  Event anisotropy measurements at RHIC suggest the strongly interacting matter
created in heavy ion collisions flows with very little shear viscosity. Precise
determination of "shear viscosity-to-entropy" ratio is currently a subject of
extensive study.
  We present preliminary results of measurements of the evolution of transverse
momentum correlation function with collision centrality of $Au +Au$
interactions at $\sqrt{s_{NN}}$ = 200 GeV.
  We compare two differential correlation functions, namely {\it inclusive} and
a differential version of the correlation measure $\tilde C$ introduced by
Gavin ${\it et. al.}$. These observables can be used for the experimental study
of the shear viscosity per unit entropy.
