Photoproduction of $\eta$ mesons off neutrons from a deuteron target

A formalism is developed for the partial wave analysis of data on meson photoproduction off deuterons and applied to photoproduction of $\eta$ and ${\pi }^0$ mesons. Different interpretations of a dip-bump structure of the $\eta$ photoproduction cross section in the 1670 MeV region are presented and discussed. Helicity amplitudes for two low-mass $S_{11}$ states are determined.