Stochastic baryon charge transport in relativistic hydrodynamics

TL;DR

This paper develops a linearized stochastic hydrodynamics approach integrated into MUSIC to efficiently simulate baryon charge fluctuations in heavy-ion collisions, providing insights into the QCD phase diagram.

Contribution

It introduces a computationally efficient linearized stochastic hydrodynamics method for baryon transport in relativistic fluids, compatible with existing hydrodynamic codes.

Findings

Accurately describes two-point baryon charge correlations.

Demonstrates sensitivity of fluctuations to baryon diffusion coefficients.

Shows rapidity separation probes different evolution times.

Abstract

We utilize 3+1D stochastic hydrodynamics to study correlations and fluctuations of baryon charge in high-energy heavy-ion collisions. The baryon charge fluctuations are important observables to probe the QCD phase diagram, yet a dynamical description with stochastic hydrodynamics remains challenging due to numerical instabilities and high computational demands. In this work, we employ a linearized approach, allowing us to separately simulate the background energy-momentum evolution of a charge-neutral fluid and the stochastic baryon transport processes, thereby largely reducing computational cost while maintaining sufficient accuracy. We implement this linearized stochastic charge evolution in the viscous hydrodynamic code MUSIC, and find that it nicely describes the two-point correlation of 1+1D analytical solutions for various equations of state and transport coefficients. In particular, the hydrodynamic calculations demonstrate how different rapidity separations probe charge fluctuations originating at different times of the evolution. We also investigate the net baryon correlations after the Cooper--Frye freeze out, which show good consistency with the analytical calculations and indicate that these fluctuation-induced correlations are sensitive to the baryon diffusion coefficient.