Neutron contribution to nuclear DVCS asymmetries

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.