Experiment “EPECURE”: first results. .

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V.V.Sumachev

Contents.

1. About the missing resonance problem. 2. Phenomenology. 3. Standard PWA restrictions for N-resonance quest. 4. The quest for N(1710)P11 baryon states. 5. First results of the differential cross-section measurements.

( ITEP-PNPI-ACU Collaboration).I.G.Alekseev, I.G. Bordyuzhin, D.A. Fedin V.P. Kanavets, L.I. Koroleva, B.V. Morozov,

V.M. Nesterov, V.V. Ryltsov, A.D. Sulimov, D.N. Svirida, ( Institute for Theoretical and Experimental Physics, B. Cheremushkinskaya 25, Moscow,

117259, Russia; e-mail: Igor.Alekseev@itep.ru ). V.A. Andreev, Ye.A. Filimonov, A.B. Gridnev, V.V. Golubev, E.A.Konovalova, A.I. Kovalev, N.G. Kozlenko, V.S. Kozlov, A.G. Krivshich, D.V. Novinsky, V.V.Sumachev, V.I.Tarakanov,

V.Yu. Trautman,( Petersburg Nuclear Physics Institute, Gatchina, Leningrad district,188300, Russia;

e-mail: sumachev@pnpi.spb.ru ). 

M.E.Sadler (Abilene Christian University, 320B Foster Science Building, Abilene, TX 79699; e-mail: sadler@physics.acu.edu)

Baryonic multiplets in the harmonic quark shell model.(Inroductory remarks on baryon spectroscopy R. H. Dalitz, 1976)

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A hadronic system of finite size can be expected to have at least two types of exited states:

(a) rotational excitations (or Regge recurrences, in field theoretical language)

(b) radial vibrations (pulsations)

Following Greenberg’s early shell-model proposal, the harmonic oscillator SU(6) x O(3) quark model has

had much success in accounting for the low-lying multiplets observed for baryonic resonance states.

The SU(6) multiplets are best characterized by giving symmetry of the representation with

respect to permutations of the labels of the three quarks. The 56 representation has complete

symmetry (S), the 70 representation has mixed symmetry (M), and the 20 representation is

antisymmetric (A). Baryons are classified into bands that have the same number N of quanta of

excitation. Each band consists of a number of supermultiplets, specified by (D, LPN) , where D is

dimensionality of the SU(6) representation, L is the total quark orbital angular momentum, and P is

the total parrty.

The N=0 band, which contains the nucleon and (1232), consists only of the (56,0+

0) supermultiplet.

SU(6) x O(3) classification of nucleon resonance by G.Hoeler at al. (from KH78).

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SU(6)LP 

Resonance from KH78

(56,0+) P11(938),) P33(1233) 2

(56,2+) P13(1710), F15(1684), P31(1888), P33(1868), F35(1905), F37(1913) 6

(56,4+) F17(2005), H19(2205), F35( - ), F37(2425), H39(2217), H3,11(2416) 6

(70,1-) S11(1526), D13(1519), S11(1670), D13(1731), D15(1679), S31(1610), D33(1680)

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(70,3-) D15( - ), G17(2140), D13(2081), D15(2228), G17( - ), G19(2268), D35(2305), G37(2215)

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(70,5-) G19( - ), I 1,11( - ), G17( - ), G19(2792), I1,11(2577), I1,13( - ), G39(2468), I3,11( - )

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(70,7-) I1,13( - ), L1,15( - ), I1,11( - ), I1,13( - ), L1,15( - ), L1,17( - ), I3,13(2794), L3,15( - )

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(70,2+) P13( - ), F15( - ), P11(1723), P13( - ), F15(1882), F17( - ), P33( - ), F35( - )

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(56,6+) H 1,11( - ), K1,13(2612), H39( - ), H3,11( - ), K3,13( - ), K3,15(2990) 6

(56,1-) S11(1880), D13(1920), S31(1908), D33(2070), D35(1901) 5

= 630 = 39 (64) = 64

It would must be 630 baryon resonance, if all revealed 70-multiplets and 56-multiplets were filled in.

Comparison of the N* and resonance number predictions.

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References N*resonance number

resonance numberRev. of Part. Phys. (1980) 26 19

Rev. of Part. Phys. (2010) 23 22

KH80 21 18

KA84 18 16

CMB (Phys.Rev.D 20 1979 ) 16 13

T.P.Vrana et al.( nucl-th/9910012 ) 14 13

SM95 (Phys.Rev.C 52 1995 ) 13 8

FA02 ( Phys.Rev.C 69, 2004 ) 10 7

SP06 ( nucl-th/0605082 ) 13 9

S.Capstick et al.(Phys.Rev.D 49,1994) 40 27

U.Loring et al.(hep-ph/0103289) 99 82

Skyrme model (Phys.Rev.D31,1985) 10 13

J.Vijande et al.( hep-ph/0312165 ) 19 21

In the PDG 2010 Baryon summary table there are in general (N*, and others) 131 baryon.n=4, three 70-plets and four 56-plets are given in summary tables. In general 434 baryons must be.

QM prediction and experimental situation.

75Excitation spectrum of the nucleon. (J.Phys.G Vol. 37, №7A , 2010)

Summary of N* and * finding (from I.I.Strakovsky)

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Standard PWA reveals only wide Resonances, but not too wide

( < 500 MeV) and possessing not too small BR (BR > 4%)

PWA (by construction) tends to miss narrow Resonances with

< 30 MeV

Our study does not support several N* and * reported by PDG2006:

*** (1600)P33, N(1700)D13, N(1710)P11, (1920)P33

** N(1900)P13, (1900)S31, N(1990)F17, (2000)F35, N(2080)D13,

N(2200)D15, (2300)H39, (2750)I313

* (1750)P31, (1940)D33, N(2090)S11, N(2100)P11, (2150)S31,

(2200)G37, (2350)D35, (2390)F37

Our study does suggest several ‘new’ N* and *:

**** (2420)H311

*** (1930)D35, N(2600)I111 [no pole]

** N(2000)F15, (2400)G39

new N(2245)H111 [CLAS ?]

N(1710)P11 – What was Known.

[W.-M. Yao et al. [RPP] J Phys G 33, 1 (2006)]

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SASA DPP97 1710 [inp] ~40 [est]

PWA-BWPWA-BW Ref Mass(MeV) Width(MeV) KH 1979 1723 9 120 15 * Bn-A 2001 1729 CMU 1980 170050 90 30 * KSU 1992 171728 480230 * GW06 not seen

PWA-Pole PWA-Pole Re(MeV) -2xIm(MeV) CMU80 169020 80 20 CMU90 1698 88 KH93 1690 200 [Sp(W)]

GW06 not seen

The spread of, selected by PDG, is very large It would be more natural for the same unitary multiplet (with + and N*) to have comparable widths

No BW, No pole, No Sp

PDG06=PDG04

(From I.I.Strakovsky.)

Pentaquark antidecuplet.

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“Usual” resonance N(1710).

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The following summary on the non-exotic P11 resonance N(1710) is taken mainly from the “Review

of Particle Properties” (RPP, 2010). This resonance has a rating of three stars (***).

According to the results of the energy independent partial wave analyses (IPWA): KH80 – MR=1723±9 MeV, Γ=120±15 MeV; CMB80 – MR=1700±50 MeV, Γ=90±30 MeV.

Pion photoproduction IPWA gives MR=1720±10 MeV, Γ=105±10 MeV, having the branching ratios

for Nπ and KΛ channels (10-20)% and (5-25)% respectively.

The combined analysis of the πN→πN+Nππ processes (KSU) has two solutions, predicting either a wide resonance with Γ=480±230 MeV or a narrow one with Γ=50±40 MeV at the same mass of MR=1717±28 MeV.

In the energy dependent (DPWA) analysis SP06 of GWU group the resonance N(1710) is not observed.

Experiment motivation and layout.

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The general idea of the PNPI-ITEP-ACU collaboration proposal is to look for the effects in the cross-section in the “formation” type experiments using the elastic pion-nucleon scattering and reaction π-p→KΛ.

The scan of the mass interval under investigation will be done by changing the initial pion momentum. Secondary pion beams with appropriate intensity and energy are available at ITEP from its 10 GeV proton synchrotron.

Two-focused beam line optics provides the possibility to analyses the individual momentum of the beam pion with the accuracy up to (0.06-0.15)%, having the total momentum range of Δp/p=±2%. Wide energy range of (0.8–2.5) GeV/c can be covered by changing of the magnetic elements currents.

The results of the measurements may be analyzed by the standard procedure of the partial-wave (PWA) analysis, which is the important advantage of the “formation” type experiments.

In particular it means that all the quantum numbers of the resonance, if found, can be unambiguously determined. The results of the measurements in the two channels will be compared.

Next figure illustrates how could be seen in the elastic scattering assuming its full width equal 6 MeV, elasticity X=5% and mass 1671 MeV. The insertion in the top right corner is the zoom of the area around the resonance. Error bars and the point density correspond to the proposed statistical accuracy and momentum resolution. It’s worth mentioning that the effect of the resonance can be either a minimum (as in the figure), a maximum or a bipolar structure, dependent on its unpredictable pole residue phase.

10N

Sensitivity of the elastic scattering measurements.

–p –p6

Elastic scattering

K

Width (2-20) MeV (2-20) MeV Elastic width, Гel >0.1 MeV >0.02 MeV Elasticity, X >0.05 >0.01

• Elastic scattering:• We measure differential cross-section with statistical precision 0.5 % and step in the invariant mass 0.5 MeV at the angles 40-120o CM.• Momentum range 900-1200 MeV/c 1610-1770 MeV• ~20 days of running

• K:• Differential cross-section with statistical precision 1% and step in the invariant mass 0.5 MeV at the angles 0-180o CM.• Momentum range 900-1200 MeV/c 1610-1770 MeV• ~24 days of running

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EPECURE – elastic scattering.

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–p –p

•Method: measure differential cross-section at the angles 40-120o CM as function of the invariant mass of -p-system. Main parts of experimental setup are liquid hydrogen target and proportional and drift chambers.

•“Formation”-type experiment: invariant mass resolution (0.7 MeV) is based on the high momentum resolution (0.1%) of the magneto-optic channel.We want to reach statistic resolution as high as 0.5 %. We can get clear evidence for a narrow (2-20 MeV) resonance even if its elastisity is only 1%.

EPECURE – current status.

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Pion channel № 322.

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h=1.5m

сп94

сп94верт

корр.

кг50

20к100 h=1.5mЭ

. Щ.

211

350

321322

k320i1k320i2

k320p3k320p4

kollkorr

b322c2

1 foc

2 foc

b322v1

b322v3

b322v4

20k100b

sp94

ml17

sp12

ml17

U10tg303

212

DC1DC2

DC3DC4

DC5DC6

55

0.25m*1.2m

Tr+TOF

H2

H3

DC11DC12DC13

Titorenko

Spin

Newexperiment 2F

3F

ML15

20K100

sp12

20K100

ML15

303

305

307

0 10m 20m 30m

Elastic events selection.

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Resonances and channel thresholds in the differential cross sectionResonance influence on the cross section

Other channel threshold influence on the cross section

π-p→K0Σ0 – Minv=1690.2 MeV Pbeam = 1033 MeV/cπ-p→K+Σ- – Minv=1691.1 MeV Pbeam = 1035 MeV/cπ-p→ωn – Minv=1722.3 MeV Pbeam = 1092 MeV/cπ+p→K+Σ+ – Minv=1683.1 MeV Pbeam = 1021 MeV/c

S-wave only

Any wave

N(1685) – Minv=1685 МэВ → Pbeam = 1024 MeV/cEnergy

А.И. Базь, Я.Б. Зельдович, А.М. Переломов

Statistics

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0

10

20

30

40

50

6013

3013

1513

0012

8512

7012

5512

4012

2512

1011

9511

8011

6511

5011

3511

2011

0510

9010

7510

6010

4510

3010

1510

00 985

970

955

940

925

910

895

880

865

850

835

820

April 09 pi-, 453 mln. trg.April 10 pi-, 1250 mln. trg.June 10 pi+, 688 mln. trg.February 11 pi+, 275 mln. trg.February 11 pi-, 292 mln. trg.

Statistics so far 2.97 billion triggers

Pbeam, MeV/c

Many thanks to ITEP accelerator!

dd, p – p

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dd, p – p

19

dd, p – p

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dd, p – p

There is some irregularity. We are planning to accumulate in the

regions of the disagreements.

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22

–pK0S +––p

Most of the events have either all 4 particles going forward or 3 particles including the proton going forward and one pion going in some other direction

We keep the target and the beam equipment The drift chambers we already

have

New wide-aperture drift chambers

New hodoscopes

Conclusions.

The “missing” resonance problem is one of the radical problem of the modern physics.It is clear today, that the problem of the “missing” baryon resonances can’t be resolved without of additional investigation of the pion-nucleon interactions. The problem of the narrow resonances must be resolved.The inelastic channels must be systematically investigated for pion-nucleon interaction in the whole resonance region.

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