On the cross section ratio sigma_n/sigma_p in eta photoproduction

TL;DR

This paper explains the enhancement in eta photoproduction on the neutron around 1.67 GeV using a coupled channel model, highlighting the role of S-wave effects and photon coupling to intermediate states.

Contribution

It introduces a SU(3) coupled channel model to quantitatively explain the sigma_n/sigma_p ratio and the peak structure in eta photoproduction on the neutron.

Findings

The peak in sigma_n/sigma_p is due to coupled channel effects in S-wave.

Photon coupling to intermediate meson-baryon states is crucial.

Results are stable and consistent with various pion- and photon-induced reactions.

Abstract

The recently discovered enhancement of eta photoproduction on the quasi-free neutron at energies around sqrt(s)~1.67 GeV is addressed within a SU(3) coupled channel model. The quasi-free cross sections on proton and neutron, sigma_n and sigma_p, can be quantitatively explained. In this study, the main source for the peak in sigma_n/sigma_p is a coupled channel effect in S-wave that explains the dip-bump structure in gamma n --> eta n. 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.