Direct versus thermal particle emission in high-energy heavy-ion collisions

Abstract

Recent measurements of proton inclusive cross sections for heavy-ion collisions at several hundred MeV per nucleon are discussed in a phenomenological model which assumes coexistence of direct and thermal particle emission. The model postulates the existence of an additive twocomponent structure for inclusive spectra. The two components consist of a direct and a thermal one. The direct component is described in an extended impulse approximation and the thermal component in the participant-spectator geometrical model. Their normalizations are fixed by geometrical considerations. With this model we calculate the charged particle and proton inclusive spectra for Ne on U at 250 MeV per nucleon, Ne on U and Ne on Al at 400 MeV per nucleon, and Ne on NaF at 800 MeV per nucleon. A comparison is made with corresponding data. At 250 MeV and 400 MeV per nucleon, we find the postulated two-component structure to be instrumental in reproducing satisfactorily the slopes and the magnitudes of the data in the critical forward angle region. At 800 MeV per nucleon, due to the larger transparency of the nuclei, non-equilibrium statistical components appear to be important.