On coherent particle production in central 4.3 A Gev/c Mg-Mg collisions

Features of dense groups, or spikes, of negative pions produced in Mg-Mg collisions at 4.3 GeV/c/nucleon are studied to search for a coherent, Cerenkov-like, mechanism of particle production process. We investigate the distributions of spike centers and, for the first time, the energy spectra of particles in spikes. The spike-center distributions are obtained to exhibit the structure due to the coherent gluon-jet emission dynamics. This structure is similar to that observed recently for all-charged-particle spikes in hadronic and nuclear interactions. The energy distribution within spikes is found to have a significant peak over the inclusive background, while the inclusive spectrum shows exponential decrease with two characteristic values of average kinetic energy. The value of the peak energy and its width are in a good agreement with those expected for pions produced in a nuclear medium in the framework of the Cerenkov quantum approach. The peak energy obtained is consistent with the value of the cross-section maximum observed in coincidence experiments of nucleon-nucleus interactions.