Beam-energy dependence of correlations between mean transverse momentum and anisotropic flow of charged particles in Au+Au collisions at RHIC

TL;DR

This study measures how the correlation between mean transverse momentum and anisotropic flow varies with beam energy in Au+Au collisions, providing insights into initial conditions and shear viscosity.

Contribution

It presents the first detailed energy-dependent analysis of $[p_T]$ and $v_n^2$ variances and covariances in heavy-ion collisions, comparing results with hydrodynamic models.

Findings

Variances and covariances show distinct energy dependence.

The dimensionless ratio remains similar across energies.

Results help differentiate initial-state models and constrain shear viscosity.

Abstract

The correlation between the mean transverse momentum, $[p_{\mathrm{T}}]$, and the squared anisotropic flow, $v^{2}_{n}$, on an event-by-event basis has been suggested to be influenced by the initial conditions in heavy-ion collisions. We present measurements of the variances and covariance of $[p_{\mathrm{T}}]$ and $v^{2}_{n}$, along with their dimensionless ratio, for Au+Au collisions at various beam energies: $\sqrt{\textit{s}_{NN}}$ $=$ 14.6, 19.6, 27, 54.4, and 200~GeV. Our measurements reveal a distinct energy-dependent behavior in the variances and covariances. In addition, the dimensionless ratio displays a similar behavior across different beam energies. We compare our measurements with hydrodynamic models and similar measurements from Pb+Pb collisions at the Large Hadron Collider (LHC). These findings provide valuable insights into the beam energy dependence of the specific shear viscosity ($\eta/s$) and initial-state effects, allowing for differentiating between different initial-state models.