Velocity Fluctuations in a Homogeneous 2D Granular Gas in Steady State

We have measured the spectrum of velocity fluctuations in a granular system confined to a vertical plane and driven into a homogeneous, steady state by strong vertical vibration. The distribution of horizontal velocities is not Maxwell-Boltzmann and is given by P(v)0ex0ex=0ex0exCexp[-β(|v|/σ)^α] where α0ex0ex=0ex0ex1.55±0.1 at all frequencies and amplitudes investigated, and also for varying boundary conditions. The deviation from Maxwell-Boltzmann statistics occurs in the absence of spatial clustering and does not result from an inhomogeneous average over regions of varying local density. Surprisingly, $P(v)$ has the same shape over a wide range of densities.