Subthreshold π 0-production in the Boltzmann-Uehling-Uhlenbeck theory

Abstract

π 0-production in medium energy heavy ion reactions is studied via the Boltzmann-Uehling-Uhlenbeck approach. The mass dependence and bombarding energy dependence of the calculated absolute pion cross sections agree remarkably well with the recent data of Noll et al. for 12 C(60, 75, 85 MeV/N) + C, Ni, Au . Assuming a reabsorption length of 3 fm, pion reabsorption occurs in ⪆ 50% of the events. Shadowing is important for the angular distributions of pions produced in heavy systems and also changes the apparent velocity of the “pion emitting source”.