Structure and Dynamics of a uniformly heated granular fluid

Despite a long tradition amongst engineers, over the last decade granular media have attracted a considerable amount of attention within the physics community. This has been partly due to the realization that statistical mechanics could be useful in understanding granular materials. We report results from an experimental investigation where we try to test and explore some of these ideas. In our experiment we uniformly heat a quasi-2-dimensional ensemble of spherical particles and study the structure and dynamics of the resulting homogeneous granular fluid. We focus primarily on the vicinity of crystallization, at high filling fractions. This transition onto a crystal phase can be directly mapped to what happens for hard-disks in equilibrium. Moreover, prior to crystallization we analyze the caging dynamics of trapped individual grains which has a direct analogy with glassy behavior in colloidal systems. This strong connection with colloids and hard- disks in equilibrium is surprising since our system is both driven and dissipative and, therefore, inherently far from equilibrium.