Photoproduction of eta meson within a coupled-channels K-matrix approach

Abstract

We investigate photoproduction of eta mesons off protons and neutrons within a coupled-channels effective-Lagrangian method which is based on the K-matrix approach. The two-body final channels included are pi-N, eta-N, phi-N, rho-N, gamma-N, K-Lambda, and K-Sigma. Non-resonant meson-baryon interactions are included in the model via nucleon intermediate states in the s- and u-channels, meson exchanges in the t-channel amplitude and the u-channel resonances. The nucleon resonances S_{11}(1535), S_{11}(1650), S_{31}(1620), P_{11}(1440), P_{11}(1710), P_{13}(1720), P_{33}(1232), P_{33}(1600), D_{13}(1520), D_{13}(1700), and D_{33}(1700) are included explicitly in calculations. Our model describes simultaneously the available data as well on total and differential cross sections as on beam and target asymmetries. This holds for the p(gamma,eta)p reaction for photon energies ranging from very close to threshold to up to 3 GeV. The polarization observables show strong sensitivity to resonances that otherwise contribute only weakly to the total cross section. It is found that the pronounced bump-like structure seen in the excitation function of the n(gamma,eta)n cross section at gamma energies around 1 GeV, can be explained by the interference effects of S_{11}, P_{11} and P_{13} resonance contributions.