  We find in complementary experiments and event driven simulations of sheared
inelastic hard spheres that the velocity autocorrelation function $\psi(t)$
decays much faster than $t^{-3/2}$ obtained for a fluid of elastic spheres at
equilibrium. Particle displacements are measured in experiments inside a
gravity driven flow sheared by a rough wall. The average packing fraction
obtained in the experiments is 0.59, and the packing fraction in the
simulations is varied between 0.5 and 0.59. The motion is observed to be
diffusive over long times except in experiments where there is layering of
particles parallel to boundaries, and diffusion is inhibited between layers.
Regardless, a rapid decay of $\psi(t)$ is observed, indicating that this is a
feature of the sheared dissipative fluid, and is independent of the details of
the relative particle arrangements. An important implication of our study is
that the non-analytic contribution to the shear stress may not be present in a
sheared inelastic fluid, leading to a wider range of applicability of kinetic
theory approaches to dense granular matter.
