Differential cross sections for K + photoproduction at SPring-8/LEPS.

1. Differential cross sections for K+ photoproduction at SPring-8/LEPS. Mizuki Sumihama Department of physics Tohoku university For LEPS collaboration JPS meeting at Kochi 9.27 2004

2. The LEPS collaboration 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 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

3. Physics motivations Eg = 1.5 - 2.4 GeV at LEPS • Data of Kaon photoproduction at sub-GeV energy • Cross sectionfrom SAPHIR, CLAS • Recoil polarizationfrom SAPHIR, CLAS • Photon beam asymmetryfrom LEPS Missing baryon resonance search (D13, ….) Meson exchange in t-channel (K, K*, K1) There still remains a controversy in theoretical descriptions.

4. Discrepancy between Bonn/SAPHIR and Jlab/CLAS g + p K+ + L g + p K+ + S0 It is important to solve the discrepancy between SAPHIRand CLAS, and obtain the data overall energy and angle range.

5. g + p K+ + L (2.2x104 events) g + p K+ + S0 (1.5x104 events) Experiment • Photon energy 1.5 – 2.4 GeV. • Liquid hydrogen target with a 5 cm. • ~1x1011 photons at the target. • K+ angle cos(Qcm) = 0.75, 0.85, 0.925, 0.975. Detected by spectrometer.

6. Data analysis • g + p K+ + L • + p K+ + S0 Event selection 1K+ selection with Mass (3s). 2 Reject decay-in-flight with c2 of track fitting. 3 Reject e+e- cut (remove events in-plane). 4Proton selection with z-vertex point. 5Photon selection at tagging counter. 6 Hyperon selection with missing mass (2s).

7. ds a(NK+ - b) = d(cosQcm) NB・NT・d(cosQcm) Differential cross sections NK+ : number of selected K+ events NB : number of protons NT : number of photons a = acceptance of K+ and detectors b = background contaminations (pions, protons, start counter) < 2.2% < 6.5%

8. Results of differential cross sections SAPHIRCLASLEPS g + p K+ + L g + p K+ + S0

9. Theoretical models I g + p K+ + L g + p K+ + S0 K + K* and K* : Regge theory by Guidal (NPA627, 645,1997) Isobar model with missing resonance ofD13 (PRC65,015201, 2002)

10. Theoretical models II g + p K+ + L g + p K+ + S0 Regge, Feynman (D13), Mix by Bennhold and Mart

11. Theoretical models III g + p K+ + L g + p K+ + S0 Regge, Feynman (D13), Mix by Bennhold and Mart

12. Summary • Differential cross sections of K+ photoproduction at Eg = 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 g + p K+ + L. No resonance nor forward peaking in g + p K+ + S0. • Refitting with new LEPS data and CLAS data and LEPS photon asymmetries data.

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

14. Photon beam asymmetry