Observations of PentaQuarks: A Mini-Review

M.Kubantsev ITEP,Moscow/NWU

HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

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Observations of PentaQuarks:A Mini-Review

By A. Dolgolenko and M. Kubantsev



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•Introduction •Observations of the Θ+(1540) state: year of 2003:

•2004 results (up to mid-May):

• Other possible exotic baryons.

• Further studies, summary and outlook

Content

First evidence from photo production (Spring-8) Low energy kaon beam (ITEP) Photo/electro-production (JLAB, ELSA, HERMES)

High energy electro-production (ZEUS) Low energy proton beam (COSY) High energy hadron beams (Serpukhov, Dubna, Fermilab,CERN, RICK) e+ e- -collisions at BES and LEP

Neutrino beam (ITEP-CERN-FNAL)

} over 200 citations!



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IntroductionAll well established baryon states can be understood as combinations of three valence quarks: u, d, s.These combinations are grouped in SU(3) singlets, octets and decuplets:



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Any baryons that can not be made with this triplet are to be considered as exotic. The simplest configuration might consist of four quarks plus anti-quark: QQQQQ. This state is called a pentaquark. Truly exotic states has Q with other flavor then other four quarks: uudds (S =+1, Q =+1) ssuud (S = -2, Q = +1) ssddu (S= -2, Q =-2) Other states can mix with standard baryons. (No heavy flavors considered in this talk (see H1 talk)

Why is the Baryon State called Exotic?



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Indeed, history of S = +1 system search was not encouraging:



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In 1997 D. Diakonov, V. Petrov and M. Polyakov proposed, on basis of a chiral soliton model, a low-mass anti-decuplet of pentaquarks (qqqqq). Predicted lower mass, s=+1 state has mass of 1530 MeV/c2 and narrow width <15 MeV/c2. Three baryons in the triangle corners are exotic. They have been bold enough to persuade experimentalists to look for these states, so in the beginning of 2003…

-1

Z+(1530), later Θ+(1530)

S = +1

N(1710)

Σ(1890)

Ξ(2070)

nK+ or pK0

uudds

uussdΞ0 π+ or Σ+K0ddssu

Ξ- π- or Σ-K-

Prediction of narrow and exotic light baryons

0

-2

-3/2 I-1/2 1/2 3/2-1 1



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LEPS at SPRING-8: FIRST OBSERVATION

S = +1 baryon resonance in K- missing mass spectrum of γn K+K-n reaction on carbon was found:

Mass of 1540 ± 10 Mev/c2. Peak significance is 4.6 σ Peak width is < 25 MeV/c2

γ K-

K+

nn Θ+



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DIANA BC at ITEP(MOSCOW)

The peak near 1540 MeV/c2 of total 73

events has estimated background of 44 events,

resulting in statistical significance of 4.4 σ Gaussian fit of the peak yields:

M = 1539 ± 2 MeV/c2 Γ

<9MeV/ c2 (compatible with instrumental

resolution)



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CLAS with D target at JLAB



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Θ+ signal(fit):NΘ+= 63±13 events M = 1540 ± 4 ± 2 MeV/c2 Γ < 25 MeV/c2 Significance: 5.2 σ

•σ(Θ+): σ(Λ0(1520))= 1:15•No signal in Θ++ K+p suggests isoscalar state

SAPHIR at ELSA



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26 events with ~15 events of the background;significance of 6.7 σ.

Neon plus Deuterium

Mass=1533 ± 5 MeV/c2

Width <20MeV/c2

Observation of Θ+ in neutrino interactions:ITEP-FNAL-CERN

A.E.Asratyan et al.,hep-ex/0309042Phys. Atom.Nucl. 67,682(2004)

Re-analysis of data from FNAL (E180,E632) and CERN(WA21,WA25,WA59) bubble chamberswith H, D, Ne fills.

Signal is seen only on D and Ne.



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CLAS with p-target at JLAB

V. Kubarovsky et al., hep-ex/0311046Phys. Rev.Lett.92,032001(2004)

NΘ+= 41±10 events M = 1555 ± 10 MeV/c2 Γ = 26 ± 7 MeV/c2 Significance: 7.8 ± 1 σNo signal in pK+ system, so

Θ+ is possibly isoscalar



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Propane 2-meter bubble chamber in heavy ion beam (C) of Dubna accellerator.

The signal is impressive: ~ 9 σ effect(!?)

R. Togoo et al., Proc. MongolianAcad.Sci.,4(2003),2

Dubna:C-C interactions at 4.2 GeV/nucleon



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A. Airapetian et al., hep-ex/0312044,Phys.Lett.B585,213(2004)

HERMES(e+D) at DESY

NΘ+= 56 events

M = 1528 ± 2.6 ± 2.1 MeV/c2

Γ = 19 ± 5 ± 2 MeV/c2

Significance: 4 – 6 σ

e+(27.6 GeV)D K0(π+π-)pX



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SVD(pA) at SerpukhovA.Aleev et al., hep-ex/0401024

NΘ+= 50 events

M = 1526 ± 3.1 MeV/c2

Γ <24 MeV/c2

Significance: 4 – 6 σ

Production cross section for XF > 0 (30-120) mkb



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COSY -TOF

M =1530 ± 5 MeV



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S. Chekanov for ZEUS:hep-ex/0405013(latest update)

ep @ 300-318 GeV C.M.S. energy with integrated luminosity 121 pb-1

NΘ+= 221 ± 48 events M = 1522 ± 3.1 MeV/c2 Γ = 8 ± 4 MeV/c2 Significance: 4.6 σ

No Θ++ observed: isoscalar(?)

Evidence from e-p collider experiment ZEUS



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S.Salur for STAR at RHIC:hep-ex/0403009

Preliminary results from STAR(p-p collisions)

pp @ 200 GeV C.M.S. energy with 8 million events Possible bump @ ~1520 Mev/c2



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Average 1531±3±4

Summary of observations



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Summary of observations (supplemental)Reaction and energy (GeV) Θ++ signal

Production cross-

section, μbCollaboration

γd→ K-p K+n (2.5<Pγ<3.1) γp→ K0

S K+n ( Pγ<2.6) γp→ π+ K- K+n (3<Pγ<5) ed→ pKSX (Pe=27.6) ep→ KS p()X (√s=300-318) pA→ pKSX (Pp=70) pp→Σ+K0p (Pp=2.95)

Not seen

Not seen

Not seen

Not seen

Not seen

N/A

N/A

N/A

0.03-0.04

N/A

N/A

N/A

30-120

0.4±0.1±0.1

CLAS

SAPHIR

CLAS

HERMES

ZEUS

SVD

TOF-COSY



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CERN: K+p pK0X Bubble Chamber Data

1.54 GeVA. Berthon, et al., Nucl. Phys. B63, 54 (1973)

The unclaimed (1540) ?

Presented by V.D.Burkert at Penta-Quark 2003.



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Estimation of Θ+ width (summary)

Direct high resolution width measurements are under way now.

Experimental Θ width(upper limits or values with errors)

259

2125

2026

208

1024

2622

LEPSDIANA

CLAS(D)CLAS(p)ITEP(ν)

SAPHIRHERMES

ZEUSNA-49

SVDDubna(CC)COSY-TOF



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Estimation of Θ+ width (summary,cont.)Kaon experiments

Direct observation(DIANA): < 9 MeV

R. Cahn and G.Trilling (DIANA re-analysis) 0.9 MeVS. Nussinov (K+n and K+d) <6 MeVR. Arndt et al (K+n and K+d) <1.5 MeVI.Strakovsky et al: PWA for K+n(I=0) with P01 (Jp=3/2+) <1-2 MevOther partial waves: S01(Jp=1/2-) and P03(Jp =3/2+ ) are not conclusiveW.R. Gibbs (K+d cross section re-analysis) 0.9±0.2

Mev (nucl-th/0405024, May 9 2004)Data from T. Bowen et al. Phys.Rev. D2,2599(1970), A.S. Carrol et al. Phys. Lett.45B, 531(1973) :• Masses 1520 -1550 are peferable for S01 and P01



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Possible two candidates for members in the anti-decuplet with strangeness -2 and possible isospin 3/2 are observed:Ξ--

3/2 Ξ- π- - an exotic state

Ξ03/2

Ξ– π+ - a non-exotic state

Ξ(?!)

NA49(pp)at CERN SPS

Experiment NA49 at CERN study proton-proton interactions on at √ s = 17.2 GeV with large acceptance (-0.2 <xF <0.2)



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Decay Ξ--

3/2 Ξ- π-

of the exotic state with mass M = 1862 ± 2 MeV/c2

Γ = 18 Mev/c2 Significance ~ 4 σAt the same mass the non-exoticstate decay is observed:Ξ0

3/2 Ξ– π+

Corresponding antiparticles spectrashow enhancements at the same place.

Ξ- π-

Ξ- π-

Ξ- π+

Ξ- π+

NA49(pp)at CERN SPSC.Alt et al., hep-ex/0310014,Phys.Rev.Lett.92, 042003(2004)

pp Ξ πX



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H1 Collaboration, submitted to Phys. Lett. B (Mar 2004)

M=3.099± 0.006 GeV uuddcH1: Narrow anti-charm baryon state



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However,not all experiments NOW

looking for pentaquarks see the

signal(after 2003)



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Summary of Observations 2004(May)Where Reaction Mass interval

Limit Comment

BES e+ e-J/ψ KNX 1520-1560

<10-5 (branching)

Azimov: < 10-5

HERA-B

pA K0p X 15 N/A vs NA49,SVD

PHENIX

dAu K+n X 1500-1600

N/A vs STAR, Dubna

CDF pp Z K0p X 1525–1545

<87(79) events

vs ZEUS, STAR

ALEPH e+ e-Z K0p X 1525–1545

<.003 (events)

No D-events (K-L)

DELPHI e+ e-Z K0p X 1500–1750

<.006(events)

No D-events (K-L)

ZEUS ep Ξ π X 1840-1880

N/A vs NA49

CDF pp Ξ π X 1840-1880

126/? vs NA49

FOCUS A Dp X N/A N/A vs H1WA89 Σ-A Ξ π X 1840-

1880N/A vs NA49

Summary of 2004 non-observations(by May)



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LEPS(04) is a dedicated experiment for pentaquark search.

Preliminary results are presented by T.Nakano on March 24 and K. Hicks on May 4.

Jefferson Lab has an pentaquark experimental program (V.D. Burkert):

CLAS-G11 –> 20X increase of statistics (March-April)PQE(Jlab 04-012) –> high resolution study(running)Several Jlab experiments are under preparation.

All previous experiments were not designed for pentaquark

search(except LEPS(03) and DIANA).Several high statistics

dedicated experiments are now in progress:



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LEPS: new deuterium results• Preliminary data (not yet

published)• Higher statistics (5-10 times more)• Minimal “cuts” on the data:

– Particle ID of K+, K-– Missing mass = Nucleon mass– Remove -meson production events

• Further cuts:– Photon energy– Remove events with more than 2

tracks– Remove (1520)

New LEPS experiment (2004) : γD K+K-n



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New LEPS experiment (2004) : γD K+K-n

LEPS d: remove (1520)Ken Hicks (Ohio University)Denver APS MeetingMay 2, 2004

Θ-peak: 2003: 18 events2004: ~100 events(x5-10 fold statistics)

Preliminary!



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Last news: CLAS-G11(2004) CLAS: Neutron peak

has about 10 timesthe statistics of the earlierCLAS data.

This data setwill provide a high-statisticstest of the +.

MM(K+K-

p)

Ken Hicks (Ohio University)Denver APS MeetingMay 2, 2004 Preliminary!



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