Internal nuclear momentum and subthreshold anti-proton production in p-nucleus and nucleus-nucleus collisions

Abstract

We investigate subthreshold anti-proton production in p-nucleus and nucleus-nucleus collisions in terms of the internal nuclear momentum of the nucleons in the colliding nuclei. We employ a first collision model which contains the kinematics of individual NN collisions, with the inclusion of internal nuclear momentum distributions extracted from data on quasi-elastic electron scattering and backward proton production. Calculations for subthreshold particle production in p-nucleus collisions show excellent agreement with experimental data on subthreshold anti-proton and K + production in p + Cu collisions. An extension of the model to nucleus-nucleus collisions includes also the internal momentum for the incoming projectile nucleons, and contains the parameters obtained from a best fit to the p + Cu → p + X data. Despite the excellent agreement with the p + Cu → p + X data, this model underestimates recent experimental data on subthreshold p production in nucleus-nucleus collisions by large factors. Implications for collective phenomena at large nuclear densities and temperatures are discussed.