Extraction of the specific shear viscosity of quark-gluon plasma from two-particle transverse momentum correlations

The specific shear viscosity, η/ s, of the quark-gluon plasma formed in ultrarelativistic heavy-ion collisions at RHIC and LHC is estimated based on the progressive longitudinal broadening of transverse momentum two-particle correlators, G₂, reported as a function of collision centrality by the STAR and ALICE experiments. Estimates are computed as a function of collision centrality using the Gavin ansatz which relates the G₂ longitudinal broadening to the specific shear viscosity. Freeze out times required for the use of the ansatz are computed using a linear fit of freeze out times reported as a function of the cubic root of the charged particle pseudorapidity density (d N_ch/dη) ^{1 / 3}. Estimates of η/ s based on ALICE data exhibit little to no dependence on collision centrality at LHC energy, while estimates obtained from STAR data hint that η/ s might be a function of collision centrality at top RHIC energy.