Hyperon Photoproduction by Linearly Polarized Photons at SPring-8/LEPS Mizuki Sumihama RCNP, Osaka Univ. for the LEPS collaboration SPIN2006 Oct. 6th 2006

Physics motivation It is essential to fully know N * and  * to understand baryon structure. Many nucleon resonances predicted by quark model are still missing. D 13 (1900) resonance in SAPHIR / CLAS data was found  K+K+ Y(   ) p  N, N *,  * Some resonances should couple to K  or K  channel. Kaon photoproduction is good means to search for missing resonances. Missing resonances N* and  * in s-channel

Meson exchange in t-channel K+K+ Y(   ) p  K *, K, K 1 E  = 1.5  2.4 GeV Transition region, s-channel  t-channel Contribution of t-channel meson exchange becomes large above 2GeV. Photon-beam asymmetry  natural parity exchange (K*)   = + 1 unnatural parity exchange (K, K1)   = － 1 at t = 0 and large E .

 LEPS spectrometer – forward acceptance 1m1m TOF wall MWDC 2 MWDC 3 MWDC 1 Dipole Magnet (0.7 T) Liquid Hydrogen Target (50 mm thick ) Start counter Silicon Vertex Detector Aerogel Cherenkov (n=1.03) Linearly polarized

Particle identification by time-of-flight and momentum measurements Momentum resolution ~0.8% for 2GeV/c Kaons. Time resolution ~150 ps.

K + Missing mass spectrum K+K+  p  K +  (1116)  p  K +  0 (1193 ) Z-vertex distribution LH2 target

Photon asymmetry –  (1116)  K+K*-exchange (K*-exchange is dominant) by M. Guidal.  Isobar + Regge by T. Mart and C. Bennhold.  Gent isobar model by T. Corthals. Agreement is not so bad, but still need fine optimization. Positive sign data nucl-th / SNP2004 Phys. Rev. C68, (2003) Phys. Rev. C73, (2006)

Photon asymmetry –   (1193)  K+K*-exchange (K*-exchange is dominant) by M. Guidal.  Isobar by T.Mart and C.Bennhold.  Gent isobar model by T. Corthals Agreement is not so bad, but still need fine optimization. Positive sign data nucl-th / SNP2004 Phys. Rev. C68, (2003) Phys. Rev. C73, (2006)

Differential cross sections –  (1116)  LEPS data agree with SAPHIR and CLAS at cos  = 0.75, 0.85 but discrepancy for SAHIR data is large at cos  =  LEPS data shows a small bump at W= 1960MeV.  Regge K+K*-exchange  Isobar (with D 13 )+Regge by T.Mart and C.Bennhold.  Good agreement. Resonance-like structure W (GeV) SAPHIR CLAS LEPS

Differential cross sections –   (1193)  Good agreement with CLAS.  Slightly smaller than SAPHIR.  Small bump structure around W = 2070 MeV.  Regge K+K*-exchange  Isobar model by T.Mart and C.Bennhold.  Gent isobar model by T. Corthals  Good agreement W (GeV) LEPS SAPHIR CLAS

Differential cross sections –  (1116)  Regge model K+K*-exchange K-exchange makes forward peak for K  channel.  Isobar (Feynman) only  Isobar (Feynman) + Regge by T.Mart and C.Bennhold. Forward peaking Cannot be reproduced By Feynman diagram only, at E  >2GeV. Need Regge poles. CLAS LEPS - angular dependence

Differential cross sections –  0 (1193)  Regge model K+K*-exchange K*-exchange is dominate for K  channel.  Isobar (Feynman) by T. Mart and C. Bennhold. No forward peaking. Can be explained by Feynman diagram only. - angular dependence CLAS LEPS

Differential cross sections for  p  p  0 -  Check photon normalization LEPS data Old data Curves SAID (fit data at E  < 2GeV) Good agreement with SAID  Photon normalization is OK.

Summary The K + photoproduction was measured by linearly polarized photons at SPring-8/LEPS. Photon beam asymmetry is good tool to define theoretical models. Theoretical models are still needed to be optimized. Differential cross sections were obtained at very forward angles, up to cos  cm = Bump structure was seen at W=1960 MeV in the K +  mode. We see a forward peaking in K +  while no peaking in K +  0. In order to fit the forward-angle data, a Regge pole is necessary in addition to s-channel resonances and t-channel K and K*-exchanges. Combination of isobar (Feynman) and Regge is successful to explain this forward peaking in K + . Photon normalization was checked by  p  p  0 cross sections. The data show a good agreement with SAID. LEPS photon normalization is OK. PRC73, (2006) / PRL 91, (2003).

LEPS collaboration D.S. Ahn, J.K. Ahn, H. Akimune, Y. Asano, W.C. Chang, S. Date, H. Ejiri, H. Fujimura, M. Fujiwara, K. Hicks, K. Horie, T. Hotta, K. Imai, T. Ishikawa, T. Iwata, Y.Kato, H. Kawai, Z.Y. Kim, K. Kino, H. Kohri, N. Kumagai, Y.Maeda, S. Makino, T. Matsumura, N. Matsuoka, T. Mibe, M. Miyabe, Y. Miyachi, M. Morita, N. Muramatsu, T. Nakano, Y. Nakatsugawa, M. Niiyama, M. Nomachi, Y. Ohashi, T. Ooba, H. Ookuma, D. S. Oshuev, C. Rangacharyulu, A. Sakaguchi, T. Sasaki, T. Sawada, P. M. Shagin, Y. Shiino, H. Shimizu, S. Shimizu, Y. Sugaya, M. Sumihama H. Toyokawa, A. Wakai, C.W. Wang, S.C. Wang, K. Yonehara, T. Yorita, M. Yosoi and R.G.T. Zegers, a Research Center for Nuclear Physics (RCNP), Ibaraki, Osaka , Japan b Department of Physics, Pusan National University, Pusan , Korea c Department of Physics, Konan University, Kobe, Hyogo , Japan d Japan Atomic Energy Research Institute, Mikazuki, Hyogo , Japan e Institute of Physics, Academia Sinica, Taipei 11529, Taiwan f Japan Synchrotron Radiation Research Institute, Mikazuki, Hyogo , Japan h School of physics, Seoul National University, Seoul, Korea i Department of Physics, Ohio University, Athens, Ohio 45701, USA j Department of Physics, Kyoto University, Kyoto, Kyoto , Japan k Laboratory of Nuclear Science, Tohoku University, Sendai , Japan l Department of Physics, Yamagata University, Yamagata, Yamagata , Japan m Department of Physics, Chiba University, Chiba, Chiba , Japan n Wakayama Medical College, Wakayama, Wakayama , Japan o Department of Physics, Nagoya University, Nagoya, Aichi , Japan p Department of Physics, Osaka University, Toyonaka, Osaka , Japan q Department of Physics, University of Saskatchewan, Saskatoon, S7N 5E2, Canada r Department of Applied Physics, Miyazaki University, Miyazaki , Japan

Photon asymmetry -difference between  and     

Photon asymmetry -energy dependence E  (GeV)   