Probing chiral-even and chiral-odd leading twist quark generalised parton distributions through the exclusive photoproduction of a $ \gamma \rho $ pair

TL;DR

This paper investigates a new exclusive process involving gamma and rho meson production to access chiral-even and chiral-odd generalized parton distributions across various experimental setups, predicting measurable cross sections and asymmetries.

Contribution

It introduces the analysis of gamma-rho pair photoproduction as a novel method to probe both chiral-even and chiral-odd GPDs at leading twist, applicable across multiple energy regimes.

Findings

Cross sections are large enough for experimental detection at JLab.

Linear photon polarization asymmetry is significant for longitudinal rho mesons.

Predictions are consistent for both asymptotic and holographic distribution amplitudes.

Abstract

We extend our studies of a new class of $2 \to 3$ exclusive processes using the collinear factorisation framework by considering the exclusive photoproduction of a $\gamma\,\rho$ pair, in the kinematics where the pair has a large invariant mass, {and the outgoing $ \rho $-meson has a sufficiently large transverse momentum to not resonate with the nucleon}. We cover the whole kinematical range from medium energies in fixed target experiments to very large energies of colliders, by considering the experimental conditions of JLab~12-GeV, COMPASS, future EIC and LHC (in ultra-peripheral collisions) cases. One of the main interest in studying the present process is that it provides access to both chiral-even and chiral-odd GPDs, depending on the polarisation of the outgoing $\rho$-meson, both at leading twist. Our analysis covers both neutral and charged $ \rho $-mesons. We find that the order of magnitude of the obtained cross sections are sufficiently large for a dedicated experimental analysis to be performed, especially at JLab, for both longitudinally and transversely polarised $\rho$. Furthermore, we compute the linear photon beam polarisation asymmetry {which is} sizeable for a longitudinally polarised meson. These predictions are obtained for both asymptotic distribution amplitude (DA) and the \textit{holographic} DA.