Effective potentials of dissipative hard spheres in granular matter.

We present an experimental study of the spatial correlations of a quasi-two-dimensional dissipative gas kept in a non-static steady state via vertical shaking. From high temporal resolution images we obtain the Pair Distribution Function (PDF) for granular species with different restitution coefficients. Effective potentials for the interparticle interaction are extracted using the Ornstein-Zernike equation with the Percus-Yevick closure. From both the PDFs and the corresponding effective potentials, we find a clear increase of the spatial correlation at contact with the decreasing values of the restitution coefficient.