Particle Dynamics at the Onset of the Granular Gas-Liquid Transition

We study experimentally the dynamical behavior of few large tracer particles placed in a quasi-2D granular ``gas'' made many small beads low-gravity environment. Multiple inelastic collisions transfer momentum from uniaxially driven gas to tracers whose velocity distributions are studied through particle tracking. Analyzing these for an increasing system density reveals that translational energy equipartition is reached at onset gas-liquid transition corresponding emergence local clusters. The dynamics thus appears as simple and accurate tool detect this transition. A model proposed describing accurately formation heterogeneities.