Photoproduction of a \pi \rho Pair and Transversity GPDs

TL;DR

This paper proposes a method to access transversity GPDs of the nucleon via exclusive photoproduction of a pi-rho pair, demonstrating feasibility at current experimental facilities.

Contribution

It introduces a novel process for probing chiral-odd transversity GPDs through photoproduction and provides a perturbative calculation and a simple GPD model.

Findings

Feasibility of measuring transversity GPDs at JLab and COMPASS.

A perturbative calculation of the scattering amplitude at leading order.

A simple double distribution model for the transversity GPD HT.

Abstract

We demonstrate that the chiral-odd transversity generalized parton distributions (GPDs) of the nucleon can be accessed through the exclusive photoproduction process gamma + N -> pi + rho + N', in the kinematics where the meson pair has a large invariant mass and the final nucleon has a small transverse momentum, provided the vector meson is produced in a transversely polarized state. We calculate perturbatively the scattering amplitude at leading order in alpha_s: We build a simple model for the dominant transversity GPD HT (x; chi; t) based on the concept of double distribution. Counting rates estimates show that the experiment looks feasible with the real photon beam characteristics expected at JLab@12 GeV, in low Q2 leptoproduction at Jlab@12 GeV and in the COMPASS experiment.