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Observations of PentaQuarks: A Mini-Review

Observations of PentaQuarks: A Mini-Review. By A. Dolgolenko and M. Kubantsev. Content. 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.

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Observations of PentaQuarks: A Mini-Review

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  1. Observations of PentaQuarks: A Mini-Review By A. Dolgolenko and M. Kubantsev HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  2. Content • 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 First evidence from photo production (Spring-8) Low energy kaon beam (ITEP) Photo/electro-production (JLAB, ELSA, HERMES) }over 200 citations! Neutrino beam (ITEP-CERN-FNAL) 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 HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  3. Introduction All 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: HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  4. Why is the Baryon State called Exotic? 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) HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  5. Indeed, history of S = +1 system search was not encouraging: HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  6. Prediction of narrow and exotic light baryons 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… Z+(1530), later Θ+(1530) nK+ or pK0 uudds S = +1 N(1710) 0 -3/2 -1 -1/2 1/2 1 3/2 I Σ(1890) -1 Ξ(2070) -2 uussd Ξ0 π+ or Σ+K0 ddssu Ξ- π- or Σ-K- HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  7. LEPS at SPRING-8: FIRSTOBSERVATION γ K- K+ Θ+ n n 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 HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  8. DIANA BC at ITEP(MOSCOW) The peak near 1540 MeV/c2of 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) HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  9. CLAS with D target at JLAB HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  10. SAPHIR at ELSA • 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 HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  11. Observation of Θ+ in neutrino interactions:ITEP-FNAL-CERN Neon plus Deuterium A.E.Asratyan et al.,hep-ex/0309042 Phys. Atom.Nucl. 67,682(2004) Re-analysis of data from FNAL (E180,E632) and CERN(WA21, WA25,WA59) bubble chambers with H, D, Ne fills. Signal is seen only on D and Ne. Mass=1533 ± 5 MeV/c2 Width <20MeV/c2 26 events with ~15 events of the background; significance of 6.7 σ. HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  12. CLAS with p-target at JLAB V. Kubarovsky et al., hep-ex/0311046 Phys. Rev.Lett.92,032001(2004) NΘ+= 41±10 events M = 1555 ± 10 MeV/c2 Γ = 26 ± 7 MeV/c2 Significance: 7.8 ± 1 σ No signal in pK+ system, so Θ+ is possibly isoscalar HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  13. Dubna:C-C interactions at 4.2 GeV/nucleon R. Togoo et al., Proc. Mongolian Acad.Sci.,4(2003),2 Propane 2-meter bubble chamber in heavy ion beam (C) of Dubna accellerator. The signal is impressive: ~ 9 σ effect(!?) HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  14. HERMES(e+D) at DESY • Airapetian et al., hep-ex/0312044, • Phys.Lett.B585,213(2004) e+(27.6 GeV)D K0(π+π-)pX NΘ+= 56 events M = 1528 ± 2.6 ± 2.1 MeV/c2 Γ = 19 ± 5 ± 2 MeV/c2 Significance: 4 – 6 σ HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  15. SVD(pA) at Serpukhov A.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 HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  16. COSY -TOF M =1530 ± 5 MeV HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  17. Evidence from e-p collider experiment ZEUS 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(?) HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  18. Preliminary results from STAR(p-p collisions) pp @ 200 GeV C.M.S. energy with 8 million events Possible bump @ ~1520 Mev/c2 S.Salur for STAR at RHIC: hep-ex/0403009 HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  19. Summary of observations Average 1531±3±4 HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  20. Reaction and energy (GeV) Θ++ signal Production cross-section, μb Collaboration Summary of observations (supplemental) γd→ K-p K+n (2.5<Pγ<3.1) γp→ K0S 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 HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  21. 1.54 GeV The unclaimed Q+(1540) ? CERN: K+p  pK0X Bubble Chamber Data • Berthon, et al., • Nucl. Phys. B63, 54 (1973) Presented by V.D.Burkert at Penta-Quark 2003. HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  22. Estimation of Θ+ width (summary) Direct high resolution width measurements are under way now. HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  23. Estimation of Θ+ width (summary,cont.) Kaon experiments • Direct observation(DIANA): < 9 MeV • R. Cahn and G.Trilling (DIANA re-analysis) 0.9 MeV • S. Nussinov (K+n and K+d) <6 MeV • R. Arndt et al (K+n and K+d) <1.5 MeV • I.Strakovsky et al: PWA for K+n(I=0) with P01 (Jp=3/2+) <1-2 Mev • Other partial waves: S01(Jp=1/2-)and P03(Jp =3/2+) are not conclusive • W.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 HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  24. 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) Possible two candidates for members in the anti-decuplet with strangeness -2 and possible isospin 3/2 are observed: Ξ--3/2Ξ- π- - an exotic state Ξ03/2Ξ– π+ - a non-exotic state Ξ(?!) HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  25. NA49(pp)at CERN SPS pp ΞπX C.Alt et al., hep-ex/0310014, Phys.Rev.Lett.92, 042003(2004) Ξ- π- Decay Ξ--3/2Ξ- π- of the exotic state with mass M = 1862 ± 2 MeV/c2 Γ = 18 Mev/c2 Significance ~ 4 σ At the same mass the non-exotic state decay is observed: Ξ03/2Ξ– π+ Corresponding antiparticles spectra show enhancements at the same place. Ξ- π+ Ξ- π- Ξ- π+ HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  26. H1: Narrow anti-charm baryon state uuddc M=3.099± 0.006 GeV H1 Collaboration, submitted to Phys. Lett. B (Mar 2004) HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  27. However, not all experiments NOW looking for pentaquarks see the signal (after 2003) HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  28. Summary of 2004 non-observations(by May) Summary of Observations 2004(May) HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  29. All previous experiments were not designed for pentaquark search(except LEPS(03) and DIANA).Several high statistics dedicated experiments are now in progress: 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. HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  30. LEPS: new deuterium results New LEPS experiment (2004) : γD  K+K-n • 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 f-meson production events • Further cuts: • Photon energy • Remove events with more than 2 tracks • Remove L(1520) HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  31. New LEPS experiment (2004) : γD  K+K-n Ken Hicks (Ohio University) Denver APS Meeting May 2, 2004 LEPS gd: remove L(1520) Preliminary! Θ-peak: 2003: 18 events 2004: ~100 events (x5-10 fold statistics) HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  32. Last news: CLAS-G11(2004) CLAS: Neutron peak has about 10 times the statistics of the earlier CLAS data. Ken Hicks (Ohio University) Denver APS Meeting May 2, 2004 Preliminary! This data set will provide a high-statistics test of the Q+. MM(K+K-p) HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

  33. AFTER COFEE BREAK… Continue… HSQCD-2004,St.Petersburg, Repino,Russia, May 21 2004

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