Exploring GPDs through the photoproduction of a $\gamma \rho$ pair

TL;DR

This paper investigates how the exclusive photoproduction of a gamma-rho pair at high invariant mass can be used to access and distinguish between different types of quark generalized parton distributions (GPDs) within the collinear QCD framework, with relevance to upcoming JLab experiments.

Contribution

It introduces a method to probe both chiral-even and chiral-odd GPDs through gamma-rho production, highlighting the process's insensitivity to gluon GPDs and the separation of polarization states.

Findings

Provides estimates of production rates for JLab 12-GeV kinematics.

Shows the process can access both chiral-even and chiral-odd GPDs.

Demonstrates the separation of polarization states helps distinguish GPD contributions.

Abstract

We describe the process $\gamma N \to \gamma\,\rho N'$ in the generalized Bjorken regime where the $\gamma\,\rho $ pair has a large invariant mass. In the collinear QCD factorization framework, the amplitude gives access to both chiral-even and chiral-odd quark generalized parton distributions (GPDs), and is insensitive to gluon GPDs. The separation of longitudinally and transversely polarized $\rho$ meson production allows to distinguish chiral-even and chiral-odd contributions. Production rates are estimated in the kinematics of the near-future JLab~12-GeV experiments.