Hydrodynamic elliptic and triangular flow in Pb-Pb collisions at sqrt(s)=2.76ATeV

TL;DR

This study compares hydrodynamic models with LHC Pb-Pb collision data to determine the quark-gluon plasma's shear viscosity, finding that a small viscosity value best reproduces observed flow patterns.

Contribution

It demonstrates that a specific shear viscosity of approximately 1/(4pi) accurately describes both elliptic and triangular flow in Pb-Pb collisions at the LHC.

Findings

MC-Glauber initial conditions match flow data with eta/s ≈ 1/(4pi)

MC-KLN initial conditions require higher viscosity and underpredict flow

Small shear viscosity is favored for quark-gluon plasma modeling

Abstract

It is shown that a simultaneous comparison of both elliptic and triangular flow from (2+1)-dimensional viscous fluid dynamics with recent measurements in Pb+Pb collisions at the Large Hadron Collider (LHC) favors a small specific shear viscosity (eta/s)_QGP approximately equal to 1/(4pi) for the quark-gluon plasma. Using this viscosity value, the relative magnitude of the elliptic and triangular flow is well described with Monte-Carlo Glauber (MC-Glauber) initial conditions while Monte-Carlo Kharzeev-Levin-Nardi (MC-KLN) initial conditions require twice as large viscosity to reproduce the elliptic flow and then underpredict triangular flow by about 30%.