Particle production in nucleon-nucleus and nucleus-nucleus collisions: Fermi motion versus collective tube mechanisms

Abstract

Within the general framework of multiple scattering theory for particle production in nucleon-nucleus and nucleus-nucleus collisions we investigate the results of two limiting situations: independent multiple collisions with Fermi motion effects versus the collective tube model with the assumption of universality for the elementary cross sections. Dramatically different predictions may be obtained. We summarize the results for pion multiplicity distributions in nucleus-nucleus collisions to assess the possible evidence for a coherent-collective mechanism and find that no strong conclusion is possible with the currently available pion multiplicity data. Attention is then focused on potentially more conclusive tests---subthreshold (in the nucleon-nucleon kinematics) production of massive particles, $\overline{p}$, $\frac{\ensuremath{\psi}}{J}$, and $W$ as examples. Evidence for a collective mechanism is found by examining subthreshold $\overline{p}$ production data in particle-nucleus collisions. However, owing to the limited scope of these data a firm conclusion is probably premature. Further $\overline{p}$ production experiments are proposed. With the assumption that the collective mechanism can be proved, it is worth studying the possibility of producing other massive particles, especially in nucleus-nucleus collisions where the collective effects have large subthreshold consequences. Within the (limited) framework of universality we then present predictions for the subthreshold production of $\frac{\ensuremath{\psi}}{J}$ and the $W$ boson. Owing to the qualitative nature of our assumptions and since these approaches bracket the $\overline{p}$ data, we expect that the collective tube model provides an optimistic limit and independent multiple collisions a pessimistic limit for $W$ production cross sections.NUCLEAR REACTIONS Nucleon-nucleus and nucleus-nucleus at high energies; particle production subthreshold; pion, antiproton, $\frac{\ensuremath{\psi}}{J}$, $W$ production, Fermi motion and collective effects.