Minijets: Cross section and energy distribution in very-high-energy nuclear collisions

The energy spectrum from semihard partonic interactions in nucleus-nucleus collisions with c.m. energies of the order of 1 TeV per nucleon is discussed. The presence of a large number of nucleons induces incoherence among most of the partonic collisions, while the large number of partonic interactions makes the unitarization of the cross section an essential tool for a meaningful description of the processes. This goal is achieved, accounting for all semihard partonic scatterings, namely, including both disconnected collisions and rescatterings. The characteristic feature of the interaction resulting from this analysis is that it is basically a geometrical one. As a consequence of the unitarization, the energy distribution of the scattered partons turns out to be a regular function of the cutoff ${\mathit{p}}_{\mathit{t}}^{\min }$ which separates semihard events from soft ones.