Cross sections for the exclusive photon electroproduction on the proton and Generalized Parton Distributions

TL;DR

This paper reports extensive measurements of exclusive photon electroproduction cross sections on the proton, providing new insights into the Generalized Parton Distributions and offering a tomographic view of the nucleon structure.

Contribution

It presents the widest phase space measurement of unpolarized and polarized cross sections, testing GPD models and extracting Compton Form Factors to image the nucleon.

Findings

GPD models describe data well in most kinematics

Confirms the dominance of GPD H in the observables

Provides a tomographic image of the nucleon

Abstract

Unpolarized and beam-polarized four-fold cross sections $\frac{d^4 \sigma}{dQ^2 dx_B dt d\phi}$ for the $ep\to e^\prime p^\prime \gamma$ reaction were measured using the CLAS detector and the 5.75-GeV polarized electron beam of the Jefferson Lab accelerator, for 110 ($Q^2,x_B,t$) bins over the widest phase space ever explored in the valence-quark region. Several models of Generalized Parton Distributions (GPDs) describe the data well at most of our kinematics. This increases our confidence that we understand the GPD $H$, expected to be the dominant contributor to these observables. Through a leading-twist extraction of Compton Form Factors, these results reveal a tomographic image of the nucleon.