Abstract
Complete evolution of the strongly interacting matter formed in ultrarelativistic heavy-ion collisions is studied within a coupled Boltzmann and relativistic viscous hydrodynamics approach. For the initial nonequilibrium evolution phase, we employ a multiphase transport (AMPT) model that explicitly includes event-by-event fluctuations in the number and positions of the participating nucleons as well as of the produced partons with subsequent parton transport. The ensuing near-equilibrium evolution of quark-gluon and hadronic matter is modeled within the -dimensional relativistic viscous hydrodynamics. We probe the role of parton dynamics in generating and maintaining the spatial anisotropy in the preequilibrium phase. Substantial spatial eccentricities are found to be generated in the event-by-event fluctuations in parton production from initial nucleon-nucleon collisions. For ultracentral heavy-ion collisions, the model is able to explain qualitatively the unexpected hierarchy of the harmonic flow coefficients observed at energies currently available at the CERN Large Hadron Collider (LHC). We find that the results for are rather insensitive to the variation (within a range) of the time of switchover from AMPT parton transport to hydrodynamic evolution. The usual Grad and the recently proposed Chapman-Enskog-like (nonequilibrium) single-particle distribution functions are found to give very similar results for . The model describes well both the BNL Relativistic Heavy Ion Collider and LHC data for at various centralities, with a constant shear viscosity to entropy density ratio of 0.08 and 0.12, respectively. The event-by-event distributions of are in good agreement with the LHC data for midcentral collisions. The linear response relation is found to be true for , except at large values of , where a larger value of is required, suggesting a small admixture of positive nonlinear response even for .
2 More- Received 27 February 2015
DOI:https://doi.org/10.1103/PhysRevC.92.014903
©2015 American Physical Society