Production mechanism of backward energetic protons studied from two-particle correlations in 800 MeV proton-nucleus collisions

The relative importance of various mechanisms which may play a role in the production of backward energetic protons has been studied in 800 MeV proton-nucleus collisions. Energetic protons (P350 MeV/c) at =118°were measured in coincidence with particles emitted in the angular range from 15°to 100°. Both in-plane (=180°) and out-of-plane (=90°) coincidences were measured. The data have been decomposed into several categories depending on the excitation energy of the residual nucleus. Momentum spectra, angular distributions, and target mass dependences of these categories have been studied. The scattering of the incident proton by a correlated nucleon cluster seems to play an important role. From the proton spectrum associated with the p-d quasi-elastic scatterings, the momentum spread of the pn system (d) inside the nucleus has been determined. The momentum spread of the d obtained by the p-d quasi-elastic scatterings is found to be smaller than the spread observed in heavy-ion projectile fragmentation into deuterons. From the mass dependence of the ratio of the p-d to p-p quasi-elastic scattering cross sections, the mean free path of deuterons inside the nucleus has been determined.