Longitudinal target-spin asymmetries for deeply virtual Compton scattering

TL;DR

This study measures target-spin asymmetries in deeply virtual Compton scattering to explore the proton's internal structure, providing extensive data that constrains theoretical models of generalized parton distributions.

Contribution

It presents the first wide-kinematic-range measurement of target-spin asymmetries in DVCS, offering new constraints on GPD parametrizations and insights into proton axial charge distribution.

Findings

Asymmetries vary with kinematic variables, revealing the proton's internal structure.

Data constrains GPD models, especially regarding the axial charge distribution.

Results suggest axial charge is concentrated at the proton's center.

Abstract

A measurement of the electroproduction of photons off protons in the deeply inelastic regime was performed at Jefferson Lab using a nearly 6-GeV electron beam, a longitudinally polarized proton target and the CEBAF Large Acceptance Spectrometer. Target-spin asymmetries for $ep\to e'p'\gamma$ events, which arise from the interference of the deeply virtual Compton scattering and the Bethe-Heitler processes, were extracted over the widest kinematics in $Q^2$, $x_B$, $t$ and $\phi$, for 166 four-dimensional bins. In the framework of Generalized Parton Distributions (GPDs), at leading twist the $t$ dependence of these asymmetries provides insight on the spatial distribution of the axial charge of the proton, which appears to be concentrated in its center. These results also bring important and necessary constraints for the existing parametrizations of chiral-even GPDs.