Bayesian calibration of viscous anisotropic hydrodynamic simulations of heavy-ion collisions

TL;DR

This paper presents a Bayesian calibration of viscous anisotropic hydrodynamics (VAH) for heavy-ion collisions, demonstrating its ability to constrain QGP viscosities at early times more effectively than traditional models.

Contribution

It introduces a Bayesian calibration of VAH, showing its advantage in constraining QGP viscosities at higher temperatures compared to previous models.

Findings

VAH can be calibrated using experimental LHC data.

VAH constrains QGP viscosities at higher temperatures.

The model transitions smoothly from early to late-stage hydrodynamics.

Abstract

Due to large pressure gradients at early times, standard hydrodynamic model simulations of relativistic heavy-ion collisions do not become reliable until $O(1)$\,fm/$c$ after the collision. To address this one often introduces a pre-hydrodynamic stage that models the early evolution microscopically, typically as a conformal, weakly interacting gas. In such an approach the transition from the pre-hydrodynamic to the hydrodynamic stage is discontinuous, introducing considerable theoretical model ambiguity. Alternatively, fluids with large anisotropic pressure gradients can be handled macroscopically using the recently developed Viscous Anisotropic Hydrodynamics (VAH). In high-energy heavy-ion collisions VAH is applicable already at very early times, and at later times transitions smoothly into conventional second-order viscous hydrodynamics (VH). We present a Bayesian calibration of the VAH model with experimental data for Pb--Pb collisions at the LHC at $\sqrt{s_\textrm{NN}}=2.76$\,TeV. We find that the VAH model has the unique capability of constraining the specific viscosities of the QGP at higher temperatures than other previously used models.