Coherent deeply virtual Compton scattering off 3He and neutron generalized parton distributions

TL;DR

This paper presents an impulse approximation calculation of the spin-dependent GPD tilde-H for 3He, demonstrating neutron dominance at low momentum transfer, crucial for planning experiments to access neutron GPDs via coherent DVCS.

Contribution

It provides the first detailed IA calculation of the spin-dependent GPD tilde-H for 3He, highlighting neutron dominance and proposing a nuclear effects correction procedure.

Findings

Neutron contribution dominates the GPD tilde-H in 3He at low momentum transfer.

The IA calculation correctly reproduces the polarized parton distributions in the forward limit.

The results are essential for interpreting coherent DVCS experiments at Jefferson Lab.

Abstract

It has been recently proposed to study coherent deeply virtual Compton scattering (DVCS) off 3He 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 3He, H and E, is dominated by the neutron contribution. This peculiar result makes the 3He target very promising to access the neutron information. We present here the IA calculation of the spin dependent GPD tilde-H of 3He. 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 of tilde-H, yielding the polarized parton distributions of 3He, 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 and tilde-H, represent a crucial step for planning possible experiments at Jefferson Lab.