Moving forward to constrain the shear viscosity of QCD matter

TL;DR

This paper shows that rapidity differential anisotropic flow measurements in heavy ion collisions can effectively constrain the temperature-dependent shear viscosity to entropy density ratio of QCD matter, revealing a small ratio in the cross-over region and strong temperature dependence in the hadronic phase.

Contribution

It introduces a method to constrain the temperature dependence of shear viscosity in QCD matter using rapidity differential flow data, providing new insights into QCD transport properties.

Findings

Small {ta}/s pprox 0.04 in the cross-over region

Strong temperature dependence of {ta}/s in the hadronic phase

Rapidity-dependent flow measurements can constrain initial state fluctuations and transport properties

Abstract

We demonstrate that measurements of rapidity differential anisotropic flow in heavy ion collisions can constrain the temperature dependence of the shear viscosity to entropy density ratio {\eta}/s of QCD matter. Comparing results from hydrodynamic calculations with experimental data from RHIC, we find evidence for a small {\eta}/s $\approx$ 0.04 in the QCD cross-over region and a strong temperature dependence in the hadronic phase. A temperature independent {\eta}/s is disfavored by the data. We further show that measurements of the event-by-event flow as a function of rapidity can be used to independently constrain the initial state fluctuations in three dimensions and the temperature dependent transport properties of QCD matter.