  Although jammed granular systems are athermal, several thermodynamic-like
descriptions have been proposed which make quantitative predictions about the
distribution of volume and stress within a system and provide a corresponding
temperature-like variable. We perform experiments with an apparatus designed to
generate a large number of independent, jammed, two-dimensional configurations.
Each configuration consists of a single layer of photoelastic disks supported
by a gentle layer of air. New configurations are generated by alternately
dilating and re-compacting the system through a series of boundary
displacements. Within each configuration, a bath of particles surrounds a
smaller subsystem of particles with a different inter-particle friction
coefficient than the bath. The use of photoelastic particles permits us to find
all particle positions as well as the vector forces at each inter-particle
contact. By comparing the temperature-like quantities in both systems, we find
compactivity (conjugate to the volume) does not equilibrate between the
systems, while the angoricity (conjugate to the stress) does. Both independent
components of the angoricity are linearly dependent on the hydrostatic
pressure, in agreement with predictions of the stress ensemble.
