Coherent deeply virtual Compton scattering off³He and neutron generalized parton distributions

Abstract

Abstract. It has been recently proposed to study coherent deeply virtual Compton scattering (DVCS) off 3 He nuclei to access neutron generalized parton distributions (GPDs). In particular, it has been shown that, in Impulse Approximation (IA) and at low momentum transfer, the sum of the quark helicity conserving GPDs of 3 He, H and E, is dominated by the neutron contribution. This peculiar result makes the 3 He target very promising to access the neutron information. We present here the IA calculation of the spin dependent GPDH of 3 He. Also for this quantity the neutron contribution is found to be the dominant one, at low momentum transfer. The known forward limit of the IA calculation ofH , yielding the polarized parton distributions of 3 He, is correctly recovered. The extraction of the neutron information could be anyway non trivial, so that a procedure, able to take into account the nuclear effects encoded in the IA analysis, is proposed. These calculations, essential for the evaluation of the coherent DVCS cross section asymmetries, which depend on the GPDs H , E andH , represent a crucial step for planning possible experiments at Jefferson Lab.Generalized parton distributions (GPDs), introduced in Ref.[1], describe the hadron non perturbative structure in hard exclusive processes. The study of these quantities is very important to understand several open issues of hadrons, such as, e.g., their spin structure. GPDs are related to the total angular momentum of partons inside the hadron; their knowledge, once the helicity quark contribution were subtracted, would make possible to access their orbital angular momentum (OAM) content.The most promising process for these studies is likely deeply virtual compton scattering (DVCS), i.e., the reaction eH −→ e H when Q 2 M 2 (Q 2 = −q · q is the momentum transfer between the leptons e and e , 2 the one between hadrons H and H with momenta P and P , and M the nucleon mass). Another relevant kinematical variable is the so called skewedness, = − + /(P + + P + ) 1 .