Measurements of Spin Asymmetries for Deeply Virtual Compton Scattering off the Proton using the Extended Maximum Likelihood Method

Generalised Parton Distributions (GPDs) provide a theoretical framework that promises to deliver new information about proton structure. In the impact parameter interpretation, they describe the substructure of the proton in terms of its quark (and gluon) constituents in three dimensions: two transverse spacial dimensions and one longitudinal momentum dimension. Through Ji’s sum rule, they offer a means by which to determine the total angular momentum contribution of quarks to the proton’s spin of h̄/2. GPDs are directly related to Compton Form Factors (CFFs), which are distributions that are measurable using Deep Exclusive Scattering (DES) processes such as deeply virtual Compton scattering (DVCS). DVCS is characterised by the scattering of a single photon with large virtuality off a single quark (or gluon) inside the proton, resulting in the production of a hard photon: γ∗p→ γ p′. In this work, data recorded with the CLAS detector at Jefferson Laboratory during the EG1DVCS experimental run were analysed. This experiment ran for over 80 days with a longitudinally polarised electron beam and a solid NH3 target containing longitudinally polarised protons. The resulting data set accommodated precise measurements of DVCS beam, target and double spin asymmetries, each of which is sensitive to different combinations of CFFs. The final results presented here are fits to these three asymmetries, which were performed using the Extended Maximum Likelihood method. It is intended that these results will be used in the future, along with other DES asymmetry and cross-section measurements, to constrain CFFs and thus move towards a more complete understanding of the structure of the proton.