Jamming in weakly perturbed granular media

A granular system is weakly vibrated and we observe how it reaches a static configuration when the perturbation intensity is decreased. This behavior is investigated using an immersed torsion oscillator whose angular deflections are analyzed to give information on the granular agitation. The oscillator can thus be seen as a low-frequency “thermometer” sensing the granular noise. The observed diffusive noise appears to approach the final static (or jammed) state according to the same expressions that describe the temperature dependence of viscosity or diffusivity in supercooled liquids, thus showing strong analogies with the vitrification process. We then discuss a simple model that relates the microscopic dynamics to the macroscopic rearrangements and accounts for that dependence.