uc l - th / 9 80 70 02 v 2 2 2 A ug 1 99 8 Coherent Photoproduction of Eta - Mesons on Spin - Zero Nuclei in a Relativistic , Non - local Model ∗ †

The coherent photoproduction of η-mesons on spin-zero nuclei is studied in a relativistic, non-local model, which we have previously applied to the coherent photoproduction of pions. We find that different off-shell extrapolations of the elementary production operator lead to large effects in the cross section. We also show that the almost complete suppression of the N (1535) seen in earlier studies on this reaction is a result of the local or factorization approximation used in these works. Non-local effects can lead to a considerable contribution from this resonance. The relative size of the N (1535) contribution depends on the structure of the nucleus under consideration. We give an estimate for the contribution of the N (1520) resonance and discuss the effect of an η-nucleus optical potential.