FREEZE-OUT IN RELATIVISTIC HEAVY-ION COLLISIONS AT ACS ENERGIES

The dynamics of the light (S+S) and heavy (Au+Au) colliding systems at 11.6 A GeV/c is analyzed on the basis of the microscopic Quark Gluon String Model (QGSM). The freeze-out picture, predicted by the QGSM, is quite different from the one adopted in fluid-dynamical models. Even for the most heavy systems particle emission takes place from the whole space-time domain available for the evolution of the system, but not from the thin ''freeze-out hypersurface''. Pions are continuously emitted from the whole volume of the reaction and reflect the main trends of the evolution of the system. Nucleons in Au+Au collisions initially come from the surface region. For both reactions there is a separation of the elastic and inelastic freeze-out.