Can we observe effects of early nonequilibrium dynamics using collective flow

Abstract

The rapid expansion of the fireball created in a heavy-ion collision causes strong departures from local equilibrium. Such effects are especially important in the very early phase of the collision, bringing a substantial pressure asymmetry. We investigate effects of this early stage pressure asymmetry in a kinetic model without boost-invariance. In the kinetic evolution the pressure asymmetry results from the competition of the longitudinal expansion and the kinetic relaxation. Unlike the transverse flow, the directed flow is found to be very sensitive to the equilibration rate and the pressure anisotropy.