Interplay of longitudinal and transverse expansion in the kinetic dynamics of heavy-ion collisions

Abstract

The early dynamics in heavy-ion collisions involves a rapid, far from equilibrium evolution. This early pre-equilibrium stage of the dynamics can be modeled using kinetic equations. The effect of this pre-equilibrium stage on final observables derived from transverse momenta of emitted particles is small. The kinetic equations in the relaxation time approximation for a nonboost invariant system are solved. The asymmetry of the flow with respect to the reaction plane at different rapidities is found to be very sensitive to the degree of nonequilibrium in the evolution. This suggests that the rapidity odd directed flow could be studied to identify the occurrence of nonequilibrium effects and to estimate the asymmetry of the pressure between the longitudinal and transverse directions in the collision.