*Diffusion and elastic energy measurements in dense granular shear flows*

**Abstract:** We present experiments on granular shear in a 2D Couette geometry. The
system consists of photoelastic disks, allowing us to observe the behavior
of stresses and kinematic properties at the particle scale. In particular,
we study particle diffusion and stored elastic energy, with the goal of
generalizing the concept of a granular temperature to dense granular
flows. We find particle motion to be diffusive at small time scales with
a diffusivity proportional to local shear rate. Diffusivities along the
direction of flow are measured to be larger than those perpendicular to
the shear band. At larger scales, effects due to particle size and
coordinated motion are observed. We find that in dense granular flows the
anisotropic stress network induces an anisotropy in the particle
diffusivity which is not observed at larger shear rates. Elastic energy
storage in the grains is measured as a key factor in determining the
thermodynamic analog to temperature in dense systems, where velocity
fluctuations form an incomplete picture.