Photoproduction of Charmonia and Total Charmonium-Proton Cross Sections

Abstract

Elastic virtual photoproduction cross sections gamma^*p -> J/psi(psi')p and total charmonium-nucleon cross sections for J/psi, psi' and chi states are calculated in a parameter free way with the light-cone dipole formalism and the same input: factorization in impact parameters, light-cone wave functions for the gamma^* and the charmonia, and the universal phenomenological dipole cross section which is fitted to other data. The charmonium wave functions are calculated with four known realistic potentials, and two models for the dipole cross section are tested. Very good agreement with data for the cross section of charmonium photoproduction is found in a wide range of s and Q^2. The inclusion of the Melosh spin rotation increases the psi' photoproduction rate by a factor 2-3 and removes previously observed discrepancies in the psi' to J/psi ratio in photoproduction. We also calculate the charmonium-proton cross sections whose absolute values and energy dependences are found to correlate strongly with the sizes of the states.