Beam charge asymmetries for deeply virtual Compton scattering off the proton

TL;DR

This paper reports on measurements of beam charge asymmetries in deeply virtual Compton scattering off protons using polarized electron and positron beams, providing insights into the real part of the Compton Form Factor and improving its determination.

Contribution

It introduces new measurements of beam charge asymmetries with polarized beams at Jefferson Lab, enhancing the understanding of the Compton Form Factor and testing theoretical hypotheses.

Findings

Positron data significantly reduce CFF correlations.

Measurements access the real part of the Compton Form Factor.

Results challenge the Bethe-Heitler dominance hypothesis.

Abstract

The unpolarized and polarized Beam Char\-ge Asymmetries (BCAs) of the $\vv{e}^{\pm}p \to e^{\pm}p \gamma$ process off unpolarized hydrogen are discussed. The measurement of BCAs with the CLAS12 spectrometer at the Thomas Jefferson National Accelerator Facility, using polarized positron and electron beams at 10.6 GeV is investigated. This experimental configuration allows to measure azimuthal and $t$-dependences of the unpolarized and polarized BCAs over a large $(x_B,Q^2)$ phase space, providing a direct access to the real part of the Compton Form Factor (CFF) ${\mathcal H}$. Additionally, these measurements confront the Bethe-Heitler dominance hypothesis and eventual effects beyond leading twist. The impact of potential positron beam data on the determination of CFFs is also investigated within a local fitting approach of experimental observables. Positron data are shown to strongly reduce correlations between CFFs and consequently improve significantly the determination of $\Re {\rm e} [\mathcal{H}]$.