Attractors for Flow Observables in 2+1D Bjorken Flow

TL;DR

This paper investigates how second-order hydrodynamics can model the early-time behavior of quark-gluon plasma in heavy-ion collisions, emphasizing the role of the Bjorken flow attractor and the impact of initial conditions.

Contribution

It demonstrates that rescaling initial energy density in hydrodynamics improves agreement with kinetic theory in far-from-equilibrium regimes.

Findings

Hydrodynamics captures early-time dynamics via the Bjorken flow attractor.

Discrepancies with kinetic theory occur at late times in far-from-equilibrium.

Rescaling initial energy density restores agreement with kinetic theory for large opacities.

Abstract

We examine the capabilities of second-order Israel-Stewart-type hydrodynamics to capture the early-time behaviour of the quark-gluon plasma created in heavy-ion collisions. We point out that at very early times, the dynamics of the fireball is governed by the local 0+1-D Bjorken flow attractor due to the rapid expansion along the longitudinal direction. Discrepancies between hydrodynamics and kinetic theory in this far-from-equilibrium regime leads to disagreement at the level of late-time observables, such as elliptic flow. We show that rescaling the initial energy-density profile for hydrodynamics accounts for such discrepancies, restoring agreement with kinetic theory for large opacities (small shear viscosity / large system size / high energy).