Longitudinal target-spin asymmetries for deeply virtual Compton scattering

Understand

A measurement of the electroproduction of photons off protons in the deeply inelastic regime was performed at Jefferson Lab using a nearly 6-GeV electron beam, a longitudinally polarized proton target and the CEBAF Large Acceptance Spectrometer.

• Target-spin asymmetries for $ep\to e'p'\gamma$ events, which arise from the interference of the deeply virtual Compton scattering and the Bethe-Heitler processes, were extracted over the widest kinematics in $Q^2$, $x_B$, $t$ and $\phi$, for 166 four-dimensional bins.
• In the framework of Generalized Parton Distributions (GPDs), at leading twist the $t$ dependence of these asymmetries provides insight on the spatial distribution of the axial charge of the proton, which appears to be concentrated in its center.
• These results also bring important and necessary constraints for the existing parametrizations of chiral-even GPDs.