Constraining $\eta /s$ through high-p$_\perp$ theory and data

TL;DR

This study investigates whether high-$p_ot$ data and theory can effectively constrain the temperature dependence of shear viscosity over entropy density ratio ($/s$) in quark-gluon plasma created in heavy-ion collisions, using two different approaches.

Contribution

It introduces a novel method to connect high-$p_ot$ observables with the temperature-dependent $/s$, demonstrating the potential to constrain $/s(T)$ more precisely at high temperatures.

Findings

High-$p_ot$ data alone cannot distinguish different $/s(T)$ assumptions when low-$p_ot$ data are fitted.

The second approach's $/s(T)$ estimates align well with Bayesian analyses near $T_c$.

The second approach yields smaller uncertainties in $/s$ at high temperatures.

Abstract

We study whether it is possible to use high-$p_\perp$ data/theory to constrain the temperature dependence of the shear viscosity over entropy density ratio $\eta/s$ of the matter formed in ultrarelativistic heavy-ion collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC). We use two approaches: i) We calculate high-$p_\perp$ $R_{AA}$ and flow coefficients $v_2$, $v_3$ and $v_4$ assuming different $(\eta/s)(T)$ of the fluid-dynamically evolving medium. ii) We calculate the quenching strength ($\hat{q}/T^3$) from our dynamical energy loss model and convert it to $\eta/s$ as a function of temperature. It turned out that the first approach can not distinguish between different $(\eta/s)(T)$ assumptions when the evolution is constrained to reproduce the low-$p_\perp$ data. In distinction, $(\eta/s)(T)$ calculated using the second approach agrees surprisingly well with the $(\eta/s)(T)$ inferred through state-of-the-art Bayesian analyses of the low-$p_\perp$ data even in the vicinity of $T_c$, while providing much smaller uncertainties at high temperatures.