Pre-equilibrium evolution effects on heavy-ion collision observables

Jia Liu, Chun Shen, and Ulrich Heinz
Phys. Rev. C 91, 064906 – Published 8 June 2015; Erratum Phys. Rev. C 92, 049904 (2015)

Abstract

To investigate the importance of pre-equilibrium dynamics on relativistic heavy-ion collision observables, we match a highly nonequilibrium early evolution stage, modeled by free-streaming partons generated from the Monte Carlo Kharzeev-Levin-Nardi (MC-KLN) and Monte Carlo Glauber (MC-Glb) models, to a locally approximately thermalized later evolution stage described by viscous hydrodynamics and study the dependence of final hadronic transverse momentum distributions, in particular their underlying radial and anisotropic flows, on the switching time between these stages. Performing a three-parameter fit of the measured values for the average transverse momenta p for pions, kaons, and protons, as well as the elliptic and triangular flows of charged hadrons v2,3ch, with the switching time τs, the specific shear viscosity η/s during the hydrodynamic stage, and the kinetic decoupling temperature Tdec as free parameters, we find that the preferred “thermalization” times τs depend strongly on the model of the initial conditions. MC-KLN initial conditions require an earlier transition to hydrodynamic behavior (at τs0.13 fm/c), followed by hydrodynamic evolution with a larger specific shear viscosity η/s0.2, than MC-Glb initial conditions, which prefer switching at a later time (τs0.6 fm/c) followed by a less viscous hydrodynamic evolution with η/s0.16. These new results including pre-equilibrium evolution are compared to fits without a pre-equilibrium stage where all dynamic evolution before the onset of hydrodynamic behavior is ignored. In each case, the quality of the dynamical descriptions for the optimized parameter sets, as well as the observables which show the strongest constraining power for the thermalization time, are discussed.

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  • Received 8 April 2015

DOI:https://doi.org/10.1103/PhysRevC.91.064906

©2015 American Physical Society

Erratum

Authors & Affiliations

Jia Liu1,*, Chun Shen2,1, and Ulrich Heinz1

  • 1Department of Physics, The Ohio State University, Columbus, Ohio 43210-1117, USA
  • 2Department of Physics, McGill University, 3600 University Street, Montreal, Quebec, Canada H3A 2T8

  • *liu.2053@osu.edu

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Vol. 91, Iss. 6 — June 2015

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