  Using X-ray tomography, we experimentally investigate granular packings
subject to mechanical tapping for three types of beads with different friction
coefficients. We validate Edwards volume ensemble in these three-dimensional
granular systems and establish a granular version of thermodynamic zeroth law.
Within Edwards framework, we also explicitly clarify how friction influences
granular statistical mechanics as modifying the density of states, which allows
us to determine the entropy as a function of packing fraction and friction
subsequently. Additionally, we obtain a granular jamming phase diagram based on
geometric coordination number and packing fraction.
