Why photoproduction of charmonium on nuclei does not measure the charmonium-nucleon total cross section
We show that color transparency produces either strong nuclear shadowing or antishadowing, depending on the specific (semi)exclusive photoproduction reaction off nuclei. Neither coherent nor quasielastic diffractive photoproduction of charmonium on nuclei measures the charmonium-nucleon total cross section and the vector-dominance-model interpretation of nuclear photoproduction data cannot be applied. We relate the A dependence of the coherent and quasielastic photoproduction cross sections and derive the energy dependence of shadowing. The results are in good agreement with the New Muon Collaboration data.