Helicity Dependent Cross Sections in $\eta$ Photoproduction off Quasi-Free Protons and Neutrons

Abstract

Preliminary results for the double polarisation observable E and the corresponding helicity dependent cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$ of $\eta$ photoproduction off quasi-free protons and neutrons have been obtained by a recent experiment at the MAMI electron accelerator at Mainz, Germany. The results will help to constrain the origin and quantum numbers of the bump-like structure in the $\eta$ cross section off the neutron