Energy Loss at Propagating Jamming Fronts in Granular Gas Clusters

We explore the initial moments of impact between two dense granular clusters in a two-dimensional geometry. The particles are composed of solid CO$_{2}$ and are levitated on a hot surface. Upon collision, the propagation of a dynamic "jamming front" produces a distinct regime for energy dissipation in a granular gas in which the translational kinetic energy decreases by over 90%. Experiments and associated simulations show that the initial loss of kinetic energy obeys a power law in time, $\Delta E=-Kt^{3/2}$, a form that can be predicted from kinetic arguments.