Two-Particle Transverse Momentum Correlations in Pb–Pb Collisions at $\sqrt {{{{\text{s}}}_{{{\text{NN}}}}}} = 2.76$ TeV

Two-particle correlations are powerful tools for studying the medium produced in heavy-ion collisions. In particular, two-particle transverse momentum correlations enable measurements of the collision dynamics sensitive to momentum currents. Their evolution with collision centrality, which is related to the system lifetime, provides information about the shear viscosity, $\eta {\text{/}}s$, and the system relaxation time, ${{\tau }_{\pi }}$. We report on measurements of two-particle transverse momentum correlations as a function of centrality in Pb‒Pb collisions using the ALICE detector at the LHC. The centrality dependence of the near side peak of the correlation function, particularly its longitudinal width, provides information about the shear viscosity of the produced medium. The data are compared to predictions from selected Monte Carlo models. The charge independent momentum correlator exhibits a longitudinal broadening from peripheral to central collisions that is qualitatively consistent with expectations from a model with viscous effects. An interpretation of the observed broadening in the context of this model will be discussed.