Analytical treatment of high-energy nucleus-nucleus collisions including mean field effects: Boltzmann equation approach.

Abstract

We study nucleus-nucleus collisions at high energy on the basis of Boltzmann's kinetic theory under the assumption that the incident energy per nucleon is high enough for nucleon-nucleon collisions to dominate the strength of the mean field so that the latter may be treated perturbatively. Then, by use of multiple collision expansion as well as linearization techniques and the eikonal approximation, we obtain the stationary distribution function from the Boltzmann equation with the nuclear mean field as external force. The distribution consists of an infinite sum over multiple collision components. Their momentum dependent parts obey a transport equation linear in the nuclear mean force field, and can be evaluated analytically. They differ from the solution of a Fokker-Planck-type equation without external forces, obtained previously, only by a shift in the momentum caused by the nuclear mean field. The present investigation confirms a recently developed phenomenological approach which has been successful in explaining the sideward kinetic energy flow of the particles emitted in individual nucleus-nucleus collision events.