- /'. //1 / ' '-~ c) ''{ "-' LI -.J -~r1 ~ ~ ~1'1'~''''~2'1~1 I

~

RECENT RESULTS FROM TRISTAN AT ( KEK

Shiro Suzuki�

Dept. of Physics, Nagoya University�

Foro-eIlo, Chikusa-ku, Nagoya 464-01, Japan� c·)

t"· .... ~,j

ABSTRACT Cv (.j

lLJRecent results of TRISTAN experiment with high luminosity run are t:::4 reviewed.

Upda.ted results on lepton and qua.rk pair production in the annihi­

Iatiopn processes are presented, and limits on the compositeness scale

and lower mass limit for extra Z boson a.re giv~n. Total hadronic cross

section is presented in the effective Born approxiamtion. A search for a

resonance suggested by L3 group is done in several different final states.

Strong coupling o. is derived from several observables with improved

theoretical framework. Running nature of a. is studied in comparison

with PEP4 and ALEPH data. Different property of quark and gluon

jet is examined. Ha.rd scattering of two photons are established and

the data provide information on quark and gluon distribution in the

photon.

Talk presented at the XXI SLAC Summer Institute on Pa.rticle Physics, Stanford,

California, July 26 • August 6, 1993 ~

{l~j ..,

1 Introduction

TRISTAN was comissioned in late 1986. It started up at the center of mass energy

of 50 GeV, and gradually ramped up to 64 GeV. Since 1990, after SLC and LEP

started operation at around 90 GcV, we set our operation encrgy at 58 GcV,

where we can expect high luminosity with much stable opearting condition. This

is also the energy region where we can observe la.rge interference effed of virtual

photon and ZO. After QCS insertion, current typical integrated luminosity per

day reaches to 800nb- l • Our goal is to collect 300pb- l in 2 years, and move

to TRISTAN-II, i.e. KEK asymmetricB-fa.ctory. Since the ma.chine has bccn

operated quite nicely for this one and a half years (fig. 1), we are quite confident

of achieving this value.

This report is based on the analysis work with the data sample of a.bout

100 '" 150pb-1 •

250

.0i TOPAZ.E: 200

>.... 'S1". ~ 100 'Q Ql... ld

~ 60 Ql.... .E

0 Hf9-O 1991 1992 1993

Figure 1: Accumulated integrated luminosity since 1987.

2 Electroweak Processes

First we present the updated results in the basic annihilation processes in the

interference regin of "1. and Zoo

2

_ _ _ _ _ _

Tahlel: Total cross sedion and forward-ba.ckward asymmetry of l(~pt.OlI {mir

production by three groups. Errors are quoted in the order of sta.tistir..s and

systematics.

.;s 1J+,r T+T- S.M.

GeV

TOPAZ 57.9 0.99 ± 0.03 ± 0.05 1.06 ± o.oa ± 0.05 1.0;':l

R VENUS 58.0 0.98 ± 0.02 ± 0.03 0.99 ± 0.03 ± 0.03 1.054

AMY 58.0 0.96 ± 0.03 ± 0.03 1.02 ± 0.03 ± 0.03 1.054

TOPAZ 57.9 -0.312 ± 0.025 ± 0.011 -0.313 ± 0.039 ± 0.010 -0.334

A VENUS 58.0 -0.320 ± 0.020 -0.300 ± 0.030 -0.338

AMY 58.0 -0.342 ± 0.024 ± 0.007 -0.337 ± 0.028 ± 0.014 -0.338

2.1 Lepton .pair production

The iotal cross section and forwa,rd-backward asymmetry of lepton pair produc­

tion reported from three groups are summarized in table 1. Still we ha.ve somewhat

lower cross scct.ion in '£+'1- and T+r- pair production than the standard model

expectation, but with Tlot much significance. On the other hand, asymmetry

shows good agreement with t:he standard mod<;l. Overall agreement of TRISTAN

aver~.ge data with the standard model is good (fig. 2).

flecause the data arc consistent with the standard model, we can place sev­

eral limits from its deviation. TRISTAN is in better position than SLC/LEP

for setting compositcnC'..5s limit becausc there is no amplitude saturat.ion by Zoo

From the angular distribution, ,we can set limit of the compositeness parameter

A as in table 2. They now exceed the previous TRISTAN, PEP arid PETRA

experiments.'

TRlSTAN is also in a good position of looking for extra Z bosons (Z'). With

high precision data, we can look for contribut.ion from Z' which interferes with Zoo

Fig. 3 shows a sensitivity of our measurement to the various types of Z', assuming

Mz• =150 GeV and no mixing. From ,these da.ta plus hadronic data from TOPAZ

expcriment,2 and also combining data from other TRISTAN experiments,3,.. we

slImmarisc the 95% C.L. mass limits of extra Z bosons5 associated with Ea ex­

tensions of the standard model(table 3), which are compa.red with the vahle from "

3

1000

500 4°tsJ30

+ -C e ... +­J.L It

• :D ..e:

100

50 20

Vl J:: 0 :;; 0 v : III 0 ....

10

1000

500 :Frl + -e e .... +­T T

v

]. 100 0 20~

E­ 50

10 40 60 80 100

EeN (GeV)

1.0 + - +­e e ... J.L J.L

0.5 -OT:sJ� -----=;:~ ~~-~-----------. u;p

0.0>. ........ OIll3 -0.5

III « III

~ -O.2CSJ +­-0.3 e e .... r+T­I ~ 0.5

=.::..!::....._-0.4 LEB 0.0 ----------­

-0.5

-1.0 40 60 80 100

ECN (GeV)

Figure 2: TRISTAN avera.ge of tota.l cross section and forwa.rd-backward asym­

metry of lepton pl'l.ir production. Data. from PETRA a.nd LEP are also plotted

for comparison.

4

Table 2: Limits on the compositeness scale in TeV at the 95% confidence level.

A+ / A-(TeV) e+C -+ J.l+J.l- e+e- -+ r+r- e+e- -+ /+/­

RR c01lpling > 2.1 /3.1 > 1.8/2.7 > 2.2/,tJ

LL > 2.1/3.0 > 1.7/2.6 > 2.2/3.9

VV > 11.2/3.4 > 3.5/4.3 > 7.1/4.2

AA > 3.1/7.0 > 2.7/3.9 > 3.2/8.7

JO

19 MZ'=l5OGeV :c'.e 11

.~ n -U ~u

::JfU U

H

·0.J2 ;.-.=".J.U ee ·0.36

~

...:

~

,'.31

1-. fz" ••••0

·O.U

.0.44,.' I , , I , , I ,

:15 56 57 58 59 60 61 61

Eat (GeV)

Figure 3: Scsitivity of lepton pair measurements to the existence of va.rious Z'S as

a. fundion of ECM ' where Mz,=150GeV is assumed with no Z' - ZO mixing. The

data points are from TOPAZ with J.l and r combined.

Table 3: The 95% C.L. lower limits for various Z's with a comparison to pp data.

Mz, limit (GcV) Zl ZvZ'" Z" Z" TOPAZ > 290 > 146 > 134 > 100 > 164

TRISTAN all > 430 > 166 > 245 > 145 > 196

CDF(pfi ) > 412 > 320 > 340 > 340 -­

CDF collaboration.6

2.2 Total hadronic cross section

Our traditional way of presenting RhfJd data was to derive 'trce level' cross section

by making electroweak radiative correction up to 2nd order. With tha.t method

we were not free from a few % uncertainty in the higher order correction ('short

distance effect'), for instance, the effect of unknown parameters such as Mtop and

Mhigg3' Also a big problem was that the presented 'expcrimantal' data. could not

simply be compared with others if different correction models were taken.

New method which have been adopted by LEP group is only to make QED

correction up to 2nd order, which can be ca.Jculated accurately, and leave other

'short distance' correction untouched ('effective Born' approximation). Effective

cross section by this correction scheme, which is free from higher order ambigu­

ity, is to be compared with theoretical calculation in which all 'short distance'

phenomena are included., Then the definition of corrected experimental data will

not be changed group by group, since 1 +6QED is well defined quantity. Another

merit of taking this method for us is capability of direct comparison with the LEP

data. We used the I<ORALZ program7 to calcula.te the ra.diative corrccti011s up

to O(a2) with exponentiation of leading logarithm effect. TOPAZ data is shown

in figA utilising this correction scheme. Highest statistics data at 58 GeV gives

u eJJ = 143.8 ±1.5 (stat.) ±'S.4 (sys.) pb for an integrated luminosity of 85.5pb-1•

This is a good a.greement with the expectation value of Jt12.0pb for the S.M. with

Mz=91.13GeV, Mtop =150GeV and Mhigg.=100GeV.

In the S.M. framework, we can determine the running QED coupling a. The

gotten value a;Ji = 128.6 ± 2.6 at Q2 = 582GeV2 also agrees well with the

expectation of 129.8 from the S.M.

65

~ 104

'. :~~~ 1\ jr:t 0 :;: 0 41 103 III

:0-

OJ \~". 00III III ~0 H 0 +PETRA .. ~ .... 102 0

E-o

101 20 40 60 80 100

ECII (GeV)

Figure 4: Comparison of the total hadronic cross section with effective Born cross

section and lowest order EW cross section of the standard model.

2.3 D* production

Forward-backward asymmcty of charm pair productin was measured by detect,ing

fast going D- in the jets.

One method is to look for mass difference b.M = Mh - MD, which gives very

sharp peak due to small Q-value of D- ..... D7r decay. t:1M for several different D

final stat(',S are shown in fig. 5(a)-(c). Combination of (a)-(e) is shown in fig. 5(d),

where the histogram underneath is estimated background. Angular distribution

thus determined is compared with the standard model (fig. 6). Asymmetry ACf is

-0.57 ± 0.22 ± 0.05 by VENUS8 and -O.50!~:: ± 0.08 by TOPAZ.9

Another method is to detect inclusive soft 'If from D- decay. Small Q-va.lue

gives very sharp peak at low Pc distribution, 40 MeVIe at most, with respect to

the jet a.xis (see fig. 7). By this method, we got AFB = -0.49 ± 0.15 ± 0.08 from

TOPAZ,9 -0.73!~:~ from VENUS8 and -0.67 ± 0.20 from AMY.t°

Hcsults combining above measurement, C-C asymmetry are plotted in fig. 8

together wit.h the results from other laboratories with different center of mass

energies. This shows overall good a.greement with the S.M.

Also bb asymmetry is shown in fig.9 for reference.

7

~ I ...l:ir ~ .01 D--lr t

J 1!010

... ...uJ .n

SN 10

.r!

.!

Figure 5: Mass difference AM = Mb-MD mC'A\Surcd by VENUS collaboration for

D-* -+ 1r'!= DO(DO) following DO(VO) ..... J('f 7r* (a), J('f 7r±1r0 (b) and J('f 1r*7r* 7r'f

(c). Combined result is shown in (d). The dotted line underneath is estimated

background.

40, iiI • , , , ii' i I I , , i

30

'c ::J

Figure 6: Angular distribution of charm quark pair production m('..as\lrcd by Jr%s

with the AM = MiJ - MD method (VENUS).

8

250 .. 250 .......� 0 t (a) t (b) .......�

200 ~ 200 .........� .... "�

150 g 150 d

100 "2100 .,c::>�

50 -I.LJ 50� 0�

o .8 '-

0 E ~ I ::J

-50 z -50 0 0.020.04 0.060.08

Figure 7: p: distributions of 1r±S in (a) forward and (b) backward angular regions.

Dots are the experimental data after subtracting estimated backgrounds.

0.25

0,00

III -0.25 <

+HRS D' -0.50 l-><TPC e".

.TPC D' OIADE .,. +JADE D·

-0.75 !-w1ASSO. OAlDll e". +TASSO D' XILUUU IA

-1.00" ataJ,O _/I ! t I! ! J I , , ! I ! , I ! !

20 40 60 80 100 (VS)(GeV)

Figure 8: Ac~ by various measurement methods a.nd experimental groups. Curve

presents the prediction of the standard model.

9

0.5

Ie AllY ". • TOPAZ .,,,.

• y'!;~.S.+l ....0.0

1..0 J:>

~

x OPAL(}.&)-0.5 + L3(.,II)

o WARIC1(P) Ie ALEPH(e.p..Jet)

x CELLO(.,II) o TASSO(e.p.,J.t) + IADE(••II)

-1.0 I , " I""',,, " I I I I

20 40 60 60 100

-IS (GeV)

Figure 9: Summary of Ab~ by various groups and labs. The solid curve shows the

standard model with no BB mixing, and the dashed curve shows the ca.se with

Xd = 0,17 and x. = 0.5.

3 Search for a resonance

Last year, excess of" distribution around 59 GeV in /+/-" events was reported

by L3 group.ll This excess could be a non-higgs like pa.rticle with mass 59GcV/ c2,

which has Ia.rge branching fraction to l' final state and spin 0 or 2 or more (sca.lar

or tensor). If it is a new boson 'X' couples to e+e-, we could be very much sensitive

to this state even if its tot~1 width is very narrow, We carried out energy scan

to search for X in the final states of "1'''(; e+e-, p.+/,,- and hadrons in the energy

range of 58 to 60 GeV with 250MeV step, with integrated luminosity of more than

Iplr l at each scan point. Sincc the energy sprea.d of TRISTAN beam is about

tOOMeY in 0', the sensitivity is continuous with energy and has no gaps in this

energy range.

l~ig.lO shows t.he result.s (rom VENUS 17 .and AMylJ (or" a.nd c+c- flnal

stateS. Solid lines are the S.M. prediction, and dotted or dashed lines are with

hypothetical resonance with small coupling. AMY results gives smaller X2 with a

resonance, but with less significance. TOPAZ results for several final states1" are

shown in fig.ll(a). VENUS, AMY and TOPAZ data do not show discrepancies

(rom the S.M. prediction.

10

0.75

Icos81 < 0.743 VENUS 600 I I iii

e+e-� ... e+e­

400tl • ~ • • •0 , I • ast A.f 1• 0 Cl I

200 7i ~ ........� o� J 100 o

b

50 fI 9 I • t x' i • 8. l', + I) _ 1

58 59 60 61

(GeV)ECK

1.'75 Iii , , i , i , iii , i , ,

---QED only ------QED + Resonance

1.50

~ 1.25 Z

~

Z 1.00 10- F::1:f t BZ: I 1 I -.........:i, :I�

O.&06~

I

Figure 10: Scan results by VENUS (top fig.) and AMY (bottom fig.).

r:- 80 I-� "17700.-.. V~ 60 ,.e 50 0 (.I� 40�

30�~ • I ha ~ rons180�JA' 160�b.e 140

120

,i. 100~ co� e+e­r: 500�

~.-.. 450� 400�

0 ..... 350 (.I 300

.~+~-50 " Ii� "0 30

b ..... 20� 10�

L..-..--..L.

57� 58 59 ECII (CeV)

Bcalar 10.0 5.0

1.0 0.5r

..:l� ~ 50�

I� III�.. III 10

5iii d

1.a0

CI 103 .cl

102~

I >< " 101

Ar >'� 100

:! ~ 10.0 ..... 5.0

1.0 0.5

0.1 5'7� 58 59

Wx (GeV)

Figure 11: (a) Scan results of TOPAZ in the final states of ii, hadrons, e+e- and

/,+/,-, a.nd (b) 95% C.L. upper limit or fee' 8r(X -+ "'I"'I,hadron,s,ee,p/,).

1211

Table 4: 95% C.L. limit for the case of broa.d resonance, assuming M x = 58GeV

and fTOT =lGeV.

Scalar Tensor

fee' Dr(X -. "Y"Y) < 8.9 keY < 0.05 keY

fee' Br(X -. had) < 11.6 keY < 2.6 keY

r.~e .Dr(X -. ee) < 22.9 keV < 13.2 keY

f ce • Dr{X -. I&}&) < 5.3 keY < 1.4 keY

We can set limits on the fcc x branching fmction for narrow resonance based

on the formula;

J 21r2

O'readW = (2J +1)-2 f ce ' Br(X -. i"Y, ..etc.). mx

We assumed rIat detector a.cceptance for scalar particle. For tensor particle, we

took calculation by lIagiwara et alY; (KEK theory group) for the determination

of angular acceptance. Production cross section of tensor particle is simply 5

times of scalar particle except for the e+ e- final Rtate. In fig. 11 (b) IimitR given

by TOPAZ1'I arc shown. Typi~ally, limit of f ce ' Br{X -. "Y"Y) is around 0.3 to 1.0

keV in this region.

In the case of very broad resonance, our limit is somewhat larger, but on the

other hand, our sensitive area is extended outside the scanned area due to its

broadness. In general, for broa.d resonance, the limit is a few times larger than

the case of na.rrow resonance (table 4).

Concludingly, no significant evidence has been found in those reactions for

hypothetical particle'X' suggested by L3, and the measurements are all consistent

with the standard model.

13

-QeD . ... Abelian

AMY VENUS I I TOPAZ

o 0.2 0.4 0.6 o.e o 0.2 0.. 0.6 0.8 1 0 0.2 0.4 0.6 0.6 1

COs8NR•

Figure 12: Angular distribution of 4-jcl. events compared to QeD and Abelian

models.

4 QeD studies

4.1 Gluon self coupling

The triplc gluon coupling is a unique propert.y of t.he non-Abelia.n nature of QCD.

Measurement of the triple coupling was pioneered by AMY group16 at TRISTAN.

Now we have an order of magnitude larger sample of events than tha.t t.ime, we

Can verify it with much accuracy. The triple gluon coupling is effectively studied

by the angular distribution of 4-jet events, extracting the contribution of the

radiated gluon splits to two gluonsY Severa.l testing quantities are defined by 4

jet momentum vectors Pl> P2, Pa, ii4 whose suffix numbers are ordered a.ccording to

the jet energies. For example, O'NR is the angle between Pl - fiz and Pa - fi.t.18 The

results from 3 groups are shown in 11g.12 comparcd with QCD and Abelian models.

AMY's pioneering work was confirmed by a.ll groups with higher statistics. From

those results, Abelian model is excluded a.t more than 99% confidence level.

4.2 Measurernent of as with less ambiguity

Perturbative QCD predicts running coupling o~ with momentum transfer Q2. It is

importa.nt to measure ex, with less uncertainty a.t different energy, and sec how it

runs. PEP-4, TOPAZ and ALEPH groups a.greed to push a joint analysis program

of ex, mcarsurement with the same method to explore the energy dependence (PTA

collaboration).

11

It. is important to note tha.t the measuring a.ccuracy of 0, is not bound by

sta.t.istics, but bound by systematic error a.nd theoretical ambiguity. Recently

there arc severa.l theoretical progresses in calculating 0, from experimental data..

One is NLL (Next to Leading Log) parton shower program by Kato and Mune­

hisa.19 from TRISTAN theory group. Because AMS is arbitrary in Leading Log

Approximation, we have to go to Next to Leading Log Approximation in defining

Am· Another method is called as 'resummcd formula', which analytically calcu­

la.tes various observables up to complete second order a" and a resummation of

the leading a.nd next to leading logarithms t.o all orders of 0, is done. This Wi\.S

applied to the recent LEP experiments.2G--22

Hcre we like to present the analysis done by TOPAZ groupH which is a

typical example of these works in TRISTAN. We obtained a, from thrust (T),

heavy jet mass (p = (Mt:~tJy/ ElJi,)2) and differential jet rate (113)' Mt:~lJ'II is

the heavier jet invariant mass in two hemispheres separated by a perpendicular

plane to T a.xis. Y3 is defined i\.S the smallest va.lue of jet resolution parame­

ter Yij = 2[Min(E?, EJ)](l - cos Oi,)/E~i, which recognizes the three separated

jets with Durham jet clustering algorithm.23 These variables are supposed to be

collinear Sil.rC, a.nd give close values for parton level and hadron level distribution.

Comparison is done betwccn acceptance correctcd experimental data and cal­

culated particle distribution afterhadronized and smeared by Monte Carlo (see

fig.13). Fit is done in the region where hadron/pa.rton correction is small. Solid

hist.ograms show the fit by NLLjct Monte Carlo, and smooth curves show tIlC fit

by resummed formula. Best fit values for o. for each observablcs and theoretical

method are summarised in table 5.

Syst.crnal,ic crror in NLLjet method mainly comes from cut ofT para.meter Qo

in thc fragmentation model. Main source of the systematic error in the rcsummcc!

formula arc theoretical uncertainty in matching linear or log in the resummation

process, and scale parameter dependence which is small but still remains. We have

changcd In(p,1'/s) from -1 to I, and the difference is included in the syst.ematic

error.

Comparison of TOPAZ and AMY results with similar method at 58 GeV is

given in fig.14. Preliminary result of PTA collabora.tion at different energies with

resummed formula is summarized in fig.lS. At this moment, Am = 364 MeV fits

well with the results of 3 groups.

15

~

~

.e:. I'l c:l 0 '­'d II =

H 'd "­b 'd

b "­.....

~

~

Po ";; d 0

~

III:x:

...:l "0 "­b "d

b "­.....

1.6 1.4 1.2 1.0 0.6 0.6

0.4

0.2

0.0 I

1.6 1.4 1.2 1.0 0.8 0.6

0.3

0.2

0.1

0.0

III� I'l� 1.60

1.4~ 1.2Po "- 1.0 !II I'l o.n ..0 0.6 'd Cl 0.6a) :I:

>-l "0 0.4"­b

"0

b "­..... 0.2

I I I I I I tn.I

234 5 2 3 4

L = -In(l-T) L = -In p

2 4 6 8�

L = -In Y3�

Figure 13: T,p and Y3 distributions compa.red to NLLjet (solid histograms) and

resummation method (smooth curve) a.t ECM = 58GcV.

16

Table 5: The fitLing results of a,(58GeV) from T, p and Y3 by NLLjct and rcsum­

mation method.

Method obs. a.(58GcV) stat. expo ha.dr. theor.

T 0.1249 ±0.0050 ±0.OO12 ±0.OO35 ±O.0029

NLLjet p 0.1235 ±0.O059 ±O.OO06 ±0.0013 ±0.OO36

0.1309 ±0.OO50 ±O.0024 ±O.OO26 ±O.OI03 +0.0070

Y3

T 0.1339 ±O.0040 ±0.OOO8 ±O.OO22 -D.0059 +0.0057resum. p 0.1287 ±0.OO41 ±O.OO05 ±O.OO20� -0.0046 +0.00550.1322 ±0.OO56 ±O.OO25 ±O.OOlOY3� -0.0041

~ AMY thrust. /resummed'

~ AMY Jel momenls/NLLJet.

~ AMY jet. rale /NIJ.Jet.

AMY thrust /NLLjet.

TOPAZ Jet. rat.e /resummed

~

TOPAZ jet. mass Irosummed

TOPAZ t.hrust. /rellummed

TOPAZ Jet rate /NLLjet

I---e-i TOPAZ Jet. mass /NLLJet.

~ TOPAZ t.hrust /NLLjel

I I ! , I I I ! I I . ! ! I I I I I I I I • ! ! I 0.1 0.125 0.15 0.175 0.2 0.225

oll(q2=582GeV2)

Figure 14: Comparison of a. value measured by TOPAZ and AMY with several

different methods.

17

0.20 ", ii' , I , I ' , iii iii iii iii iii i

x Thrust o Differential 2-jet ratio o Heavy jet mass

O.lB

IIne...An = 364 },jeV

0.16 OJ

c:s

A. a 500 MeV 0.14

0.12 f- An = 200 MeV

0.10 ••• I ! I I ! , , , I� I • , i ' I • , I I I IIi II i

20 40 60 60 100 120

Ecm (GeV)

Figure 15: Preliminary result on ECM dependence of 0', by PTA collaboration.

4.3 Property of glUOll jet

In QCD, gluons ha.ve larger color charge than quarks. According to the AllardJi­

Parisp5 splitting kernels, the ra.tio of gluon to quark bremsstrahlung probability

ill roughly 9/4. Therefore, gluon jet is expected to have higher multiplicity, a.nd

consequently has softer particle distribution than a quark jet.

VENUS group26 tried to'derive the pa.rticle spectra for gluon jets by comparing

the spectra of two types of event sample; (i) three-fold symmetric ('Mercedes like')

:I jet eventll (qqg sample), and (ii) three-fold symmetric 2 jets + 'Y events (qq("()

sample), where'Y was emitted by initial state radiation towards the beam pipe and

undetected. Since the two qua.rk jets in the qqg sample are identica.J to the qq( 'Y)

sample topology, definite comparison between gluon jet and quark jet is possible

in the same detector and the same kinematical condition.

Common requirements to the 3-jet and 2-jet, + 'Y sample is that the tota.l

energy should be la.rger than 5 GeV, no hard "I emittion in the a.ctive region of

Lile dcLedor,:J allglcs betwccn jets (or "I) arc in between 100° and HO°, a.nd toLal

of these angles is larger than 3580 For qqg candidate, visible energy should be •

18

la.rger tha.n 1/2 of collision energy and momentum should be balanced. For qq(-y)�candidat.e, visibl<l energy should be more than J/:1 of collision en<lrgy, and requires�momentum balance should be between 0.3 and 0.7, which mea.ns "t escapes in the 1000�beam pipe. After those selections are done, averaged jet energy is around 19 GeV cal (bl�

for both candidat.es. \ --+~\00 -----::t+�In qq(-y) sample, jets arc supposed to be purely quark jet. On the other�!liI.nd, in qqg sctmplc, 1/3 of jets are from gluon and 2/3 arc from quark. For <~ach

\:) ...... 10 +=f,.,�

"''''sample, fra.ctional momentum (xp) distribution of the charged particles arc plotted 't...... b'§

...in fig.16{a). Significa.nt deviation ca.n be observed between two distributions. The ... ;i;i..�

contribution from the ghlOn jets can be extra.cted by a waigh ted subtraction of�qij(-y) sample from qqg samplc as shown in flg.16(b). Assuming qq(-y) sample t.o

0.\

be a. purely quark jet, we can clearly soo that gluon jet is significantly softer than 0.0\quark jet. 0.0\ 0.\ 0.0\ 0.1

Another wa.y to present the difference is to calculate the following ratio R(x,,); Xp

R{x ) = !_1_ d<T(qq9)/! 1 dO'(qq(-y» Figure 16: (a) Xp

distributions for qq9 (open circles) and qq(-y) (solid circles)p 3 O'tot X 2 utotqqg" qq(-y) x" • sample. The prediction of the PS model are shown with a solid (dashed) curve

This ratio is plotted in fig.l i together with the prediction of the various Monte for qqg (qq(;» sampl~. (b) The extra.cted x" dist.ributions for gluon jets (open�

Ca.rlo models. Aga.in it shows that the gluon jets arc softer than the quark jets, circles) and for quark jets (solid circlcs).� (l,nd a.lso t.hat. the parton shower model agrees well with the experimcnt.�

5 . Two photon process

5.1 Inclusive jet production 1.5

It has been known27,28 that the hadron production in "t'Y process is not completely

explained by Vcctor Domin(l,ncc Model (VOM) and Qllil,rk Part.on Model (QPM). PSDrees et al. 29 mentioned that hadronic component of "t plays an important role -­

in hadron production in the high energy "t"t processes, and multi-jet events are 0.5

expected (fig.l8). In resolved photon processes shown in fig.l8, one or two specta­ 01tor jets are produced predominantly along the beam direction. Those events will o 0.25 0.5 0.75 I.

provide us information on gluon density in the photon as well as quark density, xp

which are ambiguous at present and several models give quite different distribu­ Figure 17: The ratio R(xp ) V.s. Xp together with several model predictions.tion functions especially for gluons (fig.19). TRISTAN energy region starts to bedomina.ted by hard sca.ttering of photons.

19 20

0) bl - -" ~...� jel

e- ~ e+Tr.� : + crossed -~-~ ~

e' e+�

cl� jet e-� <J). jet

e- '¥-.-£ ~

-~ ~

e+

d) jet e- spectOfor <f).. •

G+j~t•• ~..L....V--i~

spectotor q ~ jet

e+

Figure 18: Diagrams and the final state event topology for (a) the YOM, (b)

the QPM (direct), and examples of (c) single resolved and (d) double resolved

processes.

Q2=10.{GeV/c)2 100

'h 10- 1�

.<� 0­M

10-2

10-3

0.2� 0.4 0.8 0.8

X

Figure 19: Comparison or the gluon distribution fundion in the photon by va.rious

for the DG and LACI, LAC2 and LAC3 models at Q2 = lO(GeVIc)2. The solid,

dolt-dashed, dashed and dotted curves represent the LACI, LAC2, LAC3 and OG

models, respectively.

..

.. I t

Lj .

.. ,'­_ _ t .

~ .. ~ ..

..~•D" D.' ... ... ThruaL

Figure 20: Thrust distribution for the events with p~e' > 3GeVIe, compared with

(i) VOM+QPM (dotted), (ii) VDM+QPM+MJET (solid) for DG pa.rton den­

sity with P.pi"=1.6GeVIe, (iii) VDM+QPM+MJET (dot-dashed) for 00 with

PT""=2.4GeVIe, and (iv) VOM+QPM+MJET (dashed) with no gluon contribu­

tion.

AMY group30 demonstrated the hard scattering of photons in thrust distribu­

tion from notag "11 events with ';';' > 3GeVIe, which is .compared with YOM,

QPM, and Multi-JET (MJET) model with and without taking care of gluon con­

tent of the photon (fig.20). Contribution of MJET with gluon is evident.

TOPAZgroup31 tried to define a jet as a cluster comprising particles inside a'

unit circle on pseudorapidiLy ('1 == -In tan(012» and azimuthal angle (4)) plane.

Par~icle i is included in a jet J if (fJ. - T/J)2 + (4), - 4>J)2 < 1. This jet clustering

method has been used for hadron cO]]jder experiments, which is also suitable for

this case since a high PT jet (~;t > 2.5GeV/c in this case) can be well separated

from the remnant spectator jets in the '1 - ,plane. A typica.l 2-jct event is shown

in fig.21.

To make direct quantitati,ve comparison with theoretical prediction, jet inclu­

sive cross sections are defined as follows;

. dtT dcr(ljct) == 1+o~7 dfJ111l d'12 dTf dT/2 Pt

dpt -O.T l d

21� 22

~ II III I�

Figure 21: Lego plot of the typical 2-jet event in the." - if> pla.ne.

for c-c+ -t c-e+ + jet + X, and

1 7du(2jets) _1+0. 1+0. du"-'-----'- = d'11 d'12--~

dPI -0.7 -0.7 d'11 d'12dpt

for c- c+ -t c- e+ + jet + jet + X. In fig.22, inclusive one jet and two jet cross

section' as a function of rl;t for the pseudorapidity interval 1711 < 0.7 are compared

wit.h direct only process (VDM+QPM) and various hard scatteing model with

different assumptions on gluon density distribution (11g.19). In the two-photon

process, PT distribution is sensitive to parton distribution at relatively larger x

region (x > 0.1). This is complementa.ry to the ep collision experiment at HER.A

which is sensitive to very small x region, say x < 0.02. From comparison with

the data, LAC3,32 D033+ VMD and DG without gluon34 contribution are excluded

and DG with gluon,34 LACI and LAC2J2 are acceptable. Detailed information on

the gluon density distribution in the photon will he revealed by further study of

"Y"Y hard scattering processes.

5.2 cc production in two-photon collision

cc production in 'Y'Y process also provide us information OTI parton distribution in

the photon (fig.23).

VENUS tried this by inclusive e- detection with lead glass Ccrcnkov countcr

a.nd transition radiation detector, and obtained 93 candidate events in the kinemti­

cal region of 0.8 < p < 4.0GeVIc and Icos 01 < 0.68. Background subtraction were

done by two different methods, (i) using vetex chamber information and (ii) us­

23

8+8- --> 8+e- + jel + X '>' lOS

TOPAZ lP

CJ "'­ V8= 56 GeV ,D Po ... : Dola

11]1 < 0.7 102 QI.PTI

~.. , .... .... .... • "110__ ~

~

'b' 101 'C

100 ­3 4 5 6 7 8

PT (GeV)

8+8- --> 8+e- + jel + jel + X TOPAZ

~. r V9= 58 GeV~ 102 .0 + :Dale.Po "

111 .1.11121 < 0.7 QI.PTI

101 ~KJ'

~

~

'd 10°

10-1 3 5 6 7 8"�

P'l' (GeV)

Figurc 22: Inclusive (a) onc jet" and (b) two jet cross section as a function of

the jet transverse momentum. Data are compared with DG (with and without

gluon)" LACl, LAC2, LAC3 a.nd DO+VMD.

24

6

~ ro i

):)=:+ ~

Figure 23: Charm pair prodction mechanism in "1"1 collision.

ing impa.ct pa.ra.meter distribution, which give 50.0 ± 11.7 events and 41.9 ± 12.5

ebvcnts, respectively. Both are 2-3 times larger than the calculation by VDM + QPM.+ 1 resolved processes, which gives 16.7 ± 1.3 events.

Another method is to identify n* by mass difference method liM = MiJ ­

MD in various exclusivc decay channels35 (fig.24(a)). Cross section is plotted in

fig.24(b) together with prediction by QVM + QPM + MJET model with rea­

sonable assumption of gluon density. Cross section for 2.6 < Pc < 6.4 GeV is

19.8 ± 7.0 ph, which is about a.s twioo as the expected valuc 9.0 ph. This is lUI

excess of more than 10 pb, and parametrization in the resolved process, which is

most ambiguous at this moment, can count f9r 2",.3 ph, hut this excess is much

more than that.

There are still large ambiguity in calculating QCD processes in the two photon

collision, and the apparent excess of charm events could be explained by those

effects. If QCD processes are not enough to fill the gap, we may have to consider

somc new process, for example, production of light scalar top with mass around

15-25 GeV, which dominantly decays to c + Zt. This excess should be checked

further at various final states and with much high statistics.

Summary and Future Prospects

Test of electroweak theory in I-Z interference region was improved in both lepton

and quark sectors. Heavy neutral boson suggested by L3 data was searched in the

mass range of 58-60 GeV. No anomalous signal was observed, leading to limits

on partial decay width.

25

~: ~ ~ ~ 7 ~ JO ~ 6 ~

i ; ~~ n~ :~

b

;~" VV, I ,,~ • J '0

'0' o 0.14 OJ, OJ6 fJJ7 2 J -4 j 6

Mml ()i//~,«IttI« (G~V) Pl (GeV)

Figure 24: (a) Mass difference liM = MiJ - MD shows n* signal in two photon

process. (b) Differentia] cross section dq(D*Z)/dpc.

Triple gluon coupling was established. Strong coupling Q, was measured by .

several ohservables in the theoretical framework with less uncertainty. Running

nature of 0'. was tested in comparison with PEP and LEP data. Significant

dilTcrene<: was observed in x p spectrum for 3-folcJ symmetric qqg and q(lb) sample,

implying gluon jets were softer than quark jets.

Ha.rd scattering of photons was confirmed in "11 processes, wich carriy infor­

mations on quark/gluon distribution in the photon. Excess of cc production in

21 process were seen, which could be a.ttributed to QeD effect still having large

uncertainty or some new physics.

More precise results with high integrated luminosity will extend our search area

for compositeness and Z'. Also precision test of QED will be made in e+e- ~

e+c- and "'1"'1 processcs. Joint PTA (',oJJaboration will cover much more subjects

such as soft QCD and two photon physics. In two photon prcesscs, we will have

better understanding of quark/gluon distribution in the p~oton. We also need

this knowledge to reveal what is happcning in cC production in the "'II process.

Results with JLdt ~ 300pb-1 will be available soon, and we hope this will

allow us to have deeper understanding on these subjects.

26

References

[1]� Particle data group, Phys. Rev. D45 (1992) IX.12

[2]� Topaz Collab., I. Adachi ct a.I., Phys. Lett. 234B (1990) 525, Phys. Lett. 25513�

(HHll) (il3�

[3]� VENUS Collab., K. Abe et al., Phys. Lett. 246B (1990) 297, Phys. Lett.�

234B (1990) 382, Z. Phys. 48C (1990) 13; H. Yoshida. et al., Phys. Lett. 198B�

(1987) 570�

[4]� AMY Collab., T. Kumita et aI., Phys. Rev. D42 (1990) 1339,; T. Mori ct aI.,�

Phys. Lett. 218B (1989) 499; A. Bacala ~t al., Phys. Lett. 198B (1989) 112�

[5J Part,ide data group, Phys. Rev. IH5 (1992) V.H�

[6]� COF Collab., F. Abe et al., Phys. Rev. Lett. 68 (1992) 1463�

[7]� S. Jada.ch et at, Camp. Phys. Comm. 66 (1991) 276�

[8]� VENUS Collab., F. Hinode et al., Phys. Lett. 313B (1993) 245�

[9] TOPAZ Collah., E. Nakano ct aI., Phys. Lett. 3143 (1993) 471�

[10J AMY Collab., LiYu Zhcng et aI., Proceedings of the Workshop on TRISTAN�

Physics at High Luminosity p.265, I<EK Proceedings 93-2�

[11) L3 ~ol1a.b., O. Adriani et al., Phys. Lett. 295B (1992) 337�

[12) VENUS Colla.b., 1<. Abe et at, Phys. Lett. 302B (1993) 119�

[13) AMY CoUab., K. L. Sterner et a.1., Phys. Lett. 303B (1993) 385�

[14) TOPAZ Collab., K. Abe et al., Phys. Lett. 304B (1993) 373�

[15) K. Hagiwara et a1., I<EK Preprint 92-202�

(16) AMY Collab., I. H. Park et al., Phys. Rev. Lett. 62 (1989) 423�

[17) M. Bengtsson and P. Zcrwas, Phys. lett. 208B (1988) 306�

[18]� O. Nachtmann and A. Reiter, Z. Phys. 16C (1982) 45�

[19]� K. Kato and T. Mllnchisa, Phys. Rev. 039 (1989) 156, Camp. Phys. ComTn.�

64 (1991) 67�

[20]� L3 Collab., O. Adriani et aI., Phys. Lett. 284B (1992) 471�

[21]� ALEPH Collab., O. Decamp et at, Phys. Lett. 284B (1992) 163�

27�

[22) OPAL Collab., P. D. Acton et aI., Z. Phys. C55 (1991) 1�

[231 S. Catani, Yu. L. Ookshitzcr, M. Olsson, G. Turrock and B. W. Webber,�

Phys. Lett. 269B (1991) 432�

(24)� TOPAZ Collah., Y. OhniRh et al, Phys. Lett. 31:10 (1993) 475�

{25} G. Altareli and G. Pa.risi, Nucl. Phys. B126 (1977) 298�

[26J VENUS Collab., H. Takaki et al., Phys. Rev. Lett. 71 (1993) 38�

[27] PLUTO Collab., Ch. Berger et a1., Z. Phys. C33 (1987) 351�

[28J TPCj2"t Collab., H. Aihara et al. , Phys. Rev. 041 (1990) 2667�

(29J M. Drees and R. H. -Godbole, Nucl. Phy~. B33!> (1990) 355�

[30]� AMY Collab., R. Tana.ka et al., Phys. Lett. 277B (1992) 215�

[31] TOPAZ Collab., H.Hayashii et a1., Phys. Lett. 314B (1993) 149�

[32J A. Ley, H. Abramwics and K. Charchula, Phys. Lett. 269B (1991) 458�

[33]� D. W. Duke and .J. F. Owens, Phys. Rev. D26 (1982) 1600�

[34]� M. Drees an"d I<. Grassic, Z. Phys. C28 (1985) 451�

[35]� TOPAZ Collab., R. Enomoto ct al., KEI< Prcprint 93-107�

28�