Helicity Asymmetry for Proton Emission from Polarized Electrons in the Eikonal Regime

Abstract

The nuclear response to longitudinally polarized electrons, detected in coincidence with out-of-plane high-energy protons, is discussed in a simple model where the ejectile wave function is approximated as a plane wave with a complex wave vector. This choice is equivalent to solve the problem of Final-State Interactions (FSI) in homogeneous nuclear matter, as the residual nucleus can be described to a first approximation when dealing with very fast emitted protons. The main advantage of the present method is that in the framework of the Distorted-Wave Impulse Approximation (DWIA) it allows for an analytical derivation of all the components of the nuclear response. It emerges that cancellations among the leading contributions determine the very small absolute size of the socalled fifth structure function and produce a nontrivial asymptotic scaling of the related helicity asymmetry for large values of the momentum transfer.