In-medium effects in the eta-photoproduction through the S11 resonance with the relativistic approach

In-medium effects in photon excitation of the S11 resonance from nucleon and its decay to η-meson using the RMF (Relativistic Mean-Field) approach is studied. We examine the in-medium effects by varing the Dirac fields of the nucleon and the S11 resonance separately. We obtain a conclusion that the Dirac fields of the nucleon, which reduce the nucleon effective mass, enlarges the width of S11 resonance, and small Dirac-fields of the resonance shift the peak position, and these combined effects can explain the in-medium properties observed in the experimental data for 12C(γ, η) reaction. (author)