1. 1 Single  0 photoproduction at SPring-8/LEPS Mizuki Sumihama Osaka university, RCNP JPS meeting March 2007

2. 2 Introduction Pion photoproduction is well studied experimentally and theoretically as a spectroscopy of N* and  * resonances. The proprieties of many resonances are determined at W < 1.7 GeV. However above the resonance region, the production mechanism is not well studied partly due to lack of data. We measured single  0 photoproduction in 1.9-2.3 GeV in total energy at backward angles where less experimental data. The production mechanism will be investigated in a transition range from nucleon-meson degrees of freedom to quark-gluon degrees of freedom. High mass resonances, u-channel contribution, quark counting rule …

3. 3 Diagram in tree level  00 p p  00   00 p p  00 N*,  * P 33 (1232),P 11 (1440), D 13 (1520),S 11 (1535), S 31 (1620), S 11 (1650), D 15 (1675), F 15 (1680), D 33 (1700), P 13 (1720), F 35 (1905),P 31 (1910) and F 37 (1950) in MAID2005.  W < 1.7 GeV Models are well established. Data are well explained by four-star N* and  *.  W ~1.9 GeV There are one or two star N* and  * but doubtful.  W > 1.9 GeV at very backward angles non-resonant u-channel is expected to be dominant.  Much higher, W > 3 GeV in 60s, 70s. Regge baryon pole explains data well. Regge ~ s 2  (u)-2 at u~small, follow quark counting rule.(JLab) t-channel (forward) 1.9 – 2.3 GeV +Backward - medium s-channel u-channel s-channel List of four-star nucleon resonances Born term

4. p  p  Detect protons By spectrometer in missing mass Measurement of  + p  p +  0 Detect protons by LEPS spectrometer at forward angles Identify  0 in missing mass spectrum. Measure differential cross sections and photon beam backward angles asymmetries at backward angles -1 < cos  cm < -0.6. Polarization degree is ~95% at the maximum E , 2.4 GeV. Linearly polarized photons Liquid hydrogen 4

5.  5 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 +-~10 o in y +-~20 o in x

6. 6 Particle identification by time-of-flight and momentum measurements  Proton selection with 4 .  Kaon/pion contamination is negligible.

7. 7 Missing mass spectrum  p  pX Missing mass spectrum  p  pX Z-vertex distribution LH2 target 1/10 total statistics ~18000 counts Measurement region: 1.5 < E  < 2.4 GeV 1.9 < W < 2.3 GeV - 1 < cos  cm < -0.6

8. 8 Background reactions  p  p   p  p   p  p   p  p     Missing mass square No-scale! 2  cut (~ 0.13) 2,3 reactions are above the 2  cut point. 4 is much less than pion production by ~2-3 orders. (demonstration) Data MC

9. 9 Background subtraction Single pion and double pion productions generated by MC simulation are fitted to data by a template fit. Systematic uncertainty was estimated by doing a fits by Gaussians for  0 peaks with 2  and 1.5  cuts. Example of results of template fits

10. 10 Systematic error 1.Target protons 1.0% (fluctuation of temp. and pressure) 2.Photon normalization 1.2%, Photon transmission 3% 3.AC over veto 1.6% 4.Background subtraction, < 5% Obtain yield by subtracting two-pion photoproduction. Detector acceptance is obtained Monte Carlo simulation based on GEANT3. Photon normalization is obtained by tagging counter. Determine differential cross section

11. 11 Differential cross section, E  LEPS data Existing data. Eur.Phys.J.A26(2005)399, PRL,94(2005)012503, PLB,48(1974)463, NPB60(1973)267… SAID -partial-wave analysis (fit of existing data) PRC66,055213(2002) MAID2005 - isobar model nucl-th/0603012 Good agreement with existing data (SAID). Not follow ~s 2  (u)- 2 (Regge), ~ s 7 ( counting rule) at E  > 1.8 GeV.

12. 12 Differential cross section cos  cm LEPS data Existing data. SAID MAID2005 1.8GeV Change angular distribution drastically at E  ~1.8GeV, Backward peaking Backward peaking, small bump structure 1.85<E  <1.95GeV. Discrepancy with MAID becomes large at higher energy.

13. 13 Photon beam asymmetry  nN v  N h nN v + N h P   cos(2  ) = LEPS data Existing data. PLB544(2002)113 NPB104(1976)253… SAID MAID2005 Data show a good agreement with SAID/MAID. 1.8GeV Strong angular dependence above 1.8GeV. Positive sign:  Negative sign:  2.1 GeV < W < 2.3 GeV

14. 14Summary Differential cross sections at very backward angles have been measured and new data at E  > 1.8 GeV. Photon beam asymmetries have been measured at the first time at backward angles E  > 1.5 GeV. Angular dependence of both observables changes at 1.8 GeVstrong angular dependence E  1.8 GeV. A strong angular dependence is seen at E  > 1.8 GeV. Energy dependence cannot be explain by nucleon Regge pole nor scaling. At low energy region, the data is explained with models including well-known-nucleon resonances, but the strong angular dependence at high energy cannot be explained. Can the data be explained by Born term only? Does u- channel contribution dominate? Quark-hadron duality? High spin states? Challenge to theorists. Measurement at side angles and higher photon energy, Homework to experimentalist.

15. 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 15