Psi' to J/Psi Ratio in Diffractive Photoproduction

We evaluate the Psi' to J/Psi ratio in diffractive photoproduction in a light-cone framework, using charmonium wave functions extracted from non-relativistic potential models. Contrary to current belief, we find that the best estimate for the ratio is a factor 2 to 5 below the data. The measured ratio constrains the distribution of the charm quark-antiquark component of the charmonium light-cone wave function and indicates that it is more compact than in potential models. We predict that the inelastic photoproduction ratio will be bigger than the elastic one, and will equal that measured in hadroproduction.