Probing axial quark generalized parton distributions through exclusive photoproduction of a $\gamma\,\pi^\pm$ pair with a large invariant mass

TL;DR

This paper investigates exclusive photoproduction of a gamma-pion pair with large invariant mass to probe axial quark generalized parton distributions, providing theoretical predictions relevant for upcoming experiments at JLab.

Contribution

It introduces a collinear factorization framework for this process and estimates cross sections, highlighting its sensitivity to specific axial GPD combinations.

Findings

Predicted cross sections are within measurable range for JLab experiments.

The process is highly sensitive to the axial GPD combination .

Theoretical calculations are at leading order in _s.

Abstract

Exclusive photoproduction of a $\gamma\,\pi^\pm$ pair in the kinematics where the pair has a large invariant mass and the final nucleon has a small transverse momentum is described in the collinear factorization framework. The scattering amplitude is calculated at leading order in $\alpha_s$ and the differential cross sections for the process are estimated in the kinematics of the JLab~12-GeV experiments. The order of magnitude of the predicted cross-sections seems sufficient for a dedicated experiment to be performed. The process turns out to be very sensitive to the axial generalized parton distribution combination $\tilde{H}_u - \tilde{H}_d$.