Helium Compton Form Factor Measurements at CLAS

TL;DR

This paper reports measurements of the Helium Compton Form Factor using DVCS at Jefferson Lab, providing insights into the nuclear GPDs and the spatial structure of helium-4.

Contribution

It introduces a novel experimental approach to extract the real and imaginary parts of the Helium-4 Compton form factor via beam spin asymmetry measurements.

Findings

Demonstrated the feasibility of extracting GPD information from helium-4.

Found the Bethe-Heitler process dominates in the studied kinematic range.

Provided data supporting the use of DVCS for nuclear structure studies.

Abstract

The distribution of the parton content of nuclei, as encoded via the generalized parton distributions (GPDs), can be accessed via the deeply virtual Compton scattering (DVCS) process contributing to the cross section for leptoproduction of real photons. Similarly to the scattering of light by a material, DVCS provides information about the dynamics and the spatial structure of hadrons. The sensitivity of this process to the lepton beam polarization allows to single-out the DVCS amplitude in terms of Compton form factors that contain GPDs information. The beam spin asymmetry of the $^4$He($\vec {\mathrm e}$,e$' \gamma ^4$He) process was measured in the experimental Hall B of the Jefferson Laboratory to extract the real and imaginary parts of the twist-2 Compton form factor of the $^4$He nucleus. The experimental results reported here demonstrate the relevance of this method for such a goal, and suggest the dominance of the Bethe-Heitler amplitude to the unpolarized process in the kinematic range explored by the experiment.