High-energy velocity tails in uniformly heated granular materials

TL;DR

This study experimentally examines the velocity distributions in uniformly heated granular materials, revealing density-independent high-energy tails with an exponent of approximately 1.5, consistent with kinetic theory predictions across various densities.

Contribution

The paper provides experimental evidence that high-energy velocity tails in uniformly heated granular materials follow a universal exponent, aligning with kinetic theory even at high densities.

Findings

High-energy tails characterized by an exponent of 1.50±0.03

Velocity distributions are non-Gaussian and density-independent

Results agree with kinetic theory predictions at high densities

Abstract

We experimentally investigate the velocity distributions of quasi two-dimensional granular materials, which are homogeneously driven, i.e. uniformly heated, by an electromagnetic vibrator, where the translational velocity and the rotation of a single particle are Gaussian and independent. We observe the non-Gaussian distributions of particle velocity, with the density-independent high-energy tails characterized by an exponent of $\beta=1.50\pm0.03$ for volume fractions of $0.111\le\phi\le0.832$, covering a wide range of structures and dynamics. Surprisingly, our results are in excellent agreement with the prediction of the kinetic theories of granular gas, even for an extremely high volume fraction of $\phi=0.832$ where the granular material forms a crystalline solid. Our experiment reveals that the density-independent high-energy velocity tails of $\beta=1.50$ are a fundamental property of uniformly heated granular matter.