Abstract

We present first measurements of the evolution of the differential transverse momentum correlation function, C, with collision centrality in Au + Au interactions at root s(NN) = 200 GeV. This observable exhibits a strong dependence on collision centrality that is qualitatively similar to that of number correlations previously reported. We use the observed longitudinal broadening of the near-side peak of C with increasing centrality to estimate the ratio of the shear viscosity to entropy density, eta/s, of the matter formed in central Au + Au interactions. We obtain an upper limit estimate of eta/s that suggests that the produced medium has a small viscosity per unit entropy. (C) 2011 Elsevier B.V. All rights reserved.