Velocity Distributions of Granular Gases with Long-Range Interactions

We study velocity statistics of electrostatically driven granular gases with long-range interactions. Our experiments involve anisotropic dipole forces between particles due to either magnetic or hydrodynamic interactions. Generally, the velocity distribution is non-Maxwellian, and its high-energy tail has a stretched exponential form $P(v)\sim \exp\left(-|v|^\xi\right)$. We find a simple exponential tail, $\xi=1$, for long-range dipole interactions, whereas $\xi=3/2$ for short-range, hard-core interactions. This behavior is consistent with kinetic theory of driven dissipative particles. We conclude that velocity statistics of dissipative gases are sensitive to the form of the particle interaction.