Photoproduction of a large invariant mass $\gamma \rho$ pair at small momentum transfer

TL;DR

This paper calculates the leading-order scattering amplitude and differential cross sections for exclusive photoproduction of a high invariant mass gamma-rho pair, demonstrating its measurability at JLab 12-GeV within the collinear factorization framework.

Contribution

It provides the first leading-order calculation of the process in the generalized Bjorken regime for gamma-rho photoproduction, including polarization states, relevant for upcoming experiments.

Findings

Cross sections are sizable and measurable at JLab 12-GeV.

The process can be described using collinear factorization with generalized parton distributions.

Both longitudinal and transverse rho polarizations are considered.

Abstract

The collinear factorization framework allows to describe the exclusive photoproduction of a $\gamma\,\rho$ pair in the generalized Bjorken regime in terms of a perturbatively calculable coefficient function and universal generalized parton distributions. The kinematics are defined by a large invariant mass of the $\gamma \rho$ pair and a small transverse momentum of the final nucleon. We calculate the scattering amplitude at leading order in $\alpha_s$ and the differential cross sections for the process where the $\rho-$meson is either longitudinally or transversely polarized, in the kinematics of the near future Jlab experiments. Our estimate of the cross section demonstrates that this process is measurable at JLab 12-GeV.