The QGP shear viscosity -- elusive goal or just around the corner?

TL;DR

This paper discusses how combining elliptic and triangular flow data with advanced hydrodynamic models can precisely determine the QGP shear viscosity, reducing current uncertainties from initial state model differences.

Contribution

It demonstrates that simultaneous analysis of v_2 and v_3 flow data can significantly constrain initial state models, enabling more accurate extraction of QGP shear viscosity.

Findings

Elliptic and triangular flow data constrain initial state models.

Combined flow analysis reduces uncertainty in shear viscosity measurement.

Differential elliptic flow variation tests evolution models across energies.

Abstract

With the new viscous hydrodynamic + hadron cascade hybrid code VISHNU, a rather precise (O(25%)) extraction of the QGP shear viscosity (eta/s)_QGP from heavy-ion elliptic flow data is possible if the initial eccentricity of the collision fireball is known with <5% accuracy. At this point, eccentricities from initial state models differ by up to 20%, leading to an O(100%) uncertainty for (eta/s)_QGP. It is shown that a simultaneous comparison of elliptic and triangular flow, v_2 and v_3, puts strong constraints on initial state models and can largely eliminate the present uncertainty in (eta/s)_QGP. The variation of the differential elliptic flow v_2(p_T) for identified hadrons between RHIC and LHC energies provides additional tests of the evolution model.