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K + L and K + S 0 photoproduction at SPring-8/LEPS

K + L and K + S 0 photoproduction at SPring-8/LEPS. Mizuki Sumihama Department of physics Osaka Univ. for LEPS collaboration 1. Introduction 2. Experiment 3. Data analyses 4. Experimental results

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K + L and K + S 0 photoproduction at SPring-8/LEPS

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  1. K+L and K+S0 photoproduction at SPring-8/LEPS Mizuki Sumihama Department of physics Osaka Univ. for LEPS collaboration 1. Introduction 2. Experiment 3. Data analyses 4. Experimental results 5. Summary

  2. LEPS collaboration M. Nomachi, A. Sakaguchi, Y. Sugaya, M. Sumihama Dept. of physics Osaka Univ. H. Fujimura, M. Fujiwara, T. Hotta, H. Kohri, T. Matsumura, N. Matsuoka, T. Mibe, M. Morita, T. Nakano, R.G.T.Zegers RCNP Osaka Univ. K. Imai, M. Miyabe, M. Niiyama, M. Yosoi Dept. of physics Kyoto Univ. D.S. Ahn, J.K. Ahn Pusan Nat’l Univ.. Korea T. Iwata Dept. of physics Yamagata Univ. Y. Asano,N. Matsumura JAERI T. Ishikawa, H. Shimizu Tohoku Univ. H. Kawai, T. Ooba, Y. Shiino Chiba Univ. S. Date, N. Kumagai, Y. Ohashi, H. Ookuma, T. Yorita JASRI W.C. Chang, D.S. Oshuev, C.W. Wang, S.C. Wang Academia Sinica, Taiwan A. Wakai Akita Industry Promotion Foundation K. Hicks Ohio Univ.USA C. Rangacharyulu Univ.. of Saskatchewan Canada H. Akimune Konan Univ. P. Shagin Minnesota Univ. S. Makino Wakayama Med. Univ.

  3. K+ g N, N*, D* p Y(L, S) 1. IntroductionMissing resonances N* and D*in strangeness channels • Information on nucleon resonances mainly comes from the pN channel. • Many nucleon resonances predicted by quark model are still missing. • It is essential to fully know N* and D* to understand the structure of baryons. Some resonances may couple to KL or KS channel. K+ photoproduction is good means to search missing resonances.

  4. Resonance structure? ~ 1.9 GeV • Resonance like structure in the total cross section for p(g,K+)L from SAPHIR and CLAS. • Missing resonance D13(1960) ? without D13 with D13 calculations by Mart and Bennhold • There still remains a controversy of the theoretical description. • Only cross section data is not conclusive. SAPHIR data Additional observables are required. Photon beam asymmetryis one of the candidates.

  5. Theoretical predictions of photon asymmetry by Mart & Bennhold byJanssen et al without D13(1960) with D13(1960) Hadronic form factor A B C Davidson&Workman Haberzettl A) Small cut-off mass B) L* in u-channel C) No restriction on gKYp With D13(1960) Need more study to fix parameters. Photon beam asymmetry is sensitive to model differences.

  6. 2. Experiment • 2000.12 ~ 2001.6 • Liquid hydrogen target : 5cm • Linearly polarized photons Tagged photons 1.5 ~ 2.4 GeV Resolution 15 MeV Beam intensity 5 x 105 cps (Tagged photons) High polarization ~92% at 2.4 GeV ~55% at 1.5 GeV • 52% data with vertical polarization 48% data with horizontal polarization • 2 x 1012 photons at the target Photon beam asymmetries for the p(g,K+) L and p(g,K+)S0 reactions

  7. Beam 3. Data analyses Event selections for p(g,K+)L and p(g,K+)S0 • Tagged photons recoil electron byTagging counter • Events from the proton target z-vertex point of K+ contamination from the trigger counter ~ 8% qlab< 5o < 2% qlab> 5o • K+ events mass distribution by tracking and TOF c2probability cut - confidence level 98% p and proton contaminations ~ 2% • L and S0events missing mass of p(g, K+)X L and S0contamination < 1%

  8. Missing mass spectrum • p(g,K+)L (1116) 72,500 events • p(g,K+)S0 (1193) 48,900 events • 1.5 ~ 2.4 GeV • 0.6 < cosqcm < 1 Photon beam asymmetry

  9. ds ds dW dWv ds ds dWunpol dWunpol ds dWh Photon beam asymmetry S • Vertical = [ 1 + PgScos(2f) ] • Horizontal = [ 1 - PgScos(2f) ] N = Facc = PgScos(2f) • N : K+ photoproduction yield • f : K+ azimuthal angle • Pg: Polarization of photon • n : Normalization factor for Nv nNv- Nh nNv+ Nh For all events

  10. 4. Experimental results p(g,K+)L • Correction 1 • p & proton contaminations • DS < 0.03 • Correction 2 • TRG contaminations • DS < 0.02 • Systematic error 1 • from pol. degree & angle • 1.5% • Systematic error 2 • from normalization factor • DS ~ 0.03 p(g,K+)S0 • Positive sign • Different angular distribution • Increase as the Eg increases

  11. L Comparison with models by Mart & Bennhold without D13(1960) with D13(1960) Currently, no models reproduce our data, perfectly. byJanssen et al Hadronic form factor A B C Davidson&Workman Haberzettl S0 A) Small cut-off mass B) L* in u-channel C) No restriction on gKYp with D13(1960)

  12. 5. Summary • K+ photoproduction is good means to search missing resonances. • Photon beam asymmetries were obtained for the p(g,K+) L and p(g,K+)S0 reactions at the first time in Eg = 1.5 ~ 2.4 GeV at SPring-8/LEPS. Positive sign • Our data will stimulate the further development of the theoretical models and extend our knowledge of this reaction including missing resonances.

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