Subthreshold pion production in nucleus-nucleus collisions — A cooperative process!

Abstract

We examine various reaction mechanisms to explain the pion production at “subthreshold” energies. They range from the single collision mechanism to a cooperative multi-nucleon process. With a shell-model prescription for the initial state energies the single collision picture cannot explain the data. Rather, the cooperative action of many nucleons and also the freezing of degrees of freedom in the final channel (formation of composite nuclei) are seen vital to understand the observed cross sections.