Differential cross section and photon-beam asymmetry for the (gamma)over-right-arrow p -> pi(+) n reaction at forward pi(+) angles at E-gamma=1.5-2.95 GeV

Abstract

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.