Relativistic predictions of quasielastic proton-nucleus spin observables based on a complete Lorentz invariant representation of the NN scattering matrix

Abstract

Within the framework of the relativistic plane wave impulse approximation (RPWIA), complete sets of quasielastic $(\vec{p}, \vec{p}^{'})$ and $(\vec{p}, \vec{n})$ spin observables are calculated employing a general Lorentz invariant representation of the NN scattering matrix (referred to as the IA2 representation). The use of a complete representation eliminates the arbitrariness of a previously-used five-term parameterization (commonly called the IA1 representation) and allows for the correct incorporation of effective-mass-type medium effects within the RPWIA framework and within the context of the Walecka model. For quasielastic scattering from a $^{40}$Ca target at incident proton energies between 200 and 500 MeV, we investigate the sensitivity of complete sets of spin observables to effective nucleon masses for both IA1 and IA2 representations. In general it is seen that the IA1 representation may overestimate the importance of nuclear medium effects, whereas the IA2-based predictions nearly correspond to values for free nucleon-nucleon scattering.