K + Photoproduction and p 0 photoproduction by Linearly Polarized Photons at SPring-8/LEPS

1. K+ Photoproduction and p0 photoproduction by Linearly Polarized Photons at SPring-8/LEPS 8 GeV ring Mizuki Sumihama RCNP, Osaka Univ. for the LEPS collaboration MENU2007 Sep. 2007

2. g K+ (p0) g K+ (p0) N, N*, D* K, K*, K1(r,w) p L, S0(p) p L, S0(p) Diagram of K+ / p0 photoproduction s-channel t-channel u-channel Intermediate angle forward angle backward angle g K+ (p0) L, S0, Y* (N,N*) p L,S0(p) Spectrometer acceptance : 0.7<cosqcm <1 LEPS spectrometer covers the region where other facilities cannot access. Forward data  Detect K+, ID L,S0 in missing mass Backward data  Detect L(pp-), ID K+ in missing mass.

3. K+ (p0) g N, N*, D* p L, S0(p) Missing resonances N* and D* in s-channel • It is essential to fully characterize N* and D* to understand baryon structure. • Many nucleon resonances predicted by quark model are still not observed. • Some resonances could couple to KL or KS channel. • Many one or two star resonances, above 1700 MeV (W > 1.7 GeV). • Structures in SAPHIR / CLAS data were found, possibly connected with missing resonances like D13(1900). • Need more complete K+ data to reach the conclusion. • Polarization observables (Photon-beam asymmetry etc..) are sensitive to resonance states and model differences because of interference between states.

4. g K+ g K+ K*, K, K1 p L, S0 L, S0, Y* p L • LEPS energy Eg = 1.5 - 2.4 GeV is in the transition region, s-channel  t-channel (forward), u-channel (backward) • Photon-beam asymmetry S at t = 0 and large Eg: natural parity exchange (K*) S = + 1 unnatural parity exchange (K, K1) S =－1 • gpKY coupling constant in the u-channel. Studies of coupled-channel analysis show non-negligible effect. Meson / hyperon exchange in t- /u-channel

5. Laser-electron photon beam • Linearly polarized photon beam.  photon beam asymmetry. • Polarization degree is 95% (55%) at the maximum (minimum) energy. • Use horizontally ( ) and vertically ( ) polarized beam. • Energy 1.5 – 2.4 GeV, RMS=15 MeV. • Intensity 1x106 cps. Forward spectrometer Forward data  Detect K+ (p), ID L,S0 (p0) in missing mass Backward data  Detect L (pp-), ID K+ in missing mass.

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

7. Particle identificationby time-of-flight and momentum measurements Detect K+ at forward angles, ID L, S0 in missing mass Detect pp-at forward angles, ID K+ in missing mass.

8. Forward K+ photoproduction K+ missing mass spectrum K+

9. Energy distribution of differential cross sections Resonance-like structure LEPSSAPHIR CLAS W (GeV) W (GeV) S0(1193) L(1116) • K+K*-exchange by M. Guidal (Regge model). • Isobar + Regge by T. Mart and C. Bennhold. • Gent isobar model by T. Corthals

10. Angular distribution of differential cross sections L(1116) S0(1193) LEPS CLAS Forward peaking Need Regge poles. No forward peaking. • Regge model K+K*-exchange • Isobar (Feynman) only • Isobar + Reggeby T.Mart and C.Bennhold.

11. Photon-beam asymmetry S-single polarization observable L(1116) S0(1193) • K+K*-exchange by M. Guidal. • Isobar + Regge by T. Mart and C. Bennhold. • Gent isobar model by T. Corthals Some resonances are hidden by other resonances due to their wide widths in cross sections. Polarization observables are a good mean to extract such hidden states.

12. Still large variation of models at backward angles Photon asymmetry Used data for fitting in models. SAPHIR/LEPS CLAS/LEPS SAPHIR/CLAS/LEPS T. Mart and A. Sulaksono PRC74 (2006) 055203

13. Backward K+L photoproduction Detect L(pp-) at forward spectrometer Identify K+ by missing mass technique M(pp-) L(1116) g p  LX K+ g p  p p- p+ K+S0, K*L, KY*

14. Backward K+ photoproduction nucl-ex/ arXiv:0707.4412, K.Hicks, T.Mibe, M.Sumihama, et al. Curves are theoretical calculation using L, S0 and S* u-channel poles.

15. Complementary with CLAS data CLAS LEPS

16. Photon asymmetry at backward angles New data at backward angles give constraints to theoretical models. g p  K+L 1.5 GeV < Eg < 2.0 GeV • Experiment with time- • projection chamber will • start soon. Photon • asymmetry at medium • region will be measured. 2.0 GeV < Eg < 2.4 GeV

17. Backward p0 photoproduction 1/10 total statistics M. Sumihama et. al, nucl-ex/0708.1600 proton missing mass spectrum 17

18. Differential cross sectioncosqcm Existing data. LEPS data SAID MAID2005 • Change angular distribution at Eg~1.8 GeV, • Backward peaking u-channel contribution

19. Energy dependence of slope in differential cross sections sqrt(s) (GeV) s-7 :quark counting rule 19

20. Photon beam asymmetryS LEPS data Existing data. PLB544(2002)113 NPB104(1976)253… SAID MAID2005 Positive sign: s < s Negative sign: s > s • Strong angular dependence above 1.9 GeV. • Higher mass resonances need to be included. 20

21. Summary K+ photoproduction • Photon-beam asymmetry and differential cross sections were obtained at very forward angles, and backward angles. • Bump structure was seen around W=1960 MeV in the K+L mode as well as the CLAS/SAPHIR data. • At forward angles, we observed a forward peaking in K+L but no peaking in K+S0. • Photon asymmetry data provide further constraints for models. • Backward peaking is due to u-channel dominance. • Strong angular dependence of asymmetry reflects the contribution of higher-mass resonances at Eg > 1.9 GeV. p0 photoproduction

22. 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 567-0047, Japan b Department of Physics, Pusan National University, Pusan 609-735, Korea c Department of Physics, Konan University, Kobe, Hyogo 658-8501, Japan d Japan Atomic Energy Research Institute, Mikazuki, Hyogo 679-5148, Japan e Institute of Physics, Academia Sinica, Taipei 11529, Taiwan f Japan Synchrotron Radiation Research Institute, Mikazuki, Hyogo 679-5198, Japan h School of physics, Seoul National University, Seoul, 151-747 Korea i Department of Physics, Ohio University, Athens, Ohio 45701, USA j Department of Physics, Kyoto University, Kyoto, Kyoto 606-8502, Japan k Laboratory of Nuclear Science, Tohoku University, Sendai 982-0826, Japan l Department of Physics, Yamagata University, Yamagata, Yamagata 990-8560, Japan m Department of Physics, Chiba University, Chiba, Chiba 263-8522, Japan n Wakayama Medical College, Wakayama, Wakayama 641-0012, Japan o Department of Physics, Nagoya University, Nagoya, Aichi 464-8602, Japan p Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan q Department of Physics, University of Saskatchewan, Saskatoon, S7N 5E2, Canada r Department of Applied Physics, Miyazaki University, Miyazaki 889-2192, Japan