Effects of initial-state dynamics on collective flow within a coupled transport and viscous hydrodynamic approach

TL;DR

This study investigates how initial nonequilibrium dynamics influence final observables in ultrarelativistic heavy-ion collisions by combining transport and viscous hydrodynamic models, showing insensitivity to switching time and good data agreement.

Contribution

It introduces a coupled transport and hydrodynamic approach with careful matching, demonstrating that preequilibrium effects have limited impact on final observables and that initial shear viscous tensor is not large.

Findings

Final-state observables are insensitive to switching time.

Model describes experimental data well across various observables.

Initial shear viscous tensor is not large.

Abstract

We evaluate the effects of preequilibrium dynamics on observables in ultrarelativistic heavy-ion collisions. We simulate the initial nonequilibrium phase within A MultiPhase Transport (AMPT) model, while the subsequent near-equilibrium evolution is modeled using (2+1)-dimensional relativistic viscous hydrodynamics. We match the two stages of evolution carefully by calculating the full energy-momentum tensor from AMPT and using it as input for the hydrodynamic evolution. We find that when the preequilibrium evolution is taken into account, final-state observables are insensitive to the switching time from AMPT to hydrodynamics. Unlike some earlier treatments of preequilibrium dynamics, we do not find the initial shear viscous tensor to be large. With a shear viscosity to entropy density ratio of $0.12$, our model describes quantitatively a large set of experimental data on Pb+Pb collisions at the Large Hadron Collider(LHC) over a wide range of centrality: differential anisotropic flow $v_n(p_T) ~(n=2-6)$, event-plane correlations, correlation between $v_2$ and $v_3$, and cumulant ratio $v_2\{4\}/v_2\{2\}$.