Differential cross sections for K + photoproduction at SPring-8/LEPS. Mizuki Sumihama Department of physics Tohoku university For LEPS collaboration JPS meeting at Kochi

The LEPS collaboration Research Center for Nuclear Physics, Osaka University D.S. Ahn, M. Fujiwara, T. Hotta, K. Kino, H. Kohri, T. Matsumura, T. Mibe, T. Nakano, 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 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

Missing baryon resonance search (D 13, …. ) Meson exchange in t-channel (K, K*, K1) Physics motivations Data of Kaon photoproduction at sub-GeV energy  Cross section from SAPHIR, CLAS  Recoil polarization from SAPHIR, CLAS  Photon beam asymmetry from LEPS E  = GeV at LEPS There still remains a controversy in theoretical descriptions.

Discrepancy between Bonn/SAPHIR and Jlab/CLAS It is important to solve the discrepancy between SAPHIR and CLAS, and obtain the data overall energy and angle range.  + p K + +   + p K + +  

Experiment Photon energy 1.5 – 2.4 GeV. Liquid hydrogen target with a 5 cm. ~1x10 11 photons at the target. K + angle cos(  cm) = 0.75, 0.85, 0.925,  + p K + +  (2.2x10 4 events)  + p K + +   (1.5x10 4 events) Detected by spectrometer.

Event selection 1 K + selection with Mass (3  ). 2 Reject decay-in-flight with   of track fitting. 3 Reject e+e- cut (remove events in-plane). 4 Proton selection with z-vertex point. 5 Photon selection at tagging counter. 6 Hyperon selection with missing mass (2  ). Data analysis  + p K + +   + p K + +  

d(cos  cm ) a(N K + - b) dd N B ・ N T ・ d(cos  cm ) = Differential cross sections N K+ : number of selected K+ events N B : number of protons N T : number of photons a = acceptance of K + and detectors b = background contaminations (pions, protons, start counter) < 2.2% < 6.5%

Results of differential cross sections  + p K + +  + p K + +   SAPHIR CLAS LEPS

Theoretical models I  + p K + +  + p K + +   K + K* and K* : Regge theory by Guidal (NPA627, 645,1997) Isobar model with missing resonance of D 13 (PRC65,015201, 2002)

Theoretical models II  + p K + +  + p K + +   Regge, Feynman (D 13 ), Mix by Bennhold and Mart

Theoretical models III  + p K + +  + p K + +   Regge, Feynman (D 13 ), Mix by Bennhold and Mart

Summary Differential cross sections of K + photoproduction at E  = 1.5 – 2.4 GeV and forward angles. LEPS data shows a good agreement with CLAS data. Solve the discrepancy between SAPHIR and CLAS. Resonance structure at W=1.86 GeV and forward peaking can be seen in  + p K + + . No resonance nor forward peaking in  + p K + +  . Refitting with new LEPS data and CLAS data and LEPS photon asymmetries data.

 LEPS detector 1m1m TOF wall MWDC 2 MWDC 3 MWDC 1 Dipole Magnet (0.7 T) Liquid Hydrogen Target (50mm thick ) Start counter Silicon Vertex Detector Aerogel Cerenkov (n=1.03)

Photon beam asymmetry