Nucleon-nucleus reactions at ultrarelativistic energies

In order to discern coherent processes from incoherent and collective processes in nucleon-nucleus reactions at high energies, we study these reactions with an incoherent-multiple-collision model. In this model, the projectile nucleon makes successive inelastic collisions with nucleons in the target nucleus, the probability of such collisions being given by the thickness function and the nucleon-nucleon inelastic cross section. It is assumed that each baryon-baryon collision produces particles and degrades momenta just as a baryon-baryon collision in free space, and that there are no secondary collisions between the produced particles and the nucleons. We found that the inelastic proton data, the pseudorapidity distribution data ${\mathrm{dN}}^{\mathrm{pA}}$/dη, and the total nucleon-nucleus absorption data can be well explained by the incoherent-multiple-collision model. However, the single-particle fragmentation data for nonleading particles indicate that there is a reduction of the fragmentation cross section because of subsequent collisions of the leading baryon along the collision chain. Modification of the incoherent-multiple-collision model is suggested. The modified model gives cross sections for the reactions pA→${\pi }^{+}$X, pA→${\pi }^{\mathrm{-}}$X, pA→$K^{+}$X, pA→$K^{\mathrm{-}}$X, and pA→p¯X in the projectile fragmentation region in good agreement with experiment.