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

Estimates of the specific shear viscosity, $\eta/s$, of the quark-gluon plasma formed in ultrarelativistic heavy-ion collisions at RHIC and LHC based on the longitudinal broadening of transverse momentum two-particle correlator, $G_2$, were published by both STAR and ALICE collaborations. In this work using the progressive evolution with collision centrality of the correlator longitudinal widths in both systems, values of $\eta/s$ are computed as a function of charged particle pseudorapidity density using the Gavin ansatz which relates the $G_2$ 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 (${\rm d}N_{\rm ch}$/d$\eta)^{1/3}$ for different collision systems. Estimated values of $\eta/s$ based on ALICE data exhibit little to no dependence on charged particle pseudorapidity density at LHC energy, while estimates obtained from STAR data hint that $\eta/s$ might be a function of charged particle pseudorapidity density at top RHIC energy.