A bstract Non-relativistic QCD (NRQCD) is used to calculate the relativistic correction to the amplitude for exclusive photoproduction of vector Quarkonia in the near-threshold region within the generalized parton distribution (GPD) framework. The relativistic corrections are found to be large for J / ψ , and lead to a breakdown of the GPD moment expansion near threshold. Cross-sections for both J / ψ and Υ are calculated with the former being compared to the data. We also demonstrate the presence of endpoint divergences for the relativistic correction away from the near-threshold regime.
Blask et al. (Thu,) studied this question.