Momentum space approach to microscopic effects in elastic proton scattering

The microscopic nonrelativistic first-order optical potential for proton-nucleus scattering is studied in some detail. Momentum-space calculations have been performed for a number of different target nuclei at proton energies above ∼100 MeV and these microscopic predictions are compared with experimental cross section, analyzing power, and spin-rotation function data. The input to these calculations consists of the free on-shell nucleon-nucleon $t$ matrix, its nonlocal and off-shell structure, the treatment of the full-folding integral, and target densities obtained from electron scattering. Off-shell and nonlocal effects, as well as various factorization approximations, are studied. The sensitivity to uncertainties in the off-shell extension of the $t$ matrix, within the context of the Love-Franey model, is explicity displayed. Similarly, uncertainties due to nonlocalities and incomplete knowledge of nuclear densities are shown. Explicit calculations using the $t$ matrix of Love and Franey indicate that these effects play significant roles only for relatively large angles ($\theta \lesssim 60°$) and/or lower energies (∼150 MeV). These studies reinforce the conclusion that the lack of agreement between such first-order predictions and the data for spin observables at small angles arises from a physical effect not included in the nonrelativistic first-order theory, rather than from any uncertainty in the calculation or in its input.