Speaker
Description
A key step toward a better understanding of the nucleon structure is the study of Generalized Parton Distributions (GPDs). GPDs are nowadays the object of an intense effort of research since they convey an image of the nucleon structure where the longitudinal momentum and the transverse position of the partons inside the nucleon are correlated. Moreover, GPDs give access, via Ji's sum rule, to the contribution of the orbital angular momentum of the quarks to the nucleon spin. Deeply Virtual Compton scattering (DVCS), the electroproduction of a real photon off the nucleon at the quark level, is the golden process directly interpretable in terms of GPDs of the nucleon. The GPDs are accessed in DVCS mainly through the measurements of spin-dependent asymmetries. Combining measurements of asymmetries from DVCS experiments on both the neutron and the proton will allow performing the flavor separation of relevant quark GPDs via linear combinations of proton and neutron GPDs.
This talk will be dedicated to the presentation of recent results, from the CLAS12 experiment at Jefferson Lab with the upgraded ~11 GeV CEBAF polarized electron beam, regarding the measurement of the Beam-Spin Asymmetry (BSA) from DVCS off the proton. Both the cases with a hydrogen target and a deuterium target will be shown. The BSA measurements with free-proton feature a never before examined region of the phase space reaching low values of invariant four-momentum transfer t. Those from bound proton in deuterium will give a hint on medium effects on GPDs. Further discussion will motivate the foreseen upgrade of the CLAS12 experiment to $\mu$CLAS12 aiming, in particular, to measure Double-DVCS and gain access to GPDs outside the phase-space region restricted by the kinematics of DVCS and its time-reversal counter process, time-like Compton scattering.