Influence of temperature dependent shear viscosity on elliptic flow at back- and forward rapidities in ultrarelativistic heavy-ion collisions

TL;DR

This study investigates how a temperature-dependent shear viscosity affects azimuthal flow anisotropies in heavy-ion collisions at different energies and rapidities, highlighting the dominance of hadronic viscosity at all rapidities at RHIC and a combined plasma-hadronic influence at LHC midrapidity.

Contribution

It demonstrates the impact of temperature-dependent shear viscosity on flow harmonics across rapidities and energies, providing a way to distinguish viscosity parametrizations through experimental data.

Findings

Flow anisotropies are dominated by hadronic viscosity at all rapidities in RHIC collisions.

At LHC energies, flow coefficients are influenced by both plasma and hadronic viscosities at midrapidity.

Centrality and rapidity dependence of flow can differentiate viscosity models.

Abstract

We explore the influence of a temperature-dependent shear viscosity over entropy density ratio $\eta/s$ on the azimuthal anisotropies v_2 and v_4 of hadrons at various rapidities. We find that in Au+Au collisions at full RHIC energy, $\sqrt{s_{NN}}=200$ GeV, the flow anisotropies are dominated by hadronic viscosity at all rapidities, whereas in Pb+Pb collisions at the LHC energy, $\sqrt{s_{NN}}=2760$ GeV, the flow coefficients are affected by the viscosity both in the plasma and hadronic phases at midrapidity, but the further away from midrapidity, the more dominant the hadronic viscosity is. We find that the centrality and rapidity dependence of the elliptic and quadrangular flows can help to distinguish different parametrizations of $(\eta/s)(T)$. We also find that at midrapidity the flow harmonics are almost independent of the decoupling criterion, but show some sensitivity to the criterion at back- and forward rapidities.