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Evidence for S=+1 Pentaquark State T. Nakano (RCNP, Osaka Univ)

Evidence for S=+1 Pentaquark State T. Nakano (RCNP, Osaka Univ). Introduction Experiment Evidence for Q + Confirmation from other labs Conclusion & Outlook. September 17, 2003 @ Kyoto Univ. Q + (Z + ) Baryon. Q + (1530). D. Diakonov, V. Petrov, and M. Polyakov, Z. Phys. A 359 (1997) 305.

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Evidence for S=+1 Pentaquark State T. Nakano (RCNP, Osaka Univ)

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  1. Evidence for S=+1 Pentaquark StateT. Nakano (RCNP, Osaka Univ) • Introduction • Experiment • Evidence for Q+ • Confirmation from other labs • Conclusion & Outlook September 17, 2003 @ Kyoto Univ.

  2. Q+(Z+) Baryon Q+(1530) D. Diakonov, V. Petrov, and M. Polyakov, Z. Phys. A 359 (1997) 305. • Exotic: S=+1 • Low mass: 1530 MeV • Narrow width: < 15 MeV • Jp=1/2+ M = [1890-180*Y] MeV

  3. Exotic S=+1 Baryon • NOTE ON THE S = + 1 BARYON SYSTEM • (PDG 1986; Phys. Lett. B170, 289) • The evidence for strangeness +1 baryon resonances was reviewed in our 1976 edition,1 and more recently by Kelly2 and by Oades.3 Two new partial-wave anaIyses4 have appeared since our 1984 edition. Both claim that the P13 and perhaps other waves resonate. • However, the results permit no definite conclusion- the same story heard for 15 years. The standards of proof must simply be much more severe here than in a channel in which many resonances are already known to exist. The general prejudice against baryons not made of three quarks and the lack of any experimental activity in this areamake it likely that it will be another 15 years before the issue is decided. • References • 1. Particle Data Group, Rev. Mod. Phys. 48, SI88 ( 1976). • 2. R.L. Kelly, in Proceedings of the Meeting on Exotic Resonances (Hiroshima, 1978), ed. I. Endo et al. • 3. G.C. Oades, in Low and Intermediate Energy Kaon-Nucleon Physics (1981), ed. E. Ferrari and G. Violini. • 4. K. Hashimoto, Phys. Rev. C29, 1377 (1984); and R.A. Arndt and L.D. Roper, Phys. Rev. D31, 2230 (1985).

  4. Possible Q+ Production Reactions LEPS/SPring-8 CLAS/JLAB Q+ Q+ Q+ Q+ DIANA/ITEP KEK-PS/E522

  5. Super Photonring-8GeVSPring-8 • Third-generation synchrotron radiation facility • Circumference: 1436 m • 8 GeV • 100 mA • 62 beamlines

  6. Laser Electron Photon facility at SPring-8 in operation since 2000 g

  7. The Wakayama Medical University S. Makino Nagoya University T. Fukui Osaka University H. Nakamura, M. Nomachi, A. Sakaguchi, Y. Sugaya, University of Saskatchewan C. Rangacharyulu Institute for High Energy Physics (IHEP), Moscow P. Shagin Laboratory of Nuclear Science, Tohoku University H. Shimizu, T. Ishikawa University of Michigan K. Yonehara Michigan State University R.G.T. Zegers Seoul National University H. Fujimura Miyazaki University T. Matsuda, Y. Toi

  8. LEPS collaboration Research Center for Nuclear Physics, Osaka University T. Nakano, D.S. Ahn, M. Fujiwara, T. Hotta, K. Kino, H. Kohri, T. Matsumura, T. Mibe, A. Shimizu, M. Sumihama Pusan National University J.K. Ahn Konan University H. Akimune Japan Atomic Energy Research Institute / SPring-8 Y. Asano, N. Muramatsu Institute of Physics, Academia Sinica, Taiwan W.C. Chang, T.H. Chang, D.S. Oshuev, C.W. Wang, S.C. Wang Japan Synchrotron Radiation Research Institute (JASRI) / SPring-8 S. Date, H. Ejiri, N. Kumagai, Y. Ohashi, H. Ookuma, H.Toyokawa, T. Yorita Ohio University K. Hicks Kyoto University K. Imai, M. Miyabe, M. Niiyama, T. Sasaki, M. Yosoi Chiba University H. Kawai, T. Ooba, Y. Shiino Yamagata University T. Iwata

  9. Energy Spectrum and Polarization Intensity : 2.5 * 106g/sec > 1.5 GeV: 1.0 * 106g/sec 8 GeV 2.4 GeV Polarization : 95 % at 2.4 GeV

  10. LEPS detector g 1m

  11. LH2 Target Start Counter Drift Chamber g SSD Cerenkov Detector

  12. 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 identificationPhoton beam asymmetries for K+ photoproduction s(mass) = 30 MeV(typ.) for 1 GeV/c Kaon

  13. 30 Hz for 800 kHz@tagger Charge veto AC(n=1.03) Target(LH2) Start counter (SC) Summary of data taking • Total number of trigger • 1.83*108 trigger • Dec, 2000 to Jun, 2001 • Number of events with reconstructed charged tracks 4.37*107 events • About a half of events were produced in SC Optimized for g p  f p  K+ K- p Small distance between LH2 and SC High index of AC g p  K0Q+  p+p- K+ n

  14. Non-resonant KK L(1520) Q+? Identification of Q+ • Problems: • “background” • fK+K- • (produced from n & p) • Fermi motion distorts a missing mass spectrum. g n → K-Q+ → K- K+ n • K- missing mass gives Q+ mass • K+K- missing mass gives n

  15. Fermi motion correction Test-case: g n → K+ S-→K+ p- n g p → K+ L→K+ p- p L S- K+p-missing mass Correction works better when is small. K+missing mass K+missing mass (corrected) Startcounter (CH) L LH2 target K+missing mass K+missing mass (corrected) Correction: MMgK+ (corrected)= MMgK+- MMgK+p-+ Mn

  16. Proton-recoil cut • gnK+K-n no recoil proton(proton is a spectator) • gpK+K-p slow recoil proton is present • proton is too slow to be seen in full detector, but might be seen in SSD vertex detector. tof dc dc dc ssd K+ g target (SC) K- p dipole Remove all events for which proton is detected in SSD, or for which predicted proton track does not hit SSD.

  17. Effectiveness of proton recoil cut g p(n)K+K-p(n) MMcgK+ = MMgK+- MMgK+K-+ Mn • select KK events from startcounter • construct K+ missing mass (corrected) plot • apply p-recoil cut • reverse p-recoil cut • （proton is present) gp L(1520)K+ K-p No L(1520) peak in events with a spectator proton. The cut enhances g nK+K-n

  18. Background? n(g,K-) missing mass g n → K-Q+ → K- K+ n Q+ • select KK events from SC • apply KK invariant mass cut (f) • apply KK missing mass cut (0.9<MMkk<0.98) • apply proton recoil cut • construct K- missing mass plot • Backgroundshape can be determined from events from LH2 target using the same cuts except for: • Proton-recoil cut is removed • L(1520) events are removed • (only from p)

  19. Q+ identification 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

  20. Confirmation from other labs DIANA/ITEP CLAS/JLAB g d → p K+ K-n K+Xe → K0p X (K+n→ K0p) M = 15392 MeV G < 9 MeV M = 15425 MeV G < 21 MeV hep-ex/0304040 hep-ex/0307018

  21. Questions to be answered • Why is it so light? • Why is the width so narrow? • S.Nussunov (hep-ph/0307357) based on K+d scattering data G(Q+)<6MeV • Arndt,Strakovski & Workman (nucl-th/0308012) based on existing K+N elastic scattering data estimate that G(Q+) can/should be as small as 1 MeV • Pentaquark or KN molecule? • Excited S=+1 states? • Is this really an I=0, Jp=1/2+ state? • Lattice QCD calculations suggest positive parity (S. Sasaki, Hadron03) , (F. Csikor et al, hep-lat/0309090)

  22. Theoretical activities • Exotic baryon states in topological soliton models Walliser, H ; Kopeliovich, V B, hep-ph/0304058 • Interpretation of the Theta+ as an isotensor resonance with weakly decaying partners Capstick, Page, Roberts, hep-ph/0307019 • Stable $uudd\bar s$ pentaquarks in the constituent quark model Stancu, Fl ; Riska, D O, hep-ph/0307010 • The Constituent Quark Model Revisited - Quark Masses, New Predictions for Hadron Masses and KN Pentaquark Karliner, Marek; Lipkin, Harry J, hep-ph/0307243 • Pentaquark states in a chiral potential Hosaka, Atsushi hep-ph/0307232 • Group theory and the Pentaquark Wybourne, B G, hep-ph/0307170 • Diquarks and Exotic Spectroscopy Jaffe, R L ; Wilczek, F, hep-ph/0307341 • Understanding Pentaquark States in QCD Zhu, Shi-Lin, hep-ph/0307345 • The anticharmed exotic baryon Theta_c and its relatives Karliner, Marek; Lipkin, Harry J hep-ph/0307343 • Determining the $\Theta^+$ quantum numbers through the $K^+p\to \pi^+K^+n$ reaction Hyodo, T ; Hosaka, A ; Oset, E nucl-th/0307105

  23. Very recent results with proton target M = 154042 MeV G < 25 MeV M = 153710 MeV G < 32 MeV CLAS/Jlab hep-ex/0307088 SAPHIR/ELSA hep-ex/0307083 Require cos qK > 0.5

  24. Q+: Ks photoproduction at CLAS INFN group analysis • Even with very little background, the Q+ is not seen in gp  Ks X. • Upper limit on the Q+ production cross section: <20 nb. (MC efficiency with t-channel production at 3 s confidence level) • It is possible that the coupling of the pK*Q+ vertex is smaller than the pKQ+ vertex or that the mass of the virtual meson exchanged is a factor.

  25. Q+: Ks production (forward angles) Ohio Univ. analysis • Still cut on forward angles (cosQcm > 0.5) as done by SAPHIR • Additional requirement: only 3 charged particles (+ 1 neutral) • Note: 2/3 of the data (Ee = 2.4 and 2.9 GeV) • A small peak appears at ~1.54 GeV, but with only 3-4 s, depending on background • Still small cross section!

  26. Neutrino scattering hep-ex/0309042 Reanalysis of bubble chamber experiments from WA21, WA25, WA59, E180, E632 M(Ksp) spectrum

  27. New proton target result from CLAS gp  K-K+p+n 4.8 < Eg < 5.4 GeV (g6c) D. P. Weygand HADRON03

  28. g K* K0 Q+ p To determine Spin and Parity • Polarize Q+ and measure the K+ direction and the neutron spin. • Double or triple polarization experiment? K Q+

  29. g K* K*(1430) or K0 Q+ p Photoproducion by linearly polarized photon Decay Plane // g if natural parity exchange (-1)J In K* rest frame (Helicity frame) p+ p+ • Decomposition of • natural parity exchange • unnatural parity exchange Polarization vector of g K- K- Decay Plane g if unnatural parity exchange -(-1)J (Pseudoscaler mesons) gp  K*Q+Eth = 2.65 GeV 4p detector TPC

  30. Conclusion & Outlook • Observation of Nariirow Peak in Missing Mass of g n → K- X. • Evidence for Narrow S=+1 baryon at LEPS at 1.54 GeV with a narrow width. • Confirmation from other facilities (CLAS(d)/Jlab, DIANA/ITEP,CLAS(p)/Jlab, SAPHIR/ELSA). • Narrow S=+1 baryon state at 1.54 GeV is getting established. • Further data taking with LD2 target finished at LEPS and scheduled at CLAS. • Next things to do. • Determination of Spin and Parity. Is this really Q+? • Other pentaquark resonances ? (S=+1 or not) • More theoretical works including lattice are needed.

  31. Conclusion & Outlook (cont.) • For further experimental study • 4p Coverage .  A new TPC (Readout system will be ready in a few month.) • Photon energy upgrade (Max. 3 GeV) to study Q in K*(892) photo-production. (Use linearly polarized photons as a parity filter.) • Measurement of a recoiled nucleon polarization OR a Polarized target. (Technically the latter is easier.)

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