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. 
A.V.Anisovich, I.Jaegle, E.Klempt, B.Krusche, V.A.Nikonov,   A.V.Sarantsev, U.Thoma