Deeply virtual Compton scattering at Jefferson Laboratory

TL;DR

This paper reviews recent Jefferson Laboratory experiments on deeply virtual Compton scattering (DVCS), demonstrating how these measurements help map the three-dimensional structure of nucleons through generalized parton distributions (GPDs).

Contribution

It provides an overview of experimental results on DVCS at Jefferson Laboratory, highlighting the extraction of Compton form factors and nucleon imaging.

Findings

Extraction of Compton form factors from experimental data

Mapping of the 3D nucleon structure

Validation of GPD-based descriptions of hadrons

Abstract

The generalized parton distributions (GPDs) have emerged as a universal tool to describe hadrons in terms of their elementary constituents, the quarks and the gluons. Deeply virtual Compton scattering (DVCS) on a proton or neutron ($N$), $e N \rightarrow e' N' \gamma$, is the process more directly interpretable in terms of GPDs. The amplitudes of DVCS and Bethe-Heitler, the process where a photon is emitted by either the incident or scattered electron, can be accessed via cross-section measurements or exploiting their interference which gives rise to spin asymmetries. Spin asymmetries, cross sections and cross-section differences can be connected to different combinations of the four leading-twist GPDs (${H}$, ${E}$, ${\tilde{H}}$, ${\tilde{E}}$) for each quark flavors, depending on the observable and on the type of target. This paper gives an overview of recent experimental results obtained for DVCS at Jefferson Laboratory in the halls A and B. Several experiments have been done extracting DVCS observables over large kinematics regions. Multiple measurements with overlapping kinematic regions allow to perform a quasi-model independent extraction of the Compton form factors, which are GPDs integrals, revealing a 3D image of the nucleon.