Central heavy-ion collisions with emulsion at 4.2 GeV/c per incident nucleon

Abstract

Multiplicity and angular distributions of particles produced in central collisions between12C ions and emulsion nuclei were studied at momentum 4.2 GeV/c per incident nucleon. The investigated data represent the most central collisions which had ever been studied yet. Events of central collisions are defined, here, as those having no projectile charged fragments, even a singly charged one, emitted within 3° of the beam direction. The analysis of the experimental data shows agreement with the limiting-fragmentation hypothesis. The multiple production of particles in central collisions is not in disagreement with the assumption of a superposition of nucleon-nucleon collisions. The angular distributions of target fragmentation particles, grey and black particle tracks corresponding to proton kinetic energies 27 <T⩽ 400 andT⩽ 27 MeV, respectively, do not show any statistically significant peak which would have been attributed to a collective « shock wave » phenomenon. The longitudinal velocity of the emitting system, found from black-track analysis, is low and typically equals (0.014 ± 0.002)c.