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Hyperon Photoproduction by Linearly Polarized Photons at SPring-8/LEPS

Hyperon Photoproduction by Linearly Polarized Photons at SPring-8/LEPS. Mizuki Sumihama RCNP, Osaka Univ. for the LEPS collaboration. SPIN2006 Oct. 6th 2006. K +. g. N, N * , D *. p. Y( L, S 0 ). Physics motivation. Missing resonances N* and D * in s-channel.

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Hyperon Photoproduction by Linearly Polarized Photons at SPring-8/LEPS

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  1. Hyperon Photoproduction by Linearly Polarized Photons at SPring-8/LEPS Mizuki Sumihama RCNP, Osaka Univ. for the LEPS collaboration SPIN2006 Oct. 6th 2006

  2. K+ g N, N*, D* p Y(L, S0) Physics motivation Missing resonances N* andD* in s-channel • It is essential to fully know N* and D* to understand baryon structure. • Many nucleon resonances predicted by quark model are still missing. • D13(1900) resonance in SAPHIR / CLAS data was found. Some resonances should couple to KL or KS channel. Kaon photoproduction is good means to search for missing resonances.

  3. g K+ K*, K, K1 p Y(L, S0) Eg = 1.5 - 2.4 GeV Transition region, s-channel  t-channel Contribution of t-channel meson exchange becomes large above 2GeV. Meson exchange in t-channel Photon-beam asymmetry S natural parity exchange (K*) S = + 1 unnatural parity exchange (K, K1) S =－1 at t = 0 and large Eg.

  4. 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

  5. Particle identificationby time-of-flight and momentum measurements Momentum resolution ~0.8% for 2GeV/c Kaons. Time resolution ~150 ps.

  6. K+ Missing mass spectrum g p  K+L(1116) g p  K+S0(1193) Z-vertex distribution LH2 target K+

  7. Photon asymmetry–L(1116) data Positive sign Phys. Rev. C68, 058201 (2003) • K+K*-exchange (K*-exchange is dominant) by M. Guidal. • Isobar + Regge by T. Mart and C. Bennhold. • Gent isobar model by T. Corthals. • Agreement is not so bad, but still need fine optimization. nucl-th 0412097 / SNP2004 Phys. Rev. C73, 045207 (2006)

  8. Photon asymmetry–S0(1193) data Positive sign Phys. Rev. C68, 058201 (2003)  K+K*-exchange (K*-exchange is dominant)by M. Guidal. • Isobar by T.Mart and C.Bennhold. • Gent isobar model by T. Corthals • Agreement is not so bad, but still need fine optimization. nucl-th 0412097 / SNP2004 Phys. Rev. C73, 045207 (2006)

  9. Differential cross sections –L(1116) • LEPS data agree with SAPHIR and CLAS at cosQ = 0.75, 0.85 but discrepancy for SAHIR data is large at cosQ = 0.95. • LEPS data shows a small • bump at W= 1960MeV. • Regge K+K*-exchange • Isobar (with D13)+Regge by T.Mart and C.Bennhold. • Good agreement. Resonance-like structure LEPS SAPHIR CLAS W (GeV)

  10. Differential cross sections –S0(1193) Good agreement with CLAS. • Slightly smaller than SAPHIR. • Small bump structure • around W = 2070 MeV. • Regge K+K*-exchange • Isobar model by T.Mart and C.Bennhold. • Gent isobar model by T. Corthals • Good agreement LEPS SAPHIR CLAS W (GeV)

  11. Differential cross sections –L(1116) - angular dependence CLAS LEPS Forward peaking Cannot be reproduced By Feynman diagram only, at Eg>2GeV. Need Regge poles. • Regge model K+K*-exchange K-exchange makes forward peak for KL channel. • Isobar (Feynman) only • Isobar (Feynman) + Reggeby T.Mart and C.Bennhold.

  12. Differential cross sections –S0(1193) - angular dependence CLAS LEPS No forward peaking. Can be explained by Feynman diagram only. • Regge model K+K*-exchange K*-exchange is dominate for KS channel. • Isobar (Feynman) by T. Mart and C. Bennhold.

  13. Differential cross sections for gp  pp0 -Check photon normalization LEPS data Old data Curves SAID (fit data at Eg < 2GeV) Good agreement with SAID  Photon normalization is OK.

  14. Summary • The K+ photoproduction was measured by linearly polarized photons at SPring-8/LEPS. • Photon beam asymmetry is good tool to define theoretical models. Theoretical models are still needed to be optimized. • Differential cross sections were obtained at very forward angles, up to cosQcm = 0.975. • Bump structure was seen at W=1960 MeV in the K+L mode. • We see a forward peaking in K+L while no peaking in K+S0. • In order to fit the forward-angle data, a Regge pole is necessary in addition to s-channel resonances and t-channel K and K*-exchanges. • Combination of isobar (Feynman) and Regge is successful to explain this forward peaking in K+L. • Photon normalization was checked by gp  pp0 cross sections. The data show a good agreement with SAID. LEPS photon normalization is OK. PRC73, 035214 (2006) / PRL 91, 092001-1 (2003).

  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

  16. Photon asymmetry-difference between L and S0 L(1116)/S0(1193)

  17. Photon asymmetry-energy dependence L(1116)/S0(1193) Eg (GeV)

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