Three-Body Analysis of Incoherent Photoproduction of η Mesons on the Deuteron near Threshold

The importance of three-body dynamics in the $\eta np$ system in elastic and inelastic $\eta$-deuteron scattering as well as coherent and incoherent $\eta$ photoproduction on the deuteron in the energy region from threshold up to 30 MeV above has been investigated. It is shown that a restriction to first order rescattering with respect to the $NN$- and $\eta N$-final state interactions, i.e., restriction to rescattering in the two-body subsystems, does not give a sufficiently accurate approximation to the s-wave reaction amplitude and that higher order terms, as described by the three-body dynamics give very substantial contributions.