i t h y - m e s o n p r o d u c t i o n i n t h e p r o p o r t i o n

n / T T ° * 3 0 ± 1 0 % .

T h e c u r v e s i n f i g . 1 4 ( b ) s h o w t h e r e s u l t s o f M o n t e - C a r l o c a l c u l a t i o n s b a s e d

o n e a c h o f t h e s e h y p o t h e s e s . C l e a r l y e i t h e r i n t e r p r e t a t i o n i s c o m p a t i b l e

w i t h o u r d a t a . T h e c o p i o u s p r o d u c t i o n o f n - m e s o n s s e e m s t h e m o s t p l a u s i b l e

e x p l a n a t i o n o f o u r r e s u l t s , a n d r e c e i v e s s o m e s u p p o r t f r o m t h e o b s e r v a t i o n

o f n - m e s o n s a t p ^ , > 1 . 4 G e V i n t h e U A 2 e x p e r i m e n t [ 1 5 ] , a n d i n d i r e c t l y f r o m

t h e c a l o r i m e t e r d a t a o f UA1 [ 1 6 ] .

T o i n v e s t i g a t e t h e c o r r e l a t i o n b e t w e e n p h o t o n a n d c h a r g e d p a r t i c l e

p r o d u c t i o n w e h a v e e s t i m a t e d t h e a v e r a g e n u m b e r o f p h o t o n s p r o d u c e d < n > a s

- 8 8 -

8 . S e a r c h f o r C e n t a u r o E v e n t s [ 3 ]

We h a v e u s e d o u r p h o t o n d a t a t o s e a r c h f o r C e n t a u r o - l i k e e v e n t s . T h e

c h a r a c t e r i s t i c f e a t u r e s o f t h e C e n t a u r o e v e n t s o b s e r v e d i n t h e M t . C h a c a l t a y a

e m u l s i o n c h a m b e r e x p e r i m e n t C l ] a r e h i g h p r i m a r y e n e r g y ( ^ 1 0 0 0 - 2 0 0 0 T e V ) ,

h i g h h a d r o n i c m u l t i p l i c i t y a n d e s s e n t i a l l y n o p h o t o n s . S p e c i f i c a l l y , f o r

" C e n t a u r o I " , t h e b e s t c o n s t r a i n e d e v e n t , 56 h a d r o n s w e r e o b s e r v e d i n t h e

* c m . r a p i d i t y r a n g e w h e r e t h e d e t e c t i o n e f f i c i e n c y w a s g o o d , n > 2 . T o

s i m u l a t e t h e e m u l s i o n c h a m b e r a c c e p t a n c e w e h a v e t h e r e f o r e e x a m i n e d o u r d a t a

* * i n t h e r a n g e n > 2 ( o r n < - 2 ) . A l l o w i n g f o r o u r a c c e p t a n c e , a s s u m i n g a n o r m a l

I

m i x t u r e o f n e u t r a l a n d c h a r g e d h a d r o n s ( § 9 ) b u t e x c l u d i n g TT S a n d n ' s , a n d

t a k i n g t h e d i f f e r e n t c m . e n e r g i e s i n t o a c c o u n t w e w i s h t o l o o k f o r e v e n t s

w i t h i> 3 0 t o 4 0 c h a r g e d p a r t i c l e s a n d 1±1 p h o t o n ( f r o m s e c o n d a r y i n t e r a c t i o n s

e t c , b a s e d o n a M o n t e - C a r l o w i t h n o p r i m a r y p h o t o n s ) .

F i g . 16 s h o w s a p l o t o f n ° ^ S a g a i n s t n ° ^ S i n |n |>2 ( o r |n | < 2 ) . We

s e e n o e v e n t s a n y w h e r e n e a r t h e C e n t a u r o r e g i o n , c o r r e s p o n d i n g t o a l i m i t

o f < 1 i n 3 6 0 0 e v e n t s . T h e m o s t e x t r e m e a s s u m p t i o n w e c o u l d m a k e i s t h a t

^ 5 0 % o f p a r t i c l e s i n C e n t a u r o e v e n t s m i g h t b e l o n g l i v e d n e u t r a l s ( e . g .

b a r y o n / a n t i b a r y o n d o m i n a n c e ) , i n w h i c h c a s e C e n t a u r o s m i g h t a p p e a r t o h a v e

- 17 c h a r g e d t r a c k s i n |n | > 2 . We o b s e r v e s u c h e v e n t s a t a r a t e ^ 1 i n 150

e v e n t s , b u t i t i s e v i d e n t f r o m f i g . 16 t h a t t h e s e a r e m o s t p r o b a b l y j u s t a

t a i l o f n o r m a l e v e n t s . U s i n g a c a l o r i m e t r i c t e c h n i q u e t h e UA1 c o l l a b o r a t i o n

a f u n c t i o n o f c h a r g e d m u l t i p l i c i t y T h e r e s u l t s ( c o r r e c t e d t o r e f e r t o

t h e f u l l r a p i d i t y r a n g e ) a r e s h o w n i n F i g . 1 5 ( a ) . T h e d a t a a r e c o n s i s t e n t

w i t h a l i n e a r r i s e , o f t h e f o r m

< n > = ( 8 ± 3 ) + ( 0 . 9 0 ± . 0 8 ) n , . y e n

T h e c o r r e l a t i o n s t r e n g t h , a s m e a s u r e d b y t h e g r a d i e n t o f t h i s l i n e , i s

c o m p a r e d w i t h l o w e r e n e r g y d a t a [ 1 7 ] i n f i g . 1 5 ( b ) .

- 8 9 -

h a v e l i k e w i s e f o u n d n o e v i d e n c e f o r C e n t a u r o s [ 1 8 ] .

O n e m a y t h e n s p e c u l a t e w h e t h e r a t h r e s h o l d f o r C e n t a u r o p r o d u c t i o n

e x i s t s j u s t a b o v e / s = 5 4 0 G e V . F i g . 1 7 , t a k e n f r o m r e f [ 1 9 ] , s h o w s t h e

f r a c t i o n o f " u n u s u a l e v e n t s " ( C e n t a u r o , M i n i - C e n t a u r o , G e m i n i o n , C h i r o n ) a s

a f u n c t i o n o f / s . T h e p r o d u c t i o n o f t h e s e e v e n t s a p p e a r s t o i n c r e a s e s t e e p l y

w i t h e n e r g y , a n d t h e d a t a t h e r e f o r e s u g g e s t t h a t i f t h e c o l l i d e r e n e r g y c o u l d

b e i n c r e a s e d t o ^ 8 - 9 0 0 G e V t h e s e p h e n o m e n a s h o u l d b e c o n c l u s i v e l y e s t a b l i s h e d

o r d i s p r o v e d .

9 . P a r t i c l e C o m p o s i t i o n a t / s = 5 4 0 G e V [ 8 ]

U s i n g t h e a b o v e r e s u l t s o n y i e l d s o f c h a r g e d p a r t i c l e s , p h o t o n s a n d

s t r a n g e p a r t i c l e s , a n d m a k i n g s o m e p l a u s i b l e a s s u m p t i o n s , w e c a n e s t i m a t e t h e

p a r t i c l e c o m p o s i t i o n i n p p i n t e r a c t i o n s a t / s = 5 4 0 G e V . We s h a l l n o t c o n s i d e r

h e r e t h e r e g i o n |ri|>5 w h e r e o u r d e t e c t i o n e f f i c i e n c y i s z e r o ; o u r M o n t e - C a r l o

s i m u l a t i o n s u g g e s t s t h a t t h e r e w i l l b e t y p i c a l l y ^ 3 p a r t i c l e s / e v e n t i n t h i s

r e g i o n , n o r m a l l y i n c l u d i n g o n e l e a d i n g b a r y o n a n d o n e l e a d i n g a n t i b a r y o n ,

a n d t h e a n a l y s i s m a y t h e r e f o r e b e t a k e n t o b e r e p r e s e n t a t i v e o f t h e p r o d u c t i o n

o f n o n - l e a d i n g p a r t i c l e s ( n o t e t h a t n 'v- 5 c o r r e s p o n d s t o a v a l u e o f t h e

F e y n m a n s c a l i n g v a r i a b l e x ^ . 1 1 f o r p^, ^ 0 . 4 G e V / C ) .

T h e a s s u m p t i o n s w e m a k e a r e a s f o l l o w s :

i ) T h e y i e l d s o f k a o n s a n d A / A c a n b e e x t r a p o l a t e d f r o m | r i| < 3

t o |n| < 5 u s i n g t h e o b s e r v e d y i e l d s o f a l l c h a r g e d p a r t i c l e s ,

a s s u m i n g t h a t a l l t h e s e p a r t i c l e s h a v e r o u g h l y t h e s a m e f o r m

o f r a p i d i t y d i s t r i b u t i o n s , i . e . m u l t i p l y i n g b y

< n c h ( | n | < 5 ) > / < n c h ( | n | < 3 ) = 2 6 . 5 / 1 9 . 5 .

i i ) T h e r a t i o a ( p ) / c ( A ) i s t a k e n t o b e 3 . T h e r e g i o n | n | < 5

w i l l l a r g e l y e x c l u d e b a r y o n s c o m i n g f r o m b e a m f r a g m e n t a t i o n ,

s o i t i s a p p r o p r i a t e t o e x a m i n e l o w e r e n e r g y p p d a t a o n p

- 9 0 -

a n d A p r o d u c t i o n t o e s t i m a t e t h e p r o d u c t i o n o f c e n t r a l

b a r y o n - a n t i b a r y o n p a i r s . F i g . 18 s h o w s t h e e x i s t i n g , t h o u g h

r a t h e r s p a r s e , d a t a [ 1 2 , 1 3 ] , w h i c h a r e c o m p a t i b l e w i t h t h i s

a s s u m p t i o n . We a l s o n o t e t h a t o u r A / A d a t a a r e c o n s i s t e n t

w i t h t h e U A 2 m e a s u r e m e n t s o f p / p p r o d u c t i o n [ 1 4 ] i f t h i s

r a t i o i s a s s u m e d .

i i i ) We a s s u m e CT(A) = a ( E + + E . T h e c o n t r i b u t i o n i s a s

u s u a l i n c l u d e d i n t h e A y i e l d .

i v ) We a s s u m e a ( n + n ) = a ( p + p ) .

U s i n g t h e s e a s s u m p t i o n s t h e f i r s t p a r t o f t h e t a b l e b e l o w h a s b e e n c o m p l e t e d .

I f w e m a k e t h e f u r t h e r a s s u m p t i o n t h a t t h e p h o t o n e x c e s s i s c a u s e d b y

t h e n - m e s o n p r o d u c t i o n t h e n t h e l o w e r p a r t o f t h e t a b l e , g i v i n g p i o n a n d

n - m e s o n y i e l d s , m a y b e d e r i v e d . F o r c o m p a r i s o n w e a l s o s h o w p a r t i c l e y i e l d s

a t / s = 5 3 G e V u s i n g I S R d a t a o n p , u a n d K p r o d u c t i o n ( R o s s i , [ 1 2 ] ) a n d

p h o t o n p r o d u c t i o n [ 1 7 ] , a p p l y i n g t h e s a m e a s s u m p t i o n s d e t a i l e d a b o v e , a n d

e x c l u d i n g l e a d i n g b a r y o n s .

We c o n c l u d e t h a t a t y p i c a l e v e n t a t / s = 5 4 0 G e V h a s ^ 4 3 p r i m a r y s t a b l e

p a r t i c l e s p r o d u c e d i n |n| < 5 , o b t a i n e d b y s u m m i n g t h o s e m a r k e d w i t h a n

a s t e r i s k * i n t h e t a b l e . O f t h e s e ^ 12% a r e k a o n s a n d ^ 9% b a r y o n s o r a n t i -

b a r y o n s . F o r c o m p a r i s o n t h e c o r r e s p o n d i n g f i g u r e s a t / s = 5 3 G e V a r e 9% a n d

5 % . We t h u s i n f e r a n i n c r e a s e i n t h e p r o p o r t i o n s o f k a o n s a n d b a r y o n s

p r o d u c e d a t t h e S P S c o l l i d e r a s c o m p a r e d w i t h I S R e n e r g i e s . T h e s e r e s u l t s

t a k e n o a c c o u n t o f t h e e f f e c t o f s t r o n g l y d e c a y i n g r e s o n a n c e s ; i n v i e w o f t h e

o b s e r v e d s i m i l a r i t y o f c o r r e l a t i o n p h e n o m e n a a t S P S a n d I S R [ 2 0 ] w e m a y g u e s s

t h a t t h e p r o p o r t i o n o f p a r t i c l e s o r i g i n a t i n g f r o m r e s o n a n c e d e c a y s h a s n o t

a l t e r e d t o o m u c h .

- 91 -

A v e r a g e p a r t i c l e m u l t i p l i c i t i e s a t S P S c o l l i d e r a n d I S R . T h e S P S d a t a r e f e r t o | r ) | < 5 , a n d t h u s e x c l u d e l e a d i n g p a r t i c l e s , w h i l s t i n t h e I S R d a t a w e h a v e e x c l u d e d l e a d i n g b a r y o n s ( d e f i n e d a s t h e d i f f e r e n c e b e t w e e n p a n d p e t c . )

S P S C o l l i d e r - / s = 5 4 0 G e V I S R < n >

P a r t i c l e t y p e < n > f o r | n | < 3 <n> f o r 1 n| < 5 / s = 5 3 G e V

A l l c h a r g e d 1 9 . 5 2 6 . 5 1 0 . 1 +

KT 1 . 8 2 . 5 * . 7 5 * p + p 1 . 5 * si *

. 2 5 * . 0 4 * +

ir 2 2 . 3 9 . 0

A+Ä . 3 5 . 5 * .1 * K°+K° 2 . 0 2 . 7 * ri_ *

n + n 1 . 5 * . 3 * A l l Y 31 . 5 11 . 8

n 3 . 5 1.1 * Y ( f r o m n) 1 1 . 2 3 . 4

Tr ± ( f r o m n) 2 . 1 . 6

ir~(not f r o m n) 2 0 . 1 * 8 . 4 * TT° ( n o t f r o m n) 1 0 . 1 * 4 . 2 *

T h e i t e m s u n d e r l i n e d a r e d i r e c t l y m e a s u r e d . T h e o t h e r v a l u e s h a v e b e e n e s t i m a t e d f o l l o w i n g t h e a s s u m p t i o n s i n t h e t e x t . T h e i t e m s m a r k e d w i t h a n a s t e r i s k a r e t h e l o n g l i v e d p a r t i c l e s p r o d u c e d i n t h e p r i m a r y i n t e r a c t i o n , i n c l u d i n g t h e p r o d u c t s o f s t r o n g d e c a y s .

1 0 . F u t u r e p l a n s f o r U A 5

I n t h e s h o r t t e r m w e s h a l l c o n t i n u e t h e a n a l y s i s o f o u r 1 9 8 2 d a t a , w i

p a r t i c u l a r e m p h a s i s o n t h e f o l l o w i n g t o p i c s :

i ) A n a l y s i s o f t h e d i f f r a c t i v e t r i g g e r s , i n o r d e r t o d e r i v e f u l l

- 9 2 -

i n c l u s i v e d a t a a n d , w e h o p e , r e s u l t s o n t h e s i n g l e d i f t r a c t i v e

c o m p o n e n t .

i i ) E x t e n s i o n o f s t r a n g e p a r t i c l e s t u d i e s w i t h b e t t e r s t a t i s t i c s ,

w i t h p a r t i c u l a r e m p h a s i s o n k a o n a n d b a r y o n p r o d u c t i o n i n h i g h

m u l t i p l i c i t y e v e n t s .

i i i ) D e t a i l e d s t u d y o f h i g h m u l t i p l i c i t y e v e n t s , i n t h e g r o w i n g t a i l

o f t h e d i s t r i b u t i o n .

i v ) A n a l y s i s o f t h e c a l o r i m e t e r d a t a , i n v o l v i n g t h e e s t i m a t i o n o f

n / n y i e l d s , s t u d y o f E T s p e c t r a f o r c h a r g e d p a r t i c l e s a n d p h o t o n s ,

a n d t h e i r c o r r e l a t i o n w i t h m u l t i p l i c i t y .

T h e U A 5 c o l l a b o r a t i o n h a s a l s o p r o p o s e d t o c a r r y o u t a n e x p e r i m e n t a t

/ s = 8 - 9 0 0 G e V , u s i n g t h e S P S c o l l i d e r i n a c y c l i c m o d e [ 2 1 ] . T h e o b j e c t i v e

o f t h i s e x p e r i m e n t w o u l d b e t o c o m p l e t e a n o v e r v i e w o f h a d r o n i c i n t e r a c t i o n s

u s i n g a s i n g l e d e t e c t o r o v e r a l a r g e r a n g e o f c m . e n e r g i e s , 5 3 , 2 0 0 , 5 4 0

a n d 9 0 0 G e V . S u c h a s u r v e y w o u l d b e a b l e t o c o v e r a n u m b e r o f i n t e r e s t i n g

t o p i c s , f o r e x a m p l e t h e s t u d y o f K N O s c a l i n g v i o l a t i o n s , s t r a n g e n e s s p r o d u c t i o n

( r i s e o f e t c ) , b a r y o n p r o d u c t i o n ( w h e r e c o s m i c r a y d a t a s u g g e s t

i n t e r e s t i n g c h a n g e s i n t h i s e n e r g y r a n g e [ 1 9 ] ) , t h e p h o t o n e x c e s s a n d F e y n m a n

s c a l i n g v i o l a t i o n s . We w o u l d a l s o r e p e a t o u r s e a r c h f o r u n u s u a l p h e n o m e n a ,

a n d h o p e t o r e s o l v e d e f i n i t i v e l y t h e l o n g s t a n d i n g C e n t a u r o q u e s t i o n .

1 1 . S u m m a r y

T h e m a i n f e a t u r e s o f h a d r o n i c i n t e r a c t i o n s a t / s = 5 4 0 G e V , d e t e r m i n e d

i n t h e U A 5 e x p e r i m e n t , a r e a s f o l l o w s :

i ) T h e a v e r a g e c h a r g e d m u l t i p l i c i t y i s m e a s u r e d t o b e 2 8 . 9 ± 0 . 4 f o r

n o n s i n g l e - d i f t r a c t i v e ( N S D ) p r o c e s s e s a n d 2 6 . 5 ± 1 . 0 ( p r e l i m i n a r y )

f o r i n c l u s i v e s . T h e e n e r g y d e p e n d e n c e o f < nc n

> s e e m s t o f o l l o w

2 a f o r m a + b l o g s + c l o g s .

- 93 -

* i i ) T h e c h a r g e d p a r t i c l e p s e u d o r a p i d i t y d e n s i t y n e a r n = 0 i s

3 . 1 ± 0 . 1 f o r N S D a n d 2 . 7 ± 0 . 1 5 ( p r e l i m i n a r y ) f o r i n c l u s i v e e v e n t s .

T h i s c e n t r a l d e n s i t y f o l l o w s a ^ l o g s e n e r g y d e p e n d e n c e .

i i i ) T h e c h a r g e d p a r t i c l e r a p i d i t y d i s t r i b u t i o n i s f o u n d t o s c a l e t o

•v» ± 10% i n t h e f r a g m e n t a t i o n r e g i o n ( l v t j e a m ~ n J £ 3 ) , w i t h

t h e 5 4 0 G e V d a t a p o s s i b l y l y i n g l o w e r .

i v ) T h e c h a r g e d m u l t i p l i c i t y d i s t r i b u t i o n h a s b e e n d e r i v e d , a n d i t s

e n e r g y d e p e n d e n c e d i s c u s s e d . F o r t h e N S D c o m p o n e n t a c l e a r v i o l a t i o n

o f i d e a l K N O s c a l i n g i s o b s e r v e d , a s s o c i a t e d w i t h a g r o w i n g t a i l

o f h i g h m u l t i p l i c i t y e v e n t s .

v ) A t f i n i t e e n e r g i e s a m o d i f i e d f o r m o f K N O s c a l i n g , i n t h e v a r i a b l e

z 1 = ( n - a ) / ( < n > - a ) w i t h a ^ 2 , m a y a p p r o x i m a t e t h e N S D d a t a . T h i s

w o u l d l e a d t o K N O s c a l i n g a t a s y m p t o t i c e n e r g i e s .

v i ) T h e v a l u e o f f o r k a o n s i s s i g n i f i c a n t l y h i g h e r t h a n a t I S R

o r F N A L e n e r g i e s .

v i i ) T h e p r o p o r t i o n s o f k a o n s a n d b a r y o n s ( i n f e r r e d f r o m A/A p r o d u c t i o n )

a r e h i g h e r t h a n a t I S R e n e r g i e s .

v i i i ) A n e x c e s s o f p h o t o n s o v e r c h a r g e d p a r t i c l e s i s o b s e r v e d , a n d

i n t e r p r e t e d a s p r o b a b l y c a u s e d b y n - m e s o n p r o d u c t i o n i n t h e r a t i o

TI/TT ° <v 3 0 % .

i x ) A s t r o n g p h o t o n - c h a r g e d c o r r e l a t i o n i s o b s e r v e d , e x t e n d i n g t o t h e

h i g h e s t m u l t i p l i c i t i e s .

x ) N o e v i d e n c e h a s b e e n f o u n d f o r C e n t a u r o e v e n t s a t t h e c o l l i d e r .

- 94 -

R e f e r e n c e s

C l ] C M . G . L a t t e s e t a l , P h y s . R e p 6 5 C ( 1 9 8 0 ) 1 5 2 .

[ 2 ] U A 5 C o l l a b o r a t i o n , P h y s . S c r i p t a 23 ( 1 9 8 1 ) 6 4 2 .

[ 3 ] K . A l p g â r d e t a l , P h y s . L e t t . 1 1 5 B ( 1 9 8 2 ) 7 1 .

[ 4 ] G . A r n i s o n e t a l , UA1 C o l l a b o r a t i o n , C E R N p r e p r i n t , C E R N - E P / 8 2 - 1 3 4 .

[ 5 ] K . A l p g â r d e t a l , P h y s . L e t t . 1 0 7 B ( 1 9 8 2 ) 3 1 5 .

[ 6 ] W . T h o m é e t a l , N u c l . P h y s . B 1 2 9 ( 1 9 7 7 ) 3 6 5 .

[ 7 ] S . T a s a k a , e t a l , U n i v . o f T o k y o , I n s t , o f C o s m i c R a y R e s e a r c h p r e p r i n t , I C R 9 3 - 8 1 - 9 .

N . K . Y a m d a g n i , P r o c . P h y s i c s i n C o l l i s i o n I I , S t o c k h o l m ( 1 9 8 2 ) .

[ 8 ] K . A l p g â r d e t a l , P h y s . L e t t . 1 2 1 B ( 1 9 8 3 ) 2 0 9 .

[ 9 ] Z . K o b a , H . B . N i e l s e n a n d P . O l e s o n , N u c l . P h y s . B 4 0 ( 1 9 7 2 ) 3 1 7 .

[ 1 0 ] P . S l a t t e r y , P h y s . R e v . D 7 ( 1 9 7 3 ) 2 0 7 3 .

[ 1 1 ] K . A l p g â r d e t a l , P h y s . L e t t 115B ( 1 9 8 2 ) 6 5 .

[ 1 2 ] V . B l o b e l e t a l , N u c l . P h y s . B 6 9 ( 1 9 7 3 ) 4 5 5 .

M . A l s t o n - G a r n j o s t e t a l , P h y s . R e v . L e t t . 3 5 ( 1 9 7 5 ) 1 4 2 .

J . W . C h a p m a n e t a l , P h y s . L e t t . 4 7 B ( 1 9 7 3 ) 4 6 5 .

K . J a e g e r e t a l , P h y s . R e v . D U . ( 1 9 7 5 ) 2 4 0 5 .

A . S h e n g e t a l , P h y s . R e v . D1J_ ( 1 9 7 5 ) 1 7 3 3 .

A . M . R o s s i e t a l , N u c l . P h y s . B 8 4 ( 1 9 7 5 ) 2 6 9 .

[ 1 3 ] H . K i c h i m i e t a l , P h y s . R e v . D 2 0 ( 1 9 7 9 ) 3 7 .

R . D . K a s s e t a l , P h y s . R e v . D 2 0 ( 1 9 7 9 ) 6 0 5 .

D . D r i j a r d e t a l , Z . P h y s . Cl_2 ( 1 9 8 2 ) 2 1 7 .

W . T h o m é e t a l , N u c l . P h y s . B 1 2 9 ( 1 9 7 7 ) 3 6 5 .

[ 1 4 ] J . - P . R e p e l l i n , P r o c . X X I I n t . C o n f . o n H E P , P a r i s ( 1 9 8 2 ) , 5 7 1 .

[ 1 5 ] M . B a n n e r e t a l , P h y s . L e t t 1 1 5 B ( 1 9 8 2 ) 5 9 .

[ 1 6 ] G . A r n i s o n e t a l , UA1 C o l l a b o r a t i o n , C E R N p r e p r i n t , C E R N - E P / 8 2 - 1 2 2 .

[ 1 7 ] H . A l b r e c h t , T h e s i s , U n i v . o f H e i l d e l b e r g ( 1 9 7 9 ) .

[ 1 8 ] G . A r n i s o n e t a l , UA1 C o l l a b o r a t i o n , C E R N p r e p r i n t , C E R N - E P / 8 2 - 1 2 1 r e v .

- 9 5 -

[ 1 9 ] J . G . R u s h b r o o k e , C E R N p r e p r i n t , C E R N - E P / 8 2 - 1 5 7 , P r o c . X X I I n t . C o n f . o n H E P , P a r i s ( 1 9 8 2 ) , 1 7 7 .

[ 2 0 ] K . Â l p g â r d e t a l , " F o r w a r d - b a c k w a r d m u l t i p l i c i t y c o r r e l a t i o n s i n p p c o l l i s i o n s a t 5 4 0 G e V " , s u b m i t t e d t o P h y s . L e t t . B .

G . E k s p o n g , t a l k a t t h i s c o n f e r e n c e

[ 2 1 ] J . G . R u s h b r o o k e , C E R N p r e p r i n t , C E R N - E P / 8 2 - 6 .

SCHEMATIC LAYOUT OF THE STREAMER CHAMBER SYSTEM

F I G . 2(a) Elements of the detector used in the trigger

I N C L U S I V E ( I N E L A S T I C )

N O N S I N G L E D I F F R A C T I V E

S I N G L E D I F F R A C T I V E

' e n * , . 5 0 0 / 6 S M A L L

V

MINIMUM B I A S

T R I G G E R

D I F F R A C T I V E

T R I G G E R S

F I G . 2(b) Relationship of triggers and physical process

- 98 -

y b c a m ^

J L CT d-n*

2 -

1

T

T T

• \

v. UA5

_ <f 540 G e V N S D

T 540 G e V I N C L U S I V E ( P R E L I M I N A R Y )

•r 53 G e V I N C L U S I V E

(at 5 4 0 G e V )

F I G . 3

Charged particle rapidity distribution at 540 GeV for N.S.D. and inclusive (preliminary) events. Data at 53 GeV are shown for comparison.

- 9 9 -

- 1 . ( 4 2 . > e r v d T | '

« Thome et al.

A - P I F W A L data

+ P P J

U A 5 ( N S D )

i ' U A 5

, INCLUSIVE ^ P R E L I M I N A R Y )

j \ i i 11111 J ' I ' ' ' I t i i t [ i I I u 10 100 1000

FIG. A

Central charged particle rapidity density, ^ > against /s.

- 101 -

T t t 10

: 4 A

4 A

4 A A

f 4 t

5 • • • •

A

B t U

r A

dCT dT)

• • • • •

A

a

•

2 - • • • • • • •

1 T

O

f t

+ A A

tt • • O

X

UA5

N > 61 51îsNs£ 60 41^Ns= 50 31$Nî= 40 21<N Î£ 30 1 1 Í N < 20

7i=N:£ 10 N i 6

I • I

1

FIG. 6 Charged particle rapidity distribution for various ranges of observed multiplicity.

- 102 -

Fig- 7 Charged particle multiplicity distributions (a) uncorrected (b) corrected. The curves are based on KNO scaling (see text).

- 103 -

N O N S I N G L E - D I F F R A C T I V E D A T A

U A 5

6 %

2 ° / .

o N A M

2 1 . 5 » / .

z Ü J > LU U. O . O 1 %

Z O = 2

J L 1 0 1 0 0 1 0 0 0

P y y

y

Z 0 = 2 . 5

y y

s ' U A 5

0 . 5 °/O

y y

y y

J L X 1 0 2 0 5 0 1 0 0 2 0 0 5 0 0 1 0 0 0

FIG.8 Fraction of events with z > z against /s. The curves merely serve to guide the eye.

- 104 -

U A 5 I N C L U S I V E

( P R E L I M . ) O I N C L U S I V E D A T A I /

/

O S I N G L E D I F F R A C T I O N E X C L U D E D J / .

Fig. 9 Plot of D 2 = (<n > - <n> ) against <n>. The significance of the lines is explained in the text.

- 105 -

10

0.1

0,01

0.001

I/)

•P 2 0 a CD >

Lü

T T

( Q )

T 1 1 1 1 r

_ L J I !_!_ i . i I I I

( b)

t t M f

0 5 10 15 2 0 2 5 et , in cm

Fig. 10 (a) Ratio of the A and K° lifetime probabilities plotted against cos8 K'

(b) Distribution of cosöjj, compared with a Monte-Carlo calculation using a mixture of A and K°.

(C) Lifetime distribution for K° having |cos8k|<0.5. The line IS THE EXPECTED LIFETIME DEPENDENCE.

- 106 -

CM i > CU C D

b CM i_

o r •lb

0,01

0 . 8

bl.p-•o ho

b 0 . 4

b)

0 . 5 1.0 1.5 2 . 0 P T , in G e V / c

• p p — K ° / K ° X

o p p - * K ± X

0

P s e u d o r a p i d i t y I77I

Fig. 11 (a) p_ distribution for K and A/A. o ±

(b) Pseudorapidity distribution for K and K ,

- 107 -

0.8

0.6

0.4

0.2

0

1

- ( P T ) in GeV/c i

<

U A 5

. • t . i... -

i (a)

0.15- O K * / T T *

0.10

0.05

0

• K ' + K ' J / T T *

UA5

U A 5

( b )

Fig. 12

10 100

"/s , in GeV

(a) Variation of <p^ for kaons with /s. (b) Dependence of the K/iv ratio on /s.

1000

8 0

6 0

4 0

20

Average opening ongle

( Monte Car lo)

Allshowers

EM showers

120

8 0

4 0

il — i 1 1 r Average opening ongle

( Data )

F i g . 13 A v e r a g e o p e n i n g a n g l e s o f s h o w e r s i n 2 < | n | < 3 . T h e c u t u s e d t o

i m p r o v e t h e p u r i t y o f e l e c t r o m a g n e t i c s h o w e r s i s s h o w n .

U A 5

b T 3

- l b

i 1 •

Photons f r o m A Ploie D Beom pipe _ Chorged T porticles

t 9 t

- l b

U A 5 T 1

Photons from A Plote

D Beam pipe

v Chorged porticles

O

( a )

2 3 4 5 h i O I 2 3

Fig. 14 (a) Pseudorapidity distribution of photons, with charged particle

data for comparison. (b) as (a), but with K ° •* 2TT° -»• by, K*

and p/p contributions removed. The dashed curve is the

expected photon distribution assuming all y's come from T.° • . O i o

decays and the solid curve assuming <TT >=|<TT"> and R/TT = 30Z,

taking i r ° and n to have the same rapidity distribution as IT*.

(b)

- 109 -

'ch

1.0

-S 0.5

c

0

i i i i M i 1 — n — i — I I M I

10 i i i i 111 i i i i i i 111

50 100

T 1 — I — r — r

UA 5 '

(b)

j i I i i 500

7s ( GeV ) Fig. 15 (a) Average number of photons produced, < n

Y> > a s a function of n^.

i Y

(b) Photon-charged correlation strength, d<nv>/dnc^ as a function of cm. energy.

- 1 1 0 -

UA 5

Fig. 16 Number of photons observed in n>2 (or n < -2) against the number of charged particles observed in the same rapidity range. The shaded region shows where Centauro-like events are expected.

- I I I -

- 1 1 2 -

M U L T I P L I C I T Y C O R R E L A T I O N S IN P P - COLLISIONS A T 540 G e V

U A 5 Collaboration: Bonn - Brussels - Cambridge - C E R N - Stockholm

Presented by G. Ekspong, Stockholm University

S U M M A R Y

Multiplicity correlations of long range in pseudorapidity are found to be stronger

than at ISR energies. The analysis gives no evidence for intrinsic long range corre

lations. The data are consistent with a physical picture involving random emission

of small clusters along the rapidity plateau. The average cluster size is about 2

charged particles, the same as at ISR energies.


The experiment has been carried out by the U A 5 collaboration using its streamer

chamber system as described in the literature and by the previous speaker, D. Ward

[1 ]. At the C E R N SPS Collider one has available a rapidity plateau which is long

compared with the correlation range of about ± 1 unit of rapidity typical for the

decay of small mass resonances. W e observe two-particle short range correlations

of the mentioned type but concentrate here on our observation and analysis of the

longer range correlations between the number of charged particles, n and n , F B

falling into two selected rather large regions, one forward (F) and one backward

(B), chosen symmetric around 90° in the center - of - mass system ( 7 7 = 0 ) . The

pseudorapidity, r\= -In tan6/2, where the angle 6 is the polar angle with the re

spect to the beam axis, is the variable used to label the charged particles.

- 113 -

OBSERVATIONS

The p r o b l e m c o n c e r n s the f luc tua t ions of the n u m b e r of p a r t i c l e s in the F - and

B - r e g i o n s . If t h e s e v a r i a b l e s w e r e independent of e a c h o t h e r the c o r r e l a t i o n

s t r e n g t h would be z e r o . At ISR e n e r g i e s a pos i t i ve c o r r e l a t i o n w a s found 2] which

i n c r e a s e s with e n e r g y within the ISR e n e r g y r a n g e . The fol lowing two ways to

m e a s u r e the c o r r e l a t i o n s t r e n g t h a r e equ iva len t : (1 ) one c o m p u t e s the a v e r a g e of

n a t fixed n and f inds the s lope b in a s t r a i g h t l ine fit , <n (n ) > = a b • n , B F B F F

(2) one c o m p u t e s the c o r r e l a t i o n coeff ic ient of n and n , involving main ly the F B

m e a n value of the p r o d u c t of the two f a c t o r s (n ( i ) - \ n > and (n ( i ) - ( n !v ) F F B B

w h e r e n ( i ) , n ( i ) a r e the o b s e r v e d n u m b e r of c h a r g e d t r a c k s in event ( i ) F B

fal l ing into the s e l e c t e d F and B r e g i o n s . A s t r a i g h t l ine fit with uni t weight to

a l l even t s g ives b - cov(n^ , , n ^ / v a r n ^ which i l l u s t r a t e s above m e n t i o n e d e q u i v a

l e n c e . We p r e s e n t h e r e the r e s u l t s for t h r e e def in i t ions of the r e g i o n s F and B .

(A) F = (0 < T J < 4 ) and B = (-4 < T / ^ 0 )

which m e a n s that the two r e g i o n s a r e in con tac t but n o n - o v e r l a p p i n g .

(B) F = (1 ^ T ) < 4 ) and B = ( -4 < T] < - 1 )

which m e a n s that a gap of s i z e Ar¡ = 2 h a s been i n t r o d u c e d be tween the two

n o n - o v e r l a p p i n g r e g i o n s

(C) F -- (0 < T ) < 1 ) and B = (-1 ^ *7 — 0)

which c o r r e s p o n d s to the s i z e of the o b s e r v e d r a n g e of the t w o - p a r t i c l e

c o r r e l a t i o n funct ion.

O u r s a m p l e c o n s i s t s of about 4000 m i n i m u m b ia s e v e n t s . The t r i g g e r r e q u i r e s at

l e a s t one p a r t i c l e into each h e m i s p h e r e , which l e a d s to an a l m o s t c o m p l e t e e l i m i

nat ion of s ingle d i f f rac t ion e v e n t s . The t r i g g e r i n g eff ic iency for non s ing le dif

f rac t ive ine la s t i c e v e n t s i s about 95%. The s t r e a m e r c h a m b e r s c o v e r the rap id i ty

r a n g e - 5 S rj ^ 5. The da t a p r e s e n t e d r e f e r to the r a n g e | A n | — 4 w h e r e the g e o

m e t r i c a l a c c e p t a n c e i s g r e a t e r than 85%.

Long r ange c o r r e l a t i o n s w e r e f i r s t r e p o r t e d by S. Uhlig e t a l [2] a t ISR. Our

r e s u l t s in p r e l i m i n a r y v e r s i o n s have been given l a s t y e a r and a r e now submi t t ed

for publ icat ion [3~l.

- 114 -

A N A L Y S I S

T h e p r e s e n c e o f c o r r e l a t i o n s m e a n s t h a t t h e t w o - d i m e n s i o n a l d i s t r i b u t i o n o f e v e n t s

( F i g . 1 a ) d o e s n o t f a c t o r i z e , F ( n , n ) , ^ f ( n ) • f ( n ) . I n o t h e r w o r d s n a n d F B F B F

n a r e n o t i n d e p e n d e n t . W e f i n d i t a d v a n t a g e o u s t o t r a n s f o r m t h e p r o b l e m i n t o t h e B

v a r i a b l e s - ( n ^ , t n ^ ) a n d z = ( n ^ , - n g ) » i ' e - r o t a t i n g t h e c o o r d i n a t e s y s t e m

o f F i g . 1 a b y 4 5 ° . T h e m a r g i n a l d i s t r i b u t i o n o f t h e c o m b i n e d m u l t i p l i c i t y n , o b -

t a i n e d b y p r o j e c t i n g a l l e v e n t s i n t h e s c a t t e r p l o t o n t o t h e n e w n - a x i s , d o e s n o t o

s e e m b y i t s e l f t o c o n t a i n i n f o r m a t i o n r e l e v a n t t o o u r p r o b l e m . H o w e v e r , w e w i l l f i n d t h e f i r s t t w o m o m e n t s t o b e o f d e c i s i v e i n t e r e s t . T h e s e a r e t h e m e a n ( n ) =•

2 - 1 6 . 0 - 0 . 2 a n d t h e v a r i a n c e D " - 7 8 . 0 - 1 . 8 f o r t h e c a s e w i t h a g a p b e t w e e n t h e

I n a l l t h r e e c a s e s t h e F a n d B r e g i o n s a r e s y m m e t r i c . W e c o n s i d e r a l s o t h e i n i t i a l

s t a t e t o b e s y m m e t r i c s i n c e w e d o n o t i d e n t i f y p a r t i c l e s , o n l y c o u n t t h e n u m b e r o f

c h a r g e d p a r t i c l e s .

T h e s c a t t e r p l o t F i g . 1 a , s h o w s t h e t w o - d i m e n s i o n a l d i s t r i b u t i o n , F ( n , n ) , o f F B

e v e n t s i n c a s e A a b o v e ( n o g a p ) , w h i l e F i g . 1 b s h o w s h o w r e m a r k a b l y w e l l t h e

d a t a f i t t o a s t r a i g h t l i n e . T h e l e a s t s q u a r e s f i t g i v e s a s l o p e o f b - 0 . 5 4 - 0 . 0 1 .

T h e v a l u e d r o p s t o b = 0 . 4 1 - 0 . 0 1 w h e n a g a p o f s i z e AT¡ - 2 i s i n t r o d u c e d

( c a s e B a b o v e ) . W e i n t e r p r e t e t h i s d r o p a s m a i n l y d u e t o a d e c o u p l i n g o f t h e F

a n d t h e B r e g i o n s f r o m e f f e c t s d u e t o c l u s t e r s ( s u c h a s p ° - > 7 T 7T ) p r o d u c e d n e a r

V 0 a n d e m i t t i n g o n e ( o r m o r e ) p a r t i c l e s i n t o e a c h r e g i o n s i m u l t a n e o u s l y .

F i g . 2 s h o w s t h e U A 5 v a l u e s f o r t h e c o r r e l a t i o n s t r e n g t h p a r a m e t e r b t o g e t h e r

w i t h p u b l i s h e d r e s u l t s f r o m t h e R 7 0 1 e x p e r i m e n t a t I S R 2 j . T h e i n c r e a s e w i t h

e n e r g y i s s e e n t o c o n t i n u e . T o b e n o t e d i s t h a t b f 0 e v e n i n t h e c a s e w h e n a g a p

i s i n s e r t e d , f i g . 2 c , a n d i n c r e a s e s w i t h e n e r g y . T h i s o b s e r v a t i o n c o n s t i t u t e s t h e

m a i n r e a s o n f o r i n t r o d u c i n g t h e t e r m l o n g - r a n g e c o r r e l a t i o n i n r a p i d i t y s p a c e . T h e

a l m o s t z e r o v a l u e a t t h e l o w e s t I S R e n e r g y s e e m s t o b e a c c i d e n t a l . O u r a n a l y s i s

o f f e r s a r a t h e r s i m p l e e x p l a n a t i o n f o r t h e e x i s t e n c e o f t h e e f f e c t a n d t h e i n c r e a s e

o f i t s s t r e n g t h w i t h e n e r g y .

- 115 -

F- and B-regïons (case B ) . The two-dimensional distribution describing the den

sities of events in the scatterplot, such as Fig. 1a, is studied by us at each fixed

n and is formally denoted f (n ) [at fixed n_ the use of the variables n or o S F o F

z = (2n - n ) is equivalent]. This set of functions describes the distribution of F S

events with any n at fixed n . The distributions f (n ) must trivially be sym-F o o F metric with a mean (n > = — n . All odd moments must vanish. It turns out that

2 the correlation strength parameter b is related to the second moments, d (n ), S F

by the following identity

1 2 , 2 v

b Î D S - < d s ' n F ) >

" K + «s<v> where ( ) denotes an average value over the marginal n -distribution.

The proof of this relation rests on the following steps: (1 ) the least squares fit

gives

cov (n F, n ß ) E(n F(i) - <n F> ) (n ß(i) - <n ß>) Q — — = —

varn^ ~ , ,.v / N . 2 F L(n F(i)-<n F>)

(2) the sums over all events (i = 1 — M , in our case M ~4000) are carried out in two steps: (i) over all events with a given fixed value of n^, (ii) over the m a r ginal n -distribution.

2 The variances, d (n ), depend on the shape of the f (n ) distributions which in S F o F turn are sensitive to the kind of physical process (or processes) which dominate.

The discussion is summarized in Table 1. W e cannot exclude that a suitable mixture

of processes with intrinsic long range correlations can describe the data but we do

not find evidence for a dominance of any single such process. The data can be de

scribed as due to a random emission of clusters of an average size (k) close to 2.

The random process is described by a binomial distribution in the number of clus

ters (C) falling into F with probability p = . The variance is expected to be 2 1 2 1 F -

d (n ) = — k C = — k • n , if all clusters have the same size k. The more realistic o F 4 4 o

case of a mixture of sizes is treated in the Appendix. As an example we take n - 12

which means (5 clusters in case the sizes are all k - 2. The probability to find all

- 116 -

—6 1

A closer study of the expectations for this physical picture has been m a d e by a

Monte Carlo simulation. The simple assumptions made are summarized in Fig.3.

In an event with C clusters these are positioned at random along the pseudorapi-

dity axis. Their sizes are k.(i = 1 .... C ) so that the number of charged par

ticles is given by

C n , = £ k. . ch 1 = 1 i

The experimental distribution of n ^ was used to generate a distribution in C

once the k-distribution was selected. Average values of k near k = 2 are of interest

and the k-distribution was chosen to follow a Poisson distribution in the range

k = 1 , 5. The k\ cluster products were assigned positions on the pseudorapidity

axis in the neighbourhood of the cluster itself using the two-particle correlation

function. In this way some leakage of cluster products will occur. A cluster in the

F (or B ) region will sometimes appear smaller than generated. Also clusters out

side the considered region will at times leak particles into the region. This com

pensation will generally not occur in the same event so that fluctuations (variances)

will be influenced whereas m e a n values will remain the same (if the net leakage is

zero). The observed variances are given in Fig. 4 together with curves obtained

by the M . C . simulations. The agreement is excellent provided the average clus

ter size is about 2 charged particles. When the sizes of the F- and B-regions are

reduced from AT = 3 to AT J = 2 and An = 1, respectively, the increased leakages 2

lead to reductions of the ratio d (n )/<n > in the data and in the M . C . in the o F o

same way. One notices also that the plotted ratio is rather independent of the

total multiplicity n (up to n ~ 3 u ) . W e interpret this to support the assumption

in M . C . that large and small multiplicities are produced by the same cluster

sizes. This determination of the average (or effective) cluster size is also in

dependent of the gap size once it is larger that about two units as seen in Fig. 5-

6 clusters (i.e. all 12 particles) in the F-region is 2 = — • whereas if, instead 64

of clusters, particles were randomly emitted the probability for all 12 particles to -12 1

be in F is only 2 = . Our observed number of events with all 12 particles

in one region is 4 events out of 185 events as expected for the model with random

cluster emission.

- 117 -


W e o b s e r v e b o t h s h o r t r a n g e ( A T 7 ~ 1 ) a n d l o n g e r r a n g e c o r r e l a t i o n s i n c h a r g e d

p a r t i c l e m u l t i p l i c i t i e s . T h e s t r e n g t h o f t h e l o n g r a n g e ( f o r w a r d - b a c k w a r d ) c o r

r e l a t i o n i n c r e a s e s w i t h e n e r g y a n d b 0 . 5 i s o b s e r v e d a t t h e S P S c o l l i d e r e n e r g y .

T h e d a t a a r e c o n s i s t e n t w i t h a p h y s i c a l p i c t u r e i n v o l v i n g r a n d o m e m i s s i o n o f

c l u s t e r s a l o n g t h e r a p i d i t y a x i s i n t h e p l a t e a u r e g i o n . T h e a v e r a g e c l u s t e r s i z e i s

T h e M . C . e v e n t s w e r e u s e d t o c o m p u t e t h e c o r r e l a t i o n s t r e n g t h b a n d t h e r e s u l t s

f o r t h e l o n g r a n g e c o r r e l a t i o n , g i v e n i n F i g . 2 , a r e i n g o o d a g r e e m e n t w i t h d a t a .

T h e M . C . s i m u l a t i o n w a s r e p e a t e d a t I S R e n e r g i e s w i t h a g a i n g o o d a g r e e m e n t p r o

v i d e d t h e a v e r a g e c l u s t e r s i z e w a s s e t e q u a l t o a b o u t 2 c h a r g e d p a r t i c l e s .

E n e r g y d e p e n d e n c e o f t h e c o r r e l a t i o n s t r e n g t h ( b )

T h e p h y s i c a l p i c t u r e a s p r e s e n t e d r e p r o d u c e s t h e e n e r g y d e p e n d e n c e w e l l . T h e

r e a s o n f o r t h i s i s s e e n f r o m t h e i d e n t i t y f o r m u l a . A s s u m i n g r a n d o m c l u s t e r e m i s

s i o n t h e f o r m u l a r e a d s

4^) - k e f f

b = ~~z

V < n > + k e f f

w h e r e t h e e f f e c t i v e c l u s t e r s i z e k ^ i s r e l a t e d t o t h e a v e r a g e c l u s t e r s i z e b y

k = < k > + d / < k > ( s e e A p p e n d i x ) i n t h e l i m i t o f n o l e a k a g e s . I t i s a f a i r l y g o o d 6 1 1 K

a p p r o x i m a t i o n t o c o n s i d e r k t o b e a n e n e r g y i n d e p e n d e n t c o n s t a n t . T h e e n e r g y 2

d e p e n d e n c e o f b i s t h e n t o t a l l y d u e t o t h e D / \ n ) r a t i o w h i c h i n c r e a s e s a p p r o x i m a

t e l y l i n e a r l y w i t h ( n > . S i n c e t h e p a r t i c l e d e n s i t y i n t h e p l a t e a u r e g i o n i n c r e a s e s

a p p r o x i m a t e l y l i n e a r l y w i t h I n s (Vs = c m . e n e r g y ) o n e f i n d s t h a t i t i s p o s s i b l e

t o r e p r e s e n t t h e c o r r e l a t i o n s t r e n g t h p a r a m e t e r b y

I n s - B 1

b = I n s + B 9

w h e r e t h e c o n s t a n t s B^ a n d B 9 , h o w e v e r , d e p e n d o n t h e s i z e i n r a p i d i t y o f t h e F -

a n d B - r e g i o n s , a n d o n t h e s i z e o f t h e r a p i d i t y g a p b e t w e e n t h e m .

- 118 -

Table 1. S u m m a r y of discussion of various hypothetical physical processes

b =0.41 (case 1 |Ar)| ¿ 4 ) observed

Physical picture Shape of

w ds(V b Comments

I. INTRINSIC C O R R E L A T I O N

(a) 2 fireballs with peaked at small large Not observed strongly correlated 1

2 n S sizes 1 2 n S

(b) 1 large + 1 small fireball

double peaked

large small (or neg. )

Not observed

II. U N C O R R E L A T E D sizes of 2 fireballs

broad 0 Not observed

III. Mixture of above Not excluded

IV. N O INTRINSIC C O R R E L A T I O N

(a) Random emission Binomia^ with p = —

1 — n„ 4 S 0.66 Too high b

of particles Binomia^ with p = —

1 — n„ 4 S

(b) Random emission of clusters of fixed size k

(Binomial in clusters)

1 . 4 S

0.42 (k = 2)

O.K. but unrealistic

(c) Random emission Binomial < > = 0.42 Agrees well of clusters of mixed sizes

in clusters ïkeffV if k =2.0 eff

about 2 charged particles, the same as at ISR energies. It seems natural to as

sume that the clusters are small mass particles and resonances (IT, 77, p, oc,

K, K ) or small groups of them. These are then copiously produced and

constitute the dominant part of minimum bias events. This hypothesis is support

ed by our published observation that the average number of y-rays increases

strongly with the number of charged particles in the events [4].

- 119 -

A P P E N D I X

T h e effective cluster size, k ... eit

C o n s i d e r C clusters in a n event with sizes k. (i = 1 C ) c h a r g e d particles. Both

C a n d k. a r e stochastic variables. T h e resulting n u m b e r of c h a r g e d particles,

n g , is given by

C "s - . * k t 1=1

F r o m this o n e gets the first two m o m e n t s of the n -distribution:

ñ g = C • k ( 1 )

-2

v a r n = k v a r C + C v a r k (2)

T h i s p r o b l e m is a c a s e of b r a n c h i n g p r o c e s s e s w h e r e cluster i b r a n c h e s into k.

particles. N e x t , w e introduce a binomial branching into f o r w a r d a n d b a c k w a r d 1

regions with probabilities p ^ a n d p for e a c h cluster. W e a s s u m e no leakage

so that all k. particles f r o m cluster i r e m a i n s in the s a m e region as the cluster

itself. In this c a s e the first two m o m e n t s of the n -distribution a r e given by: F

ñ F = C . p F - k (3)

2 - 2 - -2 v 4 v w = p k v a r C + C • k p (1 - p _ ) + C • p v a r k (4)

F F F F F

the variance

of the bino

m i a l distr.

If o n e in (4) eliminates the m o m e n t s C a n d var C using ( 1 ) a n d (2) o n e obtains

the desired result :

1 2 1 — — v a r n

F = 4 D

s

+ 4 n

s ( k + v a r k / k ) (5)

1 _ 2 w h e r e p = — a n d v a r n g = D g h a v e b e e n substituted.

A s a special c a s e the s i m p l e f o r m u l a for the c a s e of fixed size clusters (k) is r e

c o v e r e d if v a r k = 0 is a s s u m e d , n a m e l y

v a r n F = i D g + i k . n s

F o r m u l a (5) is of the s a m e f o r m with the r e p l a c e m e n t k -* k = k + v a r k / k . T h e

distribution of cluster sizes is not k n o w n . W e r e it P o i s s o n the result is k =

= (k + 1 ). W e h a v e truncated the P o i s s o n distribution by setting the probability to

zero outside the interval 1 < k . ^ 5 , w h e n k is n e a r 2. In this c a s e

v a r k / k ~ 0 . 5 - 0.6 a n d w e believe the truncation to be s o m e w h a t m o r e realistic.

T h e c o v ( n F > n ß ) is finally obtained f r o m the relation n = n^, + through

v a r n g = v a r n ^ + v a r n ^ + 2 c o v ( n F > n ) a n d the s y m m e t r y r e q u i r e m e n t v a r n =

= v a r n . T h u s

c o v ( V n B ) = Í D S - V a r n F = i D H k e f f • 'nS

T h u s the ident i ty r e l a t ion for the c o r r e l a t i o n s lope b is Ds * kerr • "s

- 1 2 0 -


Fig. 1a) The two-dimensional distribution of events (scatterplot) with the two coordinate systems used. The area of a ring is proportional to the number of events. These data correspond to the case with no gap between the F- and B-regions.

1b) The linear relation between the average of n (at fixed n )and n„ . B F F The slope b is a measure of the correlation strength.

Fig. 2 The energy dependence of the correlation slope b.

Fig. 3 Illustration of the Monte Carlo simulation. The C clusters in an event with random sizes (k. ) are assigned random positions in pseudorapidity.

Fig. 4 The observed dispersions dg(n^) and the Monte Carlo results (lines) for two assumed average sizes (k) of the clusters. The F- and B-intervals are 3, 2, and 1 units of pseudorapidity, respectively. In all three cases the gap is two units.

Fig. 5 The effective cluster size, k ^ , is shown to be independent of the gap size once it is larger than 2 units of pseudorapidity.

R E F E R E N C E S

[i] U A 5 Collaboration, Phys. Scr. 23 (1981 ) 642. D.R. Ward, "UA5-Results" (this conference).

[2] S. Uhlig et al. Nucl. Phys. B 132 (1978) 15.

[ 3 ] K. Alpgârd et al, U A 5 Collaboration "Forward-Backward Multiplicity Correlations in pp - Collisions at 540 GeV", C E R N EP/83-January 1983. Submitted to Physics Letters B.

[ 4 ] K. Alpgârd et al, Phys. Lett. 115 B (1982) 71. D.R. Ward, "UA5-Results" (this conference).

- 121 -

- 1 2 2 -

M O N T E CARLO S I M U L A T I O N

C =7 clusters

Fig . 3 4 5 p a r t i c l e s

1 — I ( a )

/ Il kz2 1

( b ) '

' A\\ú 11

( 0 ' UA S

k = 3 1

i ü T T

An.: 3

1 1 1

( b ) '

' A\\ú 11

( 0 ' UA S

k = 3 1

i ü T T

An.: 3

1 1 1

i i 1 i 1 1 1 w

1 1

( 0 ' UA S

k = 3 1

i ü T T

An.: 3

1 1 1

i i 1 i 1 1 1 w

1 1

A n / i

I , I [ 1 I I I 1 -

0 10 20 30 10 20 0 5 10

Fig . 4

UA5

x r- = 2

S 6 GAP SIZE, 6-11

0 " 1 F ig . 5 - 6 1 , . .

: r ~ o n GAP ,

- 123 -

E X P E R I M E N T A L O B S E R V A T I O N O F I S O L A T E D L A R G E T R A N S V E R S E E N E R G Y E L E C T R O N S

W I T H A S S O C I A T E D M I S S I N G E N E R G Y A T /s = 540 G e V

U A 1 C o l l a b o r a t i o n , C E R N , G e n e v a , S w i t z e r l a n d

A a c h e n 1 - A n n e c y ( L A P P ) 2 - B i r m i n g h a m 3 - C E R N ' * - H e l s i n k i 5 - Q M C , L o n d o n 6 - P a r i s

(Coll. d e F r a n c e ) 7 - R i v e r s i d e 8 - R o m e 9 - R u t h e r f o r d A p p l e t o n L a b . 1 0 -

S a c l a y ( C E N ) 1 1 , V i e n n a 1 2 C o l l a b o r a t i o n

Presented by C. Rubbia

1 0 1 0 2 9 irk %

G . A r n i s o n , A . A s t b u r y , B. A u b e r t , C . B a c c i , G . B a u e r , A . B é z a g u e t ,

R. B ö c k " , T . J . V . B o w c o c k ' , M . C a l v e t t i " , T . C a r r o l l " , P. C a t z * , P. C e n n i n i " ,

S. C e n t r o * , F. C e r a d i n i " , S. C i t t o l i n " , D. C l i n e * * , C . C o c h e t ' 1 , J . C o l a s * ,

3 1 2 1 1 2 h

M . C o r d e n , D. D a l l m a n , M . D e B e e r , M . D e i l a N e g r a , M . D e m o u l i n ,

D e n e g r i 1 1 , A . D i C i a c c i o ' , D . D i B i t o n t o " , L. D o b r z y n s k i ' , J . D . D o w e l l ' , M . E d w a r d s ,

K. E g g e r t ' , E. E i s e n h a n d l e r 6 , N . Ellis'", P . E r h a r d ' , H . F a i s s n e r ' , G . F o n t a i n e 7 ,

„ „ 0 1 2 3 7 . ^ 7

R . Frey , R. F r u h w i r t h , J . G a r v e y , S. G e e r , C . G h e s q u i è r e , 2 . 1 C 7 1 1

P . G h e z , K . L . G i b o n i , W . R . G i b s o n , Y . G i r a u d - H é r a u d , A . G i v e r n a u d ,

A . G o n i d e c * , G . G r a y e r ' * , P . G u t i e r r e z ' , T . H a n s l - K o z a n e c k a 1 ,

1 0 * • 1 H

W . J . H a y n e s , L.O. H e r t z b e r g e r , C . H o d g e s , D. H o f f m a n n , H . H o f f m a n n , •ic 3 S H % T

D . J . H o l t h u i z e n , R . J . H o m e r , A . H o n m a , W . J a n k , G . J o r a t , P . I . P . K a l m u s , S 6 3 » S . »

V . K a r i m ä k i , R. K e e l e r , I. K e n y o n , A . K e r n a n , R. K i n n u n e n , H . K o w a l s k i ,

W . K o z a n e c k i * , D. K r y n " , F . L a c a v a " , J . - P . L a u g i e r ' ' , J . - P . L e e s * , H . L e h m a n n ' ,

K . L e u c h s ' , A . L é v ê q u e ' ' , D . L i n g l i n * , E . L o c c i ' ' , M . L o r e t ' ' , J . - J . M a l o s s e ' ' ,

T . M a r k i e w i c z " , G . M a u r i n " , T . M c M a h o n ' , J . - P . M e n d i b u r u 7 , M . - N . M i n a r d * ,

S H % . 1 0 H «

M . M o r i c c a , H . M u i r h e a d , F. M u l l e r , A . K . N a n d i , L. N a u m a n n , A . N o r t o n ,

A . O r k i n - L e c o u r t o i s 7 , L . P a o l u z i ' , G . P e t r u c c i " , G . P i a n o M o r t a r i ' , M . Pimi'à',

A . P l a c c i " , E . R a d e r m a c h e r 1 , J . R a n s d e l l ' , H . R e i t h l e r ' , J . - P . R e v o l " , J . R i c h " ,

M . R i j s s e n b e e k " , C . R o b e r t s " , J . R o h l f " , P. R o s s i " , C . R u b b i a " , B. S a d o u l e t " ,

G . S a j o t ? , G . S a l v i ' , G . S a l v i n i ' , J . S a s s ' * , J . S a u d r a i x ' ' , A . S a v o y - N a v a r r o ' ' ,

D . S c h i n z e l " , W . S c o t t ' 0 , T . P . S h a h " , M . S p i r o ' ' , J . S t r a u s s ' * , K. S u m o r o k ' ,

F . S z o n c s o ' * , D. S m i t h * , C . T a o " , G . T h o m p s o n ' , J . T i m m e r " , E. T s c h e s l o g ' ,

J . T u o m i n i e m i ' , S. V a n d e r M e e r " , J . - P . V i a l l e " , J . V r a n a 7 , V . V u i l l e m i n " ,

H . D . W a h l 1 1 , p. W a t k i n s ' , J . W i l s o n * , G . Y . X i e " , M . Y v e r t * , E. Z u r f l u h "

* N I K H E F , A m s t e r d a m , T h e N e t h e r l a n d s

* * U n i v e r s i t y of W i s c o n s i n , M a d i s o n , W i s c o n s i n , U S A

- 124 -

A B S T R A C T

W e r e p o r t t h e r e s u l t s o f t w o s e a r c h e s m a d e o n d a t a r e c o r d e d a t t h e

C E R N S P S P r o t o n - A n t i p r o t o n C o l l i d e r : o n e f o r i s o l a t e d l a r g e - E ^ e l e c t r o n s ,

t h e o t h e r f o r l a r g e - E ^ , n e u t r i n o s u s i n g t h e t e c h n i q u e o f m i s s i n g t r a n s v e r s e

e n e r g y . B o t h s e a r c h e s c o n v e r g e t o t h e s a m e e v e n t s , w h i c h h a v e t h e

s i g n a t u r e o f a t w o - b o d y d e c a y o f a p a r t i c l e m a s s i n e x c e s s o f 70 G e V / c 2 .

T h e t o p o l o g y a s w e l l a s t h e n u m b e r o f e v e n t s f i t s w e l l t h e h y p o t h e s i s

t h a t t h e y a r e p r o d u c e d b y t h e p r o c e s s p + p ->• W - + X , w i t h W _ -> e ~ + v ;

w h e r e W* i s t h e I n t e r m e d i a t e V e c t o r B o s o n p o s t u l a t e d b y t h e u n i f i e d

t h e o r y o f w e a k a n d e l e c t r o m a g n e t i c i n t e r a c t i o n s .

- 125 -


It is g e n e r a l l y p o s t u l a t e d t h a t t h e b e t a d e c a y , n a m e l y (quark) -> (quark) +

+ e * + v is m e d i a t e d b y o n e of two c h a r g e d I n t e r m e d i a t e V e c t o r B o s o n s ( I V B s ) , W +

a n d W of v e r y large m a s s e s . If t h e s e p a r t i c l e s e x i s t , a n e n h a n c e m e n t of the

c r o s s - s e c t i o n for the p r o c e s s (quark) + ( a n t i q u a r k ) -*• e * + v s h o u l d o c c u r at

c e n t r e - o f - m a s s e n e r g i e s i n the v i c i n i t y of the IVB m a s s ( p o l e ) , w h e r e d i r e c t e x

p e r i m e n t a l o b s e r v a t i o n a n d a s t u d y of the p r o p e r t i e s of s u c h p a r t i c l e s b e c o m e

p o s s i b l e . T h e C E R N S u p e r P r o t o n S y n c h r o t r o n (SPS) c o l l i d e r , i n w h i c h p r o t o n a n d

a n t i p r o t o n c o l l i s i o n s a t /s" = 5 4 0 G e V p r o v i d e a r i c h s a m p l e of q u a r k - a n t i q u a r k

e v e n t s , h a s b e e n d e s i g n e d w i t h t h i s s e a r c h as the p r i m a r y g o a l Q l ] .

P r o p e r t i e s of I V B s b e c o m e b e t t e r s p e c i f i e d w i t h i n the t h e o r e t i c a l f r a m e of

the u n i f i e d w e a k a n d e l e c t r o m a g n e t i c t h e o r y a n d of t h e W e i n b e r g - S a l a m m o d e l ^ 2 ^ .

T h e m a s s of the IVB is p r e c i s e l y p r e d i c t e d [[3]:

= 82 ± 2.4 G e V / c 2

for the p r e s e n t l y p r e f e r r e d f_4] e x p e r i m e n t a l v a l u e o f the W e i n b e r g a n g l e s i n 2 0 ^ =

= 0 . 2 3 ± 0 . 0 1 . T h e c r o s s - s e c t i o n f o r p r o d u c t i o n is a l s o r e a s o n a b l y w e l l a n t i c i

p a t e d [ 5 ]

a ( p p -> W 1 e ± + v) * 0.4 x 1 0 ~ 3 3 k c m 2 ,

w h e r e k is a n e n h a n c e m e n t f a c t o r of ^ 1.5, w h i c h c a n b e r e l a t e d to a s i m i l a r

w e l l - k n o w n e f f e c t i n the D r e l l - Y a n p r o d u c t i o n of l e p t o n p a i r s . It a r i s e s f r o m

a d d i t i o n a l Q C D d i a g r a m s i n t h e p r o d u c t i o n r e a c t i o n w i t h e m i s s i o n of g l u o n s . I n

o u r s e a r c h w e h a v e r e d u c e d t h e v a l u e o f k b y a c c e p t i n g o n l y t h o s e e v e n t s w h i c h

s h o w n o e v i d e n c e for a s s o c i a t e d j e t s t r u c t u r e i n t h e d e t e c t o r .

T H E D E T E C T O R

T h e U A 1 a p p a r a t u s h a s a l r e a d y b e e n e x t e n s i v e l y d e s c r i b e d e l s e w h e r e f_6].

H e r e w e c o n c e n t r a t e o n t h o s e a s p e c t s o f t h e d e t e c t o r w h i c h a r e r e l e v a n t to the

p r e s e n t i n v e s t i g a t i o n .

T h e d e t e c t o r is a t r a n s v e r s e d i p o l e m a g n e t w h i c h p r o d u c e s a u n i f o r m f i e l d of

0.7 T o v e r a v o l u m e of 7 x 3.5 * 3.5 m 3 . T h e i n t e r a c t i o n p o i n t is s u r r o u n d e d b y

- 126 -

the c e n t r a l d e t e c t o r ( C D ) : a c y l i n d r i c a l d r i f t c h a m b e r v o l u m e , 5.8 m l o n g a n d

2.3 m i n d i a m e t e r , w h i c h y i e l d s a b u b b l e - c h a m b e r q u a l i t y p i c t u r e of e a c h pp i n

t e r a c t i o n i n a d d i t i o n to m e a s u r i n g m o m e n t u m a n d s p e c i f i c i o n i z a t i o n of a l l c h a r g e d

t r a c k s .

M o m e n t u m p r e c i s i o n for h i g h - m o m e n t u m p a r t i c l e s is d o m i n a t e d b y a l o c a l i z a t i o n

e r r o r i n h e r e n t to t h e s y s t e m (^ 100 ym) a n d t h e d i f f u s i o n of e l e c t r o n s d r i f t i n g

i n t h e gas ( p r o p o r t i o n a l to JÏ, a n d a b o u t 350 y m a f t e r il = 22 c m m a x i m u m d r i f t

l e n g t h ) . T h i s r e s u l t s i n a t y p i c a l r e l a t i v e a c c u r a c y of ± 2 0 % for a i m long t r a c k

a t p = 40 G e V / c , a n d i n t h e p l a n e n o r m a l to t h e m a g n e t i c f i e l d . T h e p r e c i s i o n ,

of c o u r s e , i m p r o v e s c o n s i d e r a b l y for l o n g e r t r a c k s . T h e i o n i z a t i o n of t r a c k s c a n

b e m e a s u r e d b y t h e c l a s s i c a l m e t h o d of t h e t r u n c a t e d m e a n of the 60% l o w e s t

r e a d i n g s to a n a c c u r a c y of 1 0 % . T h i s a l l o w s a n u n a m b i g u o u s i d e n t i f i c a t i o n of

n a r r o w , h i g h - e n e r g y p a r t i c l e b u n d l e s ( e + e ~ p a i r s or p e n c i l jets) w h i c h c a n n o t b e

r e s o l v e d b y t h e d r i f t c h a m b e r d i g i t i z i n g s .

T h e c e n t r a l s e c t i o n of e l e c t r o m a g n e t i c a n d h a d r o n i c c a l o r i m e t r y h a s b e e n

u s e d i n t h e p r e s e n t i n v e s t i g a t i o n to i d e n t i f y e l e c t r o n s o v e r a p s e u d o r a p i d i t y i n

t e r v a l |ri I < 3 w i t h full a z i m u t h a l c o v e r a g e . A d d i t i o n a l c a l o r i m e t r y , b o t h e l e c t r o

m a g n e t i c a n d h a d r o n i c , e x t e n d s to t h e f o r w a r d r e g i o n s of the e x p e r i m e n t , d o w n to

0 . 2 ° (for d e t a i l s , see t a b l e 1 ) .

T h e c e n t r a l e l e c t r o m a g n e t i c c a l o r i m e t e r s c o n s i s t of two d i f f e r e n t p a r t s :

i) 4 8 s e m i c y l i n d r i c a l m o d u l e s of a l t e r n a t e l a y e r s of s c i n t i l l a t o r a n d l e a d ( g o n

d o l a s ) , a r r a n g e d i n two c y l i n d r i c a l h a l f - s h e l l s , o n e o n e i t h e r s i d e of t h e b e a t

a x i s w i t h a n i n n e r r a d i u s of 1.36 m . E a c h m o d u l e e x t e n d s o v e r a p p r o x i m a t e l y

1 8 0 ° i n a z i m u t h a n d m e a s u r e s 2 2 . 5 c m i n the b e a m d i r e c t i o n . T h e l i g h t p r o d u c e i

i n e a c h o f the f o u r s e p a r a t e s e g m e n t a t i o n s i n d e p t h is s e e n b y w a v e l e n g t h

s h i f t e r p l a t e s o n e a c h s i d e of t h e c o u n t e r , i n t u r n c o n n e c t e d to f o u r p h o t o -

m u l t i p l i e r s ( P M s ) , two at the top a n d two a t t h e b o t t o m . L i g h t a t t e n u a t i o n

is e x p l o i t e d in o r d e r to f u r t h e r i m p r o v e t h e c a l o r i m e t r i c i n f o r m a t i o n : t h e

c o m p a r i s o n of the p u l s e h e i g h t s of t h e top a n d b o t t o m P M o f e a c h s e g m e n t

g i v e s a m e a s u r e m e n t o f t h e a z i m u t h a l a n g l e <J> f o r l o c a l i z e d e n e r g y d e p o s i t i o n s ,

- 127 -

A<> ( r a d ) = 0 . 3 / / E ( G e V ) . A s i m i l a r l o c a l i z a t i o n a l o n g t h e b e a m d i r e c t i o n i s

p o s s i b l e u s i n g t h e c o m p l e m e n t a r y p a i r i n g o f P M s . T h e e n e r g y r e s o l u t i o n f o r

e l e c t r o n s u s i n g a l l f o u r PMs i s A E / E = 0 . 1 5 / / E ( G e V ) .

i i ) 6 4 p e t a l s o f e n d - c a p e l e c t r o m a g n e t i c s h o w e r c o u n t e r s ( b o u c h o n s ) , s e g m e n t e d

f o u r t i m e s i n d e p t h , o n b o t h s i d e s o f t h e c e n t r a l d e t e c t o r a t 3 m d i s t a n c e

f r o m t h e b e a m c r o s s i n g p o i n t . T h e p o s i t i o n o f e a c h s h o w e r i s m e a s u r e d w i t h

a p o s i t i o n d e t e c t o r l o c a t e d i n s i d e t h e c a l o r i m e t e r a t a d e p t h o f 11 r a d i a t i o n

l e n g t h s , i . e . a f t e r t h e f i r s t t w o s e g m e n t s . I t c o n s i s t s o f t w o p l a n e s o f

o r t h o g o n a l p r o p o r t i o n a l t u b e s o f 2 x 2 c m 2 c r o s s - s e c t i o n a n d i t l o c a t e s t h e

c e n t r e o f g r a v i t y o f e n e r g e t i c e l e c t r o m a g n e t i c s h o w e r s t o ± 2 mm i n s p a c e .

T h e a t t e n u a t i o n l e n g t h o f t h e s c i n t i l l a t o r h a s b e e n c h o s e n t o m a t c h t h e

v a r i a t i o n o f s i n 6 o v e r t h e r a d i u s o f t h e c a l o r i m e t e r s , s o a s t o d i r e c t l y

m e a s u r e i n f i r s t a p p r o x i m a t i o n E^, = E s i n 8 r a t h e r t h a n t h e t r u e e n e r g y d e

p o s i t i o n E , w h i c h c a n , h o w e v e r , b e d e t e r m i n e d l a t e r , u s i n g t h e i n f o r m a t i o n

f r o m t h e p o s i t i o n d e t e c t o r . T h i s t e c h n i q u e p e r m i t s u s t o r e a d o u t d i r e c t l y

f r o m t h e e n d - c a p d e t e c t o r s t h e a m o u n t o f t r a n s v e r s e e n e r g y d e p o s i t e d , w i t h o u t

r e c o n s t r u c t i o n o f t h e e v e n t t o p o l o g y .

3 . E L E C T R O N I D E N T I F I C A T I O N

E l e c t r o m a g n e t i c s h o w e r s a r e i d e n t i f i e d b y t h e i r c h a r a c t e r i s t i c t r a n s i t i o n

c u r v e , a n d i n p a r t i c u l a r b y t h e l a c k o f p e n e t r a t i o n i n t h e h a d r o n c a l o r i m e t e r

b e h i n d t h e m . T h e p e r f o r m a n c e o f t h e d e t e c t o r s w i t h r e s p e c t t o h a d r o n s a n d e l e c

t r o n s h a s b e e n s t u d i e d e x t e n s i v e l y i n a t e s t b e a m a s a f u n c t i o n o f t h e e n e r g y ,

t h e a n g l e o f i n c i d e n c e , a n d t h e l o c a t i o n o f i m p a c t . T h e f r a c t i o n o f h a d r o n s

( p i o n s ) d e l i v e r i n g a n e n e r g y d e p o s i t i o n E^ b e l o w a g i v e n t h r e s h o l d i n t h e h a d r o n

c a l o r i m e t e r i s a r a p i d l y f a l l i n g f u n c t i o n o f e n e r g y , a m o u n t i n g t o a b o u t 0 . 3 % f o r

p = 4 0 G e V / c a n d E £ < 2 0 0 M e V . U n d e r t h e s e c o n d i t i o n s , 9 8 % o f e l e c t r o n s a r e d e

t e c t e d .

4 . N E U T R I N O I D E N T I F I C A T I O N

T h e e m i s s i o n o f o n e ( o r m o r e ) n e u t r i n o s c a n b e s i g n a l l e d o n l y b y a n a p p a r e n t

v i s i b l e e n e r g y i m b a l a n c e o f t h e e v e n t ( m i s s i n g e n e r g y ) . I n o r d e r t o p e r m i t s u c h

- 1 2 8 -

a m e a s u r e m e n t , c a l o r i m e t e r s h a v e b e e n m a d e c o m p l e t e l y h e r m e t i c d o w n t o a n g l e s o f

0 . 2 ° w i t h r e s p e c t t o t h e d i r e c t i o n o f t h e b e a m s . ( I n p r a c t i c e , 97% o f t h e m a s s o f

t h e m a g n e t i s c a l o r i m e t r i z e d . ) I t i s p o s s i b l e t o d e f i n e a n e n e r g y f l o w v e c t o r ¿É,

a d d i n g v e c t o r i a l l y t h e o b s e r v e d e n e r g y d e p o s i t i o n s o v e r t h e w h o l e s o l i d a n g l e .

N e g l e c t i n g p a r t i c l e m a s s e s a n d w i t h a n i d e a l c a l o r i m e t e r r e s p o n s e a n d s o l i d - a n g l e

c o v e r a g e , m o m e n t u m c o n s e r v a t i o n r e q u i r e s AE = 0 . We h a v e t e s t e d t h i s t e c h n i q u e o n

m i n i m u m b i a s a n d j e t - e n r i c h e d e v e n t s f o r w h i c h n e u t r i n o e m i s s i o n o r d i n a r i l y d o e s

n o t o c c u r . T h e t r a n s v e r s e c o m p o n e n t s AE^ a n d AE^ e x h i b i t s m a l l r e s i d u a l s c e n t r e d

o n z e r o w i t h a n r . m . s . d e v i a t i o n w e l l d e s c r i b e d b y t h e l a w AE = 0 . 4 / Y.lE ^ I ,

w h e r e a l l u n i t s a r e i n G e V a n d t h e q u a n t i t y u n d e r t h e s q u a r e r o o t i s t h e s c a l a r

s u m o f a l l t r a n s v e r s e e n e r g y c o n t r i b u t i o n s r e c o r d e d i n t h e e v e n t ( f i g . 1 ) . T h e

d i s t r i b u t i o n s h a v e G a u s s i a n s h a p e a n d n o p r o m i n e n t t a i l s . T h e l o n g i t u d i n a l c o m

p o n e n t o f e n e r g y AE^ i s a f f e c t e d b y t h e e n e r g y f l o w e s c a p i n g t h r o u g h t h e 0 ° s i n g u

l a r i t y o f t h e c o l l i d e r ' s b e a m p i p e a n d i t c a n n o t b e o f m u c h p r a c t i c a l u s e . We

r e m a r k t h a t , l i k e n e u t r i n o s , h i g h - e n e r g y m u o n s e a s i l y p e n e t r a t e t h e c a l o r i m e t e r

a n d l e a k o u t s u b s t a n t i a l a m o u n t s o f e n e r g y . A m u o n d e t e c t o r , c o n s i s t i n g o f s t a c k s

o f e i g h t p l a n e s o f d r i f t c h a m b e r s , s u r r o u n d s t h e w h o l e a p p a r a t u s a n d h a s b e e n u s e d

t o i d e n t i f y s u c h p r o c e s s e s , w h i c h a r e o c c u r r i n g a t t h e l e v e l o f 1 e v e n t p e r n a n o -

b a r n f o r AE > 10 G e V .

5 . D A T A - T A K I N G A N D I N I T I A L E V E N T S E L E C T I O N S

T h e p r e s e n t w o r k i s b a s e d o n d a t a r e c o r d e d i n a 3 0 - d a y p e r i o d d u r i n g N o v e m b e r

a n d D e c e m b e r 1 9 8 2 . T h e i n t e g r a t e d l u m i n o s i t y a f t e r s u b t r a c t i o n o f d e a d - t i m e a n d

o t h e r i n s t r u m e n t a l i n e f f i c i e n c i e s w a s 18 n b c o r r e s p o n d i n g t o a b o u t 1 0 9 c o l l i

s i o n s b e t w e e n p r o t o n s a n d a n t i p r o t o n s a t / s = 5 4 0 G e V .

F o r e a c h b e a m - b e a m c o l l i s i o n d e t e c t e d b y s c i n t i l l a t o r h o d o s c o p e s , t h e e n e r g y

d e p o s i t i o n s i n a l l c a l o r i m e t e r c e l l s a f t e r f a s t d i g i t i z a t i o n w e r e p r o c e s s e d , i n

t h e t i m e p r i o r t o t h e o c c u r r e n c e o f t h e n e x t b e a m - b e a m c r o s s i n g , b y a f a s t a r i t h

m e t i c p r o c e s s o r i n o r d e r t o r e c o g n i z e t h e p r e s e n c e o f a l o c a l i z e d e l e c t r o m a g n e t i c

e n e r g y d e p o s i t i o n , n a m e l y o f a t l e a s t 10 G e V o f t r a n s v e r s e e n e r g y e i t h e r i n t w o

g o n d o l a e l e m e n t s o r i n t w o b o u c h o n p e t a l s . I n a d d i t i o n , w e h a v e s i m u l t a n e o u s l y

- 129 -

operated three other trigger conditions: i) a jet trigger, with ^ 15 GeV of

transverse energy in a localized cluster f_7] of electromagnetic and hadron

calorimeters; ii) a global trigger, with > 40 GeV of total transverse energy

from all calorimeters with |r)| < 1.4; and iii) a muon trigger, namely at least

one penetrating track with \ï]\ < 1.3 pointing to the diamond.

The electron trigger rate was about 0.2 event per second at the (peak)

luminosity L = 5 x 1 0 2 8 c m - 2 s - 1 . Collisions with residual gas or with vacuum

chamber walls were completely negligible, and the apparatus in normal machine

conditions yielded an almost pure sample of beam-beam collisions. In total,

9.75 x 1 0 s triggers were collected, of which 1.4 x 10 5 were characterized by an

electron trigger flag.

Event filtering by calorimetric information was further perfected by off-line

selection of 28,000 events with E T > 15 GeV in two gondolas, or E T > 15 GeV in two

bouchon petals with valid position-detector information. These events were finally

processed with the central detector reconstruction. Of these events there are

2125 with a good quality, vertex-associated charged track of p^ > 7 GeV/c. This

sample will be used for the subsequent analysis of events in the gondolas.

6. SEARCH FOR ELECTRON CANDIDATES

We now require three conditions in succession in order to ensure that the

track is isolated, namely to reject the debris of jets:

i) The fast track (p T > 7 GeV/c) as recorded by the central detector must hit an

pair of adjacent !gondolas with transverse energy E T > 15 GeV (1106 events),

ii) Other charged tracks, entering the same pair of gondolas, must not add up to

more than 2 GeV/c of transverse momenta (276 events),

iii) The <) information from pulse division from gondola phototubes must agree

within 3a with the impact of the track (167 events).

Next we introduce two simple conditions to enhance its electromagnetic

nature:

iv) The energy deposition E £ in the hadronic calorimeters aimed at by the track

must not exceed 600 MeV (72 events).

- 1 3 0 -

v ) T h e e n e r g y d e p o s i t e d i n t h e g o n d o l a s E g Q n m u s t m a t c h t h e m e a s u r e m e n t o f t h e

m o m e n t u m o f t h e t r a c k p r n , n a m e l y | l / p - 1/E | < 3 a .

A t t h i s p o i n t o n l y 39 e v e n t s a r e l e f t , w h i c h w e r e i n d i v i d u a l l y e x a m i n e d b y

p h y s i c i s t s o n t h e v i s u a l s c a n n i n g a n d i n t e r a c t i v e f a c i l i t y M e g a t e k . T h e s u r v i v i n g

e v e n t s b r e a k u p c l e a n l y i n t o t h r e e c l a s s e s , n a m e l y 5 e v e n t s w i t h n o j e t a c t i v i t y

f ^ 8 ] , 11 w i t h a j e t o p p o s i t e t o t h e t r a c k w i t h i n a 3 0 ° a n g l e i n a n d 2 3 w i t h

t w o j e t s ( o n e o f w h i c h c o n t a i n s t h e e l e c t r o n c a n d i d a t e ) o r c l e a r e + e ~ c o n v e r s i o n

p a i r s . A s i m i l a r a n a l y s i s p e r f o r m e d o n t h e b o u c h o n h a s l e d t o a n o t h e r e v e n t w i t h

n o j e t s . T h e c l a s s e s o f e v e n t s h a v e s t r i k i n g d i f f e r e n c e s . We f i n d t h a t w h i l s t

e v e n t s w i t h j e t a c t i v i t y h a v e e s s e n t i a l l y n o m i s s i n g e n e r g y ( f i g . 2 b ) t h e

o n e s w i t h n o j e t s s h o w e v i d e n c e o f a m i s s i n g t r a n s v e r s e e n e r g y o f t h e s a m e m a g n i

t u d e a s t h e t r a n s v e r s e e l e c t r o n e n e r g y ( f i g . 3 a ) , w i t h t h e v e c t o r m o m e n t a a l m o s t

e x a c t l y b a l a n c e d b a c k - t o - b a c k ( f i g . ; 2 a ) . I n o r d e r t o a s s e s s h o w s i g n i f i c a n t t h e

e f f e c t i s , w e p r o c e e d t o a n a l t e r n a t i v e a n a l y s i s b a s e d e x c l u s i v e l y o n t h e p r e s e n c e

o f m i s s i n g t r a n s v e r s e e n e r g y .

7 . S E A R C H F O R E V E N T S W I T H E N E R G E T I C N E U T R I N O S

We s t a r t a g a i n w i t h t h e i n i t i a l s a m p l e o f 2 1 2 5 e v e n t s w i t h a c h a r g e d t r a c k o f

p j, > 7 G e V / c . We n o w m o v e t o p i c k u p v a l i d a t e d e v e n t s w i t h a h i g h m i s s i n g t r a n s

v e r s e e n e r g y a n d w i t h t h e c a n d i d a t e t r a c k n o t p a r t o f a j e t :

i ) T h e t r a c k m u s t p o i n t t o a p a i r o f g o n d o l a s w i t h d e p o s i t i o n i n e x c e s s o f

E T > 15 G e V a n d n o o t h e r t r a c k w i t h p T > 2 G e V / c i n a 2 0 ° c o n e ( 9 1 1 e v e n t s ) .

i i ) M i s s i n g t r a n s v e r s e e n e r g y i m b a l a n c e i n e x c e s s o f 15 G e V .

O n l y 70 e v e n t s s u r v i v e t h e s e s i m p l e c u t s , a s s h o w n i n f i g . 4 . T h e p r e v i o u s l y

f o u n d 5 j e t l e s s e v e n t s o f t h e g o n d o l a s a r e c l e a r l y v i s i b l e . A t t h i s p o i n t , a s

f o r t h e e l e c t r o n a n a l y s i s , w e p r o c e s s t h e e v e n t s a t t h e i n t e r a c t i v e f a c i l i t y M e g a t e

i i i ) T h e m i s s i n g t r a n s v e r s e e n e r g y i s v a l i d a t e d , r e m o v i n g t h o s e e v e n t s i n w h i c h

j e t s a r e p o i n t i n g t o w h e r e t h e d e t e c t o r r e s p o n s e i s l i m i t e d , i . e . c o r n e r s ,

l i g h t - p i p e d u c t s g o i n g u p a n d d o w n . S o m e v e r y e v i d e n t , b i g s e c o n d a r y i n t e r

a c t i o n s i n t h e b e a m p i p e a r e a l s o r e m o v e d . We a r e l e f t w i t h 31 e v e n t s , o f

w h i c h 2 1 h a v e E > 0 . 0 1 E a n d 10 e v e n t s in w h i c h E < 0 . 0 1 E c gon c gon

- 1 3 1 -

i v ) We r e q u i r e t h a t t h e c a n d i d a t e t r a c k b e w e l l i s o l a t e d , t h a t t h e r e i s n o t r a c k

w i t h p^, > 1 . 5 G e V i n a c o n e o f 3 0 ° , a n d t h a t E T < 4 G e V f o r n e u t r a l s i n

n e i g h b o u r i n g g o n d o l a s a t s i m i l a r (f> a n g l e . E i g h t e e n e v e n t s s u r v i v e : t e n

w i t h E ^ 0 a n d e i g h t w i t h E = 0 . c c

T h e e v e n t s o n c e a g a i n d i v i d e n a t u r a l l y i n t o t h e t w o c l a s s e s : 1 1 e v e n t s w i t h

j e t a c t i v i t y i n t h e a z i m u t h o p p o s i t e t o t h e t r a c k , a n d 7 e v e n t s w i t h o u t d e t e c t a b l e

j e t s t r u c t u r e . I f w e n o w e x a m i n e E c , w e s e e t h a t t h e s e t w o c l a s s e s a r e s t r i k i n g l y

d i f f e r e n t , w i t h l a r g e E^ f o r t h e e v e n t s w i t h j e t s ( f i g . 5 b ) a n d n e g l i g i b l e E^ f o r

t h e j e t l e s s o n e s ( f i g . 5 a ) . We c o n c l u d e t h a t w h i l s t t h e f i r s t o n e s a r e m o s t

l i k e l y t o b e h a d r o n s , t h e l a t t e r c o n s t i t u t e a n e l e c t r o n s a m p l e .

We n o w c o m p a r e t h e p r e s e n t r e s u l t w i t h t h e c a n d i d a t e s o f t h e p r e v i o u s a n a l y s i s

b a s e d o n e l e c t r o n s i g n a t u r e . We r e m a r k t h a t f i v e o u t o f t h e s e v e n e v e n t s c o n s t i

t u t e t h e p r e v i o u s f i n a l s a m p l e ( f i g . 5 a ) . T w o n e w e v e n t s h a v e b e e n a d d e d , e l i m i

n a t e d p r e v i o u s l y b y t h e t e s t o n e n e r g y m a t c h i n g b e t w e e n t h e c e n t r a l d e t e c t o r a n d

t h e g o n d o l a s . C l e a r l y t h e s a m e p h y s i c a l p r o c e s s t h a t p r o v i d e d u s w i t h t h e l a r g e -

P T e l e c t r o n d e l i v e r s a l s o h i g h - e n e r g y n e u t r i n o s . T h e s e l e c t i v i t y o f o u r a p p a r a t u s

i s s u f f i c i e n t t o i s o l a t e s u c h a p r o c e s s f r o m e i t h e r i t s e l e c t r o n o r i t s n e u t r i n o

f e a t u r e s i n d i v i d u a l l y . I f (V g, e ) p a i r s a n d (v , x) p a i r s a r e b o t h p r o d u c e d a t

c o m p a r a b l e r a t e s , t h e t w o a d d i t i o n a l n e w e v e n t s c a n r e a d i l y b e e x p l a i n e d s i n c e

m i s s i n g e n e r g y c a n a r i s e e q u a l l y w e l l f r o m V ß a n d v . I n d e e d , c l o s e r i n s p e c t i o n

o f t h e s e e v e n t s s h o w s t h e m t o b e c o m p a t i b l e w i t h t h e x h y p o t h e s i s , f o r i n s t a n c e ,

T~ -*• Tf —TT°v^. w i t h l e a d i n g T T ° . H o w e v e r , o u r i s o l a t i o n r e q u i r e m e n t s o n t h e c h a r g e d

t r a c k s t r o n g l y b i a s e s a g a i n s t m o s t o f t h e X d e c a y m o d e s .

8 . D E T A I L E D D E S C R I P T I O N O F T H E E L E C T R O N - N E U T R I N O E V E N T S

T h e m a i n p r o p e r t i e s o f t h e f i n a l s a m p l e o f s i x e v e n t s ( f i v e g o n d o l a s , o n e

b o u c h o n ) a r e g i v e n i n t a b l e 2 a n d m a r k e d A t h r o u g h F . T h e e v e n t G i s a X c a n d i

d a t e . O n e c a n r e m a r k t h a t b o t h c h a r g e s o f t h e e l e c t r o n s a r e r e p r e s e n t e d . T h e s u c

c e s s i v e e n e r g y d e p o s i t i o n s i n t h e g o n d o l a s a m p l e s a r e c o n s i s t e n t w i t h t e s t b e a m

f i n d i n g s . A l l b u t e v e n t D h a v e n o e n e r g y d e p o s i t i o n i n t h e h a d r o n c a l o r i m e t e r ;

e v e n t D h a s a 4 0 0 M e V v i s i b l e , 1% e n e r g y l e a k a g e b e y o n d 25 r a d i a t i o n l e n g t h s . T e s t

- 1 3 2 -

b e a m m e a s u r e m e n t s s h o w t h a t t h i s i s a p o s s i b l e f l u c t u a t i o n . M u l t i p l i c i t y o f t h e

e v e n t s i s w i d e l y d i f f e r e n t : e v e n t F ( f i g . 6 b , f i g . 7 b ) h a s a s m a l l c h a r g e d m u l t i

p l i c i t y ( 1 4 ) , w h i l s t e v e n t A ( f i g . 6 a , f i g . 7 a ) i s v e r y r i c h i n p a r t i c l e s ( 6 5 ) .

E v e n t B i s t h e b o u c h o n e v e n t , a n d i t h a s a n u m b e r o f f e a t u r e s w h i c h m u s t b e m e n

t i o n e d . A 1 0 0 M e V / c t r a c k e m e r g e s f r o m t h e v a c u u m c h a m b e r n e a r t h e e x i t p o i n t o f t h

e l e c t r o n t r a c k , w h i c h m i g h t f o r m a p a r t o f a n a s y m m e t r i c e l e c t r o n p a i r w i t h t h e

c a n d i d a t e . T h e i n i t i a l a n g l e b e t w e e n t h e t w o t r a c k s w o u l d t h e n b e 1 1 ° , n o t i n

c o m p a t i b l e w i t h t h i s h y p o t h e s i s o n c e C o u l o m b s c a t t e r i n g a n d m e a s u r e m e n t e r r o r s o f

t h e t w o t r a c k s a r e t a k e n i n t o a c c o u n t . T h e r e i s a l s o s o m e a c t i v i t y i n t h e m u o n

d e t e c t o r o p p o s i t e t o t h e e l e c t r o n c a n d i d a t e ; t h e m u o n t r a c k i s u n m e a s u r a b l e i n

t h e c e n t r a l d e t e c t o r . F o r t h e s e r e a s o n s w e p r e f e r t o l i m i t o u r f i n a l a n a l y s i s t o

t h e e v e n t s i n t h e g o n d o l a s , a l t h o u g h w e b e l i e v e t h a t e v e r y t h i n g i s s t i l l c o n s i s t e n t

w i t h e v e n t B b e i n g a g o o d e v e n t .

9 . B A C K G R O U N D E V A L U A T I O N S

We f i r s t c o n s i d e r p o s s i b l e b a c k g r o u n d s t o t h e e l e c t r o n s i g n a t u r e f o r e v e n t s

w i t h n o j e t s . M i s s i n g e n e r g y ( n e u t r i n o s i g n a t u r e ) i s n o t y e t a d v o c a t e d . W e h a v e

t a k e n t h e f o l l o w i n g i n t o c o n s i d e r a t i o n :

1 ) A h i g h - p ^ , c h a r g e d p i o n ( h a d r o n ) m i s i d e n t i f i e d a s a n e l e c t r o n , o r a h i g h - p ^ ,

c h a r g e d p i o n ( h a d r o n ) o v e r l a p p i n g w i t h o n e o r m o r e I T 0 .

T h e c e n t r a l d e t e c t o r m e a s u r e m e n t o b v i o u s l y g i v e s o n l y t h e m o m e n t u m p o f t h e

c h a r g e d p i o n . I n a d d i t i o n , t h e e l e c t r o m a g n e t i c d e t e c t o r s c a n a c c u m u l a t e a n

a r b i t r a r y a m o u n t o f e l e c t r o m a g n e t i c e n e r g y f r o m T T ° ' S , w h i c h w o u l d s i m u l a t e t h e

e l e c t r o n b e h a v i o u r . S i n c e g o n d o l a s a r e t h i c k e n o u g h t o a b s o r b t h e e l e c t r o m a g n e t i c

c a s c a d e , t h e e n e r g y d e p o s i t i o n i n t h e h a d r o n c a l o r i m e t e r i s d o m i n a t e d b y t h e

p u n c h - t h r o u g h o f t h e c h a r g e d p i o n o f m o m e n t u m p m e a s u r e d i n t h e c e n t r a l d e t e c t o r ,

f o r w h i c h r e j e c t i o n t a b l e s e x i s t f r o m t e s t b e a m r e s u l t s . I n o u r 18 n b " 1 s a m p l e w e

h a v e s e a r c h e d f o r s i n g l e - t r a c k e v e n t s w i t h p T > 2 0 G e V / c , n o a s s o c i a t e d j e t , E £ >

> 6 0 0 M e V t o e n s u r e h a d r o n i c s i g n a t u r e , a n d a r e a s o n a b l e e n e r g y b a l a n c e ( w i t h i n

3 s t . d e v . ) b e t w e e n t h e c h a r g e d t r a c k m o m e n t u m m e a s u r e m e n t a n d t h e s u m o f h a d r o n i c

a n d e l e c t r o m a g n e t i c e n e r g y d e p o s i t i o n s . We h a v e f o u n d n o s u c h e v e n t . O n c e t h e

- 1 3 3 -

1 0 . CONCLUSIONS

I n c o n c l u s i o n , w e h a v e b e e n u n a b l e t o f i n d a b a c k g r o u n d p r o c e s s c a p a b l e o f

s i m u l a t i n g t h e o b s e r v e d h i g h - e n e r g y e l e c t r o n s . T h u s w e a r e l e d t o t h e c o n c l u s

t h a t t h e y a r e e l e c t r o n s . L i k e w i s e w e h a v e s e a r c h e d f o r b a c k g r o u n d s c a p a b l e o f

s i m u l a t i n g l a r g e - E T n e u t r i n o e v e n t s . A g a i n , n o n e o f t h e p r o c e s s e s c o n s i d e r e d

a p p e a r t o b e e v e n n e a r t o b e c o m i n g c o m p e t i t i v e . T h e m o s t l i k e l y c a n d i d a t e f o r

m e a s u r e d p i o n r e j e c t i o n t a b l e i s f o l d e d i n , t h i s b a c k g r o u n d i s e n t i r e l y n e g l i g i b l e .

A f u r t h e r t e s t a g a i n s t p i l e - u p i s g i v e n b y t h e m a t c h i n g i n t h e x - d i r e c t i o n b e t w e e n

t h e c h a r g e d t r a c k o f t h e c e n t r a l d e t e c t o r a n d t h e c e n t r o i d o f t h e e n e r g y d e p o s i

t i o n s i n t h e g o n d o l a s , a n d w h i c h i s v e r y g o o d f o r a l l e v e n t s .

2 ) H i g h - p T T T 0 , n°, o r y i n t e r n a l l y ( D a l i t z ) o r e x t e r n a l l y c o n v e r t e d t o a n

e + e _ p a i r w i t h o n e l e g m i s s e d . T h e n u m b e r o f i s o l a t e d e . m . c o n v e r s i o n s ( T T 0 , n» Y »

e t c . ) p e r u n i t o f r a p i d i t y h a s b e e n d i r e c t l y m e a s u r e d a s a f u n c t i o n o f E^, i n t h e

b o u c h o n s , u s i n g t h e p o s i t i o n d e t e c t o r s o v e r t h e i n t e r v a l 1 0 - 4 0 G e V . F r o m t h i s

s p e c t r u m , t h e B e t h e - H e i t l e r f o r m u l a f o r p a i r c r e a t i o n , a n d t h e K r o l l - W a d a f o r m u l a

f o r D a l i t z p a i r s £ l 0 ] , t h e e x p e c t e d n u m b e r o f e v e n t s w i t h a " s i n g l e " e * w i t h p T >

> 2 0 G e V / c i s 0 . 2 p 0 ( i n G e V / c ) , l a r g e l y i n d e p e n d e n t o f t h e c o m p o s i t i o n o f t h e

e . m . c o m p o n e n t ; p 0 i s t h e e f f e c t i v e m o m e n t u m b e l o w w h i c h t h e l o w - e n e r g y l e g o f

t h e p a i r b e c o m e s u n d e t e c t a b l e . V e r y c o n s e r v a t i v e l y , w e c a n t a k e p 0 = 2 0 0 M e V / c

( c u r v a t u r e r a d i u s 1 . 2 m) a n d c o n c l u d e t h a t t h i s b a c k g r o u n d i s n e g l i g i b l e .

3 ) H e a v y q u a r k a s s o c i a t e d p r o d u c t i o n , f o l l o w e d b y p a t h o l o g i c a l f r a g m e n t a t i o n

a n d d e c a y c o n f i g u r a t i o n , s u c h t h a t Q x -*• e ( v X ) w i t h t h e e l e c t r o n l e a d i n g a n d t h e

r e s t u n d e t e c t e d , a n d Q 2 -»• v ( £ X ) , w i t h t h e n e u t r i n o l e a d i n g a n d t h e r e s t u n d e t e c t e d .

I n 5 n b - 1 w e h a v e o b s e r v e d o n e e v e n t i n w h i c h t h e r e i s a m u o n a n d a n e l e c t r o n i n

s e p a r a t e j e t s , w i t h p , ^ = 4 . 4 G e V / c a n d p ^ e ^ = 1 3 . 3 G e V / c . R e q u i r i n g i ) e x t r a

p o l a t i o n t o t h e e n e r g y o f t h e e v e n t s , i i ) f r a g m e n t a t i o n f u n c t i o n s f o r l e a d i n g

l e p t o n , a n d i i i ) a d e t e c t i o n h o l e f o r a l l r e m a i n i n g p a r t i c l e s , m a k e s t h e r a t e o f

t h e s e b a c k g r o u n d e v e n t s n e g l i g i b l e .

- 134 -

t h e s e e v e n t s a p p e a r s t o b e t h e I n t e r m e d i a t e V e c t o r B o s o n o f w e a k i n t e r a c t i o n s .

P r o p e r t i e s o f t h e e v e n t s s e e m t o b e i n a g r e e m e n t w i t h e x p e c t a t i o n s o f W e i n b e r g -

S a l a m e x p e c t a t i o n s f 2 j .

- 1 3 5 -

R.:F.:K.:N_C.;S A N D F O O T N O T E S

[ l ] C . R u b b i a , P . M r l n t y r e a n d D . C l i n e , P r o c . I n t . N e u t r i n o C o n f e r e n c e , A a c h e n ,

1 9 7 6 ( V i e w e g , B r a u n s c h w e i g , 1 9 7 7 ) , p . 6 8 3 .

S t u d y G r o u p , D e s i g n s t u d y o f a p r o t o n - a n t i p r o t o n c o l l i d i n g b e a m f a c i l i t y , i

C E R N / P S / A A 7 8 - 3 ( 1 9 7 8 ) , r e p r i n t e d i n P r o c . W o r k s h o p o n P r o d u c i n g H i g h -

L u m i n o s i t y , H i g h - E n e r g y P r o t o n - A n t i p r o t o n C o l l i s i o n s , B e r k e l e y , 1 9 7 8

( r e p o r t L B L - 7 5 7 4 , U C 3 4 c ) , p . 1 8 9 .

T h e s t a f f o f t h e C E R N p r o t o n - a n t i p r o t o n p r o j e c t , P h y s . L e t t . 1 0 7 B ( 1 9 8 1 ) 3 0 6 .

[ 2 ] S . W e i n b e r g , P h y s . R e v . L e t t . 19 ( 1 9 6 7 ) 1 2 6 4 .

A . S a l a m , P r o c . 8 t h N o b e l S y m p o s i u m , A s p e n ' â s g a r d e n , 1 9 6 8 ( A l m q v i s t a n d

W i k s e l l , S t o c k h o l m , 1 9 6 8 ) , p . 3 6 7 .

[ 3 j W.J. M a r c i a n o , P h y s . R e v . D 2 0 ( 1 9 7 9 ) 2 7 4 .

F . A n t o n e l l i , M . C o n s o l ! , G . C o r b ö , P h y s . L e t t . 9 1 B ( 1 9 8 0 ) 9 0 .

M . V e l t m a n , P h y s . L e t t . 9JLB ( 1 9 8 0 ) 9 5 .

A . S i r l i n , P h y s . R e v . D22^ ( 1 9 8 0 ) 9 7 1 .

W.J. M a r c i a n o , A . S i r l i n , P h y s . R e v . D 2 2 ( 1 9 8 0 ) 2 6 9 5 .

F . A n t o n e l l i , M . C o n s o l i , G . C o r b ö , 0 . P e l l e g r i n o , N u c l . P h y s . B 1 8 3

( 1 9 8 1 ) 1 9 5 .

F . A n t o n e l l i , L . M a i a n i , N u c l . P h y s . B 1 8 6 ( 1 9 8 1 ) 2 6 9 .

C . H . L l e w e l l y n S m i t h , J . A . W h e a t e r , P h y s . L e t t . 1 0 5 B ( 1 9 8 1 ) 4 8 6 .

£ 4 ] F o r a r e v i e w , s e e M. D a v i e r , P r o c . 2 1 s t I n t . C o n f . o n H i g h - E n e r g y P h y s i c s ,

P a r i s , 1 9 8 2 f_J. P h y s . ( F r a n c e ) , N o . 1 2 , t . 4 3 , 1 9 8 2 ] , p . C 3 - A 7 1 .

r_5 F . E . P a i g e , P r o c . T o p i c a l C o n f e r e n c e o n t h e P r o d u c t i o n o f N e w P a r t i c l e s a t

S u p e r - H i g h E n e r g i e s , U n i v . W i s c o n s i n , M a d i s o n , 1 9 7 9 .

L . B . O k u n a n d M . B . V o l o s h i n , N u c l . P h y s . B 1 2 0 ( 1 9 7 7 ) 4 5 9 .

C . Q u i g g , R e v . M o d . P h y s . 9 4 ( 1 9 7 7 ) 2 9 7 .

J. K o g u t a n d J. S h i g e m i t s u , N u c l . P h y s . B 1 2 9 ( 1 9 7 7 ) 4 6 1 .

R . H o r g a n a n d M . J a c o b , P r o c . C E R N S c h o o l o f P h y s i c s , M a l e n t e ( F R G ) , 1 9 8 0

( C E R N 8 1 - 0 4 ) , p . 6 5 .

- 136 -

[ l O ] H.M. K r o l l a n d W . W a d a , P h y s . R e v . 9 8 (1955) 1 3 5 5 .

R . F . P e i e r l s , T . T r u e m a n a n d L . L . W a n g , P h y s . R e v . D 16 (1977) 1 3 9 7 .

[[ô] U A 1 p r o p o s a l : A 4TT s o l i d - a n g l e d e t e c t o r f o r t h e S P S u s e d as a p r o t o n -

a n t i p r o t o n c o l l i d e r a t a c e n t r e - o f - m a s s e n e r g y o f 5 4 0 G e V , C E R N / S P S C 7 8 - 0 6

( 1 9 7 8 ) .

M . B a r r a n c o L u q u e e t a l . , N u c l . I n s t r u m . M e t h o d s 176 ( 1 9 8 0 ) 1 7 5 .

M . C a l v e t t i et a l . , N u c l . I n s t r u m . M e t h o d s 176_ ( 1 9 8 0 ) 2 5 5 .

K. E g g e r t e t a l . , N u c l . I n s t r u m . M e t h o d s 176 ( 1 9 8 0 ) 2 1 7 a n d 2 3 3 .

A. A s t b u r y , P h y s . S c r . 2 3 (1981) 3 9 7 .

l»V d e f i n e a c l u s t e r a s : i) a ".roup of e i g h t p.ondolas a n d the two h a d r o n

c a l o r i m e t e r e l e m e n t s i m m e d i a t e l y b e h i n d ; or ii) a q u a d r a n t of b o u c h o n

e l e m e n t s (8) w i t h the c o r r e s p o n d i n g h a d r o n c a l o r i m e t e r s .

[]8] T h e d e f i n i t i o n o f a j e t is b a s e d o n t h e U A 1 s t a n d a r d a l g o r i t h m , a p p l i e d

s e p a r a t e l y o n the c a l o r i m e t r y a n d o n the c e n t r a l d e t e c t o r d a t a . P o s i t i v e

r e s u l t s o n e i t h e r set a r e t a k e n as e v i d e n c e f o r a j e t . I n t h e c a l o r i m e t r y

a f o u r - v e c t o r ( k ^ , E ^ ) p o i n t i n g to the i n t e r a c t i o n v e r t e x is a s s o c i a t e d

w i t h e a c h s t r u c k c e l l . W o r k i n g in the t r a n s v e r s e p l a n e , a l l v e c t o r s w i t h

kj. > 2.5 G e V a r e o r d e r e d a n d a r e u s e d as p o t e n t i a l j e t i n i t i a t o r s . T h e y

a r e c o m b i n e d if t h e i r s e p a r a t i o n i n p h a s e s p a c e s a t i s f i e s t h e c u t

A R = /(Ar)) 2 + (Ac) 2 < 1 (A<J> i n r a d i a n s ) . T h e r e m a i n i n g s o f t p a r t i c l e s a r e

a d d e d to the n e a r e s t j e t i n An a n d Ac), p r o v i d e d t h e r e l a t i v e p^, is < 1 G e V

a n d A6 < 45 . A j e t is c o n s i d e r e d v a l i d if E^, > 10 G e V . T h i s s a m e p r o

c e d u r e is u s e d f o r c e n t r a l d e t e c t o r t r a c k s w i t h a p p r o p r i a t e l y a d j u s t e d

p a r a m e t e r s .

£9] T h e 11 e v e n t s w i t h a n e l e c t r o n a n d a j e t e x h i b i t a p"1* s p e c t r u m w i t h t h e

h i g h e s t e v e n t at p^, = 32 G e V / c .

Table 1

Calorimetry

A n g u l a r • c o v e r a g e 8

n T h i c k n e s s C e l l s i z e

S a m p l i n g s t e p

S e g m e n t a t i o n i n d e p t h C a l o r i m e t e r A n g u l a r •

c o v e r a g e 8

n N o . r a d .

l e n g t h s N o . a b s .

l e n g t h s A8

( ° )

A<|>

(°)

S a m p l i n g s t e p

S e g m e n t a t i o n i n d e p t h R e s o l u t i o n

B a r r e l e . m . :

h a d r . :

g o n d o l a s

c ' s

2 5 - 1 5 5 2 6 / s i n 8 1 . 1 / s i n 6

5 . 0 / s i n 8

5

15

180

18

1.2 mm P b 1.5 mm s c i n t .

50 mm F e 10 mm s c i n t .

3 . 3 / 6 . 6 / 9 . 9 / 6 . 6 X 0

2 . 5 / 2 . 5 X

0 . 1 5//B

0.8//E"

E n d - c a p s e . m . :

h a d r . :

b o u c h o n s

T s

5 - 2 5

1 5 5 - 1 7 5

2 7 / c o s 8 1.1/cos 8

7.1/cos 8

20

5

11

10

4 mm Pb 6 mm s c i n t .


4/7/9/7 X 0

3 . 5 / 3 . 5 X

0 . 1 2//Ep

0 . 8//E

C a l c o m e . m .

h a d r .

0 . 7 - 5

1 7 5 - 1 7 9 . 3

30 1.2

1 0 . 2

4 45 3 mm P b 3 mm s c i n t .


4 x 7 . 5 X 0

6 x 1.7 X

O . l S / i / E

0 . 8 / . ^

V e r y f o r w a r d e . m .

h a d r .

0 . 2 - 0 . 7

1 7 9 . 3 - 1 7 9 . 8

2 4 . 5 1.0

5 . 7

0 . 5

0 . 5

90

90

3 mm Pb 6 mm s c i n t .


5 . 7 / 5 . 3 / 5 . 8 / 7 . 7 X 0

5 x 1.25 X

0 . 1 5//Ë

0 . 8//E

Table 2

Main parameters of electron events with a large missing transverse energy

Properties of the electron track Calorimeter information General event topology

tain, event E T E P Ap a ) Q dE/dx y b) Track Length Sagitta Electromagnetic energy deposition

Khad Etot

(GeV)

Missing Ej A* °) Charged £ I > V

(GeV) (GeV) (GeV/c) I/I 0

No. (in) (mm) Sample 1

(GeV) Sample 2 (GeV)

Sample 3 (GeV)

Sample 4 (GeV) (GeV)

Etot

(GeV) (GeV) (dcg.) tracks

(GeV)

A 2 9 5 8

1279 24 39 33.8 +6.3 -4.6 - 1.22

+0.2 +1.1 36 1.36 1.7 3 34 2 0.2 0 278 24.4 ± 4.6 179 65 81

A Î S 2 2 B 214 17 46 47.5 +8.2

-6.1 - 1.37 ±0.16 +1.7 18 1.64 1.5 2 32 10 0.5 0 296 11.6 ± 4.0 219 49 60

- 3524 197 34 4S 21.6 +21.8

-7.2 - 1.37 +0.3 -0.8 26 1.25 2.11 1 30 14 0.2 0 367 41.3 ± 3.6 187 21 68

n 3610 " 760 38 40 33.4 +33.0

-11.1 - 1.64 +0.34 +0.3 9 0.98 0.75 3 9 26 2.2 0.4 111 40.0 ± 2.0 181 10 47

c 3701 c 305 37 37 56.2 +121.3

-22.8 + 1.54 +0.28 -0.1 12 0.95 0.4 1 18 17 0.9 0 363 35.5 ± 4.3 173 39 87

P 4017 r 838 36 70 53.1 +6.6

-5.3 - 1.30 ±0.26 +1.4 3 2.01 2.0 19 48 3 0.3 0 177 32.3 ± 2.4 179 14 49

r 3262 u 1108 40 40 6.7 +1.9

-1.2 - 1.23 +0.28 0.0 21 0.85 3.0 2 22 15 0.9 0 218 33.4 ±2.9 172 21 63

a) Including 200 um systematic error. b) y is defined as positive in the direction of outgoing p. c) Angle between electron and missing energy (neutrino).

- 139 -

Table 3

Transverse mass and transverse momentum of a W decaying into an electron and a neutrino computed from the events of table 2

Run, event P Í S ) of electron (GeV/c)

PÍV> = • T. missing E T

(GeV) Transverse mass

(GeV/c2)

„(W) _ ,-íe) ¿(v), P T - IP T + P T 1 (GeV)

A 2 9 5 8

1 2 7 9 2 4 ± 0 . 6 2 4 . 4 ± 4 . 6 4 8 . 4 ± 4 . 6 0 . 6 ± 4 . 6

B 3 5 2 2

2 1 4 1 7 ± 0 . 4 1 1 . 6 ± 4 . 0 2 6 . 5 ± 4 . 6 1 0 . 8 ± 4 . 0

C 3 5 2 4

1 9 7 3 4 ± 0 . 8 4 1 . 3 ± 3 . 6 7 4 . 8 ± 3 . 4 8 . 6 ± 3 . 7

D 3 6 1 0

7 6 0 3 8 ± 1 . 0 4 0 . 0 ± 2 . 0 7 8 . 0 ± 2 . 2 2 . 1 ± 2 . 2

E 3 7 0 1

3 0 5 3 7 ± 1 . 0 3 5 . 5 ± 4 . 3 7 2 . 4 ± 4 . 5 4 . 7 ± 4 . 4

F 4 0 1 7

8 3 8 3 6 ± 0 . 7 3 2 . 3 ± 2 . 4 6 8 . 2 ± 2 . 6 3 . 8 ± 2 . 5

- 1 4 0 -

F i g u r e c a p t i o n s

F i g . 1 : T h e m i s s i n g t r a n s v e r s e e n e r g y i n t h e y d i r e c t i o n £ A E y ( G e V ) ] p l o t t e d

v e r s u s t h e s c a l a r s u m o f m i s s i n g t r a n s v e r s e e n e r g y £ E ^ ( G e V ) ] f o r

m i n i m u m b i a s t r i g g e r s . T h e y - a x i s i s p o i n t i n g u p v e r t i c a l l y .

F i g . 2 : T h e m i s s i n g t r a n s v e r s e e n e r g y ( E ^ ) i s p l o t t e d v e c t o r i a l l y a g a i n s t

t h e e l e c t r o n d i r e c t i o n f o r t h e e v e n t s y i e l d e d b y t h e e l e c t r o n s e a r c h :

a ) w i t h o u t j e t s , b ) w i t h j e t s .

F i g . 3 : T h e c o m p o n e n t s o f t h e m i s s i n g e n e r g y p a r a l l e l a n d p e r p e n d i c u l a r t o

t h e e l e c t r o n m o m e n t u m p l o t t e d v e r s u s t h e e l e c t r o n e n e r g y f o r t h e

e v e n t s f o u n d i n t h e e l e c t r o n s e a r c h : a ) w i t h o u t j e t s , b ) w i t h j e t s .

F i g . 4 : T h e d i s t r i b u t i o n o f t h e s q u a r e o f t h e m i s s i n g t r a n s v e r s e e n e r g y f o r

t h o s e e v e n t s w h i c h s u r v i v e t h e c u t s r e q u i r i n g a s s o c i a t i o n o f t h e

c e n t r a l d e t e c t o r i s o l a t e d t r a c k a n d a s t r u c k g o n d o l a i n t h e m i s s i n g -

e n e r g y s e a r c h . T h e f i v e j e t l e s s e v e n t s f r o m t h e e l e c t r o n s e a r c h

a r e i n d i c a t e d .

F i g . 5 : A p l o t o f t h e t r a n s v e r s e e n e r g y i n t h e e . m . c a l o r i m e t e r s v e r s u s t h e

f r a c t i o n o f e n e r g y d e p o s i t e d i n t h e h a d r o n c a l o r i m e t e r s f o r e v e n t s

w h i c h s u r v i v e t h e m i s s i n g - e n e r g y s e a r c h : a ) w i t h o u t j e t s , b ) w i t h

j e t s .

F i g . 6 : T h e d i g i t i z a t i o n s f r o m t h e c e n t r a l d e t e c t o r f o r t h e t r a c k s i n t w o

o f t h e e v e n t s w h i c h h a v e a n i d e n t i f i e d , i s o l a t e d , w e l l - m e a s u r e d

h i g h - p ^ e l e c t r o n : a ) h i g h - m u l t i p l i c i t y , 6 5 a s s o c i a t e d t r a c k s ;

b ) l o w - m u l t i p l i c i t y , 14 a s s o c i a t e d t r a c k s .

- 1 4 1 -

T h e e n e r g y d e p o s i t e d i n t h e c e l l s o f t h e c e n t r a l ) c a l o r i m e t r y a n d t h e

e q u i v a l e n t p l o t f o r t r a c k m o m e n t a i n t h e c e n t r a l d e t e c t o r f o r t h e

t w o e v e n t s o f f i g . 6 . T h e t o p d i a g r a m s h o w s t h e e l e c t r o m a g n e t i c

c e l l s , t h e m i d d l e s h o w s t h e c e n t r a l d e t e c t o r t r a c k s , a n d t h e b o t t o m

p l o t , w i t h a v e r y m u c h i n c r e a s e d s e n s i t i v i t y , s h o w s t h e e n e r g y i n

t h e h a d r o n c a l o r i m e t e r . T h e p l o t s r e v e a l n o h a d r o n i c e n e r g y b e h i n d

t h e e l e c t r o n a n d n o j e t s t r u c t u r e ; a ) h i g h m u l t i p l i c i t y , b ) l o w

m u l t i p l i c i t y .

T h e m i s s i n g t r a n s v e r s e e n e r g y c o m p o n e n t p a r a l l e l t o t h e e l e c t r o n ,

p l o t t e d v e r s u s t h e t r a n s v e r s e e l e c t r o n e n e r g y f o r t h e f i n a l s i x

e l e c t r o n e v e n t s w i t h o u t j e t s ( 5 g o n d o l a s , 1 b o u c h o n ) . A l l t h e e v e n t s

i n t h e g o n d o l a s a p p e a r w e l l a b o v e t h e t h r e s h o l d c u t s u s e d i n t h e

s e a r c h e s .

- 142 -

F i g . 1

- 143 -

E V E N T S WITHOUT J E T S

GeV

-40 -20

Ev,parallel to electron

40

20

Electron direction

20 40 GeV — i 1 1 1 •

20

Ev, normal to electron

EVENTS WITH JETS

H h - 4 0 - 2 0

GeV Ev, parallel to electron

4 0

2 0

- 2 0

4 - 4 0

20 - H —

4 0 — i —

Electron direction

CeV

Ev, normal to electron

•(V) MISSING TRANSVERSE ENERGY E; V |

Transverse ro electron Parallel to electron —» r o

£71 ro <

CI <

1 1 1 - 1 — \ 1 1 1 1

\ \

\ "*~ \

-+- — 1 —

\ \ .

\ \

1 i i i V

1 i • i .

OO

OO

00

00

Number of events/(5 GeV)

- 7<7T -

- 145 -

F i g . 5

EVENT- 2958. 1279.

F i g . 6

Fig. 7

- 1 4 8 -

EVENTS WITHOUT JETS

E v e n t s /2GeV

GeV

50 c o

eu ai

— ro

40 h

30 h

en L . ( U c O l

O l l/t i _ O l > l/l c m

2 0

2 £ 10 en c ¡Ti

> O J

i n \ </) c O J >

4 /

/

10 2 0 30

0 10 1

20 30 40 GeV

i iÜ i 1 i : 40 GeV

Transverse electron energy (GeV)

F i g . 8

- 149 -

C. RUBBIA (ÜA1)

" J E T S , LARGE Pp E T C "

12 J A N U A R Y 1983

- 150 -

G. A r n i s o n 1 ' , A. A s t b u r y 1 ' , B. Aubère*, C. B a c c i ' , G. Bauer**, A. aézaguec* ,

R. Böck*, T .J .V. Bowcock', M. C a l v e t t i * . T. C a r r o l l * , P. C a t z \ P. Cennini* . F . C e r a d i n i ' , S. C i t C o l i n * , D. C l ine** , C. Cochet , J . Colas ,

M. Corden , D. Dallman _ M. DeBeer , M. D e l i a Negra , M. bemoulin , i l » . t

D. Denegrí , A. DiCfacc io , D. DiBi tonto , L. Dobrzynski , I I 2 t * Z

J . Dowe11 , H. Edwards , K. Eggert , E. Eisenhandler , N. E l l x s , P. Erhard , H. F a i s s n e r * , G. F o n t a i n e 7 , R. Frey*, R. F r ü h w i r t h 1 1 , J . Garvey' , S. Geer*,

7 ' l l , 1 1

C. Ghesquiere , P. Ghez , K.L. Giboni , W.R. Gibson , "Y. Giraud-Heraud , A. G i v e m a u d 1 ' , A. Gonidec*, G. G r a y e r ' P . G u t i e r r e z ' , T. Hansl-Kozanecka' ,

11 * • i "> W.J. Haynes , L.O. Hertzberger , C. Hodges ,D. Hoffmann , H. Hoffmann ,

D .J . Ho l thu izen* , R.J . Homer', A. Honma', W. Jank*, G. J o r a t * ,

P . I . P . Kalmus', V. Karimäki', R. K e e l e r ' , I . Kenyon', A* Kernan', R. Kinnunen', H . Kowalski*, W. Kosanacki ', D. Kryn*, F. Lacava*, J-P. L a u g i e r M, J.P. Lees 1 » Hi Lehmann', K. Laucha', A. L é v ê q u e ' 1 , D. L i n g l i n ' , E. L o c c i ' 1 , M. L o r e t ' ' ,

J - J . M a l o s s e 1 1 , T. Markiewicz*, G. Maurin*, T. McMahon', J - P . Mendiburu", M-N. Minard*,

M.. Horicca , H. Muirhead , F. Muller , A.K. Nandi , L. Naumann , A. Norton , 7 t » I » 1

A. Orkin-Lecourto is , L. Pao luz i , G. Piano Hortar i , H. Pimi'i , A. P l a c c i , E. Radermacher i i » 11 » i •

J . Ransdel l , H. R e i t h l e r , J - P . Revol , J . Rich , H. Ri jssenbeek , C. Roberts , J . Rohlf*, P. R o s s i * , C. Rubbia*, B. Sadoule t* , G'. S a j o C 7 , G. S a l v i ' ,

i ' i i i l i l « i • G. S a l v i n i , J . Sass , J . Saudraix , A. Savoy-Navarro , D. Sch inze l , W. S c o t t ,

T .P. S h a h 1 ' , M. S p i r o 1 1 , J . S t r a u s s 1 * , K. Sumorok*, F. Szoncso *, 0 . Smith ,

C. Tao , G. Thompson , J . T immer , E. Tsches log , J . Tuomimemi ,

J - P . V i a l l e * , J . Vrana 7 , V. Vui l l emin* , H.D. Wahl *, P. Watkins ' ,

J . W i l s o n ' , G.Y. X i e * , M. Yvert* , E. Zurfluh*

- 151 -

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P R E L I M I N A R Y S E A R C H E S F O R H A D R O N J E T S

A N D F O R L A R G E T R A N S V E R S E M O M E N T U M E L E C T R O N S

A T T H E SPS pp C O L L I D E R

T h e U A 2 C o l l a b o r a t i o n .

M. B a n n e r ^ , R. B a t t i s t o n * ' £ , P h . B l o c h ^ , F. B o n a u d i ^ b \ K. B o r e r ^ ,

M . B o r g h i n i ^ , J . - C . C h o l l e t ( d \ A . G . C l a r k ( b ) , C . C o n t a ( e ) , P. D a r r i u l a t ^ b ) ,

L. D i L e l l a ^ b \ J . D i n e s - H a n s e n ^ , P-A. D o r s a z ^ b \ L. F a y a r d ^ , M . F r a t e r n a l i ^ e \

D. F r o i d e v a u x ( b ) , J-M. G a i l l a r d ( d ) , 0 . G i l d e m e i s t e r ( b ) , V . G . G o g g i ( e \ H . G r o t e ( b \

B. H a h n ^ . H . H a n n i ( a ) , J.R. H a n s e n ( b ) , P. H a n s e n ( c \ T . H i m e l ( b ) , V . H u n g e r b ü h l e r ( b ) ,

P . J e n n i ^ b \ 0 . K o f o e d - H a n s e n ^ , E . L a n ç o n ^ , M . L i v a n ^ b , e \ S . L o u c a t o s ^ f \

B. M a d s e n ^ c \ P. M a n i ^ a \ B . M a n s o u l i ë ^ \ G . C . M a n t o v a n i * , L. M a p e l l i ^ b \

B. M e r k e l ^ , M . M e r m i k i d e s ^ , R. M t f l l e r u d ^ , B. N i l s s o n ^ , C . O n i o n s ^ b \

G . P a r r o u r ( b ' d ) , F. P a s t o r e ( b , e ) , H . P l o t h o w - B e s c h ( b , d ) , M . P o l v e r e l ( f * ,

J-P. R e p e l l i n ^ d \ A . R o t h e n b e r g a , A . R o u s s a r i e ^ , G . S a u v a g e ^ d \ J . S c h a c h e r ^ a \

J - L . S i e g r i s t ^ b ) , H . M . S t e i n e r + ^ b \ G . S t i m p f l ^ b \ F. S t o c k e r ( a ) , J . T e i g e r ( f \

V. V e r c e s i ^ e ) , A . W e i d b e r g ( b ) , H . Z a c c o n e ^ f ) a n d W . Z e l l e r ( a ) .

Presented by P. Darriulat

a) L a b o r a t o r i u m f ü r H o c h e n e r g i e p h y s i k , U n i v e r s i t ä t B e r n , S i d l e r s t r a s s e 5, B e r n ,

S w i t z e r l a n d .

b) C E R N , 1211 G e n e v a 2 3 , S w i t z e r l a n d .

c) N i e l s B o h r I n s t i t u t e , B l e g d a m s v e j 1 7 , C o p e n h a g e n , D e n m a r k .

d) L a b o r a t o i r e de l ' A c c é l é r a t e u r L i n é a i r e , U n i v e r s i t é d e P a r i s - S u d , O r s a y , F r a n c e .

e) I s t i t u t o di F i s i c a N u c l e a r e , U n i v e r s i t é di P a v i a a n d I N F N , S e z i o n e di P a v i a ,

V i a B a s s i 6, P a v i a , I t a l y .

f) C e n t r e d ' E t u d e s n u c l é a i r e s de S a c l a y .

* G r u p p o I N F N d e l D i p a r t i m e n t o di F i s i c a d e l l ' U n i v e r s i t à di P e r u g i a (Italy)

t O n l e a v e f r o m L a w r e n c e B e r k e l e y L a b o r a t o r y , U S A .

£ A l s o a t S c u o l a N o r m a l e S u p e r i o r e , P i s a , I t a l y .

- 191 -

ABSTRACT

We present a preliminary analysis of the UA2 data collected during the last Collider run (20 n b - 1 integrated luminosity) with particular emphasis on large transverse momentum hadron jets and on electrons having the configuration expected from the decay of electroweak bosons. The data provide very strong evidence of two-jet dominance in events with large transverse energy in the central region.

Four electron candidates have been observed with a transverse momentum in excess of 20 GeV/c, which are associated with no other large transverse energy production within the UA2 acceptance. While this result is in all respects consistent with a W •*• ev hypothesis, more work is needed to ensure that the background is well understood and to further ascertain electron identification.

No electron pair was detected with an invariant mass in excess of 40 GeV/c 2.

- 1 9 2 -

1. INTRODUCTION

During the months of October and November 1982 the UA2 experiment took data at the SPS pp Collider [l] for an integrated luminosity of nearly 20 nb" 1, namely ^ 250 times larger than in the earlier 1981 period of data collection [2,3] . Less than two months later the Rome Workshop provides an opportunity to present a preliminary analysis of a selected sample of the collected data, with particular emphasis on a search for electroweak bosons. The conjecture that such particles exist [4] has been the main incentive behind the construction of the SPS pp Collider and of its associated detectors. According to current expectations [5], and for an integrated luminosity of ^ 20 n b - 1 , the numbers of events in which an electroweak boson decays within the UA2 acceptance are respectively

^ 20 for (W*, Z°) hadrons ^ 4 for \T •+ e\ , p^ > 15 GeV/c

and <v# i¡ for Z° -»• e e .

2. DETECTOR AND DATA TAKING : GENERAL DESCRIPTION

2.1 - DETECTOR.

The UA2 detector [2,3,6] was designed mainly with the aims to observe electroweak boson decays and to study final states containing large transverse momentum hadron jets : such phenomena are expected to result from the collisions at very short distance accessible to the SPS pp Collider, the only existing facility providing a sufficient centre of mass energy, /s = 540 GeV. The expectation that the collision products relevant to the study of such processes populate mostly the central rapidity region led to restrict the detector coverage to ^ 3.5 rapidity units, within which, for example, z/3 of Z° decays are expected to occur. The cones corresponding to scattering angles 6 < 20°, 9 > 140° are not covered by UA2 but are left open to house the detectors of experiment UA4 [7] designed to measure the elastic and total pp cross sections.

Despite their small branching fractions the leptonic decay modes of the electroweak bosons

+ + W" l~v (BR = 8% per lepton type)

and Z • 1 1 (BR * 3% per lepton type) are supposed to be the least difficult to detect because of the very small expected background contamination. For this reason UA2 was designed to detect and identify electrons over its whole acceptance; electrons were preferred over muons because excellent energy resolutions can be achieved in compact calorimeters.

- 193 -

Hadron detection is also implemented over the whole UA2 acceptance but different approaches have been adopted in the central (40 < 8 < 140°) and forward (20 < 9 < 40°, 140 <8< 160°) regions. The central region is instrumented with a highly segmented hadron calorimeter having a cell configuration well suited to the observation of hadron jets independently of their mode of fragmentation. The forward regions, where important W -*• ev charge asymmetries are expected to occur, are equipped with two magnetic spectrometers, each consisting of a toroidal field magnet followed by nine drift chamber planes.

A set of cylindrical wire chambers densely packed around the beam in the collision region provide measurements of the position of the event vertex and of the directions of the charged particles produced in the collision. It is made of four proportional chambers with helicoidal cathode strips and of two drift chambers of 24 azimuthal cells each, with six drift wires per cell.

The measurement of a track pointing to an energy deposition localised in one of the electron calorimeter cells provides a powerful means of selecting electron candidates but it leaves a significant contamination of narrow T T°— charged hadron pairs (overlap background). This is strongly reduced by using preshower counters -in front of the electron calorimeters to provide improved space resolution. The central preshower counter is a cylindrical proportional chamber with helicoidal cathode strips and the forward preshower counters are proportional tube planes. Each is preceded by a ^ 1.5 radiation length thick converter.

In the central region a A <|> = 60° azimuthal wedge was left open to house a large angle magnetic spectrometer [3] instrumented over a A <j). A 8 = 30° x 70° solid angle with drift chambers, scintillator hodoscopes and a lead-glass array. It has provided detailed information on inclusive particle production around 90°. It is now in the process of being closed to lead to an azimuthally symmetric detector configuration better suited to the study of the topics of present interest (electroweak bosons and large transverse momentum jets).

The main detector parameters are listed in Table 1. Figures la and b show schematic views of the detector assembly.

2.2 - DATA TAKING The data discussed in this report were recorded using triggers sensitive to

events with large transverse energy in the central and forward calorimeters. They were of three types : - The £E,p trigger required a total transverse energy (EE^) measured in the central calorimeter (electron and hadron cells linearly added) in excess of ^ 35 GeV, - the W trigger required the presence of at least one quartet (2 x 2) of electron calorimeter cells (central or forward) in which the measured transverse energy exceeded ^ 8 GeV,

- 1 9 4 -

T A B L E 1

M A I N P A R A M E T E R S O F T H E U A 2 D E T E C T O R

I . S O L I D A N G L E C O V E R A G E

C e n t r a l r e g i o n . E l e c t r o n - h a d r o n c a l o r i m e t r y .

A y = 2 , A 0 » 1 0 0 ° , A<|> = 3 0 0 °

F o r w a r d - b a c k w a r d r e g i o n s . E l e c t r o n c a l o r i m e t r y a n d m a g n e t i c s p e c t r o s c o p y .

A y « 1 . 5 , A 8 - 3 5 ° , A<j> - 8 2 % o f 3 6 0 °

W e d g e r e g i o n . E l e c t r o n c a l o r i m e t r y a n d m a g n e t i c s p e c t r o s c o p y .

A y - 1 . 3 , A 0 = 6 8 ° , A * « 2 8 °

I I . C E N T R A L C A L O R I M E T E R

2 0 0 c e l l s , e a c h c o v e r i n g A 6 x A(|> = 1 0 ° x 1 5 ° .

L o n g i t u d i n a l s e g m e n t a t i o n

1 7 r . l . ( l e a d - s c i n t i l l a t o r ) + 2 x 2 a b s . 1 . ( i r o n - s c i n t i l l a t o r )

E l e c t r o n c a l o r i m e t r y 26 x 3 . 5 mm l e a d p l a t e s

2 7 x 4 mm N E 1 0 4 s c i n t i l l a t o r p l a t e s

H a d r o n c a l o r i m e t r y ( 1 8 + 2 2 ) x 1 5 mm i r o n p l a t e s

( 1 8 + 2 2 ) x 5 mm s c i n t i l l a t o r p l a t e s

( P M M A , 10% n a p h t a l e n e , 1% P B D , 0 . 0 1 % P O P U P )

L i g h t g u i d e s : 2 mm l u c i t e , 8 0 m g / 1 BBQ

P h o t o t u b e s : 7 p e r c e l l , X P 2 0 1 2 f o r e l e c t r o n c a l o r i m e t r y a n d X P 2 0 0 8 f o r

h a d r o n c a l o r i m e t r y

I I I . F O R W A R D D E T E C T O R S

2 4 i d e n t i c a l s e c t o r s e a c h c o v e r i n g A 6 x i f = 1 7 . 5 ° x 2 5 °

F i e l d i n t e g r a l 0 . 3 8 T m .

9 d r i f t c h a m b e r s p e r s e c t o r

- w i r e o r i e n t a t i o n w i t h r e s p e c t t o f i e l d : - 7 ° , 0 ° , + 7 ° .

- d r i f t c e l l w i d t h ± 5 c m

- f i e l d s h a p i n g w i r e s e v e r y 5 mm

- t o t a l n u m b e r o f s i g n a l w i r e s 2 3 0 4 .

p r e s h o w e r c o u n t e r

- p r e c o n v e r t e r 1 . 4 r . l . l e a d + i r o n

- 4 t u b e p l a n e s ( b r a s s ) 2 0 mm O . D . , 0 . 3 mm t h i c k .

- t u b e o r i e n t a t i o n w i t h r e s p e c t t o f i e l d : 0 ° , 0 ° , 7 7 ° , 7 7 ° .

- 1 9 5 -

- a n o d e 3 0 m i c r o n g o l d p l a t e d t u n g s t e n

f o r w a r d c a l o r i m e t e r s

- 1 0 c e l l s p e r s e c t o r , e a c h c o v e r i n g A 9 x A<() - 4 ° x 1 5 °

- c e l l t r a n s v e r s e s i z e s 2 7 x 3 3 t o 2 7 x 6 0 c m 2

- l o n g i t u d i n a l s e g m e n t a t i o n : 3 3 x ( 4 mm l e a d + 4 mm A l t u s t i p e 1 0 1 0 5 ) +

8 x ( 4 mm l e a d + 4 mm A l t u s t i p e 1 0 1 0 5 ) = 2 4 + 6 r . l .

- l i g h t g u i d e s a n d p h o t o t u b e s a s i n c e n t r a l c a l o r i m e t e r .

IV. VERTEX DETECTOR

- f i v e p r o p o r t i o n a l c h a m b e r s w i t h c a t h o d e s t r i p r e a d - o u t , o n e o f w h i c h

i s l o c a t e d b e h i n d a 1 . 5 r . l . t u n g s t e n c o n v e r t e r .

n u m b e r o f s t r i p s 4 8 0 , 4 8 0 , 5 2 8 , 6 7 2 a n d 4 8 0 .

n u m b e r o f w i r e s 2 8 8 , 3 8 4 , 5 7 6 , 8 6 4 a n d 5 7 6 .

c h a m b e r r a d i i 1 0 0 , 1 2 4 , 2 3 6 , 3 1 5 a n d 3 5 5 mm.

c h a m b e r l e n g t h s 1 0 4 , 1 1 0 , 1 5 0 , 1 7 8 a n d 8 0 c m .

w i r e p i t c h 2 . 2 , 2 . 0 , 2 . 6 , 2 . 3 a n d 3 . 9 mm.

s t r i p a n g l e t a n a - ± 0 . 9 , 1 . 3 , 1 . 0 , 1 . 0 , 1 . 0 .

h a l f g a p 4 mm

s t r i p p i t c h = 4 mm.

- t w o d r i f t c h a m b e r s o f 2 4 a z i m u t h a l c e l l s e a c h , 6 s e n s e w i r e s / c e l l

( c h a r g e d i v i s i o n , m u l t i h i t c a p a b i l i t y ) , s e n s e w i r e l e n g t h s 1 5 2 0 a n d

1 7 8 5 mm

- 2 4 s c i n t i l l a t o r p l a t e s .

- 1 9 6 -

b)

F i g u r e 1.

S c h e m a t i c d e t e c t o r a s s e m b l y :

a ) l o n g i t u d i n a l c u t a l o n g t h e b e a m ,

b ) t r a n s v e r s e c u t n o r m a l t o t h e b e a m .

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- the Z° trigger required the presence of two such quartets, each having a transverse energy in excess of ^ 3.5 GeV, and azimuthally separated by A (j) > 60°.

In addition the EE^ and W triggers (but not the Z° trigger) required a coincidence with two signals obtained from scintillator arrays covering an angular range 0.47 < 9 < 2.84° on both sides of the collision region. This additional condition is satisfied by nearly all non-diffractive collisions T7]. Early signals measured in these scintillator arrays were used to tag background events induced by beam halo particles interacting in the detector.

3. LARGE TRANSVERSE ENERGY HADRONS.

3.1 - THE CENTRAL CALORIMETER.

In the present Section we restrict the analysis to events which satisfy the ZE T trigger. The central calorimeter is the part of the UA2 detector which is most relevant to the present study. It is segmented into 200 cells, each covering 15° in <)) and 10° in 8, and built in a tower structure pointing towards the centre of the interaction region. The cells (Figure 2) are segmented longitudinally into a 17 radiation length thick electromagnetic compartment (lead-scintillator) followed by two hadronic compartments (iron-scintillator) of two absorption lengths each. The light from each compartment is collected by two BBQ-doped light guide plates on opposite sides of the cell.

All calorimeters, including the forward modules, have been calibrated in a 10 GeV/c beam from the CERN PS using incident electrons and muons. The calibration has since be tracked with a Xe light flasher system. In addition, the response of the electromagnetic compartments is checked regularly by accurately positioning a Co 6 0 source in front of each cell and measuring the direct current from each pho-tomultiplier. The systematic uncertainty in the energy calibration for the data discussed here is less than ±2% for the electromagnetic calorimeter and less than ±3% for the hadronic one.

The response of the calorimeter to electrons, single hadrons and multi-hadrons (produced in a target located in front of the calorimeter) has been measured at the CERN PS and SPS machines using beams from 1 to 70 GeV. In particular we have studied the longitudinal and transverse shower development and the effect of particles impinging near the cell boundaries.

The energy resolution for electrons is measured to be a_,/E « 0.14 / /E (E in GeV). In the case of hadrons, a„/E varies from 32% at 1 GeV to 11% at

- V 70 GeV, approximately like E - . The resolution for multi-hadron systems of more than 20 GeV is similar to that of single hadrons.

- 198 -

Figure 2. Exploded view of a central calorimeter cell.

1.0

0.S

EET (GeV)

o y/*—'—i—i—i—i—i—i—«—i—i i i . . . SO 100 150

EET (GtV)

Figure 3 .

Observed (uncorrected) EE^, distribution

in the central calorimeter. The line

is an exponential eye-fit to the data at

low E E m .

Figure A.

Two-jet dominance : the dependence

of hi and ti2 upon E E T (see text).

- 1 9 9 -

3.2 - DATA REDUCTION. The responses of the electromagnetic calorimeter to energies deposited by

photons and by hadrons differ by typically 20%. In the present very preliminary analysis we ignore this fact and simply measure the energy in a cell as the sum of the energies in the three compartments (at least one compartment must have 150 MeV, well above pedestal fluctuations). We also join adjacent cells, each containing at least 400 MeV, in clusters having an energy measured as the sum of the cell energies (we split clusters having a "valley" more than 5 GeV deep). The errors resulting from these simplifications and from the fact that the dependences of the calorimeter response upon impact and energy are not taken into account are of the order of ±10%. They can be reduced to a negligible level after proper correction but only uncorrected data are presented in this Section.

A small background contamination of beam halo particles interacting in the detector survives the time of flight selection in the small angle scintillator arrays. It is easily recognised from an abnormally large energy fraction measured in the hadronic compartments and is rejected from the event sample.

3.3 - TWO-JET DOMINANCE. Figure 3 shows the distribution of the observed events as a function of their

total transverse energy, EE^,, measured in the central calorimeter. Seventy events have EE T >100 GeV. The increased statistical accuracy is now sufficient to evidence a departure from exponential when EE^, exceeeds "V 60 GeV. Figure 4 illustrates clearly that this departure corresponds to the emergence of two-jet dominance at large values of EE T. It shows the dependence upon EE T of hi and ti2, the mean values of the fractions E^/EE^, and (E , + E,2,) /EE^,, where E , and E 2 are the largest and second largest transverse energies of the clusters in an event, respectively. An event containing only two jets of equal transverse energies would have hi =0.5 and h 2 = 1. Immediate evidence for two-jet dominance is also obtained from a simple inspection of the energy distribution in the 8-<() plane : examples are shown in Figures 5a to d.

The azimuthal separation between the two clusters having the largest transverse energies (E^ 2 > 15 GeV) in events having EE T > 80 GeV is observed to peak near 180° (Figure 6).

In the present data (Figure 7) 400 events (compared to 3 in the 1981 data) contain a large cluster (jet) having a transverse energy in excess of 40 GeV. The evaluation of the jet production cross-section from the observed distribution of jet transverse energies shown in Figure 7 implies corrections to the energy scale and evaluations of acceptance and detection efficiencies which are beyond the scope of this preliminary report.

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T R A N S V E R S E E N E R G Y D E P O S I T I O N ^

ENERGY SCALE 10 GEV [REDUCED)

LIST ü r l T O ^ w l l H ENERGY ABOVE 5.0 GEV

cooaos THETA/PM

UAQ.

TOTAL. CENTRAL TTHHS OCRCT 188.0 G£V IMXMUU COL TRAHSV EHERGV «5.9 CEV

LIIPSF* CLUSTERS WHH ENERGY ABOVE 5.0 GEV

COOROS HUH5V THCtyPM OCRCV

T R A N S V E R S E E N E R G Y D E P O S I T I O N CEWIML M P F/B

ENERGY SCALE 10 GEV (REDUCED)

U A 2

0 <0

a) b )

T R A N S V E R S E E N E R G Y D E P O S I T I O N

ENERGY SCALE 10 GEV

ENERGY ABOVE 5.0 GEV C0OR03 ncu/m 11] 13S 53.12» M 316 92.731

U A 2

360

0 tO lOW. CENTRAL TOM ENERGY "0.7 OV IWOWM CEU. TMN» ENERGY 2 U CLV

T R A N S V E R S E E N E R G Y D E P O S I T I O N

usT opflffifflTlum ENERGY SCALE 0 GEV

ENERGY ABOVE S.O GEV noter THCTA/Ptf

47 194 131 263 46.187 M 62 70.Í7»

UA-2

IDT FOR CVCNT RUN NO. 1611 •110

TOW. CENTRAL TRANS D«« 126-0 CCV MNUMUM CELL TRMSV CNiftCY 23J CE»

c ) d )

F i g u r e 5 a t o d .

T y p i c a l 8-tj) d i s t r i b u t i o n s o f t h e

t r a n s v e r s e e n e r g y i n l a r g e ZE T e v e n t s ,

- 201 -

Figure 6. Azimuthal separation A<J>

between two jets, each having E , > 15 GeV, in events with E E T > 30 GeV.

10«

Figure 7. Observed (uncorrected) transverse energy distribution of jets having E , 40 GeV.

20

Mj-j » 80 GtV/c2

,„,1 ... 0 10 20 30 40

PT (J-JI IGtV/c)

SO 100 150 M w (GtV/c2)

Figure 8. Two-jet invariant mass (M._j) distribution (uncorrected). The observed (uncorrected) transverse momentum distribution of two-jet systems having Mj_j > 80 GeV/c2 is shown in the insert.

- 2 0 2 -

Finally we show in figure 8 the uncorrected invariant mass (Mj_j) distribution of the two-jet systems and their transverse momentum distribution for M. . > 80 GeV/c 2. While the invariant mass distribution shows no significant

3-1

structure, it is not inconsistent with the presence of "v. 20 events in the 80 ± 10 GeV/c2 region from hadronic decays of the electroweak bosons. Such decays are expected to proceed mainly via qq pairs.

4. SEARCH FOR W -»• ev DECAYS.

± + . - . . The decay into e v of a W~ produced at rest in a pp collision would generate el

a monochromatic electron with energy E = $ M , M w being the rest mass of the W boson. In practice W's are expected to be produced with important longitudinal momenta. This does not affect the transverse momentum distribution of the decay el electron which peaks near its end point at E T = ¡¡ M (Jacobian peak). An interes-T ± w ting feature of the leptonic decay mode of the W is the presence of parity vio-

+ latmg terms in the angular distribution of the leptons. If the W~ is produced with helicity e « ±1, the angular distribution of the lepton (e for W , V for W +)

* 2 * is of the form (1 - e cos6 ) , where 9 is the lepton angle in the W centre of mass with respect to the W momentum.

W's are also expected to be produced with important transverse momenta [8], similar to that of a two-jet system of a same mass (see Figure 8, where however part of the measured transverse momentum is of instrumental origin). This results mainly in a smearing of the Jacobian peak but does not induce significant correlations between the transverse momentum of the decay electron and that of the W (or of its associated recoil particles). We shall therefore search for large transverse momentum electrons which are not accompanied by other particles at small angle to the electron momentum. This simplified approach will strongly reduce a possible two-jet background and should not affect seriously the W •*• ev signal. However it precludes any search for large transverse momentum electrons among jet fragments.

We shall deal separately with the central and forward regions in which different experimental methods are used. In both cases the initial event sample is that of W-triggers. 4.1 - SEARCH FOR W -»• ev IN THE CENTRAL REGION.

We first search for energy clusters in the central calorimeter which have a configuration consistent with that expected from an isolated electron : the cluster must be contained in a 2 x 2 cell quartet of the electromagnetic calorimeter, the leakages in the associated hadronic cells and in the adjacent electromagnetic cells must not exceed 10% each. In addition we exclude clusters having

- 2 0 3 -

F i g u r e 9 .

T r a n s v e r s e e n e r g y d i s t r i b u t i o n o f a n i n i t i a l s a m p l e o f

365 e v e n t s f r o m w h i c h e l e c t r o n c a n d i d a t e s i n t h e c e n t r a l

c a l o r i m e t e r a r e s e l e c t e d . T h e c r o s s - h a t c h e d d i s t r i b u t i o n

(133 e v e n t s ) i s f o r e v e n t s h a v i n g a t r a c k p o i n t i n g t o

t h e c a l o r i m e t e r c l u s t e r .

- 204 -

their centroid in a cell located at a boundary of the calorimeter acceptance. These straightforward requirements leave only 365 events in which such a cluster has a transverse energy in excess of 15 GeV (including transverse and longitudinal leakages), with only seven events above E^ = 30 GeV. The E^ distribution is shown in Figure 9.

This sample is further reduced by simply requiring that at least one track measured in the vertex detector points to the energy cluster. If 6 0 and 6<j> are the angles between the track and the line joining the event vertex to the cluster centroid we require that ô = | (66 / 1 0 0 ) 2 + C<Sd>/15°)2 j < 1, a condition always satisfied by single electrons. Figure 9 shows the E^ distribution in the remaining event sample. We note that much of the reduction from 365 to 133 events occurs at low E T values.

At this stage of the analysis, hadron jets having unusual fragmentation modes are expected to be the main background contamination. In particular narrow pairs consisting of a I T 0 and a charged hadron are still to be rejected. To further enrich the sample of electron candidates we apply the following additional selection criteria : - no other track should point to a charge cluster measured in the preshower

counter. The quality of the match with the cluster measured on the proportional wires should be < ±1 cm, and with the cluster measured on the cathode strips < ±2 cm. These values are obtained from "normal events" collected with a trigger requiring a simple coincidence between the small angle scintillator arrays (Figure 10a). In the event sample presently under study the track-cluster correlation is obscured by the presence of TT° conversions (Figure 10b).

- the charge of the preshower cluster should be at least four times larger than the most probable charge deposited by a minimum ionizing particle (Figure 11). This condition ras measured (using 28 and 50 GeV electron beams) to be satisfied by electrons with a probability of ^ 90%. Together with the requirement of no hadron calorimeter leakage, it rejects single charged hadrons at a level of ^ 10 3 (Figure 12).

- if other preshower clusters are measured within 10° of the selected track, their total charge should not exceed 25% of the charge of the cluster to which the selected track is observed to point.

Figures 13a to c illustrate the efficiency of the preshower counter at rejecting overlap background. Note that radiative corrections to W + ev decays should result in *\» 5% of the decay electrons being accompanied by a photon of 10 MeV or more within 10°.

The application of the above selection criteria leaves only 9 events containing an electron candidate having E in excess of 15 GeV. The E distribution is

- 205 -

2000

1000

1S00

soo

n Livigifudinal

-10

Transvtr»

il RJ Lr P U ruv u

Lotgirudinil

- J I I I I I I I l _

liMlliatrm) -30 -20 -10 o 10

flüUmttrtsl

Figure 10. a) b)

Track-cluster distance in the central preshower counter in the transverse (wires) and longitudinal (strips) views a) for minimum bias events b) for the sample of electron candidates.

f 10 -

100

50

100

50

e" 50 GeV 2 rt

u

• S , 1

30 10 VSS cluitir chargi

Figure 11. Charge distribution of the preshower counter (wires) for the sample of electron candidates. Charges are measured in minimum ionising particle equivalents.

Ln n- 55 GeV 2 rl

"Ln

r 55 GeV no lead

»0 60 0 2 ( 6 Pulse height in MWPC

Figure 12. Pulse height distributions measured in the preshower counter using electrons and pions from a test beam. Units are minimum ionising particle equivalents.

- 206 -

,Hadronic leakage

,Energy mesured in Electron calorimeter

©

Pulse heiqhts mesured on preshower wires

Preconverter (t tungsten) F i g u r e 1 3 .

A t y p i c a l e x a m p l e

o f " o v e r l a p " b a c k g r o u n d .

a) t r a n s v e r s e v i e w : t h e c h a r g e d t r a c k m e a s u r e d i n t h e v e r t e x d e t e c t o r p o i n t s

to the smaller preshower c l u s t e r .

b ) l o n g i t u d i n a l v i e w i n t h e a z i m u t h a l p l a n e o f t h e t r a c k . F a c i n g s t r i p c l u s t e r s

i n t h e p r e s h o w e r c o u n t e r h a v e s m a l l p u l s e h e i g h t s .

c ) l o n g i t u d i n a l v i e w i n t h e a z i m u t h a l p l a n e o f t h e l a r g e r w i r e c l u s t e r . F a c i n g

s t r i p c l u s t e r s i n t h e p r e s h o w e r c o u n t e r h a v e l a r g e p u l s e h e i g h t s . T h e y a r e

a t t r i b u t e d t o a TT° ( d o t t e d l i n e ) h a v i n g c o n v e r t e d i n t h e t u n g s t e n p r e c o n v e r t e r .

- 207 -

shown in Figure 14. It is remarkable that most of the reduction has taken place at low E T values.

Background from standard sources are expected to contribute a negligible contamination to the remaining event sample. In particular we have observed ^ 10 3

jets in a 10 GeV wide band around = 30 GeV (Figure 7). At a same value of E , we expect to have o> 10 single hadrons since the ratio between jet and hadron inclusive production cross sections is ^ 10 2 [2]. The rejection against charged hadrons provided by the detector is ^ 10 3 corresponding to a background contamination of only "V 10~ 2 event. Similarly the contribution of photon conversions in the vacuum pipe or of internal Dalitz conversions can only amount to "\# 3% per photon. If they were dominant in the final sample many more unconverted photons should have been found (as long as they do not belong to very high multiplicity photon clusters). This is contrary to the observation that of 7 clusters with

> 30 GeV only 2 were not associated with a track. More work is however needed to ensure that we did not overlook other possible background sources and to further ascertain electron identification.

For W •*• ev decays, the non observation of the decay neutrino should result in an apparent transverse momentum imbalance. To study this effect we evaluate the total transverse momentum carried by particles detected within the whole UA2 acceptance, P j 0 t . This evaluation accounts for particles detected in the wedge and forward spectrometers. The fraction

f = |P Tt 0 t| /

should near 1 for actual W decays and take smaller values in events without balancing neutrino - to the extent that the detector coverage is sufficient to catch most of the transverse energy produced in the collision.

The distribution of f in the sample of the nine retained events is shown in Figure 15. The events with the larger f values (f > 0.6) are indicated on

el Figure 14. It is remarkable that they are also the events having the larger E^ values. Figure 16 illustrates the ability of the UA2 detector to measure the transverse momentum imbalance on hadron jets selected from the W trigger sample by requiring a hadronic leakage exceeding 25%. The nine events of the final sample are shown on the same plot.

The energy distribution in the 9-<j> plane of one of the three imbalanced events is shown in Figure 17 and the corresponding electron track in Figure 18. In all three events there is very little transverse energy observed beside that of the large transverse momentum electron candidate.

- 208 -

> 2

20 30 40 ET (GeV)

Figure 14. Transverse energy distribution of the 9 electron candidates having E T > 15 GeV. The three cross-hatched events satisfy the cut f > 0.6 (see Figure 15),

| 2 h

0.5 f

1.0

Figure 15. Transverse energy imbalance for the central calorimeter electron candidates (see text).

0 10 20 30 40 50 60 70 80 Et (GeV)

Figure 16. The nine electron candidates (black circles) are compared with two-jet events (dots) in the "transverse energy" versus "imbalance" plane (see text).

- 209 -

T R A N S V E R S E E N E R G Y DEPOSITION U!?Tur'cLUi>ILttt> WIIH ENERGY ABOVE 5.0 GEV

i e V M m e r as «

360

ENERGY SCALE

1 0 GEV (REDUCED)

I M P I C * EVEHT R U N M X 1 1 2 1 L 4 1 7 2 7 ww. connu, H U M S ENERGY «14 an

H U M U M C O L nUNSV ENERGY 41.0 « V

Figure 17. Transverse energy distribution of one of the

imbalanced electron candidates in the 6-(j) plane.

Figure 18. Longitudinal view of the electron track for

one of the imbalanced candidates.

- 210 -

4.2- SEARCH FOR W ev IN THE FORWARD REGIONS. The search for W -*• ev decays in the forward regions follows the same general

guidelines as in the central region. Each of the two forward detectors covers a range of scattering angles

20° < 9 < 37.5° and is instrumented in 12 azimuthal sectors (A $ ^ 30°) with magnetic spectometers (Figure 19). The magnetic fields are generated from two "lamp-shade" magnets of 12 coils each. The field integral is 0.38 Tm on the average and the loss of azimuthal coverage caused by the magnet coils is ^ 18%.

Depending on the sign of their charge, particles are bent towards or away from the beam line and their deflected tracks are measured in three triplets of drift chambers. Each triplet is made of chambers having sense wires at -7°, 0° and +7° to the magnetic field direction. In the present preliminary analysis the resolution achieved in momentum measurement is A( - ) = 2% GeV - 1. This value will

P

be substantially improved in the future. Each magnetic spectrometer sector is followed by a preshower counter and an electromagnetic calorimeter. The preshower counter consists of a 1.4 radiation length thick lead converter preceding two proportional tube chambers. Each electromagnetic calorimeter sector is subdivided in 10 cells, each covering a rapidity x azimuth domain Ay x A(j> = 0.17 x 15° similar to that covered by the central calorimeter cells. Each cell is segmented in two compartments, one 24 radiation length thick in which most of electromagnetic showers are contained, the other 6 radiation length thick serving as a veto against hadronic showers. The response and performance of the preshower counters and calorimeters have been extensively studied in a 10 GeV electron beam. In particular the dependence of the calorimeter response upon impact point in each cell has been accurately measured. A comparison of the two phototube signals receiving light from the wave-shifting light guides on each side of a cell allows to localise the impact point to within ±2 cm.

The following selection criteria are applied to the sample of W triggers to select possible electron candidates : - a transverse energy deposition exceeding 10 GeV must be measured in one of the

forward sectors. It must be associated with a track measured in the corresponding spectrometer and, depending upon the position of the track impact, it must be contained in one or at most two cells.

- leakage in the veto compartment must not exceed 2%, a condition satisfied by "V« 98% of 40 GeV electrons (Figure 20).

- the proportional tubes associated with the selected track must give signals. The quality of the matching between the track, the preshower counter cluster and the energy deposition in the calorimeter must fulfill selection criteria illustrated in Figures 21a to c.

- 2 1 2 -

Figure 20. Leakage into the hadron veto compartment of the forward calorimeters

a) for events associated with a signal in the preshower counter, b) for events not associated with a signal in the preshower counter.

The cut used in the analysis rejects events in the cross-hatched region.

(1/p-1/E)/4(1/p-1/E)

Figure 21. Matching quality criteria. a) between the position in the calorimeter (measured from phototube ratio) and

the preshower cluster (measured along the magnetic field), b,c) between the track measured in the drift chambers and the preshower cluster

(measured along the magnetic field and normal to it respectively) d) between the momentum measurement in the drift chambers and the energy measured

in the calorimeter for events having E > 10 GeV.

- 213 -

- the momentum p measured in the magnetic spectometer must be consistent with the energy E measured in the calorimeter. Specifically we require - and - to be equal within three standard deviations (Figure 21d).

- in addition to the above selection criteria we require that the electron candidate is isolated : the energy measured in adjacent calorimeter cells (including the contribution of track momenta) must not exceed 3 GeV, no other track must point to the same cell as the electron candidate and no other signal facing this cell must be measured in the preshower counter.

Ten events are found to survive these straightforward selection criteria for an integrated luminosity of ^ 16 n b - 1 (the magnets were turned off during part of the running period). The corresponding distribution is shown in Figure 22.

In order to detect a possible transverse momentum imbalance we evaluate the quantity £ l = -tot > ^ ; ßel ^

where ê is the unit vector directed along the transverse momentum of the electron candidate. The f distribution in the remaining sample of 10 events is shown in Figure 23 and the four events having f > 0.6 are indicated in Figure 22. It is

el remarkable that the event with the largest E , value survives this cut. Some features of this event are illustrated in Figures 24 and 25.

4.3 - CONCLUSION.

The application of rather straightforward selection criteria has reduced the original sample of W-trigger events to a level of only 9 events in the central region and 4 events in the forward regions containing an electron candidate having E T > 15 GeV.

We have scanned visually a large number of events containing an electron candidate, in particular the 365 events of the originally selected sample in the central region. The scan has confirmed the results of the analyses presented in the preceding sections.

It is remarkable that the four events containing an electron candidate having > 15 GeV and a strong transverse momentum imbalance have an E T distribution

which is consistent with that expected for W ev decays. More over their rate of occurence is also in excellent agreement with current expectations.

The nine events in which the transverse momentum of the candidate electron is partly balanced by other hadrons detected in the UA2 apparatus often contain a clear jet at opposite azimuth to the electron candidate. While background from obvious sources (conversions, misidentified single hadrons) are expected to be small more work is needed to ensure that possible unexpected backgrounds have not been overlooked and to further ascertain electron identification.

- 214 -

u -

ET (G*V)

Figure 22. Transverse energy distribution for the ten electron candidates in the forward detectors. The four cross-hatched events are imbalanced (f >0.6)

2 UFL

Figure 23. Transverse energy imbalance for the forward detector electron candidates (see text).

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mr N» NON MM NO. ITAS H O L COMA, T U « H O S T IM CU moca HO. U N UUOMM au. n u N s r OOCR AA.I CCV

Figure 24. Transverse energy distribution of the imbalanced electron candidate having E T = 3 GeV in the 9-<|> plane.

- 2 1 5 -

5. SEARCH FOR Z° e +e~ decays.

A search for electron pairs having an invariant mass in excess of 40 GeV/c2

has been conducted by selecting events of the Z-trigger sample in which two quartets of electromagnetic cells (central and forward regions were considered together) were found to have transverse energies E^ and E 2 such that E^ + E 2 > 30 GeV.

Although the Z-trigger did not require a coincidence with the small angle scintillator arrays, all events of the selected sample in which this coincidence was not satisfied have been observed to result from sources other than p-p collisions (cosmic rays, beam halo, etc...).

Of the 257 events selected, none survived very simple selection criteria. All were scanned visually and most of them show typical two-jet configurations.

ACKNOWLEDGEMENTS

We gratefully acknowledge the remarkable performance of the Staff of the pp project and of the operation crews of the relevant CERN accelerators. We thank the UA4 Collaboration who let us use their small angle scintillator hodoscopes.

We are deeply indebted to the technical staffs of the Institutes Collaborating in UA2. Financial support from the Danish Natural Science Research Council to the Niels Bohr Institute group and from the Schweizerischer National fonds zur Förderung der wissenschaftlichen Forschung to the Bern group are acknowledged.

- 2 1 6 -

REFERENCES

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e l a s t i c s c a t t e r i n g a n d o f t h e t o t a l c r o s s - s e c t i o n .

E l a s t i c s c a t t e r i n g e v e n t s a r e o b s e r v e d b y m e a n s o f d e t e c t o r s p l a c e d

i n s i d e m o v a b l e s e c t i o n s o f t h e S P S v a c u u m c h a m b e r ( " R o m a n p o t s " ) . E a c h

d e t e c t o r c o n s i s t s o f a c o u n t e r h o d o s c o p e a n d a w i r e c h a m b e r h a v i n g r e s o

l u t i o n o f 0 . 1 3 mm i n t h e v e r t i c a l a n d 0 . 4 mm i n t h e h o r i z o n t a l c o o r d i

n a t e ^ . T h e " R o m a n p o t s " a r e a r r a n g e d i n t e l e s c o p e s p l a c e d s y m m e t r i c a l l y

w i t h r e s p e c t t o t h e c r o s s i n g p o i n t a b o v e a n d b e l o w t h e m a c h i n e p l a n e .

P a r t i c l e s l e a v i n g t h e i n t e r a c t i o n r e g i o n t r a v e r s e t h e q u a d r u p o l e o f t h e

m a c h i n e a n d t h e n r e a c h t h e s e t e l e s c o p e s . I d e n t i f i c a t i o n o f e l a s t i c e v e n t s

i s b a s e d o n t h e r e q u i r e m e n t o f c o l l i n e a r i t y .

T h e t o t a l c r o s s - s e c t i o n i s o b t a i n e d b y m e a n s o f a m e t h o d f i r s t u s e d 2 )

a t t h e I S R . I t i s b a s e d o n t h e s i m u l t a n e o u s m e a s u r e m e n t o f l o w - t

e l a s t i c s c a t t e r i n g a n d o f t h e t o t a l i n e l a s t i c r a t e . B y u s i n g t h e o p t i c a l

t h e o r e m t h e t o t a l c r o s s - s e c t i o n i s o b t a i n e d f r o m t h e f o l l o w i n g e x p r e s s i o n

0 . 1 6 » » c ) » K / d t ] t - o ( 1 )

fc 1 + p 2 N , + N . e l i n

w h e r e p i s t h e r a t i o o f t h e r e a l t o t h e i m a g i n a r y p a r t o f t h e f o r w a r d

e l a s t i c a m p l i t u d e , w h i l e N , a n d N . a r e t h e o b s e r v e d r a t e s o f t h e e l a s t i c e l m

a n d i n e l a s t i c i n t e r a c t i o n s , r e s p e c t i v e l y . T h e e l a s t i c d i f f e r e n t i a l r a t e

a t t = 0 , ( d N / d t ) t _ Q » i s o b t a i n e d b y e x t r a p o l a t i o n . T h i s m e t h o d

d o e s n o t r e q u i r e a n i n d e p e n d e n t d e t e r m i n a t i o n o f t h e m a c h i n e l u m i n o s i t y .

I n o u r e x p e r i m e n t i n e l a s t i c i n t e r a c t i o n s a r e d e t e c t e d b y t e l e s c o p e s o f

w i r e c h a m b e r s a n d c o u n t e r h o d o s c o p e s p l a c e d s y m m e t r i c a l l y o n t h e l e f t a n d

r i g h t s i d e o f t h e c r o s s i n g r e g i o n , a n d c o v e r i n g t h e p s e u d o r a p i d i t y r a n g e

f r o m 2 . 5 t o 5 . 6 .

I n e l a s t i c i n t e r a c t i o n s o f d i f f r a c t i v e k i n d c o r r e s p o n d i n g t o t h e

p r o c e s s p p -> p X w h e r e t h e a n t i p r o t o n l o s e s a v e r y s m a l l f r a c t i o n o f i t s

- 239 -

initial momentum, are also observed in our system. Taking advantage of

the deflection in the magnetic field of the machine quadrupoles, the

momentum spectrum of the antiproton is measured.

RESULTS FROM THE FIRST COLLIDER RUN IN 1981

During the first physics run of the Collider elastic scattering at

low-t and the total cross-section were measured at a centre-of-mass

energy /^s = 540 GeV . Data were taken in a short run ('v- 15 hours) with

luminosity of about 1 0 2 6 c m - 2 s - 1 when the machine optics in the inter

section region was the same as for normal SPS operation (normal-ß optics). 3) .

Elastic scattering was measured in the four-momentum transfer range

0.05 <-t <0.19 GeV 2 . The collinearity plot in the vertical plane shows

a peak with standard deviation 5 8 - 0.05 mrad corresponding to a trans

verse momentum unbalance less than 15 MeV/c. Background of inelastic

events was negligible. The observed t-distribution of about 1500 elastic

events could be fitted by the exponential shape exp (bt) with slope

parameter b = 17.2 ± 1.0 G e V - 2 .

Inelastic interactions were measured in the same run. It was ensured

that the elastic and inelastic rates were obtained at the same luminosity

by alternatively enabling the two triggers. The number of bunch crossing

between the enabling and the occurrence of a trigger was recorded. The

average rates of elastic and inelastic events were obtained from the total

live times of the elastic and inelastic triggers respectively. The in

elastic trigger was made as inclusive as possible by using a single-arm

trigger in the pseudorapidity range 3.0 < n< 5.6 in addition to a left-

right trigger covering the same n-range in both hemispheres. The single-

arm trigger allows detection of events that escape the left-right trigger,

in particular single diftractive interactions. Beam-beam events are

recognized by reconstructing a vertex from the observed tracks. The

fraction of events escaping detection due to the limited coverage in

polar angle of the detectors was estimated by extrapolation to be less

than 2%.

- 2 4 0 -

T h e t o t a l n u m b e r o f e l a s t i c e v e n t s w a s c a l c u l a t e d f r o m t h e o b s e r v e d

n u m b e r o f e v e n t s u n d e r t h e a s s u m p t i o n o f a n e x p o n e n t i a l t - d i s t r i b u t i o n

w i t h c o n s t a n t s l o p e p a r a m e t e r b = 1 7 . 2 G e V 2 e q u a l t o t h e v a l u e m e a s u r e d

i n t h e a c c e s s e d t - r a n g e . I n t h a t c a s e , a s s u m i n g p = 0 , e q . ( 1 ) c a n b e

r e w r i t t e n a s

a = 16 TT ( l i e ) 2 ~ — ( 2 ) t , . N i n 1 +

e l

T h e r a t i o N . / N , w a s f o u n d t o b e 4 . 0 7 ± 0 . 2 2 . T h e m e a s u r e d v a l u e o f i n 6 1 . 4 )

t h e t o t a l c r o s s s e c t i o n i s = 66 ± 7 m b . T h e q u o t e d e r r o r i s p u r e l y

s t a t i s t i c a l a n d i s m a i n l y d u e t o t h e u n c e r t a i n t y o n t h e s l o p e p a r a m e t e r .

A g r a p h i c a l r e p r e s e n t a t i o n o f t h i s r e s u l t , f o l l o w i n g f r o m e q . ( 2 ) i s

s h o w n i n F i g . 1 w h e r e t h e d a t a p o i n t c o r r e s p o n d i n g t o t h e m a x i m u m I S R

e n e r g y i s a l s o s h o w n f o r c o m p a r i s o n . O u r r e s u l t o n a i s p l o t t e d i n

F i g . 2 t o g e t h e r w i t h p p a n d p p d a t a a t l o w e r e n e r g i e s . T h e f u l l l i n e i n

F i g . 2 i s t h e r e s u l t o f t h e d i s p e r s i o n r e l a t i o n f i t o f r e f . 5 ) w h i c h

f o l l o w s a ( l o g s ) 2 d e p e n d e n c e .

We a l s o f i n d a ,/a = 0 . 2 0 ± 0 . 0 2 a n d o,,,. rjr„/o = 0 . 1 7 ± 0 . 0 3 , w h e r e e l t d i f f t

a i i j - ü : i i r e f e r s t o t h e e v e n t s h a v i n g t r a c k s i n o n e h e m s ( ï . p h e r e o n l y . T h e s e d i r t

v a l u e s , w i t h i n e r r o r s , a r e c o n s i s t e n t w i t h t h o s e o b s e r v e d i n t h e I S R

e n e r g y r a n g e .

T h e r e l e v a n c e o f t h e C o l l i d e r d a t a f o r t h e u n d e r s t a n d i n g o f t h e v e r y

h i g h - e n e r g y b e h a v i o u r o f t h e e l a s t i c a m p l i t u d e h a s b e e n d i s c u s s e d b y

A . M a r t i n ^ . O u r r e s u l t o n t h e s l o p e p a r a m e t e r a t l o w - t i s c o m p a t i b l e

w i t h t h e p r e d i c t i o n o f t h e R e g g e o n F i e l d T h e o r y ^ . A c c o r d i n g t o t h i s

t h e o r y , h o w e v e r , t h e r a i s e o f t h e t o t a l c r o s s - s e c t i o n w i t h e n e r g y i s n o t

a s f a s t a s s u g g e s t e d b y o u r m e a s u r e m e n t . T h e p r e d i c t i o n a t t h e C o l l i d e r

i s o f a b o u t 5 5 m b .

8 )

T h e g e o m e t r i c a l p i c t u r e o f h i g h - e n e r g y s c a t t e r i n g w h i c h u s e s f o r

t h e p r o t o n o p a q u e n e s s a s h a p e d e r i v e d f r o m t h e e l e c t r o - m a g n e t i c f o r m

f a c t o r , p r e d i c t s a t o o l o w v a l u e f o r t h e f o r w a r d s l o p e .

- 2 4 1 -

F o r a t o t a l c r o s s - s e c t i o n o f 66 m b , t h e p r e d i c t i o n i s b = 14 G e V ,

w h i c h d o e s n o t s e e m t o b e c o n s i s t e n t w i t h o u r e x p e r i m e n t a l r e s u l t .

R e c e n t l y , f i t s o f t h e a v a i l a b l e d a t a o n t h e s l o p e p a r a m e t e r b o v e r 9 )

t h e F N A L a n d I S R e n e r g y r a n g e h a v e b e e n p r e s e n t e d . E x t r a p o l a t i o n o f

t h e s e f i t s t o t h e C o l l i d e r e n e r g y d o e s n o t l e a d , h o w e v e r , t o u n a m b i g u o u s

c o n c l u s i o n s .

P R E L I M I N A R Y R E S U L T S F R O M T H E 1 9 8 2 R U N

B e f o r e t h e 1 9 8 2 r u n o u r e l a s t i c s c a t t e r i n g a p p a r a t u s w a s i m p l e m e n t e d

a s s h o w n i n F i g . 3 . T h e s y s t e m , s y m m e t r i c w i t h r e s p e c t t o t h e c r o s s i n g

p o i n t , c o n s i s t s o f s i x t e e n d e t e c t o r s , e a c h o n e p l a c e d i n a " R o m a n p o t " ,

w h i c h a r e a r r a n g e d i n e i g h t t e l e s c o p e s . T h e " i n n e r " t e l e s c o p e s a r e a t

a d i s t a n c e o f a b o u t 2 3 m f r o m t h e c r o s s i n g p o i n t , w h i l e t h e " o u t e r "

t e l e s c o p e s a r e a t a b o u t 4 0 m . T h e m i n i m u m d i s t a n c e o f t h e p o t s f r o m

t h e b e a m a t w h i c h t h e d e t e c t o r s c o u l d s t i l l o p e r a t e s a f e l y w a s f o u n d t o

b e r o u g h l y e q u a l t o t w e n t y t i m e s t h e r . m . s . v a l u e o f t h e b e a m s i z e ,

a l m o s t i n d e p e n d e n t l y o f t h e m a c h i n e o p t i c s . T h i s d i s t a n c e d e t e r m i n e s t h e

m i n i m u m v a l u e o f t h e s c a t t e r i n g a n g l e w h i c h d e p e n d s o n t h e o p t i c s i n t h e

i n t e r s e c t i o n r e g i o n . T h e r a n g e o f t w h i c h i s a c c e s s i b l e f o r e a c h o p t i c s

a n d t h e R o m a n p o t t e l e s c o p e s u s e d i n t h e m e a s u r e m e n t a r e l i s t e d i n

T a b l e 1.

T a b l e 1

M a c h i n e o p t i c s ß H X i 3 V (m)

R o m a n p o t t e l e s c o p e s a c c e s s i b l e t - r a n g e

( G e V 2 )

N o r m a l - ß

H i g h - ß

M e d i u m - ß

L o w - ß

5 0 x 5 0

1 0 0 x l O O

7 x 3 . 5

2 x 1

o u t e r

o u t e r

i n n e r j p : i n n e r a n d o u t e r |p : i n n e r

0 . 0 5 - 0 . 1 9

0 . 0 2 - 0 . 3 5

0 . 2 - 0 . 5

0 . 4 - 1 . 5

- 2 4 2 -

A s s e e n f r o m T a b l e 1 , o u r e l a s t i c s c a t t e r i n g a p p a r a t u s i s q u i t e f l e x i b l e

a n d a l l o w s t o c o v e r a r a t h e r w i d e r a n g e o f t w i t h s o m e o v e r l a p b e t w e e n

m e a s u r e m e n t s d o n e w i t h d i f f e r e n t o p t i c s .

T h e a n g u l a r r e s o l u t i o n i s d e t e r m i n e d b y b o t h t h e s p a t i a l a c c u r a c y

o f t h e d e t e c t o r s a n d t h e i n t r i n s i c a n g u l a r s p r e a d o f t h e b e a m s w h i c h v a r i e s

a s l / / ß . F o r t h e h i g h - ß o p t i c s t h e t w o e f f e c t s a r e c o m p a r a b l e i n s i z e

g i v i n g r i s e t o a c o l l i n e a r i t y d i s t r i b u t i o n w i t h r . m . s . v a l u e 6 8 - 0 . 0 4 m r a d ,

w h i l e f o r t h e l o w - ß o p t i c s t h e b e a m d i v e r g e n c e d o m i n a t e s c o m p l e t e l y a n d

t h e c o l l i n e a r i t y p e a k i s m u c h w i d e r (6 8 - 0 . 2 m r a d ) .

T h e e l a s t i c t r i g g e r w a s p r o v i d e d b y t h e c o i n c i d e n c e o f t h e t r i g g e r

c o u n t e r s o f t h e l e f t a n d r i g h t a r m . U s u a l l y , w i t h s t a b l e b e a m c o n d i t i o n s

t h e f r a c t i o n o f g o o d e l a s t i c e v e n t s i n t h e t r i g g e r w a s o f 30 - 5 0 % .

I n t h e f i r s t f e w d a y s o f t h e 1 9 8 2 r u n t h e C o l l i d e r w a s o p e r a t e d w i t h

m e d i u m - ß o p t i c s . E l a s t i c s c a t t e r i n g w a s m e a s u r e d u s i n g t h e " i n n e r "

t e l e s c o p e s i n t h e r a n g e 0 . 2 1 < - t < 0 . 5 G e V 2 . T h e t - d i s t r i b u t i o n o f a b o u t

7 . 0 0 0 e v e n t s i s s h o w n i n F i g . 4 . T h e s e d a t a c a n b e w e l l f i t t e d b y a n

e x p o n e n t i a l s h a p e . A s a p r e l i m i n a r y v a l u e o f t h e s l o p e w e q u o t e

b = 1 3 . 6 ± 0 . 5 G e V " 2 .

I n a s h o r t t e s t r u n w i t h h i g h - ß o p t i c s a t l o w l u m i n o s i t y

( ^ 2 - 1 0 2 5 c m ~ 2 s - 1 ) , a b o u t 7 0 0 e l a s t i c e v e n t s w e r e c o l l e c t e d i n t h e r a n g e

0 . 0 2 5 < - t < 0 . 1 9 G e V 2 . T h e o b s e r v e d t - d i s t r i b u t i o n a g r e e s w i t h t h a t 3)

m e a s u r e d i n t h e 1 9 8 1 r u n

I n F i g . 5 t h e d a t a a l r e a d y p u b l i s h e d b y U A l ^ ^ a n d U A 4 " ^ o n t h e s l o p e

p a r a m e t e r b a s a f u n c t i o n o f t a r e p l o t t e d t o g e t h e r w i t h o u r n e w p r e l i m i n a r y

r e s u l t . A d d i t i o n a l d a t a f r o m t h e U A 1 C o l l a b o r a t i o n ' ^ r e p o r t e d a t t h i s

C o n f e r e n c e a r e c o n s i s t e n t w i t h t h o s e s h o w n i n F i g . 5 . I t i s c l e a r t h a t

a f a s t v a r i a t i o n o f t h e s l o p e i s t a k i n g p l a c e a t - t ^ 0 . 1 5 G e V 2 , a n 1 2 )

e f f e c t w h i c h w a s f i r s t o b s e r v e d a t t h e I S R . I n F i g . 6 a c o m p i l a t i o n

o f t h e p r o t o n - p r o t o n r e s u l t s o n t h e s l o p e b a s a f u n c t i o n o f t a t / s = 5 3 G e V

i s p r e s e n t e d . F o r e a c h d a t a p o i n t i n F i g . 5 a n d 6 t h e h o r i z o n t a l b a r

i n d i c a t e s t h e r a n g e i n t w h e r e t h e e x p o n e n t i a l f i t w a s p e r f o r m e d .

- 243 -

A t / T = 5 3 GeV, when moving from -t = 0.4 GeV 2 down to -t < 0 . 1 GeV 2,

the slope increases by A b - 2.5 G e V - 2 . While the shrinkage of the

elastic peak from the ISR to Collider energy is well demonstrated by

present data, it is not clear, however, whether the increase of the slope

with energy is larger at very low values of t.

General arguments^ indicate that if a ^ (log s ) 2 and a Ja -*• t el t

constant £ 0, as s 0 0, then b (s, t = 0) ^ (log s ) 2 but b (s, t < 0) < logs .

The present experimental situation can be summarized as follows.

For pp scattering at /"s = 53 GeV, by taking the averages of available data

we get:

for -t < 0.1 GeV 2 b = 13.0 ± 0 . 2 GeV" 2

for -t = 0.4 GeV 2 b = 10.4 + 0.2 GeV" 2

Then, using the U A 4 results of Fig. 5, the change of slope from /s" = 5 3 GeV

to / s = 540 GeV is :

for -t < 0.1 GeV 2 Ab = 4 . 2 ± 1 GeV" 2

for -t = 0.4 GeV 2 Ab = 3.2 ± 0.5 GeV~ 2

More accurate data at very low t are needed in order to reach a conclusion.

The good spatial resolution of our wire chambers in the Roman pots

allows to measure the antiproton momentum by tracking the trajectory

through the Q and Q quadrupoles (see Fig. 3 ) . For low-ß optics, the F D bending of the first quadrupole pair Q in the vertical plane is roughly

F twice the scattering angle while the bending of the second pair is

about equal to the scattering angle. The typical value of the scattering

angle in the low-8 optics is around 2.5 mrad. The p momentum is determined

by a best fit on the particle trajectory using the quadrupole transfer

matrices with constraint on the vertical position of the interaction point.

The momentum resolution, as determined experimentally on elastic events

has standard deviation of 0 . 7 ' 1 0 ~ 2 as shown in Fig. 7. The main contribution

to the observed resolution is from measurement errors. In fact the momentum

spread of the beam is less than 1 0 ~ 3 and for the SPS quadrupoles the relative

- 244 -

v a r i a t i o n o f t h e i n t e g r a t e d g r a d i e n t a c c r o s s t h e a p e r t u r e i s l e s s

t h a n 3 - 1 0 " 3 .

T h e m e a s u r e m e n t o f t h e m o m e n t u m i s r e l e v a n t f o r t h e r e j e c t i o n o f

i n e l a s t i c b a c k g r o u n d , e s p e c i a l l y i n t h e l o w - ß o p t i c s . I n a d d i t i o n i t

a l l o w s t o d e t e r m i n e t h e m o m e n t u m s p e c t r u m o f t h e p i n t h e i n e l a s t i c

s c a t t e r i n g r e a c t i o n p p -*• p X . D a t a h a v e b e e n t a k e n u s i n g a t r i g g e r t h a t

d e m a n d e d t h e f o u r - f o l d c o i n c i d e n c e o f t h e f o u r p o t s ( " i n n e r " a n d " o u t e r " )

o n t h e p s i d e t o g e t h e r w i t h a t l e a s t a c h a r g e d p a r t i c l e i n t h e o p p o s i t e

h e m i s p h e r e i n t h e p s e u d o r a p i d i t y r a n g e 3 <n < 5 . 6 . T h i s t r i g g e r p e r m i t s

t h e s t u d y o f t h e d i f f r a c t i v e d i s s o c i a t i o n p r o c e s s w i t h e x c i t a t i o n o f

s y s t e m s h a v i n g l a r g e m a s s . A n e x a m p l e o f t h e m o m e n t u m s p e c t r u m o f t h e

p f o r t h e d i f f r a c t i v e t r i g g e r i s s h o w n i n F i g . 7 .

- 2 4 5 -

R E F E R E N C E S

1 ) J . B u s k e n s e t a l . , N u c l . I n s t r . a n d M e t h o d s ( 1 9 8 3 ) , i n p r i n t .

2 ) C E R N - P i s a - R o m a - S t o n y B r o o k C o l l a b o r a t i o n , P h y s . L e t t . 6 2 B ( 1 9 7 6 )

4 6 0 a n d N u c l . P h y s . B 1 4 5 ( 1 9 7 8 ) 3 6 7 .

3 ) R . B a t t i s t o n e t a l . , P h y s . L e t t . 1 1 5 B ( 1 9 8 2 ) ; 3 3 3 .

4 ) R . B a t t i s t o n e t a l . , P h y s . L e t t . 1 1 7 B ( 1 9 8 2 ) 1 2 6 .

5 ) U . A m a l d i e t a l . , P h y s . L e t t . 6 6 B ( 1 9 7 7 ) 3 9 0 .

6 ) A . M a r t i n , P r o c e e d i n g s o f t h e X X I I n t e r n a t i o n a l C o n f e r e n c e o n H i g h E n e r g y P h y s i c s , P a r i s 1 9 8 2 , p . 5 7 9 , a n d P r o c e e d i n g s o f t h i s C o n f e r e n c e .

7) J . B a u m e l e t a l . , N u c l . P h y s . B 1 9 8 ( 1 9 8 2 ) 1 3 .

A . R . W h i t e , P r o c e e d i n g s o f t h e X I I I I n t e r n a t i o n a l S y m p o s i u m o n M u l t i p a r t i c l e D y n a m i c s , V o l e n d a m , 1 9 8 2 .

8 ) T . T . C h o u a n d C . N . Y a n g , P h y s . R e v . D 1 9 ( 1 9 7 9 ) ; 3 2 6 8 .

9 ) J . P . B u r q e t a l . , P h y s . L e t t . 1 0 9 B ( 1 9 8 2 ) 1 2 4 ;

M . B l o c k a n d R . C a h n , C E R N p r e p r i n t T H 3 3 4 2 ( 1 9 8 2 ) ;

T . E k e l ö f , P r o c e e d i n g s o f t h e X V I I R e x o n t r e d e M o r i o n d o n E l e m e n t a r y H a d r o n i c P r o c e s s e s a n d S p e c t r o s c o p y , l e s A r c s , 1 9 8 2 .

1 0 ) G . A r n i s o n e t a l . , P h y s . L e t t . 1 2 1 B ( 1 9 8 3 ) 7 7 .

1 1 ) F . C e r a d i n i , C o n t r i b u t i o n t o t h i s C o n f e r e n c e .

1 2 ) G . B a r b i e l l i n i e t a l . , P h y s . L e t t . 3 9 B ( 1 9 7 2 ) 6 6 3 .

1 3 ) U . A m a l d i e t a l . , P h y s . L e t t . 36_B ( 1 9 7 1 ) 5 0 4 ;

H . D e K e r r e t e t a l . , P h y s . L e t t . 6 8 B ( 1 9 7 7 ) 3 7 4 ;

L . B a k s a y e t a l . , N u c l . P h y s . B 1 4 1 ( 1 9 7 8 ) 1.

M. A m b r o s i o e t a l . , P h y s . L e t t . 1 1 5 B ( 1 9 8 2 ) 4 9 5 ;

A . B r e a k s t o n e e t a l . , p r e p r i n t I F U B 8 2 / 1 7 .

N . A m o s e t a l . , P h y s . L e t t . 1 2 0 B ( 1 9 8 3 ) 4 6 0 .

- 2 4 6 -

F i g u r e C a p t i o n s

F i g . 1 G r a p h i c a l p r e s e n t a t i o n o f o u r t o t a l c r o s s - s e c t i o n m e a s u r e m e n t

T h e r e s u l t a t t h e m a x i m u m I S R e n e r g y i s a l s o s h o w n f o r c o m p a r

i s o n .

F i g . 2 T o t a l c r o s s - s e c t i o n f o r p r o t o n - p r o t o n a n d p r o t o n - a n t i p r o t o n

i n t e r a c t i o n s . T h e l i n e s r e p r e s e n t t h e d i s p e r s i o n r e l a t i o n

f i t o f r e f . 5 ) .

F i g . 3 S k e t c h o f t h e e l a s t i c s c a t t e r i n g l a y o u t s h o w i n g t h e t e l e s c o p e s

o f R o m a n p o t s . T h e s y s t e m i s s y m m e t r i c w i t h r e s p e c t t o t h e

c r o s s i n g p o i n t . T h e s m a l l b o x i n s i d e e a c h p o t r e p r e s e n t s a

d e t e c t o r c o n s i s t i n g o f a w i r e c h a m b e r a n d a c o u n t e r h o d o -1 3 ) . . .

s c o p e ' . Q r e p r e s e n t s a p a i r o f q u a d r u p o l e s f o c u s i n g i n t h e F v e r t i c a l p l a n e w h i l e Q i s a d e f o c u s - l n g p a i r . T h e p t r a j e c t o r y

B

i n t h e v e r t i c a l p l a n e f o r 2 . 5 m r a d s c a t t e r i n g a n g l e a n d l o w - 3

o p t i c s i s a l s o s h o w n .

F i g . 4 P r e l i m i n a r y t - d i s t r i b u t i o n o f a b o u t 7 0 0 0 e l a s t i c s c a t t e r i n g

e v e n t s . T h e r e s u l t f o r t h e s l o p e i s b = 1 3 . 6 ± 0 . 5 G e V ~ 2 .

F i g . 5 T h e C o l l i d e r d a t a o n t h e s l o p e p a r a m e t e r b a r e p l o t t e d v e r s u s t .

T h e p u b l i s h e d r e s u l t s f r o m U A l ^ ^ a n d U A 4 ~ ^ a r e s h o w n t o g e t h e r

w i t h t h e n e w U A 4 p r e l i m i n a r y v a l u e . T h e h o r i z o n t a l b a r

i n d i c a t e s t h e r a n g e o f t u s e d i n t h e e x p o n e n t i a l f i t .

12 1 3 )

F i g . 6 T h e I S R d a t a ' o n t h e s l o p e b f o r p r o t o n - p r o t o n s c a t t e r i n g a r e

p l o t t e d v e r s u s t . A s i n F i g . 5 , t h e h o r i z o n t a l b a r i n d i c a t e s

t h e t - r a n g e o f e a c h m e a s u r e m e n t .

F i g . 7 M o m e n t u m d i s t r i b u t i o n o f t h e a n t i p r o t o n f o r e l a s t i c s c a t t e r i n g

a n d i n e l a s t i c d i f f r a c t i v e e v e n t s . T h e v a r i a b l e x i s d e f i n e d a s

t h e r a t i o o f t h e m e a s u r e d m o m e n t u m t o t h e n o m i n a l b e a m m o m e n t u m .

T h e s e d a t a a r e n o t n o r m a l y z e d a n d n o t c o r r e c t e d f o r a c c e p t a n c e .

4 )

- 248 -

ELASTIC S C A T T E R I N G L A Y O U T

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- 250 -

F i g . 7

- 2 5 1 -

Experiment R210 has been designed with the primary aim of measuring precisely a (pp) and a (pp) over the ISR energy range. The experiment tot tot is also equipped with small-angle detectors which allow us to measure da ,/dt, and with a system of drift chambers and scintillation hodoscopes el to measure charged multiplicities and angular distributions of emitted secondaries. Data have been collected at /s = 31, 53, and 63 GeV. Results at 53 GeV have already been published — results at 31 and 63 GeV must still be considered preliminary.

The total cross-section is obtained by measuring simultaneously the total interaction rate and the ISR luminosity: a = R /L. Excellent machine performance and accurate calibrations of rííe beam°ciisplacement scale allowed us to attain a better than 1% accuracy_in pp runs. Our data reproduce well the old ISR results, except at /s = 63 GeV, where, however, the agreement is good if we restrict the comparison to total-rate results only. We plan to collect more data at this energy in order to clarify this point. The difference Aa = a ^(pp) - a _ . (pp) is

tot tot tot — positive over the range measured, showing conclusively that at o t ( P P )

increases in the ISR energy range. As expected from Regge phenomenology, A a t o t behaves a s s • This result disfavours exotic possibilities, such as odderons, which would have a different s dependence. Both pp and pp data, moreover, favour a In 2s behaviour for a , and the extrapolation of this behaviour to the Collider agrees wellîth the result of UA4.

The elastic cross-section has only been analyzed at 53 GeV, and all the elastic cross-section parameters are the same for pp and pp, and consistent with geometrical scaling. Extrapolation of the elastic rate to measure the total cross-section via the optical theorem gives good agreement with the total-rate method.

As far as particle distributions are concerned, we focus our attention more on the comparison of pp and pp than on absolute numbers,

MEASUREMENTS OF O , da /dt, AND EVENT DISTRIBUTIONS tot el

IN pp AND pp COLLISIONS AT /s = 3 1 , 5 3 , AND 6 3 GEV

CERN - Napoli - Pisa - Stony Brook Collaboration

M. Ambrosio, G. Anzivino, G. Barbarino, G. Carboni, V. Cavasinni,

T. Del Prête, P.D. Grannis, D. Lloyd Owen, M. Morganti,

G. Paternoster, S. Patricelli, F. Schiavo, and M. Valdata-Nappi

(Presented by G. Carboni)

- 252 -

since most instrumental effects disappear in the comparison. In single-particle pseudorapidity distributions, a small excess (5%) is observed in the central region for pp. Moreover, the average charged multiplicity <n > is 2% higher for pp than for pp. Both pp and pp distributions satisfy KNO scaling fairly well.

A more interesting quantity is the difference of pp and pp topological cross-sections A a . The mean charged multiplicity of this distribution is 3 0 - 4 0 % higher than <n > for the individual reactions, ch and this effect occurs at all energies. The normalized form < n > A a / A a n tot is not fitted by the KNO function, but the distribution is similar to that obtained for annihilation at lower energy and for e e reactions.

A further difference in pp is the presence of an excess in the two-particle correlation function around 9 0 ^ . The excess (roughly the same at the three energies measured) has a very short pseudorapidity range ( A n = ± 0 . 3 ) compared to the classical short-range correlation ( A n = ± 1 ) . This effect depends on the multiplicity of the event, being present only for those multiplicities corresponding to the largest values of A a , suggesting that it is related to the "annihilation" mechanism, which still seems to be important at these energies.

- 253 -

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R210 LAYOUT

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MULTIPLICITY DISTRIBUTIONS /s = 31 GeV

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TWO-BODY CORRELATIONS /s = 31 GeV (INCLUSIVE) (CHAMBERS)

- 1 4 -

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(CHAMBERS) | n | < 2

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- 270 -

MEASUREMENT OF SMALL-ANGLE pp AND pp ELASTIC SCATTERING AT THE CERN INTERSECTING STORAGE RINGS

D. FAVART U n i v e r s i t é C a t h o l i q u e de Louvain

B - 1348 L o u v a i n - l a - N e u v e Belgium

SUMMARY

The small angle e l a s t i c s c a t t e r i n g o f protons w i t h protons and a n t i -p r o t o n s has been measured a t 52.8 and 30.4 GeV c e n t e r - o f - m a s s e n e r g y . Using the known t o t a l c r o s s - s e c t i o n f o r pp s c a t t e r i n g , a simultaneous f i t t o the pp and pp d i f f e r e n t i a l c r o s s s e c t i o n s a l l o w s t o determine the d i f f e r e n c e between the pp and pp t o t a l c r o s s - s e c t i o n s and the r a t i o o f the r e a l - t o - i m a g i n a r y p a r t o f the pp and pp f o r w a r d n u c l e a r s c a t t e r i n g a m p l i tudes a t both e n e r g i e s . In a d d i t i o n , the n u c l e a r s lope parameter a t low momentum t r a n s f e r i s obtained f o r pp and pp a t 52.8 GeV.

- 2 7 1 -

The comparison o f p r o t o n - p r o t o n and p r o t o n - a n t i p r o t o n i n t e r a c t i o n s a t v e r y h igh c e n t e r - o f - m a s s e n e r g i e s has been a c c e s s i b l e t o exper iment o v e r t h e l a s t two y e a r s owing t o the s u c c e s s f u l o p e r a t i o n o f the a n t i p r o t o n a c cumulator a t CERN and the p o s s i b i l i t y t o s t o r e a beam o f a n t i p r o t o n s i n one o f the CERN i n t e r s e c t i n g s t o r a g e r i n g s ( I S R ) . The L o u v a i n - N o r t h w e s t e r n c o l l a b o r a t i o n [1] has endeavoured i n t o a s e r i e s of accurate measurements o f pp and pp e l a s t i c s c a t t e r i n g a t small momentum t r a n s f e r , aiming a t the d e t e r m i n a t i o n o f the d i f f e r e n c e Aa between the pp and pp t o t a l c r o s s - s e c t i o n s , the r a t i o s p(pp) and p(pp) o f the r e a l t o the imaginary p a r t o f the f o r w a r d n u c l e a r s c a t t e r i n g a m p l i t u d e s a n d the s l o p e s b(pp) and b(pp) o f the n u c l e a r e l a s t i c d i f f e r e n t i a l c r o s s - s e c t i o n s .

The experiment uses the method and p a r t o f the equipment o f the CERN-Rome c o l l a b o r a t i o n w h i c h , t o g e t h e r w i t h the P i s a - S t o n y - B r o o k c o l l a b o r a t i o n , d i s c o v e r e d the r i s e o f the pp t o t a l c r o s s - s e c t i o n a t the ISR [2] and p e r f o r -

2 med the measurement o f the p(pp) parameter [ 3 J . Four m i n i a t u r e (48 x 28 mm ) s c i n t i l l a t o r hodoscopes are i n s t a l l e d above and below the two beams, i n movab l e s e c t i o n s o f the vacuum pipes ("Roman pots") at 8.7 m downstream o f the i n t e r s e c t i o n r e g i o n . The pots and the hodoscopes can be a c c u r a t e l y moved (± 0.02 mm) under remote c o n t r o l and can approach the c i r c u l a t i n g beams t o e x p l o r e s c a t t e r i n g angles down t o 1 mrad. With the use o f t h e T e r w i l l i g e r f o c u s i n g mode o f momentum compaction, the s p a t i a l e x t e n s i o n o f the beam i n t e r s e c t i o n r e g i o n i s much reduced. The t r i g g e r i n g of the data a c q u i s i t i o n can be s imply made on the c o i n c i d e n c e between the upper hodoscope i n one arm and the lower one i n the o t h e r and p r o v i d e s an almost b a c k g r o u n d - f r e e sample o f e l a s t i c e v e n t s . The l u m i n o s i t y o f the i n t e r s e c t i o n i s monitored w i t h f o u r

2 p a i r s o f l a r g e (0.5 m ) s c i n t i l l a t o r counters l o c a t e d s y m m e t r i c a l l y above and below the beam and c a r e f u l l y c a l i b r a t e d through the van der Meer beam v e r t i cal displacement method [ 4 ] . Such c a l i b r a t i o n was r e p e a t e d l y performed dur ing the pp and pp data t a k i n g r u n s , showing r e p r o d u c i b i l i t y a t the percent l e v e l . D e t a i l s on the a p p a r a t u s , the i n f o r m a t i o n r e c o r d e d , the background s u b t r a c t i o n and the data r e d u c t i o n can be found elsewhere [ 5 , 6 ] .

Data have been c o l l e c t e d a t t h r e e c e n t e r - o f - m a s s e n e r g i e s : /s = 3 0 . 4 , 52.8 and 62.3 GeV i n s u c c e s s i v e pp and pp r u n s . During the pp r u n s , the a n t i p r o t o n beam i n t e n s i t y was o f the o r d e r o f 2 t o 4 mA whereas the proton

26 - 2 - 1 beam i n t e n s i t y was about 10 A , g i v i n g l u m i n o s i t i e s up t o 7.10 cm s .

- 272 -

F o r t h e p p r u n s , b o t h b e a m s w e r e k e p t a t 5 A r e s u l t i n g i n a l u m i n o s i t y o f 29 - 2 - 1 5

a b o u t 5 . 1 0 cm s . T h e t o t a l p p s t a t i s t i c s c o l l e c t e d w a s 1.7 10 e l a s t i c p p e v e n t s a t 5 2 . 8 a n d 6 2 . 3 G e V a n d 0 . 5 5 1 0 5 e v e n t s a t 3 0 . 4 G e V . T h e s t a t i s t i c s o f t h e p p c o m p a r i s o n r u n s w e r e o f t h e o r d e r o f 2 . 1 0 ^ e v e n t s . We s h o w i n f i g s . 1 a n d 2 , t y p i c a l d i f f e r e n t i a l c r o s s - s e c t i o n s o b s e r v e d f o r p p a n d p p c o l l i s i o n s a t /s = 3 0 . 4 G e V a n d 5 2 . 8 G e V .

T h e d a t a w e r e f i t t e d t o t h e s t a n d a r d e x p r e s s i o n o f t h e d i f f e r e n t i a l

c r o s s - s e c t i o n :

& = i r | f c . f „ | 2 (1)

w h e r e t h e C o u l o m b a m p l i t u d e f ^ a n d t h e n u c l e a r e l a s t i c s c a t t e r i n g a m p l i t u d e

f N a t s m a l l m o m e n t u m t r a n s f e r s q u a r e d t a r e p a r a m e t r i z e d i n t h e u s u a l w a y :

f « - ¿ « + P ) < W e b t / 2 ( 3 )

I n t h e e x p r e s s i o n ( 2 ) , G =

f o r m f a c t o r a n d a * i s

ai> = a

N ~ 3 ? v P J ° t o t

1 + ^ i s t h e p r o t o n e l e c t r o m a g n e t i c

£ n - 0 . 5 7 7

h e C o u l o m b p h a s e t a k e n f r o m r e f e r e n c e 7 :

; t h e u p p e r a n d l o w e r s i g n s a r e f o r p p a n d p p

s c a t t e r i n g r e s p e c t i v e l y .

T h e r e s u l t s o b t a i n e d a t v s = 5 2 . 8 G e V h a v e a l r e a d y b e e n p u b l i s h e d [ 6 ] . T h e y

w e r e o b t a i n e d t h r o u g h t h e s i m u l t a n e o u s a d j u s t m e n t o f e x p r e s s i o n s ( 1 - 3 ) t o p p

a n d pp d a t a , u s i n g t h e k n o w n p p t o t a l c r o s s s e c t i o n a t Q t ( p p ) [8] a s i n p u t t o

t h e f i t a n d a d j u s t i n g t h e f o l l o w i n g p a r a m e t e r s : a t Q t ( p p ) , p ( p p ) » p ( p p ) » b ( p p ) ,

b ( p p ) , N , A h . N i s a n o v e r a l l n o r m a l i z a t i o n f a c t o r w h i c h a l l o w s f o r s m a l l e v e n t

s e l e c t i o n i n e f f i c i e n c i e s a n d a b s o l u t e l u m i n o s i t y c a l i b r a t i o n e r r o r , a n d i s

a s s u m e d t o b e t h e same f o r pp a n d pp m e a s u r e m e n t s ; a n d A h r e p r e s e n t s t h e mean

d e v i a t i o n o f h o d o s c o p e v e r t i c a l s e p a r a t i o n f r o m o p t i c a l s u r v e y m e a s u r e m e n t s

a n d i s e s s e n t i a l l y a c o r r e c t i o n t o t h e t - s c a l e . T h e p r o c e d u r e u s e d i n t h e

a n a l y s i s o f t h e /s = 3 0 . 4 G e V d a t a i s b a s i c a l l y t h e s a m e . H o w e v e r , a t t h i s

e n e r g y t h e momentum t r a n s f e r r a n g e e x p l o r e d i s r e s t r i c t e d t o a m a x i m u m v a l u e

|t| s 0 . 0 1 5 G e V a n d d o e s n o t a l l o w f o r a n a c c u r a t e d e t e r m i n a t i o n o f t h e

n u c l e a r s l o p e s . T h e a n a l y s i s o f t h e * s = 6 2 . 3 G e V r u n i s s t i l l i n p r o g r e s s .

- 273 -

T h e i n p u t t o t h e f i t s a n d t h e r e s u l t s o b t a i n e d a r e s u m m a r i z e d i n

t a b l e 1. T h e e r r o r s s h o w n a r e t h e s t a t i s t i c a l e r r o r s c o m b i n e d w i t h t h e

c o n t r i b u t i o n o f a p o s s i b l e 2 % s y s t e m a t i c d i f f e r e n c e b e t w e e n p p a n d p p

n o r m a l i z a t i o n s a n d a p o s i t i o n u n c e r t a i n t y o f t h e d e t e c t o r s o f 0 . 0 2 mm

b e t w e e n pp a n d pp r u n s . I t s h o u l d b e n o t e d t h a t t h e t o t a l c r o s s -

s e c t i o n d i f f e r e n c e Aa i s e s s e n t i a l l y i n d e p e n d e n t o f t h e o " t o t ( p p ) i n p u t

v a l u e , w h e r e a s a t o t ( p p ) , g i v e n f o r c o n v e n i e n c e o f c o m p a r i s o n w i t h

s i m i l a r d a t a , d i r e c t l y d e p e n d s o n t h i s i n p u t t o t h e f i t .

I n f i g . 3 , we c o m p a r e o u r r e s u l t s f o r Aa w i t h l o w e r

e n e r g y d a t a a n d a c o n v e n t i o n a l f i t [11] t o t h e s e l o w e n e r g y d a t a . T h e

e x t r a p o l a t i o n o f t h e l a t t e r w h i c h p r e d i c t t h a t Aa-»-0 a s s °° , i s i n g o o d

a g r e e m e n t w i t h o u r r e s u l t s . I t h a s b e e n o b s e r v e d [ 1 2 ] , h o w e v e r , t h a t o n e

c a n n o t y e t e x c l u d e a n u n c o n v e n t i o n a l c o n t r i b u t i o n t o t h e s c a t t e r i n g a m p l i

t u d e ( t h e s o - c a l l e d o d d e r o n [ 1 3 ] ) w h i c h , a t I S R e n e r g y , w o u l d b e o f t h e

o r d e r o f t h e o d d - u n d e r - c r o s s i n g R e g g e c o n t r i b u t i o n t o t h i s a m p l i t u d e a n d

s u c h t h a t ¡Ao| w o u l d a s y m p t o t i c a l l y b e c o m e p r o p o r t i o n a l t o A n s . T h e Aa

d a t a a t t h e h i g h e s t e n e r g y a c c e s s i b l e (/s = 6 2 . 3 G e V ) w i l l b e c r i t i c a l f o r

t h i s i s s u e . We n o t e a l s o t h e a g r e e m e n t a t /s = 5 2 . 8 G e V b e t w e e n o u r v a l u e

f o r Aa a n d t h e l a t e s t v a l u e r e p o r t e d b y t h e C E R N - N a p o l i - P i s a - S t o n y - B r o o k

c o l l a b o r a t i o n , Aa = 1 . 4 9 ± 0 . 3 5 mb [ 1 4 ] . I n a d d i t i o n , t h e c o m p a r i s o n o f

t h e t o t a l pp c r o s s - s e c t i o n m e a s u r e d /s = 3 0 . 4 a n d 5 2 . 6 GeV w i t h t h e h i g h e s t

e n e r g y F e r m i l a b d a t a [ 1 0 ] , s h o w s c o n c l u s i v e l y t h a t t h i s c r o s s - s e c t i o n i s r i s i n g

i n t h e I S R e n e r g y d o m a i n . I n d e e d , t h e r a t e o f i n c r e a s e o f a t Q t ( p p ) i s c o m p a

t i b l e w i t h a A n ^ s b e h a v i o u r , a s f a s t a s a l l o w e d b y t h e F r o i s s a r t b o u n d .

T h e v a l u e s o f p ( p p ) a n d p ( p p ) m e a s u r e d i n t h i s e x p e r i m e n t a r e d i s p l a y e d

i n f i g . 4 t o g e t h e r w i t h p r e v i o u s d a t a . I t c a n b e s e e n t h a t p ( p p ) i s p o s i t i v e

a n d i n c r e a s i n g o v e r t h e I S R e n e r g y r a n g e . T h i s b e h a v i o u r i s p r e d i c t e d b y

m o d e l s w h e r e b o t h p p a n d p p t o t a l c r o s s - s e c t i o n s a r e a s s u m e d t o r i s e w i t h

r a t e c l o s e t o t h e F r o i s s a r t b o u n d w h i l e A a + 0 f o r s •*• ° ° . A s a n

e x a m p l e , we s h o w i n f i g . 4 t h e d i s p e r s i o n r e l a t i o n f i t o f A m a l d i e t a l . [3]

w h i c h i s made u n d e r t h e s e a s s u m p t i o n s .

I t h a s b e e n o b s e r v e d e a r l i e r [16] t h a t t h e v a l u e s o f t h e l o w - t s l o p e s ,

b ( p p ) a n d b ( p p ) , m e a s u r e d a t /s = 5 2 . 8 GeV a r e n o t s i g n i f i c a n t l y d i f f e r e n t

f r o m e a c h o t h e r , a s e x p e c t e d i f t h e r a t i o o f t h e w i d t h s o f t h e d i f f r a c t i o n

p e a k a p p r o a c h u n i t y a t h i g h e n e r g y ; t h i s p r e d i c t i o n o f a s y m p t o t i c t h e o r e m s [ 1 7 ]

- 274 -

s e e m s a l r e a d y f u l f i l l e d a t I S R e n e r g i e s a t t h e l e v e l o f e x p e r i m e n t a l a c c u

r a c y . F i n a l l y , t h e e l a s t i c c r o s s - s e c t i o n c a n b e d e t e r m i n e d f r o m o u r

m e a s u r e m e n t , t h r o u g h i n t e g r a t i o n o f t h e d i f f e r e n t i a l e l a s t i c c r o s s - s e c t i o n .

We f i n d t h a t t h e r a t i o o f t h e e l a s t i c c r o s s - s e c t i o n t o t h e t o t a l c r o s s -

s e c t i o n i s t h e same f o r pp a n d p p , w i t h i n . e x p e r i m e n t a l e r r o r s , a n d c l o s e t o

t h e v a l u e s p r e v i o u s l y o b t a i n e d a t l o w e r e n e r g y ( p - j ^ £ 100 G e V / c ) , a f e a t u r e

p r e d i c t e d b y o p t i c a l m o d e l s w i t h g o e m e t r i c a l s c a l i n g .

- 275 -

R E F E R E N C E S

[1] D. F a v a r t , C . L e r o y , P. L i p n i k , J . p . M a t h e y s ( U n i v e r s i t é C a t h o l i q u e

d e L o u v a i n , B - 1348 L o u v a i n - l a - N e u v e , B e l g i u m ) , N . A m o s , M. B l o c k ,

D. M i l l e r , S . S h u k l a , S . Z u c c h e l l i ( N o r t h w e s t e r n U n i v e r s i t y , E v a n s t o n ,

I l l i n o i s 6 0 2 0 1 ) , G . B o b b i n c k , K. P o t t e r , C . V a n d e r v e l d e - W i l q u e t + ( C E R N ,

CH - 1211 G e n e v e 2 3 , S w i t z e r l a n d ) , M. B o t j e , F . L i n d e ( S t a t e U n i v e r s i t y ,

U t r e c h t , T h e N e t h e r l a n d s ) .

[2] U . A m a l d i e t a l . , P h y s . L e t t . 4 4 B , 112 ( 1 9 7 3 ) .

S . R . A m e n d o l i a e t a l . , P h y s . L e t t . 4 4 B , 119 ( 1 9 7 3 ) .

[ 3 ] U . A m a l d i e t a l . , P h y s . L e t t . 6 6 B , 3 9 0 ( 1 9 7 7 ) .

[4] P. B r y a n t a n d K. P o t t e r , CERN I n t e r n a l R e p o r t I S R - E S - B O M / 8 2 - 1 5 .

[5] D. F a v a r t e t a l . , P h y s . R e v . L e t t . 4 7 , 1191 ( 1 9 8 1 ) .

[ 6 ] N . Amos e t a l . , P h y s . L e t t . 1 2 0 B , 4 6 0 ( 1 9 8 3 ) .

[7] G . B . W e s t a n d D . R . Y e n n i e , P h y s . R e v . W 2 , 1413 ( 1 9 6 8 ) .

T h e c a l c u l a t i o n o f t h e C o u l o m b p h a s e w a s r e c e n t l y e x a m i n e d .by R. C a h n ,

CERN T H - 3 2 9 2 ( 1 9 8 2 ) , w h o u s e s a n e i k o n a l m o d e l a n d f i n d s o n l y s m a l l

c o r r e c t i o n s t o t h e W e s t a n d Y e n n i e r e s u l t .

[8] U . A m a l d i a n d K . R . S c h u b e r t , N u c l . P h y s . B 1 6 6 , 301 ( 1 9 8 0 ) .

[9j W. G a l b r a i t h e t a l . , P h y s . R e v . 1 3 8 B , 913 ( 1 9 6 5 ) .

S . P . D e n i s o v e t a l . , N u c l . P h y s . B 6 5 , 1 ( 1 9 7 3 ) .

[10] A . S . C a r r o l l e t a l . , P h y s . L e t t . 8 0 B , 4 2 3 ( 1 9 7 9 ) .

[ 1 1 ] W. B a r t e l a n d A . N . D i d d e n s , CERN I n t e r n a l R e p o r t N P / 7 3 - 4 .

[12] P. G a u r o n a n d B . N i c o l e s c u , O r s a y p r e p r i n t I P N O / T H , 8 2 - 4 5 .

[13] L . L u k a s z u k a n d B . N i c o l e s c u , N u o v o C i m e n t o L e t t e r s 8 , 4 0 5 ( 1 9 7 3 ) .

[ 1 4 ] M. A m b r o s i o e t a l . , P h y s . L e t t . 1 1 5 B , 4 9 5 ( 1 9 8 2 ) .

[ 1 5 ] K . J . F o l e y e t a l . , P h y s . R e v . L e t t . J 9 , - 8 5 7 ( 1 9 6 7 ) .

G . G . B e z n o g i k h e t a l . , P h y s . L e t t . 3 9 B , 411 ( 1 9 7 2 ) .

V . B a r t e n e v e t a l . , P h y s . R e v . L e t t . 31^, 1367 ( 1 9 7 3 ) .

U . A m a l d i e t a l . , P h y s . L e t t . 6 6 B , 390 ( 1 9 7 7 ) .

+ p r e s e n t a d d r e s s : I I H E , U n i v e r s i t é L i b r e d e B r u x e l l e s , B e l g i u m

- 276 -

J.P . Burq e t a l . , Phys. L e t t . 109B, 124 (1982). L.A. F a j a r d o e t a l . , Phys. Rev. D24, 46 (1981).

[16] A . M a r t i n , Z. Phys. CJ_5, 185 (1982).

[17] H. C o r n i l l e and A . M a r t i n , Phys. L e t t . 40B, 671 (1972).

- 277 -

T a b l e 1

I n p u t a n d r e s u l t o f t h e s i m u l t a n e o u s f i t t o t h e p p a n d p p

d i f f e r e n t i a l e l a s t i c c r o s s - s e c t i o n d a t a . R e s u l t s a t 3 0 . 4 G e V

a r e p r e l i m i n a r y .

¿ s ( G e V ) 5 2 . 8 3 0 . 4

I n p u t a t o t ^ p p ^ = 4 2 , 6 7 m b a t o t ^ p p ) = 4 0 , 1 4 m b

b ( p p ) = 1 2 . 2 G e V " 2

b ( p p ) = 1 2 . 6 G e V " 2

R e s u l t A a = 0 . 9 8 ± 0 . 3 6 mb A o « 1 . 5 ± 0 . 5 mb

a t o t ( p p ) = 4 3 . 6 5 ± 0 . 4 1 mb o t Q t ( p p ) = 4 1 . 7 ± 0 . 5 mb

a e l ( p p ) = 7 . 3 6 ± 0 . 3 0 mb c e - , ( p p ) = 7 . H 0 . 3 mb

p ( p p ) = 0 . 0 6 0 ± 0 . 0 0 0 6 p ( p p ) = 0 . 0 4 0 ± 0 . 0 0 5

p ( p p ) = 0 . 1 0 H 0 . 0 1 8 p ( p p ) = 0.031+Ó.021 b ( p p ) = 1 2 . 8 5 ± 0 . 1 2 G e V " 2

b ( p p ) = 1 3 . 3 6 ± 0 . 5 3 G e V " 2

- 2 7 8 -


F i g . 1. T h e m e a s u r e d d i f f e r e n t i a l c r o s s - s e c t i o n d a / d t f o r e l a s t i c s c a t t e

r i n g o f p r o t o n s o n p r o t o n s ( u p p e r ) a n d a n t i p r o t o n s ( l o w e r ) a t

/ s = 5 2 . 8 G e V , a s a f u n c t i o n o f | t | .

F i g . 2 . Same a s f i g . 1 f o r Ss = 3 0 . 4 G e V .

F i g . 3 . T h e d i f f e r e n c e A a = ° t 0 t ( P P ) " a t o t ^ p p ^ v e r s u s l a b o r a t o r y m o m e n t u m

P l a b P» 1 0 , 14J* T h e c u r v e i s t n e r e s u l t o f t n e o f B a r t e l a n d D i d d e n s [ 1 1 ] t o t h e l o w e r e n e r g y d a t a .

F i g . 4 . T h e p a r a m e t e r p f o r p p a n d p p s c a t t e r i n g [ 1 5 ] a s a f u n c t i o n o f

T/S. F o r c l a r i t y , t h e p p d a t a o f F a j a r d o e t a l . w h i c h l i e a b o v e

t h e o t h e r p p d a t a h a v e b e e n o m i t t e d . T h e c u r v e i s t h e r e s u l t o f

t h e d i s p e r s i o n r e l a t i o n f i t o f A m a l d i e t a l . [3] t o t o t a l c r o s s -

s e c t i o n a n d p d a t a .

- 279 -

4 0 0

> S 200

E

I 1 0 0

"° 80

60

0.00 0.01 0.02 0 .03 0.04 0.05 Itl (GeV 2 )

400 h

f N

> CD

O 200

-t-> T) x, b

100 •o 80

60

0.00 0.01 0 . 0 2 Itl (GeV 2 )

0.03 0 .04

F i g . 1

- 2 8 0 -

i 1 1 1 1 1 r

"1 | I | , ! I ^ I

0.000 0 .003 0 .005 0.006 0 .010 C .013 0 .015 0.018 Itl ( 3 e V 2 )

i 1 1 1 1 1 • r

0.000 0 .003 0 .005 0 .008 0 .010 0 .013 0 .015 0 .018 Itl ( G s V 2 )

F i g . 2

- 2 8 1 -

i I I I 11111 I — I — I I I I I I | 1 — I — R

• Galbraith et al- (1965) • Denisovetal . (1973)

1 — i i i i 11 i l 1 i l i i i

10 1 0 2 1 0 3

P .c b ( G e V / c )

F i g . 3

F i g . 4

- 2 8 2 -

R E C E N T L A R G E T R A N S V E R S E MOMENTUM R E S U L T S F R O M T H E I S R

L . C a m i l l e r i C E R N , 1 2 1 1 G e n e v a 2 3 , S w i t z e r l a n d

_ R e s u l t s w i l l b e p r e s e n t e d o n t h e c o m p a r i s o n o f h i g h p^, p h e n o m e n a i n p p a n d p p c o l l i s i o n s a n d o n s t u d i e s o f j e t s i n t o t a l e n e r g y t r i g g e r s . T w o e x p e r i m e n t s w i l l b e d i s c u s s e d : -

a ) R - 1 1 0 , C E R N - O x f o r d - R o c k e f e l l e r C o l l a b o r a t i o n . I t c o n s i s t s o f a s u p e r c o n d u c t i n g s o l e n o i d ( F i g . 1 ) p r o d u c i n g a f i e l d

o f 1 . 4 T e s l a c o n t a i n i n g c y l i n d r i c a l d r i f t c h a m b e r s . A n e l e c t r o m a g n e t i c c a l o r i m e t e r c o v e r s t h e w h o l e a z i m u t h . I t i s m a d e u p o f l e a d s c i n t i l l a t o r

F i g . 1 : A p p a r a t u s o f E x p e r i m e n t F i g . 2 : A p p a r a t u s o f E x p e r i m e n t R - 1 1 0 . R - 8 0 7 .

s h o w e r c o u n t e r s , i n s i d e t h e m a g n e t , s u b t e n d i n g 2 2 0 ° i n a z i m u t h , a n d ± 1 . 1 u n i t s o f r a p i d i t y c e n t r e d o n y = 0 , a n d t w o l e a d g l a s s a r r a y s c o v e r i n g t h e r e s t o f t h e a z i m u t h a n d s u b t e n d i n g ± 0 . 6 u n i t s o f r a p i d i t y .

b ) R - 8 0 7 , t h e A F S C o l l a b o r a t i o n . T h i s e x p e r i m e n t u s e s a n o p e n a x i a l f i e l d m a g n e t , F i g . 2 , c o n t a i n i n g

c y l i n d r i c a l d r i f t c h a m b e r s a n d s u r r o u n d e d b y a n u r a n i u m - s c i n t i l l a t o r c a l o r i m e t e r . T h e c a l o r i m e t e r h a s b o t h e l e c t r o m a g n e t i c a n d h a d r o n i c c o m p a r t m e n t s .

W h e r e a s , i n n o r m a l p p r u n n i n g t h e I S R r u n s a t a l u m i n o s i t y o f a b o u t 5 x 1 0 3 1 c m " 2 s e c , i n t h e p p r u n n i n g d i s c u s s e d h e r e t h e l u m i n o s i t y w a s s t i l l o n l y o f t h e o r d e r o f 1 0 2 7 cm"* 2 s e c " " 1 . T h e p p d a t a u s e d t o c o m p a r e t o t h e p p r e s u l t s w a s a l s o t a k e n a t r e d u c e d l u m i n o s i t y .

1 . p p / p p C o m p a r i s o n .

1 . 1 S i n g l e P a r t i c l e s p e c t r u m . E x p e r i m e n t R - 8 0 7 c o m p a r e s t h e p_, s p e c t r u m o f h a d r o n i c s h o w e r s o f

l i m i t e d s p a t i a l e x t e n t ( c o n s i s t i n g m o s t l y o f s i n g l e I T o r TT m e s o n s )

- 2 8 3 -

o b s e r v e d a n d / s = o f t h e p

i n t h e i r c a l o r i m e t e r 1 ^ . D a t a h a s b e e n c o l l e c t e d a t / s = 3 1 6 3 G e V . p t o p p

10 -

0.1

(b) ft=63 GeV

T h e s p e c t r a e x t e n d u p t o 6 G e V / c i n p ^ a n d t h e r a t i o s p e c t r a , s h o w n i n F i g . 3 , i s a l w a y s c o n s i s t e n t w i t h 1 . 0 .

S i m i l a r l y , t h e r a t i o o f t h e i n c l u s i v e c r o s s - s e c t i o n s o f ir° m e s o n s 2

o b t a i n e d i n R - 1 1 0 i s a l s o c o n s i s t e n t w i t h 1 . 0 u p t o p ^ 5 G e V / c a t / s = 5 2 G e V . 1 . 2 T w o p a r t i c l e m a s s s p e c t r u m .

R - 8 0 7 f o r m t h e i n v a r i a n t m a s s o f t w o d i s t i n c t h a d r o n i c s h o w e t r s a s s u m i n g t h e y a r e c a u s e d b y Tr- m e s o n s . T h e m a s s s p e c t r a a t

/ s = 31 a n d 6 3 G e V b e t w e e n 5 a n d 7 G e V / c 2 e x h i b i t n o d i f f e r e n c e s b e t w e e n p p a n d p p c o l l i s i o n s a s s h o w n i n F i g . 4 . 1 . 3 T o t a l e n e r g y s p e c t r u m .

T h e t r a n s v e r s e e n e r g y o f a n e v e n t i s d e f i n e d a s t h e s u m o f t h e t r a n s v e r s e e n e r g y o f a l l t h e c l u s t e r s i n a n e v e n t . I n e x p e r i m e n t R - 1 1 0 t h i s s u m i s m a d e o v e r

)

QCD

• • 2 ) i n t h e c a l o r i m e t e r

E_ s p e c t r a o b t a i n e d

P T (GeV/c)

F i g . 3 : T h e r a t i o o f t h e p p t o p p s i n g l e i n c l u s i v e c r o s s - s e c t i o n f o r c h a r g e d p a r t i c l e s a t / s = 3 1 a n d / s = 6 3 G e V ( R - 8 0 7 ) .

100

10

>

•P P l/srSIGeV • p p

•0Jjks=63Gev]

a l l t h e c l u s t e r s T h e r a t i o o f t h e i n p p a n d p p c o l l i s i o n s , F i g . 5 , i s a g a i n c o n s i s t e n t w i t h 1 . 0 u p t o E = 1 2 . 0 G e V .

T o c o n c l u d e , n o s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e h a s b e e n

o b s e r v e d b e t w e e n p p a n d p p i n h i g h p^, i n t e r a c t i o n s .

2 . J e t S t u d i e s u s i n g T o t a l E n e r g y T r i g g e r .

2 . 1 R e s u l t s o f E x p e r i m e n t R - 1 1 0 . T h i s e x p e r i m e n t f o r m s a

T o t a l N e u t r a l E n e r g y T r i g g e r b y s u m m i n g t h e p u l s e h e i g h t i n a l l t h e c o u n t e r s i n t h e e l e c t r o m a g n e t i c c a l o r i m e t e r w h i c h s u b t e n d s t h e w h o l e a z i m u t h . T h e d a t a w a s c o l l e c t e d a t

- 2 s e c - 1 a n d

M ( C e V / c 2 )

a l u m i n o s i t y o f l O ^ c m u n d e r t h e s e c o n d i t i o n s a b o u t h a l f t h e t r i g g e r s c o n s i s t o f t w o o v e r l a p p i n g e v e n t s . T h e s e d o u b l e e v e n t s a r e r e j e c t e d u s i n g t i m i n g c u t s o n T D C s p e c t r a .

T h e T o t a l N e u t r a l T r a n s v e r s e E n e r g y o f t h e e v e n t , E„, i s f o r m e d b y s u m m i n g t h e p u l s e h e i g h t o f a l l t h e c o u n t e r s , s u i t a b l y t r a n s f o r m e d t o t h e c e n t r e o f m a s s . T h e E ^ s p e c t r a a t / s = 3 1 , 45 a n d 6 3 G e V

i F i g . 4 : + T h e i n v a r i a n t m a s s s p e c t r u m ' o f t w o TC i n p p a n d p p ( R - 8 0 7 ) .

- 2 8 4 -

2.4

2.0

1.6

1.2

0.8-

0.4-

Total transverse energy .(forward bias)

^ •*• +

0 4 6 8 E E T ( G e V )

10 12 14 1

F i g . 5 : T h e r a t i o o f t h e E s p e c t r u m o b t a i n e d i n p p a n d p p c o l l i s i o n s a t / s = 5 2 ( R - 1 1 0 )

a r e s h o w n i n F i g . 6 . N o f i t s h a v e b e e n p e r f o r m e d y e t b u t i t i s e v i d e n t t h a t t h e / s = 6 3 G e V s p e c t r u m d e p a r t s f r o m a s i m p l e e x p o n e n t i a l a r o u n d <x< 2 0 G e V .

T h e e v e n t s a b o v e 22 G e V

20 25 E T (GeV)

F i g . 6 : T h e E s p e c t r u m f r o m e x p . R - 1 1 0 o b t a i n e d a t / s = 3 1 , 4 5 a n d 6 3

w e r e s c a n n e d a n d i t w a s f o u n d t h a t i n a l a r g e f r a c t i o n o f t h e m t h e e l e c t r o m a g n e t i c e n e r g y w a s c o n c e n t r a t e d i n t w o c l u s t e r s w i t h m o s t o f t h e c h a r g e d p a r t i c l e s p o i n t i n g t o t h e m . T h e e n e r g y i n t h e c a l o r i m e t e r s w a s t h e n c l u s t e r e d a n d t h e q u a n t i t y

R = I i = 1

J T i

w h e r e E „ , , E = t r a n s v e r s e e n e r g y o f t h e t w o m o s t e n e r g e t i c c l u s t e r s

N = t o t a l n u m b e r o f c l u s t e r s i n t h e e v e n t w a s f o r m e d . T h e m e a n o f R , < R > , i s s e e n t o i n c r e a s e a s a f u n c t i o n o f E ^ , F i g . 7 , r e a c h i n g a v a l u e o f 0 . 8 5 a t E = 2 7 G e V . T h e t e n d e n c y i s t h e r e f o r e f o r t h e e n e r g y i n t h e e v e n t s t o B e c o n c e n t r a t e d m o r e a n d m o r e i n t o t w o c l u s t e r s .

T h e p a r t i c l e s i n a n e v e n t w e r e t h e n d i v i d e d i n t o t w o j e t s u s i n g a s i m p l e a l g o r i t h m . T h e a x i s t h a t m a x i m i z e d t h e l o n g i t u d i n a l m o m e n t u m o f t h e p a r t i c l e s i n a h e m i s p h e r e w a s f o u n d . A l l t h e p a r t i c l e s i n t h a t h e m i s p h e r e w e r e t h e n a s s i g n e d t o j e t 1. T h e p a r t i c l e s i n t h e o t h e r h e m i s p h e r e w e r e t h e n a s s i g n e d t o j e t 2 a n d t h e j e t 2 a x i s w a s s i m p l y d e f i n e d a s t h e u n i t v e c t o r a l o n g t h e r e s u l t i n g m o m e n t u m o f t h e p a r t i c l e s i n j e t 2 . N o t e t h a t t h e a x e s o f t h e t w o j e t s a r e n o t n e c e s s a r i l y b a c k t o b a c k . A s p h e r i c i t y f o r t h e w h o l e e v e n t w a s t h e n c a l c u l a t e d a s

- 2 8 5 -

w i t h , N .

= - E J

2 7 z i = 1 T i

N .

i = 1

N j = n u m b e r o f p a r t i c l e s i n j e t j

J , ^ = T r a n s v e r s e m o m e n t u m o f p a r t i c l e i

P ^ . m o m e n t u m o f p a r t i c l e i .

20 ET (GeV)

F i g . 7 : < R > a s d e f i n e d i n t h e t e x t a s a f u n c t i o n o f E ^ , ( R - 1 1 0 ) .

20

1.0 0 Sphericity

F o r i s o t r o p i c e v e n t s S s h o u l d b e 1 . 0 a n d f o r j e t e v e n t s i t s h o u l d t e n d t o 0 . 0 . P l o t s o f t h e s p h e r i c i t y o f e v e n t s w i t h E ^ ^ 1 0 G e V a n d E ^ , N 2 0 G e V a r e s h o w n i n F i g . 8 . T h e h i g h E ^ , e v e n t s a r e s e e n t o h a v e m u c h s m a l l e r v a l u e s o f s p h e r i c i t y t h a n t h e E ^ r v 10 G e V e v e n t s . T h e s a m e e f f e c t i s e x h i b i t e d i n F i g . 9 w h i c h s h o w s t h e m e a n v a l u e o f S p l o t t e d a s a f u n c t i o n o f E C l e a r l y , t h e v a l u e s o f J ,

j. t o b e l i m i t e d . T h i s c a n a l s o b e s t u d i e d b y e x a m i n i n g t h e c o r r e l a t i o n s o f t h e d i r e c t i o n o f c h a r g e d p a r t i c l e s r e l a t i v e t o t h e i r j e t a x i s . T o d o s o a s c a t t e r i n g p l a n e w a s d e f i n e d a s t h e p l a n e c o n t a i n i n g t h e b e a m s a n d t h e j e t a x i s . F o r a n y c h a r g e d p a r t i c l e , a s m e a s u r e d b y t h e d r i f t c h a m b e r s ,

r a r e s e e n

05

5 O.U

fe 0.3 JZ CL V) cz 0.2 Oi a

0.1

0

t •

16 18 20

E T (GeV)

22 IK 26

F i g . 8 : T h e s p h e r i c i t y , S , d i s t r i b u - F i g . 9 : T h e m e a n s p h e r i c i t y a s t i o n f o r t w o E T r e g i o n s ( R - 1 1 0 ) . a f u n c t i o n o f E ^ ( R - 1 1 0 )

a r e d e f i n e d a s t h e c o m p o n e n t s o f J T ( d e f i n e d a b o v e ) i n t h e l a n e a n d o u t o f t h e s c a t t e r i n g p l a n e . T h e m e a n v a l u e s o f a r e p l o t t e d a s a f u n c t i o n o f t h e c h a r g e d p a r t i c l e t r a n s v e r s e

m o m e n t u m p r

c h a r g e d A s P„ c h a r g e d

r e a c h e s a b o u t 1 . 5 G e V / c t h e m e a n v a l u e s

o f J _ Q a n d J L , r e a c h a l i m i t i n g v a l u e , ( F i g . 1 0 ) , a g a i n i n d i c a t i n g t h e j e t 10 l<p

- 2 8 6 -

0.6

0.5

0.4

-V 0.3

0 2

0.1

Real o Random (measure of apparatus acceptance)

M* 1

_] I 1 L_ _L I I L_

0.6

0.5

0.4.ÏÏ

0.3-?

0.2

0.1

4 0 1

p Charged | G eV/c)

F i g . 1 0 : < J T Q > , ^T^* D E F I N E D I N

t h e t e x t , a s a f u n c t i o n o f c h a r g e d p a r t i c l e p^, ( R - 1 1 0 ) .

0 . 5

0 . 4

0 . 3

0 . 2

0 . 1

i i r

n 1 1 1 r

J E T 2

J E T 1

_J I 1 I I L_ 10 12 16 18 20

E T (CeV) 22 21 26

F i g . 1 1 : T h e r . m . s . o f t h e a c o p l a -n a r i t y a n g l e , A <j>, b e t w e e n t w o j e t s a s

n a t u r e o f t h e e v e n t s . I n o r d e r t o e n s u r e t h a t t h i s l i m i t e d w a s n o t c a u s e d b y t h e a p p a r a t u s a c c e p t a n c e , t h e d i r e c t i o n o f t h e t r a c k s r e l a t i v e t o t h e j e t w e r e r a n d o m i z e d a n d r e c a l c u l t e d . T h e s e r a n d o m i z e d p o i n t s a r e a l s o s h o w n i n F i g . 10 a n d a r e c l e a r l y h i g h e r t h a n t h e r e a l v a l u e s .

T h e a z i m u t h a l c o r r e l a t i o n s b e t w e e n t h e t w o j e t s w a s s t u d i e d b y f o r m i n g t h e a c o p l a n a r i t y a n g l e A d> = TT — (cjij - <|)2) w h e r e o). = a z i m u t h o f j e t i . T h e r . m . s . w i d t h , A <j> , ( r . m . s . ) o f t h e A a) d i s t r i b u t i o n s i s s e e n ( F i g . 1 1 ) t o d e c r e a s e a s E ^ i n c r e a s e s c o n f i r m i n g t h e b a c k t o b a c k n a t u r e o f t h e t w o j e t s .

F i n a l l y t h e m e a n p ^ o f t h e d i j e t s y s t e m w a s f o u n d t o b e 2 . 9 G e V / c f o r d i j e t i n v a r i a n t m a s s e s o f •v 15 G e V i n c r e a s i n g t o 3 . 9 G e V / c f o r m a s s e s a r o u n d 2 5 G e V . T h e s e v a l u e s h a v e n o t y e t b e e n c o r r e c t e d f o r r e s o l u t i o n a n d a c c e p t a n c e e f f e c t s .

2 . 2 R e s u l t s o f E x p e r i m e n t R . 8 0 7 . T h i s e x p e r i m e n t s t u d i e s t h e

p r o d u c t i o n o f j e t s 3 ' 1 * b y t r i g g e r i n g o n a s i n g l e w a l l h a d r o n i c a n d e l e c t r o m a g n e t i c c a l o r i m e t e r s u b t e n d i n g 2 . 1 s r . . O f f - l i n e a f i d u c i a l v o l u m e o f 1 . 7 s r (AcJ> = ± 36 , A y = ± 0 . 9 3 ) i s d e f i n e d . T h e s i n g l e w a l l E^, s p e c t r a o b t a i n e d a t t w o e n e r g i e s a r e s h o w n i n F i g . 1 2 . T h e

a f u n c t i o n o f E T ( R . 1 1 0 ) j e t c r o s s - s e c t i o n a r e o b t a i n e d f r o m t h e s e s p e c t r a a s f o l l o w s . F o r e v e r y e v e n t t h e n e t m o m e n t u m v e c t o r o f t h e

p a r t i c l e s o b s e r v e d i n t h e c a l o r i m e t e r i s c a l c u l a t e d . L e t . E ' b e a u n i t v e c t o r a l o n g i t s d i r e c t i o n . T h e t h r u s t , T , o f t h e e v e n t i s t h e n c o m p u t e d a c c o r d i n g t o N .

T = Z E 1 ' E . / E . . , i 1 i 1

1 = 1

w h e r e N = n u m b e r o f e n e r g y c l u s t e r s i n t h e e v e n t

E \ = e n e r g y v e c t o r o f c l u s t e r i .

F o r p e n c i l j e t s T = 1 w h e r e a s f o r i s o t r o p i c e v e n t s T = 0 . 8 6 i n t h e R - 8 0 7 d e t e c t o r . F i g . 1 3 .

T h e t h r u s t d i s t r i b u t i o n s f o r s e v e r a l E^, i n t e r v a l s i s s h o w n i n A t / s = 6 3 t h e d i s t r i b u t i o n s t e n d p r o g r e s s i v e l y t o 1 . 0 a s E ^

i n c r e a s e s . T h e e f f e c t i s l e s s o b v i o u s a t / s = 4 5 . T h e e x p e c t e d t h r u s t s h a p e f o r j e t a n d n o n - j e t e v e n t s i s t h e n o b t a i n e d f r o m t h e I S A J E T M o n t e C a r l o p r o g r a m . T h e e x p e r i m e n t a l t h r u s t d i s t r i b u t i o n s a r e t h e n f i t t o a

- 287 -

1 0 - " y

10 i-29

ID

M O -31

10 •33

10 •35

IIIIII 1 1 * / s = 6 3 G e V p o / S = 4 5 G e V

A

: b A l

— a I

i J * 1..

--

— D *

A

- A

_ a A

A

z a A

- * * =- • A

a A

0 A

A

\ • \

—

1 1 1 1 i i i

V Í = 4 5 G e V v £ = 6 3 G e V

0 . 2 -

0.1

8 E j (GeV)

12 16

0

0.2

0.1

0

0.2

0.1

0

0.2

0.1

Fig. 12 : The single wall E^, distributions at /s = 45 and /s = 63 for exp. R-807.

0.7 0.9 1 0 0 7 0 8

THRUST

1 0

Fig. 13 : The thrust distributions in exp. R-807 for severalbands of E T >

ich E and /s. The resulting jet cross-iit of the form A(l-x ) m p " yields

sum of these two expected shapes, yielding a fraction of the events to be attributed to jet production for each E n

sections are shown in Fig. 14. A fi_ ~„ „ , r

A = 1.6 x 1 0 ~ 2 6 , m = 10.6 ± 1.0 and n = 5.3 ± 0.2. The Táata> multiplied by p,j,5*3 are plotted in Fig. 15 together with recent data on jet production 5

from the p p collider (/s = 540 GeV). Finally the value of n obtained at different x T.(=2 p^/Zs) for single TT , IT production 6 and single IT 0

production 7 ) i s compared in Fig. 16 to the value obtained by R-807 for jets. Whereas for low x^, n for single particles is about 8.0, for x > 0.25 it drops to about 5.0 in very good agreement with the value obtained for jets by R-807.

In conclusion no differences have been observed between p p and p p collisions up to E^ ^ 12 GeV or single particle p ^ 6 GeV/c. In p p collisions events with E > GeV are predominatly due to two jets at /s = 63 GeV. A measure of the jet cross-section at /s = 45 and /s = 63 GeV yields a p T dependence of the form (1 - x T> p T

n with n = 5.3 ± 0.2 in agreement with the value of n obtained from single particle production at x m > 0.25.

- 2 8 8 -

10 1-31 : 1

10 -32

7 10 > cu

CM E

i-33

10 ,-34

10 -35

• 1

/ s = 63 G e V / s = 4 5 G e V I S A J E T

10 PT ( G e V / c )

12 14

10

10

,-2<.

•25

1 0 - 2 6 | T I

:10 ,-27 _

o

•vio

lo

-28

•29

D / S

5 4 0 G e V (pp) 63 G e V 4 5 G e V

0.2 0.4 0.6 0.8

F i g . 14 : T h e i n c l u s i v e j e t c r o s s -s e c t i o n s f o r / s = 45 a n d 6 3 ( R - 8 0 7 ) .

F i g . 15 : T h e i n c l u s i v e c r o s s -s e c t i o n m u l t i p l i e d b y p T

5 , 3 a s a f u n c t i o n o f x ( R - 8 0 7 ) .

S i n g l e p a r t i c l e o n*|

R - 4 1 6 • n » R-108

J E T 2 Z . R - 8 0 7

^22ZZÉTZZZ$ZZZ ÎÇBTÏÏZQPMTYZZNL

0.1 0.2 0.3

X T = 2 p T / / s

0.4 0.5

F i g . 16 : T h e e x p o n e n t n ( d e f i n e d i n t h e t e x t ) o b t a i n e d f r o m s i n g l e p a r t i c l e c r o s s - s e c t i o n s a n d j e t c r o s s -s e c t i o n s a s a f u n c t i o n o f x m .

- 2 8 9 -

R E F E R E N C E S

1 ) T . Skesson e t a l . , C E R N E P / 8 2 - 2 0 9 . S u b m i t t e d t o P h y s i c s L e t t e r s B .

2 ) A . L . S . A n g e l i s e t a l . , P h y s . L e t t 1 1 8 B ( 1 9 8 2 ) 2 1 7 .

3 ) T . Xkesson e t a l . , P h y s . L e t t . 1 1 8 B ( 1 9 8 2 ) 1 8 5 . T . Xkesson e t a l . , P h y s . L e t t . 1 1 8 B ( 1 9 8 2 ) 1 9 3 .

4 ) T . Skesson e t a l . , C E R N E P / 8 3 - 0 1 . T o b e p u b l i s h e d i n P h y s . L e t t e r s B .

5 ) M . B a n n e r e t a l . , P h y s . L e t t . 1 1 8 B ( 1 9 8 2 ) 2 0 3 .

6 ) R e s u l t s o f e x p . R - 4 1 6 a t t h e I S R r e p o r t e d a t t h e 2 1 s t I n t e r n a t i o n a l C o n f e r e n c e o n H i g h E n e r g y P h y s i c s , P a r i s , J u l y 1 9 8 2 .

7 ) A . L . S . A n g e l i s e t a l . , P h y s . L e t t . 7 9 B ( 1 9 7 8 ) 5 0 5 .

- 293 -

SMALL ANGLE ELASTIC SCATTERING AT THE CERN PROTON-ANTIPROTON COLLIDER

Aachen 1-Annecy (LAPP) 2-Birmingham 3-CERN^-Helsinki 5-QMC, London 6-Paris (Coll. de France) 7-Riverside 8-Roma 9-Rutherford Appleton L a b . 1 0 -

Saclay ( C E N ) 1 1 - Vienna 1 2 Collaboration

U A 1 Collaboration

Presented by F. Ceradini

1 0 1 0 2 9 * * * G. Arnison , A. Astbury , B. Aubert , C. Bacci , G. Bauer , A. Bézaguet ,

tt H t , g t %

R. Böck , R. Bossart , J. Bosser , T.J.V. Bowcock , M. Calvetti , T. Carroll , P. Catz , P. Cennini , S. Centro , F. Ceradini , S. Cittolin , D. Cline ,

1 1 2 3 1 2 1 1 2 C. Cochet , J. Colas , M. Corden , D. Dallman , M. DeBeer , h. Bella Negra ,

H 1 1 H » "» 7 Demoulin , D. Denegri , R. Desalvo , A. Di Ciaccio , D. DiBitonto , L. Dobrzynski

3 3 1 S i l J. Dovvell , M. Edwards , K. Eggert , E. Eisenhandler , N. Ellis , P. Erhara ,

1 7 8 1 2 3 7 H. Faissner , G. Fontaine , R. Frey , R. Frühwirth , J. Garvey , S. Geer ,

7 2 1 S 7 C. Ghesquiere , P. Chez , K.L. Giboni , W.R. Gibson , Y. Giraud-Héraud ,

1 1 2 1 0 8 1 A. Givernaud , A. Gonidec , G. Grayer , P. Gutierrez , T. Hans1-Kozanecka ,

1 0 * 8 i * W.J. Haynes , L.O. Hertzberger , C. Hodges , D. Hoffmann , H. Hoffmann ,

* 3 6 » "» 6 D.J. Holthuizen , R.J. Homer , A. Honma , W. Jank , G. Jorat , P.I.P. Kalmus ,

S 6 3 8 5 H V. Karimäki , R. Keeler , I. Kenyon , A. Kernan , R. Kinnunen , H. Kowalski ,

» t, * ! 1 2 j W. Kozanecki , D. Kryn , F. Lacava , J.-P. Laugier , J.-P. Lees , H. Lehmann ,

1 1 1 2 1 1 1 1 1 1 R. Leuchs , A. Lévêque , D. Linglin , E. Locci , M. Loret , J.-J. Malosse ,

• t t 3 7 2 8 . Markiewicz , G. Maurin , T. McMahon , J.-P. Mendiburu , M.-N. M m a r d , K. Morgan

9 "t "t 1 0 H "t M. Moricca , H. Muirhead , F. Muller , A.K. Nandi , L. Naumann , A. Norton ,

7 9 9 S A. Orkm-Lecourtois , L. Paoluzi , G. Piano Mortari , M. Pimia , •» 1 8 i •> 1 1

A. Placci , E. Radermacher , J. Ransdell , H. Reithler , J.-P. Revol 5 J. Rich , H 1 0 <» •! H II

M. Rijssenbeek , C. Roberts , J. Rohlf , P. Rossi , C. Rubbia , B. Sadoulet , 7 6 9 1 1 1 1 1 1

G. Sajot , G. Salvi , G. Salvini , J. Sass , J. Saudraix , A. Savoy-Navarro , S 1 0 1 0 1 1 1 2 3

D. Schinzel , W. Scott , T.P. Shah , M. Spiro , J. Strauss , K. Sumorok , 1 2 8 H S H 1

F. Szoncso , D. Smith , C. Tao , G. Thompson , J. Timmer , E. Tscheslog , 5 * 7 "I

J. Tuominiemi , J.-P. Vialle , J. Vrana , V. Vuillemin , 1 2 3 3 H 2 H

H.D. Wahl , P. Watkins , J. Wilson , G.Y. Xie , M. Yvert , E. Zurfluh * NIKHEF, Amsterdam, The Netherlands ** University of Wisconsin, Madison, Wisconsin, USA

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P l o t o n - a n t i p r o t o n e l a s t i c s c a t t e r i n g at a c e n t r e of m a s s e n e r g y /s = 540

G e V h a s b e e n s t u d i e d at low m o m e n t u m t r a n s f e r . I h e m e a s u r e d v a l u e oí the

l o g a r i t h m i c s l o p e of the d i f f e r e n t i a l e l a s t i c c r o s s - s e c t i o n , b = T 7 . 1 ± 0 . 9

G e V " 2 for 0 . 0 4 < | t | < 0.16 G e V * , b =• 12.9 ± 0 . 3 G e V ~ 2 for 2

O . i y _< ttl < 0 . 4 2 G e V c o n f i r m s the p r e v i o u s e v i d e n c e f r o m the UA1 a n d

u A 4 c o l l a b o r a t i o n s tor an i n c r e a s e at s m a l l t . A p r e l i m i n a r y e s t i m a t e of t h e

p r o t o n - a n t i p r o t o n total c r o s s - s e c t i o n s h o w s an i n c r e a s e of a b o u t 5 0 % I r o m ISk

to G o l l i a e r e n e r g y .

- 295 -


T H E E X P E R I M E N T A L T E C H N I Q U E

S i n c e the e a r l y o p e r a t i o n of the ISK it w a s s h o w n t h a t to s e l e c t g e n u i n e

• • 5 6 )

p r o t o n - p r o t o n e l a s t i c c o l l i s i o n s ' t h e r e w a s no n e e d for m a g n e t i c 2

a n a l y s i s at s m a l l v a l u e s of t (t < 1 GeV ) and that the c o l l i n e a r i t y

r e q u i r e m e n t of the s c a t t e r e d p r o t o n s w a s s u f f i c i e n t p r o v i d e d t h e a n g u l a r

r e s o l u t i o n w e r e s m a l l ( p A 6 < < a v e r a g e p t o f i n e l a s t i c c o l l i s i o n s ) .

P a r a m e t r i s i n g the d i f f e r e n t i a l c r o s s - s e c t i o n w i t h a s i n g l e e x p o n e n t i a l d a / d t

_ bt - 2 3 1») 2 2 - U a / d t ) 0 e , w i t h b = ( 1 3 - 1 7 ) GeV ' and t = - p 9 ,and r e q u i r i n g

_ 2

i o / o - bAt to b e s m a l l e r t h a n 10% in a n i n t e r v a l At a r o u n d t ^ 0 . 1 G e V ,

b o u n d s the a n g l e r e s o l u t i o n to b e A6 = At/2p/-t < 0 . 0 5 m r a d for 9 ^ 1 m r a d .

The s c a t t e r i n g a n g l e 6 w a s m e a s u r e d by the d i s p l a c e m e n t , d , o n a p l a n e

at d i s t a n c e L f r o m the c r o s s i n g p o i n t . T o a v o i d the b e a m h a l o t h e m i n i m u m

v a l u e of d w a s a b o u t 15 m m . T h i s i m p l i e s that the d e t e c t o r s h a d to b e

i n s t a l l e d b e y o n d the S P S q u a d r u p o l e s l o c a t e d at i 15 m f r o m t h e i n t e r a c t i o n

p o i n t . F i g . 1 s h o w s the m a g n e t i c e l e m e n t s in the L o n g S t r a i g h t S e c t i o n 5 o f

the SPS C o l l i d e r w h e r e the U A I e x p e r i m e n t is i n s t a l l e d . T h e e l a s t i c s c a t t e r i n g

d e t e c t o r s c o n s i s t of e i g h t i d e n t i c a l h i g h p r e c i s i o n t e l e s c o p e s p l a c e d in

m o v a b l e s e c t i o n s of the S P S v a c u u m p i p e c a l l e d " r o m a n p o t s " f r o m the C E R N - R o m a

c o l l a b o r a t i o n t h a t p i o n e e r e d this t e c h n i q u e at the I S R . A f t e r the

i n j e c t i o n a n d a c c e l e r a t i o n the t e l e s c o p e s w e r e m o v e d v e r t i c a l l y to w i t h i n o n e

c m of the c o a s t i n g b e a m s . F o u r t e l e s c o p e s w e r e i n s t a l l e d a f t e r the f i r s t

d o u b l e t o f v e r t i c a l l y f o c u s i n g q u a d r u p o l e s at a d i s t a n c e of 22 m f r o m t h e

c r o s s i n g p o i n t a n d four t e l e s c o p e s a f t e r the s e c o n d d o u b l e t of v e r t i c a l l y

T h e s u c c e s s f u l o p e r a t i o n of the C E R N SPS C o l l i d e r ' , w h e r e p r o t o n s

a n d a n t i p r o t o n s c o l l i d e at c e n t r e of m a s s e n e r g y of 5 4 0 GeV c o r r e s p o n d i n g to a

l a b o r a t o r y m o m e n t u m of 155 T e V / c , has o p e n e d a n e w f r o n t i e r in the s t u d y of

h a d r o n i c c o l l e c t i v e p h e n o m e n a s u c h as h a d r o n - h a d r o n e l a s t i c s c a t t e r i n g and

t o t a l c r o s s - s e c t i o n w h e r e the e s t a b l i s h m e n t of a n a s y m p t o t i c r e g i m e c a n p r o b e

f u n d a m e n t a l a s s u m p t i o n s of q u a n t u m f i e l d t h e o r y . a •»)

R e s u l t s o n the p r o t o n - a n t i p r o t o n e l a s t i c d i f f e r e n t i a l c r o s s - s e c t i o n ' 3)

and total c r o s s - s e c t i o n f r o m a n e a r l y t e s t r u n in 1981 h a v e b e e n p u b l i s h e d .

Ive r e p o r t h e r e o n the t o d a y s t a t u s of the a n a l y s i s of the d i f f e r e n t i a l e l a s t i c 2

c r o s s - s e c t i o n in the m o m e n t u m t r a n s f e r r a n g e 0.04 _< |t| _< 0.42 G e V . T h e

d a t a w e r e c o l l e c t e d d u r i n g two s h o r t r u n s in O c t o b e r a n d N o v e m b e r 1 9 8 2 .

1 2)

- 296 -

defocusing quadrupoles at 43 m. Each telescope consists ol a trigger scintillator and a high resolution

driit chamber. The chambers (fig. 2) are maae of four planes ot wires, the drift cells being staggered to resolve the intrinsic ambiguity and to provide enough constraints to precisely calibrate the relevant parameters trom the tracks themselves, four space points were recorded per track by measuring the dritt time, vertical projection, and the charge division along the wires, horizontal projection. In addition to the trigger scintillators, two vertical finger counters, 2 mm wide and 20 mm apart, were used to calibrate the charge division coordinate. The readout electronics can record up to 16 hits per wire as close as 40 ns in time allowing a clean separation between multiple tracks and delta rays. rihe r.m.s. single wire resolution in the dritt time and charge division projection, as obtained from the actual elastic data, was 0.12 mm and 2.4 mm respectively. The position ot the chambers relative to the beam axis was known within 0.1 mm. The resolution in t was kept smaller than 0.01

2

GeV corresponding to a transverse momentum ot 15 MeV/c for elastic scattered particles.

The angular resolution of the telescopes was smaller than the smearing introduced by the natural spread of the beams due to the beam size, a, and the beam divergence, a', at the crossing point, a = l/2/eß, a" = 1/2 /e/3 where e is the beam emittance and 3 is the amplitude of the betatron function.

The elastic trigger was a coincidence up(.p.)*down(p.) or down(p)*up(p) gated by the beam-beam crossing signal. Events triggereü by coincidences up-up or down-down were also recorded for background evaluations.

DATA COLLECTION AND ANALYSIS The acceptance of the telescopes tor elastic scattering events depends on

the optics of the magnetic elements of the machine. Data have been collected during two short runs with the Collider operated in two different focusing schemes : high beta, 3^= 3^= 100 m, and intermediate beta, $ H = 7m, 3 = 3.5 m. The effect of the quadrupole field on elastic scattered

V . . eff particles can be expressed in terms of an effective distance, L , in the horizontal and vertical plane. A particle scattered at projected angles

6 , 6 , will hit the detector with displacements relative to the beam - V eff eff axis a = h 6,,, d = L 6 . Fig. 3 shows the vertical n H h ' v v v

effective distance and the beam size along the beam axis for the two different beta schemes. During data taking the bottom of the roman pots was positioned

- 297 -

at a distance d v <\, 12 a y from the beam. The minimum angle is thus determined by the beam size at the position of the roman pots while the maximum angle is determined by the aperture of the beam pipe. The telescopes in the outer roman pots, located at 43 m, were used during the high beta run, while those in the inner roman pots, located at 22 m, were used during the intermediate beta run. The relevant beam parameters and the corresponsing explored t regions are listed in Table 1.

Events selected by the elastic trigger were accepted if at least three points and not more than eight points were measured in each chamber. This requirement eliminates most of the random coincidences from beam-gas or beam-vacuum pipe interactions and beam-beam inelastic collisions. For the candidate elastic events the scattering angle is defined as :

d + d _ , , Telf „ , , eff vp vp 6 = d / L ; 6 - = d _/L _ ; 6 = — " h vp vp vp vp vp vp v err err

L v p + Lvp

(the same lor the horizontal projection)

/ 2 2 1/2 8 = ( 6 v + Qli ' » = a t S < V e v

Fig. 4 shows the difference 6 p - 6 in the drift time projection (vertical plane) and in the charge division projection (horizontal plane) for the high beta run. The r.m.s. width of the distributions is 0.04 mrad and 0.08 mrad respectively. The beam size and angular divergence at the crossing point account tor the width in the vertical plane while the resolution of the charge division coordinate accounts lor half the effect in the horizontal plane. The width of the collinearity distributions tor the intermediate beta run is larger, a(A6 v) = 0.12 mrad, a(A9 H) = 0.11 mrad, due to the wider angular spread of the beams. In both cases the distributions show that the level of background due to inelastic events is very small. Events are then

o selected requiring |<p| < 30 in order to reduce the error introduced by the charge division coordinate measurement and that A6 = I 8 - 0 - I < 4

v vp vp — standard deviations.

A displacement of the beam from the axis of the telescopes would result in a non-zero mean value of the collinearity distribution. The offset should be equal for the up-down and down-up telescopes. A tilt of the beam in the vertical plane would result in a different number of elastic events recorded in the two telescopes and would affect the t distribution. In fact a small tilt was observed in the intermediate beta run. In this case the data

- 298 -

w e r e c o r r e c t e d l e a v i n g the a n g l e b e t w e e n the b e a m and the t e l e s c o p e s as a t r e e

p a r a m e t e r a n d r e q u i r i n g the n u m b e r of r e c o r d e d e v e n t s to b e e q u a l in e v e r y t

b i n . T h e t i l t a n g l e w a s 0 . 0 2 4 m r a d .

T h e s e l e c t e d e l a s t i c e v e n t s a r e t h e n c o r r e c t e d tor the e f f i c i e n c y of the

d e t e c t o r s a n d s e l e c t i o n c u t s a n d for b a c k g r o u n d of i n e l a s t i c e v e n t s . T h i s is

e v a l u a t e d f r o m the c o l l i n e a r i t y d i s t r i b u t i o n s a n d by u s i n g the c o m p l e m e n t a r y

i n f o r m a t i o n f r o m the i n e l a s t i c t r i g g e r . In e v e n t s w i t h two t r a c k s r e c o r d e d i n o

t h e u p - u p or d o w n - d o w n t e l e s c o p e s , one of the track is r e f l e c t e d by 180

in the a z i m u t h a l a n g l e <p a n d a n a l y s e d like if it w e r e a n e l a s t i c c a n d i d a t e

e v e n t , h o t h the e f t i c i e n c y a n a b a c k g r o u n d c o r r e c t i o n s are s m a l l (<v, 5 % ) , they

t e n d to c a n c e l e a c h o t h e r a n d a r e i n d e p e n d e n t of t.

To e v a l u a t e the a c c e p t a n c e of the t e l e s c o p e s , e l a s t i c e v e n t s a r e g e n e r a t e d

w i t h a flat d i s t r i b u t i o n in <p a n d a n e x p o n e n t i a l d i s t r i b u t i o n in t u s i n g for

the s l o p e p a r a m e t e r , b, the v a l u e o b t a i n e d from the e x p e r i m e n t a l s p e c t r u m .

P a r t i c l e s a r e t h e n traced d o w n to the t e l e s c o p e s w i t h the b e a m t r a n s p o r t

m a t r i c e s and s m e a r i n g e f f e c t s d u e to the c h a m b e r r e s o l u t i o n a n d b e a m s p r e a d

a r e i n t r o d u c e d . T h e final d a t a s a m p l e is a n a l y s e d o n l y in the r e g i o n of full

a c c e p t a n c e in <p a n d t. F i g . 5 s h o w s the e x p e r i m e n t a l a n d M o n t e C a r l o d a t a o

for the h i g h b e t a run a f t e r a cut I cpl _< 26 h a s b e e n a p p l i e d to

e l i m i n a t e s h a d o w i n g e f f e c t s of the b e a m p i p e p r o f i l e in the q u a d r u p o l e s .

In T a b l e II is l i s t e d the n u m b e r of e v e n t s u s e d in the a n a l y s i s a n d F i g s .

6 a n d 7 s h o w the t s p e c t r u m of t h e s e l e c t e d e l a s t i c s c a t t e r i n g e v e n t s for the

h i g h b e t a a n d i n t e r m e d i a t e b e t a r u n . F i t t i n g the e x p e r i m e n t a l d i s t r i b u t i o n

w i t h a n e x p o n e n t i a l , the v a l u e for t h e s l o p e p a r a m e t e r is :

b = 17.1 ± 0 . 9 G e V - 2

x * = 8.4 tor 12 d . o . t . 0.04 < |t| < 0.18 G e V 2

b = 12.9 ± 0.3 G e V " 2 / = 2 3 . 1 for 21 d . o . f . 0.19 < | t | <0.42 G e V 2

w h e r e the e r r o r is s t a t i s t i c a l o n l y . S y s t e m a t i c u n c e r t a i n t i e s in the m a c h i n e

p a r a m e t e r s a n d in the t e l e s c o p e s g e o m e t r y w o u l d r e s u l t in a n e r r o r of 0.2

- 2

G e V in the e v a l u a t i o n of the s l o p e p a r a m e t e r . W e n o t e t h a t the v a l u e s

m e a s u r e d in the two t r e g i o n s a r e in g o o d a g r e e m e n t w i t h the p r e v i o u s r e s u l t s

at the C o l l i d e r ' '.

T o c o n v e r t the c o u n t i n g r a t e c o r r e c t e d for e f f i c i e n c y , b a c k g r o u n d and

a c c e p t a n c e into a d i f f e r e n t i a l c r o s s - s e c t i o n w e r e f e r to the l u m i n o s i t y

c a l c u l a t e d f r o m the b e a m c u r r e n t s a n d the b e a m p r o f i l e s at the c r o s s i n g p o i n t .

T h e b e a m p r o f i l e s w e r e m e a s u r e d by the S P S m a c h i n e g r o u p in the h o r i z o n t a l a n d

- 299 -

T O T

( l/nc) 1 6 n

1 + P 2

r d ° h L ] ) 1 / 2

l d t J t = 0 j

w h e r e p is the r a t i o of the real to i m a g i n a r y p a r t of the s c a t t e r i n g

a m p l i t u d e at t = 0. F r o m m e a s u r e m e n t s a t low e n e r g y u p to the I S R r e g i o n a n d

d i s p e r s i o n r e l a t i o n s we e x p e c t the c o n t r i b u t i o n of the real p a r t to b e s m a l l , 9 )

p = 0.1 - 0.2 , at C o l l i d e r e n e r g y .

E x t r a p o l a t i n g the d i f f e r e n t i a l e l a s t i c c r o s s - s e c t i o n to t = 0 w i t h the 2

s l o p e p a r a m e t e r m e a s u r e d m the low t r e g i o n , b = 17.1 ± 0.9 G e V > w e

o b t a i n for the e l a s t i c a n d t o t a l c r o s s - s e c t i o n s the v a l u e s l i s t e d i n T a b l e III

w h e r e in the s e c o n d and t h i r d c o l u m n the d a t a are n o r m a l i z e d to the l u m i n o s i t y

as m e a s u r e d d u r i n g the h i g h b e t a a n d i n t e r m e d i a t e b e t a r u n r e s p e c t i v e l y . T h e

s y s t e m a t i c e r r o r o n and o n the r a t i o s o E L / o T 0 T > b / a 1 0 T is

± 1 5 % .


T h e e l a s t i c d i f f e r e n t i a l c r o s s - s e c t i o n h a s b e e n s t u d i e d at the 2

p r o t o n - a n t i p r o t o n SPS C o l l i d e r i n the t r e g i o n 0.04 < |t| < 0.42 G e V .

F r o m a p r e l i m i n a r y a n a l y s i s of the d a t a t h e m e a s u r e d v a l u e of the l o g a r i t h m i c

s l o p e c o n f i r m s the r e s u l t s of the 1981 t e s t r u n ' . In the r e g i o n of t > 0.2

v e r t i c a l p l a n e s in two d i f f é r e n t p o i n t s of the m a c h i n e w i t h the w i r e s c a n

t e c h n i q u e a n d t r a c e d to the UA1 i n t e r a c t i o n r e g i o n u s i n g the b e a m

e m i t t a n c e s a n d b e t a f u n c t i o n s . T h i s m e t h o d g a v e r e p r o d u c i b l e r e s u l t s w i t h a

s y s t e m a t i c u n c e r t a i n t y of ± 2 0 % d u r i n g the i n t e r m e d i a t e b e t a r u n in O c t o b e r

1982 w h i l e the m e a s u r e m e n t w a s a f f e c t e d by l a r g e r e r r o r s d u r i n g the v e r y s h o r t

h i g h b e t a r u n in N o v e m b e r 1 9 8 2 . In t h i s s e c o n d r u n an e s t i m a t e of the

»)

l u m i n o s i t y f r o m the UA1 p r e t r i g g e r h o d o s c o p e s c o u n t i n g rate w a s n o t

fully r e l i a b l e since the r a t i o of r a n d o m b e a m - g a s to b e a m - b e a m c o l l i s i o n

c o i n c i d e n c e s w a s m u c h h i g h e r in the h i g h b e t a s c h e m e .

I n F i g . 8 the e l a s t i c d i f f e r e n t i a l c r o s s - s e c t i o n d a / d t = ( d N / d t ) / / L d t i m e is

p l o t t e d a s a f u n c t i o n of t s h o w i n g a 3 0 % d i s c r e p a n c y b e t w e e n the two s e t s of

d a t a d u e to the a b s o l u t e n o r m a l i s a t i o n . F i g . 9 s h o w s the t s p e c t r u m o b t a i n e d

r e q u i r i n g the same n u m b e r of e v e n t s tor t = 0.18 GeV .

A n e s t i m a t e ot the t o t a l p r o t o n - a n t i p r o t o n c r o s s - s e c t i o n c a n b e o b t a i n e d

u s i n g the o p t i c a l t h e o r e m w h i c h r e l a t e s the i m a g i n a r y p a r t of the f o r w a r d

s c a t t e r i n g a m p l i t u d e to the t o t a l c r o s s - s e c t i o n :

- 3 0 0 -

2 G e V t h e r e s u l t s a r e f u l l y c o n s i s t e n t w i t h e x t r a p o l a t i o n o f l o w e r e n e r g y

p r o t o n - p r o t o n a n d p r o t o n - a n t i p r o t o n d a t a w i t h a n a s y m p t o t i c b e h a v i o u r o f t h e 1 0 ) 2

l o g a r i t h m i c s l o p e a s to s . I n t h e l o w t r e g i o n , t < 0 . 1 G e V , i i)

r e c e n t p r o t o n - a n t i p r o t o n d a t a a r e a v a i l a b l e a t I S R e n e r g y , w h i c h

c o m b i n e d w i t h l o w e r e n e r g y d a t a a n d t h e C o l l i d e r r e s u l t s s h o w e v i d e n c e f o r a

f a s t e r s h r i n k a g e o f t h e d i f f r a c t i v e c o n e a t l o w t w h e r e e v e n t u a l l y a t e r m i n 2 1 2 )

In s s e t s i n b e c o m i n g d o m i n a n t i n t h e a s y m p t o t i c r e g i o n .

E x t r a p o l a t i n g t h e d i f f e r e n t i a l e l a s t i c c r o s s - s e c t i o n a t t = 0 t h e t o t a l

c r o s s - s e c t i o n i s d e r i v e d f r o m t h e o p t i c a l t h e o r e m . E v e n t h o u g h t h e e r r o r i s

l a r g e , t h e p r e s e n t r e s u l t s h o w s a n i n c r e a s e o f t h e t o t a l p r o t o n - a n t i p r o t o n

c r o s s - s e c t i o n o f a b o u t 50% f r o m I S R t o C o l l i d e r e n e r g y .

- 301 -

REFERENCES

1 ) C . R u b b i a , P . M c l n t y r e a n d D . C l i n e : P r o c . I n t e r n . N e u t r i n o C o n f e r e n c e ,

A a c h e n 1 9 7 6 , p . 6 8 3 .

2 ) T h e S t a f f o f t h e CERN P r o t o n - A n t i p r o t o n P r o j e c t : P h y s . L e t t . 1 0 7 B , 3 0 6

( 1 9 8 1 ) .

3 ) R. B a t t i s t o n e t a l . , P h y s . L e t t . 1 1 7 B , 1 2 6 ( 1 9 8 2 ) .

4 ) G . A r n i s o n e t a l . , P h y s . L e t t . 1 2 1 B , 7 7 ( 1 9 8 3 ) .

5 ) U. A m a l d i e t a l . , P h y s . L e t t . 3 6 B , 5 0 4 ( 1 9 7 1 ) .

U. A m a l d i e t a l . , P h y s . L e t t . 4 3 B , 2 3 1 ( 1 9 7 3 ) .

6 ) G . B a r b i e l l i n i e t a l . , P h y s . L e t t . 3 9 B , 6 6 3 ( 1 9 7 2 ) .

7 ) A . B a r i s y e t a l . , " A T r a n s v e r s e Beam P r o f i l e M o n i t o r f o r p p S t u d i e s " , S P S / A C / L E / I m p .

R e p . 1 7 3 ( M a r c h 1 9 8 0 ) .

8 ) F o r a d e s c r i p t i o n o f t h e UA1 d e t e c t o r s e e : M. C a l v e t t i , c o n t r i b u t i o n t o t h i s

W o r k s h o p .

9 ) II. Amaldi e t a l . , P h y s . L e t t . 6 6 B , 3 9 0 ( 1 9 7 7 ) .

M.M. B l o c k a n d R . N . C a h n , P h y s . L e t t . 1 2 0 B , 2 2 4 ( 1 9 8 3 ) .

1 0 ) J . P . B u r q e t al., P h y s . L e t t . 1 0 9 b , 1 2 4 ( 1 9 8 2 ) .

1 1 ) M. A m b r o s i o e t a l . , P h y s . L e t t 1 1 5 B , 4 9 5 ( 1 9 8 2 ) .

N. Amos e t a l . , P h y s . L e t t . 1 2 0 B , 4 6 0 ( 1 9 8 3 ) .

1 2 ) M.M. B l o c k a n d R . N . C a b n , P h y s . L e t t . 1 2 0 B , 2 2 9 ( 1 9 8 3 ) .

- 3 0 2 -

T A B L E 1

B e a m s i z e a n d a n g u l a r d i v e r g e n c e o f t h e p r o t o n a n d a n t i p r o t o n b u n c h e s a t t h e

c r o s s i n g p o i n t . E f f e c t i v e d i s t a n c e o f t h e e l a s t i c t e l e s c o p e a n d e x p l o r e d t r a n g e

H i g h b e t a I n t e r m e d i a t e b e t a

P P P P

a v (mm) 1 . 1 1 . 7 0 . 1 8 0 . 2 7

o ' v ( m r a d ) 0 . 0 1 1 0 . 0 1 7 0 . 0 5 2 0 . 0 7 6

o"H (mm) 1 . 2 1 . 8 0 . 2 6 0 . 3 9

c ' y ( m r a d ) 0 . 0 1 2 0 . 0 1 8 0 . 0 3 7 0 . 0 5 6

o u t e r r o m a n p o t s i n n e r r o m a n p o t s

L v U ) 4 4 . 5 1 4 . 2

T e f f i . L

H ( m ) 3 5 . 6 3 0 . 9

2 t r a n g e ( G e V ) 0 . 0 4 - 0 . 1 8 0 . 1 9 - 0 . 4 2

- 303 -

TABLE I I

Number of e v e n t s u sed i n t h e a n a l y s i s . The i n t e r m e d i a t e b e t a run sample

i s a b o u t 50% of t h e a v a i l a b l e d a t a

High b e t a r u n I n t e r m e d i a t e b e t a run

r u n l e n g t h ( h r ) 4 . 5 10 .7

a v e r a g e l u m i n s i t y _ 2 _ 1

(.cm s ) 2 5

2 . 5 x 10 2 7

1.5 x 10

e l a s t i c t r i g g e r 9025 59680

number of e v e n t s a f t e r

t r a c k s e l e c t i o n and

c o l l i n e a r i t y r e q u i r e m e n t 1342 7099

number of e v e n t s i n t h e

f u l l <p and t a c c e p t a n c e 929 5647

TABLE I I I

E l a s t i c and t o t a l p r o t o n - a n t i p r o t o n c r o s s - s e c t i o n

N o r m a l i s a t i o n High b e t a run l u m i n o s i t y I n t e r m e d i a t e b e t a r u n l u m i n o s i t y

76 64

17 12

0 . 2 3 0 .19

0 .22 0 .27

°TOT ^ m b '

°EL ( m b )

a E L / o T 0 T

b / a T Ü T

(GeV~ 2

m b ~ *)

- 304 -

F i g u r e C a p t i o n s

F i g . 1. L a y o u t of the UAl e x p e r i m e n t i n the L o n g S t r a i g h t S e c t i o n 5 of the SPS C o l l i d e r

1. M a i n D i p o l e M a g n e t ; 2. C o m p e n s a t o r d i p o l e s ; 3. V e r t i c a l l y f o c u s i n g

q u a d r u p o l e s ; 4. V e r t i c a l l y d e f o c u s i n g q u a d r u p o l e s ; 5. R o m a n p o t s .

F i g . 2. V i e w ot the d r i f t c h a m b e r s i n s t a l l e d in the r o m a n p o t s .

F i g . 3. V e r t i c a l e f f e c t i v e d i s t a n c e a n d b e a m size (full line : p r o t o n s , d a s h e d line :

a n t i p r o t o n s ) a l o n g the b e a m a x i s ; a) for the h i g h b e t a s c h e m e , b) for the

i n t e r m e d i a t e b e t a s c h e m e .

F i g . 4 . C o l l i n e a r i t y d i s t r i b u t i o n for c a n d i d a t e e l e c t r o n s c a t t e r e d e v e n t s ; a) v e r t i c a l

p l a n e , b) h o r i z o n t a l p l a n e .

F i g . 5. C o m p a r i s o n of the e x p e r i m e n t a l a n d M o n t e C a r l o t d i s t r i b u t i o n for e l a s t i c

s c a t t e r i n g e v e n t s for the u p - d o w n a n d d o w n - u p t e l e s c o p e s .

F i g . 6. t d i s t r i b u t i o n for e l a s t i c s c a t t e r i n g e v e n t s , h i g h b e t a r u n .

f i g . 7. t d i s t r i b u t i o n tor e l a s t i c s c a t t e r i n g e v e n t s , i n t e r m e d i a t e b e t a r u n .

F i g . 8. E l a s t i c d i f f e r e n t i a l c r o s s - s e c t i o n .

F i g . 9. t d i s t r i b u t i o n for e l a s t i c s c a t t e r i n g e v e n t s . T h e t w o s e t s of d a t a a r e

n o r m a l i z e d r e q u i r i n g the s a m e n u m b e r of e v e n t s for t = 0 . 1 8 G e V .

- 3 0 5 -

en

- 3 0 6 -

U A - I l u m i n o s i t y c h a m b e r ( m m u n i t s )

F i g . 2

Y EFFECTIVE LENGTH (M) u ro

. BERM SIZE (M . ). r- ro ro u u> *. O en a en a Ol a m ni m m m PI i PI i

a f O

s 30-

k a ro 3 a ro T 1 r - > — r

o 0 0

- 309 -

DRIFT PLANE

J t t t +

0.4 " 0.6 ©P - O, (mrad)

CURRENT DIVISION PLANE

I I

I I

t i • I

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F i g . 4

r • EXPERIMENT

• MONTE CARLO

J I I L

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0.04 0.08 0.12 0.16 0.2 0.24

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DN-UP

F i g . 5

- 311 -

F i g . 7

NUMBER OF E V E N T S P E R .01 GeV* o o

ro

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00

I - 1

I

- 3 1 3 -

F E R M I L A B p p C O L L I D E R

A l v i n V . T o l l e s t r u p

T h i s i s a r e p o r t o n t h e s t a t u s o f t h e F e r m i l a b p p

c o l l i d e r p r o g r a m . T h e c e n t e r o f m a s s e n e r g y w i l l b e 2 T e V ,

a n d p r e l i m i n a r y r u n n i n g i s b e i n g p l a n n e d f o r m i d 1 9 8 5 . I n

o r d e r f o r t h i s p r o g r a m t o c o m e t o f r u i t i o n , t h r e e c o m p o n e n t s

m u s t b e s u c c e s s f u l l y c o m p l e t e d .

1. T h e E n e r g y S a v e r

2 . p S o u r c e , c o n s i s t i n g o f t w o r i n g s

a . D e b u n c h e r

b . A c c u m u l a t o r

3 . D e t e c t o r s

a . C D F BO

b . DO ( c a l l f o r p r o p o s a l s e a r l y 1 9 8 3 )

T h e o v e r a l l l a y o u t o f t h e p r o j e c t i s s h o w n i n F i g . 1.

I w i l l n o w r e p o r t o n t h e s t a t u s o f e a c h o f t h e i n d i v i d u a l

p i e c e s o f t h e p r o g r a m .

E n e r g y S a v e r

T h e E n e r g y S a v e r i s a n e w 1 T e V r i n g o f s u p e r c o n d u c t i n g

m a g n e t s . T h e s e q u e n c e o f o p e r a t i o n i s a s f o l l o w s :

1. T h e b o o s t e r i n j e c t s i n t o t h e m a i n r i n g a s u s u a l , a n d

t h e m a i n r i n g a c c e l e r a t e s p r o t o n s t o 1 5 0 G e V .

2 . T h e p r o t o n s a r e e x t r a c t e d f r o m t h e m a i n r i n g a n d

i n j e c t e d i n t o t h e T e v a t r o n .

3 . T h e T e v a t r o n a c c e l e r a t e s t h e m i n 20 s e c o n d s t o a b o u t

800 G e V . T h e r e i s a 20 s e c o n d f l a t - t o p a n d a r e t u r n

r a m p o f d u r a t i o n o f 20 s e c o n d s . T h u s , t h e o v e r a l l

- 3 1 4 -

M a g n e t N u m b e r N e e d e d N u m b e r A v a i l a b l e 1 0 / 2 2 / 8 2

D i p o l e s 7 7 4 8 0 2 h a v e b e e n m a d e

66 i n . q u a d s 1 8 0 245

S p e c i a l q u a d s 36

T h e p r e s e n t s t a t u s o f t h e i n s t a l l a t i o n i s a s f o l l o w s :

S e c t o r S t a t u s

A T h r e e - f o u r t h s i n s t a l l e d , p o w e r t e s t s c o m p l e t e d l a s t s u m m e r .

B BO c o l l i d i n g b e a m h a l l b e i n g

i n s t a l l e d .

C M a g n e t s i n p l a c e .

D f E F i n a l l e a k c h e c k .

F I n c o o l d o w n . A v e r y s u c c e s s f u l p o w e r t e s t w a s c o m p l e t e d o n S e c t o r A

m a g n e t s l a s t s u m m e r . T h e s e t e s t s e x e r c i s e d a l l o f t h e

n o r m a l m a c h i n e c o n t r o l s y s t e m s i n o r d e r t o c o o l d o w n t h e

m a g n e t s , p u l s e t h e m , a n d p r o v i d e q u e n c h p r o t e c t i o n . T h e

t e s t w a s e x t r e m e l y s u c c e s s f u l , a n d p r o v i d e d t h e f i r s t

e x p e r i e n c e w i t h a l a r g e s t r i n g o f s u p e r c o n d u c t i n g m a g n e t s .

S o u r c e

F i g . 2 s h o w s a p l a n o f t h e n e w s o u r c e t h a t i s b e i n g

c o n s t r u c t e d a t F e r m i l a b . T h e S o u r c e c o n s i s t s o f t w o

r i n g s : A d e b u n c h e r r i n g a n d a n a c c u m u l a t o r r i n g , b o t h o f

w h i c h o p e r a t e a t a b o u t 8 G e V . B e a m i s e x t r a c t e d f r o m F 1 7

a n d b r o u g h t t o b e a r o n a t a r g e t a s s o o n a s i t i s

s u f f i c i e n t l y c l e a r o f t h e m a i n r i n g t u n n e l . T h e p ' s

c y c l e t i m e i s o n e p e r m i n u t e . E i t h e r a l o n g s p i l l

o n t h e f l a t - t o p o r f a s t e x t r a c t i o n i s b e i n g p l a n n e d .

T h e s t a t u s o f m a g n e t p r o d u c t i o n i s a s f o l l o w s :

- 3 1 5 -

p r o d u c e d a t t h e t a r g e t a r e c o l l e c t e d b y a l i t h i u m l e n s a n d a

t r a n s p o r t s y s t e m a n d i n j e c t e d i n t o t h e d e b u n c h e r r i n g . T h e

d e b u n c h e r r i n g i n t e r c h a n g e s a l a r g e m o m e n t u m s p r e a d o f t h e

a n t i p r o t o n s a n d a s h o r t t i m e s p r e a d f o r a l o n g t i m e s p r e a d

a n d a s m a l l m o m e n t u m s p r e a d . I n a d d i t i o n , t r a n s v e r s e

c o o l i n g i s b e i n g p l a n n e d t o r e d u c e t h e t r a n s v e r s e s i z e o f

t h e b e a m . A f t e r 2 s e c o n d s , t h e p ' s a r e e x t r a c t e d f r o m t h e

d e b u n c h e r a n d i n j e c t e d i n t o t h e a c c u m u l a t o r . T h e

a c c u m u l a t o r u t i l i z e s s t o c h a s t i c s t a c k i n g (à l a V a n d e r M e e r )

a s w e l l a s t r a n s v e r s e c o o l i n g d u r i n g t h e s t a c k i n g p r o c e s s .

T h e d e t a i l s o f t h e s t e p s a r e a s f o l l o w s :

1 2

1 . O n e b a t c h o f 3 x 1 0 p r o t o n s i s a c c e l e r a t e d t h r o u g h

t h e b o o s t e r a n d t h e m a i n r i n g t o 1 2 0 G e V . A t t h i s

p o i n t , t h e r e a r e 8 2 b u n c h e s o f p r o t o n s w h i c h a r e

s e p a r a t e d b y 2 0 n a n o s e c o n d s e a c h .

2 . T h e i n d i v i d u a l b u n c h l e n g t h o f t h e p r o t o n s i s

s h o r t e n e d t o a s i g m a o f . 1 6 n a n o s e c o n d s b y m e a n s o f

R F m a n i p u l a t i o n s .

3 . P r o t o n s a r e e x t r a c t e d f r o m t h e m a i n r i n g a n d

f o c u s s e d t o a s p o t w h o s e s i g m a i s . 0 3 8 c m a t t h e

t a r g e t .

4 . T h e p ' s a r e c o l l e c t e d b y a m e a n s o f a l i t h i u m l e n s

a n d t r a n s p o r t e d t o t h e d e b u n c h e r . T h e e m i t t a n c e o f

t h e b e a m i s 2 0 mm m r i n e a c h p l a n e a n d a A p / p o f 4

p e r c e n t . T h e t o t a l n u m b e r o f p ' s c o l l e c t e d p e r 7 _

p u l s e i s 7 x 1 0 , a n d t h e d e n s i t y o f t h e p ' s i s a b o u t . 2 p e r e l e c t r o n v o l t .

- 316 -

5 . T h e v e r y t i g h t l y b u n c h e d p ' s n e x t u n d e r g o a b u n c h

r o t a t i o n i n t h e d e b u n c h e r . T h e i n i t i a l c o n d i t i o n

a n d t h e c o n d i t i o n s 30 t u r n s l a t e r a r e s h o w n i n

F i g s . 3 a n d 4 . T h e f i n a l m o m e n t u m s p r e a d a c h i e v e d

a f t e r c o m p l e t e r o t a t i o n i s s h o w n i n F i g . 5 . T h e

m o m e n t u m s p r e a d h a s b e e n d e c r e a s e d f r o m 4 p e r c e n t t o

. 2 p e r c e n t . A s a r e s u l t , t h e r e a r e n o w a b o u t 5 p ' s

p e r e l e c t r o n v o l t .

6 . T r a n s v e r s e c o o l i n g i s n o w a p p l i e d i n e a c h d i m e n s i o n

i n o r d e r t o d e c r e a s e t h e t r a n s v e r s e e m i t t a n c e f r o m

20 I T mm mr t o l e s s t h a n 7 T T . T h i s t a k e s a b o u t 2

s e c o n d s . T h e p r o c e s s i s s h o w n i n F i g . 6 .

7 . T h e a n t i p r o t o n s a r e e x t r a c t e d i n t h e d e b u n c h e r a n d

i n j e c t e d i n t o t h e a c c u m u l a t o r . T h e a c c u m u l a t o r u s e s

s t o c h a s t i c s t a c k i n g i n o r d e r t o a c h i e v e a p d e n s i t y

1 0 ^ p e r e l e c t r o n v o l t , s e e F i g . 7 . T h e r e i s a l s o

t r a n s v e r s e c o o l i n g d u r i n g t h e s t a c k i n g p r o c e s s .

8 . F i n a l l y , t h e p ' s a r e e x t r a c t e d f r o m t h e a c c u m u l a t o r ,

i n j e c t e d i n t o t h e m a i n r i n g , a c c e l e r a t e d t o 150 G e V ,

t r a n s f e r r e d t o t h e T e v a t r o n w h e r e t h e y a r e j o i n e d

w i t h t h r e e b u n c h e s o f p r o t o n s , a n d a c c e l e r a t e d t o

f u l l e n e r g y .

T h e d e s i g n l u m i n o s i t y i s 10 , a n d t h e S o u r c e c a n

s u p p l y e n o u g h p ' s t o a c h i e v e t h i s l u m i n o s i t y e v e r y t w o h o u r s

a f t e r a n i n i t i a l f i l l i n g t i m e o f f o u r h o u r s . T h e g o a l s o f

t h e S o u r c e d e s i g n w e r e t o o b t a i n a h i g h l u m i n o s i t y , a s w e l l

a s a h i g h f l u x o f a n t i p r o t o n s . I n o r d e r t o a c h i e v e t h i s

h i g h f l u x , i t w a s n e c e s s a r y t o g o t o a s t o c h a s t i c s t a c k i n g

s y s t e m o p e r a t i n g a t 1 t o 2 G H z . S i n c e t h e s i z e o f t h e

- 3 1 7 -

e l e c t r o d e s a s w e l l a s t h e i r s p a c i n g f r o m t h e b e a m m u s t a l l

b e c o n s i d e r a b l y l e s s t h a n a w a v e l e n g t h , i t w a s n e c e s s a r y t o

r e d u c e t h e t r a n s v e r s e e m i t t a n c e o f t h e beam b e f o r e i n j e c t i o n

i n t o t h e a c c u m u l a t o r . A f t e r a c o n s i d e r a b l e a m o u n t o f s t u d y ,

i t b e c a m e a p p a r e n t t h a t a n a d d i t i o n a l r i n g , t h e d e b u n c h e r

r i n g , w a s t h e m o s t e c o n o m i c a l s o l u t i o n t o a c h i e v e t h e

i n i t i a l momentum c o m p a c t i o n a s w e l l a s r e d u c t i o n o f

t r a n s v e r s e e m i t t a n c e . T h e c o n c e p t o f t w o s e p a r a t e r i n g s i s

b e i n g c o p i e d i n t h e p r o p o s a l f o r t h e new S o u r c e a t CERN.

An i n t e n s i v e R&D p r o g r a m i s b e i n g c a r r i e d o u t i n o r d e r

t o i m p r o v e t h e c o m p o n e n t s t h a t a r e n e c e s s a r y f o r o u r S o u r c e .

F o r i n s t a n c e , i n o r d e r t o o p e r a t e a t t h e h i g h e r f r e q u e n c i e s ,

i t i s n e c e s s a r y t o c o n s t r u c t d e l a y l i n e f i l t e r s f r o m

s u p e r c o n d u c t i n g d e l a y l i n e s . Low n o i s e w i d e b a n d a m p l i f i e r s

a r e p a r t i c u l a r l y a d v a n t a g e o u s f o r t h e t r a n s v e r s e c o o l i n g i n

t h e d e b u n c h e r . C r y o g e n i c a l l y c o o l e d a m p l i f i e r s a r e b e i n g

d e v e l o p e d f o r t h i s p u r p o s e . W i d e b a n d l o o p - c o u p l e r s b e c o m e

i n c r e a s i n g l y d i f f i c u l t t o c o n s t r u c t a s a f r e q u e n c y i s

r a i s e d , a n d a n i n t e n s i v e R&D p r o g r a m i s u n d e r w a y o n t h i s

s u b j e c t . We a r e a l s o i n v e s t i g a t i n g t h e n o n l i n e a r i t i e s

i n h e r e n t i n t r a v e l l i n g w a v e t u b e s s i n c e t h e s e c a u s e u n w a n t e d

h e a t i n g o f t h e b e a m . T h e e f f e c t c a n b e r e d u c e d b y o p e r a t i n g

t h e TWT's a t a s m a l l f r a c t i o n o f t h e i r r a t e d p o w e r .

H o w e v e r , t h i s b e c o m e s a n i m p o r t a n t e c o n o m i c c o n s i d e r a t i o n i n

d e s i g n i n g a h i g h p o w e r c o o l i n g s y s t e m s i n c e t u b e s a r e v e r y

e x p e n s i v e . F i n a l l y , i n t e n s i v e R&D i s u n d e r w a y o n t h e

l i t h i u m l e n s w h i c h c o l l e c t s t h e p ' s f r o m t h e t a r g e t .

- 3 1 8 -

A r o u g h s c h e d u l e f o r t h i s p r o j e c t i s a s f o l l o w s : T h e

S a v e r c o m m i s s i o n i n g w i l l s t a r t i n t h e s p r i n g o f 1 9 8 3 a n d

c o n t i n u e u n t i l t h e f a l l , a t w h i c h p o i n t t h e r e w i l l b e a

f i x e d t a r g e t r u n f o r p h y s i c s t h a t w i l l o c c u p y f r o m t h e f a l l

o f 1 9 8 3 a n d t h e s p r i n g o f 1 9 8 4 . T h e r e w i l l t h e n b e a s h o r t

s h u t d o w n t o f i x t r o u b l e s t h a t h a v e d e v e l o p e d d u r i n g t h i s

r u n n i n g p e r i o d a n d t o i n s t a l l n e w f e a t u r e s a s e x p e r i e n c e

w i l l i n d i c a t e . T h e r e w i l l t h e n b e a n e i g h t m o n t h f u l l

e n e r g y T e V I I r u n f o r f i x e d t a r g e t p h y s i c s . I n m i d - 1 9 8 5 ,

t h e r e w i l l b e a o n e - m o n t h l o n g T e V I S o u r c e a n d d e t e c t o r

r u n , a f t e r w h i c h t h e m a c h i n e w i l l b e s h u t d o w n t o c o n s t r u c t

DO a n d t h e o v e r p a s s a t BO w h i c h c a r r i e s t h e m a i n r i n g b e a m

a r o u n d t h e d e t e c t o r . T h e f i r s t m a j o r p h y s i c s r u n f o r T e V I

w i l l t a k e p l a c e s t a r t i n g i n t h e s u m m e r o f 1 9 8 6 . A t t h i s

p o i n t , I e s t i m a t e t h a t t h e i n t e g r a t e d l u m i n o s i t y a t C E R N 3 6

w i l l b e a f e w t i m e s 10 .

D e t e c t o r

T h e c o l l i d e r p r o g r a m c a l l s f o r t w o e x p e r i m e n t a l h a l l s .

O n e a t B O , w h i c h i s a t t h e p r e s e n t u n d e r c o n s t r u c t i o n , a n d a

s e c o n d a t D O , w h i c h w i l l b e b u i l t l a t e r . A b y p a s s t o s h u n t

t h e m a i n r i n g b e a m o v e r t h e d e t e c t o r a t BO i s b e i n g p l a n n e d .

A t p r e s e n t , BO i s u n d e r c o n s t r u c t i o n a n d i s e v e n s o m e w h a t

a h e a d o f s c h e d u l e . A l l o f t h e c o n c r e t e w o r k f o r t h e

a s s e m b l y h a l l s a n d t h e c o l l i s i o n h a l l h a v e b e e n c o m p l e t e d ,

a n d t h e a b o v e g r o u n d b u i l d i n g i s u n d e r c o n s t r u c t i o n . We

h a v e b e e n f o r t u n a t e i n h a v i n g a m i l d w i n t e r a t F e r m i l a b , a n d

t h e c o n t r a c t o r h a s m a d e o p t i m u m u s e o f t h i s o p p o r t u n i t y .

F i g s . 8 a n d 9 s h o w t h e c o l l i s i o n a n d t h e a s s e m b l y h a l l . T h e

- 3 1 9 -

l e n g t h a l o n g t h e b e a m i s g r e a t e r t h a n a v a i l a b l e a t C E R N d u e

t o t h e h i g h e r c o l l i s i o n e n e r g i e s t h a t w e a n t i c i p a t e .

P r o p o s a l s f o r t h e DO c o l l i s i o n a r e a w i l l b e c o n s i d e r e d

i n t h e s p r i n g o f 1 9 8 3 . T h e d e s i g n o f t h e c o l l i s i o n h a l l

w i l l b e d e p e n d e n t o n t h e p r o p o s a l s t h a t a r e a c c e p t e d .

H e n c e , i n t h e r e s t o f t h i s t a l k , I w i l l c o n c e n t r a t e o n t h e

d e t e c t o r t h a t i s b e i n g c o n s t r u c t e d f o r t h e BO h a l l .

T h e D e s i g n R e p o r t w a s c o m p l e t e d A u g u s t 1 9 8 1 . T h e

m e m b e r s o f t h e c o l l a b o r a t i o n a t t h a t p o i n t a r e s h o w n i n

F i g . 1 0 . S i n c e t h e D e s i g n R e p o r t w a s c o m p l e t e d , t h r e e n e w

i n s t i t u t i o n s h a v e j o i n e d t h e c o l l a b o r a t i o n i n J u n e 1 9 8 2 .

T h e d e s i g n g o a l w a s t o c o n s t r u c t a d e t e c t o r t h a t w o u l d

d o t h e p h y s i c s o f q u a r k s , g l u o n s , a n d l e p t o n s o v e r t h e

l a r g e s t p o s s i b l e p a r t o f t h e r a p i d i t y r a n g e . T h i s r e q u i r e d

h i g h g r a n u l a r i t y w i t h t h e e l e c t r o m a g n e t i c a n d h a d r o n

c a l o r i m e t r y w h i c h i s a l l i n t h e f o r m o f t o w e r s t h a t p r o j e c t

b a c k t o w a r d t h e c o l l i s i o n p o i n t . T h e c e n t r a l

e l e c t r o m a g n e t i c a n d h a d r o n c a l o r i m e t r y i s d o n e b y m e a n s o f

s c i n t i l l a t i o n p l a s t i c w h e r e a s t h e r e s t o f t h e c a l o r i m e t r y i s

b y m e a n s o f p r o p o r t i o n a l t u b e s . C h a r g e d p a r t i c l e t r a c k i n g

i s p r o v i d e d b e t w e e n 2 ° a n d 1 7 8 ° , a n d p r e c i s i o n m o m e n t u m

m e a s u r e m e n t i s p r o v i d e d i n t h e c e n t r a l r e g i o n b y m e a n s o f a

3 m e t e r d i a m e t e r x 5 m e t e r l o n g s u p e r c o n d u c t i n g s o l e n o i d

o p e r a t i n g a t 1 . 5 T e s l a . I n a d d i t i o n , t h e r e a r e t o r o i d s i n

t h e f o r w a r d a n d b a c k w a r d d i r e c t i o n f o r t h e m e a s u r e m e n t o f

m u o n m o m e n t u m . F i g . 11 s h o w s t h e o v e r a l l r e s o l u t i o n o f t h e

c a l o r i m e t r y . T h e s q u a r e s a r e t h e i n d i v i d u a l c e l l s , a n d t h e

d o t t e d e l l i p s e s a r e t h e s i z e o f a t y p i c a l Q C D j e t .

- 320 -

T h e f o l l o w i n g F i g s . 1 2 - 1 6 c o m p a r e c r o s s s e c t i o n s a t

CERN a n d a t F e r m i l a b f o r s e v e r a l p r o c e s s e s . I n s o m e c a s e s ,

I h a v e d r a w n a l i n e t h a t c r o s s e s a t a l e v e l e q u a l t o a

l u m i n o s i t y o f 1 0 . I ' v e d o n e t h i s f o r t w o r e a s o n s : T h e

f i r s t i s t h a t i t i n d i c a t e s a p p r o x i m a t e l y t h e l e v e l t h a t I

b e l i e v e CERN w i l l h a v e a c h i e v e d b y t h e t i m e t h e c o l l i d e r a t

F e r m i l a b s t a r t s t o o p e r a t e , a n d s e c o n d , w i t h a l u m i n o s i t y o f

3 0

10 , i t i s r e a s o n a b l e t o e x p e c t a n i n t e g r a t e d l u m i n o s i t y o f

1 0 i n a n y i n d i v i d u a l r u n . I b e l i e v e we c a n e x p e c t t h i s

k i n d o f l u m i n o s i t y o r e v e n a f a c t o r o f 1 0 h i g h e r w i t h i n t h e

n e x t f e w y e a r s .

F i g . 16 s h o w s t h e t o t a l c r o s s s e c t i o n f o r a s s o c i a t e d t t

p r o d u c t i o n . F o r a t m a s s n e a r 25 GeV, a n i n t e g r a t e d 3 6 4 —

l u m i n o s i t y o f 1 0 g i v e s 6 x 1 0 e v e n t s . I f a t q u a r k

d e c a y s v i a f l a v o r c a s c a d e , we c a n a r r i v e a t a s i t u a t i o n t h a t

a p p r o x i m a t e s t h r e e j e t s , p r o v i d e d t h e r e a r e n o s e m i l e p t o n i c

d e c a y s i n t h e c h a i n . F o r i n s t a n c e , i f a t g o e s i n t o a W +

a n d b , t h e b w i l l d e c a y v i a i t s f l a v o r c a s c a d e i n t o a n

a p p r o x i m a t i o n o f a s i n g l e j e t s i n c e n o n e o f t h e p a r t i c l e

m a s s e s a r e v e r y h i g h . I f a W d e c a y s i n t o a u a n d d , w e w i l l

t h e n h a v e t h r e e j e t s . I f t h e a s s o c i a t e d t d e c a y e d i n t o a b

a n d a W~, w h i c h i n t u r n d e c a y e d l e p t o n i c a l l y , we w o u l d h a v e

o p p o s i t e t h e t a s i n g l e j e t e v e n t w i t h a h i g h e n e r g y l e p t o n .

We c o n s i d e r t h e c a s e w h e r e we c a n t r i g g e r o n t h e h i g h e n e r g y

l e p t o n a n d t r y t o r e c o n s t r u c t t h e t m a s s f r o m i t s a s s o c i a t e d

t h r e e j e t s . T h i s t y p e o f t o p o l o g y h a s b e e n d e s c r i b e d i n

d e t a i l i n a CDF r e p o r t , C D F - 7 0 . T h e e f f i c i e n c y o f

r e c o n s t r u c t i o n i s n o t h i g h . H o w e v e r , M o n t e C a r l o s t u d i e s

i n d i c a t e t h a t i t s h o u l d b e p o s s i b l e t o i s o l a t e s u c h e v e n t s .

A m a s s r e c o n s t r u c t i o n u s i n g t h e c a l o r i m e t r y i n f o r m a t i o n o n l y

o f t h e t h r e e j e t s i s s h o w n i n F i g . 1 7 . O n e h u n d r e d e v e n t s 4

o u t o f t h e o r i g i n a l 6 x 10 h a v e s u r v i v e d a l l o f t h e c u t s ,

t h e m o s t s e r i o u s o f w h i c h i s a p f c c u t o f g r e a t e r t h a n 50 G e V

f o r t h e t h r e e j e t s .

We w i l l n o w p r o c e e d t o a d e s c r i p t i o n o f t h e i n d i v i d u a l

c o m p o n e n t s o f t h e d e t e c t o r . A n o v e r a l l d r a w i n g o f t h e

d e t e c t o r i s s h o w n i n F i g . 1 8 . I n a d d i t i o n , F i g . 19 a n d

T a b l e 1 i n d i c a t e s t h e p r o p e r t i e s o f t h e d e t e c t o r i n t h e

v a r i o u s a n g u l a r r e g i o n s .

T h e p r e s e n t s t a t u s o f t h e c a l o r i m e t r y i s a s

f o l l o w s : A l l o f t h e c o m p o n e n t s h a v e h a d p r o t o t y p e s

c o n s t r u c t e d a n d t e s t e d i n b e a m s . F i g . 20 s h o w s a 1 5 ° w e d g e

f r o m t h e c e n t r a l c a l o r i m e t r y . F i g . 21 s h o w s i t s

s e g m e n t a t i o n s i n r a p i d i t y . T h e f r o n t p a r t o f t h e m o d u l e

c o n s i s t s o f a l e a d s c i n t i l l a t o r s a n d w i c h w i t h a s t r i p

c h a m b e r e m b e d d e d a t s h o w e r m a x i m u m f o r p o s i t i o n i n f o r m a t i o n .

T h e n e x t s e c t i o n c o n s i s t s o f 1 i n c h s t e e l p l a t e s w i t h

s c i n t i l l a t o r s e m b e d d e d a n d r e a d o u t b y s h i f t e r b a r s . T h e

l a s t s e c t i o n a t t h e b a c k h o u s e s t h e m u o n t r a c k e r .

T h e s t e e l f o r t h e m o d u l e s h a s b e e n c u t u s i n g a c o m p u t e r

c o n t r o l l e d p l a s m a c u t t e r i n a s h o p a t P u r d u e . T h e g r e a t

n u m b e r o f d i f f e r e n t s h a p e s o f s c i n t i l l a t o r f o r t h e h a d r o n

c a l o r i m e t e r h a v e b e e n c u t w i t h a c o m p u t e r c o n t r o l l a s e r

f a c i l i t y a t F r a s c a t i , a n d a n a s s e m b l y l i n e t o w r a p t h e

s c i n t i l l a t o r a n d f a b r i c a t e t h e l i g h t s h i f t e r s h a s b e e n s e t

u p a t P i s a ( s e e F i g . 2 2 a ) . T h e e l e c t r o m a g n e t i c t o w e r s a r e

b e i n g f a b r i c a t e d a t A r g o n n e a s w e l l a s t h e s t r i p c h a m b e r s

w h i c h a r e l o c a t e d a t s h o w e r m a x i m u m t o g i v e p o s i t i o n

- 322 -

i n f o r m a t i o n ( s e e F i g . 2 2 b ) . T h e s c i n t i l l a t o r a n d s h i f t e r

f o r t h i s c a l o r i m e t e r w a s d e v e l o p e d i n J a p a n . T h e m u o n

t r a c k i n g s y s t e m i s b e i n g f a b r i c a t e d a t U r b a n a . A l l o f t h e s e

c o m p o n e n t s w i l l c o m e t o g e t h e r i n a n a s s e m b l y l i n e t h a t i s

b e i n g c o n s t r u c t e d a t F e r m i l a b a n d w h i c h w i l l c o m e i n t o

o p e r a t i o n i n t h e s u m m e r o f 1 9 8 3 . O n e c o m p l e t e w e d g e m o d u l e

w a s t e s t e d i n t h e b e a m b e f o r e t h e d e s i g n w a s f i n a l i z e d .

T h e e n d w a l l h a d r o n c a l o r i m e t r y m o d u l e s a r e n o w s t a r t i n g

t o b e c o n s t r u c t e d . A g a i n , t h e p l a t e s f o r t h i s u n i t a r e

f a b r i c a t e d u s i n g a p l a s m a c u t t e r u n d e r c o m p u t e r c o n t r o l .

T h e f o r w a r d e n d p l u g c a l o r i m e t r y i s a l s o n o w u n d e r

c o n s t r u c t i o n . T h e e l e c t r o n i c p a r t i s c o n s t r u c t e d o f l e a d

s h e e t s i n t e r s p e r c e d w i t h r e s i s t i v e p l a s t i c t u b e c h a m b e r s a n d

w i t h p a d a n d s t r i p r e a d o u t a s w e l l a s s e g m e n t a t i o n i n d e p t h .

T h e s e c h a m b e r s a r e t h e r e s p o n s i b i l i t y o f T s u k u b a U n i v e r s i t y .

T h e h a d r o n c a l o r i m e t r y s e c t i o n c o n s i s t s o f 5 cm t h i c k s t e e l

p l a t e s i n t e r s p e r c e d w i t h r e s i s t i v e t u b e p r o p o r t i o n a l

c h a m b e r s w i t h p a d r e a d o u t a n d i s t h e r e s p o n s i b i l i t y o f L B L .

T h e p a d s o f t h e s e t w o s e t s o f c h a m b e r s a r e a r r a n g e d i n t h e

f o r m o f p r o j e c t i v e t o w e r s . T h i s p a r t o f t h e c a l o r i m t r y w a s

p a r t i c u l a r l y d i f f i c u l t t o d e s i g n b e c a u s e i t i s a l s o p a r t o f

t h e m a g n e t i c c i r c u i t , a n d t h e f o r c e s a r e v e r y h i g h . F i g . 23

s h o w s a v i e w o f o n e s e c t i o n o f t h e e n d p l u g w i t h i t s

a s s o c i a t e d c a l o r i m e t r y . F i g . 24 s h o w s a n e x p l o d e d v i e w o f

t h e c h a m b e r s i n t h e e l e c t r o m a g n e t i c s e c t i o n , a n d F i g . 25 a n d

26 s h o w t h e r e s p o n s e o f t h e e l e c t r o m a g n e t i c c a l o r i m e t e r t o

100 G e V T T ~ a n d e ~ , r e s p e c t i v e l y . T h e s e p l o t s a r e m a d e o n

t h e b a s i s o f b e a m m e a s u r e m e n t s .

- 323 -

T h e m a g n e t i s a s u p e r c o n d u c t i n g s o l e n o i d t h a t i s 3

m e t e r s i n d i a m e t e r a n d 5 m e t e r s l o n g , a n d i t i s p r e s e n t l y

b e i n g c o n s t r u c t e d b y H i t a c h i i n J a p a n . P r e l i m i n a r y d e s i g n

a n d s p e c i f i c a t i o n s f o r t h i s c o i l w e r e m a d e b y a

c o l l a b o r a t i o n o f T s u k u b a U n i v e r s i t y a n d F e r m i l a b . T h e c o i l

i s s c h e d u l e d f o r c o m p l e t i o n t h i s y e a r a n d w i l l b e d e l i v e r e d

t o F e r m i l a b f o r m a g n e t i c t e s t s i n 1 9 8 4 .

T h e p a r t s o f t h e d e t e c t o r t h a t I h a v e d e s c r i b e d u p

u n t i l n o w a r e t h e m o s t a d v a n c e d i n t h e i r c o n s t r u c t i o n p h a s e .

T h i s i s b e c a u s e s o m e o f t h e c a l o r i m e t r y i s i n t e g r a l w i t h t h e

m a g n e t r e t u r n c i r c u i t a n d , h e n c e , m u s t b e c o m p l e t e d b e f o r e

m a g n e t t e s t s c a n b e c a r r i e d o u t . Some o f t h e s e c o m p o n e n t s

a l s o h a d a n i n f l u e n c e o n t h e d e s i g n o f t h e BO c o l l i s i o n h a l l

a n d a s s e m b l y a r e a , a n d h e n c e t h e i r d e s i g n h a d t o p r o c e e d a t

a r a t h e r r a p i d p a c e i n o r d e r t o i n s u r e c o m p a t a b i l i t y b e t w e e n

t h e b u i l d i n g a n d t h e d e t e c t o r .

T h e c e n t r a l t r a c k i n g s y s t e m i s s t i l l u n d e r s t u d y ,

a l t h o u g h d e t a i l e d m o d e l t e s t s h a v e b e e n c a r r i e d o u t o n o n e

p r o p o s e d s y s t e m w h i c h c o n s i s t s o f t e n s e t s o f h a l f s t a g g e r e d

d o u b l e p l a n e s . I n a d d i t i o n , t h e r e a r e f i v e u a n d f i v e v

p l a n e s g i v i n g a t o t a l o f 20 r a d i a l p l a n e s o f t r a c k i n g . T h e

w i r e s a r e i n t h e z d i r e c t i o n a n d t y p i c a l c e l l s a r e s h o w n i n

F i g . 2 7 . A n o v e r a l l v i e w o f t h e c e n t r a l c h a m b e r i s s h o w n i n

F i g . 2 8 . T h e c o n c a v e e n d s u p p o r t s a l l o w a d e q u a t e w i r e

t e n s i o n w i t h a m i n i m u m t h i c k n e s s o f m a t e r i a l i n t h e w a y o f

t h e p a r t i c l e s . T w o o t h e r t r a c k i n g s y s t e m s i n t h e c e n t r a l

r e g i o n a r e u n d e r s t u d y . T h e f i r s t i s a s i l i c o n v e r t e x

d e t e c t o r t h a t w o u l d f i t v e r y c l o s e a r o u n d t h e b e a m p i p e .

T h e s e c o n d i s a t r a c k i n g s y s t e m t h a t w o u l d b e u s e f u l f o r

- 324 -

a n g l e s s m a l l e r t h a n t h a t w h i c h t h e c e n t r a l t r a c k i n g c h a m b e r

c o v e r s .

A l l o f t h e c a l o r i m e t r y a n d t r a c k i n g s o f a r d e s c r i b e d

a r e a t t a c h e d t o t h e m a g n e t a n d m o v e i n a n d o u t o f t h e

a s s e m b l y h a l l . A 1 0 ° h o l e i n t h e w e d g e a l l o w s p a r t i c l e s i n

t h i s a n g u l a r r e g i o n t o p r o c e e d i n t o t h e f o r w a r d a n d b a c k w a r d

c a l o r i m e t r y a n d t r a c k i n g s y s t e m s . T h e s e s y s t e m s a r e f i x e d

i n p l a c e a n d d o n o t r o l l i n a n d o u t . T h e s e s y s t e m s a r e

s y m m e t r i c a l i n t h e f o r w a r d a n d b a c k w a r d d i r e c t i o n a n d a l l o w

f o r e l e c t r i c a l a n d h a d r o n c a l o r i m e t r y a s w e l l a s m u o n

t r a c k i n g . T h e e l e c t r o m a g n e t i c c a l o r i m e t r y i s b e i n g

c o n s t r u c t e d a t H a r v a r d ; t h e h a d r o n c a l o r i m e t e y i s b e i n g

c o n s t r u c t e d a t T e x a s A S M , a n d t h e m u o n t o r o i d s a n d t r a c k i n g

s y s t e m a r e b e i n g c o n s t r u c t e d a t W i s c o n s i n . .

T h e d a t a a c q u i s i t i o n s y s t e m m u s t h a n d l e o v e r 7 5 , 0 0 0

c h a n n e l s . I t m u s t b e s i m p l e , r e l i a b l e , a n d i n e x p e n s i v e .

M a n y c o m p o n e n t s o f t h i s s y s t e m a r e p r e s e n t l y b e i n g d e s i g n e d

a n d t e s t e d . H o w e v e r , t h e b a s i c a r c h i t e c t u r e o f t h i s s y s t e m

h a s b e e n s e t t l e d . T h e h i g h l e v e l C P U w i l l b e a V A X , a n d t h e

v a r i o u s p r o c e s s o r s i n t h e s y s t e m w i l l b e l i n k e d b y m e a n s o f

F A S T B U S . M u c h o f t h e f r o n t e n d e l e c t r o n i c s w i l l b e p l a c e d

o n t h e d e t e c t o r s i n c e w e a r e r e l y i n g o n a f a s t r e g e n e r a t i o n

t i m e i n t h e S o u r c e t o m a k e t h e d e t e c t o r e a s i l y a v a i l a b l e i n

c a s e o f m a l f u n c t i o n i n t h e c o l l i s i o n h a l l . F i n a l l y , i t h a s

b e e n d e c i d e d t h a t t h e m a j o r m e a n s o f c o m m u n i c a t i n g o f d a t a

b e t w e e n t h e d e t e c t o r a n d t h e e l e c t r o n i c s h o u s e w i l l b e d o n e

b y m e a n s o f DC a n a l o g s i g n a l s . A b l o c k d i a g r a m o f t h i s

s y s t e m i s s h o w n i n F i g . 2 9 . T h e p o s i t i o n o f t h e v a r i o u s

e l e c t r o n i c s c o m p o n e n t s r e l a t i v e t o t h e s h i e l d i n g w a l l i s

- 325 -

The s i g n a l coming i n from a w i r e , a p a d , o r a phototube

i s i n t e g r a t e d i n a charge s e n s i t i v e a m p l i f i e r and s t r e t c h e d

to the order of 100 microseconds. The two switches l a b e l l e d

" b e f o r e " and " a f t e r " are actuated b e f o r e the beam c r o s s i n g

and a f t e r the beam c r o s s i n g . The d i f f e r e n c e of these two

times forms a gate f o r the exper iment , and the two s i g n a l s

from the sample and h o l d a m p l i f i e r s are then s u b t r a c t e d i n a

d i f f e r e n c e a m p l i f i e r to g i v e the channel o u t . I n the case

a l s o i n d i c a t e d i n t h i s diagram. The system may be

s u b d i v i d e d i n t o s m a l l s e c t i o n s f o r t r o u b l e s h o o t i n g . The

processors t h a t c o n t r o l a l l the subsystems are t i e d to the

VAX CPU by means of FASTBUS.

A t y p i c a l channel of f r o n t end e l e c t r o n i c s i s shown

- 3 2 6 -

o f n o e v e n t , t h e c o n d e n s e r s a r e r e s e t b e f o r e t h e n e x t

c r o s s i n g .

T h e f u n c t i o n o f t h e t r i g g e r i s t o k e e p t h e c o n d e n s e r s

f r o m b e i n g r e s e t a n d t o k e e p t h e " b e f o r e " a n d " a f t e r "

s w i t c h e s o p e n . T h e e v e n t i s t h u s s t o r e d i n a n a l o g f a s h i o n

u n t i l i t i s r e a d o u t i n t h e n e x t f e w m i l l i s e c o n d s . T h e

d r i f t i n t h e s a m p l e a n d h o l d s y s t e m i s s m a l l e n o u g h s o t h a t

t h i s c a n b e d o n e q u i t e a c c u r a t e l y . T h e i n d i v i d u a l c h a n n e l s

a r e s c a n n e d u n d e r c o m p u t e r c o n t r o l , a n d t h e a n a l o g s i g n a l i s

s e n t f r o m t h e d e t e c t o r t o t h e e l e c t r o n i c s h o u s e . T h i s

s y s t e m r e s u l t s i n a n e n o r m o u s r e d u c t i o n o f t h e n u m b e r o f

c a b l e s t h a t m u s t c o n n e c t t h e d e t e c t o r w i t h t h e r e s t o f t h e

d a t a a c q u i s i t i o n s y s t e m . I t h a s t h e d i s a d v a n t a g e t h a t a

c o n s i d e r a b l e a m o u n t o f c o m p l e x e l e c t r o n i c s i s i n s t a l l e d a t

t h e d e t e c t o r , a n d h e n c e , n o t a c c e s s i b l e d u r i n g a s t o r e .

T h e t r i g g e r i s b r o k e n u p i n t o t h r e e l e v e l s . L e v e l 1,

t h e l o w e s t l e v e l , o p e r a t e s f r o m a n a l o g s i g n a l s s e n t f r o m t h e

d e t e c t o r . T h e L e v e l 2 t r i g g e r u t i l i z e s t h i s a n a l o g

i n f o r m a t i o n i n a m o r e s o p h i s t i c a t e d w a y t o f i n d c l u s t e r s o r

o t h e r i n t e r e s t i n g c o n f i g u r a t i o n s f r o m t h e c a l o r i m e t r y

i n f o r m a t i o n . F i n a l l y , a v e r y s o p h i s t i c a t e d L e v e l 3 t r i g g e r

u t i l i z i n g a l l d i g i t a l i n f o r m a t i o n c o n t r o l s t h e d a t a l o g g i n g

o p e r a t i o n .

M a n y c o m p o n e n t s o f t h i s s y s t e m h a v e b e e n b u i l t a n d

t e s t e d . T h e r e i s a n e n o r m o u s a m o u n t o f w o r k l e f t t o d o o n

b o t h t h e f r o n t e n d e l e c t r o n i c s a n d o n t h e F A S T B U S

c o m p o n e n t s . T h e i n t e n t i o n i s t o g e t t h e m a j o r c o m p o n e n t s o f

t h e s y s t e m b u i l t b y i n d u s t r y a f t e r t h e i n i t i a l d e v e l o p m e n t

p h a s e i s f i n i s h e d .

- 327 -

F i n a l l y , I w o u l d l i k e t o f i n i s h b y s h o w i n g s o m e o f t h e

e v e n t s f r o m o u r s i m u l a t i o n p r o g r a m . S i n c e t h e f i e l d i s

a x i a l a l o n g t h e b e a m , t h e e v e n t d i s p l a y i s c o n s i d e r a b l y

d i f f e r e n t i n a p p e a r a n c e t h a n t h e o n e s w e h a v e s e e n f r o m U A l .

F i g . 30 s h o w s a t y p i c a l h i g h p f c e v e n t i n t h r e e v i e w s .

F i g . 31 s h o w s a n e x p a n d e d v i e w o f t h e v e r t e x o f t h e s a m e

e v e n t . F i g s 32 a n d 33 s h o w t h e s a m e e v e n t w i t h a p f c c u t o f

1 G e V .

T h i s c o n f e r e n c e h a s b e e n h i s t o r i c i n t h a t i t h a s

e x p o s e d t h e r i c h n e s s o f t h e p h y s i c s t h a t u n d e r l i e s h i g h

e n e r g y p p c o l l i s i o n s . T h e w o r l d i s r e a l l y c o m p o s e d o f

q u a r k s , g l u o n s , a n d l e p t o n s ! T h e s o p h i s t i c a t i o n a n d

g r a n u l a r i t y i n o u r d e t e c t o r i s s u f f i c i e n t t o d o a n e x c e l l e n t

j o b o f a n a l y z i n g t h i s t y p e o f p h y s i c s . We l o o k f o r w a r d w i t h

g r e a t a n t i c i p a t i o n t o t h e d a y w h e n w e c a n j o i n y o u i n

a n a l y z i n g r e a l d a t a i n s t e a d o f M o n t e C a r l o e v e n t s .

- 328 -

C O L L I D E R P L A N

Colliding Beam Hall

F i g . 1

- 3 2 9 -

- 330 -

- 2 4 1 2 4 2 3 *

L E A V I N G T H E T A R G E T

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43 2 4 *

2 4 *

3 4 3 •3442

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3 4 3

2 4 4 3 3 4 4 3 4 3 4 4 4 4 2

-7T TT

R F P H A S E

F i g . 3

- 3 3 1 -

-3433433»

y "- , 33, T = 3 0 T U R N S

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4 4 4 2 2 4 * Ï 5 +

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-7T 0

R F P H A S E

F i g . 4

M)

C H A N N E L S 100 10 1

C O N T E N T S 10 1.

L O W - E D C E I O O O 100 10 1. 0

i • 5 6 i J :>4 i i 5 2 i i i S O ) 3 ] -411 I 1 1 i

1 1 1 1 i -44 1 1 1 1 11 -12 11 1 1 1 i 1 0 1 1 1 1 1 .i au •1 i 3 6 • 1 i 3-1 j 1 i 3 2 1 i 3 0 i i I i an i i i •1 i — - • i 2 / . i 'i i i 11

t 1 < i , 11 ;.*.' i i i i 11 2 0 i i i i 1 0 i i 1 6 i i 1 1 i

j i 1 0 i A P / P i

u -*—] U j 1 4 i - i a i - î

9 5 % OF BEAM ^ r - = 0 . 2 % FULL WIDTH

T= 7500 TURNS (5 KV)

i —• - i 11

i V o

'.'/OVO 1 234 Ï 6 7 U V 0

O 0 i :• : i A \i i, i o 1 2 3 * : 567090 J 2 3 4 5 6 7 0 9 0 1 2 3 1 S 6 7 B 7 0 1 2 3 4 Ü 6 7 0 V 0 I 2 3 1 5 6 7 Ü 9 0 1 2 3 4 5 ¿,71)701234 Í67U90123 - 1 5670701 ¡ ' ¡ f ü

3:ti'.3i 2 2 ; . ' J ' ) * 4 5 6 5 4 5 4 & 1 2 2 2 2 2 3 1

112 a" m i í i , J l 9 4 9 / ' / J : J 0 ; i H O - H 0 S 7 ; - l l D 0 1 S 2 : i 21 45

e8Ü8BBBaB0üOOBHHBUDtlQ0mU' M I M U I M M H D D H H R I M I N ^ 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 V 9 9 9 9 V V 9 9 9 7 9 9 9 9 V 9 9 V 9 9 9 V V 9 7 7 V 9 V V 7 9 7 V 7 9 7 7 9 V 9 9 V 7 9 9 7 9 V 7 9 V 7 9 7 7 7 9 7 7 7 7 7 7 V V 7 V V 7 9 7 7 7 7 7 7 7 7 7 9 9 1111111111111111122222222222222222333333333.1.J33333 - 1 4 4 4 H 4 . 1 4 4 4444444a53ü55S5ü:>555.^:<^.V.¿6666.i666¿6^6 001 1233 -14 5¿67709900] 2 2 3 3 4 5 5 6 6 7 U Ü 9 7 0 1 1 2"jn4 4 5J677lJli900U 2 J 3 4 4 3 6 6 7 7U7700122331 5 : i 6 í , 7 U : i 7 V ( U I 2 2 3 4 4 5 5 : ,7/ l l i¡7 06204062B40t2ü4062Ü ' 1 0 6 2 ü 4 0¿2ü4062Ü4062ü406204062tí4062Ü4062Q'lOÍ,2Ü'l062U'10í l 2 U - 1 0 6 2 U 4 0.'.;'¡i ' l¡i . , . 2 U ' l 0 6 2 ü 1 0 i J2B4

F i g . 5

Particle Density ( H z-7rmm - m r a d )

- eee -

- 3 3 4 -

F i g . 9

- 336 -

DESIGN REPORT

F o r t h e F e r m i l a b C o l l i d e r D e t e c t o r F a c i l i t y (CDF)

A r g o n n e N a t i o n a l L a b o r a t o r y B . M u s g r a v e , L . N o d u l m a n , A . B . W i c k l u n d

U n i v e r s i t y o f C h i c a g o - H. M. S h o c h e t

D . A y r e s , R. D i e b o l d , E . May , J . S a u e r , R. W a g n e r ,

F r i s c h , C . G r o s s o - P i l c h e r ,

F e r m i N a t i o n a l A c c e l e r a t o r L a b o r a t o r y - M. A t a c , F . B e d e s c h i , A . B r e n n e r , T . C o l l i n s , T . D r o e g e , J . E l i a s , J . F r e e m a n , I . G a i n e s , J . C r i m s o n , D . G r o s s , D . H a n s s e n , H. J e n s e n , R. K a d e l , H. K a u t z k y , R. K e p h a r t , T . O h s k a , M. O n o , R. T h a t c h e r , D . T h e r i o t , A . T o l l e s t r u p , K. T u r n e r , R. Y a m a d a , J . Yoh

L a b o r a t o r i N a z i o n a l i d e l l ' INFN - F r a s c a t i - S . B e r t o l u c c i , M. C o r d e l l i , P . G i r o m i n i , P . S e r m o n e t a

H a r v a r d U n i v e r s i t y - G. B r a n d e n b u r g , R. S c h w i t t e r s

U n i v e r s i t y o f I l l i n o i s - G. A s c o l i , B . E i s e n s t e i n , L . H o l l o w a y , U . K r u s e

KEK - S . I n a b a , M. M i s h i n a , K. O g a w a , F . T a k a s a k i , Y . W a t a s e

L a w r e n c e B e r k e l e y L a b o r a t o r y - W. C a r i t h e r s , W. C h i n o w s k y , R. K e l l y , K. S h i n s k y

U n i v e r s i t y o f P i s a - G. B e l l e t t i n i , R. B e r t a n i , L . B o s i s i o , C . B r a d a s c h i a , R. D e l F a b b r o , E . F o c a r d i , M. A . G i o r g i , A . M e n z i o n e , L . R i s t o r i , A . S c r i b a n o , G. T o n e l l i

P u r d u e U n i v e r s i t y - V . B a r n e s , R. S . C h r i s t i a n , C . D a v i s , A . F . G a r f i n k e l , A . L a a s a n e n

T e x a s A&M - P . M c l n t y r e , T . M e y e r , R. Webb

T s u k u b a U n i v e r s i t y - Y. A s a n o , S . K i m , K. K o n d o , S . M i y a s h i t a , H. M i y a t a , S . M o r i , I . N a k a n o , Y. T a k a i w a , K. T a k i k a w a , Y . Y a s u

U n i v e r s i t y o f W i s c o n s i n - D . C l i n e , R. L o v e l e s s , R. M o r s e , L . P o n d r o m , D . R e e d e r , J . R h o a d e s , M. S h e a f f

T h r e e n e w i n s t i t u t i o n s , S p o k e s m a n i n p a r e n t h e s e s , j o i n e d t h e c o l l a b o r a t i o n i n J u n e 1 9 8 2 : B r a n d e i s U n i v e r s i t y ( J i m B e n s i n g e r ) , U n i v e r s i t y o f P e n n s y l v a n i a (H. H. W i l l i a m s ) , a n d R u t g e r s U n i v e r s i t y (Tom D e v l i n ) .

F i g . 10

- 337

A forward wall

Plug

plug e m

central

o CM

Iß

10" 30° 43.6°51.8° 9 0 '

- 3 - 2 0 - 7?

Fig. 11

- 3 3 8 -

- 339 -

i — - — i 1 i r

4 8 12 16 20 24 28 32 RECONSTRUCTED 3-JET MASS (GeV /c )

Pig. 17

EM SHOWER COUNTERS

Property Central Plug Forward Sampling medium Scintillator MWPC MWPC

Thickness 17 X 0 2IX 0 2 3 X 0

1/2 x(ö-range) 3 6 0 - 9 0 o 10° -37° 2 " -10°

Element size I 5 ° x 0 . l 5°xO.I 5 ° x 0 . l

""E/E I 5 % A / Ê 2 5 % / , / Ê 2 5 % A / È

^x.y (E>50GeV) ~ 3mm ~lmm ~lmm

Hadron rejection ~ I 0 3 ~ 5 x l 0 2 few x I 0 2

Hadron Calorimeters Property Central Wall Plug Forward

Sampling medium Scintillator Scintillator MWPC MWPC

AfTg Perpendicular 5A 4.4 A 6A 8 . 3 A

l /2x(S-range) 4 0 ° - 9 0 " 3 0 « - 5 0 ° 10° - 3 0 " 2° - IO°

Element size 15-xO.I I5°x0. l 5"xO.I 5°xO.I

5 % + &2% ^/F

100% -ft

100% **** r- '

VF ~ 5cm ~ 5cm ~ lcm ~ l c m

IRON YOKE

MUON CHAMBERS ^ = 0 . 2 % P T

Punchthrough Prob.=-jgQ

CENTRAL HADRON CALORIMETER

V E

CENTRAL E-M SHOWER COUNTER oy E = I 5 % / V Ê 3

Charged Hadron rejection » 10

SOLENOID COIL AND CRYOSTAT

CENTRAL TRACKING CHAMBER

AP *jT = 0 . 2 % P T

END PLUG E-M

SHOWER COUNTER!

^ _ 2 5 %

END WALL HADRON CALORIMETER

a 9 0 %

END PLUG HADRON CALORIMETER

a- |QQ% TORODS

2 " - 17" AP

VERTEX DETECTOR

17%

INTERACTION REGION

-INTERMEDIATE TRACKING T 0 — P — FORWARD

CALORIMETERS 2° < 8 < 10"

Fig. 19 E M _, 2 5 %

7E 100%

- 3 4 1 -

Fig. 21

- 3 4 2 -

S c H O T

4s F i g . 22a

- 343 -

HADRON CALORIMETER E.M. CALORIMETER

Fig. 23

Unit : m m

Flcj. 24

- 3 4 4 -

R n * i - 14 o x

I5.709r<-

o

o X o X o

O o o

o o o o o

O X O X O X O X O

o o o o o u

60

60

15.709

o X o X o X o X o X o X o X o X o

- ^ j — o o o o o o o o o o o o o o o o

14 O X O X O X Q X O X O X O X O

• o o o o o o o o

o o o o o o o o o

o x o x o x o x o x o x o x o x o

o o o o o o o o o

X - SENSE WIRE o-FIELD WIRE

Fig. 27

- 3 4 5 -

- 346 -

D A T A L O G G E R

F R O N T E N D

E L E C T R O N I C S

tr IT M N h- (-o O c 3 O

R E R E S E T E N A B L E

R I R E S E T I N H I B I T

H I H O S T I N T E R F A C E

S I S E G M E N T I N T E R C O N N E C T snc S F R V I C E A N D D I A G N O S T I C C O M P U T E R

Pig. 29

C D F E V E N T D I S P L A Y E V E N T N O : t O

L E G E N R D S T A T U S T Y P E

O N N E U T R A L O N O F F

P O S I T I V E N E G A T I V E

P A R T I C L E S P A R T I C L E S P A R T I C L E S

3 - 1 . 5 0 0 - 1 . 1 2 0 - . 7 5 - . 3 7 0 . 0 0 , . 3 7 7 7 5 7 1 . 12 1 . 5 f t o

u>

o o

ex*

- 6 0 0 . 0 : - * 3 0 0 . 0 : # 0 . 0 0 A Y

3 0 0 . 0 0 6 0 0 . 0 0

- 348 -

F i g -

o *s

O ~Z

y—

~Z. LU >• LU

V E N T D I S P L A Y E V E N T N O r t O

L E G E N A D S T A T U S T Y P E

ON N E U T R A L P A R T I C L E S ON P O S I T I V E P A R T I C L E S O F F N E G A T I V E P A R T I C L E S

- 3 5 0 -

Fig

2 : LU UJ

- 3 5 1 -

R e f . T H . 3 5 2 7 - C E R N

E L A S T I C S C A T T E R I N G A N D T O T A L C R O S S - S E C T I O N S

A. M a r t i n

C E R N - G e n e v a

A B S T R A C T

We c o n f r o n t r e c e n t d a t a o n pp a n d pp a t the ISR a n d a t t h e c o l l i d e r w i t h r i g o r o u s r e s u l t s a n d w i t h v a r i o u s m o d e l s . W e s h o w t h a t p r e c i s e m e a s u r e m e n t s a t p r e s e n t l y a v a i l a b l e e n e r g i e s a n d a t h i g h e r e n e r g i e s w i l l a l l o w u s to c l a r i f y the s i t u a t i o n .

R e f . T H . 3 5 2 7 - C E R N

F e b r u a r y 1 9 8 3

- 3 5 2 -

1 . - INTRODUCTION

I shall talk on elastic scattering and naturally total cross-sections which are linked to elastic scattering by the optical theorem. This morning, when I was asked by Leon Lederman why I was interested in elastic scattering while I was working currently on heavy quarkonium states, I answered that it was an old love. It is as if you would meet again a girl that you have courted many years ago without success, and she would offer herself to you. You cannot resist. Indeed many years ago theorists spent a lot of time deriving asymptotic theorems, asymptotic bounds on hadronic scattering amplitudes, but we were still very far from the asymptotic regime. Now, with the possibility of comparing the pp and pp scattering at the ISR and the observation of pp collisions at the collider, a new experimental window is open, through which we can look at much higher energies.

In a way there is not much new experimental material since the Paris Conference in July 1982 except perhaps the fact that UA1 and UA4 have cross-checked their measurements of the slopes at |t| < 0.2 GeV 2

and |t| > 0.2 GeV 2 a n c j S O m e measurements of the cross-section dif-3) 4 )

ferences at the ISR ' . There is not much new theoretical material either. All theorems are old. The models have been known, for quite some time. Nevertheless, theoreticians can always manage to discuss about anything and even if what they say is not always useful, at least they have fun, as shown by Fig. 1 , a cartoon by my elder son, an economist.

Perhaps we should go back first a little bit in history and try to realize that a major discovery has been made many years ago at the ISR , which is the rise of total cross-sections. Somehow, this discovery has been under-rated because it is not the prediction of one precise theory and because "explanations" have been given only after the discovery, some of them are rather sophisticated and claim to start from first principles but nevertheless necessitate the postulate, at a certain point of the calculations, that certain mechanisms are dominant.

- 353 -

The rise of total cross-sections was a complete surprise. The previous belief was that total cross-sections were approaching constants at infinite energy and that high energy scattering was dominated by a simple Regge pole, the Pomeron. In fact, at the Lund Conference in 1969, there was a moment of panic when it was announced that the ir+p and T T ~ P cross-sections were approaching different limits at high energy. It was thought that this was the end of local field theory. This was doubly wrong. The experiment was wrong but it was also wrong to believe that first principles force the Tr~p - 7 T +p cross-section difference to approach zero. There are (ugly) ways out, like odderons, about which I shall say a few words later.

6 ) It was also thought that the Froissart bound

0~

as beautiful as it was, could be improved and that it was only for technical inability that theoreticians could not prove that a ^ Q ^ w a s

bounded by a constant, a fact which seems so natural when you think that elementary particles have a finite, fixed size. It is only very recently that the hope to improve the Froissart bound in a qualitative way has been

7) essentially given up, when Kupsch has constructed a crossing symmetric amplitude, with Mandelstam analyticity, with the unitarity constraint on partial wave amplitudes,

fulfilled in all three channels, and with a forward amplitude behaving like

At the ISR, the rise of total cross-sections was only 10%. Yet it is remarkable that with this measurement, combined with a measurement of the real part and dispersion relations, the "pioneers" predicted that the cross-section would rise up to at least 200 GeV centre-

8 ) of-mass energy and exceed a value of 55 millibarns . The present measurement of UAA,

- 3 5 4 -

i s c o m p a t i b l e w i t h t h e i r b e s t f i t , a n d r e p r e s e n t s n o w a n i n c r e a s e o f 5 0 %

w i t h r e s p e c t t o l o w e n e r g y ( F i g . 2 ) .

2 . - p p - p p C O M P A R I S O N

L e t u s n o w s p e n d s o m e t i m e o n t h e p p a n d p p c o m p a r i s o n .

P r e v i o u s l y t h i s w a s l i m i t e d t o p r e t t y l o w e n e r g i e s (_< 2 0 0 G e V i n t h e

l a b ) b u t n o w , t i l l 1 9 8 4 , w e h a v e t h e I S R , i . e . , a r a n g e o f c e n t r e - o f - m a s s

e n e r g i e s b e t w e e n 3 0 a n d 6 2 G e V . T h e h o p e t o c o n t i n u e t h e c o m p a r i s o n a t

h i g h e r e n e r g i e s i s v e r y s m a l l . E v e n i f CBA ( e x - I s a b e l l e ) i s b u i l t , s y s

t e m a t i c e r r o r s w i l l b e d i f f e r e n t i n C B A a n d i n t h e S P S c o l l i d e r a n d m a k e

t h e m e a s u r e m e n t o f t h e c r o s s - s e c t i o n d i f f e r e n c e v e r y d i f f i c u l t .

A t p r e s e n t , a n a ï v e R e g g e f i t A a = c o n s t x E ~ a i s n o t i n c o m -4 )

p a t i b l e w i t h t h e d a t a ( F i g . 3 ) . I r e f e r y o u t o t h e t a l k s o f D . F a v a r t , 3 )

a n d G . C a r b o n i . H o w e v e r , G a u r o n a n d N i c o l e s c u a r g u e t h a t w h e n o n e u s e s

t h e n o t i o n o f d u a l i t y o n e i s l e d t o m a k e t h e R e g g e f i t w o r k e v e n t o r e l a

t i v e l y l o w e n e r g y a n d t h e i r b e s t f i t c o n t a i n s a n " o d d e r o n " ( a r a t h e r

o d d o d d - s i g n a t u r e a m p l i t u d e ! ) :

T T I f t h e y a r e r i g h t , t h e d i f f e r e n c e a - - a s h o u l d d e c r e a s e u p t o a ' p p p p

c e r t a i n e n e r g y , r e a c h a m i n i m u m , a n d i n c r e a s e a g a i n l i k e l o g E ( F i g . 4 ) .

T h i s i s n o t i n c o n f l i c t w i t h f i r s t p r i n c i p l e s i f t h e t o t a l c r o s s - s e c t i o n s

i n c r e a s e s e p a r a t e l y l i k e ( l o g E ) 2 . I am p e r s o n a l l y s l i g h t l y s c e p t i c a l

a b o u t t h e e x i s t e n c e o f t h e o d d e r o n . T h e m a i n p o s i t i v e a s p e c t o f t h i s

a t t e m p t i s t h a t i t s h o w s t h a t o n e s h o u l d t r y t o i m p r o v e a s m u c h a s p o s

s i b l e t h e a c c u r a c y o f t h e m e a s u r e m e n t o f c r o s s - s e c t i o n d i f f e r e n c e a t 6 3 G e V

c e n t r e - o f - m a s s e n e r g y . A w e a k i n d i c a t i o n i n f a v o u r o f o^- - -> 0 i s P P P P

t h e f a c t t h a t f r o m R 2 1 1 m e a s u r e m e n t , o n e i n f e r s t h a t R e F a n d I m F ~ h a v e

t h e s a m e s i g n a t 5 0 G e V c e n t r e - o f - m a s s e n e r g y . I f t h i s w o u l d p e r s i s t a t

h i g h e r e n e r g i e s , t h e F i s c h e r t h e o r e m w o u l d t e l l u s t h a t t h e c r o s s -

s e c t i o n d i f f e r e n c e g o e s t o z e r o .

F i n a l l y , c o n c e r n i n g g e n e r a l t h e o r e m s o n t h e p p - p p c o m p a r i s o n :

- 3 5 5 -

w h e r e t h e b ' s a r e t h e s l o p e s o f t h e d i f f r a c t i o n p e a k s ,

" T o u t e s t e n o r d r e " a s t h e y s a y i n S w i t z e r l a n d .

3 . - p p A T C O L L I D E R E N E R G I E S A N D B E Y O N D

I r e m i n d y o u f i r s t t h e a s y m p t o t i c t h e o r e m s w h i c h c o n t r o l h i g h

e n e r g y s c a t t e r i n g . U n d e r t h e o n l y a s s u m p t i o n o f l o c a l i t y ( n o s i g n a l c a n

t r a v e l f a s t e r t h a n l i g h t e v e n o n m i c r o s c o p i c d i s t a n c e s ) a n d e x i s t e n c e o f

a m i n i m u m m a s s o f t h e h a d r o n s p e c t r u m , t h e m a s s o f t h e p i o n ( r e m e m b e r t h a t

g l u o n s , a n d p r o b a b l y q u a r k s , a r e c o n f i n e d p a r t i c l e s w h i c h d o n o t p l a y a

r ô l e i n t h i s g a m e ) , o n e c a n p r o v e t h e f a m o u s F r o i s s a r t b o u n d ^ :

( L = a n g u l a r m o m e n t u m )

T h e r e a r e v e r y i n t e r e s t i n g a s y m p t o t i c p r o p e r t i e s i f t h e

F r o i s s a r t b o u n d i s q u a l i t a t i v e l y s a t u r a t e d , i . e . , i f

I t h a p p e n s t h a t t h i s i s n o t i n c o m p a t i b l e w i t h e x p e r i m e n t .

F o r i n s t a n c e , t h e b e s t f i t o f t h e C E R N - R o m e - P i s a - S t o n y B r o o k e x p e r i

m e n t c o n t a i n e d a t e r m ( l o g s ) ^ i n t h e t o t a l c r o s s - s e c t i o n a n d y 1 4 )

w a s f o u n d t o b e 2 . 1 ± 0 . 1 . S i m i l a r l y t h e m o r e r e c e n t f i t s b y R 2 1 0 1 5 )

a n d b y B l o c k a n d C a h n f a v o u r , w i t h o u t p r o v i n g i t , a s a t u r a t i o n o f

t h e F r o i s s a r t b o u n d . I t i s u n d e r s t a n d a b l e t h a t t h e c o e f f i c i e n t o f

( l o g s ) 2 i s v e r y f a r f r o m b e i n g s a t u r a t e d .

- 356 -

16 ) The asymptotic effects in the case of a qualitative sa

turation of the Froissart bound are

1)

2) a scaling property

(Mr (where f is an entire function of order |)

3) the slope of the diffraction peak,

17) satisfies

X ffëj ° There is therefore a non-uniform behaviour of the slope parameter at high energies. At which energy ? I do not know. I cannot really tell

1) 2) you whether the change of the slope observed by UA4 and UA1 at the collider (b ~ 17 for |t| < 0.2 GeV 2, b ~ 13.5 for |t| > 0 . 2 GeV 2) is connected with this phenomenon.

Now I would like to discuss three classes of models. Here I must apologize to all the people I shall not quote, for the literature in this domain is very abundant. In Classes I and I I , the Froissart bound is qualitatively saturated. However, the difference between I and I I is that in I one believes that the asymptotic regime is already reached at I S R and collider energies. In Class I I , asymptopia is much more remote and eventually the nucleón looks like a black disk, which is far from being the case now. I l l is the model of the critical Pomeron, in which very precise asymptotic predictions are made, not only for elastic scattering but also for soft inelastic processes.

- 357 -

I, as we said, is a model where the asymptotic regime is already reached. The main argument in favour of I is the fact that there is no visible variation of the ratio a ,/a, , over all the ranee of

el tot energies of the ISR from 30 to 60 GeV centre-of-mass energy, where it is

18 ) close to 0.175 . At collider energies a -,/a. , is 0.20±0.03, also

el tot ' compatible with this value, but the need for an improved accuracy is obvious. Also the dip motion is consistent with the model. However, this is not terribly significant because all models claim agreement with this dip motion. Why is a

e ] / a t 0 t s o small ? The only model I know which "explains" that is the overlap model of Van Hove 19). if the "overlap function" is taken to be a Gaussian for simplicity one finds

20) a

e ] / at o t < 0.21. Figure 5 shows a prediction of Dias de Deus and Kroll

based on this idea that they call "geometrical scaling", and Fig. 6 shows their prediction for the larger t region. Notice the sad fact that in their curve the dip, around 1.2 GeV 2 has disappeared and has been replaced by a shoulder. This is due to a contribution of the real part of the

21) scattering amplitude which, as I noticed it in 1973 , modifies the cross-section which becomes

where p(s,0) is ReF/ImF in the forward direction. If p = 0.15, which is inferred from dispersion relations (however, 0.10 would also be possible in my opinion) the dip disappears. At higher energies, for instance if the LEP tunnel is used one day as pp collider, the dip will reappear because the real part will become negligible.

In II, as we said, asymptopia is very remote and we have a black disk eventually. While I is just a possibility, II is supported by various models which look very different from one another but have probably hidden ties. For instance, we have the Cheng-Wu-Walker model based on the summation of a very large class of diagrams supposed to be

23) dominant, the model of Kaidalov and Ter Martyrosian which uses as basic unit a kind of supercritical Pomeron, the model of Chou and Yang which uses a kind of geometrical picture of the nucleón.

- 3 5 8 -

Perhaps the most precise model is that of Chou and Yang which uses as an input the nucleón electromagnetic form factor and the total cross-section. Once the total cross-section is given there is no free parameter. a

e ] / a t o t ' ^ n e sl°P e» t n e dip position, etc., are fixed. It is remarkable that this model has been, up to now, relatively successful. It predicts beautiful diffraction patterns reminiscent of nuclear physics. Figure 7 shows curves for proton-calcium scattering at 1 GeV. Figure 8 shows the Chou-Yang patterns for pp scattering at high energy. They look the same. I summarize here the Chou-Yang predictions.

M dip M •

second rank

el tot

b do7dt(max) do7dt( forward)

38.9 mb 1.46 (1.44 exp)

1.85 (1.97)

0.165 12.3

43.0 mb 1.23 (1.31 exp)

1.61 (1.81)

0.179 12.5

60 mb 0.78 1.10 0.226 13.6 2.44xl0~ 5

80 mb 0.55 0.83 0.269 15.1 1.65x10""* 100 mb 0.42 0.54 0.300 16.9 0.5 xl0~ 3

oo mb 0 0 0.5 GO 0.017

We see that the variation of G e ^ / a t o ^ . predicted over the ISR range is just barely compatible with the experimental data, and that the slope at collider energies is already in serious difficulty. At this meeting, G. Matthiae has given preliminary indications that if the cross-section is really 66 millibarns, the observed value of da/dt at the place where should be the second maximum is much less than what is theoretically predicted. A crucial test will be a precise measurement of G ., /a, . . I believe that the fact that the second maximum is relatively el tot higher and higher as the energy increases is not particular to the Chou-Yang model but common to all models in which °e±/°tot a P P r o a c n e s \ a t infinite energy. Naturally we must remember that as happened in the calculation of Dias de Deus and Kroll, real part effects may fill the dips, partly or completely.

- 3 5 9 -

Finally, model III is that of the critical Pomeron, which has been extensively studied many years ago and which is now confronted with

25 ) 26 ) experiment by a certain number of people like Moshe Moshe , Jan Dash ,

27 ) Alan White , etc. The asymptotic predictions of RFT (Regge field theory) with a critical Pomeron are very precise :

, 0.2 €

(The Froissart bound is therefore not saturated !)

4T^ erf***) ±(&ï*f13). Next-to-leading order effects have also been calculated. However, the supporters of the critical Pomeron explain that non-asymptotic effects are certainly needed in a fit to present energies. Dash , in particular, points out that the asymptotic regime is pushed further away by the delayed effect of successive flavour thresholds. As a success of the

28 ) model I show a test of scaling (Fig. 9) by Dash and Bourrely . However, even with non-asymptotic effects, it seems difficult to reach 66 millibarns at 540 GeV (Fig. 10). It seems also difficult to prevent the ratio o -,/a. . from decreasing, el tot

What I would like to say, in conclusion, is that experiment can distinguish between these various models, provided a small fraction of the running time of the collider is devoted to elastic scattering. Dividing the errors on 0" ^, a

e ] / a t 0 t » ^ a factor two would already provide a valuable information. Another accessible information is the observation of the dip or a precise upper bound on the differential cross-section. Naturally, all these effects, like deciding whether a

e i / a £ 0 t increases or decreases, are more and more marked with increasing energy.

24) This is particularly clear in the table of the model of Chou and Yang who take the great risk and have the great merit of being very explicit

- 3 6 0 -

in their predictions. So increasing, for instance, the pp collider energy to 2x400 GeV in a non-continuous mode would be very useful in this respect. Naturally, the Fermilab collider with 2x1000 GeV would still be better, since the various extrapolations put O " ^ o t between 80 and 100 millibarns. Therefore, I wish all the success to Alwin Tollestrup and Leon Lederman.

- 3 6 1 -

R E F E R E N C E S

1) G . M a t t h i a e - C o n t r i b u t i o n to t h i s C o n f e r e n c e .

2) F. C e r a d i n i - C o n t r i b u t i o n to t h i s C o n f e r e n c e .

3) G . C a r b o n i - C o n t r i b u t i o n to t h i s C o n f e r e n c e .

4) D. F a v a r t - C o n t r i b u t i o n to t h i s C o n f e r e n c e .

5) U . A m a l d i e t a l . - P h y s . L e t t e r s 3 6 B (1971) 504 ; 43B (1973) 231 ; G . B a r b i e l l i n i et a l . - P h y s . L e t t e r s 3 9 B (1972) 6 6 3 ; V . B a r t e n e v et a l . - P h y s . R e v . L e t t e r s 31 (1973) 1 0 8 8 ; C E R N - P i s a - S t o n y B r o o k C o l l a b o r a t i o n - P h y s . L e t t e r s 62B (1976) 4 6 0 .

6) M . F r o i s s a r t - P h y s . R e v . 123 (1961) 1 0 5 3 .

7) J . K u p s c h - N u o v o C i m e n t o 71A (1982) 8 5 ;

8) U . A m a l d i e t a l . - P h y s . L e t t e r s 6 2 B (1976) 4 6 0 .

9) P. G a u r o n a n d B. N i c o l e s c u - O r s a y P r e p r i n t , I P N O / T H

to a p p e a r in P h y s . L e t t e r s . 8 2 - 4 5 ( 1 9 8 2 ) ,

10) J . F i s c h e r - P h y s i c s R e p o r t s 76 (1981) 1 5 8 .

11) R . J . E d e n - P h y s . R e v . L e t t e r s 16 (1966) 39 ; T. K i n o s h i t a - in P e r s p e c t i v e s in M o d e m P h y s i c s , R . E . M a r s h a k E d .

p. 2 1 1 . W i l e y , N e w Y o r k (1966) ; G . G r u n b e r g a n d T r a n N . T r u o n g - P h y s . R e v . L e t t e r s 31 (1973) 6 3 .

12) H . C o r n i l l e a n d A. M a r t i n - P h y s . L e t t e r s 4 0 B (1972)

P h y s . B 4 8 (1972) 104, B 4 9 (1972) 4 1 3 a n d B 7 7 671 ; N u c l e a r (1974) 1 4 1 .

13) A. M a r t i n - N u o v o C i m e n t o 42 (1966) 9 3 0 .

14) G . C a r b o n i e t a l . - P h y s . L e t t e r s 1 1 5 B (1982) 4 9 5 .

15) M . B l o c k a n d R. C a h n - C E R N P r e p r i n t s T H . 3 3 0 7 a n d 3 3 4 2 (1982) s u b

m i t t e d to P h y s . R e v . L e t t e r s .

16) S e e , for i n s t a n c e : A. M a r t i n - Z e i t s c h r i f t für P h y s i k C , 15 (1982) 1 8 5 .

17) A. M a r t i n - in P r o c e e d i n g s o f t h e 2 1 s t I n t e r n a t i o n a l C o n f e r e n c e o n

H i g h E n e r g y P h y s i c s , P. P e t i a u a n d M . P o r n e u f E d s . , p. 1 6 4 ,

L e s E d i t i o n s de P h y s i q u e , P a r i s ( 1 9 8 2 ) .

18) U . A m a l d i a n d K.R. S c h u b e r t - N u c l e a r P h y s . B 1 6 6 (1980) 3 0 1 .

19) L. V a n H o v e - R e v s . M o d e r n P h y s . 36 (1964) 6 5 5 .

- 3 6 2 -

20) J. Dias de Deus and P. Kroll - Preprint CFMC-E21/82, Lisbon (1982). See also : P. Kroll - Zeitschrift für Physik C, 15 (1982) 67.

21) A. Martin - Nuovo Cimento Letters 7 (1978) 811.

22) H. Cheng, J.K. Walker and T.T. Wu - Phys.Letters 44B (1973) 283.

23) A.B. Kaidalov and K.A. Ter Martyrosian - Nuclear Phys. B75 (1974) 471.

24) T.T. Chou and C.N. Yang - Phys.Rev. D19 (1979) 3268.

25) M. Moshe - Physics Reports 37 (1978) ; Nuclear Phys. B198 (1982) 13.

26) J.W. Dash and S.T. Jones - Preprint CPT 82/1451, Marseille (1982).

27) A. White - Fermilab Preprint CONF-82/16 THY (1982), and Proceedings of the Topical Conference on Forward Collider Physics, Madison, Wisconsin (1981), F. Halzen Ed.

28) C. Bourrely and J.W. Dash - Nuclear Phys. B192 (1981) 509.

- 3 6 3 -

FIGURE CAPTIONS

Fig. 1 A discussion between theoreticians seen by Philippe Martin.

Fig. 2 Extrapolation of total cross-sections from total cross-sections and real part measurements at the ISR.

Fig. 3 The proton-antiproton - proton-proton cross-section difference seen by R210.

Fig. 4 A fit by Gauron and Nicolescu to the cross-section difference with and without odderon.

Fig. 5 The low t region at collider energies obtained by geometrical scaling according to Dias de Deus and Kroll.

Fig. 6 The large t predictions of Dias de Deus and Kroll at collider energies.

Fig. 7 Proton-calcium scattering at 1 GeV.

Fig. 8 The predictions of Chou and Yang for pp scattering for various values of the cross-section.

Fig. 9 A test of scaling in agreement with RFT by Bourrely and Dash.

Fig. 10 A prediction from RFT with a critical Pomeron for the total cross-section. The experimental point to the right is from U A 4 .

- 364 -

F i g u r e 1 -

- 3 6 5 -

- Figure 2 -

. 1 - - 1 I ! 1—1 • l _ l _

1 5 10 50 x / s f G e V )

- F i g u r e h -

- 367 -

- F i g u r e 5 -

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-f-(GeV)2

- Figure 6 -

- F i g u r e 7 - - F i g u r e 8 -

- 3 7 0 -

s IGeV*)

- F i g u r e 1 0 -

- 371 -

B. N I C O L E S C U : I w i l l t r y t o a n s w e r t o t h e q u e s t i o n o f M a u r i c e J a c o b

c o n c e r n i n g t h e m a g n i t u d e o f O d d e r o n e f f e c t s . L e t me f i r s t c l a r i f y t h e m e a n i n g

o f t h e w o r d s " b i g " a n d " s m a l l " w h i c h c a n be v e r y c o n f u s i n g i n t h i s c o n t e x t . We

know d i r e c t l y f r o m t h e d a t a t h a t A o < o T a t h i g h e n e r g i e s . T h e r e f o r e we d o n o t

n e e d a n y k i n d o f t h e o r y o r m o d e l i n o r d e r t o know t h a t t h e i m a g i n a r y p a r t

I m F _ o f t h e o d d - u n d e r - c r o s s i n g a m p l i t u d e ( a n d , i n p a r t i c u l a r , t h e p o s s i b l e

O d d e r o n c o n t r i b u t i o n ) h a s t o be much s m a l l e r t h a n I m F + . H o w e v e r , i n s p i t e o f

t h i s " s m a l l n e s s " , A o i s d i f f e r e n t f r o m z e r o a n d c o n t i n u e s t o s h o w , a t h i g h

e n e r g i e s , a r e m a r k a b l e s t r u c t u r e . I n o t h e r w o r d s , i t i s m e a n i n g l e s s t o c o m p a r e

t h e O d d e r o n c o n t r i b u t i o n w i t h t h e e v e n - u n d e r - c r o s s i n g a m p l i t u d e : t h e O d d e r o n

h a s t o be c o m p a r e d w i t h t h e o t h e r ( s e c o n d a r y - R e g g e ) c o n t r i b u t i o n s t o t h e o d d -

u n d e r - c r o s s i n g a m p l i t u d e . When t h i s i s d o n e ( s e e P. G a u r o n a n d B. N i c o l e s c u ,

O r s a y p r e p r i n t IPNO/TH 8 2 - 4 5 , t o be p u b l i s h e d i n " P h y s i c s L e t t e r s " ) i t i s s e e n

t h a t t h e O d d e r o n c o n t r i b u t i o n becomes c o m p a r a b l e t o t h a t o f t h e c o r r e s p o n d i n g

R e g g e p o l e s a t I S R e n e r g i e s . T h e p r e s e n t d a t a a r e c o m p a t i b l e w i t h t h e e x i s t e n c e

o f t h e O d d e r o n l e a d i n g t o a m i n i m u m i n A o l o c a t e d a t /s" = 80 G e V .

L e t me f i n a l l y s a y , o n a m o r e g e n e r a l l e v e l , t h a t t h e £ n 2 s b e h a v i o r o f o T c o u l d

be u n d e r s t o o d a s a m a n i f e s t a t i o n o f t h e p r i n c i p l e o f m a x i m a l s t r e n g t h o f s t r o n g

i n t e r a c t i o n s . I f t h i s i s t r u e , i t w o u l d be r e a l l y o d d t h a t t h e O d d e r o n ( l e a d i n g

t o t h e £ns b e h a v i o r o f A o ) d o e s n o t e x i s t : t h e O d d e r o n i t s e l f c a n be u n d e r s t o o d

a s a m a n i f e s t a t i o n o f t h i s p r i n c i p l e .

QCD and PP COLLIDER PHYSICS

G.Altarelli Istituto dî Fisica dell'Université di Roma I

INFN - Sezione di Roma

Although QCD essentially imposes itself as the only theory of the strong interactions within reach of the weapon arsenal of conventional quantum field theory, yet QCD is still the less established sector of the standard model. Testing OCD is in fact more difficult than testing the electroweak sector. In the latter domain perturbation theory can always be applied. Also the leptons and the weak gauge bosons are at the same time the fields in the lagrangian and the particles in our detectors. Instead QCD is a theory of quarks and gluons while only hadrons are observable. Moreover perturbation theory can only be applied in those particular domains of the strong interactions where approximate freedom, which is only asymptotic, can be reached.

This difficulty of testing QCD is the reason why a substantial evidence in support of this theory is only gathered from a collection of converging indications from many different processes, while no single feasible test is by itself decisive.

Thus the relevance for QCD of experiments at the SPS collider rests on the possibility they offer of testing parton dynamics in a new and highly non trivial configuration. For example, hadron-hadron interactions in the deep inelastic, large , region are non linear in parton densities. Also the relevant predictions cannot be derived by less committed formulations than the explicit QCD improved parton model, as for example light cone dominance and operator expansion. This complexity, which is important for providing qualitatively new testing grounds is however paid for by a loss of precision in predictive power. _

In addition to that, PP collisions are also important as jet sources with an energy scale comparable to that of an e + e - ring with beam energy up to 50 GeV and more.

As partons are studied through their jets and there are many kinds of partons, we need different jet factories in order to be able to disintangle quark flavors and gluons. In particular the problem of evidentiating gluon jets is of special relevance. As we shall see, most of the jets produced at large P_ in PP collisions at high energy are predicted to be gluon jets. This fact adds further interest to the jet studies that will be carried out in the future at the SPS Collider.

- The Cross Section for Inclusive Jet Production 2 3

The clear observation ' of large Pj_ jets at the SPS Collider is by itself a distinct success of the parton picture of deep inelastic processes. Once more the early apparent failure of a parton prediction has been demonstrated to be merely due to lack of sufficient energy. Not only that, but the

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observed cross section, as a function of for inclusive jet production agrees remarkably well with the OCD estimates 4 . This is particularly significant in that the very steep dependence from energy and transverse momentum of the cross section makes the occurrence of large factors very easy, as for example in the comparison -> of jet yields at ISR with that at Collider energies.

The leading term of the inclusive jet yield is computed as a convolution of a product of two parton densities with the corresponding cross--sections for the two initial partons into any two final partons, evaluated in lowest order QCD. An inclusive trigger is necessary in order to identify the Pj_ of each final parton with the measured P¿_ of the corresponding jet (defined as the sum of the P of the hadrons in the jet). Intricate questions about how to define a correct infrared safe observable are skipped here . We just stress that inclusiveness in principle allows to do without fragmentation functions, thus simplifying the cross section.

There are many two into two parton processes that contribute . For central production, i.e. for almost zero rapidity, which is the dominant case, each incoming parton has an energy£=xE, E being the P or P c.o.m. energy. That is the energy fractions of the two incoming partons are nearly the same x ^ a X j x. Then the average energy per parton is given by E= 3c, where yfs = 540 GeV at Collider and "x in the average x of a given kind of partons in the nucleón. For valence x-~ 0.25T0.30, corresponding to €«v 70-^80 GeV. The final parton transverse momentum is Pj_ = €sin© . The perturbative region is at large angle Q , where P is not much smaller than €T, i.e. x, = ~â <• x. At Collider this means P.">, 10 T20 GeV. At such small values of x^ the production of gluon jets is seen to be dominant, both because there are many gluons in the nucleón at small x and because the cross section for qq -> gg has comparatively large color factors. Thus the Collider is a good gluon factory, as already mentioned. In the near future one can attempt to establish the gluon nature of the jets by studies of the multiplicities in the jet fragmentation, of the P_ distribution with respect to the jet axis of the hadrons in the jet ^ , of the baryon content of the jet fragments and of the lepton yield from quark pairs of heavy flavor created by the parent gluon ^ and so on.

At fixed x Jc^jj£is predicted to fall as P£"4 f apart from logarithms : « W d r £ ~ P f 1 * j - C *-L / s^xi) • A t f i x e d s a change in PA implies a proportional variation of X j ^ . The steeper dependence on P_ which is observed in this case is well reproduced by the decrease of parton densities as X j _ is increased. p

For Px of order -j x the theory is in principle relatively clean. In practice the prediction for the cross section is affected by uncertainties because the next to the leading corrections are not known. These corrections are important for a precise qualification of the leading term. For example their form and magnitude fix the correct energy scale to be used for the parton densities and the running coupling (the leading term is of order ) . Also the gluon density in the nucleón is ill known. Actually without better knowledge of the densities it is not worthwhile to attempt the computation of the non leading corrections for the large number of parton processes involved. The only existing ® fragment of this computation refers to q L + qj q k + X, where i , ¿ , K are different flavors. In that case the optimal scale (i.e. that corresponding to the smallest next to leading terms) was found ^ to be reduced with respect to P¿ .

At smaller values of P the theory is more complicated. For K <« PjJ*^ C terms of order log Ç /P *•* log are no more negligible with respect to log Pjp/A*" i and one is led to a hard process with two scales 1° * ^ . Moreover the separation of spectator jet effects becomes more difficult.

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As a side remark i t is i n t e r e s t i n g to observe t h a t the n e c e s s i t y of c o l o r rearrangement'- imposes t h a t some i n t e r a c t i o n has to take place between the h i g h P j e t s and the spectator j e t s . I n other words c o l o r has t o be r e a r r a n ged i n a plane i n these e v e n t s . One can t r y to detect the e f f e c t s o f t h i s c o l o r rearrangement i n t e r a c t i o n . For example, one can compare.the forward j e t s i n the l a r g e P,_ events w i t h the forward j e t s i n D r e l l - Y a n events o r i n W/Z production e v e n t s . The l a t t e r processes are a l s o hard processes occurr ing at comparable values of the t r a n s f e r r e d momentum, but c o l o r has to be rearranged along a l i n e . I t i s reasonable to expect t h a t the forward j e t s might be broader when c o l o r has to be rearranged i n a plane than i n the cases where t h i s r e s h u f f l i n g occurs along the forward l i n e .

- M u l t i p l i c i t i e s A set o f v e r y i n t e r e s t i n g data on m u l t i p l i c i t y d i s t r i b u t i o n s have

been c o l l e c t e d at the S P S - C o l l i d e r ÎÎ^-^ . Experiments have shown that ^ ( y - Q • the t o t a l charged m u l t i p l i c i t y p e r . u n i t r a p i d i t y y a t ^ = 0 , i n creases from ISR to C o l l i d e r energy at a r a t e compatible w i t h g-jJ^ ^ l n S . T h i s implies t h a t Feynman scal ing i s v i o l a t e d (which i s no news) and that the t o t a l average m u l t i p l i c i t y ñ increases w i t h energy i n a way compatible w i t h riA/ln^S. The bulk o f the m u l t i p l i c i t y i s determined by s o f t processes which l i e f a r away from the domain of p e r t u r b a t i v e QCD. On the other hand QCD leads to important p r e d i c t i o n s f o r the scale dependence of m u l t i p l i c i t i e s w i t h i n hard j e t s , as f o r example those produced at l a r g e i n PP o r i n e +e~ a n n i h i l a t i o n at l a r g e 0 2 . I n hard j e t s the parton m u l t i p l i c i t y (i. e. as i f partons could be d i r e c t l y observed) i s p r e d i c t e d 13 * 1 to e v o l v e w i t h Q 2 as ñ(Q2)=n"(Q2) exp (y log Q 2 /^ 2 )^ 2 - \ where ^ = C ^ i s the number o f f l a v o r s and Q 0 is a f i x e d s c a l e . Thus i f one assumes t h a t the h a d r o n i z a t i o n mechanism does not s i g n i f i c a n t l y depend on Q 2 , the same behavior can be expected to hold f o r the measurable hadronic m u l t i p l i c i t y i n the j e t . Extending t h i s p r e d i c t i o n to the t o t a l m u l t i p l i c i t y i n PP c o l l i s i o n s i s not j u s t i f i e d , because the mechanisms at work i n s o f t p r o cesses might be d i f f e r e n t . However i t i s i n t e r e s t i n g t o observe that n I n S and ñ" /oexp(^J ln 2 S/s„ are both compatible 1 9 w i t h the a v a i l a b l e data. I t has been argued 15 that i n PP c o l l i s i o n s , the e f f e c t o f the s o f t region might be e g u i v a l e n t to a reduction o f the e f f e c t i v e scale.from S down to A^S" w i t h A~10 GeV. As the data become more p r e c i s e i t w i l l be i n t e r e s t i n g to see which form o f energy dependence i s favoured by experiment.

Another i n t e r e s t i n g experimental r e s u l t i s the approximate v a l i d i t y o f KNO s c a l i n g 1^. As w e l l known Feynman s c a l i n g i m p l i e s KNO s c a l i n g . Since the former i s v i o l a t e d the question i s whether there are arguments f o r the l a t t e r t o be respected. The question can be discussed i n QCD. Again one must d i s t i n g u i s h the case o f m u l t i p l i c i t y d i s t r i b u t i o n s i n hard j e t s and i n s o f t processes 1 . I n the f i r s t case one can study the d i s t r i b u t i o n o f c o l o r s i n g l e t c l u s t e r s o f gluons i n a j e t 14,18 _ T h i s d i s t r i b u t i o n shows KNO s c a l i n g broken by logar i thms. Probably t h i s conclusion i s l i k e l y to be true i n g e n e r a l . On the other hand the shape o f the KNO scal ing f u n c t i o n appears t o be more model dependent 17,18

- 3 7 5 -

References 1. For a recent review see G.Altarelli, Phys.Reports 81(1982)1. 2. UAj_ Collaboration, these Proceedings. 3. UÄ2 Collaboration, these Proceedings. 4. R.Horgan, M.Jacob, Nucl.Phys. B179(1981)441. 5. M.Jacob, these Proceedings. 6. JADE Collaboration, Proceedings of the 2 1 s t Int. Conf. on High En. Phys.,

Paris 1982, presented by G.Heinzelmann, page 59. 7. European Muon Collaboration, E M C , K.H.Becks et al., Univ.Wuppertal,

Preprint WU B 82-13(1982). 8. R.K.Ellis, M.A.Furman, H.E.Haber, I.Hinchliffe, Nucl.Phys. B173(1980)

397, M.A.Furman, Columbia Univ. Preprint CU-TP-182. 9. W.Furmanski- Private Communication.

10. Yu.L.Dokshitzep, D.I.Dyakonov, S.I.Troyan, Phys.Lett.78B(1978)290, G.Parisi, R.Petronzio, Nucl.Phys. B154(1979)427.

11. M.Greco, These Proceedings. 12. UA5 Collaboration. These Proceedings. 13. A.H.Mueller, Phys.Lett. 104B(1981) 161, A.Bassetto, M.Ciafaloni, G.

Marchesini, A.H.Mueller, Univ. of Florence, preprint 82/11. 14. A.Bassetto, M.Ciafaloni, G.Marchesini, Nucl.Phys. B163 (1980) 477; W.

Furmanski, R.Petronzio, S.Pokorski, Nucl.Phys. B155(1979)253. 15. J.Kalinowski, M.Krawczyk, S.Pokorski, Z.Phys.C 15(1982)281. 16. Z.Koba, H.B.Nielsen, P.Olesen, Nucl.Phys. B40(1972)317. 17. G.Pancheri, these Proceedings. 18. F.Hayot, G.Sterman, Stony Brook Preprint ITP-SB-82-60.

19. R.V.Gavai, H.Satz; Phys.Lett. 112B(1982)413.

- 376 -

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arises from the relalivistic density of states, which r coordinate space volume V grows as expiai3'1)1'*. V is Lotenti-conlracled, V » 1m VQIS/H, then ont .tains eq. (7). Since the different transverse and longitudinal mo-:ntum spectra or actual collisions certainly do not tee with the isotropic picture of the Fermi model, may be noted that by use of the hydrodynamical jdel |18J one can retain eq. (7) even for anisotropic xncnlum-space distributions. Let us note at this point that both multiplicity and ictrum measured in a fixed (cenital) rapidity inter-I will in the various approaches exhibit similar dif-tncct. With Feynman scaling, the multiplicity per >idity interval becomes constant, in the soft pion minance case it should grow lograrithmically, in other cases stronger. The transverse-momentum :ctra in the range |p T| < 1 GeV/c remain as p[-X(pf +m 1) 1' ,l for the unconelated jet model •h with and without quantum statistics; the soft on summation as well as any hydrodynamical ap->ach will eventually lead to weaker p T damping, to fig. 1 wo now show the overall charged multlpll* f.fiu which the five diffeient approaches provide

5.

ft(GeV) I. Charted multiplicity vcnui CMS eneriy Vt < 100 CeV.

2 .

ft (GtV) Fif. 2. Chuiod multiplicity prediction for 100 <-Ji < 1000 GeV.

ta the pp data in the range 20 < \/i < 60 CeV. Both fig. 1 and the X 2 values " given in table 1 indicate that these data alone do not allow us to claim that a specific model,gives the best description. . . .

In fig. 2 we extrapolate the fits just shown into the energy range 100 <-Js < 1000 CeV. It is seen that pp collides data, if taken with statistics similar to that of the pp data below 60 CeV, should indeed allow us to exclude some of Ihe theoretical approaches discussed here.

On the other hand, we can also conclude that a fundamental revision of our present view of soft . hadron physics may be necessary if ñ*c lacreases much stronger with > than any of the models studied in this work.

It is a pleasure to thank R. Baier, J. Cleymans and B. Petersson for stimulating discussion. One of us (R.V.G.) would also like to thank the Alexander von Humboldt Foundation for financial support.

Appendix. Here we give explicit expressions for the coefficients A, B and C, occurring in eqs. (3) and (4), in terms of the model parameters f.m and X and

*' The reason for the relatively lajge x 3 values, in comparison to the food "optical quality" of the tits, Ues.in the very small errors quoted in the data of réf. (11.

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- 393 -

OBSERVATION AND STUDY OF JETS AT HIGH P T

WITH UA1 CENTRAL CALORIMETRY

UA1 Collaboration

Aachen-Annecy-Birmingham-CERN-Collëge de France, Paris-Helsinki-QMC, London-Riverside-Roma-Rutherford-Saclay-Vienna Collaboration

Presented by J. Sass

CEN-Saclay, France

- 394 -

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- 4 0 7 -

11 J a n u a r y , 1 9 8 3

G i o r g i o S a l v i n i h a s a s k e d me o v e r t h e t e l e p h o n e m y o p i n i o n r e g a r d i n g

t h e f u t u r e o f , o n t h e o n e h a n d h a d r o n a c c e l e r a t o r s a n d s t o r a g e r i n g s a n d

e l e c t r o n / p o s i t r o n a c c e l e r a t o r s a n d s t o r a g e r i n g s o n t h e o t h e r . I am v e r y

s o r r y I c a n n o t p a r t i c i p a t e i n t h e R o u n d T a b l e t a k i n g p l a c e i n Rome o n t h e

o c c a s i o n o f t h e S y m p o s i u m d e d i c a t e d t o t h e p h y s i c s o f t h e p p - c o l l i d e r . A s

G i o r g i o k n o w s , m y t a s k a n d t h e r e f o r e a l l m y e f f o r t s a r e c o n c e n t r a t e d o n t h e

M a n a g e m e n t o f t h e t e a m b u i l d i n g L E P , I h o p e i n t h e m o s t e f f i c i e n t w a y , b u t

p a r t o f m y h e a r t ( w h i c h i s q u i t e b i g ) a n d p a r t o f m y m o r e i m m e d i a t e s c i e n t i f i c

i n t e r e s t l i e i n p p ~ .

A s a p h y s i c i s t a n d a s a m e m b e r o f C E R N ' s D i r e c t o r a t e , I am c o n v i n c e d

t h a t w e m u s t h a v e a w e l l - b a l a n c e d s c i e n t i f i c p r o g r a m m e a t C E R N , w h i c h c l e a r l y

r e f l e c t s t h e s c i e n t i f i c p r i o r i t i e s w i t h i n t h e L a b o r a t o r y . M o r e p a r t i c u l a r l y I

am d e e p l y c o n v i n c e d t h a t t h e t w o e s s e n t i a l p r i o r i t i e s a t t h i s m o m e n t m u s t b e

t h e c o n t i n u a t i o n o f t h e p p - p r o g r a m m e a n d t h e c o n s t r u c t i o n o f L E P . I t i s

q u i t e o b v i o u s t h a t i t i s a l s o n e c e s s a r y t o c a r r y o u t ( m a i n t a i n ) a s c i e n t i f i c

p r o g r a m m e a t t h e S P S ( f i x e d t a r g e t ) , t h e P S a n d t h e S C , b u t i t m u s t b e a

p r o g r a m m e r e a l l y w o r t h w h i l e a n d u n f o r t u n a t e l y r e d u c e d w i t h r e s p e c t t o t h e

p r e s e n t - d a y p r o g r a m m e .

I t i s e v i d e n t t h a t i n o r d e r t o b a l a n c e t h i s p r o g r a m m e , t a k i n g i n t o

a c c o u n t t h e f i n a n c i a l c o n d i t i o n s a n d t h e p e r s o n n e l a t t h e d i s p o s a l o f t h e C E R N

L a b o r a t o r y , i t w i l l b e a d i f f i c u l t t a s k a n d m o r e t h a n l i k e l y c o n s i d e r a b l e

s a c r i f i c e s w i l l h a v e t o b e m a d e . I d o n ' t t h i n k w e a r e d o i n g a g o o d t u r n t o

t h e S c i e n t i f i c C o m m u n i t y b y d e n y i n g t h e e x i s t e n c e o f t h e s e d i f f i c u l t i e s ,

b e c a u s e a t s o m e s t a g e o r o t h e r i n t h e f u t u r e w e s h a l l h a v e t o f a c e t h e m . I f I

h a d t o d e v e l o p t h o r o u g h l y t h e s e f e w p o i n t s m y l e t t e r w o u l d b e e x t r e m e l y l o n g

a n d t h a t w a s n o t t h e p u r p o s e o f G i o r g i o ' s r e q u e s t . W h a t I w o u l d l i k e t o b e

k n o w n i s t h a t m y p e r s o n a l p r i o r i t i e s , a n d n o w I am s p e a k i n g a s E m i l i o P i c a s s o

( a n d n o t a s a m e m b e r o f t h e D i r e c t o r a t e ) , a r e : t h e c o n t i n u a t i o n a n d f u l l

d e v e l o p m e n t o f t h e p p - p r o g r a m m e . I f t h e i n t e r m e d i a t e b o s o n s o f t h e e l e c t r o

w e a k i n t e r a c t i o n W± a n d Z ° e x i s t , t h e y m u s t b e r e v e a l e d f i r s t o n t h e p p - a t

t h e S P S . I am e n t i r e l y i n f a v o u r o f a p r o g r a m m e o f d e v e l o p m e n t w h i c h w i l l

e n a b l e u s t o i n c r e a s e t h e l u m i n o s i t y o f t h e c o l l i d e r . T h e p p ~ i s a f o r m i d a b l e

a n d s t u p e n d o u s o p p o r t u n i t y f o r C E R N , i t m u s t t h e r e f o r e b e u s e d t o i t s f u l l e s t

- 408 -

e x t e n t . I am c o n v i n c e d that g o o d p h y s i c s r e q u i r e s the s u i t a b l e e n e r g y , t h e

p r o p e r l u m i n o s i t y a n d t h e a p p r o p r i a t e d e t e c t i n g e q u i p m e n t . A n d last but not

l e a s t the i n t e l l i g e n c e , the d e v o t i o n and the p e r s e v e r e n c e of the e x p e r i m e n t a l

p h y s i c i s t and of the e n g i n e e r o n the a c c e l e r a t i n g m a c h i n e s : it is a n a s s e t

far too i m p o r t a n t to f o r g e t . In o r d e r to do t h i n g s w e l l , o n e n e e d s the t i m e ,

be it f r o m t h e p o i n t of v i e w of a c c e l e r a t o r e f f i c i e n c y , or f r o m the

e x p e r i m e n t e r ' s point o f v i e w . W e all k n o w it is a c o m p l e t e w a s t e d r i n k i n g a

g o o d b o t t l e of R i c h e b o u r g o n e or two y e a r s a f t e r it w a s m a d e .

M y o t h e r p r i o r i t y is the c o n s t r u c t i o n of LEP a n d of t h e e x p e r i m e n t s

for a g o o d u s e of i t . I a m c o n v i n c e d that the c h o i c e of e + e ~ p h y s i c s at h i g h

e n e r g i e s ( g r e a t e r t h a n or e q u a l to 100 GeV in the c e n t r e of m a s s ) is a g o o d

c h o i c e , w h i c h w i l l o p e n u p g r e a t p o s s i b i l i t i e s in the f i e l d of p a r t i c l e

p h y s i c s for E u r o p e a n d for C E R N . LEP m u s t be b u i l t p r o p e r l y , at the v e r y

e a r l i e s t , c o m p a t i b l e w i t h the f i n a n c i a l and h u m a n r e s o u r c e s of C E R N a n d the

n a t i o n a l l a b o r a t o r i e s . A l l t h i s is v e r y e a s i l y said b u t d i f f i c u l t to

r e a l i z e . It is a v e r y g r e a t m o m e n t for C E R N and for E u r o p e ! W e m u s t all do

our u t m o s t to c a r r y t h i s t h r o u g h . In o r d e r to h a v e a p r o p e r p l a n of the

p h y s i c s h e r e in E u r o p e for t h e y e a r s to c o m e , we m u s t h a v e a s o u n d p l a n n i n g

for L E P t o g e t h e r w i t h the L E P e x p e r i m e n t s as w e l l as for the p p - p r o g r a m m e .

A l l this w i l l e n a b l e us to a n a l y s e w h a t o t h e r r e s o u r c e s a r e a v a i l a b l e in

E u r o p e for a c o n c e r t e d a n d h e a l t h y s c i e n t i f i c p r o g r a m m e .

A s y o u c a n w e l l i m a g i n e I c o u l d c o n t i n u e for a w h i l e this

i n t e r v e n t i o n of m i n e by l e t t e r , but to read the w r i t i n g of s o m e o n e e l s e is

g e n e r a l l y not c o n s i d e r e d t o o i n t e r e s t i n g . P l e a s e forgive m e o n c e m o r e for

n o t b e i n g w i t h y o u .

T h a n k y o u a g a i n .

S i n c e r e l y .

P . S . Y o u a s k e d m e if it w e r e p o s s i b l e to adapt the e n e r g y of the L E P m a c h i n e

as a f u n c t i o n of the r e s u l t s o b t a i n e d o n the pp~". T h e a n s w e r is y e s . It is

s u f f i c i e n t for that to i n s t a l l e x t r a c a v i t i e s in the R F s e c t i o n a n d I h o p e

t h e s e to be s u p e r c o n d u c t i n g c a v i t i e s ( 3 M V / m ) .

- 4 0 9 -

H A D R O N C O L L I D E R S V E R S U S e + e C O L L I D E R S

( a c o n t r i b u t i o n t o t h e r o u n d t a b l e f r o m t h e B C F g r o u p )

M. B a s i l e , G . B o n v i c i n i , G . C a r a R o m e o , L . C i f a r e l l i , A . C o n t i n ,

M. C u r a t o l o , G . D ' A l i , C . D e l P a p a , B . E s p o s i t o , P . G i u s t i ,

T . M a s s a m , R . N a n i a , G . N a t a l e , F . P a l m o n a r i , G . S a r t o r e l l i ,

M. S p i n e t t i , G . S u s i n n o , L . V o t a n o a n d A . Z i c h i c h i

C E R N , G e n e v a , S w i t z e r l a n d

I s t i t u t o d i F i s i c a d e l l ' U n i v e r s i t à d i B o l o g n a , I t a l y

I s t i t u t o N a z i o n a l e d i F i s i c a N u c l e a r e , B o l o g n a , I t a l y

I s t i t u t o N a z i o n a l e d i F i s i c a N u c l e a r e , L N F , F r a s c a t i , I t a l y

( P r e s e n t e d b y A . Z i c h i c h i )

1. I N T R O D U C T O R Y N O T E S

I w o u l d l i k e t o c o n t r i b u t e j u s t t w o p o i n t s t o t h e d i s c u s s i o n o f

h a d r o n c o l l i d e r s v e r s u s e + e c o l l i d e r s . B o t h w i l l b e b a s e d o n e x p e r i m e n t a l

d a t a o b s e r v e d a t t h e I S R a n d e x t r a p o l a t e d a t e x t r e m e e n e r g i e s . T h e f i r s t

i s i n t h e f i e l d o f n e w , v e r y h e a v y f l a v o u r s ; t h e s e c o n d i s o n t h e m u l t i -

p a r t i c l e p r o d u c t i o n . B o t h c o u l d c o n t r i b u t e t o c h a n g i n g o u r p r e s e n t v i e w s

a n d t o f a v o u r i n g , f o r t h e f u t u r e , v e r y h i g h e n e r g y h a d r o n c o l l i d e r s —

n o t ( e + e ) .

1) A v e r y h i g h e n e r g y h a d r o n c o l l i d e r e x i s t s : t h e C E R N ( p p ) . C a n

t h i s m a c h i n e b e u s e d t o s e a r c h f o r n e w f l a v o u r s s u c h a s " t o p " a t 25 G e V

a n d " s u p e r b e a u t y " a t 55 G e V m a s s e s ? T h e a n s w e r i s Y e s i f t h e p r o d u c t i o n

m e c h a n i s m a n d o t h e r d e t a i l e d f e a t u r e s f o l l o w o u r e x p e c t a t i o n s .

A d e t a i l e d a c c o u n t o f h o w t h i s c a n b e d o n e h a s b e e n g i v e n d u r i n g

a n o t h e r s e s s i o n £ l ] . L e t me j u s t r e m i n d y o u o f t h e c r u c i a l p o i n t s .

A s t u d y o f a n e w e f f e c t ( t h e e + / e a s y m m e t r y i n t h e p r o t o n a n d a n t i -

p r o t o n h e m i s p h e r e s ) s h o w s t h a t i t i s p o s s i b l e t o s e a r c h f o r v e r y h e a v y +

f l a v o u r s t a t e s . T h i s n e w e f f e c t d e p e n d s o n t h e e e n e r g y a n d i s t h e r e i f t h e v e r y h e a v y s t a t e s (A + a n d A 0 , ^ ) a r e p r o d u c e d i n a l e a d i n g

J t s u p e r b e a u t y

- 4 1 0 -

w a y , as f o u n d a t the C E R N I S R e n e r g i e s w i t h " c h a r m " a n d " b e a u t y " [^2,3].

If these s t a t e s w e r e f o u n d at the C E R N pp C o l l i d e r , this w o u l d b e a v e r y

i m p o r t a n t s t e p i n f a v o u r of h a d r o n m a c h i n e s . I n f a c t it c o u l d b e that

the 25 G e V a n d 55 G e V m a s s e s d e c a y s e m i l e p t o n i c a l l y i n a p a t t e r n w h i c h is

s i m p l e to d i s e n t a n g l e f r o m the " s t a n d a r d " s o f t p h y s i c s p r o d u c e d in a v e r y

h i g h e n e r g y i n t e r a c t i o n .

O n the b a s i s of this d e t a i l e d s t u d y w e t h i n k t h a t the o b s e r v a t i o n of

n e w f l a v o u r s in h a d r o n c o l l i d e r s is by n o m e a n s o u t of r e a c h .

O f c o u r s e the g r e a t a d v a n t a g e of e e c o l l i d e r s is t h a t they are

" c l e a n " . H o w e v e r t h e i r e n e r g y is m u c h b e l o w t h a t of the h a d r o n c o l l i d e r s .

If the h a d r o n c o l l i d e r s w i l l show t h a t , a f t e r a l l , they are n o t so

d i f f i c u l t to w o r k w i t h , a n d the c o m p l e x i t y of the final states is n o t s u c h

as to f o r b i d d o i n g n e w p h y s i c s — for e x a m p l e , to d i s c o v e r n e w f l a v o u r s —

in few y e a r s our v i e w c o u l d d r a s t i c a l l y c h a n g e in f a v o u r of them.

So the f i r s t c o n c l u s i o n is to w a i t u n t i l a c l e a r m e s s a g e comes f r o m

the C E R N pp C o l l i d e r .

2) T h e s e c o n d p o i n t refers to a n e w w a y of s t u d y i n g (pp) i n t e r a c t i o n s .

I w i l l d i s c u s s this s e c o n d p o i n t in d e t a i l . I n f a c t , this n e w w a y of

s t u d y i n g (pp) i n t e r a c t i o n s a l l o w s a c o m p a r i s o n of the m u l t i p a r t i c l e s y s t e m s

p r o d u c e d in a h a d r o n c o l l i d e r ( s u c h as the ISR) w i t h the m u l t i p a r t i c l e

s y s t e m s p r o d u c e d in a l e p t o n c o l l i d e r ( s u c h as P E T R A ) .

In o t h e r w o r d s , in so far as the m u l t i p a r t i c l e h a d r o n i c s t a t e s are

c o n c e r n e d , the I S R looks like an e + e c o l l i d e r , w h o s e e n e r g y g o e s b e y o n d

the h i g h e s t P E T R A v a l u e s . T h e r e is a d i f f e r e n c e b e t w e e n ( e + e ) and h a d r o n

m a c h i n e s : the p r o d u c t i o n of o p e n a n d h i d d e n h e a v y - f l a v o u r s t a t e s . This

d i f f e r e n c e can e a s i l y b e a c c o u n t e d for in terms of the c o u p l i n g s w h i c h

are j u s t g i v e n b y the u p - l i k e or d o w n - l i k e e l e c t r i c c h a r g e s in the e e

c o l l i d e r s , w h i l s t in the h a d r o n case the m a s s of the h e a v y f l a v o u r s c o m e s

in w i t h a n inverse p o w e r law. B u t the s t r u c t u r e of the m u l t i b o d y final

states l o o k s v e r y s i m i l a r at the I S R a n d at P E T R A . M o r e o v e r , if a l e p t o n -

h a d r o n c o l l i d e r w o u l d b e b u i l t at e q u i v a l e n t I S R e n e r g i e s , the s t r u c t u r e

of the m u l t i b o d y f i n a l states w o u l d b e i d e n t i c a l , as s h o w n b y the c o m p a r i

s o n of the l o w e s t - e n e r g y I S R d a t a w i t h the h i g h e s t - e n e r g y ( V p ) , ( V p ) , a n d

(yp) s c a t t e r i n g d a t a .

- 4 1 1 -

A d i r e c t c o n s e q u e n c e o f t h e s e f i n d i n g s i s t h a t a n o l d m y t h h a s b e e n

s h a t t e r e d .

2. T H E E N D O F A M Y T H : T H E H I G H - p ^ , P H Y S I C S

2 . 1 G e n e r a l r e m a r k s

S o f a r , t h e h i g h - p ^ p h y s i c s h a s h a d a h i g h l y p r i v i l e g e d r o l e i n

h a d r o n p h e n o m e n a . F o r e x a m p l e , h i g h - p ^ h a d r o n p h y s i c s w a s t h e o n l y c a n d i

d a t e t o a t t e m p t a c o m p a r i s o n w i t h ( e + e ) p h y s i c s a n d d e e p - i n e l a s t i c s c a t

t e r i n g ( D I S ) [ 4 ] . T h i s t r e n d h a s b e e n c o n t i n u i n g f o r a l o n g t i m e .

R e c e n t l y , t h e a d v e n t o f Q C D h a s e m p h a s i z e d t h i s p r i v i l e g e d r o l e o f

t h e h i g h - p ^ p h y s i c s [[5-7]. T h e r e a s o n i s v e r y s i m p l e : a t h i g h p ^ , t h a n k s

t o a s y m p t o t i c f r e e d o m , Q C D c a l c u l a t i o n s c a n b e a t t e m p t e d v i a p e r t u r b a t i v e

m e t h o d s , a n d c a n b e s u c c e s s f u l l y c o n f r o n t e d w i t h e x p e r i m e n t a l d a t a . T h e

n e w C E R N p p C o l l i d e r r e s u l t s a r e i n d e e d t h e l a t e s t s u c c e s s f u l a t t e m p t i n

t h i s t r e n d [ 8 - 1 0 ] .

O n t h e c o n t r a r y , l o w - p ^ , p h e n o m e n a a r e " t h e o r e t i c a l l y o f f l i m i t s " ,

d e s p i t e t h e f a c t t h a t t h e y r e p r e s e n t a n o v e r w h e l m i n g a m o u n t o f e x p e r i m e n t a l

d a t a .

I n a l o n g s e r i e s o f s y s t e m a t i c s t u d i e s a t t h e I S R o n t h e p r o p e r t i e s

o f m u l t i p a r t i c l e h a d r o n i c s y s t e m s p r o d u c e d i n l o w - p ^ ( p p ) i n t e r a c t i o n s ,

w e h a v e d i s c o v e r e d a r e m a r k a b l e s e t o f a n a l o g i e s b e t w e e n t h e p r o p e r t i e s

o f t h e m u l t i p a r t i c l e s y s t e m p r o d u c e d i n l o w - p T ( p p ) i n t e r a c t i o n s , ( e e )

a n n i h i l a t i o n , a n d i n D I S p r o c e s s e s | [ l l -273 .

T h e k e y p o i n t i n t h e s e s t u d i e s i s t h e n e w m e t h o d i n t r o d u c e d i n o r d e r

t o s t u d y ( p p ) i n t e r a c t i o n s a t t h e I S R . T h i s m e t h o d i s b a s e d o n t h e s u b

t r a c t i o n o f t h e " l e a d i n g " p r o t o n e f f e c t f r o m t h e f i n a l s t a t e o f a ( p p )

i n t e r a c t i o n . O n c e t h e " l e a d i n g " p r o t o n s a r e s u b t r a c t e d , i t i s p o s s i b l e

t o w o r k i n t h e c o r r e c t r e f e r e n c e f r a m e o f t h e m u l t i p a r t i c l e s y s t e m p r o

d u c e d . M o r e o v e r , i t i s p o s s i b l e t o c a l c u l a t e t h e " e f f e c t i v e " e n e r g y

a v a i l a b l e f o r p a r t i c l e p r o d u c t i o n , d e f i n e d a s

I , h a d , . 2 L i n c ' i n c l e a d i n g l e a d i n g s 2

y ( q t o t ) = y(qi + q2 - qi B - qz s ) , ( D w h e r e q i n c a n d q l e a d i n g a r e t h e f o u r - v e c t o r s o f t h e i n c i d e n t a n d " l e a d i n g " 1.2 ^1,2 p r o t o n s , r e s p e c t i v e l y .

- 4 1 2 -

T h i s " e f f e c t i v e " e n e r g y c a n b e v e r y d i f f e r e n t f r o m t h e " n o m i n a l " t o t a l

e n e r g y o f t h e I S R p r o t o n b e a m s .

L e t u s p o i n t o u t t h a t t h e " l e a d i n g " p r o t o n e f f e c t ( s e e F i g . 1 ) i s n o t

a p h e n o m e n o n l i m i t e d t o t h e I S R c a s e — n o r t o t h e p r o t o n - p r o t o n c o l l i

s i o n s ^ 2 8 , 2 9 ] . We h a v e i n v e s t i g a t e d t h i s p h e n o m e n o n a n d h a v e d i s c o v e r e d

t h a t t h e " l e a d i n g " h a d r o n e f f e c t i s p r e s e n t n o m a t t e r i f t h e i n t e r a c t i o n

i s i n i t i a t e d b y a h a d r o n s i g n a l , o r b y a p h o t o n , o r b y a w e a k b o s o n ( s e e

F i g . 2 ) . M o r e o v e r , w e h a v e f o u n d t h a t t h e " l e a d i n g " e f f e c t i s m o r e p r o

n o u n c e d w h e n m o r e " q u a r k s " a r e a l l o w e d t o g o f r o m t h e i n i t i a l t o t h e f i n a l

s t a t e ( s e e F i g . 1 ) . T h e s e f i n d i n g s i m p l y t h a t o u r n e w m e t h o d o f i n v e s t i

g a t i n g m u l t i p a r t i c l e h a d r o n i c s y s t e m s p r o d u c e d i n ( p p ) i n t e r a c t i o n s a t t h e

I S R i s i n d e e d o f g e n e r a l v a l i d i t y , a n d s h o u l d b e u s e d i n a l l r e a c t i o n s i n

o r d e r t o e s t a b l i s h a c o m m o n a n d u n d e r s t o o d b a s i s f o r t h e i r c o m p a r i s o n .

I t i s m a n i f e s t l y i n c o r r e c t t o c o m p a r e p r o c e s s e s w h e r e t h e " e f f e c t i v e "

e n e r g y a v a i l a b l e f o r p a r t i c l e p r o d u c t i o n i s n o t t h e s a m e .

T h i s m e a n s t h a t i t i s w r o n g t o c o m p a r e , f o r e x a m p l e , t h e m u l t i p a r t i c l e

h a d r o n i c s y s t e m s p r o d u c e d i n a ( p p ) c o l l i s i o n a t ( / s ) = 30 G e V w i t h t h e + _ p p

m u l t i p a r t i c l e h a d r o n i c s y s t e m s p r o d u c e d i n a ( e e ) a n n i h i l a t i o n a t

( / s ) . _ = 30 G e V . I n f a c t ( / s ) i s n o t t h e " e f f e c t i v e " e n e r g y a v a i l a b l e e + e p p

f o r p a r t i c l e p r o d u c t i o n , w h i l s t ( / s ) e + e _ i s ( s e e F i g . 3 ) . I n a ( p p ) i n t e r

a c t i o n t h e e f f e c t i v e e n e r g y a v a i l a b l e f o r p a r t i c l e p r o d u c t i o n i s / ( q h a d ) 2j

V t o t a s s h o w n i n f o r m u l a ( 1 ) .

A n a n a l o g o u s p r o b l e m e x i s t s i n t h e D I S c a s e . H e r e t h e q u a n t i t y W ,

d e f i n e d a s t h e t o t a l e n e r g y o f t h e h a d r o n i c s y s t e m , d o e s i n d e e d c o n t a i n

a " l e a d i n g " h a d r o n . T h i s i s t h e r e a s o n w h y t h e a v e r a g e c h a r g e d - p a r t i c l e

m u l t i p l i c i t i e s m e a s u r e d i n D I S a n d i n ( e + e ) c o u l d n o t a g r e e ( s e e F i g . 4 ) .

T h e m u l t i p a r t i c l e h a d r o n i c s y s t e m , p r o d u c e d i n ( e + e ) a n d ( D I S ) c a n b e

c o m p a r e d , o n a s o u n d b a s i s , o n l y i f ( / s ) + _ i s c o m p a r e d n o t w i t h W b u t

W i t h / q J £ > 2 .

2 . 2 T h e i d e n t i f i c a t i o n o f t h e c o r r e c t v a r i a b l e s

T h e i d e n t i f i c a t i o n o f t h e c o r r e c t v a r i a b l e s i n d e s c r i b i n g h a d r o n

p r o d u c t i o n i n ( p p ) i n t e r a c t i o n s , ( e + e ) a n n i h i l a t i o n , a n d D I S p r o c e s s e s ,

i s t h e b a s i c s t a r t i n g p o i n t f o r s t u d y i n g a n a l o g i e s a m o n g a n d d i f f e r e n c e s

b e t w e e n t h e s e t h r e e w a y s o f p r o d u c i n g m u l t i p a r t i c l e h a d r o n i c s y s t e m s .

L e t me s h o w h o w t h i s i s d o n e .

- 413 -

2.2.1 e e a n n i h i l a t i o n is i l l u s t r a t e d in the f o l l o w i n g d i a g r a m :

w h e r e q i n ° a n d q | n C are the f o u r - m o m e n t a of the i n c i d e n t e l e c t r o n e a n d

+ h

p o s i t r o n e ; q is the f o u r - m o m e n t u m of a h a d r o n p r o d u c e d in the f i n a l

s t a t e , w h o s e total e n e r g y is

e + e » m c

qi inc

q 2 ) = 2E. b e a m

(2)

( w h e n the c o l l i d i n g b e a m s h a v e the same e n e r g y )

A s w e w i l l see l a t e r ,

inc qi

h a d qi

inc q 2

h a d q 2

h a d w h e r e q i , 2 are the f o u r - m o m e n t a a v a i l a b l e in a (pp) c o l l i s i o n f o r the

p r o d u c t i o n of a final s t a t e w i t h t o t a l h a d r o n i c e n e r g y

TA3 had hadx 2 , F, + q 2 ) = y (

h a d . 2

« t o t * (3)

It is this q u a n t i t y ^ q ^ * ^ ) w h i c h s h o u l d b e u s e d in the c o m p a r i s o n w i t h

( e + e ) a n n i h i l a t i o n , a n d t h e r e f o r e w i t h

<»£) + -eê (4)

- 4 1 4 -

This means that

(/i) + _ =J(¿aáy . (5) e +e V ntot

Moreover, the fractional energy of a hadron produced in the final state + -of an (e e ) annihilation is given by

h had q ' qtot „ E h

e e had . had r r\ ^tot ^tot eê

where the dots indicate the scalar product and E is the energy of the hadron "h" measured in the (e +e ) c m . system. Notice that the four-momentum q^ a f has no space-like part:

^tot * *

^tot (_ e Te J

2.2.2 PIS processes are illustrated in the diagram below:

where qi and qi are the four-momenta of the initial- and final-sta inc

leptons, respectively; qz is the four-momentum of the target nucleón; had

qi is the four-momentum transferred from the leptonic to the hadronic vertex whose time-like component is usually indicated as V :

- 4 1 5 -

had - , .-'•had , _ „had N qi = d p i ; V = Ei )

Notice that in order to easily identify the equivalent variables in (pp) interactions, we have introduced a notation in terms of E^ a <* and -*had Pi •

A basic quantity in DIS is the total hadronic mass

/ „ 2 \ _ / had inc. ( ) D I S

= (qi + qz )

and the fractional energy

h . inc ( Z ) = -3. 12

DIS had . inc ' qi q2

where again the dots between the four-momenta indicate their scalar product.

2.2.3 (pp) interactions are illustrated in the following graph:

- 416 -

i.e.

, h a d . , h a d h a d . (q ) = (qi + q 2 )

t O t p p p p

in f a c t

V ^ t o t p p e + e

M o r e o v e r ,

h . h a d

.had „ q q t o t ( x ) " a u = 2

p p h a d h a d ' q • q H t o t H t o t

to b e c o m p a r e d w i t h

h . ( h a d . , , h a d _ q ( q t o t > e + e -(x) . _ = 2

o — a e + e f h a d . , h a d . (q_ J • (q_

n t o t + _ n t o t + _ e T e e e

w h e r e the s u b s c r i p t s ( e + e ) i n q ^ ^ a r e t h e r e to m a k e it c l e a r t h a t t h e s e

q u a n t i t i e s are m e a s u r e d in ( e + e ~ ) c o l l i s i o n s a n d are the q u a n t i t i e s e q u i

v a l e n t to qî* 3^ m e a s u r e d in (pp) i n t e r a c t i o n s . n t o t

T h e same (pp) d i a g r a m s h o w n a b o v e c a n b e u s e d in o r d e r to w o r k o u t

the k e y q u a n t i t i e s n e e d e d w h e n w e w a n t to c o m p a r e (pp) p h y s i c s w i t h D I S .

I n this case w e h a v e

* ) N o t i c e t h a t : r^-t _ h a d h a d _ * y ( q t o t ) - 2E , a n d ( x ) p p « x R

w h e r e q î n 2 are the f o u r - m o m e n t a of the t w o i n c i d e n t p r o t o n s ; q i ^ 2 ^ i n ^

a r e t h e f o u r - m o m e n t a of the two l e a d i n g p r o t o n s ; q ^ f are the s p a c e

l i k e f o u r - m o m e n t a e m i t t e d b y the two p r o t o n v e r t i c e s ; is t h e f o u r -

m o m e n t u m of a h a d r o n p r o d u c e d in the f i n a l s t a t e .

N o w , a t t e n t i o n ! A ( p p ) c o l l i s i o n c a n b e a n a l y s e d i n s u c h a w a y as

to p r o d u c e the k e y q u a n t i t i e s p r o p e r to ( e + e ) a n n i h i l a t i o n a n d D I S p r o

c e s s e s .

I n f a c t , f r o m the a b o v e d i a g r a m w e c a n w o r k out the f o l l o w i n g q u a n t i -*) + —

ties , w h i c h are n e e d e d if w e w a n t to c o m p a r e (pp) p h y s i c s w i t h (e e ),

- 4 1 7 -

a n d

/ T I2Nhad _ , h a d i n c x2

PP

( Z ) h a d = <j • R 2 , P P q ^ a d - q | n c

N o t i c e t h a t i n W t h e l e a d i n g p r o t o n N o . 2 i s n o t s u b t r a c t e d . T h i s i s t h e

r e a s o n f o r t h e d i f f e r e n c e s f o u n d i n t h e c o m p a r i s o n b e t w e e n D I S d a t a a n d

e e ( s e e F i g . 4 ) . I n f a c t ( W 2 ) i s n o t t h e e f f e c t i v e t o t a l e n e r g y a v a i l

a b l e f o r p a r t i c l e p r o d u c t i o n , o w i n g t o t h e p r e s e n c e t h e r e o f t h e l e a d i n g

p r o t o n .

2 . 3 E x p e r i m e n t a l r e s u l t s

A s e r i e s o f e x p e r i m e n t a l r e s u l t s , w h e r e ( p p ) i n t e r a c t i o n s h a v e b e e n

a n a l y s e d à la e + e a n d à la D I S , h a v e g i v e n i m p r e s s i v e a n a l o g i e s i n t h e

m u l t i p a r t i c l e s y s t e m s p r o d u c e d i n t h e s e — s o f a r c o n s i d e r e d — b a s i c a l l y

d i f f e r e n t p r o c e s s e s : ( p p ) , ( e + e ) , D I S .

T h e e x p e r i m e n t a l d a t a w h e r e ( p p ) i n t e r a c t i o n s a r e c o m p a r e d w i t h ( e e )

a r e s h o w n i n F i g s . 5 - 1 2 .

T h e e x p e r i m e n t a l d a t a w h e r e ( p p ) i n t e r a c t i o n s a r e c o m p a r e d w i t h D I S

a r e s h o w n i n F i g s . 1 3 - 1 5 .

T h e s e c o m p a r i s o n s s h o w s t r i k i n g a n a l o g i e s w i t h r e s p e c t t o t h e f o l l o w i n g

q u a n t i t i e s :

i ) t h e i n c l u s i v e f r a c t i o n a l e n e r g y d i s t r i b u t i o n o f t h e p r o d u c e d p a r

t i c l e s [ 1 1 , 1 2 , 1 9 , 2 1 ] ( s e e F i g s . 5 , 6 , 1 5 ) ;

i i ) t h e a v e r a g e c h a r g e d - p a r t i c l e m u l t i p l i c i t i e s [ 1 3 , 1 8 , 2 2 , 2 6 , 2 7 ] ( s e e

F i g s . 7 , 1 3 , 1 4 ) ;

i i i ) t h e r a t i o o f t h e a v e r a g e e n e r g y a s s o c i a t e d w i t h t h e c h a r g e d p a r t i c l e s

o v e r t h e t o t a l e n e r g y a v a i l a b l e f o r p a r t i c l e p r o d u c t i o n [ 1 5 ] ( s e e

F i g . 8 ) ;

i v ) t h e i n c l u s i v e t r a n s v e r s e m o m e n t u m d i s t r i b u t i o n o f t h e p r o d u c e d p a r

t i c l e s [ l 7 , 2 0 ] ( s e e F i g s . 9 - 1 1 ) ;

v ) t h e c o r r e l a t i o n f u n c t i o n s i n r a p i d i t y [ 2 5 ] ( s e e F i g . 1 2 ) ;

- 4 1 8 -

N o t i c e the p o w e r of the (pp) i n t e r a c t i o n . O n c e this is a n a l y s e d in

the c o r r e c t w a y it p r o d u c e s r e s u l t s e q u i v a l e n t to ( e + e ) a n d D I S .

T h i s m e a n s t h a t t h e r e is a n i m p o r t a n t u n i v e r s a l i t y g o v e r n i n g these —

so far c o n s i d e r e d — d i f f e r e n t w a y s of p r o d u c i n g m u l t i h a d r o n i c s y s t e m s .

2.4 C o n c l u s i o n s

F r o m the a b o v e a n a l y s i s w e c a n c o n c l u d e t h a t

1) the l e a d i n g e f f e c t m u s t b e s u b t r a c t e d if w e w a n t to c o m p a r e p u r e l y

h a d r o n i c i n t e r a c t i o n s w i t h ( e + e ) and D I S ;

2) the o l d m y t h , b a s e d o n the b e l i e f that i n o r d e r to c o m p a r e (pp) w i t h

(e e ) a n d DIS y o u n e e d high-p^, (pp) i n t e r a c t i o n s , is d e a d . I n f a c t

w e h a v e p r o v e d t h a t low-p^, (pp) i n t e r a c t i o n s p r o d u c e r e s u l t s i n e x c e l

lent a n a l o g y w i t h ( e + e ) a n n i h i l a t i o n a n d P I S p r o c e s s e s , the b a s i c

V' h a ( J 2 ( q t o t ) for a c o m p a r i s o n w i t h

( e r e ), a n d - ^ W ^ p p ^ for a c o m p a r i s o n w i t h D I S .

T h e e x i s t e n c e of h i g h - p ^ e v e n t s m e a n s that p o i n t - l i k e c o n s t i t u e n t s

e x i s t i n s i d e the n u c l é o n . B u t l o w - p ^ e v e n t s c o n t a i n the s a m e a m o u n t

of b a s i c i n f o r m a t i o n as high-p^, e v e n t s . N o s p e c i a l f e a t u r e s — a p a r t

f r o m (p,j,) [[see p o i n t (3) below]] — s h o u l d e m e r g e i n the h i g h - p ^ e v e n t s

b e c a u s e l o w - p ^ e v e n t s f o l l o w ( e + e ~ ) a n d D I S .

3) N o w _ t w o _ e x t r a p o l a t i o n s :

Vf 2

( q t o t _ ) :

i) one is at low p^, a n d w e h a v e s e e n w h a t h a p p e n s ;

ii) the o t h e r is at h i g h p^: w e h a v e n o t b e e n a b l e to c o m p a r e , at

c o n s t a n t v a l u e s of , / ( q h a d ) 2 , the m u l t i p a r t i c l e s y s t e m s p r o d u c e d V t o t #

in (pp) i n t e r a c t i o n s at h i g h p^ a n d at low p^,.

O u r a n a l y s i s of the i n c l u s i v e t r a n s v e r s e m o m e n t u m d i s t r i b u t i o n ,

in terms of the r e n o r m a l i z e d v a r i a b l e p^,/(p^) [[notice t h a t h e r e

p^ i n d i c a t e s the t r a n s v e r s e m o m e n t u m of the p a r t i c l e s p r o d u c e d

w i t h r e s p e c t to the jet a x i s , n o t to the c o l l i d i n g (pp) or (pp)

axisjj is s u g g e s t i v e of a v e r y i n t e r e s t i n g p o s s i b i l i t y : i.e.

m u l t i p a r t i c l e s y s t e m s p r o d u c e d at h i g h p^, c o u l d s h o w , at e q u i v a l e n t

( q h a d ) 2 s h i g h e r v a l u e s of ( p T ) . T h i s w o u l d m e a n t h a t h i g h - p _ tot 1 1

m u l t i p a r t i c l e s y s t e m s are p r o d u c e d b y h e a v y q u a r k s .

- 4 1 9 -

A n e x t r a p o l a t i o n o f o u r m e t h o d t o t h e C E R N p p C o l l i d e r w o u l d a l l o w

a l a r g e e n e r g y j u m p a n d c o u l d p r o d u c e c l e a r e v i d e n c e f o r h e a v y

q u a r k p r o d u c t i o n .

L e t u s g i v e a n e x a m p l e . I f t w o j e t s a t t h e p p C o l l i d e r a r e p r o

d u c e d b a c k - t o - b a c k w i t h t h e s a m e t r a n s v e r s e e n e r g y E^,, t h e n w e

h a v e

S u p p o s e t h a t w e a r e a t

2 E T = 1 0 0 G e V .

T h i s s y s t e m , a c c o r d i n g t o o u r e x t r a p o l a t i o n , s h o u l d b e l i k e a

m u l t i p a r t i c l e s t a t e p r o d u c e d b y ( ^ s ) e + e _ = 1 0 0 G e V .

T h e k e y p o i n t i s t o s e e i f , a t t h e C E R N p p C o l l i d e r , a m u l t i

p a r t i c l e s y s t e m p r o d u c e d a t l o w b u t w i t h

yo2 = 100 Gev

l o o k s l i k e t h e o n e p r o d u c e d a t h i g h E^,. T h e m a i n d i f f e r e n c e w e

c a n e x p e c t i s t h e v a l u e o f ( p ^ , ) .

T o c h e c k t h e s e p o i n t s i s a n o t h e r i m p o r t a n t c o n t r i b u t i o n i n o r d e r

t o u n d e r s t a n d h o w h a d r o n c o l l i d e r s c o m p a r e w i t h e + e c o l l i d e r s . 3 . C O N C L U S I O N S

1 ) T h e n e w w a y o f e x p l o i t i n g t h e C E R N p p C o l l i d e r c o u l d b r i n g a b o u t a

s e r i o u s c o m p e t i t i o n w i t h t h e ( e + e ) c o l l i d e r s i n a v e r y i m p o r t a n t

f i e l d : t h e s e a r c h f o r n e w f l a v o u r s a t v e r y h i g h m a s s e s .

2 ) T h e n e w m e t h o d o f s t u d y i n g ( p p ) a n d ( p p ) c o l l i s i o n s — b a s e d o n t h e

s u b t r a c t i o n o f t h e " l e a d i n g " e f f e c t s — a l l o w s u s t o p u t o n e q u a l

f o o t i n g t h e m u l t i p a r t i c l e s y s t e m s t h a t a r e p r o d u c e d i n p u r e l y h a d r o n i c

i n t e r a c t i o n s , i n ( e + e ) a n n i h i l a t i o n , a n d i n D I S p r o c e s s e s .

Purely hadronic interactions m e a n s u s i n g m a c h i n e s s u c h a s t h e I S R ,

t h e C E R N p p C o l l i d e r , t h e B N L - C B A C o l l i d e r , a n d t h e F e r m i l a b ( p p )

C o l l i d e r .

- 420 -

(e e ) annihilation m e a n s u s i n g m a c h i n e s s u c h a s L E P a n d i t s p o s s i b l e

d e v e l o p m e n t s .

D J S processes m e a n s u s i n g m a c h i n e s s u c h a s H E R A .

T h e " l e a d i n g 1 1 s u b t r a c t i o n a l l o w s u s t o s h o w t h a t a u n i v e r s a l f e a t u r e

i s a t w o r k i n t h e m e c h a n i s m , w h i c h p r o d u c e s m u l t i b o d y f i n a l s t a t e s

i n ( p p ) , ( e + e ) , a n d D I S .

S o , i n t h e f i e l d o f n e w , v e r y h e a v y f l a v o u r s , a n d o f m u l t i p a r t i c l e

p r o d u c t i o n , o u r v i e w s o n h a d r o n c o l l i d e r s c o u l d c h a n g e i n t h e n e a r f u t u r e .

T h e c r u c i a l m a c h i n e i s t h e C E R N p p C o l l i d e r .

- 4 2 1 -

R E F E R E N C E S

"l"j A . Z i c h i c h i , N e w f l a v o u r s : e x p e r i m e n t v e r s u s t h e o r y . F r o m c h a r m t o t h e

4 t h f a m i l y , T a l k g i v e n a t t h i s c o n f e r e n c e .

£ 2 ] M. B a s i l e e t a l . , N u o v o C i m e n t o L e t t e r s 3 0 , 4 8 7 ( 1 9 8 1 ) .

[33 M . B a s i l e e t a l . , N u o v o C i m e n t o 6 5 A , 4 0 8 ( 1 9 8 1 ) .

[43 M . J a c o b a n d P . V . L a n d s h o f f , P h y s . R e p . 4 8 , N o . 4 ( 1 9 7 8 ) .

f _ 5 ] E . R e y a , P h y s . R e p . 6 9 , N o . 3 ( 1 9 8 1 ) .

| ~ 6 J P . V . L a n d s h o f f , T e s t i n g Q C D i n h a d r o n i c p r o c e s s e s , L e c t u r e g i v e n

a t t h e " E t t o r e M a j o r a n a " I n t . S c h o o l o f S u b n u c l e a r P h y s i c s ,

E r i c e , 1 9 8 2 .

£ 7 ] M . J a c o b , C E R N - T H / 3 5 1 5 ( 1 9 8 3 )

[ 8 ] U A 2 C o l l a b o r a t i o n , P h y s . L e t t . B 1 1 8 , 2 0 3 ( 1 9 8 2 ) .

f_9] U A 1 C o l l a b o r a t i o n , p r e p r i n t C E R N - E P / 8 3 - 0 2 ( 1 9 8 3 ) .

[l0] H . B o g g i l d , C E R N - E P / 8 2 - 1 8 7 ( 1 9 8 2 ) .

[ i l ] M. B a s i l e e t a l . , P h y s . L e t t . 9 2 B , 3 6 7 ( 1 9 8 0 ) .

[ 1 2 ] M . B a s i l e e t a l . , N u o v o C i m e n t o 5 8 A , 1 9 3 ( 1 9 8 0 ) .

[ 1 3 ] M . B a s i l e e t a l . , P h y s . L e t t . 9 5 B , 3 1 1 ( 1 9 8 0 ) .

£l4J M. B a s i l e e t a l . , N u o v o C i m e n t o L e t t . 2 9 , 4 9 1 ( 1 9 8 0 ) .

[ 1 5 ] M. B a s i l e e t a l . , P h y s . L e t t . 9 9 B , 2 4 7 ( 1 9 8 1 ) .

[ l 6 ] M . B a s i l e e t a l . , N u o v o C i m e n t o L e t t . 3 0 , 3 8 9 ( 1 9 8 1 ) .

[ 1 7 ] M . B a s i l e e t a l . , N u o v o C i m e n t o L e t t . 3 1 , 2 7 3 ( 1 9 8 1 ) .

f_18] M . B a s i l e e t a l . , N u o v o C i m e n t o 6 5 A , 4 0 0 ( 1 9 8 1 ) .

[ i g ] M. B a s i l e è t a l . , N u o v o C i m e n t o 6 5 A , 4 1 4 ( 1 9 8 1 ) .

- 422 -

[20] M. Basile et al., Nuovo Cimento Lett. 32, 210 (1981).

[ 2 1 ] M. Basile et al., Nuovo Cimento 67A, 53 (1982).

[22] M. Basile et al., Nuovo Cimento 67A, 244 (1982).

[23] M. Basile et al., preprint CERN-EP/81-147 (1981).

[24] M. Basile et al., preprint CERN-EP/82-182 (1982), submitted to Nuovo Cimento.

[25] G. Bonvicini et al., preprint CERN-EP/83-29 (1983), submitted to Nuovo Cimento Letters.

[26] M. Basile et al., Nuovo Cimento Letters 36, 303 (1983).

[27] G. Bonvicini et al., preprint CERN-EP/83-33 (1983), submitted to Nuovo Cimento Letters.

[28] M. Basile et al., Nuovo Cimento 66A, 129 (1981).

[29] M. Basile et al., Nuovo Cimento Letters 3_2, 321 (1981).

- 4 2 3 -

p-p /s = 25+62 GeV

ln° of propagating 3 quarks)

/V n

/ i

p

• 1 i i i i

0 1 2 3 4 5 U.2,.4,.8)

F i g . 1 T h e l e a d i n g q u a n t i t y 1 . ( 0 . 2 , 0 . 4 , 0 . 8 ) , f o r v a r i o u s f i n a l - s t a t e h a d r o n s i n ( p p ) c o l l i s i o n s a t I S R e n e r g i e s ( 2 5 t o 6 2 G e V ) , i s p l o t t e d v e r s u s t h e n u m b e r o f p r o p a g a t i n g q u a r k s f r o m t h e i n c o m i n g i n t o t h e f i n a l -s t a t e h a d r o n s . L ( x o , x i , X 2 ) i s d e f i n e d a s L ( x 0 , x i , x 2 ) = / x ? F ( x ) d x / / x l F ( x ) d x , w h e r e F ( x ) = ( l / " i ï ) / [ ( 2 E / / ô ( d 2 a / d x d p £ ) ] d p | . T h e d a s h e d 1 i n e i s o b t a i n e d b y u s i n g a p a r a m e t r i z a t i o n o f t h e s i n g l e - p a r t i c l e i n c l u s i v e c r o s s - s e c t i o n , a s d e s c r i b e d i n R e f s . 2 8 a n d 2 9 .

N P (n° of

propagating quarks)

• v - p o e - p

W = 4.5 GeV W = 3 G e V

A"

1 - /

o •/

I 1 I I I I

0 1 2 * 3 4 5 U.2,.4,.8)

F i g . 2 L ( 0 . 2 , 0 . 4 , 0 . 8 ) f o r A 0 p r o d u c t i o n i n ( v p ) a n d ( e p ) r e a c t i o n s . T h e d a s h e d l i n e i s t h e s a m e a s f o r F i g . 1.

- 4 2 4 -

100

F i g . 3 T h e i n c l u s i v e f r a c t i o n a l m o m e n t u m d i s t r i b u t i o n s o f n e g a t i v e p a r t i c l e s f o r ( p p ) i n t e r a c t i o n s u s i n g t h e s t a n d a r d a n a l y s i s a t ( v / s ) p p = 3 0 G e V ( o p e n p o i n t s ) ; u s i n g t h e m e t h o d o f r e m o v i n g t h e l e a d i n g p r o t o n s a t ( / s ) p p = 6 2 G e V a n d 2 E h a d = 2 8 t o 32 G e V ( b l a c k c i r c l e s ) ; t h e ( e + e ~ ) d a t a a t ( v / s ) e + e - = 2 7 . 4 t o 3 1 . 6 G e V ( b l a c k t r i a n g l e s ) .

to

0.1

1 0 -

' 1 , rfW('-) 1 1 r O (pp)-L 2 I L (vÇ) p p=30GeV

* l p p N e v dxg ( 2 E H A D = 28. r 32. GeV

A ( e V ) - ( V S " )J . . -=274T3 I .6G * / 2a d x R

e e "

( -Îpp' 62 GeV

O • o

o

0.1 X R > X R

0.2 0.3 0.4 0.5 0.6 0.7 0.8

14

12

10

n r n i i i i i r

j IVe")

l (pp)deading p r o t o n s removed)

4 6 W (/s),

J i i i

e*e-,

8 10

< 2 EHAD>.

20 40

PP (GeV)

J L 60

F i g . 4 T h e d a s h e d l i n e i s t h e b e s t f i t t o ( n c n ) m e a s u r e d i n ( e + e ~ ) v e r s u s ( v / s ) e + e - » a n d i n ( p p ) r e m o v i n g l e a d i n g p r o t o n s v e r s u s 2 E n a a . T h e p o i n t s a r e t h e m e a s u r e m e n t s o f ( n c h ) v e r s u s W i n ( v p ) D I S , a n d t h e c o n t i n u o u s l i n e i s t h e b e s t f i t t o t h e s e d a t a .

100

1.0

0.1

• p-p (ISR) 3í 2E H A D S 4 GeV o e*»-(SLAC) VS.3 GeV

o4o°° i. o ^ ^ o 0

J I I I I I L

100

10 b

1.0 h

• a Z x •a -a

0.1b

o e'e-(SLAC) V5*4.8 GeV

T °?o T °, °o

°o t

I I I I J L 0.1 0.2 0.3 0.« 0.5 0.6 0.7 0.6 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

100

b „*

1.0

0.1

• p-p (ISR) 6i2E H A OS9GeV o e«e- (SLAC) V5 = 7.4 GeV

o r° I o

i

J J I I . ,1 I L 0 0.1 0.2 0.3 0.4 OS 0.6 0.7 0.8

a) b) c)

F i g . 5 T h e i n c l u s i v e s i n g l e - p a r t i c l e f r a c t i o n a l m o m e n t u m d i s t r i b u t i o n s ( 1 / N e v ) ( d N t r a c c / d x ^ ) f o r d a t a t a k e n a t ( / s ) p p = 30 G e V a n d f o r t h r e e i n t e r v a l s o f 2 E h a d . A l s o s h o w n a r e d a t a f r o m S P E A R .

100

10b

b •o m

1.0

W h

• Jp-p(ISR) 10Í 2 E H A D S 16 GeV

o e'e- (TASSO) Vä = 13 GeV

0.1

i I A 62 GeV

VSpps j • 44 GeV I 30 GeV

r :

_1_ 0.2 0.3 0.4 0.5

• • X

0.6 0.7 0.8

100

10

b „°= "O "D

1.0

0.11-

5*

0.1

• J p-p (ISR) 16 Í 2 E H A D S 22 GeV

o e'e- (TASSO) Vä = 17 +22 GeV

A 62 GeV V5p„= • 44 GeV

I 30 GeV

0.2 0.3 0.4 0.5 0.6 0.7 0.8

100

| . A Jj p-p (ISR) 28 í 2 E H A 0 Í 32 GeV

o e'e- (TASSO) V5 27.431.6 GeV

10

b i

1.0

0.1

VS . I A 62 GeV v s w - f. 44 GeV

0.1

5 | r

0.2 0.3 0.4 0.5 0.6 0.7 0.8

a) b) c)

Fig. 6 The inclusive single-particle fractional momentum distributions (l/N e v)(dN l_^ o^ 1/dx*) in the same 2Ehad interval, but different d / s ) p p . Also shown are data from TASSO at PETRA. track R

- 427 -

( v ^ ) p p ( G e V )

0 I I I I I I I I I I I I I I I I I I I I I I I I I 1 I I I I I I 11 M 11 il I I I I

2 4 6 8 1 0 2 0 3 0 4 0 5 0

( ^ W ^ E n J S e V )

F i g . 7 Mean charged-particle multiplicity [averaged over different (»//s)pp3 versus 2 E n a d , compared with (e +e~) data. The continuous line is the best fit to our data according to the formula (n ch)= a + b exp [c/ln (s/A 2)]. The dotted line is the best fit using PLUTO data. The dashed-dotted line is the standard (pp) total charged-particle multiplicity with, superimposed, our data as open triangular points.

1.0

o 3> Iii v 0.5

Í A Vs = 62 GeV • Vs = 44 GeV

Vs= 30 GeV

(e+e-) x MARK I (SPEAR) O JADE (PETRA)

10 20 30 2 E HAD (GeV)

F i g . 8 The charged-to-total energy ratio obtained in (pp) collisions Oipp, plotted versus 2 E H A D and compared with (e+e -) obtained at SPEAR and PETRA.

p 2 (GeV/c)2 p 2 (GeV/c)2 p 2 (GeV/c)2

a ) b ) c )

F i g . 9 T h e i n c l u s i v e s i n g l e - p a r t i c l e t r a n s v e r s e m o m e n t u m d i s t r i b u t i o n ( 1 / N e v ) ( d N ^ ^ ^ / d p 2 ^ ) f o r d a t a t a k e n a t ( / s ) _ = 30 G e V a n d f o r t h r e e i n t e r v a l s o f 2 E n a < * . A l s o s h o w n i s t h e f i t t o t h e S P E A R d a t a ( c o n t i n u o u s l i n e ) .

100 100

10

o

H b

1.0

i f f

0.1

• p-p (ISR) 11 5 2 E H A D «13 GeV

o e* e- (PETRA TASSO) VS =12 GeV

T

_l I I I I I ' ' _ l L. 0.5 1.0

p* (GeV/c)2

a)

1.5

10

o

L P.

- b

1.0

0.1

• p-p (ISR) 28« 2 E H A D S 32 GeV

o e* e- (TASSO) Vs : 27.4 - 31.6 GeV

•t o

• \

• „, I i , i i L 0.5 1.0

p* (GeV/c)'

b)

1.5

RO

Fig. 10 The inclusive single-particle transverse momentum distributions ( l / Ne v ^ d N t r a c k ^ d p T ^ f o r t w o E h a d

range. Also shown are data from TASSO at PETRA.

V CL V

1 O. "D

b •o

0,01 -

n 1 1 r

( e V )

(pp)-

i I 1 1 j 1 1 1 I r~

° PLUTQys" = 30 GeV

• PLUTO«Jz 9.4 GeV

This experiment!. g ^2E h a c J-S¡6

*?6

9 9*

! î

_l I I L 0 1 2

P T / 

0.4

_ 0.2 >^

ce 0

-0.2

0.2

0

-0.2

-0.4

• P r e s e n t e x p e r i m e n t , ^ Itot* ) = 2 5 - 3 6 G e V

• T A S S 0 , ( / s ) e V = 2 7 " 3 5 G e V

_1 I I I 1 1 1 1 1 L_ -4 -2 0 2 4

y

. w . . . 0 2 y

0.4

0.2

-0.2

I - I I 1 I I I I u -4 -2 0 2 4

y

0.2

¿ 0 ce

-0.2

-0.4 - ¿

_ i — i — i — i i _

0 2 y

F i g . 12 T w o - p a r t i c l e c o r r e l a t i o n i n r a p i d i t y s p a c e : R ( y > y ' ) > f ° r d i f f e r e n t y ' i n t e r v a l s , a s m e a s u r e d i n

F i g . 11 T h e d i f f e r e n t i a l c r o s s - s e c t i o n ( l/a ) [ [ d 0 / d ( p ^ / ( p ^ ) )J t h e p r e s e n t e x p e r i m e n t a f t e r t h e l e a d i n g p r o t o n s u b -v e r s u s t h e " r e d u c e d " v a r i a b l e p T / ( p ^ , ) . T h e s e d i s t r i b u t i o n s t r a c t i o n i n t h e ^ ( q ^ ^ ) 2 r a n g e 25 t o 36 G e V ( b l a c k a l l o w a c o m p a r i s o n o f t h e m u l t i p a r t i c l e s y s t e m s p r o d u c e d i n p o i n t s ) , c o m p a r e d w i t h t h e r e s u l t s b y t h e T A S S O ( e + e ~ ) a n n i h i l a t i o n a n d i n ( p p ) i n t e r a c t i o n s i n t e r m s o f t h e C o l l a b o r a t i o n a t ( / s ) e + e _ b e t w e e n 27 a n d 35 G e V r e n o r m a l i z e d t r a n s v e r s e m o m e n t u m p r o p e r t i e s . ( o p e n s q u a r e s ) .

- 431 -

14

12

10

8

6

4

~l i i i i i i i i i i i i i i i i i i i i i i i i i i i i I r

• (pp) (This exp.)

l - ( v p )

0 1 L. 1

_l I ' ' I I I I I I I I I I I I I I I I I I ' I I ' I I I

10 100

W 2 (GeV 2 )

1000

F i g . 13 The average charged-particle multiplicities ( n c n ) measured in (pp) at (i/s)pp = 30 GeV, using a DIS-like analysis, are plotted versus W 2 (black points). The open points are the (Vp) data and the continuous line is their best fit.

W 2 (GeV 2 ) 1000

F i g . 14 The mean charged-particle multiplicities ( n c n ) p g ^ n t* i e forward and backward hemispheres versus W 2 , in (Vp), (Vp) , and (pp) interactions.

10

10 ri

• (pp) (This exp.) 81 = W2 = 225 GeV2

o (tip) (EMC) < W2> = KO GeV2

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 z

a )

10

5 N

10'

• (pp) (This exp.) 225 = W2 = 529 GeV2

o (|ip) (EMC) < W 2 > = 350 GeV2

_J L J L

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

b)

F i g . 15 T h e i n c l u s i v e d i s t r i b u t i o n o f t h e f r a c t i o n a l e n e r g y z f o r ( p p ) r e a c t i o n s : a ) i n t h e e n e r g y i n t e r v a l ( 8 1 < W 2 < 2 2 5 ) G e V 2 c o m p a r e d w i t h t h e d a t a f r o m (up) r e a c t i o n s a t ( W 2 ) = 1 4 0 G e V ; b ) i n t h e e n e r g y i n t e r v a l ( 2 2 5 < W 2 < 5 2 9 ) G e V 2 , c o m p a r e d w i t h t h e d a t a f r o m ( y p ) r e a c t i o n s a t < W 2 > = 3 5 0 G e V 2 .

- 4 3 5 -

NEW FLAVOURS : EXPERIMENT VERSUS THEORY. FROM CHARM TO THE 4 T H FAMILY.

M. Basile, J. Berbiers, G. Bonvicini, G. Cara Romeo, L. Cifarelli, A. Contin, M. Curatolo, G. D'Ali, C. Del Papa, B. Esposito,

P. Giusti, T. Massam, R. Nania, G. Natale, F. Palmonari, G. Sartorelli, M. Spinetti, G. Susinno, L. Votano and A. Zichichi

CERN, Geneva, Switzerland Istituto di Fisica dell'Université di Bologna, Italy Istituto Nazionale di Fisica Nucleare, Bologna, Italy

Istituto Nazionale di Fisica Nucleare, LNF, Frascati, Italy

(Presented by A. Zichichi)

ABSTRACT

A new method of searching for heavy flavours "up-like" and "down-like" in hadronic interactions at the CERN pp Collider is proposed. The method is based on the measurement of the e±

asymmetry in the proton and antiproton hemispheres. The amplitude of the asymmetry depends on the "leading" production of baryons and antibaryons — the sign on the "up-like" or "downlike" nature of the heavy flavour carried by the baryonic states. A detailed study of cross-section estimates, production and decay distributions, and detection acceptances, shows that the effect looks measurable at the CERN pp Collider.

1. INTRODUCTION

The problem of searching for heavy flavours at the CERN pp Collider is, needless to say, of the utmost importance. At this meeting you have

o ±

heard a lot about Z and W : in this case the cross-section evaluations are easy. Moreover, their "expected" masses are well known. The Z° and W"*" will play a crucial role in our understanding of the electroweak forces. If Z° and W ± are found at the expected masses, we can conclude that the heavy bosons expected as manifestations of the broken local gauge symmetry indeed exist.

This discovery will, however, shed no light on the other two key problems of subnuclear physics: the family, and the hierarchy.

- 436 -

F i n d i n g t h e " t o p " w i l l a l l o w u s t o c o n c l u d e t h a t t h e 3 r d f a m i l y d o e s

e x i s t , a n d t h a t i t l o o k s l i k e t h e o t h e r t w o . S t u d y i n g t h e 4 t h f a m i l y w i l l

o p e n a n e w w a y t o w a r d s t h e u n d e r s t a n d i n g o f t h e f a m i l i e s s t r u c t u r e . T h e

f o u r f a m i l i e s a r e s h o w n i n t h e n e x t g r a p h . T h e m a i n o b j e c t i v e s o f t h e

p r e s e n t p a p e r a r e i n d i c a t e d b y t h e d o t t e d c i r c l e s :

1 s t 2 n d 3 r d 4 t h

L e t me s a y a f e w w o r d s a b o u t t h e s e o b j e c t i v e s . T h e r e a s o n f o r a 3 r d

f a m i l y i n t h e q u a r k w o r l d c a m e f r o m t h e P C v i o l a t i o n ( s i x q u a r k s a r e

n e e d e d ) , a n d t h e A d l e r - B e l l - J a c k i w ( A B J ) a n o m a l y c a n c e l l a t i o n ( t h e n u m b e r

o f l e p t o n s s h o u l d b e e q u a l t o t h e n u m b e r o f q u a r k s ) . I n t h e 3 r d f a m i l y ,

t h e r e i s a m i s s i n g q u a r k : t h e " t o p " . (We p r o p o s e c o n t i n u i n g t o c a l l i t

" t o p " : t h e " t r u t h " s h o u l d b e t h e l a s t q u a r k e v e r t o e x i s t ) .

T h e r e i s a n i n t e r e s t i n g p r o b l e m i n S U p e r S Y m m e t r y ( S U S Y ) . A v e r y

h e a v y q u a r k i s n e e d e d s o a s t o a v o i d a c o n f l i c t w i t h t h e e x i s t i n g l o w e r

l i m i t s i n t h e g l u i n o m a s s £ l j - T h i s q u a r k s h o u l d h a v e a m a s s i n t h e f e w

1 0 2 G e V / c 2 r a n g e , i n o r d e r t o p r o d u c e r a d i a t i v e l y ( s e e F i g . 1 ) a f e w

G e V / c 2 m a s s f o r t h e g l u i n o . T h e e x i s t i n g q u a r k s ( s , b , a n d c ) a r e n o t

h e a v y e n o u g h f o r t h i s p u r p o s e .

O n t h e o t h e r h a n d , n a t u r e h a s o f t e n p r o v i d e d p h y s i c i s t s w i t h m o r e

r e g u l a r i t i e s t h a n a r e n e e d e d . F o r e x a m p l e , t h e e q u a l i t y b e t w e e n t h e p r o t o n

a n d t h e e l e c t r o n c h a r g e s , w h i c h i t t o o k m o r e t h a n t h r e e d e c a d e s t o u n d e r -

s t a n d .

We p r o p o s e t o c o n s i d e r t h e r a t i o b e t w e e n t h e m a s s e s o f t h e k n o w n

h e a v y q u a r k s a s a l i m i t f o r t h e r e g u l a r i t y i n t h e i r m a s s e s . T h e r e a r e

g o o d r e a s o n s £ 2 ] f o r c o n s i d e r i n g t h e s t r a n g e q u a r k t o b e h e a v y e n o u g h t o

b e u s e d i n o u r a r g u m e n t .

- 437 -

A t p r e s e n t w e k n o w t h a t

i) (m / m ) = (1.8/0.5) = 3.5 = 4 ; c s

ii) (n^/m ) = (5.5/0.5) = 11 = 10 .

S u p p o s e t h a t (i) a n d (ii) a r e o f g e n e r a l v a l i d i t y , i.e.

(m / m ) = fjn(up-like q u a r k ) / m ( d o w n - l i k e q u a r k ) ] = 4 , (1)

C s

a n d

(n^/in,) = [_m(family N + 1 ) / m ( f a m i l y N ) ] = 10 . (2)

W e i g n o r e t h e 1st f a m i l y (u,d) b e c a u s e of its v e r y l i g h t m a s s . T h e

v a l i d i t y of E q s . (1) a n d (2) w o u l d a l l o w us to c o n c l u d e t h a t t h e " t o p "

m a s s is in the 20 G e V / c 2 r a n g e . T h i s is too l i g h t for s u p e r s y m m e t r i c

m o d e l s to a v o i d a g l u i n o m a s s i n c o n f l i c t w i t h e x p e r i m e n t a l d a t a . O n t h e

o t h e r h a n d , S U S Y tells us t h a t the m a x i m u m n u m b e r of f l a v o u r s n ^ a l l o w e d

i n o r d e r to h a v e a c o n s i s t e n t t h e o r y (for e x a m p l e : the u n i f i c a t i o n l i m i t

n o t a b o v e the P l a n c k m a s s ) is n^ = 8. T h i s m e a n s t h a t t h e m a x i m u m n u m b e r

of f a m i l i e s is f o u r . In the t h e o r i e s t h a t i g n o r e S U S Y , t h e a s y m p t o t i c

f r e e d o m is l o s t if n ^ > 16.

W h a t is n o t f o r b i d d e n i n n a t u r e , d o e s t a k e p l a c e . T h u s t h e m e s s a g e

f r o m S U S Y is t w o f o l d :

i) f o u r f a m i l i e s of q u a r k s a r e a l l o w e d ;

ii) q u a r k s h e a v i e r t h a n (d, u, s, c, b, a n d t) a r e n e e d e d .

E q u a t i o n s (1) a n d (2) tell us t h a t t h e 4 t h f a m i l y w o u l d h a v e the

h e a v y m a s s e s r e q u i r e d b y S U S Y . In f a c t , u s i n g E q . ( 2 ) , t h e h e a v y d o w n

like q u a r k [[called, i n the f o l l o w i n g , " s u p e r b e a u t y " o r ( s b ) ] w o u l d h a v e

a m a s s i n the 50 G e V / c 2 r a n g e :

m ( d o w n - h e a v y ) = m ( " s u p e r b e a u t y " ) = 10 * 5.5 = 55 G e V / c 2 ,

a n d , u s i n g E q . ( 1 ) , the h e a v y u p - l i k e q u a r k w o u l d h a v e a m a s s i n t h e

200 G e V / c 2 r a n g e :

m ( u p - h e a v y ) = m ( " s u p e r t r u t h " ) = 55 * 4 = 220 G e V / c 2 .

T h e u p - l i k e q u a r k of the 4 t h f a m i l y s h o u l d b e c a l l e d " s u p e r t r u t h " .

In f a c t , this v e r y h e a v y m a s s is r e q u i r e d b y S U S Y ; m o r e o v e r , if S U S Y is

- 4 3 8 -

a g o o d t h e o r y , t h e 4 t h f a m i l y s h o u l d r e a l l y b e t h e l a s t o f t h e q u a r k

f a m i l i e s e v e r t o b e d i s c o v e r e d .

N o w c o m e s a k e y q u e s t i o n : I f " t o p " a n d " s u p e r b e a u t y " a r e a c c e s s i b l e

t o p p C o l l i d e r e n e r g i e s , h o w c a n t h e y b e d e t e c t e d ? I n o r d e r t o a n s w e r

t h i s q u e s t i o n w e n e e d t o d i s c u s s :

i ) p r o d u c t i o n c r o s s - s e c t i o n s ;

i i ) a n g u l a r a n d m o m e n t u m d i s t r i b u t i o n s o f t h e p r o d u c t i o n a n d t h e d e c a y ;

i i i ) b r a n c h i n g r a t i o s i n t o s e m i l e p t o n i c c h a n n e l s ;

i v ) l u m i n o s i t y ;

v ) r e j e c t i o n p o w e r o f t h e e x p e r i m e n t a l s e t - u p d e s i g n e d t o o b s e r v e t h e

l e p t o n s p r o d u c e d b y t h e d e c a y o f t h e s e " n e w " f l a v o u r s .

W e w i l l c o n c e n t r a t e o u r s e a r c h i n t h e s e m i l e p t o n i c d e c a y c h a n n e l s .

M o r e o v e r , w e w i l l r e s t r i c t t h e l e p t o n s o n l y t o e * , a n d t h e s e a r c h o n l y

t o t h e a s y m m e t r y p r o d u c e d b y t h e s e e * .

M o r e p r e c i s e l y , t h e " t o p " b a r y o n i c s t a t e w i l l d e c a y s e m i l e p t o n i c a l l y

i n t o e + a n d p r o d u c e a p o s i t i v e a s y m m e t r y i n t h e o u t g o i n g p r o t o n r a p i d i t y

h e m i s p h e r e :

A p = ( e + - e ~ ) / ( e + + e~) = p o s i t i v e .

T h e " a n t i - t o p " a n t i b a r y o n i c s t a t e w i l l p r o d u c e a n e g a t i v e a s y m m e t r y

i n t h e o u t g o i n g a n t i p r o t o n r a p i d i t y h e m i s p h e r e

A _ = ( e + - e ~ ) / ( e + + e ) = n e g a t i v e . P

T h e s i g n s o f t h e s e a s y m m e t r i e s w i l l b e r e v e r s e d f o r t h e " s u p e r b e a u t y "

c a s e .

T h e e ~ t r a n s v e r s e m o m e n t u m s p e c t r a a s s o c i a t e d w i t h " t o p " a n d " s u p e r

b e a u t y " w i l l b e q u i t e d i f f e r e n t b e c a u s e

m ( " t o p " ) = 2 5 G e V / c 2 ,

m C ' s u p e r b e a u t y " ) = 5 5 G e V / c 2 .

T h u s t h e a s y m m e t r y w i l l c h a n g e s i g n w i t h i n c r e a s i n g e l e c t r o n e n e r g y .

F i g u r e 2 s h o w s t h e m a i n t r e n d o f t h e m e a s u r e m e n t w e p r o p o s e . T h i s w i l l b e

d i s c u s s e d i n d e t a i l i n S e c t i o n 5 .

- 4 3 9 -

T h e e n e r g y r a n g e w h e r e the e~ a s y m m e t r y h a s to b e m e a s u r e d , a n d the

s e p a r a t i o n b e t w e e n the m a x i m a , d e p e n d o n t h e m a s s d i f f e r e n c e A m b e t w e e n

the two n e w f l a v o u r s :

A m = m ( " s u p e r b e a u t y " ) - m ( " t o p " ) .

A s w e w i l l s e e i n S e c t i o n 5, t h e a m p l i t u d e of the e f f e c t d e p e n d s o n

the p r o d u c t i o n c r o s s - s e c t i o n s , p r o d u c t i o n a n d d e c a y d i s t r i b u t i o n s ,

b r a n c h i n g r a t i o s , l u m i n o s i t y , a n d a c c e p t a n c e a n d r e j e c t i o n p o w e r of the

e x p e r i m e n t a l a p p a r a t u s .

T h e m a t t e r is of g r e a t r e l e v a n c e : C a n h a d r o n i c m a c h i n e s c o m p e t e w i t h

( e + e ) r i n g s i n s e a r c h i n g f o r n e w p a r t i c l e s t a t e s ? N o t e , for e x a m p l e ,

t h a t the P E T R A e + e ~ C o l l i d e r h a s a l r e a d y e s t a b l i s h e d l o w e r limits f o r a

" t o p " - l i k e f l a v o u r , a d o w n - l i k e f l a v o u r , a n d a p o s s i b l e n e w l e p t o n — a l l

t h e s e l i m i t s b e i n g at a b o u t 19 G e V / c 2 [ 3 ] .

2. A B R I E F R E V I E W O F H E A V Y - F L A V O U R P R O D U C T I O N IN H A D R O N I C M A C H I N E S

H o w to l o o k for " t o p " a n d " s u p e r b e a u t y " a t t h e C E R N pp C o l l i d e r is

a p r o b l e m a n a l o g o u s to " c h a r m " a n d " b e a u t y " i n h a d r o n m a c h i n e s , a n d i n

p a r t i c u l a r at the C E R N I S R . It is p r o b a b l y i n s t r u c t i v e to r e v i e w , v e r y

b r i e f l y , t h e m a i n s t e p s i n t h i s f i e l d .

2.1 P r o d u c t i o n c r o s s - s e c t i o n s

T h e t h e o r e t i c a l p r e d i c t i o n s f o r t h e c h a r m p r o d u c t i o n c r o s s - s e c t i o n

a n d t h e e x p e r i m e n t a l f i n d i n g s are s h o w n i n t h e f o l l o w i n g T a b l e 1.

T a b l e 1

T h e o r e t i c a l p r e d i c t i o n s f o r t h e c h a r m c r o s s - s e c t i o n at I S R e n e r g i e s as a f u n c t i o n of O ( T T ) .

T h e c r o s s - s e c t i o n v a l u e e x p e r i m e n t a l l y f o u n d is i n d i c a t e d for c o m p a r i s o n .

S t r i n g m o d e l 1 0 " 1 0 >

F e r m i - H a g e d o r n 1 0 " 5

• x a *> TT

Q C D (fusion) • x a *> TT

Q C D ( f l a v o u r e x c i t a t i o n ) 1 0 - 2 - 1 0 " 3

E x p e r i m e n t a l l y % 1 0 - 2 „

*) a = 1 0 2 m b . TT

- 4 4 0 -

I f w e w e r e t o b e l i e v e i n t h e s t r i n g m o d e l o r i n t h e s t a t i s t i c a l

t h e r m o d y n a m i c a l m o d e l , o r i n t h e f i r s t Q C D a t t e m p t s ( f u s i o n m o d e l ) , t h e

c o n c l u s i o n s h o u l d h a v e b e e n t h a t t h e p r o d u c t i o n a n d o b s e r v a t i o n o f " c h a r m "

i s o u t o f t h e q u e s t i o n i n h a d r o n m a c h i n e s .

O n l y r e c e n t l y , Q C D m o d e l s ( f l a v o u r e x c i t a t i o n ) c a m e n e a r e r t o e x p e r i

m e n t a l f i n d i n g s . I n F i g . 3 a l l t h e e x p e r i m e n t a l d a t a £ 4 ] a r e s h o w n a n d

c o m p a r e d w i t h t h e v a r i o u s s t e p s i n t h e Q C D m o d e l s . N o t i c e t h a t n e i t h e r

l n ( s ) n o r I n 2 ( s ) a r e c o m p a t i b l e w i t h t h e o b s e r v e d t h r e s h o l d b e h a v i o u r .

2 . 2 T h e " l e a d i n g " e f f e c t

A r e s u l t w h i c h w a s u n p r e d i c t e d b y t h e o r y i s t h e " l e a d i n g " e f f e c t w h i c h

s h o w s u p i n t h e p r o d u c t i o n o f h e a v y f l a v o u r s .

A d e t a i l e d s t u d y o f ( p p ) i n t e r a c t i o n s a t t h e I S R s h o w e d t h a t t h e A +

c

i s p r o d u c e d i n a " l e a d i n g " w a y L~5]].

A f t e r t h i s e x p e r i m e n t a l r e s u l t w a s o b t a i n e d , a s e r i e s o f t h e o r e t i c a l

p r o p o s a l s w e r e p r e s e n t e d , t o a c c o u n t f o r t h e " l e a d i n g " A* p r o d u c t i o n . T h e

l o n g i t u d i n a l m o m e n t u m d i s t r i b u t i o n £ 5 ] f o r A* w a s , i n f a c t , f o u n d a t t h e

I S R t o b e ( d a / d | x | ) ^ ( 1 - | x | ) a , w i t h a = 0 . 4 0 ± 0 . 2 5 .

T h e r e s u l t s a r e s h o w n i n F i g . 4 . T h e c h a r m e d - m e s o n p r o d u c t i o n £ ó j ] w a s , o n

t h e o t h e r h a n d , m e a s u r e d t o b e " n o n - l e a d i n g " , i . e .

E ( d o / d | x | ) *v» ( 1 - | x | ) a , w i t h a ~ 3 .

T h i s c a n b e a postevLovi, q u a l i t a t i v e l y u n d e r s t o o d i n t e r m s o f t h e A*

o b t a i n e d b y a r e c o m b i n a t i o n o f t h e s p e c t a t o r c - q u a r k w i t h a v a l e n c e ( u d )

p a i r i n t h e p r o t o n , w h i l s t t h e D p r o d u c t i o n i s g i v e n b y t h e r e c o m b i n a t i o n

o f t h e s p e c t a t o r c - q u a r k w i t h a t m o s t o n e v a l e n c e q u a r k [ 7 , 8 ] .

A m o r e c o m p l e t e s u m m a r y o f c h a r m p r o d u c t i o n i n p u r e l y h a d r o n i c i n t e r

a c t i o n s i s r e p o r t e d i n T a b l e 2 . T h e r e i s n o m o d e l w h i c h c a n f i t a l l

m e a s u r e d q u a n t i t i e s .

- 4 4 1 -

T a b l e 2

E x p e r i m e n t a l f i n d i n g s v e r s u s t h e o r e t i c a l p r e d i c t i o n s f o r v a r i o u s h e a v y - f l a v o u r p r o d u c t i o n p r o p e r t i e s

E x p e r i m e n t

M o d e l s

E x p e r i m e n t D i f t r a c t i v e

F l a v o u r e x c i t a t i o n

F u s i o n

L e a d i n g e f f e c t Y e s Y e s Y e s N o

T h r e s h o l d b e h a v i o u r

S t e e p e r t h a n I n 2 s

I n s S t e e p e r t h a n I n 2 s

» s t e e p e r t h a n I n 2 s

M a s s d e p e n d e n c e

? 1 / m 2 S t r o n g e r t h a n 1 / m 2

» s t r o n g e r t h a n 1 / m 2

C r o s s - s e c t i o n L a r g e L a r g e L a r g e S m a l l

A d e p e n d e n c e a < 2 / 3 * ) a = 2 / 3 a = 1 a = ...

* ) T h e p^, d e p e n d e n c e i s d e r i v e d f r o m d a t a o n s t r a n g e n e s s .

2 . 3 F u r t h e r c o m m e n t s

F o r t h e b e n e f i t o f t h o s e w h o h a v e s t r o n g f a i t h i n Q C D , i t c o u l d b e

i n t e r e s t i n g t o e x t e n d o u r r e v i e w . I n f a c t t h e p h o t o p r o d u c t i o n w a s c o n

s i d e r e d a s i m p l e r c a s e f o r Q C D . T h e r e f o r e i t s p r e d i c t i o n s s h o u l d h a v e

b e e n i n a g r e e m e n t w i t h e x p e r i m e n t a l f i n d i n g s .

A s u m m a r y o f Q C D p r o b l e m s i n p h o t o p r o d u c t i o n p h y s i c s i s a s f o l l o w s :

a ) i t i s i m p o s s i b l e t o p r e d i c t l a r g e p h o t o p r o d u c t i o n c r o s s - s e c t i o n s o f

t h e h e a v y f l a v o u r s b y m e a n s o f p e r t u r b a t i v e Q C D ;

b ) t h e p j, d e p e n d e n c e o f i n e l a s t i c ( c c ) , f o r o p e n a n d h i d d e n s t a t e s

c a n n o t b e a c c o u n t e d f o r b y Q C D ;

c ) t h e A - d e p e n d e n c e c a n n o t b e A 1 . ( P e r t u r b a t i v e Q C D p r e d i c t s A 1 . )

2 . 4 C o n c l u s i o n s

T h e c o n c l u s i o n o f t h i s s h o r t r e v i e w o n t h e " c h a r m " f l a v o u r p r o d u c t i o n

i n ( p p ) i n t e r a c t i o n s i s t h e r e f o r e a s f o l l o w s :

i ) t h e c r o s s - s e c t i o n v a l u e s f o u n d a r e a t l e a s t a n o r d e r o f m a g n i t u d e a b o v e

t h e " t h e o r e t i c a l " p r e d i c t i o n s o f p e r t u r b a t i v e Q C D ;

i i ) t h e x - d i s t r i b u t i o n f o r A + , i . e . t h e " l e a d i n g " e f f e c t , w a s t h e o r e t i c a l l y c

u n p r e d i c t e d ;

- 4 4 2 -

iii) with "new" models (essentially flavour excitation [8,9] and non-perturbative QCD [7]), both cross-section values and x-distributions can be "theoretically" derived.

All this should be quite a warning for QCD prediction on heavy-flavour production at extreme energies such as those of the CERN pp Collider.

i. EXPECTED NEW HEAVY-FLAVOUR STATES

The main purpose of this section is to call attention to the enormous number of new states which are expected on the basis of the old and new flavours. In order to attempt to give order to the vast multitude of states, we will limit ourselves to the possibility that they will follow the global symmetries already known with (udsc).

3.1 Examples from previous experience with S U ( 3 ) ^ S a n d ^ ^ ^ u d s c

The following graph illustrates what could indeed happen.

r s - S U ( 3 ) u d s

: - S U ( 4 ) u d sc

t ~ S U ( 4 ) u d s t

L s r ~ S U ( 4 ) uds(st)

S U ( 2 ) U C • b - S U ( 3 ) u d b

- s b - S U ( 3 ) u d ( s b ) -

•C - S l M J u d b c

t - S U ( 4 ) u d b t

s t — S U ( 4 ) u d b ( s T )

r - c — S U ( 4 ) u d ( s b ) c

t - S U ( 4 ) u d ( s b ) r

L s t - S U ( 4 ) ud(sb)lst)

- 4 4 3 -

With three flavours (u, d, and s) the famous SU(3) , came out. It uds

could be that "beauty" will produce another SU(3) The advent of the "charm" with four flavours (udsc) produced S U ( 4 ) u ^ s c * On the other hand, with the "top" there are two possible S U ( 4 ) : SU(4) , and SU(4) .

udst udbt Despite the large mass differences amongst the various flavours, it

could be that nature will provide, as usual, more regularities than are required. The above global symmetry groups for the structure of the various possible particle states could eventually show up, even if not expected.

If "superbeauty" was there, we would have even a larger set of SU(3) and SU(4) states and, in addition, all combinations of purely singlet states such as s, c, b, t, and (sb).

Examples of SU(4) structures using u, d, s, c, b, t, superbeauty (sb), and supertruth (st) are presented in Figs. 5 to 7. They include mesonic and baryonic states.

If we enlarge the symmetries to the Lorentz spins and angular momenta amongst quarks, the multitude of states increases further. These are indicated, for the first three flavours (u, d, and s) in Tables 3 and 4 for the mesons and for the baryons in S U ( 6 ) , respectively.

Table 3 SU(6) mesonic multiplets

SU (6) S U ( 3 ) f

Particle states

Number of states

[ ( 3 5 © 1 ) ® l]¡ (L = 0 ) 8 © 1

8 © 1

o - +

1~~

I T, K, n , n '

p, K , 0), <(> 36

[ ( 3 5 © 1 ) ® 3 ] ; (L = 1 )

8 © 1

8 © 1 .

8 © 1

8 © 1

1 + -

0 + +

1 + +

2 + +

B, Ql,2 ... ?

S, x , S*, e Ai, Qi,2, D, E A , K**, f, f'

1 0 8

- 4 4 4 -

T a b l e 4

B a r y o n s i n S U ( 6 ) m u l t i p l e t s

[ S U ( 6 ) , L P ] S ü ( 3 ) f / S t a n d a r d n a m e s o f p a r t i c l e s t a t e s

( 5 6 , 0 + ) 8

10

l / 2 +

3 / 2 +

N , A , E , S "

N * , E * , S * , Í T

( 7 0 , 1 " )

1

8

10

1

8

10

8

8

8

1 / 2 "

1 / 2 "

1 / 2 "

3 / 2 "

3 / 2 "

3 / 2 "

1 / 2 "

3 / 2 "

5 / 2 "

R e p e a t s i n g l e t

R e p e a t o c t e t

R e p e a t d e c u p l e t

R e p e a t s i n g l e t


R e p e a t d e c u p l e t




[ R e p e a t m e a n s t h a t t h e q u a n t u m n u m b e r s ( i s o s p i n a n d s t r a n g e n e s s ) o f t h e s t a t e s a r e i d e n t i c a l t o t h e " o c t e t " a n d " d e c u p l e t " a l r e a d y k n o w n f o r t h e 5 6 - c a s e . I

A n e x a m p l e o f h o w t h e m u l t i t u d e o f t h e s t a t e s g o e s w i t h t h e m a s s i s

s h o w n i n F i g s . 8 a a n d 8 b , w h e r e t h e m a s s e s o f t h e p a r t i c l e s r u n f r o m a f e w

G e V / c 2 t o 60 G e V / c 2 .

3 . 2 N o t e o n t h e s e m i l e p t o n i c d e c a y m o d e s : C a b i b b o d o m i n a n c e

A f a c t o f n a t u r e i s t h a t t h e m a t r i x w h i c h r e l a t e s t h e d o w n - l i k e " w e a k "

f l a v o u r s " C a b i b b o m i x e d " ,

t o t h e " s t r o n g " f l a v o u r s

- 4 4 5 -

i s a p p r o x i m a t e l y a u n i t m a t r i x

We w i l l n o w f o l l o w t h e e x p e c t e d g e n e r a l i z e d C a b i b b o d o m i n a n c e i n t h e

d e c a y o f t h e f l a v o u r e d q u a r k , a s i l l u s t r a t e d i n F i g s . 9 a a n d 9 b . A l l t h a t

w e n e e d i s t h e c h a r g e s i g n o f t h e l e p t o n i n a t r a n s i t i o n f r o m a n " u p - l i k e "

t o a " d o w n - l i k e " f l a v o u r . T h i s i s s u m m a r i z e d i n T a b l e 5 .

T a b l e 5

H o w t o c o m p u t e t h e e l e c t r i c c h a r g e s i g n o f t h e l e p t o n s ( e * o r \r~) p r o d u c e d i n t h e s e m i l e p t o n i c d e c a y s o f q u a r k s

o (D o a C) (I) (!) C) 5 \ / 7 \ ODD ( = U P - L I K E ) Q U A R K S

«- E V E N ( = D O W N - L I K E ) Q U A R K S

T h e c h a r g e f o r m u l a c a n b e w r i t t e n a s :

Q = ( 1 / 3 + f £ ) / 2 ,

w i t h

f ^ = + 1 f o r o d d q u a r k s ( i = 1 , 3 , 5 , 7 ) ,

f ^ = - 1 f o r e v e n q u a r k s ( i = 2 , 4 , 6 , 8 ) .

F r o m t h i s f o l l o w s t h e e l e c t r i c c h a r g e s i g n o f t h e l e p t o n i n

t h e s e m i l e p t o n i c d e c a y o f t h e f l a v o u r :

O D D -* E V E N ( U P - L I K E •+ D O W N - L I K E ) T R A N S I T I O N => P O S I T I V E L E P T O N

E V E N ->• O D D ( D O W N - L I K E -* U P - L I K E ) T R A N S I T I O N => N E G A T I V E L E P T O N

A s w i l l b e s e e n i n F i g s . 1 0 , a s e q u e n c e t ->• b ->• c ->• s w i l l b e a c c o m

p a n i e d b y t h e s e m i l e p t o n i c s e r i e s g i v i n g r i s e t o e + -*• e ~ -*• e + . F o r t h e

a n t i q u a r k s e q u e n c e t -> b -*• c -*• s , t h e c h a r g e s w i l l b e r e v e r s e d ( e ~ e + ->

-*• e ) . T h e s e r e s u l t s a r e s t r a i g h t f o r w a r d c o n s e q u e n c e s o f t h e p r e v i o u s

t a b l e .

- 4 4 6 -

4 . C R O S S - S E C T I O N E S T I M A T E S ; HOW T O GO F R O M S T R A N G E N E S S T O C H A R M , B E A U T Y ,

T O P , A N D S U P E R B E A U T Y

N o w c o m e s a k e y q u e s t i o n : O n c e w e k n o w t h e " s t r a n g e " a n d " c h a r m "

c r o s s - s e c t i o n s , i s i t p o s s i b l e t o p r e d i c t t h e h e a v i e r f l a v o u r [ c , b , t ,

o r ( s b ) ] c r o s s - s e c t i o n s i n h a d r o n i c c o l l i s i o n s ?

S i m p l e a r g u m e n t s b r i n g u s t o t h e c o n c l u s i o n t h a t

a ( m ) ^ ( 1 / m 2 ) x f ( s / m 2 ) . ( 3 )

I n f a c t , t h e o n l y q u a n t i t i e s w h i c h e n t e r i n t h e p r o b l e m o f p r o d u c i n g

a ( q q ) p a i r , h a v i n g a t d i s p o s a l t h e t o t a l e n e r g y i / s , a r e t h e q u a r k m a s s m

a n d t h e t o t a l e n e r g y

F o r m u l a ( 3 ) i s b a s e d o n d i m e n s i o n a l a n d s c a l i n g a r g u m e n t s :

D i m e n s i o n s a y s t h a t : a ^ ( 1 / m 2 ) .

S c a l i n g s a y s t h a t t h e t w o q u a n t i t i e s m a n d s a r e s u c h t h a t n o t h i n g

c h a n g e s i f t h e i r r a t i o ( s / m 2 ) i s k e p t c o n s t a n t ; t h e r a t i o ( s / m 2 )

i s t h e d i m e n s i o n l e s s q u a n t i t y n e e d e d i f n o o t h e r s c a l e w o u l d

r e m a i n i n t h e g a m e .

T h e b a s i c f o r m u l a i s t h e r e f o r e :

w h e r e

G ^ , (Jj a r e t h e p r o d u c t i o n c r o s s - s e c t i o n s ,

m . , m . a r e t h e m a s s e s , i J

E ^ , E j a r e t h e e n e r g i e s

a t w h i c h f l a v o u r s f . a n d f . a r e p r o d u c e d . i J

T h e r e s u l t s a r e s h o w n i n F i g s . 1 1 t o 1 4 , w h e r e w e h a v e u s e d

i ) t h e s t r a n g e n e s s d a t a t o p r e d i c t c , b , t , a n d ( s b ) ;

i i ) t h e " c h a r m " d a t a t o p r e d i c t b , t , a n d ( s b ) ;

i i i ) t h e " b e a u t y " d a t a t o p r e d i c t t a n d ( s b ) .

F i n a l l y , f o r c o m p l e t e n e s s , w e a l s o r e p o r t t h e m o s t r e c e n t Q C D p r e

d i c t i o n s o f [73 a n d [ 8 ] ( F i g . 1 5 ) .

- 447 -

5 . THE STUDY OF THE LEPTON CHARGE ASYMMETRY AND ITS ENERGY DEPENDENCE AS A WAY OF DETECTING THE HEAVIEST FLAVOURED STATES (BARYONIC AND ANTIBARYONIC) AT THE CERN pp COLLIDER

Many possibilities have been suggested for detecting the production of the heaviest flavours at the pp Collider. They are summarized in Table 6, together with their main difficulties.

Table 6

Summary of the various experimental methods which can be used for detecting the production of heavy

together with their flavours at the CERN pp Collider

main difficulties

States to . be observed Method Problems with the method

Hidden Invariant mass (£ +JT) pairs

Low cross-sections and low branching ratios

Open Invariant mass of the decay products

Low branching ratios for exclusive channels, and high combinatorial background due to the high multiplicity of the event

Study of multilepton events

Low cross-sections due to the multiple branching ratios involved

Study of inclusive lepton p T spectra

Need for a high rejection power against hadron background

Here we present a new method of observing the production of heavy mass states, either up-like ("top") or down-like ("superbeauty"), which is based on the "leading" baryon effect production mechanism, extended to the heaviest baryon and antibaryon states. In fact, owing to this production mechanism, a charge asymmetry of the leptons originating from these heavy flavours can be observed in a selected region of the phase space. Moreover, this asymmetry will show an energy dependence characteristic of the masses of the decaying states.

- 448 -

5 . 1 D e f i n i t i o n o f t h e a s y m m e t r y p a r a m e t e r A Q

F i g u r e 10 s h o w s t h e l e p t o n i c d e c a y c h a i n s , f o l l o w i n g t h e g e n e r a l i z e d

C a b i b b o d o m i n a n c e , f o r t h e v a r i o u s f l a v o u r s c , b , t , ( s b ) .

O n c e a p a r t i c l e - a n t i p a r t i c l e p a i r h a s b e e n p r o d u c e d , t h e n u m b e r o f

p o s i t i v e a n d n e g a t i v e l e p t o n s f r o m i t s d e c a y i s o n t h e a v e r a g e , e q u a l .

H o w e v e r , i n t h e f o l l o w i n g w e w i l l d i s c u s s u n d e r w h i c h c o n d i t i o n s w e c a n

o b s e r v e a n a s y m m e t r y i n t h e n u m b e r o f p o s i t i v e a n d n e g a t i v e l e p t o n s , w h i c h

i s d u e t o t h e d i f f e r e n t l o n g i t u d i n a l m o m e n t u m p r o d u c t i o n d i s t r i b u t i o n f o r

b a r y o n s a n d m e s o n s a n d t o t h e d e p e n d e n c e o f t h e l e p t o n p ^ s p e c t r a f r o m t h e

p r o d u c t p a r t i c l e m a s s .

L e t u s d e f i n e t h e a s y m m e t r y p a r a m e t e r a s

A" < * . . « „ J - ' < * * » - W , ( 5 ) c u z N ( £ + ) + N ( J T )

w h e r e N ( £ + ) = N ( £ + ; p T > 9 ^ ) a n d N ( J T ) = N ( £ " ; p T > 0 ) a r e t h e n u m b e r

o f p o s i t i v e a n d n e g a t i v e l e p t o n s p r o d u c e d i n t h e a n g u l a r r a n g e 0 ° < 9 <

< 0 a n d w i t h t r a n s v e r s e m o m e n t u m p m . c u t T

T h e n u m b e r o f p o s i t i v e l e p t o n s £ + i s e x p r e s s e d b y

N ( £ + ) = L [ n s ba +) + n t ( £ + ) + ^ ( Ä * ) + n J i O ] ,

w h e r e L i s t h e t o t a l i n t e g r a t e d l u m i n o s i t y a n d n ^ ( S , + ) [ [ w i t h f = ( s b ) , t ,

b , c[] i s t h e c o n t r i b u t i o n f r o m t h e d i r e c t p r o d u c t i o n o f ( s b ) , t , b , c

s t a t e s .

A n a l o g o u s l y t h e n u m b e r o f n e g a t i v e l e p t o n s i s g i v e n b y

N ( J T ) = L [ n g b ( £ " ) + n ( J O + 1 ^ ( 0 + •

T h e l e p t o n s o r i g i n a t e d b y t h e d e c a y o f t h e v a r i o u s f l a v o u r s a n d a n t i -

f l a v o u r s a r e s u m m a r i z e d i n T a b l e s 7 a a n d 7 b .

- 449 -

Table 7

All the heavy-flavour (a) and heavy-antiflavour (b) decay chains producing £ + and £~

a)

Flavour Decays producing £ + Decays producing £

sb sb t -»- b + £ +

s b - > t ^ b - > - c - > s + £ +

sb -> t + £~ sb-*t->-b->-c->-£~

t t •+ b + £ +

t->-b->-c->s + £ t -y b •+ c + £~

b b •> c ->• s + £ + b -* c -> £"

c c -+ s + £ +

b)

Antiflavour Decays producing £ + Decays producing £

sb sb -* t + £ +

sb-*t-*-b-*-c + £ +

sb t -> b + £~ sb-»-t->-b-»-S-»"S + £~

t t -* b •> c + £ + t + b + £" t->-E-»-c->-s + £~

b b -> c + £ + b" -* c -> s + £~

c c -* s + £"

In order to write down explicitly n ^ ( £ + ) , let us define the following

) a ^ o t : total cross-section for the production of open (f,f) pairs;

) P M£» Pjjp Pgf» Pgf : r a t i ° s between the inclusive cross-section for producing (M = meson, M = antimeson, B = baryon, B = antibaryon) states, and the total cross-section o"^ o t;

) B^f/» BR^j^ # , BRg£,, BRgj/: semileptonic branching ratios of the various states with flavour f' [_£' = c, b, t, (sb)];

- 4 5 0 -

± ± ± ± ± i v ) e

M f ( ¿f / ) » e M ? ^ £ f ' ^ ' S f ^ f ^ ' £ B f ^ f ' ^ : a c c e P t a n c e f o r ¿ f r o m t h e

l e p t o n i c d e c a y o f t h e f l a v o u r f' p r o d u c e d i n t h e d e c a y c h a i n o f

t h e s t a t e w i t h f l a v o u r f . T h i s a c c e p t a n c e i s a f u n c t i o n o f t h e l e p t o n

p ^ a n d o f t h e c u t i n 8 < 9 c u t a p p l i e d t o t h e l e p t o n p o l a r a n g l e .

A c c o r d i n g l y , w e h a v e f o r t h e c a s e o f " s u p e r b e a u t y " :

nS b ( Ä + > = "ï" K s b L>M t ^ s b K> + B R M c £ M s b (0]

+ Pit so" CBRM i F £ Ñ I F ^ B R M b £ M

+ P B s b f > B t £ B sb(Aî> + B R B c £ B s b ( 0 ^ + P K - r - T B R S ^ r - Es -TT-(^tr-) + B R - r £ - - _ - ( £ - ) " | ]

H B s F L B s F B s F s b B b B s F b J J

a n d

n s b ( £ _ ) » asT ípM i F ^ B R H t £ M ÏF(AÏ> + B R H c ^ i F ( £ c ^

+ P M s b CBRM s b £ M s b ( A ¡ b > + B R M b £ M 8b (V^ + P g S F CBRB t £ B s F ( ¥ +

B R B b £ B s F ( í ^ + p D , [ B R , , , E_ ) + BR,. . e n •

B s b L B s b B s b s b B b B s b T ) J J

± ± ± T h e a n a l o g o u s e x p r e s s i o n s f o r n^(SL ) , n ^ ( £ ) , a n d n c ( & ) c a n b e e a s i l y

d e r i v e d a n d a r e n o t r e p o r t e d h e r e .

F r o m t h e a b o v e f o r m u l a s i t c a n b e s e e n t h a t i n o r d e r t o e v a l u a t e t h e

a s y m m e t r y p a r a m e t e r A 0 , o n e n e e d s t o k n o w :

i ) t h e t o t a l c r o s s - s e c t i o n : a t o t ;

i i ) t h e d e c a y b r a n c h i n g r a t i o s : B R ;

i i i ) t h e e f f i c i e n c y r e l a t i v e t o t h e p r o d u c t i o n d i s t r i b u t i o n s o f t h e b a r y o n

o r m e s o n s t a t e s a n d t o t h e l e p t o n d i s t r i b u t i o n s i n t h e d e c a y s : e ;

i v ) t h e r e l a t i v e f r a c t i o n o f b a r y o n s a n d m e s o n s : p .

We w i l l n o w d i s c u s s i n s o m e d e t a i l t h e a s s u m p t i o n s w e m a d e f o r t h e s e

q u a n t i t i e s .

5 . 2 T h e t o t a l c r o s s - s e c t i o n s

We w i l l e x t r a p o l a t e t h e t o t a l c r o s s - s e c t i o n s f o r t h e h e a v y f l a v o u r s

a t t h e C E R N p p C o l l i d e r e n e r g i e s u s i n g f o r m u l a ( 4 ) a n d s t a r t i n g f r o m t h e

s t r a n g e n e s s c r o s s - s e c t i o n . U s i n g t h e k n o w n m a s s e s f o r " c h a r m " a n d " b e a u t y "

b a r y o n s a n d m e s o n s , a n d t h e v a l u e s :

- 4 5 1 -

m = 25 G e V / c ^ ,

m , = 55 G e V / c 2 ,

SD

f o r t h e " t o p " a n d " s u p e r b e a u t y " p a r t i c l e s , w e o b t a i n

a c * 2 0 0 0 y b , ( 6 a ) a, - 1 4 0 y b , ( 6 b )

b O ~ 1 . 5 y b , ( 6 c )

o ^ * 0 . 1 5 y b . ( 6 d ) s b

O t h e r e s t i m a t e s , f r o m p e r t u r b a t i v e Q C D , w i l l h o w e v e r b e t a k e n i n t o

a c c o u n t w h e n d i s c u s s i n g t h e r e s u l t s . I t w i l l b e s h o w n t h a t , u n d e r s o m e

c o n d i t i o n s , e v e n t h e s e v e r y l o w c r o s s - s e c t i o n s ( a , * 10 y b a n d 0 * b t

~ 0 . 1 y b [ [ 1 2 ] ) g i v e r i s e t o a m e a s u r a b l e a s y m m e t r y .

5 . 3 T h e d e c a y b r a n c h i n g r a t i o

R e c e n t d a t a f r o m C L E O [ l 3 ] g i v e f o r t h e s e m i l e p t o n i c b r a n c h i n g r a t i o

o f t h e " b e a u t y " m e s o n s :

(Mk i l ± ) / ( M b -> a l l ) ~ 0 . 1 3 .

F o r q u a r k m a s s e s g r e a t e r t h a n t h e " b e a u t y " m a s s , t h e s e m i l e p t o n i c

b r a n c h i n g r a t i o s h o u l d b e e v e n g r e a t e r , a p p r o a c h i n g t h e v a l u e 0 . 1 6 w h i c h

i s e x p e c t e d f r o m t h e q u a r k c o l o u r s a n d l e p t o n s c o u n t i n g .

I n o u r M o n t e C a r l o s i m u l a t i o n w e a s s u m e t h e k n o w n s e m i l e p t o n i c

b r a n c h i n g r a t i o s f o r " c h a r m " :

(D -»• J T ) / ( D -* a l l ) * 0 . 0 8 5 ,

( A + -»• J T ) / ( A + -> a l l ) * 0 . 0 4 5 , c c

a n d t h e c o n s e r v a t i v e v a l u e o f 0 . 1 f o r a l l o t h e r h e a v i e r p a r t i c l e s .

5 . 4 T h e p r o d u c t i o n d i s t r i b u t i o n s o f b a r y o n a n d m e s o n s t a t e s

T h e s t u d y o f t h e r e a c t i o n s

p p -•• D + e + + a n y t h i n g ,

p p -*• A* + e - + a n y t h i n g ,

PP -»• Aj° + e + + a n y t h i n g ,

- 4 5 2 -

a t the I S R i n d i c a t e t h a t i n baryon-baryon c o l l i s i o n s the h e a v y - f l a v o u r e d

baryons are produced accord ing t o a r a t h e r f l a t x - d i s t r i b u t i o n :

(da /dx) ^ cons t ,

w h i l s t the h e a v y - f l a v o u r e d mesons are produced w i t h s o f t e r x - d i s t r i b u t i o n

of the type

E ( d a / d | x | ) ^ ( 1 - | x | ) 3 .

T h e s e d i s t r i b u t i o n s w i l l be assumed a l l through the f o l l o w i n g d i s

c u s s i o n , t o g e t h e r w i t h the p , dependence

( d a / d p T ) ^ p T exp ( - 2 . 5 p T )

observed a t the I S R i n the p r o d u c t i o n of heavy f l a v o u r s £ l 4 ] .

5 . 5 T h e r e l a t i v e y i e l d of mesons and baryons

F r o m the data on s t r a n g e n e s s product ion a t the I S R i t can be assumed

t h a t , i n (pp) c o l l i s i o n s , the f o l l o w i n g r e a c t i o n s dominate

P P ^ c e n t r a l + h e a d i n g + a n ? t h i n * = ^ V V '

P P - C e n t r a l + C e n t r a l + = S ^ M . .

I n (pp) c o l l i s i o n s , b e c a u s e of the a n t i b a r y o n i c na ture of the p hemi

s p h e r e , the f o l l o w i n g r e a c t i o n s can take p l a c e :

P P M c e n t r a l

+ ^ l e a d i n g

+ anything =

pp -> ^ c e n t r a l

+ ^ l e a d i n g

+ anything =

P P -> ^ c e n t r a l

+ ^ c e n t r a l

+ anything = M C , M C ,

P P -> ^ l e a d i n g

+ B l e a d i n g

+ anything =

I n t h i s c a s e , t h e r a t i o o f t h e i n c l u s i v e c r o s s - s e c t i o n s f o r p r o d u c i n g

t h e f o u r c l a s s e s o f p a r t i c l e s M , M , B . , a n d B - , a n d t h e t o t a l c r o s s -c c I 1

s e c t i o n s a r e

P M = WM C ;B 1 + a M C ; M c ] / a t o t ,

P M = OivV * a M C ; M c ] / a t o t ,

P B + c i B ^ ] / ^ ,

P B = [ ^ M C ; B 1

- 4 5 3 -

w i t h :

a t o t = a Í M ; B 1 + a Í M + a J M ;M + a B 1 ; B 1 .

c 1 1 c 1 J 1 c C J 1 1 1 J

D e f i n i n g t h e r a t i o

l e a d i n g / t o t a l = p,, ,

t h e f o u r r a t i o s p c a n b e w r i t t e n a s :

P B = Pg = ( l e a d i n g / t o t a l )

P M = Pg = [ l - ( l e a d i n g / t o t a l ) ] .

A t t h e I S R , i n e a c h h e m i s p h e r e t h e r a t i o ( l e a d i n g / t o t a l ) i s ^ 1/16 f o r

s t r a n g e n e s s a n d ^ 1 / 8 f o r " c h a r m " . I n o u r d i s c u s s i o n w e w i l l s t u d y t h e

b e h a v i o u r o f A 0 a s a f u n c t i o n o f ( l e a d i n g / t o t a l ) .

5 . 6 T h e l e p t o n d e c a y d i s t r i b u t i o n s

T h e d a t a f r o m C L E O [ l 5 ] s h o w t h a t t h e s e m i l e p t o n i c d e c a y o f " b e a u t y "

m e s o n s M ^ , t h e m a g n i t u d e o f t h e m a s s r e c o i l i n g w i t h r e s p e c t t o t h e l e p t o n s

i s v e r y n e a r t o t h e D m a s s :

-> X e v , w i t h M x ^ 1 ^ ~ 2 . 0 G e V / c 2 .

M o r e o v e r , t h e m e a n c h a r g e d m u l t i p l i c i t y o f t h e d e c a y i s 3 . 5 , w h e r e

t h e D c o n t r i b u t e s w i t h 2 . 5 c h a r g e d p a r t i c l e s o n t h e a v e r a g e . We c a n

c o n c l u d e t h a t , e v e n a t v a l u e s o f t h e m a s s a s h i g h a s t h e m a s s o f t h e M ^ ,

t h e s e m i l e p t o n i c d e c a y p r o c e e d s v i a a t h r e e - b o d y d e c a y . O n t h e c o n t r a r y ,

t h e m e a n c h a r g e d m u l t i p l i c i t y i n t h e h a d r o n i c d e c a y s o f t h e M^ m e s o n s i s

6 . 3 , i . e . t h e h a d r o n i c d e c a y o f t h e M^ p r o d u c e s , o n t h e a v e r a g e , o n e D

p l u s f o u r c h a r g e d p a r t i c l e s p l u s t w o n e u t r a l p a r t i c l e s :

-> D + 6 b o d i e s .

I n t h e f o l l o w i n g w e w i l l c o n s i d e r t w o p o s s i b i l i t i e s :

i ) t h e t o t a l m u l t i p l i c i t y o f a l l d e c a y s i s 3 : t h i s i s t h e w o r s t c a s e f o r

t h e a s y m m e t r y A 0 ;

i i ) t h e t o t a l m u l t i p l i c i t y o f a l l s e m i l e p t o n i c d e c a y s i s 3 a n d t h e d e c a y

i s K ^ - l i k e f o r m e s o n s a n d p h a s e - s p a c e f o r b a r y o n s , w h i l s t t h e t o t a l

m u l t i p l i c i t i e s o f a l l t h e h a d r o n i c d e c a y s h a v e t h e k n o w n v a l u e s f o r

- 454 -

" c h a r m " a n d " b e a u t y " ( > 3 f o r " c h a r m " , 'v. c h a r m + 6 f o r " b e a u t y " ) , a n d ,

f o r " t o p " a n d " s u p e r b e a u t y " , t h e s a m e m u l t i p l i c i t y a s f o r " b e a u t y " .

I t s h o u l d b e n o t e d t h a t t h i s i s a l r e a d y a c o n s e r v a t i v e h y p o t h e s i s ,

s i n c e t h e h a d r o n i c d e c a y s o f " t o p " a n d " s u p e r b e a u t y " c a n b e e x p e c t e d

t o p r o d u c e m o r e p a r t i c l e s t h a n " b e a u t y " . H i g h e r v a l u e s o f m u l t i p l i c i t y

w o u l d p r o d u c e h i g h e r v a l u e s f o r t h e a s y m m e t r y .

5 . 7 E s t i m a t e s o f t h e a s y m m e t r y A °

T h e d e t e c t i o n a c c e p t a n c e s e h a v e b e e n e v a l u a t e d b y m e a n s o f a M o n t e

C a r l o s i m u l a t i o n , w i t h t h e c o n d i t i o n s s e t i n t h e p r e v i o u s s e c t i o n s a n d

f o r f i v e v a l u e s o f 6 (6 = 1 0 ° , 2 0 ° , 3 0 ° , 4 0 ° , a n d 9 0 ° ) . c u t c u t

± F i g u r e s 1 6 a t o 1 6 t s h o w t h e e a c c e p t a n c e s i n t h e b a r y o n h e m i s p h e r e

f o r 9 = 3 0 ° a n d m o d e l ( i i ) o f s u b s e c t i o n 5 . 6 f o r b a r y o n s , m e s o n s , a n d c u t +

J

a n t i m e s o n s . T h e a c c e p t a n c e s f o r e _ i n t h e b a r y o n h e m i s p h e r e o r i g i n a t e d

b y t h e d e c a y o f a n t i b a r y o n s , p r o d u c e d m a i n l y i n t h e a n t i b a r y o n h e m i s p h e r e

b e c a u s e o f t h e " l e a d i n g " e f f e c t , a r e , o f c o u r s e , n e g l i g i b l e .

F i g u r e 17 s h o w s t h e b e h a v i o u r o f A ° ( p , j , , 3 0 ° ) , f o r ( l e a d i n g / t o t a l ) =

= 0 . 2 5 a n d m o d e l ( i i ) o f s u b s e c t i o n 5 . 6 . T h e r e a r e t w o m a i n p e a k s : o n e

p o s i t i v e a r o u n d p ^ = 10 G e V / c , d u e t o t h e " t o p " b a r y o n d e c a y i n t o e + ; a n d

o n e n e g a t i v e a r o u n d p^, = 19 G e V / c , d u e t o " s u p e r b e a u t y " b a r y o n d e c a y i n t o

I t i s i n t e r e s t i n g t o n o t e t h a t t h e s e p a r a t i o n b e t w e e n t h e t w o p e a k s

d e p e n d s o n l y o n t h e m a s s d i f f e r e n c e b e t w e e n t h e " s u p e r b e a u t y " a n d t h e " t o p "

s t a t e s . I n f a c t , i n t h e t h r e e - b o d y s e m i l e p t o n i c d e c a y t h e t r a n s v e r s e

m o m e n t u m s p e c t r u m o f t h e e l e c t r o n s o r p o s i t r o n s s c a l e s w i t h p ^ / A m , w h e r e

Am i s t h e d i f f e r e n c e b e t w e e n t h e p a r e n t m a s s a n d t h e m a s s o f t h e h a d r o n i c

p a r t i c l e p r o d u c e d i n t h e d e c a y . T h i s i s s h o w n i n F i g . 1 8 , w h e r e t h e

n o r m a l i z e d p ^ / A m s p e c t r a o f t h e e l e c t r o n s a n d p o s i t r o n s p r o d u c e d i n t h e

f o l l o w i n g r e a c t i o n s a r e r e p o r t e d :

>° A + e v c

A' - A 0 e + v

- 4 5 5 -

T h e m a s s d i f f e r e n c e s A m h a v e t h e f o l l o w i n g v a l u e s :

i ) Am = m(A° b) - m(A*) « 3 0 G e V / c 2 f o r t h e " s b " b a r y o n d e c a y ;

i i ) Am = m(A*) - m(A^) = 1 9 . 5 G e V / c 2 f o r t h e " t " b a r y o n d e c a y ;

i i i ) Am = m(A£) - m ( A * ) ~ 3 - 2 G e V / c 2 f o r t h e " b " b a r y o n d e c a y ;

i v ) Am = m(A +) - m(A°) * 1 . 2 G e V / c f o r t h e " c " b a r y o n d e c a y ; c s

F i g u r e s 1 9 a , b a n d 2 0 a , b s h o w t h e a m p l i t u d e o f t h e t w o p e a k s a s a

f u n c t i o n o f 9 c u f c a n d ( l e a d i n g / t o t a l ) f o r : a ) m o d e l ( i ) o f s u b s e c t i o n 5 . 6

( a l l t h r e e - b o d y d e c a y s ) ; a n d b ) m o d e l ( i i ) o f s u b s e c t i o n 5 . 6 ( g r e a t e r

m u l t i p l i c i t y f o r t h e h a d r o n i c d e c a y s ) .

5 . 8 B a c k g r o u n d e v a l u a t i o n

I n w h a t h a s b e e n d e s c r i b e d s o f a r , t h e b a c k g r o u n d c o n t a m i n a t i o n i n

t h e s a m p l e o f p r o m p t e + a n d e - h a s n o t b e e n c o n s i d e r e d . I t i s m a i n l y d u e

t o :

i ) t h e m i s i d e n t i f i c a t i o n o f c h a r g e d a n d n e u t r a l h a d r o n s i n t h e e x p e r i

m e n t a l a p p a r a t u s ;

i i ) t h e p r o m p t e + o r e - p r o d u c t i o n f r o m s o u r c e s o t h e r t h a n o p e n h e a v y -

f l a v o u r s t a t e s .

T h e c o n t r i b u t i o n ( i ) c a n b e d e r i v e d b y e x t r a p o l a t i n g , a b o v e p^, *

~ 10 G e V / c , t h e i n c l u s i v e p i o n c r o s s - s e c t i o n a s m e a s u r e d b y t h e U A 1 e x p e r i

m e n t [ l 6 ] , u s i n g t h e f i t t o t h e i r d a t a :

E ( d a 3 / d p 3 ) = A x p ^ / ( p o + p T ) n , ( 7 )

w i t h A = 0 . 4 6 ± 0 . 1 0 m b 2 c 2 G e V - 2 , p 0 = 1 . 3 ± 0 . 1 8 G e V c - 1 a n d n = 9 . 1 4 ±

± 0 . 7 7 .

F o r m u l a ( 7 ) i s r e l a t i v e o n l y t o c h a r g e d p i o n s ( a v e r a g e d o v e r t h e t w o

c h a r g e s ) a n d i s g i v e n i n u n i t s o f r a p i d i t y . We h a v e a s s u m e d t h e c o n t r i b u

t i o n t o t h e b a c k g r o u n d d u e t o t h e n e u t r a l p i o n s t o b e ^ 0 . 2 o f t h e c r o s s -

s e c t i o n ( 7 ) . T h e r a p i d i t y i n t e r v a l o v e r w h i c h w e i n t e g r a t e d t h e b a c k g r o u n d

d e p e n d s o n t h e 0 : c u t

- 4 5 6 -

9 c u t = 9 0 ° , A y * 4 . 0 ,

c u t = 4 0 ° , A y * 3 . 0 ,

c u t = 3 0 ° , A y * 2 . 7 ,

c u t = 2 0 ° , A y ~ 2 . 3 ,

c u t = 1 0 ° , A y * 1 . 5 .

T h e e x t r a p o l a t e d b a c k g r o u n d r a t e s s h o u l d b e m u l t i p l i e d b y a r e d u c t i o n

f a c t o r r e p r e s e n t i n g t h e r e j e c t i o n o f t h e b a c k g r o u n d f r o m s o u r c e ( i ) .

C o n c e r n i n g t h e p r o m p t e l e c t r o n b a c k g r o u n d ( i i ) , w e a s s u m e , a s a f i r s t

a p p r o x i m a t i o n , t h a t i t w o u l d b e n e g l i g i b l e w h e n c o m p a r e d w i t h t h e c o n t r i

b u t i o n ( i ) .

5 . 9 E s t i m a t e o f t h e a s y m m e t r y p a r a m e t e r i n c l u s i v e o f b a c k g r o u n d

O w i n g t o t h e b a c k g r o u n d s o u r c e s d e s c r i b e d i n t h e p r e v i o u s s e c t i o n ,

t h e e x p e r i m e n t a l a s y m m e t r y p a r a m e t e r i s g i v e n b y :

[ N ( e + ) + N b g ( e + ) ] - [_N(e") + \ o ( e " ) ] b g '

[ N ( e + ) + N b g ( e + ) ] + [ N ( e ) + N b g ( e ) ] ( 8 )

w h e r e ^ b g ( e ) i s t h e n u m b e r o f b a c k g r o u n d p o s i t r o n s o r e l e c t r o n s ; A e x ^ c a n

t h e n b e e x p r e s s e d a s a f u n c t i o n o f A 0 a n d o f t h e s i g n a l - t o - b a c k g r o u n d

r a t i o . I n f a c t

s i g n a l - N ( e ± ) b a c k g r o u n d ~ N, ( e í ) '

b g

a s s u m i n g N b g ( e + ) = N b g ( e - ) = N ^ g ( e ) a n d s u b s t i t u t i n g i n E q . ( 8 ) t h e e x

p r e s s i o n s f o r N ( e ~ ) a n d N ( e + ) d e r i v e d f r o m t h e d e f i n i t i o n o f A 0 , t h e r e s u l t

w o u l d b e

. e x p _

1 + ( 1 + A ° ) / [ N ( e + ) / N b g ( e ) ] f o r A > 0 ;

i e x p _

1 + ( 1 - A ° ) / [ N ( e - ) / N ( e ) ] f o r A u < 0

exD

F i g u r e 21 s h o w s t h e q u a n t i t y A p l o t t e d a s a f u n c t i o n o f t h e

s i g n a l - t o - b a c k g r o u n d r a t i o f o r v a r i o u s v a l u e s o f A 0 . T h e r e s u l t s c a n b e

c

e

- 457 -

e x p r e s s e d w i t h c u r v e s o f c o n s t a n t A a s a f u n c t i o n o f ( r e j e c t i o n p o w e r )

v e r s u s ( c r o s s - s e c t i o n f o r " t o p " a n d " s u p e r b e a u t y " p r o d u c t i o n ) , f o r d i f

f e r e n t 9 c u t l e a d i n g / t o t a l , a n d d e c a y m o d e l s ( F i g s . 2 2 t o 3 1 ) .

T a b l e s 8 a , b s u m m a r i z e t h e r e s u l t s g i v e n i n F i g s . 2 2 t o 31 f o r t w o

v a l u e s o f t h e t o t a l c r o s s - s e c t i o n . T h e y s h o w t h e r e j e c t i o n p o w e r s n e e d e d

t o o b t a i n A Ê X ^ > 0 . 3 o r A e x ^ < - 0 . 3 , i . e . a r e a s o n a b l y h i g h v a l u e f o r t h e

a s y m m e t r y , a t t h e " t o p " a n d " s u p e r b e a u t y " p e a k s r e s p e c t i v e l y . I t c a n b e

s e e n t h a t , w i t h a r e j e c t i o n p o w e r o f t h e o r d e r o f 1 0 - 3 , a l a r g e r a n g e o f

6 . l e a d i n g / t o t a l , a n d c r o s s - s e c t i o n v a l u e s a r e a c c e s s i b l e , c u t

T a b l e 8

R e j e c t i o n p o w e r , i n u n i t s o f 10 , n e e d e d t o o b t a i n A e x P = 0 . 3 i n t h e " t o p " r e g i o n ( a ) ,

a n d A e x P = - 0 . 3 i n t h e " s u p e r b e a u t y " r e g i o n ( b ) , f o r v a r i o u s v a l u e s o f 0 . a n d l e a d i n g / t o t a l

a )

P T = 10 G e V / c ( t o p )

0 c u t

( l e a d i n g / t o t a l ) C r o s s - s e c t i o n e s t i m a t e s

[ [ f o r m u l a ( 6 ) [ ]

a t = 1 . 5 ub a s b = 0 . 1 5 ub

( p e r t u r b a t i v e Q C D )

a t = 0 . 1 ub a s b = 0 . 0 1 ub

M o d e l ( i ) M o d e l ( i i ) M o d e l ( i ) M o d e l ( i i )

1 0 °

0 . 1

0 . 2 5

0 . 5

3 . 0

1 0 . 0

1 5 . 0

3 . 5

1 2 . 0

1 8 . 0

0 . 2

0 . 6

1 . 0

0 . 3

0 . 7

1 . 3

2 0 °

0 . 1

0 . 2 5

0 . 5

1 . 3

8 . 0

2 0 . 0

1 . 5

9 . 0

2 3 . 0

0 . 1

0 . 5

1 . 0

0 . 1

0 . 6

1 . 2

3 0 °

0 . 1

0 . 2 5

0 . 5

6 . 0

1 9 . 0

7 . 0

2 2 . 0

0 . 4

1 . 0

0 . 4

1 . 2

4 0 °

0 . 1

0 . 2 5

0 . 5

3 . 5

1 7 . 0

4 . 8

2 1 . 0

0 . 3

1 . 0

0 . 3

1 . 1

- 4 5 8 -

b )

P l , = 19 G e V / c ( s u p e r b e a u t y )

e c u t

( l e a d i n g / t o t a l ) C r o s s - s e c t i o n e s t i m a t e s

[ f o r m u l a ( 6 ) ] ( p e r t u r b a t i v e Q C D )

a t • 1 . 5 y b at = 0 . 1 y b

a s b = 0 . 1 5 y b a s b 0 . 0 1 y b

M o d e l ( i ) M o d e l ( i i ) M o d e l ( i ) M o d e l ( i i )

0 . 1 0 . 4 1 . 0 0 . 0 2 0 . 1

1 0 ° 0 . 2 5 0 . 9 2 . 5 0 . 1 0 . 2

0 . 5 1 . 7 4 . 5 0 . 1 0 . 3

0 . 1 2 . 5 5 . 5 0 . 2 0 . 4

2 0 ° 0 . 2 5 1 0 . 0 2 0 . 0 0 . 5 1 . 0

0 . 5 1 . 7 4 . 5 0 . 1 0 . 3

0 . 1 - 2 . 2 - 0 . 2

3 0 ° 0 . 2 5 9 . 0 2 5 . 0 0 . 6 1 . 1

0 . 5 2 3 . 0 4 5 . 0 1 . 6 2 . 0

0 . 1 - - - -4 0 ° 0 . 2 5 4 . 0 1 9 . 0 0 . 3 1 . 0

0 . 5 2 0 . 0 4 0 . 0 1 . 5 2 . 0

5 . 1 0 C o n c l u s i o n s

A s a n e x a m p l e o f w h a t c a n b e o b t a i n e d e x p e r i m e n t a l l y i n t e r m s o f e x p

t h e a s y m m e t r y A , l e t u s f i x s o m e o f t h e p a r a m e t e r s i n a r e a s o n a b l e w a y .

W e t a k e ( a s i n F i g s . 2 9 b a n d 2 9 e ) : i ) ( l e a d i n g / t o t a l ) = 0 . 2 5 ,

i i ) 9 - 3 0 ° , c u t i i i ) d e c a y m o d e l ( i i ) .

M o r e o v e r , i n o r d e r t o h a v e a n e s t i m a t e f o r t h e e x p e r i m e n t a l e r r o r s o n A 6 X p

w e a s s u m e a t o t a l i n t e g r a t e d l u m i n o s i t y L = 3 0 0 n b - 1 ( f o r e s e e n f o r 1 9 8 3 a t

t h e C E R N p p C o l l i d e r ) .

6 XT)

F i g u r e s 3 2 a , b s h o w t h e p l o t o f A a s a f u n c t i o n o f p^,, f o r a r e

j e c t i o n p o w e r o f 1 0 - 3 a n d f o r t h e t w o c r o s s - s e c t i o n e s t i m a t e s : a s i n

- 4 5 9 -

s u b s e c t i o n 5 . 2 [ " f o r m u l a ( 6)1 a n d a s f r o m p e r t u r b a t i v e QCD ( a :o , = 1 0 : 1 ) , t s b

r e s p e c t i v e l y . T h e e r r o r s a r e p u r e l y s t a t i s t i c a l .

F i g u r e s 3 3 a , b s h o w t h e e x p e c t e d n u m b e r o f p r o d u c e d e l e c t r o n s a s a

f u n c t i o n o f p^,, w i t h t h e s a m e t w o a s s u m p t i o n s f o r t h e t o t a l c r o s s - s e c t i o n s .

S u p e r i m p o s e d i s t h e e x p e c t e d b a c k g r o u n d , a s d e f i n e d i n s u b s e c t i o n 5 . 8 , a n d

w i t h a r e j e c t i o n f a c t o r o f 1 0 - 3 .

I t c o u l d b e t h a t t h e r e j e c t i o n f a c t o r n e e d e d i s m u c h l e s s t h a n 1 0 - 3 .

I n f a c t , a v e r y h e a v y s t a t e ( s u c h a s A* o r A°^) d e c a y i n g s e m i l e p t o n i c a l l y

m a y h a v e t h e h a d r o n i c " j e t " r e c o i l i n g a g a i n s t t h e l e p t o n p a i r . T h e s t u d y

o f t h e h a d r o n i c p a t t e r n a s s o c i a t e d w i t h t h e ( e * ) c o u l d b e o f s u c h a h e l p • • • • — q

i n t h e s e l e c t i o n o f g o o d e v e n t s t h a t a r e j e c t i o n p o w e r m u c h b e l o w 10

w o u l d b e s u f f i c i e n t . F o r e x a m p l e , a n o r d e r - o f - m a g n i t u d e i m p r o v e m e n t w o u l d

m e a n t h a t t h e d a t a w h i c h , a t p r e s e n t , a r e q u o t e d w i t h a r e j e c t i o n o f o r d e r

1 0 - 3 ( F i g s . 2 2 - 3 4 ) , w o u l d r e a c h t h e l e v e l o f 1 0 ~ \ I n t h i s c a s e , a l l o u r

e x p e c t a t i o n s w o u l d b e s c a l e d b y t h i s f a c t o r .

F o r c o m p l e t e n e s s , l e t u s m e n t i o n t h a t , a t p r e s e n t , t h e ( e / ï ï ) r a t i o i n

t h e p^, r a n g e a b o v e ^ 20 G e V i s n o t k n o w n a t t h e C E R N p p C o l l i d e r .

I n o r d e r t o c o m p u t e t h e s t a t i s t i c a l s i g n i f i c a n c e o f t h e o b s e r v e d . ex i3

e f f e c t , i t i s c o n v e n i e n t t o i n t e g r a t e A o v e r t h e p ^ r a n g e s :

i ) 7 < p T < 12 G e V / c , c o r r e s p o n d i n g t o t h e " t o p " r e g i o n ;

i i ) 14 < p ^ < 2 3 G e V / c , c o r r e s p o n d i n g t o t h e " s u p e r b e a u t y " r e g i o n .

T h i s i s e q u i v a l e n t t o t h e e x p e r i m e n t a l p r o c e d u r e o f f i t t i n g t h e d a t a t o

r e d u c e t h e s t a t i s t i c a l e r r o r s o n t h e s i n g l e p o i n t s .

F i g u r e s 3 4 a , b s h o w t h e n u m b e r o f s t a n d a r d d e v i a t i o n s t h a t c a n b e

o b t a i n e d i n t h e m e a s u r e m e n t o f A e x ^ , i n t h e " t o p " a n d i n t h e " s u p e r b e a u t y "

r e g i o n s , r e s p e c t i v e l y , a s a f u n c t i o n o f t h e t o t a l c r o s s - s e c t i o n s a a n d

a _ a n d i n t h e s a m e c o n d i t i o n s a s t h o s e s p e c i f i e d a b o v e . T h e 9 0 % c o n f i -s b

d e n c e l e v e l i n t h e m e a s u r e m e n t i s a l s o i n d i c a t e d . T h e s e r e s u l t s s h o w t h a t

e s p e c i a l l y i n t h e " t o p " c a s e , a h i g h s t a t i s t i c a l s i g n i f i c a n c e c a n b e

r e a c h e d w i t h a m o d e r a t e r e j e c t i o n p o w e r , e v e n i f t h e t o t a l c r o s s - s e c t i o n

f o r " t o p " p r o d u c t i o n i s a s l o w a s 0 . 1 u b , i . e . t h e v a l u e p r e d i c t e d b y Q C D .

F i g u r e 35 s h o w s t h e b e h a v i o u r o f t h e r a t i o ( s i g n a l / b a c k g r o u n d ) a s a

f u n c t i o n o f t h e t o t a l c r o s s - s e c t i o n f o r " t o p " a n d " s u p e r b e a u t y " a n d f o r

d i f f e r e n t v a l u e s o f t h e r e j e c t i o n p o w e r .

- 460 -

6. CONCLUDING REMARKS

The following conclusions are in order.

i) Past experience says: do not take the "theoretical" QCD predictions too seriously; many things still do not fit between theory and experiments. In particular, neither the large "charm" cross-sections, nor the "leading" effect were predicted.

ii) A detailed study of the production mechanism of heavy flavours at the ISR is important in order to make reasonable extrapolations to the pp Collider energy,

iii) The number of "new" states with heavy flavours is very large. If their production cross-sections follow the simple extrapolation proposed by us, the CERN pp Collider would be a quasi-factory for these new states. The problem is to have the instrumentation that is able to detect their existence.

iv) The study of the electron-positron asymmetry and of its energy dependence is of the utmost importance at the pp Collider. If the "leading" effect follows the same trend as "charm" at the ISR, this asymmetry is expected to be detectable, even if the production cross-sections of the heavy-flavoured states would follow the QCD predictions .

The study of the electron asymmetry and of its energy dependence is o ±

not less important than the searches for the Z and the W . Finding o ±

the Z and the W would tell us nothing about one of the most crucial problems of subnuclear physics: the families. A detailed study of the electron asymmetry allows us to investigate the presence, in a mass range so far unaccessible to any other machine, of the new flavours, up-like ("top") and down-like ("superbeauty"), and to determine their mass relation,

v) What we will be able to do at the CERN pp Collider is going to be very important for establishing if hadronic colliders can compete with (e +e -) colliders.

- 4 6 1 -

R E F E R E N C E S

S. F e r r a r a , p r i v a t e c o m m u n i c a t i o n .

A . M a r t i n , p r e p r i n t C E R N T H - 3 3 1 4 ( 1 9 8 2 ) .

P. S ö d i n g , p r i v a t e c o m m u n i c a t i o n .

M . B a s i l e et a l . , N u o v o C i m e n t o 6 3 A (1981) 2 3 0 .

M . B a s i l e et a l . , N u o v o C i m e n t o 6 5 A (1981) 4 5 7 .

M . B a s i l e et a l . , N u o v o C i m e n t o 6 7 A (1982) 4 0 .

D. D r i j a r d e t a l . , P h y s . L e t t . 8 5 B (1979) 4 5 2 .

K. G i b o n i et a l . , P h y s . L e t t . 85B (1979) 4 3 7 .

W . L o c k m a n et a l . , P h y s . L e t t . 8 5 B (1979) 4 4 3 .

J . E i c k m e y e r et a l . , 2 0 t h I n t . C o n f . o n H i g h - E n e r g y P h y s i c s , M a d i s o n ,

1981 ( A m e r i c a n I n s t i t u t e of P h y s i c s , N e w Y o r k , 1 9 8 1 ) , p. 1 9 3 .

D. D r i j a r d e t a l . , P h y s . L e t t . 81B (1979) 2 5 0 .

P . F . J a c q u e s et a l . , P h y s . R e v . D 21 (1980) 1 2 0 6 .

P. C o t e u s et a l . , P h y s . R e v . L e t t . (1979) 1 4 3 8 .

A. Soukas et a l . , P h y s . R e v . L e t t . 44 (1980) 5 6 4 .

A . E . A s r a t y a n e t a l . , P h y s . L e t t . 74B (1978) 4 9 7 .

P. A l i b r a n et a l . , P h y s . L e t t . 74B (1978) 1 3 4 .

T. H a n s l e t a l . , P h y s . L e t t . M B (1978) 1 3 9 .

A . B o s e t t i e t a l . , P h y s . L e t t . 74B (1978) 1 4 3 .

M . F r i t z e e t a l . , P h y s . L e t t . 9 6 B (1980) 4 2 7 .

D. J o n k e r e t a l . , P h y s . L e t t . 9 6 B (1980) 4 3 5 .

H. A b r a m o w i c z et a l . , p r e p r i n t C E R N - E P / 8 2 - 1 7 ( 1 9 8 2 ) .

M . A g u i l a r - B e n i t e z et a l . , p r e p r i n t C E R N - E P / 8 2 - 1 7 ( 1 9 8 2 ) .

T. A z i z et a l . , N u c l . P h y s . B 1 9 9 (1982) 4 2 4 .

J. S a n d w e i s s et a l . , P h y s . R e v . L e t t . 44 (1980) 1 1 0 4 .

M . B a s i l e e t a l . , N u o v o C i m e n t o L e t t . 30 (1981) 4 8 7 .

M . B a s i l e e t a l . , N u o v o C i m e n t o L e t t . 33 (1982) 3 3 .

F. H a l z e n , W . Y . K e u n g a n d D . M . S c o t t , M a d i s o n r e p o r t M A D / P H / 6 3 ( 1 9 8 2 ) .

R. O d o r i c o , P h y s . L e t t . 107B (1981) 2 3 1 .

V . B a r g e r , F. H a l z e n a n d W . Y . K e u n g , P h y s . R e v . D 24 (1981) 1 4 2 8 .

M . B a s i l e et a l . , N u o v o C i m e n t o 6 5 Á (1981) 3 9 1 .

- 462 -

[ i l ] J . B a d i e r e t a l . , p r e p r i n t C E R N - E P / 8 2 - 6 7 ( 1 9 8 2 ) .

[ l 2 ^ F . H a l z e n , R a p p o r t e u r t a l k , 2 1 s t I n t . C o n f . o n H i g h - E n e r g y P h y s i c s ,

P a r i s , 1 9 8 2 [ j . P h y s . ( F r a n c e ) 4 3 , C 3 - 3 8 1 ( 1 9 8 2 ) ] .

[13] K . C h a d w i c k e t a l . , p r e p r i n t C L N S / 8 2 / 5 4 6 .

Ql4] M . B a s i l e e t a l . , N u o v o C i m e n t o L e t t . 3 0 ( 1 9 8 1 ) 4 8 1 .

M . B a s i l e e t a l . , N u o v o C i m e n t o L e t t . 33. ( 1 9 8 2 ) 1 7 .

[is] S . L . O l s e n , M o r i o n d W o r k s h o p o n N e w F l a v o u r s , L e s A r c s , 1 9 8 2

( E d i t i o n s F r o n t i è r e s , D r e u x , F r a n c e , 1 9 8 2 ) , p . 1 4 7 .

[ l 6 ] G . A r n i s o n e t a l . , U A 1 C o l l a b o r a t i o n , p r e p r i n t C E R N - E P / 8 2 - 1 7 1

( 1 9 8 2 ) .

- 463 -

q (spin V 2] Proton hemisphere

gluino irrrmn

gluino Ol E E

q (spin o

F i g . 1 The diagram illustrates how a gluino can acquire a mass from radiative processes, where a spin 1/2 quark and a spin 0 anti-quark are virtually produced. The quark mass must be in the 1 0 2 GeV/c 2 range, in order to allow a gluino mass of the order of a few GeV/c 2.

Lepton energy

High energy

Antiproton hemisphere

E E •si <

Lepton energy

High energy

F i g . 2 Main trend of the electron charge asymmetry in the proton hemisphere (a) and in the anti-proton hemisphere (b).

/ s IGeV)

F i g . 3 Cross-sections expected on the basis of gluon and quark fusion models (gg -*- cc and qq -»• cc curves) . Other QCD models are also shown. The data are taken from Ref. 4.

F i g . 4 Experimental longitudinal momentum distribution of At.

SU(MU,

x =charm, top, supertruth

y = strange, beaufy.superbeauty

F i g . 5 T h e S U ( 4 ) f m e s o n i c m u l t i p l e t s f o r J P = 0 ; t h e s a m e m u l t i p l e t s t r u c t u r e i s r e p e a t e d f o r J P = 1 : " x " r e p r e s e n t s t h e q u a r k s w i t h e l e c t r i c c h a r g e + 2 / 3 , " y " t h e q u a r k s w i t h e l e c t r i c c h a r g e - 1 / 3 . E a c h o f t h e p o s s i b l e u d y x c o m b i n a t i o n s s h o u l d p r o d u c e a n S U ( 4 ) f . T h e q u a r k c o m p o s i t i o n f o r e a c h s t a t e i s i n d i c a t e d i n p a r e n t h e s i s .

SU(4) l

X

x = charm, top, supertruth

y =strange,beauty,superbeauty

F i g . 6 S t r u c t u r e o f t h e e x p e c t e d b a r y o n i c J p = l / 2 + S U ( 4 ) f 2 0 - p l e t s .

SU(4) U 1

F i g . 7 S t r u c t u r e o f t h e e x p e c t e d b a r y o n i c J p = 3 / 2 + S U ( 4 ) f 2 0 - p l e t s .

- 4 6 5 -

• bbb

• bbc b b s • bb(u.d)

• bcc

b c s I bc(u,d)

b s ( u ' d 'l b(u,d)

• C C S

• cc(u,d)

• e s s • cs(u,d) • c(u,d)

I f f I f t 1c 2 c 3 c 1 b 2 b 3 b

a) 60

50

U0

30

2 0

10

b)

• t t b

.. • H e t t s • t t ( u . d )

t b s

t b b

• tbc I t b ( u , d )

• tec tc(u,d) • t c s

ts(u,d) t Jfs ..

1t 2 t

f

3 t

F i g . 8 The mass ranges of the baryon states with: a) from one to three charm or beauty quarks; b) from one to three top quarks.

2/3

F i g . 9a The six-quark mixing with CP F i g . 9b Transitions among the various violation. S¿ = sin C¿ = cos 6i- states. The Cabibbo mixing opens the

dashed channels. The horizontal transitions are forbidden for any value of the mixing angle. Allowed neutral currents are: uü, cc, tt, d3, ss, and bb.

- 466 -

-t v

c c

\ V

5 ¡ -VB Yb Ys Ac À' 1 Ac

t" V t v t" S

s b Ys F i g . 10 D i a g r a m i l l u s t r a t i n g all the rj j c p o s s i b l e e l e c t r i c c h a r g e s i g n s of the

/ \ e l e c t r o n s o r i g i n a t i n g f r o m t h e s e m i -

2 v v¿+ v "i* u <- u l e p t o n i c d e c a y of t h e q u a r k s c, b, t ,

Y Ny/_ V / V / and ( s b ) , a n d for t h e a n t i q u a r k s c , b,

b Tsb sb T b Ts t, a n d ( sïï) . Àz AT A' A<

/'s (GeV)

10°

10-J

• pp e*X -

• np 1 /

I |v / y

! ' N / --

îr V /A X IAS

: / y — . pDV)=3V. -

— . e*)=13%

/ A ,A» — / pD°n-)=10%

/ (B r / : / / /

e*)=20% / (B r / : / / /

j (B _ «|iXMV. -

1 (B __». i|)X)=4.S%

I i I I I I I I 1 I I I I I i . 11

102

1% (GeV)

10'

F i g . 11 C h a r m c r o s s - s e c t i o n d e r i v e d F i g . 12 B e a u t y c r o s s - s e c t i o n d e r i v e d

f r o m s t r a n g e c r o s s - s e c t i o n f o l l o w i n g f r o m s t r a n g e (full line) a n d c h a r m

f o r m u l a ( 4 ). ( d a s h e d l i n e s - n o t i c e the w i d t h d u e

to t h e e x p e r i m e n t a l u n c e r t a i n t i e s )

c r o s s - s e c t i o n s f o l l o w i n g f o r m u l a (4).

T h e d a t a a r e t a k e n f r o m R e f s . 10 a n d

11.

101

10S

I I

/s (GeV) 10>

F i g . 13 Top c r o s s - s e c t i o n d e r i v e d f r o m s t r a n g e (full l i n e ) , c h a r m ( d a s h e d lines) a n d b e a u t y ( d a s h -d o t t e d lines) c r o s s - s e c t i o n s f o l l o w i n g f o r m u l a (4).

•K Id"1

10*

I — i

103

/s (CeV) 10*

F i g . 14 S u p e r b e a u t y c r o s s - s e c t i o n d e r i v e d f r o m s t r a n g e (full l i n e ) , c h a r m ( d a s h e d lines) a n d b e a u t y ( d a s h - d o t t e d lines) c r o s s - s e c t i o n s f o l l o w i n g f o r m u l a ( 4 ) .

103

s 10»

10'

101 102

/s ICeV)

F i g . 15 N o n - p e r t u r b a t i v e Q C D

p r e d i c t i o n s ( d a s h e d line) a n d

f l a v o u r e x c i t a t i o n p e r t u r b a t i v e

Q C D p r e d i c t i o n s (full line) for

c h a r m h a d r o p r o d u c t i o n .

4 6 8 -

Fig. 16 (a) to decay chains.

(j): Acceptances e relative to baryons for the various

- 469 -

12 14 20 3* p, (GtV/t) B 12 16 20 ït PT I G C V A )

B 12 16 20 » p, (GeV/cl

4 S 12 16 20 24 Pr (GcV/c)

Fig. 16 (k) to (t): Acceptances the various decay chains.

e relative to mesons and antimesons for

3 c u t = 30°, (Leading/Total)= 0.25

o c = 2 mb, o b = 140 u.b

o>= 1.5 jib, a, b = 0.15 lib

0.8 -

0 . 4 -

0

-0.4 -

I i i i I i I i 1 1 0 5 10 15 20

p T (GeV/c)

F i g . 17 P l o t o f A 0 ( p x , 9 c u t = 30°) -as a f u n c t i o n o f p^.. The v a l u e s assumed f o r t h e c r o s s - s e c t i o n s and f o r ( l e a d i n g / t o t a l ) a r e i n d i c a t e d i n the f i g u r e .

O Superbeauty (AM= 30.0 GeV/c 2 )

A Top (AM= 19.5 GeV/c 2 )

• Beauty (AM= 3.2 GeV/c 2 )

o Charm (AM= 1.2 GeV/c 2 )

1.2

0.4 0.6 0.8 1.0 PT/AM

F i g . 18 N o r m a l i z e d (p T /Am) s p e c t r a o f t h e e l e c t r o n s :rom t h e d e c a y s : A^tf* A+ e - v ; A+ •* A ¿ e + v ; V¿ -> A*e~v; A* + A ° e + v . The Am v a l u e s r e !

t h e f o u r decays a r e i n d i c a t e d i n t h e f i g u r e .

«cur* 20" 3 c l r f: 30»

W a

1.0 i

B)

0 0.1 0.2 0.3 0.4 0.5 (LEADING/TOTAL)

F i g . 19 P l o t of A ° ( p T = 10 G e V / c , 9 c u t) ("top" p e a k )

as a f u n c t i o n of ( l e a d i n g / t o t a l ) f o r d i f f e r e n t v a l u e s

of ö c u t > a n d u s i n g : a) m o d e l (i) of s u b s e c t i o n 5.6; a n d b) m o d e l (ii) of s u b s e c t i o n 5.6.

1.0

0.8

0.6

OA

0.2h

1.0

0.8

0.6 r- y

0.4-

0.2-

acut= 10° «OIT- 20° scur=

B) 0.1 0.2 0.3

(LEADING/TOTAL) 0.4 0.5

F i g . 20 P l o t of A ° ( p T = 19 G e V / c , 9 c u t) ("super

b e a u t y " p e a k ) as a f u n c t i o n o f ( l e a d i n g / t o t a l ) f o r

d i f f e r e n t v a l u e s of 9 c u t, a n d u s i n g : a) m o d e l (i) of

s u b s e c t i o n 5.6, a n d b ) m o d e l (ii) of s u b s e c t i o n 5.6.

- 4 7 2 -

<

Signal/Background

F i g . 21 The curves give the behaviour of A e x P as a function of signal/background, for different values of A 0 .

3 C= 10°, model li)

<r (top) (nb) a superbeauty) (ub)

F i g . 22 Curves of constant A e x P , in the plot (rejection power) versus (cross-section for "top" or "superbeauty") for 6 c u t = 10° and for model (i). Plots (a), (b), and (c) refer to p T = 10 GeV/c ("top" peak); plots (d), (e), and (f) refer to p T = 19 GeV/c ("superbeauty" peak). Plots (a) and (d) are obtained with (leading/total) = 0.1; plots (b) and (e) with (leading/total) = 0.25; plots (c) and (f) with (leading/total) = 0 . 5 .

F i g . 23 A s F i g . 22 b u t f o r e _ n t . = 2 0 ° a n d m o d e l ( i ) .

F i g . 24 A s F i g . 2 2 b u t f o r 6 „ , l t . = 3 0 ° a n d m o d e l ( i ) .

F i g . 25 A s F i g . 2 2 b u t f o r 8 c u t = 4 0 ° a n d m o d e l ( i ) .

3C= 90», model (¡I 3C= 10s. model (ii)

10-3r

10"4r A" ' « 0.1 A»P > -0.1

i i wi • • * 1 —

• ' ' mill ' ' • '""I ' ' i'""I le)

i m nuil i 11 hum i , If) I I I l l l l l l I I I I Mil l '

i " 1 K)-1 10° 101 10"3 1(T2 10-' 10° o (top) l|ib) o (superbeauty) (p.b)

10"2 10"1 10° 101 10"3 10"2 10"1 10° o (top) lub) o (superbeauty) lub)

Fig. 26 A s F i g . 22 but for cut = 9 0 " and model ( i ) .

Fig. 27 A s F i g . 2 2 but for 0 c u t = 1 0 ° and model ( i i ) .

3C= 20°, model (ii)

10"2 10_1 10° 101 10"3 10-2 10"1 10° o Itop) (ub) o (superbeauty) lub)

Fig. 28 A s F i g . 2 2 but for = 2 0 ° and model ( i i ) .

Fig. 29 A s F i g . 22 but for 8 C t = 30° and model ( i i ) .

Fig. 30 A s F i g . 22 but for 9 t = 40° and model ( i i ) .

Fig. 31 A s F i g . 22 but for 9 c u t = 90° and model ( i i ) .

- 476 -

«o,* 30*. ILeid¡ng/Total)= 0.2S o(= 2 mb, oB= HO pb o,= 1.5 |ib, 0,!,= 0.15 pb

a) 3tu,= 30 , ILeading/Total)= 0.25 <JC= 2 mb, o„= 10 |jb

a,- 0.1 pb, 0,,,= 0.01 |ib

b )

1.2

08

0.4

-0.4 -

-O.B

• • • * ' t i W.: J i ü

PT (GeV/cl 10 15

PT (GeV/c) 20

F i g . 32 P l o t o f A e x P a s a f u n c t i o n o f p ^ , f o r a t o t a l l u m i n o s i t y L = 3 0 0 n b - 1 , a r e j e c t i o n p o w e r o f 1 0 " 3 , 9 c u t = 3 0 ° , a n d ( l e a d i n g / t o t a l ) = = 0 . 2 5 , u s i n g t h e c r o s s - s e c t i o n e s t i m a t e s : a ) f r o m f o r m u l a ( 4 ) ; b ) f r o m p e r t u r b a t i v e Q C D . T h e e r r o r s a r e s t a t i s t i c a l .

PT IGeV/c) PT IGeVAl

F i g . 33 E x p e c t e d n u m b e r o f p r o d u c e d e l e c t r o n s a s a f u n c t i o n o f p-j, w i t h t h e s a m e a s s u m p t i o n s a s i n F i g . 2 9 , a n d t h e t w o c r o s s - s e c t i o n e s t i m a t e s : a ) f r o m f o r m u l a ( 4 ) ; b ) f r o m p e r t u r b a t i v e Q C D . T h e e r r o r s a r e s t a t i s t i c a l . T h e s o l i d l i n e r e p r e s e n t s t h e b a c k g r o u n d , a s c o m p u t e d i n s u b s e c t i o n 5 . 8 , m u l t i p l i e d b y a r e j e c t i o n f a c t o r o f 1 0 - 3 .

- 4 7 7 -

F i g . 3 4 T h e s t a t i s t i c a l s i g n i f i c a n c e o f t h e m e a s u r e m e n t o f A e x P ( A e x P / A A e x P ) i s s h o w n , f o r a t o t a l l u m i n o s i t y o f L = 3 0 0 n b - 1 , 6 c u t = 3 0 ° a n d ( l e a d i n g / t o t a l ) = 0 . 2 5 , a n d f o r t h e t w o p T r a n g e s : a ) p T = = 7 - 1 2 G e V / c ; b ) p T = 1 4 - 2 3 G e V / c .

3 c u t=30°. (Leading/Total)= 0.25

Pr= 10 CeV/c top

pj= 19 CeV/c superbeauty

Signal/Background

F i g . 3 5 C o r r e s p o n d e n c e b e t w e e n r e j e c t i o n p o w e r a n d s i g n a l / b a c k g r o u n d a s f u n c t i o n o f t h e t o t a l c r o s s - s e c t i o n f o r " t o p " a n d " s u p e r b e a u t y " p r o d u c t i o n , a n d a t t h e t w o p v a l u e s : 1 0 G e V / c a n d 19 G e V / c .

- 478 -

P R E C I S I O N P R E D I C T I O N S FOR THE I N T E R M E D I A T E V E C T O R BOSON

P A R A M E T E R S ( * *

M. Consoli Istituto di Fisica de 1 1 ' U n i v e r s i t à , Catania INFN, Sezione di Catania (Italy)

L . H a i a n i Istituto di Fisica " G . M a r c o n i " , Roma INFN, Sezione di Roma (Italy)

(*) P r e s e n t e d by M . C o n s o l i .

- 479 -

The present e x p e r i m e n t s at the pp coll i d e r at CERN and the future ones with the next generation of e + e ~ m a c h i nes open a new area of research to test the p r e d i c t i o n of the Standard M o d e l ' 2 ' of electroweak i n t e r a c t i o n s . In p a r t i cular, accurate m e a s u r e m e n t s of the ph y s i c a l p a r a m e t e r s of the intermediate vector bosons (IVB) should be p o s s i b l e .

A very important a c h i e v e m e n t will be the detection of s m a l l , calculable d e v i a t i o n s from the values p r e d i c t e d in lowest order. These corrections are i n t e r e s t i n g by themselves since their o b s e r v a t i o n will allow a test of the theory beyond the tree l e v e l , as it is usually done in Q E D . Moreover the IVB p a r a m e t e r s , through loop e f f e c t s , are sensitive to the whole p a r t i c l e content of the t h e o r y , so t h a t , p e r h a p s , by m e a s u r i n g a shift of few h u n d r e d s MeV to the Z and W boson masses one can gain insight about the existence of new particles in the mass spectrum in the TeV region and beyond. In order to extract this kind of in f o r m a t i o n from the IVB par a m e t e r s we need a careful estimate of the t h e o r e tical uncertainty which affects the pr e d i c t e d c o r r e c t i o n s .

In the fol l o w i n g we will present the main results of an analysis of radiative c o r r e c t i o n s to IVB p a r a m e t e r s whose details will be p u b l i s h e d e l s e w h e r e ' ^ ' . Our analysis is restricted to the ma s s e s Mw and Mz and to the leptonic decay r a t e s ' * ' .

P ( 1 ) - f (W +.-* ^ + + . . .) ( 1 )

? ( 2 ) = f (Z PL ) (2)

r M 3 ) = r , ( Z - > ^ + A " + - - - ) (3)

Other q u a n t i t i e s could be added to our list, e.g. inclusive decay rates into one quark of a given flavour p l u s anything e l s e . The quantities given a b o v e , h o w e v e r , are distinctive b e c a u s e they are affected by strong i n t e r a c t i o n s in a way which can be accurately controlled. T h e s e q u a n t i ties are therefore the most p r o m i s i n g c a n d i d a t e s for a higher order test of the Standard M o d e l .

Given the fermion m a s s e s , the values of the IVB p a r a m e ters are dete r m i n e d by three basic q u a n t i t i e s : the fine structure constant oi , the Fermi coupling constant G and the G l a s h o w - W e i n b e r g - S a l a m angle sin Q = s.

(*) The dots in ( 1 ) , (3) indicate that the c o r r e s p o n d i n g rates are e l e c t r o m a g n e t i c a l l y i n c l u s i v e . On the other hand the final state in (2) is restr i c t e d to ^ >V only and the c o r r e s p o n d i n g rate gives the c o n t r i b u t i o n of the /^--flavour to the so called "dark m o d e s " of the Z.

- 4 8 0 -

It is costumary and convenient to take Ö( from the very l o w - e n e r g y measurement of the J o s e p h s o n effect

o C 1 = 1 37 . 035

and to derive G from the muon e.m. radiative c o r r e c t i o n s :

with

w h i c h gives

G = (1.16632 + 0.00002) 10

( 4 )

lifetime including first order

5 G e v " 2 (7)

~2 5 G y 192 7T

8m ( 1 - •) (1 + £ ) (5)

m

o = T 7 T ( T r -2 5 2 - ^ - ) + 0 ( oC In

m. m (6)

As for s the usual strategy is to determine it from n e u t r a l current, neutrino experiments either in the s e m i l e p t o n i c or in the p u r e l y leptonic p r o c e s s e s :

V ( V' ) + N \) ( ) + . . . . ( 8 )

V J ( v ' ) + e - ^ v ' ( v 7 ) + (9)

If this is done the vector boson masses as well as the decay rates (1) -r (3) are u n i q u e l y predicted to any desired order in perturbation theory.

This choice for the d e f i n i t i o n of s suffers, h o w e v e r , from serious d r a w b a c k s . The determination of s from p r o c e s s (8) requires a control of strong interaction e f f e c t s , very u n l i k e l y to be attainable to the precision required for a test of the higher order c o r r e c t i o n s . A p r e c i s i o n m e a s u r e m e n t of the cross section of process ( 9 ) , t h e o r e t i c a l l y very clean, is severely limited by s t a t i s t i c s . Finally the theoretical e x p r e s s i o n s for the IVB m a s s e s and decay rates in terms of s, as defined from the c r o s s -sections for process (8) or (9) at the present e n e r g i e s , contain sizeable c o r r e c t i o n s related to the v a c u u m p o l a r i z a t i o n of the photon and the IVB t h e m s e l v e s . Such terms are affected by the strong i n t e r a c t i o n s . The correction related to the photon vacuum p o l a r i z a t i o n s can be computed quite accurately in terms of the e x p e r i m e n t a l cross-section for e e — h a d r o n s , but in the case of the IVB vacuum p o l a r i z a t i o n effects we have to rely upon the p e r t u r b a t i v e QCD c a l c u l a t i o n s which may i n t r o d u c e u n c o n t r o l l e d errors and contain in any case not well defined light quark m a s s e s .

- 4 8 1 -

A n a l t e r n a t i v e s t r a t e g y w a s s u g g e s t e d in R e f s ^ ' ^ ' ^ . It c o n s i s t s in d e t e r m i n i n g s f r o m t h e I V B p h y s i c s i t s e l f , t h u s g i v i n g up o n e p r e d i c t i o n a n d t e s t i n g t h e t h e o r y b y a c o m p a r i s o n of t h e I V B m a s s e s a n d d e c a y r a t e s a m o n g t h e m s e l v e s . In t h i s c a s e w e c a n d e f i n e

s = F ( Z 1 ) , Z ( 2 ) , .. . Z ( 5 ) ) ( 10 )

w h e r e Z < 1 > = M w ' ^ = M z ' ^ ' J* 1 > < * U ) = 2 , ^ = P ^ ^ a n ¿ l F is a n a r b i t r a r y f u n c t i o n of t h e I V B p a r a m e t e r s s a t i s f y i n g t h e r e l a t i o n

s = F ( g ( 1 ) ( s ) , g ( 2 ) ( s ) , ... g ( 5 ) ( s ) ) ( 1 1 )

a n d Z ^ 1 ^ = g^-*-) (s) in l o w e s t o r d e r .

( E x a m p l e : M w = 37 .281 G e V = g ( D ( s ) ( . . . . ) E q s ( 1 0 ) a n d

( 1 1 ) i m p l y m o r e t h a n an a l t e r n a t i v e r e n o r m a l i z a t i o n s c h e m e , r a t h e r t h e y s u g g e s t t h a t a m e a n i n g f u l t e s t of t h e h i g h e r o r d e r e f f e c t s c a n be o b t a i n e d o n l y b y c o m p a r i n g p a ir o f p a r a m e t e r s .

T h i s p r o c e d u r e is i l l u s t r a t e d in F i g . 1 in t h e c a s e of Mw a n d M z f o r t h e c h o i c e

s = I 1 - M ' w / M " z 1 l / / 2 ( 1 2 ) = | j - M 2 w / M 2 z ^ 1

a s s u m i n g f o r t h e H i g g s p a r t i c l e a n d t h e t o p q u a r k t h e v a l u e s

m H = 100 G e V , m t = 20 G e V ( 1 3 )

I r r e s p e c t i v e l y f r o m t h e v a l u e of s i n 0 w , a n d i n c l u d i n g h i g h e r o r d e r c o r r e c t i o n s , t h e e x p e r i m e n t a l p o i n t in t h e M z -M w p l a n e is p r e d i c t e d to l i e on a w e l l d e f i n e d c u r v e ( c u r v e a) d i f f e r e n t f r o m t h e c u r v e c o m p u t e d in l o w e s t o r d e r ( c u r v e (b) ) .

T h u s a m e a s u r e m e n t of b o t h M w a n d M z p r o v i d e s at t h e s a m e t i m e a t e s t of t h e h i g h e r o r d e r c o r r e c t i o n s ( t h e e x p e r i m e n t a l p o i n t l i e s on c u r v e ( a ) ) a n d a m e a s u r e m e n t o f s i n w ( d e t e r m i n e d b y t h e l o c a t i o n of t h e p o i n t on t h e c u r v e i t s e l f ) . A s i m i l a r r e a s o n i n g c a n be a p p l i e d t o t h e o t h e r p a i r of p a r a m e t e r s . F i g . 2 s h o w s t h e c o r r e s p o n d i n g c u r v e in t h e c a s e of M z a n d * ^ ) .

F o r a l a r g e c l a s s of d e f i n i t i o n of s i n 0 w t h e g e n e r a l s t r u c t u r e of r a d i a t i v e c o r r e c t i o n s to t h e I V B p a r a m e t e r s c a n be e x p r e s s e d as

- 482 -

z ( i ) = g( i > ( s ) [l + d ^ ^ + l d ( i ) ( d ( i )

+ 1 ) é2 ] ( 1 4 )

w h e r e d ' = — ^ — f o r t h e m a s s e s a n d d = — | — f o r t h e w i d t h s . 6 ^ is d e f i n e d t h r o u g h t h e r e l a t i o n

oi ( M z ) 1 ( 15 )

a n d t h e ér r e p r e s e n t t h e r e m a i n i n g o r d e r o( w e a k c o r r e c t i o n s a n d d e p e n d u p o n oi , s, t h e H i g g s b o s o n a n d t-q u a r k m a s s e s .

O n e o f t e n q u o t e d s o u r c e of u n c e r t a i n t y , i . e . t h e v a l u e s of t h e l i g h t q u a r k m a s s e s , d i s a p p e a r s w h e n t h e h a d r o n i c c o n t r i b u t i o n to é¿ is e x p r e s s e d in t e r m s of t h e e x p e r i m e n t a l e + e ~ — T h a d r o n s c r o s s - s e c t i o n s . A c a r e f u l a n a l y s i s ' ^ ' (by i n c l u d i n g f i v e q u a r k f l a v o u r s a n d t h e e , /*• , ~C , l e p t o n s ) g i v e s

£ ¿ ( 1 4 z = (90 G e v ) 2 ) = ( 5 .97 + 0 . 0 4 ) x 1 0 _ 2 + .

to c o m p u t e t h e c o r r e c t i o n s to t h e IVB p a r a m e t e r s w e n e e d tru as f u n c t i o n of M z , i . e . of s i n 2 t ? w . W e s h a l l u s e t h e f r e e -q u a r k m o d e l f o r t h e v a r i a t i o n of í"^ n e a r M z = 90 G e V , o b t a i n i n g

t <s> = (5.97 + 0.04) x 10"2+ 3 -ln(4 ) (16)

s c

w h e r e c 2 = 1 - s 2 , s§ = .22 a n d €jôp is a l s o c a l c u l a t e d in

t h e f r e e - q u a r k m o d e l ^ w i t h m f c n o t n e g l e c t e d w i t h r e s p e c t t o M z .

If t h e t - q u a r k a n d t h e H i g g s b o s o n h a d e x a c t l y t h e v a l u e s g i v e n in E q ( 1 3 ) t h e t h e o r e t i c a l a c c u r a c y on t h e l o c a t i o n of t h e c u r v e (a) in F i g . 1 w o u l d be q u i t e a d e q u a t e (of t h e o r d e r of f e w p a r t s in 1 0 ~ 4 , s e e E q ( 1 6 ) ) a n d a m e a s u r e m e n t of M w a n d M z w i t h 1 0 - 3 r e l a t i v e e r r o r w o u l d d e t e c t t h e f u l l f i r s t o r d e r c o r r e c t i o n . T h e d a r k a r e a in F i g . 3 i n d i c a t e s t h e d i s p l a c e m e n t of c u r v e (a) c o r r e s p o n d i n g to t h e r a n g e s

10 G e V ¿ m R ¿ 8 0 0 G e V ( 1 7 )

20 G e V L m f c ¿ 100 G e V

In p a r t i c u l a r t h e l e f t b o u n d a r y is c a l c u l a t e d f o r m H = 10 G e v a n d m f c = 100 G e V w h i l e t h e r i g h t o n e is c a l c u l a t e d f o r m H = 8 0 0 G e V a n d m t = 60 G e V .

- 483 -

To visualize the influence of larger values of m t we have indicated the d i s p l a c e m e n t of the points of curve (a) when we let m t to vary up to 300 GeV. The effect of a large m t is quite dramatic, due to the fact that the weak corrections contain a term which diverges quadratically with m t . This term coincides with the corrections to the ratio of the neutral to charged current cross-sections found by V g l t m a n ' 8 ' and the range 20 GeV < m t ¿ 300 GeV c o r r e s p o n d s to the maximum deviation of the latter ratio from the lowest order predictions allowed by the present e x p e r i m e n t a l analysis (for an updated d i s c u s s i o n see e.g. Ref ( 9 ) ) .

The effect of m H is much less important since the Higgs boson correction does not diverge quadratically for large m H , as implied by the "screening theorem" of Ref ( 1 0 ) .

In Fig. 4 we show the corrected and uncorrected curves in the P r 3 ) - Mz p l a n e . The dark area, as in the case of the Mz - Mw plane, is enclosed by the two corrected curves obtained for m H = 10 GeV, m t = 100 GeV (lower b o u n d a r y ) and m R = 800 GeV, m f c = 60 GeV (upper b o u n d a r y ) .

A remarkable case is the - M W plane (see Fig. 5) where the corrected and uncorrected curves coincide to a high degree of accuracy.

Almost all radiative c o r r e c t i o n s , in this case, can be absorbed into a redefinition of sin S w. The same holds for the p * 2 ) - Mz relation.

The general conclusion is that a measurement of m a s s e s and widths with relative errors at the level of 1 0 - 2 and few times 1 0 ~ 2 , r e s p e c t i v e l y , gives a test of the leading corrections and an i n t e r e s t i n g information on the t-quark m a s s , if t has not already been found among the decay products of W and Z. M e a s u r e m e n t s at the level of 1 0 - 3 error for masses and a few times 1 0 ~ 3 for the widths will yield p r e c i o u s , combined i n f o r m a t i o n s on the Higgs boson and t-quark masses and in general on the presence of new heavy particles in the mass spectrum.

- 4 8 4 -

— R E F E R E N C E S —

1) G.Arnison et a l . , UA1 C o l l a b o r a t i o n , C E R N - E P / 8 3 - 1 3 . P.Darriulat et al., Results from the UA2 C o l l a b o r a t i o n , p r e s e n t e d at this Meeting.

2) S.L.Glashow, N u c l . P h y s . 22^ ( 1971) 579; S.Weinberg, Phy s . Rev. Lett. V9_ ( 1967) 1264; A.Salam, in P r o c . Eight N o b e l S y m p . , N . S v a r t h o l m Ed., Amqvist and W i k s e l l , Stockholm 1968, pag. 367; S.L.Glashow, J.Iliopoulos and L . M a i a n i , Phys.Rev. D2 ( 19 7 0 ) 12 8 5 ; G . t ' H o o f t , N u c l . P h y s . B33 (1971) 173; B35 (1971) 167; C.Bouchiat, J.Iliopoulos and P h . M e y e r , P h y s . L e t t . 38B (1972) 519.

3) M . C o n s o l i , S.Lo Presti and L . M a i a n i , "Higher order effects and the vector boson p h y s i c a l p a r a m e t e r s " , CT.PP/738 - 14/1/1983; Earlier works on the radiative corrections to the IVB masses are due to: W . J . M a r c i a n o , Phys.Rev. D20 ( 1979) 274; F . A n t o n e l l i , M . C o n s o l i , G . C o r b ô , P h y s . L e t t . 91B ( 1980) 90 ; M . V e l t m a n , P h y s . L e t t . 91B (1980) 95; A . S i r l i n , Phys.Rev. D22 (1980) 971; W . J . M a r c i a n o , A . S i r l i n , Phys.Rev. D22 (1980) 2695; F . A n t o n e l l i , M . C o n s o l i , G . C o r b ô , O . P e l l e g r i n o , N u c l . Phys.B183 ( 1981 ) 195. F . A n t o n e l l i , L . M a i a n i , N u c l . P h y s . B186 (1981) 269. The p r e d i c t i o n of M w and M z based on the value of s i n Ç w

m e a s u r e d in neutrino cross section is discussed in Ref ( 1 1 ) .

4) A . S i r l i n , and W . M a r c i a n o and A . S i r l i n , papers quoted in Ref ( 3 ) .

5) L . M a i a n i , talk p r e s e n t e d at the I n t e r n a t i o n a l C o n f e r e n c e on u n i f i e d Theories and E x p e r i m e n t a l T e s t s , March 16-18, 1982, V e n e z i a .

6) Z.Hioki, P r o g r . T h e o r . P h y s . 68 (1982) n. 6.

7) G.Penso, private communication, see also Ref 3.

8) M . V e l t m a n , N u c l . P h y s . B123 (1977) 8 9 .

9) J.Kim, P.Langacker, M . L e v i n e and H . H . W i l l i a m s , R e v . M o d . Phys . _53_ ( 198 1 ) 211; L . M a i a n i , in XXI Intern. Conf. on High Energy P h y s i c s , P a r i s , July 1982.

10) M . V e l t m a n , Acta P h y s . P o l . B8_ ( 1977) 4 7 5 .

11) W . M a r c i a n o and A . S i r l i n , N u c l . P h y s . B189 442; J.F.Wheather and C . H . L l e w e l l y n Smith, N u c l . P h y s . B20 8 (1982) 189.

- 485 -

— F I G U R E C A P T I O N S -

Fig.1 Corrected (curve (a)) and u n c o r r e c t e d (curve (b)) curves in the M 2 - M w p l a n e s . Here m H = 100 GeV, m t

= 20 GeV. The point s = .217 is e x p l i c i t l y shown, c o r r e s p o n d i n g to the present estimate deduced from the higher order corrections to neutral current

11) p r o c e s s e s '•

Fig.2 Corrected (curve (a)) and u n c o r r e c t e d (curve (b)) curves in the P ( Z —» . ¿ t ~ r + ••) ~ M Z p l a n e . As in Fig. 1, m H = 100 GeV, m t = 20 GeV.

Fig.3 The effect of varying m H and m t in the range (17) is shown by the shaded area around the corrected curve of F i g . 1 . The solid arrows represent the d i s p l a c e m e n t of the p o i n t s with a given value of sin & when we let m t to grow up to 300 G e V .

Fig.4 The effect of varying m H and m t in the range (17) is shown by the shaded area around the c o r r e c t e d curve of F i g . 2 . As in Fig.3 the solid lines represent the effect of v a r y i n g m f c up to 300 GeV.

F i g . 5 The curve in the / (W -*M + •••) - M w p l a n e . The corrected and the uncorrected curves coincide to a very good a p p r o x i m a t i o n . The arrows coming from below (above) represent the r a d i a t i v e l y corrected (bare) values of sin w with m H = 100 GeV, m f c = 20 GeV.

- 486 -

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Q C D R A D I A T I O N A N D T H E M U L T I P L I C I T Y D I S T R I B U T I O N A T T H E C O L L I D E R

G. Pancheri

I N F N , Laboratori Nazionali di Frascati P . O . B . 13, 00044 Frascati, Italy

A B S T R A C T

T h e multiplicity distribution in hadron-hadron collisions is discussed as arising from the soft gluon bremsstrahlung accompanying parton-parton scattering. K N O scaling is m e a n scaling in the energy variable and is seen to arise w h e n the microscopic system of quarks and gluons is averaged over the hadronic matter coordinates. T h e shape of the multiplicity distribution for the U A 1 data at the collider energy is well fitted by a soft Q C D radiation formula, using a Q C D parameter A - 100 M e V . T h e reduced cu mulants y ¿ are expected to decrease with energy.

T h e w o r k I will discuss has been done in collaboration with Y. Srivastava.

In this w o r k w e study the contribution of soft gluon br emsstrahlung to multi (1 2 3)

particle production at very high energy v ' ' '. This m e c h a n i s m has already (4)

been seen at w o r k in a score of high energy processes like DIS , Drell-

- Y a n ^ ' ^ \ e + e ~ C ) . Although one cannot say that all or even m o s t high ener

gy hadron physics is explained in t e r m s of soft gluon b r e m s Strahlung, w e

believe the latter to be an important m e c h a n i s m often competitive with hard

Q C D processes and s o m e t i m e s dominant.

T h e material I will present can be s u m m a r i z e d in the following three

points :

1. K N O scaling is scaling-in-the-mean; 2. T h e shape of the multiplicity distribution can be obtained from the ener-

- 504 -

gy distribution of the soft Q C D radiation emitted in parton-parton scatter

ing;

3. K N O scaling violations have the s a m e origin as scaling violations in

D e e p Inelastic Scattering and they depend on -¿IQCD* A typical value for

A is 100 M e V .

In the following, I will discuss in detail the above points in separate

sections.

1. - K N O Scaling and M e a n Scaling

In 1974, F. T. D a o et a l . ^ put forward the hypothesis that the shape of

single particle distributions in the transverse and longitudinal m o m e n t u m

variables p . and p-^ are independent of multiplicity and incident energy,

if the distributions are plotted against the " m e a n " variable x / < x > . A c

cording to their hypothesis, the energy, multiplicity and initial state de

pendence lie in the average value < x > . T o test their ansatz, they analyzed

single inclusive pion cross-sections at various energies and for different

values of the charged multiplicity and found that w h e n normalized all the

distributions (in a given variable) fell on top of each other and that this

w a s true for the transverse as well as the longitudinal m o m e n t u m variable.

T h e s e authors note that w h e n the variables are the charged and neutral m u

ltiplicity, one has the familiar K N O s c a l i n g ^ . In Figs. 1 and 3 w e s h o w

their data compilation together with the Q C D radiation curve which will be

discussed in the next section. W h a t is quite remarkable is that m e a n scal

ing can be observed also for current processes. In fact a similar analysis

for S P E A R data^ 1 0) in the energy range 3 Í W ^ 1 0 G e V again shows that

the data for p_ arrange themselves on a single c u r v e ^ l Fig. 2 illustrates

m e a n scaling for e + e " . A completely analogous scaling takes place in [i-

-pair production^ , as can be seen from Fig. 4. It should be noted that (12)

the two m a s s ranges w e have analyzed^ ' correspond to rather different

values of <P^>, one set having = 1.2 G e V and the other = 1.35

- 505 -

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- 506 -

G e V (in the ^-region). Finally, if the variable under scrutiny is n / < n > ,

one will observe K N O scaling and interpret it as one m o r e instance of seal

ing in the m e a n .

Before turning to discuss the shape of all these distributions, w e would

like to c o m m e n t upon " m e a n " scaling in general. A scaling behaviour re

flects the presence of a distribution function for which scaling in certain

parameters occur. T h e question one m a y ask is w h y these parameters are

precisely the m e a n values of the variables under scrutiny. A possible an

s w e r is that w e are observing a system which has been averaged over the

hadronic matter coordinates. A s a result of such average, the microscopic

scales characterizing the quark and gluon system are turned into their m e a n

values. A n illustration of this procedure can be seen in sect. 3 and ref. (13).

2. - T h e shape of the Scaling Function

A s discussed in the previous section, high energy inclusive distributions

s h o w scaling in the variables P t / , P L / a n d n/< n>. T h e s e three

variables can be associated to the m o m e n t u m and energy characterizing a

universal distribution which w e propose to be due to soft gluon bremsstrah

lung. W h y soft ? In Q E D the no-recoil approximation can be used only in a

limited fashion, i. e. to describe photons carrying at m o s t 10 or 2 0 % of the

emitting electron's energy. B e y o n d this value, in fact, one has to start

using the hard b r e m s Strahlung formulae, since the soft approximation

breaks down. W h y then in Q C D , the m a i n m e c h a n i s m of particle production

in the central region s e e m s to be the no-recoil one ? A tentative answer is

the following : it is a general physical law that w h e n a particle which is cou

pled to a massless field changes its m o m e n t u m through scattering or anni

hilation or pair production, then massless quanta are emitted. In Q C D ,

once two quarks are produced like in e + e " or annihilate like in D Y or scat

ter off a photon like in DIS or are s o m e h o w extracted from their hadronic

shells through a high energy process, they will start the soft bremsstrah-

- 507 -

lung process. N o w , because a g is Q -dependent, with a s Q ) > 0, a Q 2 ^ c o

hard emission process is non-leading relative to a soft one. It is "cheap

er" for a quark to l o s e m o s t of its energy in a sequence of non-recoil e-

mission events than otherwise: the loss of energy is preferentially an adi

abatic process. A check of this hypothesis can be found in the fact that the

shape of the multiplicity distribution in pp and pp collisions, w h e n plotted

in the K N O variable, is obtained f r o m the soft gluon energy distribution.

Before discussing the latter in detail, w e shall c o m m e n t upon the distribu

tion which underlies the m e a n scaling curves appearing in Figs. 1,2,3, 4.

T h e characteristics of this distribution can be s u m m a r i z e d as follows :

a) the shape of the distribution is not the s a m e (albeit is similar) for all

three variables p ., p ^ and E or n;

b) for a given variable the shape depends on the single soft gluon distribu

tion for the process under examination, a function which w e shall call ß ;

c) for a given variable and a given process, the shape depends on energy

through j3(s).

Concerning points (b) and (c), it

should be noticed that the p t distri

bution for semihadronic processes

like e + e ~ — » J t + X and pp —*• /¿+¿i.~+X

s e e m s to have exactly the .same shape

at comparable energies, while for pure <JP_ d 2 - o

ly hadronic processes the normalized

curves are "fatter". A comparison

between the normalized S P E A R distri

butions and the power-like fit

p t / ( l + ( p t / p Q ) ) is s h o w n in Fig. 5,

where the dotted curve is the empiri — oo

cal fit and the full curve is the s a m e

Q C D radiation curve fitting the S P E A R

i.c

FIG. 5

- 5 0 8 -

d 4 p ( K ) . d 4 K j_îÛL e«-*. e - i d ^ ( k ) ( l - a — )

(2JT)

3—

w h e r e d n(k) represents the (exponentiated) single gluon distribution func_

tion. W h e n integrated in all variables but K ^ , the above function w a s used

to give the longitudinal m o m e n t u m distribution of Fig. 2. Likewise for the

transverse m o m e n t u m variable and the curves s h o w n in Figs. 1, 3,4. T o

obtain the energy distribution, one will integrate in all the three m o m e n t u m

variables and obtain ß - i kt

f d t iK 0t -f dñ(k)(l-e ) d P ( K Q 1 ß ) = d K 0 Ç e e 0 . (1)

This function and its relation to the multiplicity distribution in hadronic re

actions will be discussed in detail in the next section.

3. - T h e multiplicity Distribution in pp or pp Collisions

O u r starting hypothesis is that the total energy carried by the pions, n

2 atj_, is mostly that of the soft Q C D radiation, ß v j s , emitted by the in

teracting partons, i. e. w e put

n 2 co. = Q • j i vis

T h e charged n-particle cross-section can then be written as

a C h ( s ) = 2 J d x . f . U J fdx f . ( x _ ) fdßS ( x ^ x - ß ) n i, j,final 1 1 2 3 ¿ i, j - * final 1 ¿

(2) d P ( ß . ß ) n , v

data in Fig. 3. T h e empirical fit had been used by the C F S collaboration^'''^

for their ¿t-pair data. All the Q C D curves w e r e obtained from the function

,3_„ W H -ik- x, liS.' x - \ c

,4

- 509 -

dt int 2JT e e o

T h e above equation is valid if dñ(k) scales. This is certainly not true in

Q C D . H o w e v e r , if w e write , ... d k 2

w h e r e dP(í2v s, í3)/dfíy s is the energy distribution of soft gluons as in eq.

( 1 ) and QîQiuu^, (Ú2,... , û>n) is the inclusive probability for production

of n pions out of a total available energy Q. In eq. ( 2 ) , f(x) represents the

initial parton densities, a is the parton-parton cross-section, s u m m e d o-

ver all unobserved final states. T o study the multiplicity distribution, w e n o w take the following two steps :

n i) 2 -> n<&>(s)> as a result of averaging over the pion energies;

1

and

ii) Q —* < ß ( s ) > as a result of averaging over the quark coordinates.

Lets us briefly c o m m e n t upon the above two steps.

i) W e start by m a k i n g the substitution n 2 coi — » n <o)(n, s)>

1

i. e. by considering that the effect of integrating over the individual pion

energies with the fragmentation function as weight function is that of sub-n

stituting, everywhere it appers, 1 co- with n<<w(n,s)>. W e then use the 1 1

experimental fact that the m e a n energy per charged track is approximately

a constant in n and set <cu(n, s)> ~ < C D ( S ) > + 0 ( - ) .

n »

W e can n o w scale out <a>> in dP(n<a)>, Q) and write

o f (s) * 2 ffi(x )dx R.(*2)dx2 íaurx2; Q) §g • final

ß / < < ü > . M

J dH(k)(l-e )

- 510 -

and notice that in the very large s region w e can consider the k± integration

to be independent of k, then the scaling takes place and w e can write

d - n ( k ) i â m i n l - i , . ,3)

ii) T o take the second step and use m e a n scaling, w e substitute Q/«o>

with its m e a n value. W e calculate, using eq. (2),

, . i n a ( n , s ) d n < n ( s ) > = ;

fa(n, s)dn

and, from the definition

< 0 > *I W " i W*2 ^ f i n a l ' W a ' ^

w e find

< n " s ) > = ?s) «o(s)> '

This equation has a very simple semi-classical interpretation. W e notice

that the quantity

Q Q J kdñ(k) = J d W ( k ) « ß(s)Q(s) o o

represents the energy radiated during parton scattering in the frequency

range 0-Í2 . But then w e can write for the radiated energy

j9(s)<fí(s)> = < n ( s ) X û ) ( s ) >

i. e. the m e a n energy radiated equals the m e a n energy per track times the

average multiplicity.

F r o m eq. (1), one can see that the energy distribution function d P ( ß v ^ g ,

Q) scales in ß , • C/Q , so that the function P(n,s) defined as v 1 fa

- 5 1 1 -

c h o (s) d P ( ß . , < ß > )

^ s ) = - f ¿ r - '* i d ß v i s fir. ôQvis-n«o» 2o (s) vis n

clearly will scale in n<(û>/<Q> , i.e. in 0 n/<n>. After s o m e straightforward manipulation, one obtains

1 dk -ikt i P T Z ^ t - tf J

P(n,s) = ß(s) j — e

. o n x -i r o k . , - l K t , dt te1-^!11-6 > — p 2n;

W e propose that the K N O function be given by

Vi-^-r ) = < n > P ( n , s ) . < n >

This function obeys the two normalization conditions

oo j <P(z)dz = 1 and izdz<P(z) = 1 . o

W e can calculate the m o m e n t s of this distribution. Using eq. (1) and the de

finition of refs. (1, 2, 3), w e find

Y - _ L _ = 1 = 1 2 2 8 ' 3 3 ß 2 ' ^ 4 |3 3

i. e.

2 3 2 l n l n s / ^ 1 2

T h e above equation shows h o w K N O scaling is violated. A s soon as eq. (3)

is satisfied, i. e. in the asymptotic freedom region, the cumulants

should start decreasing with increasing energy. T h e function ß(s) is the

s a m e function from which scaling violations in DIS are predicted^.

Using A = 100 M e V , w e calculate ß to be approximately 1.82. In Fig. 6

w e s h o w the fit to the U A 1 data^ 2\ W e notice that for very small values of

the multiplicity the following behaviour obtains :

- 5 1 2 -

< n > 0 n P

(ß n ß-1

<n> « 1 < n >

This shows that the closer ß is to 1, the flatter the curve will be. This can

be seen in Fig. 7 w h e r e the U A 1 data for | r¡ \ < 1.5 have been fitted using

ß = 1.1. T h e value for ß is here strictly empirical. Its m a i n justification

lies in the fact that the selection of events in the range |?7 ¡ < 1.5 m e a n s a

reduced phase space and hence a smaller ß.

VS' = 5 4 0 GeV

j UA1 iil'15

2.0 r>l<n> 3.0 2 0 3.0 n / ' i i

FIG. 6 FIG. 7

4 . - Conclusion

Finally, w e would like to give a tentative answer to the question as to

whether there is a connection between m e a n scaling, K N O scaling and geo

metric scalings^^' l^'lo"^ T h e r e certainly is a connection insofar they

- 5 1 3 -

all reflect the s a m e averaging process done on a c o m m o n universal pheno

m e n o n , like soft gluon b r e m s Strahlung. H o w e v e r , geometric scaling and

K N O scaling do s e e m to reflect different components of the s a m e distribu

tion ' geometric scaling, being related to the spatial properties of the cross

section, is probably connected to the transverse m o m e n t u m distribution,

while K N O scaling is related to the energy distribution.

References

(1) - W . T h o m é et al. , Nuclear Phys. B 1 2 9 , 365 (1977); J.Firestone et al., Phys. Rev. D 1 4 , 2902 (1976); D. F o n g et al. , Nuclear Phys. B 1 0 2 , 386 (1976).

(2) - G. Arnison et al. , Phys. Letters 107B, 320 (1981); see also U A 1 presentation in these Proceedings.

(3) - K. Alpgard et al. , Phys. Letters 107B, 310, 315 (1981); see also U A 5 presentation in these Proceedings.

(4) - G. Pancheri-Srivastava, Y. Srivastava and M . R a m o n M e d r a n o , Phys.

Rev. D 2 3 , 2533 (1981).

(5) - G. Pancheri-Srivastava and Y . Srivastava, Phys. Rev. D21, 97 (1980).

(6) - G. Parisi and R. Petronzio, Nuclear Phys. B 1 5 4 , 427 (1979); P. Chiappetta and M . G r e c o , Nuclear Phys. B l 99, 77 (1982).

(7) - G. Pancheri-Srivastava and Y. Srivastava, Phys. Rev. Letters 43,

11 (1979).

(8) - F. T. Dao et al. , Phys. Rev. Letters 33, 389 (1974).

(9) - Z. Koba, H. B. Nielsen and P. Olesen, Nuclear Phys. B 4 0 , 317(1972).

(10) - G. Hanson, 13th Rencontre de Moriond on High Energy Leptonic and Hadronic Interactions, L e s A r c s 1978.

(11) - D . M . K a p l a n et al., Phys. Rev. Letters 40, 435 (1978); A . S. Ito et al., Phys. Rev. D 2 3 , 604 (1981).

(12) - M . H. F r i e d m a n , G. Pancheri and Y. Srivastava, "Soft Gluon Corree tions to the Drell-Yan P r o c e s s " , N U B 2486 (1981) (unpublished).

(13) - G. Pancheri and Y. Srivastava, " Q C D Radiation and K N O Scaling",

Frascati report L N F - 8 2 / 8 6 (1982).

(14) - T. T. C h o u and C. N. Y a n g , Phys. Letters 116B, 301 (1982).

(15) - C.S. L a m and P. S. Y e u n g , McGill Univ. preprint (1982).

(16) - S. Barshay, Phys. Letters 11 6 B , 193 (1982).

- 5 1 4 -

HOT HADRONIC MATTER AND pp COLLIDER

Talk at pp Collider Workshop Rome, 1 2 - 1 4 January 1983

L. Van Hove CERN - Geneva

COMMENTS ON THE TRANSPARENCIES

I. - NON-DIFFRACTIVE COLLISIONS

1.1. - The diagram shows the two-quark chains attached to the valence quarks as in the simplest dual parton model, and the two chains attached to sea quarks which account for the higher central multiplicities at the collider.

1.2. - For more information, see L. Van Hove, Phys.Letters 118B (1982) 138.

1.3. - No comment.

1.4. - For example, the interaction of the many central region partons in the diagram of 1.1. could lead to (at least partial) thermalization. A similar effect could occur for the soft gluon emission mechanisms.

1.5. - At very high s, large virtual masses u¿ of partons can be induced by soft parton interactions. These virtual masses are radiated away mostly by soft gluon emission and hadronization, inducing higher central multiplicities and <Pt> a t larger s, as well as the increase of <P^> with multiplicity at fixed s (with or without thermalization).

II. - INELASTIC DIFFRACTION

No comment.

- 5 1 5 -

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- 517 -

fice»¡I êf ß >h »nji**/ nttfr*** t ¿>

'cm. . hf = !Z*-ll7l f o r -Jl-?E

C^try Act prêtons / i o 4 e ^J

]f,3. Questions tô eKj>eriy^»HÍ:a//'fh

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fraj*»t€t>¿* /Vi its ok/h r*ftp*0Li*n% .

T<&t structure ? j)/ftriliu"/Ghj efj^zyirizh-ts.

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- 5 1 8 -

Weak interactions in the region of the Fermi scale.

R.Barbieri

Istituto di Fisica, Univ. di Pisa

I.N.F.N., Sezione di Pisa

Two alternative roads are taken to describe the physical origin of

GeV and may be realized in a weak coupling theory (the Higgs model).

This is in opposition to the view that the Fermi scale is connected to

the manifestation at relatively low energy of a new strong force, giving

the binding of a composite Higgs field or even, perhaps, of composite

quarks, leptons and weak gauge bosons.

Due to our present limitations in making reliable calculations in a

strong coupling theory, the road of the fundamental scalar can be made

much more concrete. In fact it is possible to see that the instability

of the mass of the scalar field under quantum fluctuations calls for a

host of new particles all appearing at the Fermi scale. These particles

have to occur in multiplets of the (suitably extended) fermion-boson

symmetry displayed by the free kinetic lagrangian of an equal number of

bosons and fermions (supersymmetry).

The detailed prediction of the mass spectrum of all these new

particles requires an understanding of the mechanism of supersymmetry

breaking. Most promising in these respects are the models where this

breaking is triggered by the supergravity couplings, namely the

couplings obtained by promoting supersymmetry to the level of a local

symmetry, thus including gravity. The fields that describe physics at

ordinary energy ( ' V Cj ) are connected through these couplings only

the Fermi scale Cj p • The first o:

expectation value of a fundamental scalar

The first one relates it to the vacuum

- 519 -

ultimately of the Fermi scale, with 2* Cjp

Due to the relation ^ M , * " ^*/FB between the gravitino mass and

the supersymmetry breaking order parameter Gi- , in this picture

supersymmetry is broken at very high energy, in fact at the geometric

mean between the Fermi and the Planck scale. In spite of that, all known

fields will have to find at the Fermi scale a superpartner with the same

gauge quantum numbers, as required by the solution of the stability

problem of the Higgs scalar mass. It is interesting to know that the

spectrum and the couplings of all these new heavy particles are arranged

in such a way that the one loop radiative corrections will not produce,

at the percent level, any deviation from 1 of the parameter Ç? , the

ratio of the neutral to charge current Fermi constants. The agreement of

the present experimental determination of <Ç with the theoretical

prediction simply reinforces the upper bound on the top-quark mass which

now becomes •'W & 200 GeV because of the scalar top exchange

contribution.

Among all these new particles, most interesting are the gauginos,

namely the fermionic partners of the gauge vector bosons. Laying aside

possible nonminimal, kinematic terms for the vector supermultiplets or

radiative contributions from super-heavy fermions of grand unified

theories, all other sources of mass terms for these gauginos can be

examined in detail with the following conclusions:

i) A w-ino exists lighter then the W. This charged colourless fermion

will not look like a charged lepton since it decays into a gluino plus a

to a "hidden" sector of fields which do not have gauge interactions and

where supersymmetry is spontaneously broken. As a result the low energy _ - l 'a

effective lagrangian ( » T )i s a supersymmetric one, a part from

soft highly constrained intrinsic breaking terms in the scalar

potential, weighted by the appropriate power of the gravitino mass . o

These terms may be the origin of the W mass the Higgs mass and

7

- 5 2 0 -

A

a) j KtuT strong t*tttact«VK

TtibvU&u/tj tot*./***? r*#<U£&j . . .

Arc > - - •

quark-antiquark pair with a branching ratio of order O ^ / o / relative

to the decay into a photino plus a lepton-antilepton pair.

ii) Consistently with the present bounds gluinos with a mass of

^ - T^ÍGeV and relatively long lived ( C*t2i 4 C/rl* ) can be obtained only

from a virtual heavy top exchange ( 150 GeV g g 200 GeV).

iii) The photino masses are in the 100 MeV range, well above the typical

decoupling temperatures, "Til 4 MeV.

iv) No sizable gravitational radiative contribution to the gaugino

masses exists at one loop level.

More details and formulae related to these problems can be found in

the following trasparencies.

- 521 -

- 5 2 2 -

- 5 2 4 -

v V lu £

S £

£

4» w Ii • S t - *i*

W r *

4 I

f Í O Ck

•r ~ * 1 I T

4»

•3 ^

i f

i vi

1/

- 5 2 5 -

" R E A S O N A B L E " E X P E C T A T I O N S F O R H A D R O P R O D U C T I O N A T C O L L I D E R E N E R G I E S

G i u l i a n o P r e p a r a t a

D i p a r t i m e n t o d i F i s i c a - U n i v e r s i t é d i B a r i

I s t i t u t o N a z i o n a l e d i F i s i c a N u c l e a r e - S e z i o n e d i B a r i

( I t a l y )

1. I N T R O D U C T I O N

L e t me b e g i n b y m a k i n g a c o u p l e o f g l o s s e s o n t h e t i t l e o f t h i s t a l k .

E x p e c t a t i o n s s h o u l d b e c o n t r a s t e d w i t h t h e h o p e s t h a t a l l o f u s h a v e t h a t n e w a n d u n e x p e c t e d p h y s i c s s h o w u p a t t h e f a n t a s t i c a l l y h i g h e n e r g i e s r e a c h e d b y t h e p p c o l l i d e r s . T h e i r b e i n g r e a s o n a b l e i m p l i e s t h a t t h e y s h o u l d b e b a s e d o n s o m e t h e o r e t i c a l f r a m e w o r k t h a t h a s p r o v e n q u a n t i t a t i v e l y c o r r e c t a t e n e r g i e s l o w e r t h a n /s = 6 0 G e V ( i . e . a t I S R , S P S , F N A L e t c . ) .

T h e f i r s t q u e s t i o n t h e n o n e m i g h t a s k i s w h e t h e r s u c h f r a m e w o r k e x i s t s . T h e a n s w e r t h a t s h o u l d b e g i v e n i s d e f i n i t e l y p o s i t i v e , b u t w i t h t h e i m m e d i a t e w a r n i n g t h a t i t c a n n o t b e Q C D .

I n d e e d , P e r t u r b a t i v e Q C D ( P Q C D ) , t h e o n l y c a l c u l a t i o n a l s c h e m e t h a t o n e h a s a t h i s d i s p o s a l w i t h i n Q C D i s a d m i t t e d l y u n a p p l i c a b l e t o l o w p -p h y s i c s , w h e r e t h e s o f a r e l u s i v e a s p e c t s o f q u a r k c o n f i n e m e n t p l a y a n . e s s e n t i a l r o l e . T h e v a r i o u s " Q C D i n s p i r e d " d e s c r i p t i o n s w h i c h h a v e n e v e r t h e l e s s b e e n m a d e , a n d p r e s e n t e d a t t h i s W o r k s h o p , a t b e s t s h o u l d b e l o o k e d u p o n a s a w a y o f p a r a m e t r i s i n g ( w i t h a f e w m o r e o r l e s s a r b i t r a r y a s s u m p t i o n s ) t h e b a s i c f e a t u r e s o f j e t p h y s i c s . I n b r i e f , n o b o d y c a n d e n y t h a t t h e u n d e r s t a n d i n g o f l o w p ^ - p h y s i c s a f f o r d e d b y Q C D i s o n l y q u a l i t a t i v e , a n d t h a t n o u n i f i e d a n d v i a b l e s t r a t e g y b a s e d o n Q C D h a s b e e n d e v e l o p e d u p t o n o w .

A n d i f n o t Q C D , w h a t e l s e i s t h e r e t o p e r f o r m s u c h a d i f f i c u l t j o b ? I t i s t h e p u r p o s e o f t h i s t a l k t o c o n v i n c e y o u t h a t w e a r e i n d e e d i n a p o s i t i o n t o s p e l l o u t " r e a s o n a b l e " e x p e c t a t i o n s f o r h a d r o p r o d u c t i o n a t p p - c o l l i d e r e n e r g i e s .

2 . M Q M , Q G D , A C D : A N E G L E C T E D P A T H T O W A R D U N D E R S T A N D I N G H A D R O N I C I N T E R A C T I O N S .

T h i s i s n o t t h e r i g h t p l a c e t o g i v e a d e t a i l e d a c c o u n t o f t h e d e v e l o p m e n t o f a r e s e a r c h p r o g r a m m e w h i c h f r o m t h e M a s s i v e Q u a r k M o d e l (MQM

1 9 7 2 [ l ] ) , . t h r o u g h O G D ( Q u a r k G e o m e t r o D y n a m i c s , 1 9 7 5 [ 2 ] ) h a s r e a c h e d

- 5 2 6 -

i n A n i s o t r o p i c C h r o m o D y n a m i c s ( A C D , 1 9 8 0 [ 3 ] ) t h e s t a g e o f a f u n d a m e n t a l a n d c a l c u l a b l e t h e o r y o f c o n f i n e d c o l o u r e d q u a r k s . A r e c e n t a c c o u n t o f t h e b a s i c i d e a s a n d t h e o r e t i c a l s t e p s c a n b e f o u n d i n R e f s . 3 a n d 4 • T h e u n d e n i a b l e f a c t t h a t t h i s a p p r o a c h h a s b e e n l a r g e l y n e g l e c t e d b y t h e p h y s i c s c o m m u n i t y , I b e l i e v e c o u l d f o r m t h e o b j e c t o f a s o c i o l o g i c a l s t u d y r a t h e r t h a n o f a s c i e n t i f i c o n e .

B e a s i t m a y , h e r e I c a n o n l y r e c a l l t h a t t h r o u g h t h e s t e p s o f t h e a b o v e m e n t i o n e d r e s e a r c h p r o g r a m m e , o n e i s i n e v i t a b l y l e d t o t h e n o t i o n o f a n e w t y p e o f p h y s i c a l o b j e c t : t h e F I R E - S T R I N G .

A F i r e - S t r i n g i s n o t h i n g b u t a c o h e r e n t s u p e r p o s i t i o n o f e x c i t e d m e s o n i c r e s o n a n c e s ( q q ) w h i c h r e s e m b l e s a s c l o s e l y a s p o s s i b l e ( S e e F i g . 1 )

rrCE

R 1 M

F I G . l T h e s p a t i a l c o n f i g u r a t i o n o f a F i r e -S t r i n g o f m a s s M .

a q q - p a r t o n i c s t a t e . W h a t d o w e m e a n b y t h i s ? A q q - p a r t o n i c s t a t e o f c m . e n e r g y M (M l a r g e ) , c o m p r i s e s a c o u p l e o f a l m o s t m a s s l e s s p l a n e w a v e s m o v i n g i n o p p o s i t e d i r e c t i o n s w i t h m o m e n t a | p | - M / 2 . T h i s s t a t e , l a r g e l y u t i l i z e d i n P Q C D , c a n n o t c l e a r l y b e a p h y s i c a l s t a t e , n o t e n j o y i n g t h e f u n d a m e n t a l p r o p e r t y o f c o n f i n e m e n t . A F i r e - S t r i n g , o n t h e o t h e r h a n d , i s a s t a t e o b t a i n e d b y t h e s u p e r p o s i t i o n o f p h y s i c a l , c o n f i n e d , e x c i t e d m e s o n s t a t e s , o f d i f f e r e n t a n g u l a r m o m e n t a w h i c h , w h e n a n a l y z e d i n t e r m s o f q u a r k s , e x h i b i t s a q q p a i r m o v i n g i n o p p o s i t e d i r e c t i o n s w i t h m o n e n t a |p| = M / 2 , a n d c o n s t r a i n e d b y t h e c o l o u r - f i e l d t o r e m a i n w i t h i n a d i s t a n c e r = i r / R 2 M , ( R 2 = 2 G e V - 2 ) , i n c r e a s i n g l i n e a r l y w i t h t h e m a s s M o f t h e s t a t e . QGD [ 2 ] p r o v i d e s a p p r o x i m a t e e x p r e s s i o n s f o r t h e w a v e f u n c t i o n s a n d t h e s p e c t r u m ( l i n e a r R e g g e t r a j e c t o r i e s ) o f t h e q q - s t a t e s .

I t i s t h e d e c a y p r o c e s s o f a F i r e - S t r i n g t h a t l e a d s t h e c r e a t i o n o f t h e h a d r o n i c F i n a l - S t a t e . T h e w a y t h i s h a p p e n s i s r e p o r t e d i n F i g . 2

I n t h e c o l o u r f i e l d o f t h e i n i t i a l F S a q q - p a i r i s c r e a t e d f r o m t h e v a c u u m . I f t h e c o l o u r c o n f i g u r a t i o n i s r i g h t , i . e . i t i s n o t o r t h o g o n a l t o a t w o c o l o u r s i n g l e t s s t a t e , t h e c o l o u r f l u x b e t w e e n t h e t w o i n i t i a l q u a r k s b r e a k s a n d o n e o b t a i n s t w o F S ' s , F S ^ a n d F S 2 ( S e e F i g . 2 ) .

- 5 2 7 -

-CE

2

I-UJ

11 FLUCTLMTLOHL

i <i

JJ F L D X BREA Kl TIC

50

m

C a:

F I G . 2 T h e b a s i c s c h e m e o f F S - d e c a y .

N o w t h e F S j a n d F S 2 g o t h r o u g h t h e s a m e p r o c e s s , a n d s o o n , u n t i l t h e m a s s e s M o f t h e F S ' s b e c o m e q u i t e s m a l l , s a y M i 2 G e V . A t t h i s p o i n t a f e w d o m i n a n t s t a b l e p a r t i c l e s a n d r e s o n a n c e s g e t f o r m e d , s u c h a s TT , k , p , u ) , A 2 , 6 , W h e r e a s t h i s f i n a l s t e p i s r e a l i z e d , b y u s i n g k n o w n p r o p e r t i e s o f m e s o n s w i t h m a s s e s b e l o w 2 G e V , t h e b a s i c d e c a y p r o c e s s

F S F S 1+ F S 2 ( 2 . 1 )

i s e x p l i c i t l y c a l c u l a b l e t h r o u g h t h e d i a g r a m s i n F i g . 3 , a n d t h e r u l e s o f QGD a n d A C D C 5 ]

Q4D A O

"LOIV/CITI/DIML

QLUOLJ OF Acj> F I G . 3 T h e d i a g r a m s u s e d i n t h e c a l c u l a t i o n o f t h e

d e c a y p r o c e s s ( 2 . 1 )

- 5 2 8 -

T h e t y p i c a l e v o l u t i o n o f a m a s s i v e F S , c o r r e s p o n d s t o t h e k i n d o f t r e e -p r o c e s s d e p i c t e d i n F i g . 4 . I t s c a l c u l a t i o n c a n b e d o n e e f f i c i e n t l y w i t h a l a r g e c o m p u t e r , a n d t h e r e l e v a n t p r o g r a m m e E P O S i s a v a i l a b l e i n t h e C E R N l i b r a r y [ 6 ] .

F I G . 4 A t y p i c a l " t r e e " p r o d u c e d b y t h e d e c a y p r o c e s s o f t h e i n i t i a l F S .

T h u s a c c o r d i n g t o o u r t h e o r y t h e h a d r o n i c p r o d u c t i o n i n a g i v e n p r o c e s s t a k e s p l a c e a c c o r d i n g t o t h e f o l l o w i n g t w o s t e p s c h e m e :

P r o d u c t i o n

I t t u r n s o u t t h a t a l s o t h e p r o d u c t i o n m e c h a n i s m i n t h e r e l e v a n t h a d r o n i c c o l l i s i o n s c a n b e c o m p u t e d i n t e r m s o f a s m a l l n u m b e r o f i m p u t s .

3 . H A D R O P R O D U C T I O N A T T H E p p - C O L L I D E R [ 7 ]

I n o u r t h e o r e t i c a l f r a m e w o r k t h e b a s i c i n t e r a c t i o n m e c h a n i s m f o r a n i n c i d e n t h a d r o n i s t h e d i s s o c i a t i o n p r o c e s s :

H — • H + q q (3.1)

r e p o r t e d i n F i g . 5 . A c c o r d i n g t o i t t h e i n i t i a l h a d r o n r BAIWOlJ

bAHYOlJ

\M7iML

F I G . 5 T h e " d i s s o c i a t i o n " p r o c e s s ( 3 . 1 ) f o r a n i n c i d e n t B a r y o n .

- 5 2 9 -

d i s s o c i a t e s i n t o a l e a d i n g h a d r o n i c c l u s t e r ( r e s o n a n c e ) a n d a v i r t u a l q q p a i r b y h a v i n g i t s c o l o u r f l u x b r o k e n t h r o u g h t h e m e c h a n i s m o f p a i r c r e a t i o n . S u c h a d i s s o c i a t i o n i s o n l y v i r t u a l . b u t r e p r e s e n t s t h e p r e l i m i n a r y s t a g e f o r h a d r o n i n t e r a c t i o n s . W h e n i t c o m e s i n c o l l i s i o n w i t h a n o t h e r h a d r o n t h e v i r t u a l q q p a i r s a r i s i n g f r o m d i s s o c i a t i o n r e a r r a n g e t h e m s e l v e s i n t h e w a y p i c t u r e d i n F i g . 6 , t h u s g i v i n g r i s e t o t w o F S ' s . I n t h i s w a y

t 4 ii

—a F I G . 6 T h e f o r m a t i o n o f _ t w o F S ' s b y t h e r e a r r a n g e m e n t

o f t w o v i r t u a l q q - p a i r s .

t h e b a s i c p r o c e s s o f h a d r o n - h a d r o n i n t e r a c t i o n i s

H l + H 2 H * + H 2 + F S 1 + F S 2 . ( 3 . 2 )

B o t h h a d r o n d i s s o c i a t i o n a n d F S f o r m a t i o n , t h r o u g h Q G D , c a n b e . f u l l y c a l c u l a t e d , b u t f o r a n u n d e t e r m i n e d n o r m a l i z a t i o n f a c t o r . T h e d e t a i l s o f s u c h c a l c u l a t i o n c a n b e f o u n d i n R e f . 5 .

A s f a r a s p p - c o l l i s i o n a r e c o n c e r n e d w e c a n d i s t i n g u i s h 3 m a i n p r o d u c t i o n m e c h a n i s m s :

1. - I n e l a s t i c p r o d u c t i o n 2 . - S i n g l y d i f t r a c t i v e p r o d u c t i o n 3 . - D o u b l y d i f t r a c t i v e p r o d u c t i o n .

N o w w e s h a l l a n a l y z e t h e m i n t u r n .

3 . 1 I n e l a s t i c p r o d u c t i o n

T h e p r o c e s s l e a d i n g t o i n e l a s t i c p r o d u c t i o n a r e

p p — • B*B* + 2 n F S , ( 3 . 3 )

t h e r e l e v a n t d i a g r a m s f o r n = l a n d 2 a r e r e p o r t e d i n F i g . 7 . T h e r e l a t i v e i m p o r t a n c e o f t h e d i f f e r e n t d i a g r a m s c a n b e e a s i l y a s c e r t a i n e d , a n d f o r

- 5 3 0 -

F I G . 7 T h e d i a g r a m s c o n t r i b u t i n g t o t h e p r o c e s s ( 3 . 3 ) f o r n = l a n d n = 2 .

t h e i r c r o s s s e c t i o n s a „ o n e g e t s t h e a p p r o x i m a t e r e l a t i o n

a n d s e t t i n g a 2 - 2 7 m b , b = 13 G e V 2 , w e o b t a i n

ö 2 ( n + l ) = - 1 ° 2 n ' ( 3 ' 4 , )

a n i c e c o n f i r m a t i o n o f t h e p e r t u r b a t i v e s t r u c t u r e t h a t l i e s a t t h e v e r y b a s i s o f t h e M Q M - Q G D - A C D r e s e a r c h p r o g r a m m e .

I n o r d e r t o h a v e a n i d e a o f t h e e n e r g y a v a i l a b l e f o r p a r t i c l e p r o d u c t i o n i n F i g . 8 w e p l o t t h e F S - m a s s d i s t r i b u t i o n f o r t h e 2 F S a n d t h e 4 F S i n e l a s t i c p r o c e s s .

- 5 3 1 -

.05

. 0 4

.01

.oz

. (M

1 AN < M F s s = U 5 C*V N d L M f s

* <

<M t S i>= 50 C V < M f S i > = - m G i V

L •

-

zoo oo

F I G . 8 T h e m a s s d i s t r i b u t i o n s o f t h e 4 F S ' s p r o d u c e d i n t h e i n e l a s t i c c o l l i s i o n w i t h n = 2 .

3 . 2 S i n g l y d i f f r a c t i v e p r o d u c t i o n

B y t h i s n a m e w e d e n o t e t h e p r o c e s s e s :

P P — Ï £ B * + F S L + F S 2

w h o s e r e p r e s e n t a t i v e d i a g r a m s a p p e a r i n F i g . 9 ,

( 3 . 5 )

F I G . 9 T h e d i a g r a m s f o r s i n g l y d i f f r a c t i v e s c a t t e r i n g .

- 5 3 2 -

B y u s i n g t h e R e g g e - p a r a m e t r i z a t i o n f o r t h e x ^ , , a n d p ^ d i s t r i b u t i o n o f t h e d i f t r a c t i v e p ( p ) , w e c a n c o m p u t e t h e F S - d i s t r i b u t i o n s , a n d t h r o u g h t h e i r d e c a y t h e p a r t i c l e c o m p o s i t i o n o f t h e f i n a l s t a t e s .

B y e x t r a p o l a r t i n g l o w e r e n e r g y d a t a a t i/s= 5 4 0 G e V , w e e s t i m a t e

a c r . = a + a - = 10 mb . ( 3 . 6 ) bD p p

3 . 3 D o u b l y d i f f r a c t i v e p r o d u c t i o n

T h i s p r o c e s s l e a d s t o t h e f o r m a t i o n o f t w o l a r g e m a s s c l u s t e r s s e p a r a t e d b y a r a p i d i t y g a p A y ^ 2 .

I n o u r t h e o r e t i c a l f r a m e w o r k w e h a v e ( S e e F i g . 1 0 )

p p — - B * + B*+ F S 1 + F S 2 + F S 3 + F S l f ( 3 . 7 )

F I G . 1 0 D i a g r a m f o r d o u b l y d i f f r a c t i v e s c a t t e r i n g .

A f t e r t h e R e g g e - p a r a m e t r i z a t i o n i s u s e d [ 8 ] t o c a l c u l a t e t h e d i f f r a c t i v e s t a t e s m a s s d i s t r i b u t i o n s , t h e F S - m a s s d i s t r i b u t i o n i s c a l c u l a b l e . E x t r a p o l a t i o n f r o m l o w e r e n e r g i e s g i v e s f o r t h e d o u b l y d i f f r a c t i v e c r o s s s e c t i o n :

= 1 3 m b a t /s = 5 4 0 G e V . ( 3 . 8 )

- 5 3 3 -

3 . 4 B a s i c f e a t u r e s o f h a d r o p r o d u c t i o n

S o m e o f t h e r e s u l t s o f a MC c a l c u l a t i o n w i t h t h e i n p u t s d e s c r i b e d i n t h e p r e c e d i n g p a r a g r a p h s a r e s u m m a r i z e d i n T a b l e I .

M e c h .

ObS . 2 F S 4 F S I N ( * > SD D D T 0 T ( * * )

< n > C H 3 2 . 5 5 0 . 2 3 4 . 3 1 9 . 0 1 8 . 5 2 7 . 8

< n > /D 3 . 7 5 . 3 2 . 8 2 . 7 3 . 7 2 . 1

a dy y = o 4 . 0 6 . 2 4 . 3 2 . 2 1 . 2 3 . 1 7

 T 1 G e V

. 5 9 . 5 8 . 5 9 . 5 3 . 4 4 . 5 4

T A B L E I . S o m e p h y s i c a l o b s e r v a b l e s a c c o r d i n g t o d i f f e r e n t m e c h a n i s m s . ( * ) I N = . 9 ( 2 F S ) + . 1 ( 4 F S ) ; ( * * ) T 0 T = 3 0 / 5 3 ( I N ) + 1 0 / 5 3 ( S D ) + 1 3 / 5 3 ( D D ) .

I n F i g . 1 1 t h e c h a r g e d p a r t i c l e d e n s i t i e s a s a f u n c t i o n o f t h e p s e u d o r a p i d i t y n = - l o g t a n 8 / 2 a r e r e p o r t e d a c c o r d i n g t o t h e d i f f e r e n t p r o d u c t i o n m e c h a n i s m s .

í

5

5

1 1 — i r i A r

— 1 1 1

f \ - \

2 Fi \\ \

• DÑ6IA S E D A S . \

îîtHU - » \ \V \ jMFraACTiJC \

- ' N

_ cousu \ <s\

J>IFf*.ACTI</f \

\

1 1 — , 1 i

N

i — i_ â_\.

F I G . 1 1 T h e n o r m a l i z e d p s e u d o r a p i d i t y d i s t r i b u t i o n f o r t h e d i f f e r e n t i n t e r a c t i o n m e c h a n i s m s .

- 5 3 4 -

F o r t h e f u l l y - i n e l a s t i c p r o c e s s , t h e p r e d i c t i o n s f o r c h a r g e d m u l t i p l i c i t i e s , t h e p s e u d o r a p i d i t y d i s t r i b u t i o n o f c h a r g e d a r t i c l e s , I / o d a / d p ^ i n t h e c e n t r a l r e g i o n f o r c h a r g e d p a r t i c l e s , a n d f o r t h e t r a n s v e r s e e n e r g y d i s t r i b u t i o n f o r | ri | < 3 , a r e r e p o r t e d i n F i g . 1 2 , 1 3 , 1 4 a n d 15 r e s p e c t i v e l y .

TOTAL IKJÉLASTIÍ PTODUCÏIOIJ

< * ¿ 0 = 27. Í

T O T A L H J f L A S T I C

P f t O D V / C T l O l J

F I G . 1 2 T h e c h a r g e d m u l t i p l i e r t y d i s t r i b u t i o n f o r t h e t o t a l i n e l a s t i c p r o d u c t i o n .

F I G . 1 3 T h e p s e u d o r a p i d i t y d i s t r i b u t i o n f o r c h a r g e d p a r t i c l e s .

10

1 ~- **T •

\ • - • »-*

1 •

SO «0

2 4 <

s t r i b u t

c h a r g e d h a d r o n s f o r LNJ < l .

F I G . 1 4 T h e p T - d i s t r i b u t i o n f o r F I G . 1 5 T h e t r a n s v e r s e e n e r g y d i s t r i b u t i o n f o r |N | < 3 .

- 5 3 5 -

T h e r e a s o n w h y w e h a v e n o t c o m p a r e d o u r r e s u l t s w i t h e x p e r i m e n t a l d a t a i s t h a t t h e f i r s t g e n e r a t i o n ( 1 9 8 1 ) e x p e r i m e n t s a t t h e c o l l i d e r h a d t o o v e r c o m e t h e l o w l u m i n o s i t y b y s p e c i a l t r i g g e r i n g p r o c e d u r e s .

I n t h e n e x t p a r a g r a p h w e s h a l l d i s c u s s t h e b i a s e s t h a t s u c h p r o c e d u r e s i n t r o d u c e i n t h e e x p e r i m e n t a l o b s e r v a t i o n s .

3 . 5 T r i g g e r b i a s e s

T h e t r i g g e r s f o r t h e d i f f e r e n t g r o u p s a r e :

U A 1 : o n e c h a r g e d p a r t i c l e f o r n e [ ± 3 , 7 , ± 5 . 2 ] a n d o n e c h a r g e d p a r t i c l e f o r | n | < 1;

U A 2 : o n e c h a r g e d p a r t i c l e f o r n e [ ± 4 . 2 , ± 5 . 3 ] ;

U A 5 : o n e c h a r g e d p a r t i c l e f o r n e [ ± 2 , ± 6 ] .

T h e r e s u l t s o f o u r MC c a l c u l a t i o n a r e r e p o r t e d i n T a b l e I I , w h e r e w e w r i t e t h e r e j e c t i o n f r a c t i o n s f o r t h e d i f f e r e n t m e c h a n i s m s .

\ M e c h .

E x p . X . 2 F S 4 F S SD D D

U A 1 . 5 0 . 1 3 . 8 6 . 3 6

U A 2 . 7 4 . 3 8 . 9 5 . 5 5

U A 5 . 0 4 <v. 0 . 8 0 ^ 0

T A B L E I I

R e j e c t i o n r a t e s f o r t h e d i f f e r e n t m e c h a n i s m s d u e t o t h e d i f f e r e n t t r i g g e r s .

T h e r e s u l t i n g c r o s s s e c t i o n s a r e c o n t a i n e d i n T a b l e I I I , a n d c o m p a r e d w i t h a n i d e a l n o - b i a s t r i g g e r .

- 5 3 6 -

v . M e c h .

E x p . > v

2 F S 4 F S SD DD T O T

U A 1 1 3 . 5 2 . 6 1 . 4 8 . 3 2 5 . 8

U A 2 7 . 0 1 . 9 . 5 5 . 9 1 5 . 3

U A 5 2 . 6 3 2 13 4 4

n o - b i a s 2 7 3 10 13 5 3

T A B L E I I I

C r o s s s e c t i o n s i n mb f o r t h e d i f f e r e n t e x p e r i m e n t s a n d d i f f e r e n t i n t e r a c t i o n m e c h a n i s m s .

T h u s a c c o r d i n g t o o u r c a l c u l a t i o n s t h e t r i g g e r b i a s e s f o r a l l e x p e r i m e n t s b u t U A 5 , a r e q u i t e s e v e r e . N e v e r t h e l e s s w e c a n a l r e a d y s e e f r o m t h e e x p e r i m e n t a l r e s u l t s t h a t h a v e b e e n r e p o r t e d a t t h i s W o r k s h o p [ 9 ] , a n d t h e p r e d i c t i o n i n F i g s . 1 2 T 1 5 , t h a t o u r c a l c u l a t i o n i s r e m a r k a b l y s u c c e s s f u l .

4 . C O N C L U S I O N

I b e l i e v e I h a v e c o n v i n c e d y o u t h a t o u r " r e a s o n a b l e " e x p e c t a t i o n s a r e i n d e e d r e a s o n a b l e . T h e y d o d e s c r i b e c o r r e c t l y t h e b u l k o f t h e c o l l i d e r d a t a , T h i s h a s b e e n a c h i e v e d w i t h t h e f o l l o w i n g i m p u t s

^ , BB c h a n n e l F S - d e c a y : ß = r r M e s o n c h a n n e l

P r o d u c t i o n : a . ^ , o ^ , a ^ , a ^ ,

f r a n k l y a m o d e s t n u m b e r . A p a r t f r o m t h e i m p l i c a t i o n o f i n t i m a t e s i m p l i c i t y a n d c a l c u l a b i l i t y o f t h e a p p a r e n t l y c a t a s t r o p h i c p r o c e s s e s o c c u r r i n g a t c o l l i d e r e n e r g i e s , o u r r e s u l t s m a y a l s o h a v e a n i m p o r t a n t p r a c t i c a l a p p l i c a t i o n . T h e y m a y i n f a c t g i v e t h e p o s s i b i l i t y o f " c l e a n i n g o u t " t h e " b a c k g r o u n d " t o t h e u n e x p e c t e d t h i n g s t h a t w e h o p e t o f i n d .

P e r h a p s , a n d t h i s i s a n o t h e r s m a l l h o p e o f o u r s , o u r " r e a s o n a b l e " e x p e c t a t i o n s w i l l h e l p i n f u l f i l l i n g o u r h o p e s .

- 5 3 7 -

R E F E R E N C E S

1. G . P r e p a r a t a , P h y s . R e v . D 7 , 2 9 7 3 ( 1 9 7 3 ) ; f o r a r e v i e w o n MOM s e e G . P r e p a r a t a , i n L e p t o n H a d r o n S t r u c t u r e , A . Z i c h i c h i e d . , A c a d e m i c P r e s s , p . 5 4 ( 1 9 7 5 ) .

2 . G . P r e p a r a t a a n d N . C r a i g i e , N u c l . P h y s . B 1 0 2 , 4 7 8 ( 1 9 7 6 ) ; w o r k o n QGD i s r e v i e w e d i n G . P r e p a r a t a ; T h e W h y ' s o f S u b n u c l e a r P h y s i c s , A . Z i c h i c h i e d . , p . 7 2 7 ( 1 9 7 9 ) .

3 . G . P r e p a r a t a , P h y s . L e t t e r s 1 0 2 B 3 2 7 ( 1 9 8 1 ) , t h e s t a t u s o f t h i s a p p r o a c h i s r e v i e w e d i n G . P r e p a r a t a , F u n d a m e n t a l I n t e r a c t i o n s : C a r g è s e 1 9 8 1 , P l e n u m P r e s s ( 1 9 8 2 ) .

4 . J . L . B a s d e v a n t , p . C o l a n g e l o , G . P r e p a r a t a , N u o v o C i m e n t o 7 1 A , 4 4 5 ( 1 9 8 2 )

5 . T h e s t e p s o f s u c h c a l c u l a t i o n s h a v e b e e n o u t l i n e d i n r e c e n t p a p e r s o n F i r e - S t r i n g D y n a m i c s ; w h e r e a f e w p r o b l e m s o f h a d r o n i c f i n a l s t a t e s h a v e b e e n d i s c u s s e d , s e e :

- L . A n g e l i n i , L . N i t t i , M . P e l l i c o r o , G . P r e p a r a t a , G . V a l e n t i : " T h e s t r u c t u r e o f f i n a l s t a t e s i n l o w p-jj p p i n t e r a c t i o n s a t h i g h e n e r g i e s " , P h y s . L e t t . B 1 0 7 , 4 4 6 ( 1 9 8 1 )

- " I s t h e g l u o n h i d i n g u n d e r t h e 3 t h j e t ? " P h y s . L e t t . B ( i n p r e s s ) " F i r e s t r i n g f o r m a t i o n a t h i g h e n e r g i e s : h a d r o n i c p r o d u c t i o n a t C E R N p p -

c o l l i d e r " P h y s . L e t t . B ( i n p r e s s ) - " F i r e s t r i n g f o r m a t i o n a t h i g h e n e r g i e s : p r o t o n - p r o t o n v s . p r o t o n - a n t i p r o

t o n " N u c l . P h y s . B ( i n p r e s s ) " F i r e s t r i n g d e c a y i n h i g h e n e r g y e e + a n n i h i l a t i o n : o n e p a r t i c l e d i s t r i

b u t i o n s a n d s c a l i n g v i o l a t i o n " P h y s . R e v . D ( i n p r e s s ) _ - " F i r e s t r i n g d e c a y a t h i g h e n e r g i e s : b a r y o n - a n t i b a r y o n p r o d u c t i o n i n e é

a n n i h i l a t i o n " P h y s . L e t t . B ( i n p r e s s ) .

6 . L . A n g e l i n i , L . N i t t i , M . P e l l i c o r o , G . V a l e n t i : " A p r o g r a m f o r g e n e r a t i n g h a d r o n i c f i n a l s t a t e s a r i s i n g f r o m e l e c t r o n - p o s i t r o n a n n i h i l a t i o n ( E P O S ) " , C E R N C o m p . L i b r a r y ( W 1 0 3 4 ) , C E R N C o m p . N e w s l e t t e r s , N . 1 6 3 ( 1 9 8 2 ) 2 2 .

7 . A p r e l i m i n a r y a n a l y s i s c a n b e f o u n d i n t h e t h i r d p a p e r o f R e f . 5 .

8 . S e e f o r i n s t a n c e G . A l b e r i a n d G . G o g g i , P h y s . R e p . _ 7 4 , 1 - 2 0 7 ( 1 9 8 1 ) .

9 . S e e t h e c o n t r i b u t i o n s a t t h i s W o r k s h o p f r o m t h e U A 1 . U A 2 , a n d U A 5 g r o u p s .

1 0 . T h i s p a r a m e t e r i s i n t r o d u c e d i n t h e l a s t p a p e r o f R e f . 5 .

- 5 3 8 -

Ref.TH.3515-CERN

HADRONIC JETS

M. Jacob CERN ~ Geneva

A B S T R A C T

Consisting of a short series of comments after the impressive results on jets obtained at the pp collider, this talk tries to assess the progress made and to focus on some issues which, in view of the newly-collected data, should soon become topical.

Ref.TH.3515-CERN 2k January 1983

- 5 3 9 -

1. - INTRODUCTION

This paper is by no means a review of hadronic jets as possible at present. The dramatic appearance of nets in pp collisions at collider energy as reported by the UA2 D and the UA1 2; experiments, and the actual cross-section observed for these jet events, can be considered as a solid success of quantum chromodynamics as applied perturbatively to short-range processes. This has been beautifully reviewed at this meeting by G. Altarelli 3 ) . The striking similarities between hadronic jets observed in electron-positron annihilations, hadron-hadron and lepton-hadron collisions has been masterfully discussed by G. Wolf in his rapporteur talk at the Paris conference 4 ) . Against this solid background, this paper merely limits itself to a few comments, thus providing one more assessment of the situation at this particularly interesting time.

This is indeed an interesting time ! Hadronic jets have been hovering in the wings of this meeting, but only one year ago, at the previous Workshop in this series, the situation was, to say the least, far less clear. A long-time and stubborn proponent of the eventual emergence of jets in experiments using calorimeter triggers, I had to spend a fair amount of my allocated time to try to convince people that, despite the impressive results of experiment NA5 at CERN 6 ) f confirmed then by those of experiments E557 7) and E609 &) at Fermilab, jets were still going to show up clearly in the calorimeter experiment at the ISR, R807 9 ) f and then, even more so, at collider energies.

Indeed it has long been an inescapable conclusion for some theorists that the large px hadron production yields observed at the ISR and at Fermilab had to lead to dramatic jet signals, and the more so the higher the energy of the collision 1 0 ) t Moreover, the jet signal had to emerge clearly from the background, but for some totally new phenomenon. While "soft" large multiplicity configurations could, for a while, provide a dominant component in processes selected according to a large global transverse energy, extrapolations based on KNO scaling 1 1 ) had to give the two-jet configuration winning at sufficiently high energy and hence at sufficiently high required transverse energy 5),12) <

Yet there has been a fair amount of healthy debate going on and the recent results 1)»2),9) vindicate at long last what could at one time have been deemed too optimistic a point of view.

The increasing importance of jet processes in hadron collisions with increasing energy was advocated a long time ago, in fact as soon as large p^ processes could be unambiguously associated with jet production and fragmentation 13),1A) # it was, however, only with the development of calculations based on quantum chromodynamics that one could become more confident in making predictions for jet production cross-sections 15). Indeed one expects that, over a large relevant region of phase space, gluon scattering plays a leading rôle. It contributes in a very important way to the basic processes which have to be globally considered 1^), and results therefore rely greatly on the estimate of the gluon distribution function.

As discussed very clearly by Altarelli at this meeting 3 ) f perturbative QCD leads to three types of predictions : those concerned with topological signatures, those concerned with quantitative predictions and those concerned with correct estimates (at the order of magnitude level, say) of rates and cross-sections. The present results refer to categories one and three, and it is on the correct estimates of large effects that I shall centre the present discussion. Those in category one speak for themselves D » 2 ) » 9 ) >

- 5 4 0 -

At present we are faced with three large factors which stood as predictions and which have now been verified. Predictions could not be deemed reliable with great accuracy (category 3 in Altarelli's classification). Nevertheless, since one dealt with factors 1 0 2 to 1 0 3 , they were interesting. They are, respectively :

(i) The ratio of the jet yield with respect to the single-particle (inclusive) yield at large p-p, namely a factor 1 0 2 to 1 0 3 depending on x-j ( X T = 2 P T / / 3 ) . This is referred to as the "trigger bias effect" in view of the fact that triggers were long limited to a single large p<p particle 14)»17), and hence not very efficient.

(ii) The y/T¡ ratio, which was expected to be of order one (as opposed to a, hence again a factor of ~10 2) at large pj lSîjlO). This follows from (i) in so far as the factor a should actually apply to the y/jet ratio and not to the y/ir ratio, more directly accessible.

(iii) The ratio of inclusive jet yield at SPS collider energy and ISR energy for PT values which are large but yet low enough to avoid threshold effects at the ISR (10 GeV, say). Here also the ratio was expected to be large, another factor of ~ 1 0 3 .

I shall dwell on each of them in Section 2. The experimental verification of these three large factors now bears witness to the correctness of the analysis of large p^ phenomena in terms of hard scattering of partons (quarks and gluons),; to the fact that gluons as well as quarks do participate (the observed yields would otherwise be too large), and to the fact that the collidinghadrons can be considered to a good approximation as a broad band beam of quarks and gluons, acting independently of one another to a large extent. The observed yields are indeed correctly estimated in the leading log approximation of QCD

19),12),15). In Section 3 we shall turn next to other effects which one should then also

expect to see and in particular to heavy quark production at large p^ and the expected associated prompt lepton yield.

2. - USING PERTURBATIVE QCD IN HADRONIC PROCESSES

Asymptotic freedom leads one to expect some simplicity at short distances, and a perturbative study of the interactions among constituents should become reliable when the relevant probing distances (measured through the observed momentum transfers) are much less than one Fermi. In practice, one is led to take P T _> 2 GeV/c in order to tag such short-range processes according to un-typically large momentum transfers. The value of the running coupling constant a s(p|) may then appear as reasonably small, when undertaking a perturbative calculation. Assuming that such an identification between high p-p events and short-range (weak coupling) processes is correct, one still has to assume that non-leading power terms (the so-called higher twist contributions) are numerically negligible, or parametrize them. They are expected to become negligible at P T £ 10 GeV/c but nothing is certain yet. Granting that this is the case, one may still worry about the rapidity of the convergence of the perturbation series, a question which involves the still much-debated scheme dependence question 20), It is only under such a series of assumptions that a leading log calculation can be performed and confronted with experiment. It has to assume knowledge of the relevant parton distribution functions. While information from deep inelastic

- 5 4 1 -

lepton scattering is considerable, the gluon distribution, so important in practice, long imposed some guess-work. One is lucky that assumptions which have been made ^9) are now found to be in reasonable agreement with distributions inferred from the recent detailed neutrino data 2 1 ) .

To summarize, one may say that one expects simplicity at large P T ( P T > > 10 GeV/c, say) and nature does seem to be co-operative 1)>2). However, one should not be too surprised if physics turns out to be more complicated when more detailed questions meet experimental tests. Perturbative QCD is rather complicated when considered beyond its leading log approximation 20) #

A leading log calculation proceeds from parton distribution functions, and the relevant input is then the differential luminosity at the parton level, the impinging hadrons being considered as a broad band beam of quarks and gluons. Entering directly into the calculation are the quantities TdL^J/dT, with s = X j X 2 s = Ts. Here s is the hadron centre-of-mass energy squared, X j and x 2 are the fractional momenta of the relevant partons, referred to by the superscripts i and j , and s is hence the centre-of-mass energy squared at the parton level. At wide angles, p£ ~ s and /r ~ x T = 2p T//s.

Figure 1 gives the quantity T(dL/dT) for uü and gg scattering in pp collisions at large p^ (scaling violations have been included as calculated in the leading log approximation). One clearly sees' that moving up in energy at fixed p^, one moves down in /r and then uses a rapidly rising parton density. This results in a large increase in yield. Moving up or down in p^ (x^) at fixed energies, one also sees that the lower x? domain corresponds to the dominance of gluon effects while the higher domain (in practice x^ > 0.3) corresponds to dominant valence quark effects.

The former effect explains the very large rise which one thus expects with increasing energy when calculating an inclusive jet yield at high p^. The third large factor among the three mentioned corresponds to the rapid increase in the relevant parton density. Figure 2 gives the 90° inclusive jet distribution at ISR and collider energy thus calculated 1 9 ) , At 20 GeV/c, one obtains an increase by four orders of magnitude, the cross-section reaching a value of the order of 1 yb/GeV. These large cross-sections have now been experimentally confirmed 1)»2) #

The prj. dependence at a fixed energy reflects the drop of the parton distribution (Fig. 1) as pip (XT) increases, more than the P T fall-off associated with the basic process (pj1* up to logarithmic terms). When fitting an empirical power to the collider distribution of Fig. 2, one gets N ~ 9 rather than N ~ 5 (thus including scaling violation), which is the expected dependence at fixed X T« Such a sharp P T dependence, reflecting the variation of the gluon (and quark) distributions has now been experimentally confirmed D > 2 ) . The actual agreement between data and predictions must involve some element of luck in view of its precision. Since one is, however, dealing with many orders of magnitude when simultaneously comparing collider yields and ISR yields over widely different energies and p ^ values, the over-all agreement reached should be deemed meaningful (category 3 in Altarelli's classification). Comparison with ISR energies involves the beautiful results of experiment R807 2 2 ) f which clearly sees jet structures emerging from the background with a calorimeter trigger of E T > 10 GeV in a wall calorimeter of 1.7 Sr coverage. A jet cross-section can then be determined. It also agrees with expectations. As shown in Fig. 3, which presents the R807 data and the UA2 data together a jet calculation meets both sets of data at the same time.

- 542 -

In the region of overlap (Ex - 13 GeV) one sees in particular the long-announced three-order of magnitude gain, now observed when going from ISR energy to collider energy . The comparison here uses the Isajet model applied to both sets of data 23) which should take good care of edge effects at medium p T

values.

We now move to the first large factor associated with the long-known "trigger bias effect", which, however, met with an unambiguous experimental check only last year with the R807 data on jet and single pion yields at large p^ 22). The argument follows the assumed scaling property of jet fragmentation. To put it in a nutshell, one may write the single inclusive pion yield da/dp? associated with a primordial jet yield da/dQ (Q being the transverse momentum of the jet), and a fragmentation function F(z), z being the fractional momentum of the pion seen as a jet fragment

= / dQ %L Sl dz F(z) 6(p T - zQ)

d p T Q>p T

Taking (da/dQ) = AQ~^, a good approximation at fixed energy over a reasonably large p^ range, one gets

da d p T

_A_ S1

0 dz z 1^" 1 F(z) da

d p T

The inequality follows from the fact that N is large (N ~ 9 in practice) and that F(z) vanishes rapidly as z approaches 1. The over-all reduction factor turns out to be large 1 0 2 to 1 0 3 , depending on x^ since the x^ variation is wrapped into the empirical determination of N over a limited p^ range The argument can be refined including scaling violations, which enlarge the factor at large PT 15),19). Figure 4 shows the single pion yield and the jet yield as measured at the ISR 9),22) e The expected 1 0 3 factor at PT ~ 10 GeV/c is now experimentally verified. Also shown in Fig. 4 are the much earlier results of experiment E260 at Fermilab 2 4 ) # The graph combines the jet results of this experiment together with the inclusive charged pion yield also measured at Fermilab 25). There also, one could already see the expected large factor. However, the results obtained later by experiment NA5 ^) using a good coverage calorimeter have for a while been casting serious doubts on the conclusions reached, in view of the overwhelming non-jet background. One can now say that E260 was clever enough to extract the precious needle from the haystack.

The last large factor, the y/n ratio multiplied by 1/a, is now also well known thanks to beautiful results at the ISR. The key results come from experiments in II and 18 at the ISR. This has been reviewed in detail 9) and Figure 5 merely illustrates the point with some R806 data. One should also mention on this occasion the pioneering work of the Adelphi-Brookhaven-Rome collaboration at the ISR 26), The relative importance of the prompt photon yield is associated with the previously discussed jet/rr ratio. One should indeed compare jet/y in the first place and then take into account the smallness of the TR/jet ratio at fixed p T . The procedure is in agreement with a QCD leading log approximation.

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At collider energy, one expects the y/-n° ratio to reach a value of order 1 at P T ~ 40 GeV/c 19). Because of scaling violation effects the Tr°/jet ratio should be of the order of 1 0 ~ 3 15),19). This seems to be in agreement with the results presented by UAl at this meeting 2),27) < i n view of previous agreement with ISR data, this is also very interesting since it shows that scaling violations in jet fragmentation are definitely needed, as expected. The larger P T (the inverse probing distance), the stronger they are.

It seems that the experimental checking of all these large factors shows that the understanding of large P T phenomena in terms of parton hard scattering and fragmentation is basically correct, and also that our present control over the parton distributions is reasonably correct. I must say that I am impressed by the accuracy of a mere leading log calculation. The muses must have been smiling when the gluon distribution function was parametrized 28 )^ some lucky compensations taking place with the approximations made.

3. - FURTHER TESTS OF THE HARD SCATTERING APPROACH

Building on these recent successes, one may look at other predictions which it should soon be possible to check experimentally. The first one is the question of heavy quark production. Figure 6 shows the inclusive jet yields expected at 90° in pp collisions at 540 GeV. One has separated different jet types (gluon, u quark, s quark and c quark) and presented them as a function of p^,. Summing over all jet species, one gets the global jet yield of Fig. 2. The calculation is again conducted in the leading log approximation 19'. One assumes a SU(3) symmetric sea and all heavy quarks (c,b,...) thus have to be excited out of the vacuum. The s and c curves can therefore be considered as bracketing the production of heavy quarks. The yield for the t quark, assuming that inf. ~ 20 GeV, would eventually merge with the c quark yield at p-p » m^ (40 GeV/c, say). The conclusion is clear. At large P T ( P T > 20 GeV/c, say) there is a sizeable heavy quark jet yield but it is typically two orders of magnitude below the global jet yield (another big factor in category 3 ! ) . For reasons already given, the gluon jets dominate over the P T range accessible with the present luminosity. At large p^ (px > 40 GeV/c), the u (u) jets would start to dominate only at rapidities greater than 1 (-1), as follows from their association with valence quarks which have a harder distribution than gluons. The heavy quark jets will lead to prompt leptons at large P T through semi-leptonic decays, and we shall from now on assume a branching ratio of 0.1. Due to the trigger bias effect, a detector searching for large P T electrons will find a spectrum of electrons at large P T falling, with p^ following the jet yield but typically four orders of magnitude below (two orders of magnitude are due to the heavy quark yield, one is due to the branching ratio and an extra one is lost in the parent-child jet fragmentation with a steeply-falling spectrum). It turns out that the b (B) quark decay is favoured in the last step because of its decay asymmetry (helicity-favoured) when considering merely the weak decay of a quark in estimating the fractional momentum distribution. We give, in Fig. 7, the result of a particular, calculation using c and b quarks It agrees with earlier calculations 2 9 ) , and one may say that there is a wide consensus about the lepton yield associated with heavy quarks, in so far as one considers a correct order of magnitude estimate. Also shown in Fig. 7 is the signal expected from W and Z formation and leptonic decays. The anticipated yield in the leading log approximation shows a Jacobian peak 19), which is here smeared to take into account QCD corrections at the next-to-leading order 3 0 ) t The left-hand side

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S h o u l d e r should be enlarged a little m o r e through the semi-leptonic yields of heavy quarks in W, Z decays. The inclusive single l e p t o n yield should thus have a shoulder structure on a falling spectrum with a relatively small anticipated background due to heavy quarks in the W, Z range. Also shown is the expected single I T 0 yield, now verified 27). n u e to heavy quark production at large p T , the e/iT ratio should increase considerably compared with SPS and ISR values measured at lower p-p (lO-1* to 1 0 " 3 only). The inclusive electron (muon) yield over the 15-30 GeV range (below the most interesting W, Z region) should soon be known. One then expects an association with jets with, in particular, a c l e a r jet on the away side. With increasing statistics (integrated luminosity !) this should eventually provide good tagging for heavy quark jets. Tagging in a top quark search is, h o w e v e r , likely to suffer f r o m the important "background" provided by leptons from W and Z decays. Therefore, a search for top particles may also have to proceed differently 31). i n

any case, a measurement of the e/jet and e/ir r a t i o around 20 GeV would be very interesting, as would be checking that the recoiling jet to a trigger jet of 20 to 40 GeV, say, should be dominantly a gluon jet ; with, as a result, a higher branching probability into a two-jet system than at PETRA (PEP) measured while keeping the same kinematics (global energy, fractional energy and opening angles of the two jets). This is a case where the famous factor 9/4 between the qqg and ggg couplings should apply, since the branching occurs at the very first steps in jet fragmentation -'•2).

Another question worth a detailed study is the structure of large E^ events around Et = 40 GeV (Ay = 2 ) , that is, when two-jet configurations only start to dominate. This point is illustrated with the UA2 results already published which have now been confirmed with far more statistics by UA2 and also by the very clear UA1 results 2 ) . Shown in Fig. 8a is the ratio of the transverse energies of the leading clusters found in any events labelled according to decreasing transverse energy. One finds that, as the global transverse energy increases, E 2/E! tends towards 1 when ^ 3 / E

2 tends towards 0. One goes from a domain where several clusters are the rule (E^ < 40 GeV) to a domain where the dominant feature is a two-jet configuration (E^ > 60 GeV). At lower E^ one should find that very high multiplicity configurations with otherwise low p^ particles should be dominant. Nevertheless, one should also see configurations where two parton collisions take place at the same time, thus resulting in a four-jet structure at wide angle 32) (Fig. 8b). This is a new collider effect unknown at ISR energies, since one has there to be lucky enough to find two partons with enough energy to scatter at wide angle and emerge as clear jets (p? > 5 GeV, say). Going one order of magnitude higher in energy, the corresponding partons become plentiful and multiple collisions, each with jet production, should become important 12). one can see easily that such configurations should eventually become negligible at large Et. The cross-section associated with double collisions corresponds to two overlapping parton densities. One thus expects a factor R~ 2 from each hadron, R being the hadron radius and a factor R 2 due to the overlap integral. Since at fixed E^ one has no other dimensional quantities, the end result for the ratio between the double and single collision cross-sections for the same global E^ value should be

a(2) _s t_ ÏÏTîT - R 2 E 2

- 5 4 5 -

a n d h e n c e v a n i s h a t l a r g e e n o u g h E f E s t i m a t e s a r e i n a g r e e m e n t w i t h t h e o b s e r v e d r e s u l t s b u t m u c h w o r k i s s t i l l n e e d e d a l o n g t h i s l i n e . I t m a y b e t h a t s u c h a n e f f e c t i s r e s p o n s i b l e f o r a n i n c r e a s e o f t h e m e a n t r a n s v e r s e e n e r g y p e r p a r t i c l e i n l a r g e m u l t i p l i c i t y c o n f i g u r a t i o n s , o r f o r t h e e m e r g e n c e o f A ç u - t y p e o f c o n f i g u r a t i o n i n c o s m i c r a y e m u l s i o n d a t a m w h e n l o o k i n g a t c o r r e l a t i o n s i n v o l v i n g t w o l a r g e p-p p a r t i c l e s o n t h e s a m e s i d e , o n e s h o u l d s e e t h a t m o s t o f t h e t i m e t h e y a r e t o g e t h e r i n r a p i d i t y , d u e t o t h e i r b e l o n g i n g t o t h e s a m e j e t , b u t s o m e t i m e s o n e m a y s e e t h e m n e a t l y s e p a r a t e d i n r a p i d i t y , b o t h b e i n g a s s o c i a t e d w i t h s e p a r a t e j e t s i n m o r e d e t a i l e d c o r r e l a t i o n s t u d i e s .

W h i l e t h e e m e r g e n c e o f a t w o - j e t s y s t e m a t l a r g e E^ i s a p r o m i n e n t a n d w e l c o m e f a c t , w o r k n o w h a s t o b e p u t i n t o u n d e r s t a n d i n g o t h e r c o n f i g u r a t i o n s a n d t h e b a c k g r o u n d u n d e r t h e j e t s , a q u e s t i o n a s s o c i a t e d w i t h t h e o v e r - a l l l i m i t e d , b u t c e r t a i n l y n o t n e g l i g i b l e , t r a n s v e r s e m o m e n t u m o f t h e t w o - j e t s y s t e m .

I t h a s b e e n a l o n g t i m e s i n c e t h e s u g g e s t i o n t h a t t h e p r o p e r t i e s o f d e e p i n e l a s t i c e l e c t r o n s c a t t e r i n g s h o u l d l e a d t o p e c u l i a r p r o c e s s e s a t l a r g e t r a n s v e r s e m o m e n t u m i n h a d r o n c o l l i s i o n s 3 3 ) , a n d t h e b e a u t i f u l r e s u l t s o f t o d a y D » 2 ) a r e a g r e a t r e w a r d f o r t h e l a r g e a m o u n t o f w o r k w h i c h h a s b e e n p a t i e n t l y i n v e s t e d a l o n g t h i s l i n e a t t h e I S R 3 4 ) .

I s h o u l d l i k e t o t h a n k G . S a l v i n i a n d h i s c o l l a b o r a t o r s f o r t h e o r g a n i z a t i o n o f a v e r y i n t e r e s t i n g m e e t i n g a n d f o r h a v i n g p r o v i d e d me w i t h t h e o p p o r t u n i t y t o p r e s e n t t h e s e c o m m e n t s . W h i l e I o f t e n m a d e r e f e r e n c e t o S u m m e r S c h o o l l e c t u r e s o r C o n f e r e n c e R e p o r t s w h i c h I h a v e g i v e n , I s h o u l d s a y t h a t m o s t o f m y w o r k a s r e p o r t e d t h e r e w a s d o n e i n c o l l a b o r a t i o n w i t h P . L a n d s h o f f , R . H o r g a n a n d m a n y e x p e r i m e n t a l c o l l e a g u e s w h o h a v e w o r k e d i n I S R e x p e r i m e n t s o v e r t h e p a s t d e c a d e .

- 5 4 6 -

REFERENCES

1) UA2 results as presented at the Paris Conference (XXI International Conference on High Energy Physics, July 1982) ; The UA2 Collaboration - Phys.Letters B118 (1982) 203 ; UA2 results as presented at the Rome Workshop, these proceedings.

2) UAl results as presented at the Rome Workshop, these proceedings, and the UAl Collaboration - Phys.Letters B, to be published.

3) G. Altarelli - "QCD and jets in pp" - Contribution to these proceedings.

4) G. Wolf - "Jet production and fragmentation", Rapporteur talk, Paris Conference (July 1982), op.cit.

5) M. Jacob - "ISR Physics, present and prospect", Invited talk, Topical Conference on Forward Collider Physics, Madison, Wisconsin (December 1981), AIP Conference proceedings No 85, V. Barger, D. Cline and F. Halzen Editors (1982), p. 651.

6) C. De Marzo et al. - Phys.Letters 112B (1982) 173 ; K. Pretzl - SLAC Summer Institute (1981), MPI-PAE 95 (1981) and Contribution to the Madison Conference (1981), p. 585, op. cit.

7) B. Brown et al. - Fermilab Conf. 82/34 (1982).

8) M. Aventón et al. - Contribution to the Paris Conference (1982), op. cit.

9) The Axial Field Spectrometer Collaboration - Phys.Letters B118 (1982) 185. For a recent review of jet production as observed at the ISR, see : "Selected Topics in ISR Physics", CERN 82-11, edited by M. Albrow, C. Fabjan and M. Jacob.

10) For reviews stressing this point of view, see : "Large Transverse Momentum and Jet Studies", M. Jacob and P.V. Landshoff -Physics Reports 48 (1978) No 4 ; "Physics at the CERN-ISR", G. Giacomelli and M. Jacob - Physics Reports 55 (1979) No 1 ; "Application of Quantum Chromodynamics", R. Field in "Quantum Chromodynamics", AIP Conference Proceedings No 55, edited by F. Henyey (1978), p. 97.

11) Z. Koba - Ebeltoft Lecture Notes CERN 73-12 (1973) ; Z. Koba, H. Nielsen and P. Olesen - Nuclear Phys. B40 (1972) 317.

12) M. Jacob - "Physics at Collider Energies", DESY-CERN School Lecture Notes and Ste Croix Summer School Lecture Notes (1980) ; Cargèse Lecture Notes and Kupari Lecture Notes (1981). The first and fourth ones with R. Horgan.

13) The turning point was 1975 with the observation of clear correlation effects, and the rapporteur talk of P. Darriulat at the Tbilisi Conference (1976) bears witness to this fact.

14) J.D. Björken and G. Farrar - Phys.Rev. D9 (1974) 1449 ; M. Jacob - Hadron Physics at ISR Energies, CERN 74-15 (1974).

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15) R.P. Feynman, R.D. Field and G.C. Fox - Phys.Rev. D18 (1978) 3320 ; R.D. Field - Phys.Rev.Letters 40 (1978) 997. A long series of Isabelle Workshop Reports discusses in detail expectations for collider energies (see BNL Report 51443 and references therein). See also : M. Jacob - "Physics at Collider Energies", ECFA Meeting (1977) and Fermilab-Aspen Workshop (1977) ; and "pp from Very Low to Very High Energy", invited talk, Los Alamos Workshop (1979). For a detailed review of the application of QCD to jet processes, see : E. Reya - Physics Reports 69 (1981) No 3 ; and G. Altarelli - Physics Reports 81 (1982) No 1.

16) B.L. Combridge, J. Kripfganz and J. Ranft - Phys.Letters 70B (1977) 234 ; R. Cutter and D. Sivers - Phys.Rev. D16 (1977) 679 ; D17 (1978) 196.

17) S. Ellis, M. Jacob and P. Landshoff - Nuclear Phys. B108 (1976) 93 ; M. Jacob and P. Landshoff - Nuclear Phys. B113 (1976) 395.

18) H. Fritzsch and P. Minkowski - Phys.Letters 69B (1977) 316 ; G. Farrar and S. Frautschi - Phys.Rev.Letters 36 (1976) 1017 ; C. Escobar - Phys.Rev. D15 (1977) 355 ; F. Halzen and D. Scott - Phys.Letters 40 (1978) 1117.

19) R. Horgan and M. Jacob - Nuclear Phys. B179 (1981) 441.

20) p o r a detailed discussion of perturbative QCD, one may consult : "Perturbative Quantum Chromodynamics", Physics Reports Reprint Volume, (1982) 5, edited by M. Jacob. For application to large p>p processes, see also : P. Landshoff - Erice Lecture Notes (1982).

21) F. Dydak - TH Division seminar (December 1982).

22) Axial Field Magnet Collaboration - CERN Preprints (1982).

23) J. Siegrist - TH Division Seminar (October 1982).

24) C. Bromberg et al. - Phys.Rev.Letters 38 (1977) 1447 ; Nuclear Phys. B134 (1978) 189.

25) D. Antreasyan et al. - Phys.Rev.Letters 38 (1977) 112, 115.

26) E. Amaldi et al. - Phys.Letters 77B (1978) 240. For II and 18 data, see : L. Camilleri - Madison Workshop (1981), op. cit. in Ref. 5 ) .

27) C Rubbia - CERN Seminar (February 1983).

28) The parametrization is based on the sum rule (neutrino data), the quark counting rule (D. Sivers et al. - Physics Reports 23 (1976) No 1 ) , and the evolution with p T according to the Altarelli-Parisi equation using the Glück-Reya parametrization.

29) D. Scott - Invited talk, Madison Topical Conference, op. cit. in Ref. 5) ; V. Barger, F. Halzen and S. Pakvasa - Phys.Rev. D20 (1979) 2862.

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30) P. Aurenche and J. Lindfors - Nuclear Phys. B185 (1981) 274 ; F. Paige - Isabelle reports, op. cit. in Ref. 15).

31) A. Zichichi - Contribution to this Conference ; R. Horgan and M. Jacob - Phys.Letters 107B (1981) 395 ; M. Jacob - Kupari Lecture Notes (1981).

32) P. Landshoff and J. Polkinghorne - Phys.Rev. D12 (1975) 3738 ; N. Power and D. Treleani - Trieste preprints (1982).

33) S. Berman and M. Jacob - Phys.Rev.Letters 25 (1970) 1687 ; S. Berman, J. Björken and J. Kogut - Phys.Rev. D4 (197D 3388.

34) For a review at a particularly interesting time, see the Proceedings of the Copenhagen Meeting (1978), Physica Scripta 19 (1978) 69.

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FIGURE CAPTIONS

Figure 1 Differential luminosity for uü and gg scattering in pp collisions. Scaling violations have been included as calculated in the leading log approximation.

Figure_2 The inclusive jet yield at 90° for pp collisions at ISR (/s = 62 GeV) and collider (/s = 540 GeV) energy.

Figure_3 The R807 (ISR) and UA2 (collider) data reproduced by a unique jet calculation.

Figure 4 The IT/jet ratio as measured in the recent ISR experiment (R807) and in the old Fermilab experiment (E260). The ratio agrees with perturbative QCD calculations.

Figure 5 The y/~n° ratio as a function of p^ as measured at the ISR. An important prediction is the large (>1.5) ratio of prompt y yields expected when comparing prompt photon yields at large p^ (PT > 6 GeV/c) in pp and pp collisions at the ISR. This should be measured in 1983.

Figure_6 Inclusive jet yields at 90° for different types of jets (g,u,s,c) for pp collisions at 540 GeV. See Ref. 19) for the angular dependence.

Figure_7 Inclusive e* yields due to heavy quarks (c and b) and W, Z production and decay. Also shown are the inclusive jet yield and the inclusive TT° yield, all shown at 90°. All calculations are in the leading log approximation, but yields from W and Z have been smeared according to 0(a s) QCD corrections, which erode the Jacobian peaks into a unique shoulder. The top yield (with mt ~ ~ 20 GeV) would increase the heavy quark lepton yield in a region where it should be a relatively small background to the production from the W and the Z.

Figure_8 a) Energy ratios for the three leading clusters as a function of global transverse energy. Results from UA2.

b) Single and double parton collisions contributing to a large E process.

- 5 5 0 -

- Figure 3 -

1 r

=5 IO I \ X3

O CL 1

+ 10"

T

I I I R

^ \ 103

v ft.

° \ JET (FNAL)

" » N N (FNAL)

J J I I

0 2 4 6 8 p T (GeV/c)

10 J e t (ISR)

J L

• n° (ISR)

4 6 8 10 12 14 16

p T I G e V / c )

J L 18 20

Figure A

1.2

0.8

0.4

I 1 1 1 R

l/ss63GeV)

1t1 J I ' ' ' 4 6 8 10

p T (GeV/c)

- Figure 5 -

- 5 5 2 -

PT (GeV)

- Figure 7 -

80 120 E it (GeV)

160

(a)

- Figure 8 -

- 5 5 3 -

As an introduction to the session, a brief review of the main

parameters affecting the luminosities of the SPS pp collider was given.

dC(o) is The luminosity at the beginning of each run dl/(o) is given by

o£(o) = f N- -rev \ n / p ^ 1/2

where N , N- = total number of p, p P P

n = number of bunches

E = emittance (same for p,p , and for horizontal and vertical planes)

S„B = -values at crossing point H V

In the case of the SPS, all parameters have reached their design

value with the exception of N-. It is therefore justified to write :

o£(o ) i\¡ K N-.

Since N- is given by P

N- = n A.T P tr

where n = transmission efficiency between AA and the SPS coast at 270 GeV tr A = Accumulation rate in the AA

T = Run and accumulation duration

INTRODUCTION TO

"PRACTICAL AND FORESEEABLE LIMITATIONS IN

USABLE LUMINOSITY FOR COLLIDERS"

G. Brianti

- 5 5 4 -

f i n a l l y o n e h a s :

c£ (o ) % K n A T . <\J t r

P . T h e e v o l u t i o n o f CH w i t h t i s g o v e r n e d b y t h r e e e - f o l d m g d e c a y t i m e

f o r p r o t o n a n d a n t i p r o t o n b u n c h i n t e n s i t i e s a n d f o r t h e e m i t t a n c e g r o w t h : t t t

oL(t) = c £ ( o ) • e P • e p • e E = o£ ( o ) •

T h e a v e r a g e l u m i n o s i t y o h b e c o m e s t h e n : a v

a v T +

T _ t

h j ( t ) d t " K \ r A T V - 6 ) • TT

w h e r e S i s t h e s t o p i n - b e t w e e n r u n s . F o r S ->• 0 , X i a v

i s p r o p o r t i o n a l t o A a n d

l e s s t h a n p r o p o r t i o n a l t o T a n d T . T h e m o s t i m p o r t a n t p a r a m e t e r i s t h e n A .

T a b l e 1 g i v e s e x a m p l e s o f p o s s i b l e c a s e s .

T a b l e 1

T = 18 hours S = 2 h o u r s

T

( h )

N -P

(X10 1 0) X(o) (x10 2 8)

i > ( T )

(X10 2 8)

X a v

(X10 2 8)

16 4 . 5 5.0 2.0 2 . 9

2 4 6 . 7 . 7 . 4 2.0 3 . 8

32 9.0 ,10.0 1 . 7 4 . 4

T h e a i m s f o r t h e i m m e d i a t e f u t u r e o f t h e S P S p p c o l l i d e r a r e

i ) I n c r e a s e T a n d d i m i n i s h S ( i n c r e a s e r e l i a b i l i t y )

i i ) D e c r e a s e ß„ß„ -> 1 . 5 x 0 . 7 5 ni H V i i i ) I n c r e a s e n

t r

P o t e n t i a l g a i n ^ 2

P o t e n t i a l g a i n ^ 1 . 3

p o t e n t i a l g a i n ^ 1 . 1 0

T h e r e i s n o i n t e r e s t t o i n c r e a s e t h e n u m b e r o f b u n c h e s u n t i l t h e

p r e s e n t p - b u n c h e s a r e " s a t u r a t e d " ( M O p p e r b u n c h ) .

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P R A C T I C A L A N D F O R E S E E A B L E L I M I T A T I O N S

IN U S A B L E L U M I N O S I T Y F O R T H E C O L L I D E R

S. v a n d e r M e e r , C E R N , C H - 1 2 1 1 G e n e v a

SUMMARY

The p r e s e n t s i t u a t i o n a n d p o s s i b l e s h o r t - t e r m i m p r o v e m e n t s of the pp

c o l l i d e r are d i s c u s s e d . A l o n g - t e r m p l a n , a i m i n g at a n i n c r e a s e in l u m i n o s i t y

by a n o r d e r of m a g n i t u d e is t h e n d e s c r i b e d .

1. I N T R O D U C T I O N

One simple o b s e r v a t i o n w o u l d a d e q u a t e l y c o v e r the s u b j e c t p o s e d in the

title of this d i s c u s s i o n , w h a t e v e r l u m i n o s i t y w e c o u l d p r o v i d e , it w o u l d b e

u s e f u l for s o m e t h i n g . T h u s , t h e r e is no l i m i t a t i o n to " u s a b l e l u m i n o s i t y " .

E v e n t h o u g h some c o u n t e r s m i g h t s a t u r a t e if the l u m i n o s i t y w o u l d b e c o m e too

h i g h , I a m sure that s o m e b o d y w o u l d find a w a y a r o u n d t h i s . A n y w a y , t h i s p a r t

of the d i s c u s s i o n b e l o n g s to C a r l o and I shall b e c o n c e r n e d w i t h a v a i l a b l e

l u m i n o s i t y o n l y . I shall first p r e s e n t the a c t u a l s i t u a t i o n a n d p o i n t o u t

some p o s s i b l e r e l a t i v e l y s h o r t - t e r m a d j u s t m e n t s , a n d t h e n d i s c u s s a s o m e w h a t

s p e c u l a t i v e s c h e m e for an i m p r o v e m e n t by at l e a s t a n o r d e r of m a g n i t u d e .

2. P R E S E N T P E R F O R M A N C E C O M P A R E D TO T H E D E S I G N A I M

A s is p r o b a b l y w e l l k n o w n by n o w , the A A p e r f o r m a n c e is d o w n w i t h r e s

pect to its d e s i g n v a l u e by a f a c t o r b e t w e e n 4.5 a n d 5. In a d d i t i o n , w e m i s s

about a f a c t o r 2 b e c a u s e of v a r i o u s PS s t o p s , s t a c k l o s s e s a n d l i m i t e d t r a n s

fer e f f i c i e n c y . T h e f i n i t e l i f e t i m e in the SPS r e d u c e s the a c c u m u l a t i o n

p e r i o d a n d this g i v e s r o u g h l y a n o t h e r f a c t o r 2. T h u s , the p e a k l u m i n o s i t y is

20 x l o w e r than the d e s i g n v a l u e and the a v e r a g e l u m i n o s i t y is s t i l l l o w e r .

Table I s u m m a r i z e s the d i f f e r e n t e f f e c t s . I s h a l l d i s c u s s t h e m in some d e

t a i l , a l s o m e n t i o n i n g s h o r t - t e r m i m p r o v e m e n t p l a n s .

3. E F F E C T S T H A T R E D U C E T H E A A P E R F O R M A N C E A N D R E M E D I E S

A c c o r d i n g to our p r e s e n t u n d e r s t a n d i n g , a f a c t o r 2 c o m e s f r o m the p

p r o d u c t i o n f i g u r e b e i n g lower than o r i g i n a l l y a s s u m e d . W e c a n n o t do a n y t h i n g

a b o u t t h i s , b u t there is some h o p e for a 2 0 % i n c r e a s e in PS i n t e n s i t y a n d w e

have s o m e w h a t v a g u e p l a n s for i m p r o v i n g the c o l l e c t i o n e f f i c i e n c y . A l o n g ,

thin t a r g e t r e s u l t s in a b u t t e r f l y - s h a p e d p h a s e - s p a c e a r e a that d o e s n o t

m a t c h the e l l i p t i c a l m a c h i n e a c c e p t a n c e v e r y w e l l . It turns o u t t h a t a n i m

p r o v e m e n t m a y c o m e f r o m a c u r r e n t - c a r r y i n g t a r g e t . To p r o f i t f r o m t h i s , w e

w o u l d a l s o n e e d one or two l i t h i u m l e n s e s . P r e l i m i n a r y tests w i t h a c u r r e n t -

c a r r y i n g t a r g e t s e e m to show that it m i g h t j u s t s t a n d up to the s i m u l t a n e o u s

h e a t i n g f r o m the b e a m and f r o m the c u r r e n t p u l s e , b u t w e k n o w n o t h i n g a b o u t

the l i f e t i m e as y e t . Some w o r k is g o i n g o n in the f i e l d of l i t h i u m l e n s e s ;

we h o p e for a s s i s t a n c e f r o m F e r m i l a b h e r e . It is a l t o g e t h e r too e a r l y to say

w h a t f a c t o r , if a n y , we m i g h t g a i n . The t e c h n o l o g i c a l p r o b l e m s a r e f o r m i d a b l e .

A n o t h e r f a c t o r b e t w e e n 1.5 and 2 is m a i n l y a r e s u l t of the e f f e c t i v e

t r a n s v e r s e m a c h i n e a c c e p t a n c e b e i n g lower than f o r e s e e n .

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Table I - Actual parameters compared with design values

Design Report Actual

32N/ôp9o) for p production 0 . 0 2 4 6 ^ 0 . 0 1 2 s t e r - 1 GeV/c" 1

Effective machine acceptance (both planes)

1 O OTT ^ 7 0 T T mm mrad

Protons on target/pulse 1 0 1 3 1 . 3 x 1 0 1 3

p injected/pulse 2 . 5 x 1 0 7 7 . 0 x 1 0 6

p stacked/p injected 0 . 7 2 0 . 6 5

Repetition time 2 . 6 2 . 4 s

Missing factor 1 4 . 7 5

Various stops (h/day) 0 V 3 . 5

Waiting to cool down before transfers (h/day)

0 M . 5

Waiting for SPS to be ready 0 % 2

Transfer efficiency AA -* SPS stack

1 0 . 7

Number of p/bunch 1 0 1 1 9 . 5 x 1 0 1 0

Number of p/bunch 1 0 1 1 1 . 2 x 1 0 1 0

Number of bunches (each) . 1 2 3

3 values 4 . 7 x 1 m 2 x 1 M

Transverse emittance p 6 . 9 * 3 . 5 8 x 8 x 1 0 ~ 8 T T rad m

Transverse emittance p 3 . 8 x 1 . 9 5 . 5 x 5 . 5 x 1 0 " 8 T T rad m

Luminosity (max.) 1 0 3 0 5 x m 2 8 cm" 1 s" 1

The word "effective" refers to the fact that, although particles with large transverse emittance (up to nearly the design value) are present and survive in the machine, there are many fewer than foreseen compared with the low-emittance ones. This has little to do with the reduction of p production at large angles ; the angles we accept are well below the point where this becomes important. In any case, the p beam emittance is to a large

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e x t e n t c o n n e c t e d w i t h t h e l e n g t h o f t h e t a r g e t , w h i c h r e s u l t s i n a l a r g e e f f e c t i v e w i d t h .

F r o m r e c e n t e x p e r i m e n t s i t s e e m s p l a u s i b l e t h a t n o n - l i n e a r c o u p l i n g b e t w e e n h o r i z o n t a l a n d v e r t i c a l b e t a t r o n o s c i l l a t i o n s i s t h e m a i n c u l p r i t . B e c a u s e o f t h i s , p a r t i c l e s w i t h l a r g e o s c i l l a t i o n a m p l i t u d e s i n b o t h p l a n e s d o n o t s u r v i v e , b e c a u s e s o o n e r o r l a t e r t h e c o u p l i n g w i l l t r a n s f e r a l l e m i t t a n c e f r o m o n e p l a n e i n t o t h e o t h e r a n d t h e a m p l i t u d e s w i l l t h e n b e t o o l a r g e . I t w o u l d s e e m a t f i r s t s i g h t t h a t t h i s w o u l d j u s t c h a n g e t h e e f f e c t i v e a p e r t u r e o f t h e v a c u u m c h a m b e r f r o m a r e c t a n g l e i n t o i t s i n s c r i b e d e l l i p s e a n d t h e r e f o r e w e w o u l d l o s e a f a c t o r TT/4 o n l y . H o w e v e r , t h e p r o d u c t i o n a n d f o c u s i n g m e c h a n i s m i s s u c h t h a t t h e p h a s e s p a c e d e n s i t y i s n e a r l y c o n s t a n t , s o t h a t t h e r e a r e m a n y m o r e p a r t i c l e s w i t h l a r g e a m p l i t u d e s . A l t o g e t h e r , w e e s t i m a t e t h a t t h i s e f f e c t m i g h t b e r e s p o n s i b l e f o r a n i n t e n s i t y r e d u c t i o n b y a f a c t o r o f a b o u t 1 . 5 . We a r e p l a n n i n g s o m e t e s t s w i t h a n o c t u p o l e c o r r e c t i o n t o t h e n o n - l i n e a r f i e l d s , w h i c h m a y o r m a y n o t g i v e a n i m p r o v e m e n t .

A n o t h e r e f f e c t i s a n o n - e x p l a i n e d r e d u c t i o n o f v e r t i c a l a c c e p t a n c e i n t h e s t a c k r e g i o n o f t h e v a c u u m c h a m b e r . We s u s p e c t a n o b s t r u c t i o n a n d a r e t r y i n g t o l o c a l i z e i t d u r i n g t h i s s h u t - d o w n . T h i s m a y g i v e u s a n a d d i t i o n a l 10 o r 2 0 % .

T h e r e a r e p o s s i b l y s e v e r a l o t h e r s m a l l e f f e c t s i n t h e 10% r a n g e a n d i t i s c l e a r t h a t w e h a v e t o a t t a c k e v e n s u c h s m a l l s h o r t c o m i n g s b e c a u s e t h e y t e n d t o b e c u m u l a t i v e .

T h e c o o l i n g s e e m s t o p e r f o r m w e l l a t t h e p r e s e n t l e v e l o f p f l u x ( i . e . n u m b e r o f p ' s a d d e d t o t h e s t a c k p e r s e c o n d ) . T h e d e s i g n a i m w a s a n i n c r e a s e i n 6 - d i m e n s i o n a l p h a s e s p a c e d e n s i t y b y a f a c t o r 1 0 9 ; w e h a v e a c h i e v e d 3 x 1 0 s a n d m o s t o f t h e d i f f e r e n c e i s d u e t o t h e e f f e c t s d e s c r i b e d a b o v e . H o w e v e r , t h e c o o l i n g i s f a c i l i t a t e d b e c a u s e t h e i n c o m i n g f l u x i s l o w e r a n d w e s u s p e c t t h a t w i t h h i g h e r f l u x i t m i g h t b e c o m e t h e l i m i t i n g f a c t o r . We a r e t h e r e f o r e i m p r o v i n g t h e c o o l i n g s y s t e m s i n v a r i o u s w a y s .

O n e o f t h e s e i m p r o v e m e n t s ( n e w t r a n s v e r s e s t a c k c o r e p i c k - u p s ) a l s o a i m s a t r e m o v i n g a n i m p o r t a n t l i m i t a t i o n i n a c c u m u l a t i o n t i m e . A t p r e s e n t , t h e c o o l i n g s y s t e m s t h a t r e d u c e t h e t r a n s v e r s e s t a c k e m i t t a n c e s t o a c c e p t a b l e v a l u e s a r e p e r t u r b e d d u r i n g s t a c k i n g b y d i f f e r e n t e f f e c t s . A s a c o n s e q u e n c e , w e h a v e t o s t o p s t a c k i n g o n e o r t w o h o u r s b e f o r e a t r a n s f e r i s f o r e s e e n i n o r d e r t o r e d u c e t h e e m i t t a n c e s w i t h o u t t h e s e p e r t u r b i n g e f f e c t s . I n a d d i t i o n , i t o f t e n h a p p e n s t h a t a f t e r t h i s t h e t r a n s f e r i s p o s t p o n e d f o r v a r i o u s r e a s o n s ; t h i s a g a i n c a u s e s o n a v e r a g e a l o s s o f a b o u t 2 h o u r s . A l l t h i s w o u l d h o p e f u l l y b e a v o i d e d w i t h t h e i m p r o v e m e n t s t h a t w i l l b e i n s t a l l e d i n t h e b e g i n n i n g o f t h i s y e a r . I t i s h o p e d t h a t l o w e r t r a n s v e r s e e m i t t a n c e m i g h t a l s o i m p r o v e t h e t r a n s f e r e f f i c i e n c y , a l t h o u g h t h i s i s b y n o m e a n s c e r t a i n .

I n t h e S P S , a s h o r t - t e r m g a i n w o u l d p r o b a b l y r e s u l t f r o m l o w e r 3 v a l u e s a t t h e i n t e r s e c t i o n s . N o t h i n g m u c h n e w i s n e e d e d f o r t h i s e x c e p t m a c h i n e e x p e r i m e n t s t i m e .

I t m i g h t s e e n f r o m a l l t h i s t h a t r a t h e r i m p o r t a n t i m p r o v e m e n t s a r e a r o u n d t h e c o r n e r . U n f o r t u n a t e l y , e x p e r i e n c e s h o w s t h a t t h i n g s o f t e n d o n o t w o r k q u i t e a s w e l l a s h o p e d f o r . I w o u l d g u e s s t h a t w i t h h a r d w o r k w e m i g h t

- 5 5 8 -

e v e n t u a l l y g a i n a f a c t o r 2 i n A A s t a c k i n g r a t e a n d t h a t a n o t h e r f a c t o r 2 o r 3 c o u l d b e o b t a i n e d f r o m b e t t e r t r a n s f e r e f f i c i e n c y , l o w e r ß v a l u e s , b e t t e r l i f e t i m e , e t c .

A n i m p o r t a n t l i m i t a t i o n i s t h e l a c k o f t i m e f o r m a c h i n e d e v e l o p m e n t . T h e A A w a s d e s i g n e d a s a m a c h i n e t h a t w o u l d b e u s e d f o r a b o u t 1 0 0 0 h p e r y e a r f o r p r o d u c i n g a n t i p r o t o n s . T h e r e s t o f t h e t i m e w o u l d b e a v a i l a b l e f o r m a c h i n e e x p e r i m e n t s a n d i m p r o v e m e n t s . T h i s y e a r , w e h a v e 4 2 0 0 h p r o d u c t i o n t i m e p l a n n e d a n d o n l y 1 0 0 0 h m a c h i n e e x p e r i m e n t t i m e . I n f a c t , i t s e e m s a l r e a d y p r o b a b l e t h a t t h i s f i g u r e w i l l b e f u r t h e r d e c r e a s e d . I n t h e S P S , t h e s i t u a t i o n i s s i m i l a r . W h e n e v e r p r o b l e m s a r i s e , t h e p o w e r f u l u s e r ' s p r e s s u r e l e a d s t o r e d u c t i o n o f m a c h i n e e x p e r i m e n t s t i m e i n o r d e r t o p r e s e r v e p r o d u c t i o n p e r i o d s . I b e l i e v e t h a t t h e p o i n t o f d i m i n i s h i n g r e t u r n s h a s b e e n r e a c h e d .

4 . L O N G - T E R M P L A N S

U n d e r t h i s h e a d i n g I s h a l l d i s c u s s a p r e l i m i n a r y d e s i g n f o r a n a d d i t i o n a l r i n g ( c a l l e d A C ) , o f t h e s a m e s i z e a s t h e A A , w h i c h a i m s a t a n i n c r e a s e o f s t a c k i n g r a t e b y a n o r d e r o f m a g n i t u d e . I t m u s t b e s t r e s s e d t h a t t h i s i s n o t a a p p r o v e d p r o j e c t ; b o t h t h e m o n e y a n d t h e m a n p o w e r n e e d e d w i l l b e i n c o m p e t i t i o n w i t h L E P .

I n o r d e r t o c a t c h m o r e a n t i p r o t o n s t h a n t h e A A , t h e n e w r i n g w o u l d h a v e t w i c e t h e t r a n s v e r s e a c c e p t a n c e i n b o t h p l a n e s ( 2 0 0 i T mm m r a d ) , a n d f o u r t i m e s t h e m o m e n t u m a c c e p t a n c e ( 6 % ) . We w o u l d , o f c o u r s e , h a v e t o i m p r o v e t h e m a t c h i n g d e v i c e n e a r t h e t a r g e t ; i t s e e m s p r o b a b l e t h a t a t l e a s t o n e l i t h i u m l e n s w o u l d b e n e c e s s a r y . T h e n e w r i n g w o u l d h a v e t o b e b u i l t i n a t u n n e l s e p a r a t e f r o m t h e A A , n o t o n l y t o e n a b l e c o n s t r u c t i o n a n d r u n n i n g i n t o g o o n w h i l e t h e A A i s i n o p e r a t i o n , . b u t a l s o b e c a u s e t h e i n c r e a s e d i n t e n s i t y w o u l d r e s u l t i n a f a r t o o h i g h r a d i a t i o n l e v e l i n t h e A A h a l l ( s e e F i g . 1 ) .

T h e h i g h e r a c c e p t a n c e s c o u l d b e a c h i e v e d w i t h m a g n e t a p e r t u r e s o f t h e s a m e o r d e r a s t h o s e o f t h e A A , b e c a u s e w e w o u l d u s e s t r o n g e r f o c u s i n g a n d w e w o u l d n o t k e e p t h e s t a c k i n t h e s a m e r i n g . T h e A A w o u l d b e c o m e a p u r e s t a c k i n g r i n g a n d a l l o t h e r o p e r a t i o n s ( b u n c h r o t a t i o n , l o n g i t u d i n a l a n d t r a n s v e r s e p r e c o o l i n g ) w o u l d b e d o n e i n t h e n e w A C . T h e r e f o r e , t h e m o v a b l e s h u t t e r s t h a t a r e n o w n e e d e d i n t h e A A w o u l d n o l o n g e r b e n e c e s s a r y a n d i t s o p e r a t i o n w o u l d b e c o m e s i m p l e r a n d m o r e r e l i a b l e . A n y f a i l u r e s i n t h e m o r e c o m p l i c a t e d A C c o u l d b e r e p a i r e d w i t h o u t l o s i n g t h e s t a c k .

T h e f i r s t o p e r a t i o n t o b e d o n e i n t h e A C w o u l d b e a b u n c h r o t a t i o n t o r e d u c e t h e m o m e n t u m s p r e a d . T h e a n t i p r o t o n s a r r i v e i n 5 s h o r t b u n c h e s a n d i t i s p o s s i b l e t o e x c h a n g e m o m e n t u m s p r e a d a g a i n s t b u n c h l e n g t h . T h i s p r o c e s s t a k e s a f r a c t i o n o f a m i l l i s e c o n d . I t r e q u i r e s a p u l s e d R F c a v i t y w i t h a v o l t a g e o f t h e o r d e r o f 1 M V .

A f t e r t h i s , t h e b u n c h e s w i l l s m e a r o u t i n t o a c o n t i n u o u s b e a m a n d t h e t r a n s v e r s e e m i t t a n c e s w i l l b e c o o l e d f r o m 200TT mm m r a d d o w n t o ^ 3TT b y f a s t h o r i z o n t a l a n d v e r t i c a l c o o l i n g s y s t e m s . T h e s e w i l l n e e d l a r g e b a n d w i d t h ( 2 - 4 G H z ) t o c o p e w i t h t h e h i g h p i n t e n s i t y . H i g h o u t p u t p o w e r ( M O k W ) w i l l a l s o b e r e q u i r e d ( q u i t e e x p e n s i v e i n t h i s f r e q u e n c y r a n g e ) . I t a p p e a r s t h a t w e w i l l n e e d l a r g e m u l t i - p i c k - u p a n d k i c k e r s t r u c t u r e s t o k e e p t h e p o w e r r e a s o n a b l e . A l s o , t h e p i c k - u p s a n d k i c k e r s w i l l h a v e t o i n c o r p o r a t e a

- 5 5 9 -

m e c h a n i c a l s e r v o s y s t e m t h a t w i l l a d j u s t t h e i r a p e r t u r e a s t h e c o o l i n g r e d u c e s t h e b e a m s i z e . We d o n o t l i k e t h i s , b u t i t i s e s s e n t i a l t o k e e p a s u f f i c i e n t s i g n a l - t o - n o i s e r a t i o a s t h e b e a m s h r i n k s .

A f t e r t h e t r a n s v e r s e c o o l i n g w e w i l l h a v e t o p e r f o r m a f a s t l o n g i t u d i n a l c o o l i n g t o r e d u c e t h e m o m e n t u m s p r e a d b y a n o r d e r o f m a g n i t u d e b e f o r e t h e b e a m i s t r a n s f e r r e d t o t h e A A . We m a y u s e t h e s a m e p i c k - u p s , k i c k e r s a n d p o w e r a m p l i f i e r s f o r t h i s a s f o r t h e t r a n s v e r s e c o o l i n g , o n l y r e a r r a n g e d i n " c o m m o n " i n s t e a d o f " d i f f e r e n t i a l " m o d e . I t w i l l a l s o b e n e c e s s a r y t o d e v e l o p s u p e r c o n d u c t i n g t r a n s m i s s i o n l i n e f i l t e r s f o r t h e m o m e n t u m c o o l i n g ; f o r t u n a t e l y , w e w i l l b e a b l e t o p r o f i t f r o m F e r m i l a b ' s e x p e r i e n c e h e r e .

T o s t a c k t h e h i g h e r f l u x ( m a y b e 4 x t h e o r i g i n a l d e s i g n v a l u e ) i n t h e A A , i t s s t a c k - t a i l c o o l i n g c i r c u i t s w i l l a l s o h a v e t o b e u p g r a d e d t o h i g h e r -f r e q u e n c y o n e s . C a l c u l a t i o n s h o w s t h a t t h i s s h o u l d w o r k , p r o v i d e d t h a t t h e i n c o m i n g b e a m i s s m a l l i n a l l 3 p h a s e p l a n e s . T h i s f i x e s t h e r e q u i r e m e n t s f o r t h e A C c o o l i n g .

I t w o u l d n o t b e t h e r i g h t p l a c e h e r e t o g o i n t o m u c h d e t a i l a b o u t t h e p l a n n e d n e w r i n g , i f o n l y b e c a u s e t h e p a r a m e t e r s a r e f a r f r o m s e t t l e d . I t i s p l a n n e d t o p r o d u c e a c o h e r e n t d e s i g n d u r i n g t h e f i r s t h a l f o f 1 9 8 3 . A l l t h a t c a n b e s a i d i s t h a t w e t h i n k w e k n o w h o w t o s t a c k 5 x 1 0 7 p / p u l s e a n d t h a t w e a r e w o r k i n g h a r d t o p e r h a p s i m p r o v e t h i s b y a f a c t o r o f 2 . A t p r e s e n t , t h e c o r r e s p o n d i n g v a l u e i s 4 x 1 0 6 p / p u l s e a n d , a s I e x p l a i n e d , t h i s m i g h t a l s o g r o w b y a f a c t o r 2 w i t h t h e p r e s e n t r i n g .

5 . C O O L I N G I N T H E S P S

I w o u l d l i k e t o m e n t i o n s o m e v e r y s p e c u l a t i v e p l a n s t h a t m i g h t r e s u l t i n a c o n s i d e r a b l e l i f e t i m e i m p r o v e m e n t i n t h e S P S . A t p r e s e n t , t h e l u m i n o s i t y l i f e t i m e i s a b o u t 18 h ( m a i n l y f r o m b e a m - b e a m e f f e c t s ) a n d a s a c o n s e q u e n c e a b o u t t w o f i l l i n g s p e r d a y h a v e b e e n t h e u s u a l p r a c t i c e . C l e a r l y , t h e a v a i l a b l e A A s t a c k a t t h e m o m e n t o f t r a n s f e r w o u l d g r o w i f w e c o u l d i m p r o v e t h e l i f e t i m e .

E l e c t r o n c o o l i n g h a s b e e n s u g g e s t e d a s a s o l u t i o n . T h i s w o u l d , h o w e v e r , r e q u i r e q u i t e s o m e d e v e l o p m e n t ; o n e o r t w o s p e c i a l e l e c t r o n r i n g s , t a n g e n t i a l t o t h e S P S , w o u l d h a v e t o b e b u i l t .

T h e o b v i o u s a l t e r n a t i v e i s s t o c h a s t i c c o o l i n g . U n f o r t u n a t e l y , t h e n a r r o w b u n c h e s i n t h e S P S m a k e t h i s q u i t e d i f f i c u l t , b e c a u s e t h e e s s e n t i a l f e a t u r e o f s t o c h a s t i c c o o l i n g , i . e . t h e o b s e r v a t i o n o f i n d i v i d u a l p a r t i c l e s , i s v e r y d i f f i c u l t i n s i d e a 4 n s b u n c h .

O n e p o s s i b i l i t y 1 ) i s t o d e b u n c h t h e b e a m . T h i s d o e s n o t r e d u c e t h e t o t a l l u m i n o s i t y , b u t m o s t e v e n t s w i l l o c c u r o u t s i d e t h e e x p e r i m e n t a l r e g i o n s a n d a l a r g e f a c t o r i s l o s t . T h i s c a n b e g a i n e d b a c k b y s t r o n g c o o l i n g ; i t s e e m s t h a t t h e b e a m d i a m e t e r c o u l d b e r e d u c e d t o 20 o r 3 0 Urn.

T h e b e a m s w o u l d h a v e t o b e s e p a r a t e d o v e r m o s t o f t h e r i n g c i r c u m f e r e n c e b y g i v i n g t h e m s l i g h t l y d i f f e r e n t m o m e n t a a n d b y d i f f e r e n t i a l c l o s e d o r b i t o s c i l l a t i o n s m a d e w i t h e l e c t r o s t a t i c d e f l e c t o r s .

T h e s c h e m e s e e m s s o m e w h a t m a r g i n a l . A l t h o u g h i t o f f e r s a l o n g l i f e t i m e ,

- 5 6 0 -

t h e l u m i n o s i t y m i g h t s u f f e r s o m e w h a t . A l s o , c l e a r i n g e l e c t r o d e s w o u l d h a v e t o b e i n s t a l l e d a t f r e q u e n t i n t e r v a l s a l l a r o u n d t h e r i n g t o r e m o v e p o s i t i v e i o n s f r o m t h e p b e a m .

A n a l t e r n a t i v e s c h e m e t h a t i s s t u d i e d a t p r e s e n t ^ ) i s t o c o o l t h e b u n c h e d b e a m . C o o l i n g t i m e s a r e q u i t e l o n g ( i n t h e 1 0 - 2 0 h r a n g e ) b u t m i g h t b e j u s t g o o d e n o u g h t o c o m p e n s a t e t h e b e a m - b e a m d i f f u s i o n . E v e n a p a r t i a l c o m p e n s a t i o n w o u l d o f c o u r s e b e w e l c o m e .

A l l s u c h p r o j e c t s d e p e n d o n t h e d e v e l o p m e n t o f v e r y h i g h f r e q u e n c y t e c h n i q u e s ( 8 - 1 6 G H z h a s b e e n p r o p o s e d ) . T h i s w i l l c e r t a i n l y t a k e s o m e t i m e .

R E F E R E N C E S

1) S . v a n d e r M e e r , D e b u n c h e d p p O p e r a t i o n o f t h e S P S , R e p o r t C E R N / P S / A A / 7 9 - 4 2 ( D e c e m b e r 1 9 7 9 ) .

2 ) S . C h a t t o p a d h y a y , P r i v a t e C o m m u n i c a t i o n .

- 5 6 2 -

D/V T*/t poSSifr'aTi

OF A

- 563 -

- 5 6 4 -

& Ö 2. i*

- 5 6 5 -

- 566 -

- 5 6 7 -

What next?

Nicola Cabibbo

I s t i t u t o di Fi s i c a , U n i v e r s i t a di Roma

INFN, Sezione di Roma

The events observed by the UAl and UA2 c o l l a b o r a t i o n s seem to

g i v e the f i r s t c o n f i r m a t i o n of the existence of the W p a r t i c l e . I t +

is h i g h l y probable t h a t the existence o f the W and, perhaps, o f the

Z° w i l l be f i r m l y e s t a b l i s h e d during t h i s y e a r . Assuming t h i s to be

t r u e , what should we do next? In t h i s talk I would l i k e to present

two messages:

1) One should not g i v e up prematurely the hope o f p r e c i s i o n

measurements w i t h the c o l l i d e r .

2) There may be a great q u a n t i t y of "unexpected new physics"

to be discovered with the c o l l i d e r .

1 - P r e c i s i o n measurements.

The statement i s often heard that the c o l l i d e r can at best be

an e x p l o r a t i v e d e v i c e , able to e x t a b l i s h the existence o f some new par

t i d e s (W, Z perhaps the Higgs and the t quark) but not capable of de

termining w i t h p r e c i s i o n the basic p r o p e r t i e s o f these p a r t i c l e . T h i s

statement i s not e n t i r e l y c o r r e c t , and more thought should go to t h i s

area, e x p e c i a l l y i n view o f the foreseable improvement o f the c o l l i d e r

l u m i n o s i t y and r e l i a b i l i t y .

To i l l u s t r a t e t h i s , consider the problem o f measuring the Z°

- 5 6 8 -

2 ) P P — ^ Z + - •

T h e s e c r o s s s e c t i o n s c a n b e e x p r e s s e d i n t e r m s o f q q f l u x e s

a n d o f p a r t i a l a n d t o t a l d e c a y w i d t h s . N e g l e c t i n g k i n e m a t i c a l f a c t o r s ,

w i d t h . A l t h o u g h do n o t s e e a w a y t o o b t a i n a p r e c i s e d i r e c t m e a s u r e

m e n t , a n i n d i r e c t m e a s u r e m e n t c o u l d g i v e i m p o r t a n t i n f o r m a t i o n s . L e t me re-

±

c a l l t h a t w h i l e e a c h d e c a y o f t h e W c o n t a i n s a t l e a s t o n e c h a r g e d pajr

t i d e , a n d i s i n p r i n c i p l e o b s e r v a b l e , a f r a c t i o n o f Z° d e c a y s w i l l

n o t be o b s e r v a b l e . T h i s i s t r u e o f V V d e c a y s , b u t o n e m i g h t imagi^

ne t h e e x i s t e n c e o f t h e o t h e r now u n e x p e c t e d " d a r k " m o d e s . T h e e x i s t e n

ce o f s u c h modes c o u l d be i n f e r r e d t h r o u g h a p r e c i s i o n m e a s u r e m e n t o f

t h e t o t a l w i d t h P © .

I n t h e s t a n d a r d m o d e l w i t h t h r e e l e p t o - q u a r k f a m i l i e s V V mo

d e s a r e e x p e c t e d t o a c c o u n t f o r 2 0 % o f P ^ » . D o u b l i n g t h e n u m b e r o f

n e u t r i n o s w o u l d t h e n i n c r e a s e P ^° b y 2 0 % ( a s s u m e , f o r t h e s a k e o f

t h e a r g u m e n t , t h e e x i s t e n c e o f t h r e e new f a m i l i e s w i t h l i g h t n e u t r i n o s

b u t v e r y h e a v y c h a r g e d l e p t o n s a n d q u a r k s ) .

A p r e c i s e d i r e c t m e a s u r e m e n t o n P jo i s h a r d t o o b t a i n i n

t h e c o l l i d e r , b u t o n e c o u l d t r y t h e f o l l o w i n g s t r a t e g y w h i c h c o u l d l e a d

t o a m e a s u r e m e n t o f t h e r a t i o P z ° / P w w n i c n i s n e a r l y a s i n f o r m a

t i v e o n t h e e x i s t e n c e o f " d a r k " Z° d e c a y m o d e s . T o o b t a i n t h i s , c o n s i

d e r t h e e x p r e s s i o n f o r t h e c r o s s s e c t i o n f o r t h e t w o i n c l u s i v e p r o c e s

s e s :

D p p —p W -+ . • •

- 5 6 9 -

and w i t h some s i m p l i f i c a t i o n we could w r i t e :

I f we assume the v a l i d i t y o f the standard model p a r t i a l decay rates can be computed with great accuracy ( J r e f ç r you here to Co«s.o\il

s

t a l f c t h i s morning). Quark f l u x e s can also be computed on the b a s u ; o f

s c a l i n g and the parton model. This computation cannot however be c o n s i

dered as v e r y r e l i a b l e i n view o f the d i s c o v e r y (the k f a c t o r of G. A l

t a r e l l i and G. M a r t i n e l l i ) that two loop c o r r e c t i o n s lead to 100% c o r r e

c t i o n s to the simple parton model ( D r e l l - Y a n ) p r e d i c t i o n s . Most of t h e

se uncertanties would however drop out i f we take the r a t i o

an accurate measurement of could then lead to a determinationof

T h i s proposal has not been f u l l y a n a l y z e d , but i s an example o f how

more t h e o r e t i c a l work could uncover new ways o f using c o l l i d e r data

f o r p r e c i s i o n measurements.

(Ratio o f q q f l u x e s ) x ( R a t i o of p a r t i a l r a t e s ) x

- 570 -

2 - New physics - expected.

New physics can be d i v i d e d i n t o expected and Unexpected. Expec

ted physics (not less i n t e r e s t i n g ) include now both the t quark and the

Higgs p a r t i c l e . The energy o f the CERN c o l l i d e r should be s u f f i c i e n t f o r

producing both o f them, although - i n the case of the Higgs - the p r o

spects f o r d i s c o v e r y depend i n a c r i t i c a l way on i t s mass.

T h i s morning Veltman presented arguments which lead to upper bounds

f o r the H i g g s mass i n the TeV r e g i o n . I would l i k e to r e c a l l that

a much t i g h t e r bound can be g i v e n under the hypothesis t h a t there i s

no change o f regime f o r fundamental i n t e r a c t i o n s bolow the "grand u n i -15 19

f i c a t i o n energy", , which can be somewhere between 10 and 10 GeV. In g r a n d - u n i f i e d models the change o f regime cooresponds to r e s t o r a t i o n

o f a higher symmetry, such as SU(5).

Even i n the absence o f grand u n i f i c a t i o n a change o f regime has 19

to take phace i n the neighbourhood o f 10 GeV, the energy (also c a l l e d

the Planck mass) at which g r a v i t a t i o n a l i n t e r a c t i o n s become dominant.

Given t h i s h y p o t h e s i s , the argument proceeds ( i n a s i m p l i f i e d

form) as f o l l o w s : the s e l f coupling o f the Higgs p a r t i c l e :

where G i s the Fermi constant and A 0 the value o f A a t low ( ç i H , )

i s r e l a t e d to the Higgs mass through

obeys a Callan-Symanzig equation ;

- 571 -

4a - K t CM iíuE 4-TT

These equations can be i n t e g r a t e d to y e l d

I P.. e

which blows up at

£„. . ~ Hvo 4i The blowing up o f À means t h a t at Eîggs o n e h a s a c n a n 9 e

o f regime. I f , a c c o r d i n g to our h y p o t h e s i s , we r e q u i r e that t h i s should 15 19

not happen below 10 - 10 GeV, one obtains an upper l i m i t to the

Higgs mass

M , • < 170 GeV i n n * ~

A s i m i l a r argument applies to the t quark mass. T h i s would put both

the Higgs and the t i n the energy range covered by the c o l l i d e r .

- 5 7 2 -

3 - New p h y s i c s - u n e x p e c t e d .

B y u n e x p e c t e d p h y s i c s I r e f e r t o a r a n g e o f p o s s i b l e p h e n o m e n a

w h i c h i s n o t f i r m l y p r e d i c t e d b y t h e s t a n d a r d S U ( 3 ) x S U ( 2 ) x U ( I ) t h e o

r y o f e l e c t r o w e a k a n d h a d r o n i c i n t e r a c t i o n s .

Many t h e o r e t i c i a n s a r e d i s s a t i s f i e d w i t h t h i s m o d e l . A l t h o u g h

i t c e r t a i n l y f i t s l o w e n e r g y e x p e r i m e n t a l d a t a i t d o e s n o t l o o k l i k e

a f i n a l t h e o r y :

a ) i t c o n t a i n s t o o many f r e e p a r a m e t e r s , s u c h a s m a s s e s , weak

m i x i n g p a r a m e t e r s , e t c . .

b ) T h e s y m m e t r y g r o u p c o n t a i n s many i n d e p e n d e n t f a c t o r s , i t

i s n o t a t r u e u n i f i c a t i o n .

c ) I t d o e s n o t g i v e a u n i f i c a t i o n o f g r a v i t a t i o n a l f o r c e s

w i t h t h e o t h e r i n t e r a c t i o n s .

G r a n d u n i f i c a t i o n s o l v e s t h e s e c o n d p r o b l e m , b u t n o t t h e o t h e r t w o .

S u p e r g r a v i t y t h e o r i e s may s o l v e t h e l a s t p r o b l e m , b u t we s t i l l do n o t

h a v e a c o m p l e t e a n d p r e d i c t i v e m o d e l . Some p r o g r e s s i n t h i s d i r e c t i o n

i s b e i n g m a d e .

A c l a s s o f t h e o r i e s w h i c h c o u l d s o l v e t h e f i r s t p r o b l e m i n c l ^ j

d e s m o d e l s w h e r e q u a r k s a n d l e p t o n s a r e c o m p o s i t e , s o t h a t t h e i r p r o

p e r t i e s c a n i n p r i n c i p l e be c o m p u t e d . A g a i n no f u l l y d e v e l o p p e d model

o f t h i s c l a s s e x i s t s .

We a r e t h u s i n a s i t u a t i o n w h e r e we e x p e c t t h a t t h e s t a n d a r d

m o d e l h a s t o be c o m p l e t e d , b u t we do n o t know p r e c i s e l y i n w h i c h d i

r e c t i o n . T h i s s i t u a t i o n may be f e r t i l e f o r u n e x p e c t e d phenomena w h i c h

c o u l d p o i n t t o o n e o f t h e a b o v e - m e n t i o n e d d i r e c t i o n s o r t o now u n -

t h o u g h t o f p o s s i b i l i t i e s .

- 5 7 3 -

To conclude t h i s t a l k , I would l i k e to mention two kinds o f

t h e o r e t i c a l schemes (among many) which could lead to new physics i n

the c o l l i d e r energy range.

The f i r s t i s supersymmetry. Supersimmetric models r e q u i r e t h a t

each o f the p a r t i c l e s we now know has a partner o f opposite s t a t i s t i c s .

None of these p r e d i c t e d partners has been discovered. T h i s does not de

t e r t h e o r e t i c i a n s , since supersymmetry (through s u p e r g r a v i t y ) seems to

be the only avenue towards the u n i f i c a t i o n of g r a v i t a t i o n w i t h the

other fundamental f o r c e s . We are not i n the p o s i t i o n o f g i v i n g f i r m

p r e d i c t i o n s on the mass o f the expected new p a r t i c l e s such as s c a l a r

quarks, s c a l a r l e p t o n s , fermionic W and Z , e t c , but a r e l a t i v e l y low

mass ( Ç» few tens o f GeV) seems f u l l y p o s s i b l e . Supersymmetric par

tners would i n t h i s case be r e a d i l y p a i r produced a t the c o l l i d e r . I f

the mass is not too h i g h , they would appear as decay products o f W and

Z°.

A second scheme I would l i k e to mention i s one due to Maiani,

P a r i s i , and Petronzio, which leads to the p r e d i c t i o n o f a l a r g e number

( e i g h t ) of lepto-quark f a m i l i e s .

This scheme was born i n an attempt to e x p l a i n the near coincidence be

tween the energy scale o f confinement ( y\ QCD~"Z - 0 0 MeV) w i t h the

scale o f quark and lepton masses.

Remember that w h i l e confinement i s a QCD e f f e c t , quark and lepton masses

are electro-weak phenomena (they a r i s e from the Higgs breaking of SU(2)x

x U ( l ) ) . In the standard model the two energy scales are i n p r i n c i p l e ijn

dependent, and no e x p l a n a t i o n is given o f t h e i r c loseness.

Maiani, P a r i s i and Petronzio have shown that i f the number o f f a

m i l i e s i s e i g h t , the two energy scales are i n t e r l o c k e d , and the coincide]!

ce can be e x p l a i n e d . In a subsequent paper with G. F a r r a r I have checked

- 5 7 4 -

t h a t t h e same h a p p e n s i f t h e f a m i l i e s a r e c o m p l e t e d w i t h t h i r s u p e r s y m

m e t r i c p a r t n e r s . I n t h i s c a s e f i v e f a m i l i e s w o u l d be r e q u i r e d . I n t h e

s e s c h e m e s t h e q u a r k s a n d l e p t o n s b e l o n g i n g t o t h e new f a m i l i e s s h o u l d

a l l h a v e m a s s e s i n t h e 30 - 150 GeV r e g i o n , w e l l i n t h e c o l l i d e r e n e r

g y r a n g e .

- 5 7 5 -

C o n c l u s i o n s a n d F u t u r e P e r s p e c t i v e s

L . M. L e d e r m a n

I . O v e r v i e w

T h i s i s v e r y p r o b a b l y a n h i s t o r i c m e e t i n g a n d w i l l b e d i s c u s s e d i n f u t u r e y e a r s a s t h e "Rome W o r k s h o p . "

I I . P e r s o n a l a n d S u b j e c t i v e I m p r e s s i o n s

1 . T h e s p e e d w i t h w h i c h d a t a w a s a n a l y z e d a n d p h y s i c s p r e s e n t e d w a s t r u l y a s t o n i s h i n g c o n s i d e r i n g t h e c o m p l e x i t y o f t h e c o l l i s i o n s , t h e s o p h i s t i c a t i o n o f t h e d e t e c t o r s a n d t h e " h o r d e s " o f e x p e r i m e n t a l p h y s i c i s t s . T h e t w o m a j o r g r o u p s U A 1 , 2 a r e r e a l l y t o b e c o n g r a t u l a t e d . Of c o u r s e t h e a c c e l e r a t o r g r o u p t h e d e s i g n e r s a n d o p e r a t o r s o f t h e AA r i n g a n d a s s o c i a t e d a c c e l e r a t o r s y s t e m s — a d d i t i o n a l , c r u c i a l c o m p o n e n t s . T h e i r a c h i e v e m e n t o f r a i s i n g t h e p e a k l u m i n o s i t y b y a f a c t o r o f 5 0 d u r i n g t h e f a l l r u n w a s v i t a l f o r t h e p h y s i c s r e s u l t s .

2 . T h e d a t a i s a n a l y z a b l e a t l e a s t t h a t p a r t we w e r e s h o w n . I t w a s s u g g e s t e d t h a t s o f t c o l l i s i o n s i n UA1 w i l l r e q u i r e m o r e a n a l y s i s t i m e b u t much p h y s i c s h a s a l r e a d y e m e r g e d .

3 . JETS a r e a n i m p o r t a n t d i s c o v e r y . T h e d i j e t s w h i c h d o m i n a t e t h e d a t a f o r E > 5 0 GeV a r e s p e c t a c u l a r . T h e d i f f e r e n t i a l c r o s s s e c t i o n f o r h i g h P j e t s a r e a r e a l i z a t i o n o u t o f t h e p a g e s o f t h e p r o p o s a l a n d e x t e n d t o o v e r 8 0 G e V / c . I r e m i n d y o u t h a t t h i s i s a n x x o f 0 . 3 a n d i s a l r e a d y u s e f u l f o r s t u d y i n g t h e p o i n t l i k e b e h a v i o r o f q u a r k s . P e r s o n a l l y , I r e c a l l o u r CCR o b s e r v a t i o n o f T T 0 , S o f 3 - 4 G e V / c - s o s u r p r i s i n g i n 1 9 7 2

t h a t we h a d t o c h e c k a n d r e c h e c k b e f o r e we w e r e s u r e we h a d a d i s c o v e r y . I n 1 9 8 2 , t h e s a m e p h e n o m e n a a r e t e l l i n g u s s o m e t h i n g a b o u t a d i s t a n c e s c a l e n e a r 1 0 c m !

4 . T h e a p p e a r a n c e o f t h e j e t s a r e p r e t t y c l o s e t o d i r e c t o b s e r v a t i o n o f p a r t o n s - q u a r k s a n d g l u o n s e m e r g i n g f r o m t h e h a r d i m p a c t o f a n i n c i d e n t q u a r k o n a n a n t i q u a r k . I t may n o t b e t o o f u t u r i s t i c t o s a y t h a t s o m e d a y w e ' l l b e a b l e t o t a g j e t s : t h i s i s a n s - q u a r k , t h e r e i s a c - q u a r k .

5 . I v e r y much a p p r e c i a t e d P r o f e s s o r A l t a r e l l i ' s c l e a r d e s c r i p t i o n o f t h e w a y s i n w h i c h c o l l i d e r p h y s i c s c a n p r o b e QCD.

6 . T h e s o f t c o l l i s i o n p h y s i c s a s d e s c r i b e d b y D r s . C a l v e t t i , C o n t a a n d E k s p o n g a n d e l u c i d a t e d b y V a n H o v e a n d G r e c o a r e n o t b e b e i g n o r e d . T h i s i s a n ew d o m a i n w i t h e x p e r i m e n t a l s u r p r i s e s ( T h e E y i e l d s , t h e f l a t t e n i n g o f t h e m e a n P v s . m u l t i p l i c i t y ) a n d new t e s t s o f " o l d " p h y s i c s .

- 576 -

7 . E l a s t i c s c a t t e r i n g a n d t o t a l c r o s s s e c t i o n s i n t h i s n e w e n e r g y d o m a i n w e r e m o t i v a t e d f o r u s b y A n d r e M a r t i n - a n d t h e d a t a f r o m U A l a n d UA4 a r e i m p o r t a n t c o n t r i b u t i o n s .

8 . O f c o u r s e , t h e s i n g l e e l e c t r o n d a t a o f U A l a n d U A 2 h e r a l d t h e i m m i n e n t d i s c o v e r y o f t h e W a n d t h e Z . H e r e w e m u s t t r y h a r d t o m a i n t a i n o u r t r a d i t i o n a l s k e p t i c i s m i n s p i t e o f t h e s t r o n g i n f l u e n c e o f o u r t h e o r e t i c a l c o l l e a g u e s w h i c h t e n d s t o w e a k e n r e s i s t a n c e .

9 . I w a s q u i t e i m p r e s s e d w i t h t h e v a l u e o f t h e f r i e n d l y c o m p e t i t i o n b e t w e e n U A l a n d U A 2 . T h i s i s i n t h e f i n e s t t r a d i t i o n s o f h i g h e n e r g y p h v s i c s a n d r e m i n d s me o f a s t o r y a b o u t t w o s u p e r s y m m e t r i c a l p h y s i c i s t s , l e t u s c a l l t h e m C a r l i n o a n d S p i e r r e , w h o w e r e w a l k i n g i n t h e w o o d s w h e n t h e y w e r e c o n f r o n t e d b y a h u g e a n d f i e r c e b e a r .

O n e o f t h e m ( w h i c h o n e ? ) s a i d t o h i s c o l l e a g u e ; "A b e a r ! L e t ' s r u n ! " T h e o t h e r r e s p o n d e d , s o m e w h a t p e d a n t i c a l l y , " Y o u c a n ' t r u n f a s t e r t h a n a b e a r . " T o w h i c h t h e f i r s t p h y s i c i s t r e p l i e d , " I d o n ' t h a v e t o r u n f a s t e r t h a n t h e b e a r , I h a v e t o r u n f a s t e r t h a n y o u . "

1 0 . T h e t h e o r y t a l k s w e r e a l l v e r y g o o d a n d w e w e r e i n s p i r e d b y P r o f e s s o r V e l t m a n ' s t e r s e A n g l o - S a x o n e x p l e t i v e i n h i s d e s c r i p t i o n o f t h e o r i e s o f a x i o n s , m o n o p o l e s , h i g g s , t e c h n i c o l o r a n d s u p e r s y m m e t r y .

I I I . A B i t o f H i s t o r y

T h e p o s s i b l e p r o o f o f t h e e x i s t e n c e o f t h e W c a n b e c o m p a r e d w i t h t h e p r e v i o u s p r e d i c t i o n a n d v e r i f i c a t i o n o f t h e e x i s t e n c e o f a n i n t e r m e d i a t e v e c t o r b o s o n : t h e p h o t o n . T h i s o b j e c t w a s p r e d i c t e d b y E i n s t e i n i n 1 9 0 5 a n d i t s v e r i f i c a t i o n t o o k p l a c e o v e r t h e p e r i o d 1 9 1 5 - 1 9 2 3 . T h e r e w a s m u c h r e s i s t a n c e a t t h a t t i m e . T h e W p r e d i c t i o n w a s i m p l i c i t i n F e r m i ' s t h e o r y o f w e a k i n t e r a c t i o n s i n ~ 1 9 3 0 f o l l o w e d m o r e e x p l i c i t l y b y Y u k a w a ' s i n t e r m e d i a t e o b j e c t a n d , w i t h i n c r e a s i n g e x p l i c i t n e s s , i n t h e p e r i o d o f 1 9 5 5 t o ~ 1 9 7 0 w i t h S c h w i n g e r , F e y n m a n * G e l l - M a n n , M a r s h a k , B l u d m a n , L e e a n d Y a n g a n d o t h e r s , s u r e l y - u p t o t h e W e i n b e r g - S a l a m - e l e c t r o w e a k t h e o r y . We e x p e r i m e n t a l i s t s m u s t b e i m p r e s s e d w i t h t h e l i s t o f o t h e r t h e o r e t i c a l p r e d i c t i o n s - s o m e o f t h e m a j o r o n e s b e i n g :

Y , v e , T W P, v ^ , * ° o n g , c , g , W , Z , . . .

H o w e v e r , w e s h o u l d r e c a l l t h a t t h e r e h a v e b e e n m a n y e x p e r i m e n t a l s u r p r i s e s :

e , u , n , N * , K , A , P , C a n d P C v i o l a t i o n s ,

T h i s i s r e v i e w e d i n o r d e r t o c a u t i o n ( p r o b a b l y n o t n e c e s s a r y ) t h e f o r t u n a t e o b s e r v e r s a t t h e S P S , i . e . , U A . w h e r e i = 1 , . . . n : L o o k f o r s u r p r i s e s !

T o e m p h a s i z e t h i s , I q u o t e T . D . L e e :

" E V E R Y N E W L Y O P E N E D D O M A I N O F E N E R G Y U N C O V E R E D U N A N T I C I P A T E D D I S C O V E R I E S , "

i . e . , " u n a n t i c i p a t e d " d u r i n g t h e d e s i g n a n d c o n s t r u c t i o n o f t h e r e l e v a n t a c c e l e r a t o r . I n t h e T a b l e , I i l l u s t r a t e t h i s t o t h e b e s t o f m y m e m o r y a s r e c o n s t r u c t e d l a s t n i g h t w i t h t h e l i m i t e d r e s o u r c e s a v a i l a b l e i n m y h o t e l r o o m .

T . D . L e e a n d I a n d , c l e a r l y , T i n i V e l t m a n a n d , d o u b t l e s s , m a n y o t h e r s w o u l d s t a t e t h a t t h e r e i s n o r e a s o n t o b e l i e v e t h a t t h i s h i s t o r y i s n o t a v a l i d g u i d e t o t h e f u t u r e . W h a t i s r e a l l y m i n d b o g g l i n g i s t h a t t h e o r e t i c a l p h y s i c s w i t h i t s e n o r m o u s r a n g e o f s p e c u l a t i o n , e n c o m p a s s i n g G r a n d U n i f i c a t i o n , S u p e r S y m m e t r y , T e c h n i c o l o r , e t c . , e t c . , c a n l e a v e a n y r o o m f o r u n a n t i c i p a t e d d i s c o v e r i e s ! T h i s w i l l s u r e l y t e s t t h e i m a g i n a t i o n a n d r e s o u r c e f u l n e s s o f t h e G r e a t C r e a t o r - I p e r s o n a l l y h a v e g r e a t c o n f i d e n c e i n H e r .

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p p a t S P S 1 9 8 2 1 5 0 , 0 0 0 540

- 578 -

I V . M a c h i n e - i n - t h e - D e s e r t

A s a p e r s p e c t i v e f r o m a c r o s s t h e w a t e r , I ' d l i k e t o p r e s e n t s o m e i d e a s w e h a v e b e e n d i s c u s s i n g i n t h e U . S . , a t o u r r e c e n t S n o w m a s s w o r k s h o p , a t F e r m i l a b , a n d w i t h o t h e r e x p e r t s i n U . S . l a b s .

S e v e r a l I C F A s t u d i e s h a v e o u t l i n e d t h e d e s i g n o f a 20 T e V h a d r o n c o l l i d e r - a c c e l e r a t o r . T h e y h a v e c o n c l u d e d t h a t t h e r e i s n o o b s t a c l e t o w a r d s t h e c o n s t r u c t i o n o f s u c h a n a c c e l e r a t o r e x c e p t c o s t - t h e e s t i m a t e s b a s e d u p o n p r o j e c t i o n s o f s u p e r c o n d u c t i n g m a g n e t t e c h n o l o g y h a v e b e e n i n t h e $ 2 - 3 b i l l i o n n e i g h b o r h o o d a n d , i n t h e l i g h t o f t h e w o r l d - w i d e e c o n o m i c p r o b l e m s , t h i s w a s d e e m e d t o r e q u i r e a n i n t e r n a t i o n a l e f f o r t . T w o p r o b l e m s b o t h e r e d u s - i ) t h e l o n g d e l a y b e f o r e a l l r e g i o n s a r e " r e a d y " t o j o i n i n , a n d i i ) t h e r e a l l y e n o r m o u s c o m p l e x i t y o f s u p e r c o n d u c t i n g m a g n e t t e c h n o l o g y ( a s s e e n f r o m o u r F e r m i l a b p e r s p e c t i v e , c l e a r l y , w e a r e m u c h t o o d e e p l y i n v o l v e d t o b e o b j e c t i v e ! ) .

T h e s e e l e m e n t s , w h e n c o u p l e d t o t h e a p p a r e n t r e m o t e n e s s o f e x o t i c f o r m s o f a c c e l e r a t i o n a n d o u r ( h u m a n ) i m p a t i e n c e t o g e t o n w i t h p h y s i c s l e a d u s t o t h e f o l l o w i n g q u e s t i o n :

I s i t p o s s i b l e t h a t o l d t e c h n o l o g y , i r o n m a g n e t s ( e n e r g i z e d b y s u p e r c o n d u c t o r s : s u p e r f e r r i c s ) c a n b e m o b i l i z e d w i t h a m o d e r n s y s t e m s a p p r o a c h t o r e d u c e c o s t s s o t h a t a 20 T e V h a d r o n c o l l i d e r c a n b e a f f o r d e d a s p a r t o f t h e n a t i o n a l p r o g r a m ? We d e c i d e d t o a t t a c k c o s t s o n a l l f r o n t s . We s t u d i e d t h e r e d u c t i o n i n t u n n e l c o s t s , i . e . r e p l a c e w i t h s h a l l o w t r e n c h e s . S i n c e t h e f i e l d s a r e l o w ( < 3 T ) t h e r i n g c i r c u m f e r e n c e w i l l b e ~ 1 5 0 k m . T h e s i t e m u s t b e f l a t , c h e a p a n d s p a r s e l y p o p u l a t e d , h e n c e t h e n a m e D e s e r t r o n .

T h e p h y s i c s j u s t i f i c a t i o n w a s e x p r e s s e d u n a n i m o u s l y b y o u r R o u n d T a b l e c h e v a l l i e r s a n d c a n b e a b b r e v i a t e d b y t h e o b s e r v a t i o n t h a t L E P , S L C , S P S ' s p p c o l l i d e r a n d T e V I w i l l a l l e x p l o r e t h e 1 0 0 - 4 0 0 G e V e f f e c t i v e m a s s d o m a i n . T h e n e x t s t e p m u s t c l e a r l y b e i n t h e 1 - 2 T e V d o m a i n a n d b y t h e u s u a l r u l e - t h i s i s a > 10 x 10 T e V p p c o l l i d e r . C a r l o R u b b i a r e m i n d e d u s o f o n e o f t h e m o s t o p e n q u e s t i o n s : W h a t i s i n s i d e t h e q u a r k ? W h a t i s i n s i d e t h e e l e c t r o n ?

W h a t s t e p s a r e b e i n g t a k e n t o s t u d y t h e r e a l i t y o f t h e p r o p o s a l ? R&D e f f o r t s a r e u n d e r w a y a t F e r m i l a b , L B L , L A S L a n d ANIi t o l o o k a t i n j e c t o r s , p r o t o t y p e s u p e r f e r r i c s a n d 1 0 T m a g n e t s ( f o r c o m p a r i s o n ) . I t i s c l e a r t h a t a r e a s o n a b l e t i m e s c a l e w o u l d r e q u i r e a c o o p e r a t i v e e f f o r t o f e x p e r t s f r o m m a n y l a b s . A s a f i r s t s t e p , M . T i g n e r a t C o r n e l l w i l l m a n a g e a w o r k s h o p t h i s S p r i n g t o a d d r e s s t h e q u e s t i o n :

- 5 7 9 -

" O n w h a t t i m e s c a l e c a n w e g a i n u s e f u l e x p e r i m e n t a l a c c e s s t o t h e 20 T e V CM e n e r g y d o m a i n g i v e n o u r p r e s e n t t e c h n o l o g i c a l c a p a b i l i t i e s a n d l i m i t a t i o n s ? "

T h e g o a l o f t h e W o r k s h o p w i l l b e t o d e f i n e t h e Rj&D a c h i e v e m e n t s n e c e s s a r y t o p e r m i t c o n s t r u c t i o n . F o r d e f i n i t e n e s s t h e p a r a m e t e r s a r e c o n s t r a i n e d :

20 < E < 40 T e V — c m —

1 0 3 1 < L < 1 0 3 3

P A C < 1 0 8 w a t t s

c o s t < 1 0 9 $

T h e g r e a t A m e r i c a n c a p i t a l i s t H e n r y F o r d g a v e a d v i c e t o p h y s i c i s t s t r y i n g t o " s e l l " t h e i r a c c e l e r a t o r s :

" . . . I f i r s t r e d u c e t h e p r i c e t o a p o i n t w h e r e I b e l i e v e . . . s a l e s w i l l r e s u l t . T h e n w e g o a h e a d a n d t r y t o m a k e t h e p r i c e . I d o n o t b o t h e r a b o u t c o s t s . T h e p r i c e f o r c e s t h e c o s t s d o w n . . . I c a n m a k e m o r e d i s c o v e r i e s c o n c e r n i n g m a n u f a c t u r i n g a n d s e l l i n g u n d e r t h i s m e t h o d t h a n b y a n y m e t h o d o f l e i s u r e l y i n v e s t i g a t i o n . '

My f i n a l w o r d i s t o a c k n o w l e d g e , o n b e h a l f o f a l l o f t h e p a r t i c i p a n t s , t h e e l e g a n c e a n d s k i l l o f o u r h o s t G i o r g i o S a l v i n i .

1. S u b t l e i s t h e L o r d . . . T h e S c i e n c e a n d L i f e o f A l b e r t E i n s t e i n , A . P a i s , O x f o r d P r e s s , N e w Y o r k , 1 9 8 2 .

2 . I n t e r m e d i a t e B o s o n s : W e a k I n t e r a c t i o n C a r r i e r s , P . Q . H u n g a n d C . Q u i g g , S c i e n c e 2 1 0 , p . 1 2 0 5 , 1 9 8 0

- 580 -

3RÖ TOPICAL LüOflKSHoP cu P-P COLLI OER fWiiej

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L I S T O F P A R T I C I P A N T S

G.ALTARELLI

E.AMALDI

L.ANGELINI

R.ANTHOINE

A•ASTBURY

C.BACCI

R.BARBIERI

G.BELLETTINI

R.BERNABEI

P.BLOCH

F.BONAUDI

K.BORER

B.BORGIA

A.BOTTINO

P.L.BRACCINI

G.BRIANTI

P.BUDINICH

I.BUTTERWORTH

N.CABIBBO

M.CALVETTI

L.CAMILLERI

S.CENTRO

F.CERADINI

R.CESTER-REGGE

D.CLINE

G.COCCONI

V.COCCONI

C.CONTA

M.CORDEN

J.CRONIN

S.CUNSOLO

P.DARRIULAT

S.D'ANGELO

Department of Physics, University of Rome, Italy.


Department of Physics, University of Bari, Italy.

CERN, Geneva, Switzerland.



Scuola Normale Superiore, Pisa, Italy.

Department of Physics, University of Pisa, Italy.


SEE/DphpE CEN SACLAY, Gif-sur-Yvette, France.


Laboratorium für Hochenergiephysik, Bern, Switzerland.


Department of Physics, University of Torino, Italy.

Laboratori Nazionali, San Piero a Grado, Pisa, Italy.


Intern. School Advanced Studies, Trieste, Italy.

Physics Department, Imperial College, London, England.




Department of Physics, University of Padova, Italy.


Department of Physics, University of Torino, Italy.




Department of Physics, University of Pavia, Italy.

Department of Physics, University of Birmingham, England.





- 5 8 2 -

V.DE ALPARO CERN, Geneva, Switzerland. T.DEL PRETE CERN, Geneva, Switzerland.

D.DI BITONTO CERN, Geneva, Switzerland.

A.DI CIACCIO Department of Physics, University of Rome, Italy. A.DI GIACOMO Department of Physics, University of Pisa, Italy. L.DI LELLA CERN, Geneva, Switzerland. G.DIAMBRINI Department of Physics, University of Rome, Italy.

K.EGGERT CERN, Geneva, Switzerland. G.EKSPONG Department of Physics, University of Stockholm, Sweden. H.FAISSNER Department of Physics, University of Aachen, Germany. D.FAVART Department of Physics, University of Louvaine La Neuve, Bel M.FRATERNALI Department of Physics, University of Pavia, Italy. E.GABATHÜLER CERN, Geneva, Switzerland. J.GAUDAEN CERN, Geneva, Switzerland. C.GHESQUIERE College de France, Paris, France. K.L.GIBONI CERN, Geneva, Switzerland. W.R.GIBSON Department of Physics, Queen Mary College, London, England.

A.GlVERNAUD CERN, Geneva, Switzerland. G.GOGGI Department of Physics, University of Pavia, Italy.

M.GOURDIN Department of Physics, University Paris VI, France. P.GRANNIS Department of Physics, University of Stony Brook, USA. M.GRECO CERN, Geneva, Switzerland. L.GUTAY Department of Physics, University of Purdue, USA.

J.R.HANSEN CERN, Geneva, Switzerland. P.H.HANSEN Niels Bohr Institute, Copenhagen, Denmark. C.A.HEUSCH Department of Physics, University of California, USA. D.HOFFMANN CERN, Geneva, Switzerland.

D.J.HOLTHUIZEN CERN, Geneva, Switzerland.

R.J.HOMER Rutherford Lab. Chilton, Didcot, England.

E.IAROCCI Laboratori Nazionali Frascati, INFN, Frascati, Italy. M.JACOB CERN, Geneva, Switzerland.

D.JOHNSON Fermi Nat. Acc. Lab., Batavia, USA. P.KALMUS Department of Physics, Queen Mary College, London, England.

R.K.KEELER CERN, Geneva, Switzerland. U.P.KENNEY Department of Physics, University of Cambridge, England.

I.R.KENYON Department of Physics, University of Birmingham, England.

- 5 8 3 -

D.KRYN CERN, Geneva, Switzerland.

L.M•LEDERHAN Fermi Nat. A c e Lab., Batavia, USA.

A.LEVEQUE CEN, SACLAY, Gif-sur-Yvette, France.

L.MAIANI Department of Physics, University of Rome, Italy.

A.MARTIN CERN, Geneva, Switzerland.

G.MATTHIAE Department of Physics, University of Napoli, Italy.

W.MAJEROTTO Institut für Hochenergiephysik, Wien, , Austria.

T.MCMAHON Compton, Newbury, Berks, England.

R.MEINKE CERN, Geneva, Switzerland.

M.N.MINARD LAPP, Acceny, France.

M.MORICCA Department of Physics, University of Rome, Italy.

T.MÜLLER CERN, Geneva, Switzerland.

Y.MURAKI Institute for Cosmic Rays, University of Tokyo, Japan.

A.K.NANDI Rutherford Lab. Chilton, Didcot, England.

B.NICOLESCU Institut de Physique Nucléaire, Orsay, France.

L.NITTI Department of Physics, University of Bari, Italy.

A.NORTON CERN, Geneva, Switzerland.

R.ODORICO Department of Physics, University of Bologna, Italy.

L.PANCHERI Laboratori Nazionali Frascati, INFN, Frascati, Italy.

L.PAOLUZI Department of Physics, University of Rome, Italy•

G.PIANO—MORTARI Department of Physics, University of Rome, Italy.

E.PREDAZZI Department of Physics, University of Torino, Italy.

M.PELLICORO Department of Physics, University of Bari, Italy.

L.PONDRON Department of Physics, University of Wisconsin, USA.

G.PREPARATA Department of Physics, University of Bari, Italy.

E.RADERMACHER CERN, Geneva, Switzerland.

T.REGGE Department of Physics, University of Torino, Italy.

H.REITHLER Department of Physics, University of Aachen, Germany.

J.P.REPELLIN CERN, Geneva, Switzerland.

J.P.REVOL CERN, Geneva, Switzerland.

J.ROHLF Department of Physics, University of Harvard, USA.

C.RUBBIA CERN, Geneva, Switzerland.

G.SALVINI Department of Physics, University of Rome, Italy.

J.SASS CERN, Geneva, Switzerland.

W.SCANDALE CERN, Geneva, Switzerland.

G.SETTE Department of Physics, University of Genova, Italy.

- 584 -

A.N.SILVERMAN Department of Physics, University of Cornell, USA.

M.D.SMITH CERN, Geneva, Switzerland.

M.SPIRO CEN, SACLAY, Gif-sur-Yvette, France.

Y.SRIVASTAVA Laboratori Nazionali Prascati, INFN, Frascati, Italy.

J.STRAUSS Institu für Hochenergiephysik, Wien, Austria.

C.TAO CERN, Geneva, Switzerland.

J.TEIGER SEE/DphpE, CEN, SACLAY, Gif-sur-Yvette, France.

A.V.TOLLESTRUP Fermi Nat. Acc. Lab., Batavia, USA.

V.TUOMINIEMI Department of Physics, University of Helsinky, Finland.

S.VAN DER MEER CERN, Geneva, Switzerland.

L.VAN HOVE CERN, Geneva, Switzerland.

M.VELTMAN Department of Physics, University of Michigan, USA.

V.VERCESI Department of Physics, University of Pavia, Italy.

J.VRANA College de France, Paris, France.

H.WAHL Institut für Hochenergiephysik, Wien , Austria.

D.WARD Cavendish Lab. University of Cambridge, England.

P.M.WATKINS Department of Physics, University of Birmingham, England.

XIE YI-GANG CERN, Geneva, Switzerland.

N.K.YAMDAGNI Department of Physics, University of Stockholm, Sweden.

A.ZICHICHI CERN, Geneva, Switzerland.

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THIRD TOPICAL WORKSHOP ON PROTON-ANTIPROTON …