Photoproduction of a pi rhoT pair with a large invariant mass and transversity generalized parton distribution

TL;DR

This paper proposes a method to access the nucleon's transversity GPDs via exclusive photoproduction of a pi-rho pair with large invariant mass, providing theoretical calculations and experimental feasibility estimates.

Contribution

It introduces a perturbative calculation of the scattering amplitude and a simple model for the transversity GPD H_T, enabling experimental access to chiral-odd GPDs.

Findings

Estimated cross sections suggest experimental feasibility at JLab and COMPASS.

The model indicates measurable rates for transversity GPD extraction.

The approach offers a new way to probe nucleon structure.

Abstract

The chiral-odd transversity generalized parton distributions (GPDs) of the nucleon can be accessed experimentally 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 transversally polarized state. We calculate perturbatively the scattering amplitude at leading order in alpha_s. We build a simple model for the dominant transversity GPD H_T(x,xi, t) based on the concept of double distribution. We estimate the unpolarized differential cross section for this process in the kinematics of the Jlab and COMPASS experiments. Counting rates show that the experiment looks feasible with the real photon beam characteristics expected at JLab@12 GeV, and with the quasi real photon beam in the COMPASS experiment.