K +  and K +  0 photoproduction at SPring-8/LEPS Mizuki Sumihama Department of physics Osaka Univ. for LEPS collaboration 1. Introduction 2. Experiment 3. Data analyses 4. Experimental results 5. Summary

LEPS collaboration M. Nomachi, A. Sakaguchi, Y. Sugaya, M. Sumihama Dept. of physics Osaka Univ. H. Fujimura, M. Fujiwara, T. Hotta, H. Kohri, T. Matsumura, N. Matsuoka, T. Mibe, M. Morita, T. Nakano, R.G.T.Zegers RCNP Osaka Univ. K. Imai, M. Miyabe, M. Niiyama, M. Yosoi Dept. of physics Kyoto Univ. D.S. Ahn, J.K. Ahn Pusan Nat’l Univ.. Korea T. Iwata Dept. of physics Yamagata Univ. Y. Asano,N. Matsumura JAERI T. Ishikawa, H. Shimizu Tohoku Univ. H. Kawai, T. Ooba, Y. Shiino Chiba Univ. S. Date, N. Kumagai, Y. Ohashi, H. Ookuma, T. Yorita JASRI W.C. Chang, D.S. Oshuev, C.W. Wang, S.C. Wang Academia Sinica, Taiwan A. Wakai Akita Industry Promotion Foundation K. Hicks Ohio Univ.USA C. Rangacharyulu Univ.. of Saskatchewan Canada H. Akimune Konan Univ. P. Shagin Minnesota Univ. S. Makino Wakayama Med. Univ.

1. Introduction Missing resonances N * and  *  in strangeness channels Information on nucleon resonances mainly comes from the  N channel. Many nucleon resonances predicted by quark model are still missing. It is essential to fully know N * and  * to understand the structure of baryons. K+K+ Y(  ) p  N, N *,  * Some resonances may couple to K  or K  channel. K + photoproduction is good means to search missing resonances.

Resonance structure? Resonance like structure in the total cross section for p( ,K + )  from SAPHIR and CLAS. Missing resonance D 13 (1960) ? without D 13 with D 13 calculations by Mart and Bennhold There still remains a controversy of the theoretical description. Only cross section data is not conclusive. SAPHIR data ~ 1.9 GeV Additional observables are required. Photon beam asymmetry is one of the candidates.

Theoretical predictions of photon asymmetry by Janssen et al by Mart & Bennhold Hadronic form factor A B C Davidson&Workman Haberzettl A) Small cut-off mass B)  * in u-channel C) No restriction on g KYp without D 13 (1960) with D 13 (1960) With D 13 (1960) Need more study to fix parameters. Photon beam asymmetry is sensitive to model differences.

2. Experiment ~ Liquid hydrogen target : 5cm Linearly polarized photons Tagged photons 1.5 ~ 2.4 GeV Resolution 15 MeV Beam intensity 5 x 10 5 cps (Tagged photons) High polarization ~92% at 2.4 GeV ~55% at 1.5 GeV 52% data with vertical polarization 48% data with horizontal polarization 2 x photons at the target Photon beam asymmetries for the p( ,K + )  and p( ,K + )  0 reactions

3. Data analyses Tagged photons recoil electron by Tagging counter Events from the proton target z-vertex point of K + contamination from the trigger counter ~ 8%  lab < 5 o 5 o K + events mass distribution by tracking and TOF  2  probability cut - confidence level 98%  and proton contaminations ~ 2%  and  0  events missing mass of p( , K + )X  and  0  contamination < 1% Event selections for p( ,K + )  and p( ,K + )  0 Beam

Missing mass spectrum p( ,K + )   72,500 events p( ,K + )  0 (1193) 48,900 events 1.5 ~ 2.4 GeV 0.6 < cos  cm < 1 Photon beam asymmetry

Photon beam asymmetry  Vertical = [ 1 + P   cos(2  ) ] Horizontal = [ 1 - P   cos(2  ) ] N = F acc = P   cos(2  ) N : K + photoproduction yield  : K + azimuthal angle P  : Polarization of photon n : Normalization factor for N v dd dvdv dd d  unpol dd dd dhdh dd dd nN v - N h nN v + N h For all events

4. Experimental results Correction 1  & proton contaminations  < 0.03 Correction 2 TRG contaminations  < 0.02 Systematic error 1 from pol. degree & angle 1.5% Systematic error 2 from normalization factor  ~ 0.03 Positive sign Different angular distribution Increase as the E  increases p( ,K + )  p( ,K + )  0

Comparison with models Currently, no models reproduce our data, perfectly.   by Mart & Bennhold without D 13 (1960) with D 13 (1960) by Janssen et al Hadronic form factor A B C Davidson&Workman Haberzettl A) Small cut-off mass B)  * in u-channel C) No restriction on g KYp with D 13 (1960)

5. Summary K + photoproduction is good means to search missing resonances. Photon beam asymmetries were obtained for the p( ,K + )  and p( ,K + )  0 reactions at the first time in E  = 1.5 ~ 2.4 GeV at SPring-8/LEPS. Positive sign Our data will stimulate the further development of the theoretical models and extend our knowledge of this reaction including missing resonances.