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Status of Pentaquark Search

Status of Pentaquark Search. Valery Kubarovsky Rensselaer Polytechnic Institute / Jlab. Introduction Review of theoretical models Current Experimental Status Second generation experiments Conclusion . Introduction.

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Status of Pentaquark Search

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  1. Status of Pentaquark Search Valery Kubarovsky Rensselaer Polytechnic Institute / Jlab • Introduction • Review of theoretical models • Current Experimental Status • Second generation experiments • Conclusion Valery Kubarovsky BEACH2004 06/29/04

  2. Introduction • Several experiments have recently reported the observation of the baryon with exotic quantum numbers • Light: M=1525-1555 MeV • Narrow:G< 9-25 MeV (possibly ~1 MeV) • Strangeness S=+1 (opposite to the strangeness of the usual baryons) • This new state was identified as the Q+ pentaquark baryon with quark contents . • There is also evidence for two related states with the strangeness S=-2, Valery Kubarovsky BEACH2004 06/29/04

  3. The Anti-decuplet in the cSMD. Diakonov, V. Petrov, M. Polyakov, Z.Phys.A359, 305 (1997) S=+1 updated version D. Diakonov, V. Petrov, arXiv:hep-ph/0310212 Dm = 108 MeV S=0 S=-1 S=-2 Valery Kubarovsky BEACH2004 06/29/04

  4. Theory Response to the Pentaquark • Anti-charmedQoc and anti-beautyQ+b • Q+andQ+produced in quark-gluon plasma • Instantons and diquark clustering • Triquark-diquark cluster model • Pentaquarks and radially excited baryons • Peanut-shaped quark-diquark model • Pentaquarks in the color-flavor-locking • superconducting phase • ……. • Chiral soliton P=+ • Kaon-Skyrmion P=+ • (qq)2-q P=+ or P=- • Kaon-nucleon resonance • Super radiance resonance • QCD sum rules • Lattice QCD P=-, or find no signal • Higher exotic baryon multiplets • Pentaquarks in string dynamics • P11(1440) as pentaquark • P11(1710) as pentaquark • Q+as isotensor pentaquark • Topological soliton • Q+(1540) as a heptaquark • Exotic baryons in the large Nc limit More than 220 papers since July 1, 2003 Valery Kubarovsky BEACH2004 06/29/04

  5. Quark description (Jaffe, Wilczek) L=0 (ud) s L=1 (ud) L=1, one unit of orbital angular momentum needed to obtain as in the cSM Soliton: (naïve version) JP = ½+ Q-LQCD: JP = ½- Meson fields Pentaquarks models Chiral soliton model: (Diakonov, Petrov, Polyakov) Predicted the mass and the width of 5Q. ‘Pentaquark’ comes out naturally from these models. They represent rotational excitations of the soliton JP = ½+ Valery Kubarovsky BEACH2004 06/29/04

  6. Baryons (8) 4Q Mesons Mesons 5Q Baryons DiBaryons Baryons (10) QCD instantons (Shuryak hep-ph/0310270) DiQuarks are building blocks of multiquark states: pentaquarks and dibaryons A nucleon is made of a quark and deeply bound scalar-isoscalar diquarks, absent in the decuplet. In the instanton liquid model there are two kind of diquarks, the scalar and the tensor (with spin=1) Valery Kubarovsky BEACH2004 06/29/04

  7. QCD instantons • The DiQuark mass is about the constituent mass. • Two possible scenario: Scalar DiQuarks are in a P-wave M(Q+) = 1880 MeV Scalar and tensor DiQuarks in S-wave M(Q+) = 1550 MeV • G(Q+) = 2.6 MeV • The narrowness of the partial widths follows from the small overlap between the three and five quarks wave functions due to the different internal structure. Valery Kubarovsky BEACH2004 06/29/04

  8. Current Experimental Status Valery Kubarovsky BEACH2004 06/29/04

  9. Super Photonring-8GeVSPring-8 • Third-generation synchrotron radiation facility • Circumference: 1436 m • 8 GeV • 100 mA • 62 beamlines Valery Kubarovsky BEACH2004 06/29/04

  10. LEPS detector g 1m Valery Kubarovsky BEACH2004 06/29/04

  11. K/p separation (positive charge) Reconstructed mass p- p+ p+ p K+ K+ Events d Momentum (GeV) K- Mass(GeV) Mass/Charge (GeV) Charged particle identification s(mass) = 30 MeV/c2 for 1 GeV/c Kaon Valery Kubarovsky BEACH2004 06/29/04

  12. Non-resonant KK L(1520) Q+? LEPS analysis • Problems: • no neutron target • CH start counter • Fermi motion corrections • Background • fK+K- • (produced from n & p) • K- missing mass gives Q+ mass • K+K- missing mass gives n Valery Kubarovsky BEACH2004 06/29/04

  13. Q+: published mass plot M = 1.540.01 MeV G < 25 MeV Gaussian significance 4.6s • Background level is estimated by a fit in a mass region above 1.59 GeV. • Assumption: • Background is from non-resonant K+K- production off the neutron/nucleus • … is nearly identical to non-resonant K+K- production off the proton background Phys.Rev.Lett. 91 (2003) 012002 hep-ex/0301020 Valery Kubarovsky BEACH2004 06/29/04

  14. DIANA/ITEP (Moscow) • 750 MeV K+ beam incident on 700 liters Xe bubble chamber. • Interaction energy is determined by the range of the kaon. • Charged particles are identified by ionization, momentum is measured by the range. Charge exchange reaction K+N]Q+]pK0S K0S]p+p- Valery Kubarovsky BEACH2004 06/29/04

  15. DIANA • Selecting forward going protons and kaons - Qk and Qp < 100o. • p and K0 are emitted back-to-back - cosFpK < 0. • Peak at 1.539 GeV in the invariant mass of K0p. • Statistical significance4.4s. • Measured widthG < 9 MeV The best limit for width Valery Kubarovsky BEACH2004 06/29/04

  16. Jefferson Lab (CEBAF) Continuous Electron Beam Accelerator Facility Valery Kubarovsky BEACH2004 06/29/04

  17. Torus magnet 6 superconducting coils Electromagnetic calorimeters Lead/scintillator, 1296 photomultipliers Liquid D2 (H2)target + g start counter; e minitorus Drift chambers argon/CO2 gas, 35,000 cells Gas Cherenkov counters e/p separation, 256 PMTs Time-of-flight counters plastic scintillators, 684 photomultipliers CLAS - CEBAF Large Acceptance Spectrometer Valery Kubarovsky BEACH2004 06/29/04

  18. CLAS-gd: Exclusive reaction • Exclusive photoproduction on deuterium: • Experimental data from 1999 run; • Tagged photons with up to 3 GeV energy; • Target: 10 cm long liquid deuterium; Possible reaction mechanism • No correction for Fermi smearing is needed. • Aids significantly to reduce the background. Valery Kubarovsky BEACH2004 06/29/04

  19. CLAS • 15% of non pKK events within ±3sof the peak. • Almost no background under the neutron peak with tight timing cut,DtK. Valery Kubarovsky BEACH2004 06/29/04

  20. CLAS: Cut out known resonances • Several known processes can contribute to the pK+K-(n) final state • gd→fp(n), f→K+K- • gd→L(1520)K+(n), L(1520)→pK- • Both reactions proceed predominantly on the proton (neutron is a spectator). • Kinematics of both reactions are not a good match forQ+production. Valery Kubarovsky BEACH2004 06/29/04

  21. CLAS Q+ M = 1.542 GeV G < 21 MeV (sM=9 MeV) Stat.sig. = 5.2s (4.6-5.8) Gaussian background Simulated background Distribution ofL(1520) events Valery Kubarovsky BEACH2004 06/29/04

  22. CLAS: Photoproduction onhydrogen After PID n Valery Kubarovsky BEACH2004 06/29/04

  23. Possible Q+ production mechanisms in the reaction W. Liu, C.M. Ko, V. Kubarovsky, nucl-th/0310087 Valery Kubarovsky BEACH2004 06/29/04

  24. g p+ K- p p N* Q+ Q+ Production via N* decays Valery Kubarovsky BEACH2004 06/29/04

  25. Q+ • Cosq*(p+) > 0.8 g p+ K- p p N* Q+ CLAS-gp: with forward going p+ • Fitted mass 1.555 GeV • G< 28 MeV consistent with detector resolution • Estimated significance7.8s M(nK+) Valery Kubarovsky BEACH2004 06/29/04

  26. Q+ N* ? g p+ K- p p N* Q+ CLAS-gp: Indicationfor a heavy N*(2430)? There are no pN scattering data in the relevant energy range. M(K-Q+) [GeV] Valery Kubarovsky BEACH2004 06/29/04

  27. CERN/NA49 • Proton-proton collisions at 158 GeV. Similar to CLAS gp Valery Kubarovsky BEACH2004 06/29/04

  28. JP = ½- JP = ½+ What do we know about the width of Q+? Widths seen in experimental analyses are dominated by resolution effects. More precise information is obtained in analyses with theoretical constraints. • HERMES, PLB585, 213 (2004) GQ = 17+/-9+/-3 MeV • S. Nussinov et al., hep-ph/0307357 GQ < 6 MeV (non-observation) • R. Arndt et al., PRC68, 42201 (2003) GQ < 1 MeV (non-observation) • R. Cahn and G. Trilling, PRD69, 11401(2004) GQ= 0.9 +/- 0.3MeV (from DIANA results) • A. Sibirtsev, et al., hep-ph/0405099 (2004) GQ < 1 MeV (K+d Kopp) • First positive identification of Q+ in K+d, including double scattering. • W. Gibbs, nucl-th/0405024 (2004) GQ = 0.9 +/-0.2 MeV (K+d X) Valery Kubarovsky BEACH2004 06/29/04

  29. Q2 < 1 GeV2 M = (3099 +/- 3 +/- 5) MeV Minimal quark content: uuddc Yet to be confirmed! H1-A charmed pentaquark Qo(3100)? c hep-ex/040305 (2004) Q2 = 1 – 100 GeV2 Valery Kubarovsky BEACH2004 06/29/04

  30. JLab-d Spring8 DIANA ELSA ITEP SVD/IHEP JLab-p HERMES ZEUS COSY-TOF CERN/NA49 H1 pp  S+Q+. Evidence for Penta-Quark States Valery Kubarovsky BEACH2004 06/29/04

  31. K+d for ½+ W. Gibbs (nucl-th/0405024) K+d for ½- DM ~ 12 MeV HERMES Spring-8 SAPHIR CLAS-d CLAS-p DIANA COSY ZEUS IHEP ITEP Summary of Experimental Masses Shift could be due to different background shapes and interference effects. Valery Kubarovsky BEACH2004 06/29/04

  32. Null 5Q Results - - Valery Kubarovsky BEACH2004 06/29/04

  33. Dead lock ? • The direct comparison between positive and negative results is possible but difficult due to the lack of theoretical models and experimental data. • Only new high statistics experiments can “cut the knot”. • And these experiments are coming. Valery Kubarovsky BEACH2004 06/29/04

  34. Second Generation Dedicated Experiments Valery Kubarovsky BEACH2004 06/29/04

  35. Q+ K+ g K- n K+ g K- L(1520) p p p n n LEPS-2/Spring8: deuterium target Must correct for Fermi motion of target nucleon bound state in the nucleus “Standard” baryon “Exotic” S=-1 S=+1 Valery Kubarovsky BEACH2004 06/29/04

  36. LEPS: “Default” analysis Preliminary! Nucleon mass f meson M(K+K-) MM(K+K-) Q+ mass [f,N cuts] L(1520) [f,N cuts] MM(K-) MM(K-) Valery Kubarovsky BEACH2004 06/29/04

  37. LEPS-2/Spring8: deuterium target Preliminary • Dedicated experiment • Aimed for 4x statistics • of 2003 result • Announced at N*2004 Valery Kubarovsky BEACH2004 06/29/04

  38. Conclusion of LEPS experimental group • LEPS high statistics experiment has reconfirmed the peak, very unlikely to be due to statistical fluctuations. • The preliminary study shows no indication that the peak is generated by kinematical reflections, detector acceptance, Fermi-motion correction, nor cuts. • “existence ranges from very likely to certain, but further confirmation is desirable” - “three-star” definition by PDG. Valery Kubarovsky BEACH2004 06/29/04

  39. PAC24 (June 2003) approved search for Q+ on deuterium - G10 run -gd K-K+p(n) (data taking completed in May 2004) • CLAS - Search for Q+, Q*+, Q*++ • - G11 run gpvarious final states (running NOW) • Hall A - Search for Q++, So • E04-012 ep eK-X++, eK+Xo (data taking completed) • CLAS – Search for X pentaquarks • EG3 run eD X--, X- X (scheduled for 2004/5) • CLAS- Exotic hadron spectroscopy (to run in 2005/6) - G12 run gp at 6 GeV, high luminosity 5 5 5 Pentaquark Searches at JLab Major program approved by PAC25 (Jan 2004) to search for pentaquark states Valery Kubarovsky BEACH2004 06/29/04

  40. G10 performance (deuterium target) • Exceptional performance of the machine and the CLAS detector. • At each torus current setting accumulated electron beam charge is ~4 times bigger than G2a (target is 2.4 times longer). Valery Kubarovsky BEACH2004 06/29/04

  41. n f L(1520) CLAS- G10 “online” plots gd K-pK+n Fully exclusive processes: L(1820) Ks gd K-pKs(p+p-)psp Valery Kubarovsky BEACH2004 06/29/04

  42. CLAS- G11 Spectroscopy of Exotic Baryons with CLAS: Search for Ground and Excited States RUNNING NOW ! Ks Valery Kubarovsky BEACH2004 06/29/04

  43. New Start Conter: trigger & PID Specifications Extended target cell coverage (40 cm) 2mm thick scintillator + light guide Higher azimuthal segmentation (4 x 6) Time resolution < 1ns (~200 ps in rec) Valery Kubarovsky BEACH2004 06/29/04

  44. G11 status e1c Valery Kubarovsky BEACH2004 06/29/04

  45. CLAS- G11 “online” plots p K0 S- S0 S0 L(1520) L Valery Kubarovsky BEACH2004 06/29/04

  46. G10, G11 Analysis efforts Common rules for all analyses: • Fully calibrated detector system • Use only selected “golden runs” • (fully functioning equipment) • Analysis in well defined CLAS fiducial volume • Energy and momentum corrections • that use independent well-studied channels • Analysis without and with kinematical constraints • whenever possible • Independent analyses by several groups. Valery Kubarovsky BEACH2004 06/29/04

  47. Jlab: Hall A - Search forQ++and S5 Run is completed M=1540 - 1620 MeV s=1.3 MeV Online-analysis M=1560 - 1860 MeV GPDG = 15.6 +/- 1.0 MeV MPDG = 1519.5 +/-1.0 MeV MM(eK+) Valery Kubarovsky BEACH2004 06/29/04

  48. Hall A: Online missing mass distributions s=1.3 MeV Valery Kubarovsky BEACH2004 06/29/04

  49. CLAS- Search forX5Pentaquark States • The search for narrow X5 states can be approached • in at least two ways: • Missing mass technique • Reconstruction of all decay particles • We will explore both possibilities Valery Kubarovsky BEACH2004 06/29/04

  50. 1320 1530 X-(1862)? CLAS –missing mass technique Data from run at Eg < 3.8 GeV • Good missing mass • resolution and low • background. • Needs Eg > 5 GeV, • new start counter Valery Kubarovsky BEACH2004 06/29/04

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