Abstract: Shear Viscosity of Hadronic and Partonic Matter from Microscopic Transport Models

Abstract: Ultra-relativistic heavy-ion collisions at RHIC are thought to have created a Quark-Gluon-Plasma (QGP) with a very low shear viscosity in the deconfined phase. However, as the QGP hadronizes it will evolve through a hadronic phase with rapidly increasing viscosity. In order to fully characterize the QGP state, one has to separately determine the viscosity of the deconfined and hadronic phases. We present a calculation of the shear viscosity coefficient and the shear-viscosity to entropy density ratio of partonic and hadronic matter in equilibrium. The Kubo formalism enables us to compute the shear viscosity of a system by examining near-equilibrium correlations of its stress-energy tensor. The hadronic and partonic media are simulated using the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model and the Parton Cascade Model (PCM), respectively, in a box with periodic boundary conditions. We also discuss a hybrid macro+micro calculation where ideal hydrodynamics is used to model the deconfined phase, and a scheme combining the Kubo formalism with our microscopic transport model is used to obtain the time-dependence of the shear viscosity in the hadronic phase of a relativistic heavy ion collision.