# Investigating the collision energy dependence of $\eta$/s in RHIC beam energy scan using Bayesian statistics

## TL;DR

This study uses Bayesian inference to analyze how the shear viscosity to entropy density ratio varies with collision energy in RHIC experiments, revealing a trend of higher values at lower energies with uncertainties allowing for a constant ratio.

## Contribution

It introduces a Bayesian statistical framework with Gaussian process emulators to determine $ ext{eta}/s$ across different collision energies in heavy-ion collisions.

## Key findings

- Most likely $ ext{eta}/s$ increases at lower collision energies.
- Uncertainties permit a constant $ ext{eta}/s$ between 0.10 and 0.15.
- Methodologically advances the analysis of $ ext{eta}/s$ dependence using Bayesian inference.

## Abstract

We determine the probability distributions of shear viscosity over the entropy density ratio $\eta/s$ in Au+Au collisions at $\sqrt{s_{NN}}=19.6, 39$, and $62.4$ GeV, using Bayesian inference and Gaussian process emulators for a model-to-data statistical analysis that probes the full input parameter space of a transport+viscous hydrodynamics hybrid model. We find the most likely value of $\eta/s$ to be larger at smaller $\sqrt{s_{NN}}$, although the uncertainties still allow for a constant value between 0.10 and 0.15 for the investigated collision energy range.