New Solutions to Covariant Non-equilibrium Dynamics

Abstract

New solutions of 3+1D covariant kinetic theory are presented for nuclear collisions in the energy domain Ecm ~ 200 AGeV. They are obtained using MPC, a new Monte-Carlo parton transport technique that employs very high parton subdivision that is necessary to preserve covariance. The transport results are compared with ideal hydrodynamics solutions. We show that the transport evolution differs significantly from hydrodynamics. In addition, we compare the transport freeze-out distributions to those obtained from ideal hydrodynamics with the Cooper-Frye isotherm freeze-out prescription. The transport freeze-out four-volume is shown to be sensitive to the reaction rates and deviates from both time-like and space-like freeze-out 3D hypersurfaces commonly assumed. In particular, we find that there does not exist a universal freeze-out temperature. Finally, the transverse momentum distributions are found to deviate by up to an order of magnitude from (Cooper-Frye frozen) hydrodynamics for a wide range of possible initial conditions and reaction rates at RHIC energies.