J an 2 00 3 Cross Section Oscillations in the Coherent Charmonium Photoproduction off Nuclei at Moderate Energies

We calculate the coherent charmonium photoproduction at intermediate energies accounting for the physics of the charmonium bound states and the dependence of the cross section on the region occupied by color using a correspondingly adjusted generalized vector dominance model (GVDM). In the photon energy domain where the coherence lengths are comparable to the average internucleon distances in nuclei and the nuclear radii we found that significant oscillations of the total and forward photoproduction cross sections governed by the longitudinal nuclear form factor are strongly modified by the charmonium rescatterings accounting for the nondiagonal transitions related to the color screening phenomenon. We discuss how these oscillations can influence the determination of the genuine charmonium-nucleon cross sections in the forthcoming SLAC E160 experiment on low energy J/ψ and ψ ′ photoproduction off nuclei.