1. Recent results and future prospects of the Laser Electron Photon experiment at SPring-8 T. Hotta (RCNP Osaka University) the LEPS collaboration 第六届中日核物理研讨会, 上海, 2006/05/18 LEPS experiment Search for the   pentaquark Upgrade of the LEPS facilty  LEPS2

2. SPring-8: world’s largest synchrotron radiation facility (8 GeV) LEPS beamline: ~3 GeV polarized photon beam produced by backward Compton scattering of Laser photon. Laser Electron Photon beamline at SPring-8

3.  1m1m Magnetic spectrometer in the forward direction (  , K , p, d) Beam: GeV photon Target: p, d, A LEPS Experiment

4. Research Center for Nuclear Physics, Osaka University ： T. Nakano, D.S. Ahn, M. Fujiwara, K. Horie, T. Hotta, Y. Kato, K. Kino, H. Kohri, N. Muramatsu, T. Sawada, T. Tsunemi, M. Uchida, M. Yosoi, R.G.T. Zegers Department of Physics, Pusan National University ： J.K. Ahn, J.Y. Park School of Physics, Seoul National University ： H.C. Bhang, K.H. Tshoo Department of Physics, Konan University ： H. Akimune Japan Atomic Energy Research Institute / SPring-8 ： Y. Asano, A. Titov Institute of Physics, Academia Sinica ： W.C. Chang, D.S. Oshuev, Japan Synchrotron Radiation Research Institute (JASRI) / SPring-8 ： H. Ejiri, S. Date', N. Kumagai, Y. Ohashi, H. Ohkuma, H. Toyokawa, T. Yorita Department of Physics and Astronomy, Ohio University ： K. Hicks, T. Mibe Department of Physics, Kyoto University ： K. Imai, H. Fujimura, M. Miyabe, Y. Nakatsugawa, M. Niiyama Department of Physics, Chiba University ： H. Kawai, T. Ooba, Y. Shiino Wakayama Medical University ： S. Makino Department of Physics and Astrophysics, Nagoya University ： S. Fukui Department of Physics, Yamagata University ： T. Iwata Department of Physics, Osaka University ： S. Ajimura, M. Nomachi, A. Sakaguchi, S. Shimizu, Y. Sugaya Department of Physics and Engineering Physics, University of Saskatchewan ： C. Rangacharyulu Department of Physics, Tohoku University ： M. Sumihama Laboratory of Nuclear Science, Tohoku University ： T. Ishikawa, H. Shimizu Department of Applied Physics, Miyazaki University ： T. Matsuda, Y. Toi Institute for Protein Research, Osaka University ： M. Yoshimura National Defense Academy in Japan ： T. Matsumura The LEPS Collaboration

5. Pentaquark   M  1890-180*Y] MeV D. Diakonov, V. Petrov, and M. Polyakov, Z. Phys. A 359 (1997) 305. Exotic: S=+1 Low mass: 1530 MeV Narrow width: ~ 15 MeV J p =1/2 + The antiquark has a different flavor than the other 4 quarks.

6. γ + d (n ) reactions γ + p → p K s 0 γ + p → n K + K - p + K + (N) → p K s 0 lepton + D, A → p K s 0 p + A → pK s 0 + X p + p → pK s 0 +  + Other  + Upper Limits BaBar CLAS-d2 BELLE ALEPH, Z SVD2 LEPS-d2 LEPS-C CLAS-d1 DIANA SAPHIR SVD2 COSY-TOF Hermes JINR CLAS-p LEPS-d BC ZEUS BES J,  CLAS g11 SPHINX HyperCP HERA-B FOCUS WA89 CDF : Positive result : Negative result 2002 2003 2004 2005 Both positive & negative results exist. Confirmation of the existence is still most important. Theoretical attempt to explain observation vs. non-observation.  Hosaka: May 20, Session 15 in this symposium. Time dependent experimental status of  +

7.  n  K  K  n Phys.Rev.Lett. 91 (2003) 012002 hep-ex/0301020 ++ Low statistics: but Tight cut: 85% of events are rejected by the  exclusion cut. Unknown background: BG shape is not well understood. Events from a LH2 target were used to estimate it. Possible kinematical reflections. Correction: Fermi motion correction is necessary. First evidence from LEPS

8. Collected Data (LH 2 and LD 2 runs) Dec.2000 – June 2001 LH 2 50 mm ~5×10 12 photons published data (target: 5mm plastic scint.) May 2002 – Apr 2003 LH 2 150 mm ~1.4×10 12 photons Oct. 2002 – June 2003 LD 2 150 mm ~2×10 12 photons #neutrons × #photons in K ＋ K － detection mode LD 2 runs ~ ×5 statistics expected # of   : 17  85 LEPS LD 2 runs

9. MM  (GeV) MM  (GeV) A proton is a spectator (undetected). Fermi motion is corrected to get the missing mass spectra. Tight  exclusion cut is essential. Background is estimated by mixed events. preliminary  (1520)  p  K + K - p  n  K + K - n Counts/12.5 MeV Search for  + in  n  K + K - n 

10. Θ ＋ is identified by K － p missing mass from deuteron. ⇒ No Fermi correction is needed. K - n and pn final state interactions are suppressed. Isospin selection: some reaction mechanism may favor specific isospin state. CLAS(d)@JLAB:  <450 pb. – acceptance coverage is different from LEPS (forward).  + search in  d   (1520) KN reaction γ p n Θ＋Θ＋ K－K－ p  (1520) detected ?

11. A possible reaction mechanism  + can be produced by re-scattering of K +. K momentum spectrum is soft for forward going  (1520). γ p/n n/p  (1520) K + /K 0  missing momentum Formation momentum LD2 P miss GeV/c Exchanged kaon can be on-shell. KN    formation cross section.

12. Background process Quasi-free  (1520) production must be the major background. The effect can be estimated from the LH2 data. γ p n  (1520) K+K+ n The other background processes which do not have a strong pK - invariant mass dependence can be removed by sideband subtraction.

13. Event selections in K － p mode MMp(γ,K － p) GeV/c 2 π － mis-ID as K － K ＋ mass : 0.40 – 0.62 GeV/c 2 M(K － p) GeV/c 2 Λ(1520) : 1.50 – 1.54 GeV/c 2 Events with Λ(1520) production were selected. E  > 1.75 GeV was also applied. Non-resonant KKp +  p + … γp→K － pKπ

14. Sideband BG estimation M(K － p) GeV/c 2 MMd(γ,K － p) GeV/c 2 correction for  contribution 10-MeV E  smearing has been applied to remove fine structure due to fluctuation. No visible signal. Validity of the sideband method with E  smearing was checked by using two independent regions of the sideband. Counts/5 MeV LD 2 

15. K － p missing mass spectrum MMd(γ,K － p) GeV/c 2 sideband  Quasi-free  * sum Counts/5 MeVC Excesses are seen at 1.53 GeV and at 1.6 GeV above the background level. 1.53-GeV peak: preliminary MMd(γ,K － p) GeV/c 2 Counts/5 MeV Normalization of  * is obtained by fit in the region of MMd < 1.52 GeV. (in the 5 bin = 25 MeV) preliminary No visible signal in sidebands. ++ LD 2

16. MM(K － p) GeV/c 2 Counts/5 MeV preliminary Remove high frequency fluctuations by 10-MeV E  smearing All data & sideband BG data  BG Real peak or fluctuation? Within existing data, robustness of the peak has been checked by E  smearing (smoothing of the spectra). Fine structure (< experimental resolution) must be statistical fluctuations.

17. Normalization factor for LH2 data (green line) is 2.6.  No large p/n asymmetry. Quasi-free process can be reproduced by free process.  small effect from Fermi motion. Large cross-section compared with  (1520). Missing Mass resolution is worse. No excess at 1.53 GeV nor at 1.6 GeV. MMd(γ,  － p) GeV/c 2 Counts/5 MeV preliminary Search for  d   (1116)  + γ p n Θ＋Θ＋ －－ p  (1116) forward angle detection

18. Summary of   search at LEPS Confirmation of  + by using LD 2 data K  K  detection mode: –1.53 GeV/c 2 peak observed ~ expected # of events. – BG estimation is still underway. K-p detection mode in MMd(g,pK-) spectrum: – 1.53 GeV/c 2 peak (4-5σ,preliminary) + 1.6 GeV/c 2 bump associated with  (1520) production – Signal-like behavior. [M(pK  ) gate, E  dependence, & robustness of the peak under smearing.]

19. Prospects Negative and positive results on    Negative results restrict the possibility of   existence. – New CLAS@JLAB data denied their evidence. But their kinematical condition is different from LEPS. There are still some positive evidences which cannot be excluded completely. – e.g. DIANA exp. (hep-ex/0603017) If   exist, production mechanism should be also exotic. Further measurements with wider kinematical coverage & high statistics are important. LEPS: Experiment w/ Large solid angle TPC will start soon. LEPS2: New beamline is proposed.

20. Beamline map of Spring-8 BL31ID

21. Schematic view of the LEPS2 facility Backward Compton Scattering a) SPring-8 SR ring b) Laser hutch c) Experimental hutch 8 GeV electron Recoil electron (Tagging) Plan to move the BNL-E949 detector to Spring-8 (helped by RIKEN) 5 m GeV  -ray Inside building Outside building 30m long line （ LEPS 7.8m) 4   detector （ Tohoku U. ） Large decay spectrometer Forward spectrometer New DAQ system Laser or re-injected X-ray High intensity ： Multi laser LRNB Round beam ~ 10 7 photons/s （ LEPS ~ 10 6 ） High energy ： Re-injection of X-ray from undulator （ Tohoku U., JASRI ） E  < 7.5GeV (LEPS < 3GeV) modify ： JASRI Acc. group

22. Schedule 2006200720082009 Decomposition of E949 detector (BNL) Moving E949 det. Construction of the decay spectrometer Construction of the forward spectrometer High speed DAQ system Modify SR ring Construction of the beamline Building Exp hutch Infrastructure Radiation shield Laser injection system R&D of polarized HD targetExperiment with HD target X-ray re-injection system 4 photon detector Submit LEPS2 proposal Apply BL modification Beam commisioning Detector commisioning Start experiment

23. LEPS2 Collaboration Core institutes RCNP, Osaka U. LNS Tohoku U. JASRI (SPring-8) Accelerator group RIKEN Radiation Laboratory (new !) Other LEPS members Kyoto U., Osaka U., Konan U., Chiba U., Yamagata U., Miyazaki U., Pusan U.(Korea), Seoul U.(Korea), Academia Sinica (Republic of China), Ohio U. (USA), Saskachewan U. (Canada) …etc. New members National Defense Academy, … some members from the BNL-E949 experiment (domestic and foreign institutes (BNL, TRIUMF,…)) We are trying to expand the collaboration !!