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

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.

Comments: 6 pages, 2 figures, Presented by S. Nabeebaccus at `Diffraction and Low-x 2022', Corigliano Calabro (Italy), September 24-30, 2022. arXiv admin note: substantial text overlap with arXiv:2209.05380