Elliptic flow and nuclear modification factor in ultra-relativistic heavy-ion collisions within a partonic transport model

摘要

The quark gluon plasma produced in ultra-relativistic heavy-ion collisionsexhibits remarkable features. It behaves like a nearly perfect liquid with asmall shear viscosity to entropy density ratio and leads to the quenching ofhighly energetic particles. We show that both effects can be understood for thefirst time within one common framework. Employing the parton cascade BoltzmannApproach to Multi-Parton Scatterings (BAMPS), the microscopic interactions andthe space-time evolution of the quark gluon plasma are calculated by solvingthe relativistic Boltzmann equation. Based on cross sections obtained fromperturbative QCD with explicitly taking the running coupling into account, wecalculate the nuclear modification factor and elliptic flow inultra-relativistic heavy-ion collisions. With only one single parameterassociated with coherence effects of medium-induced gluon radiation, theexperimental data of both observables can be understood on a microscopic level.Furthermore, we show that perturbative QCD interactions with a running couplinglead to a sufficiently small shear viscosity to entropy density ratio of thequark gluon plasma, which provides a microscopic explanation for theobservations stated by hydrodynamic calculations.