Jamming during the discharge of grains from a silo described as a percolating transition.

We have looked into an experiment that has been termed the "canonical example" of jamming: granular material, clogging the outlet of a container as it is discharged by gravity. We present quantitative data of such an experiment. The experimental control parameter is the ratio between the radius of the orifice and the radius of the beads. As this parameter is increased, the jamming probability decreases. However, in the range of parameters explored, no evidence of criticality--in the sense of a jamming probability that becomes infinitely small for a finite radius--has been found. We draw instead a comparison with a simple model that captures the main features of the phenomenon, namely, percolation in one dimension. The model gives indeed a phase transition, albeit a special one.