Neutron contribution to nuclear DVCS asymmetries

TL;DR

This paper investigates how neutron contributions influence nuclear DVCS asymmetries using a simple GPD model, highlighting the potential to constrain neutron GPDs through asymmetry measurements at different momentum transfers.

Contribution

It introduces a model-based analysis of neutron effects on nuclear DVCS asymmetries, emphasizing the role of coherent and incoherent contributions across momentum transfer ranges.

Findings

At small t, asymmetry is dominated by coherent contributions, increasing compared to free proton.

At large t, incoherent contributions dominate, reducing asymmetry relative to free proton.

Neutron contributions significantly affect asymmetry deviations at large t, enabling neutron GPD constraints.

Abstract

Using a simple model for nuclear GPDs, we study the role of the neutron contribution to nuclear DVCS observables. As an example, we use the beam-spin asymmetry A_{LU}^A measured in coherent and incoherent DVCS on a wide range of nuclear targets in the HERMES and JLab kinematics. We find that at small values of the momentum transfer t, A_{LU}^A is dominated by the coherent-enriched contribution, which enhances A_{LU}^A compared to the free proton asymmetry A_{LU}^p, A_{LU}^A(\phi)/A_{LU}^p(\phi)=1.8-2.2. At large values of t, the nuclear asymmetry is dominated by the incoherent contribution and A_{LU}^A/(\phi)A_{LU}^p(\phi)=0.66-0.74. The deviation of A_{LU}^A(\phi)/A_{LU}^p(\phi) from unity at large t is a result of the neutron contribution, which gives a possibility to constain neutron GPDs in incoherent nuclear DVCS. A similar trend is expected for other DVCS asymmetries.