1 K + Photoproduction and  0 photoproduction by Linearly Polarized Photons at SPring-8/LEPS Mizuki Sumihama RCNP, Osaka Univ. for the LEPS collaboration MENU2007 Sep GeV ring

2 Diagram of K + /  0 photoproduction K + (       p  p  N, N *,  * K + (  0 )    p  p  K, K*, K 1  ) K + (  0 )   (p  p   , Y* (N,N*) stu s-channel t-channel u-channel Intermediate angle forward angle backward angle Spectrometer acceptance : 0.7<cos  cm <1 LEPS spectrometer covers the region where other facilities cannot access. Forward data  Detect K +, ID  0 in missing mass Backward data  Detect  (p   , ID K + in missing mass.

3   It is essential to fully characterize N * and  * to understand baryon structure.   Many nucleon resonances predicted by quark model are still not observed.   Some resonances could couple to K  or K  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 D 13 (1900).   Need more complete K + data to reach the conclusion. K + (  0 )   (p  p  N, N *,  * Missing resonances N* and  * in s-channel  Polarization observables (Photon-beam asymmetry etc..) are sensitive to resonance states and model differences because of interference between states.

4 Meson / hyperon exchange in t- / u-channel K+K+   p  K *, K, K 1  LEPS energy E  = GeV is in the transition region, s-channel  t-channel (forward), u-channel (backward)  Photon-beam asymmetry  at t = 0 and large E  : natural parity exchange (K*)   = + 1 unnatural parity exchange (K, K 1 )   = － 1  g pKY coupling constant in the u- channel. Studies of coupled-channel analysis show non-negligible effect. K+K+  p   , Y*

5 Laser-electron photon beam  Linearly polarized photon beam.  photon beam asymmetry.  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 1x10 6 cps. Forward data  Detect K + (p), ID  0 (   ) in missing mass Backward data  Detect  (p   , ID K + in missing mass. Forward spectrometer

6  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

7 Particle identification Particle identification by time-of-flight and momentum measurements Detect K + at forward angles, ID  0 in missing mass Detect p    at forward angles, ID K + in missing mass.

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

9 Energy distribution of differential cross sections W (GeV) Resonance-like structure W (GeV)  K+K*-exchange by M. Guidal (Regge model).  Isobar + Regge by T. Mart and C. Bennhold.  Gent isobar model by T. Corthals LEPS SAPHIR CLAS  0 (1193)  (1116)

10 Angular distribution of differential cross sections No forward peaking.  0 (1193)  (1116) Forward peaking Need Regge poles.  Regge model K+K*-exchange  Isobar (Feynman) only  Isobar + Regge by T.Mart and C.Bennhold. LEPS CLAS

11 Photon-beam asymmetry  -single polarization observable  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.  0 (1193)  (1116)

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

13 Backward K +  photoproduction M(p  - )  (1116)  p   X K+K+  p  p     K +  , K* , KY* Detect  (p  - ) at forward spectrometer Identify K + by missing mass technique

14 Backward K + photoproduction nucl-ex/ arXiv: , K.Hicks, T.Mibe, M.Sumihama, et al.arXiv: Curves are theoretical calculation using   and  * u-channel poles.

15 Complementary with CLAS data LEPS CLAS

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

17 Backward  0 photoproduction 17 1/10 total statistics proton missing mass spectrum M. Sumihama et. al, nucl-ex/

18 Differential cross section cos  cm 1.8 GeV Change angular distribution at E  ~1.8 GeV, Backward peaking Backward peaking Existing data. LEPS data u u-channel contribution SAID MAID2005

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

20 Photon beam asymmetry  SAID LEPS data Existing data. PLB544(2002)113 NPB104(1976)253… MAID GeV Strong angular dependence above 1.9 GeV. Higher mass resonances need to be included. Positive sign:  Negative sign: 

21 Summary  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 +  mode as well as the CLAS/SAPHIR data.  At forward angles, we observed a forward peaking in K +  but no peaking in K +  0.  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 E  > 1.9 GeV.  0 photoproduction  + 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 , 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