The energy dependence of the cross sections for electromagnetic diffractive processes can be well described by a single power, $W^{\delta }$. For $J/\psi$ photoproduction this holds in the range from 20 GeV to 2 TeV. This feature is most easily explained by a single pole in the angular momentum plane which depends on the scale of the process, at least in a certain range of values of the momentum transfer. It is shown that this assumption allows a unified description of all electromagnetic elastic diffractive processes. We also discuss an alternative model with an energy-dependent dipole cross section, which is compatible with the data up to 2 TeV and which shows an energy behavior typical for a cut in the angular momentum plane.

• Received 26 March 2015

DOI:https://doi.org/10.1103/PhysRevD.92.034002