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Kohri, H.,Wang, S. Y.,Shiu, S. H.,Chang, W. C.,Yanai, Y.,Ahn, D. S.,Ahn, J. K.,Chen, J. Y.,Daté,, S.,Ejiri, H.,Fujimura, H.,Fujiwara, M.,Fukui, S.,Gohn, W.,Hicks, K.,Hosaka, A.,Hotta, T.,Hwang, American Physical Society 2018 Physical review. C Vol.97 No.1
<P>Differential cross sections and photon-beam asymmetries for the (gamma) over right arrowp -> pi(+) n reaction have been measured for 0.6 < cos theta(pi) < 1 and E-gamma = 1.5-2.95 GeV at SPring-8/LEPS. The cross sections monotonically decrease as the photon beam energy increases for 0.6 < cos theta(pi) < 0.9. However, the energy dependence of the cross sections for 0.9 < cos theta(pi) < 1 and E-gamma = 1.5-2.2 GeV (W = 1.9-2.2 GeV) is different, which may be due to a nucleon or Delta resonance. The present cross sections agree well with the previous cross sections measured by other groups and show forward peaking, suggesting significant t-channel contributions in this kinematical region. The asymmetries are found to be positive, which can be explained by rho exchange in the t channel. Large positive asymmetries in the small-vertical bar t vertical bar region, where the rho-exchange contribution becomes small, could be explained by introducing p-exchange interference with the s channel.</P>
Kohri, H.,Shiu, S. H.,Chang, W. C.,Yanai, Y.,Ahn, D. S.,Ahn, J. K.,Chen, J. Y.,Daté,, S.,Ejiri, H.,Fujimura, H.,Fujiwara, M.,Fukui, S.,Gohn, W.,Hicks, K.,Hosaka, A.,Hotta, T.,Hwang, S. H.,Imai, American Physical Society 2018 Physical Review Letters Vol.120 No.20
<P>Differential cross sections and photon-beam asymmetries for the gamma(->)p -> Pi(-)Delta(++)(1232) reaction have been measured for 0.7 < cos Theta(c.m.)(Pi) < 1 and E-gamma= 1.5-2.95 GeV at SPring-8/LEPS. The first-ever high statistics cross-section data are obtained in this kinematical region, and the asymmetry data for 1.5 < E-gamma(GeV) < 2.8 are obtained for the first time. This reaction has a unique feature for studying the production mechanisms of a pure uu quark pair in the final state from the proton. Although there is no distinct peak structure in the cross sections, a non-negligible excess over the theoretical predictions is observed at E-gamma= 1.5-1.8 GeV. The asymmetries are found to be negative in most of the present kinematical regions, suggesting the dominance of n exchange in the t channel. The negative asymmetries at forward meson production angles are different from the asymmetries previously measured for the photoproduction reactions producing a dd(-) or an ss quark pair in the final state. Advanced theoretical models introducing nucleon resonances and additional unnatural-parity exchanges are needed to reproduce the present data.</P>
Shiu, S. H.,Kohri, H.,Chang, W. C.,Ahn, D. S.,Ahn, J. K.,Chen, J. Y.,Daté,, S.,Ejiri, H.,Fujimura, H.,Fujiwara, M.,Fukui, S.,Gohn, W.,Hicks, K.,Hotta, T.,Hwang, S. H.,Imai, K.,Ishikawa, T.,Joo, American Physical Society 2018 Physical Review C Vol.97 No.1
<P>We report the measurement of the gamma p -> K+Lambda and gamma p -> K+Sigma(0) reactions at SPring-8. The differential cross sections and photon-beam asymmetries are measured at forward K+ production angles using linearly polarized tagged-photon beams in the range of E-gamma = 1.5-3.0 GeV. With increasing photon energy, the cross sections for both gamma p -> K+Lambda and gamma p -> K+Sigma(0) reactions decrease slowly. Distinct narrow structures in the production cross section have not been found at E gamma = 1.5-3.0 GeV. The forward peaking in the angular distributions of cross sections, a characteristic feature of t-channel exchange, is observed for the production of Lambda in the whole observed energy range. A lack of similar feature for Sigma(0) production reflects a less dominant role of t-channel contribution in this channel. The photon-beam asymmetries remain positive for both reactions, suggesting the dominance of K* exchange in the t channel. These asymmetries increase gradually with the photon energy, and have a maximum value of +0.6 for both reactions. Comparison with theoretical predictions based on the Regge trajectory in the t channel and the contributions of nucleon resonances indicates the major role of t-channel contributions as well as non-negligible effects of nucleon resonances in accounting for the reaction mechanism of hyperon photoproduction in this photon energy regime.</P>
Mizutani, K.,Niiyama, M.,Nakano, T.,Yosoi, M.,Nozawa, Y.,Ahn, D. S.,Ahn, J. K.,Chang, W. C.,Chen, J. Y.,Daté,, S.,Gohn, W.,Hamano, H.,Hashimoto, T.,Hicks, K.,Hiraiwa, T.,Hotta, T.,Hwang, S. H.,I American Physical Society 2017 Physical Review C Vol.96 No.6
<P>Differential cross sections at t = t(min) and decay asymmetries for the gamma p -> phi p reaction have been measured using linearly polarized photons in the range 1.5 to 2.9 GeV. These cross sections were used to determine the Pomeron strength factor. The cross sections and decay asymmetries are consistently described by the t-channel Pomeron and pseudoscalar exchange model in the E-gamma region above 2.37 GeV. In the lower energy region, an excess over the model prediction is observed in the energy dependence of the differential cross sections at t = t(min). This observation suggests that additional processes or interference effects between Pomeron exchange and other processes appear near the threshold region.</P>