Stopping power, equilibration, and collective flow in the reactions Ar + Pb and Nb + Nb — A theoretical analysis

Abstract

The approach to local kinetic equilibrium in relativistic heavy ion collisions is studied by following the time evolution of the Wigner function for Ar (770 MeV/N)+Pb in configuration and momentum space using the Vlasov-Uehling-Uhlenbeck theory. Rapid equilibrium of the participant region is observed within 10 fm/ c. Total stopping of the projectile occurs at small impact parameters. For intermediate impact parameters, the theory predicts simultaneously the bounce-off effect of the projectile fragments and the sidewards flow of the participant matter. The latter can be displayed via a large angle peak in the flow angle, θ f, distributions, while the bounce-off is most easily observed via a pronounced peak in the rapidity dependence of the transverse momentum transfer p x ( y). A drastic dependence of p x and θ f on impact parameter and bombarding energy is predicted for Ar + Pb and Nb + Nb. Recent data support our analysis.