title: 200 A GeV Au + Au collisions serve a nearly perfect quark-gluon liquid.
abstract: A new robust method to extract the specific shear viscosity (η/s)(QGP) of a quark-gluon plasma (QGP) at temperatures T(c) < T ≲ 2T(c) from the centrality dependence of the eccentricity-scaled elliptic flow v2/ε measured in ultrarelativistic heavy-ion collisions is presented. Coupling viscous fluid dynamics for the QGP with a microscopic transport model for hadronic freeze-out we find for 200 A GeV Au + Au collisions that v2/ε is a universal function of multiplicity density (1/S)(dN(ch)/dy) that depends only on the viscosity but not on the model used for computing the initial fireball eccentricity ε. Comparing with measurements we find 1<4π(η/s)(QGP) < 2.5 where the uncertainty range is dominated by model uncertainties for the values of ε used to normalize the measured v2.
authors.affiliation: Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Huichao
authors.initials: H
authors.lastname: Song
authors.forename: Steffen A
authors.initials: SA
authors.lastname: Bass
authors.forename: Ulrich
authors.initials: U
authors.lastname: Heinz
authors.forename: Tetsufumi
authors.initials: T
authors.lastname: Hirano
authors.forename: Chun
authors.initials: C
authors.lastname: Shen