On the cross section ratio σn/σp in η photoproduction

The recently discovered enhancement of η photoproduction on the quasi-free neutron at energies around s∼1.67 GeV is addressed within a SU(3) coupled channel model. The quasi-free cross sections on proton and neutron, σn and σp, can be quantitatively explained. In this study, the main source for the peak in σn/σp is a coupled channel effect in S wave that explains the dip-bump structure in γn→ηn. In particular, the photon coupling to the intermediate meson-baryon states is important. The stability of the result is extensively tested and consistency with several pion- and photon-induced reactions is ensured.