Beam energy dependence of the linear and mode-coupled flow harmonics in Au+Au collisions

TL;DR

This study investigates how the linear and mode-coupled flow harmonics in gold-gold collisions vary with beam energy, revealing insights into the roles of shear viscosity and initial-state effects across different energies.

Contribution

It provides the first comprehensive comparison of flow harmonic responses across multiple beam energies, highlighting the energy dependence of shear viscosity and initial-state influences.

Findings

Flow coefficients depend on beam energy, indicating shear viscosity effects.

Dimensionless response coefficients are energy-independent, suggesting initial-state dominance.

Results help constrain models of initial conditions and temperature dependence of shear viscosity.

Abstract

The linear and mode-coupled contributions to higher-order anisotropic flow are presented for Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 27, 39, 54.4, and 200 GeV and compared to similar measurements for Pb+Pb collisions at the Large Hadron Collider (LHC). The coefficients and the flow harmonics' correlations, which characterize the linear and mode-coupled response to the lower-order anisotropies, indicate a beam energy dependence consistent with an influence from the specific shear viscosity ($\eta/s$). In contrast, the dimensionless coefficients, mode-coupled response coefficients, and normalized symmetric cumulants are approximately beam-energy independent, consistent with a significant role from initial-state effects. These measurements could provide unique supplemental constraints to (i) distinguish between different initial-state models and (ii) delineate the temperature ($T$) and baryon chemical potential ($\mu_{B}$) dependence of the specific shear viscosity $\frac{\eta}{s} (T, \mu_B)$.