Coherent π0η photoproduction on s-shell nuclei

Coherent photoproduction of π0η on the deuteron and 3He and 4He nuclei is considered in the energy region from threshold to a laboratory photon energy E_γ=1.2 GeV. The transition amplitude is derived in the impulse approximation. The effects of pion absorption are included by means of the Fernbach-Serber-Taylor model. For the reactions on d and 3He the interaction of the produced η meson with the recoiling nucleus is taken into account. The corresponding ηd and η3He scattering amplitudes are obtained as solutions of the few-body equations for ηNN and η-3N systems. The impact of this interaction on the differential cross section in the region of small relative η-nuclear momenta is discussed.