Beam Charge Asymmetries for Deeply Virtual Compton Scattering on the Proton at CLAS12

Abstract

The parameterization of the nucleon structure through Generalized Parton Distributions (GPDs) shed a new light on the nucleon internal dynamics. For its direct interpretation, Deeply Virtual Compton Scattering (DVCS) is the golden channel for GPDs investigation. The DVCS process interferes with the Bethe-Heitler (BH) mechanism to constitute the leading order amplitude of the $eN\to eN{\hat{I}}^3$ process. The study of the $ep{\hat{I}}^3$ reaction with polarized positron and electron beams gives a complete set of unique observables to unravel the different contributions to the $ep{\hat{I}}^3$ cross section. This separates the different reaction amplitudes, providing a direct access to their real and imaginary parts which procures crucial constraints on the model dependences and associated systematic uncertainties on GPDs extraction. The real part of the BH-DVCS interference amplitude is particularly sensitive to the $D$-term which parameterizes the Gravitational Form Factors of the nucleon. The separation of the imaginary parts of the interference and DVCS amplitudes provides insights on possible higher-twist effects. We propose to measure the unpolarized and polarized Beam Charge Asymmetries (BCAs) of the ${\vec{e}}^{\pm }p\to e^{\pm }p{\hat{I}}^3$ process on an unpolarized hydrogen target with {\tt CLAS12}, using polarized positron and electron beams at 10.6 GeV. The azimuthal and $t$-dependences of the unpolarized and polarized BCAs will be measured over a large $(x_B,Q^2)$ phase space using a 100 day run with a luminosity of 0.66$\times 10^{35}$cm${}^{-2}\cdot$s${}^{-1}$.

Proposal to the Jefferson Lab Program Advisory Committee (PAC51)