Single- and Multiple-Scattering Mechanisms in High-Energy Nuclear Collisions

We study the production of energetic protons from relativistic nuclear collisions using two approaches, the hard-scattering model and an intranuclear cascade model. The hard-scattering model combines the simplified kinematics of single scatterings and the effects of the momentum distribution for nucleons in the nucleus to provide a parameter-free description of a nucleus-nucleus collision. We use free nucleon-nucleon cross sections to describe the individual NN interactions. Good agreement with experiment is obtained in this model for the high-momentum regions of the inclusive proton spectra from collisions at 800 MeV/nucleon. Crucial to this success is the inclusion of a high-momentum tail in the momentum distribution. This model is also applied to explain the observed two-proton azimuthal correlations from these systems and, with simple assumptions, to estimate the single-scattering component of the inclusive proton spectra. This latter is at least 37% in the lower momentum regions of the spectra analyzed. We also present calculations of the one- and two-particle inclusive spectra using forms for the momentum distribution obtained both from the analysis of proton-nucleus backscattering data and from theory. Finally, we use a simple cascade model to calculate the inclusive proton spectra at 180° from 600 MeV proton-nucleus collisions. The nucleus is assumed to be a Fermi gas of uniform density, and we neglect the excitation of resonances in the intermediate state and the reflection and refraction of cascade nucleons due to variations in the mean nuclear potential, The calculated results are below the experimental values and imply the presence of other reaction mechanisms.