Accessing GPDs through the exclusive photoproduction of a photon-meson pair with a large invariant mass

TL;DR

This paper investigates the exclusive photoproduction of photon-meson pairs with large invariant mass to access generalized parton distributions (GPDs), using QCD factorisation at leading order and twist, and discusses experimental prospects.

Contribution

It provides a leading-order, leading-twist QCD analysis of photon-meson pair production for accessing GPDs, including polarization asymmetries and comparisons of distribution amplitudes.

Findings

Probes GPDs at small skewness at high energies.

Calculates polarization asymmetries for different distribution amplitudes.

Discusses experimental feasibility at JLab, COMPASS, EIC, and LHC.

Abstract

We study the exclusive photoproduction of a photon-meson pair with a large invariant mass, working in the QCD factorisation framework. Explicitly, we consider a $ \rho $-meson or a charged $ \pi $ in the final state. This process gives access to chiral-even GPDs as well as chiral-odd GPDs. We focus here on the chiral-even sector. The computation is performed at leading order and leading twist. We discuss the prospects of measuring them in various experiments such as JLab 12-GeV, COMPASS, future EIC and LHC (in ultraperipheral collisions). In particular, the high centre of mass energies available at collider experiments can be used to probe GPDs at small skewness $ \xi $. We also compute the polarisation asymmetries with respect to the incoming photon. The results for an alternative distribution amplitude (`holographic' form) are also compared with the predictions obtained with an asymptotic distribution amplitude.