Noise and diffusion of a vibrated self-propelled granular particle.

Granular materials are an important physical realization of active matter. In vibration-fluidized granular matter, both diffusion and self-propulsion derive from the same collisional forcing, unlike many other active systems where there is a clean separation between the origin of single-particle mobility and the coupling to noise. Here we present experimental studies of single-particle motion in a vibrated granular monolayer, along with theoretical analysis that compares grain motion at short and long time scales to the assumptions and predictions, respectively, of the active Brownian particle (ABP) model. Our results show that despite the unique relation between noise and propulsion, a variety of granular particles are correctly described by the ABP model. Additionally, our scheme of analysis for validating the inputs and outputs of the model can be applied to other granular and non-granular active systems.