Role of pion exchange inηmeson photoproduction on the deuteron

Incoherent $\eta$ photoproduction on the deuteron is studied, with the main emphasis on the role of final-state interactions. In addition to the previously studied mechanisms of $NN$ and $\eta N$ rescatterings, the role of an intermediate pion exchange is considered in detail, where first a pion is photoproduced on one nucleon and then rescatters into an $\eta$ meson on the other, the spectator nucleon. It is found that the role of this pion-mediated contribution is comparable in size to that of $\eta N$ rescattering. Results for total and semi-inclusive differential cross sections and associated polarization observables are presented. In particular, polarization observables show significant sensitivity to final-state interactions.