The Recoil Proton Polarization: a new discriminative DVCS observable

TL;DR

This paper introduces recoil proton polarization as a new observable in Deeply Virtual Compton Scattering (DVCS) experiments, providing a promising method to better constrain the GPD E, which is difficult to measure with existing techniques.

Contribution

The paper proposes using recoil proton polarization as a novel DVCS observable, enhancing the ability to measure the GPD E at high-luminosity facilities.

Findings

Recoil proton polarization is highly sensitive to GPD E.

Feasibility demonstrated for experiments at Jefferson Lab.

Potential to improve GPD E constraints significantly.

Abstract

Generalized parton distributions describe the correlations between the longitudinal momentum and the transverse position of quarks and gluons in a nucleon. They can be constrained by measuring photon leptoproduction observables, arising from the interference between Bethe-Heitler and Deeply virtual Compton scattering processes. At leading-twist/leading-order, the amplitude of the latter is parameterized by complex integrals of the GPDs {H, E, \~H, \~E} . As data collected on an unpolarized or longitudinally polarized target constrains H and \~H, E is poorly known as it requires data collected with a transversely polarized target, which is very challenging to implement in fixed target experiments. The only alternative considered so far has been DVCS on a neutron with a deuterium target, while assuming isospin symmetry and absence of final-state interactions. Today, we introduce the polarization of the recoil proton as a new DVCS observable, highly sensitive to E, which appears feasible for an experimental study at a high-luminosity facility such as Jefferson Lab.