  We report a peculiar dynamic phenomenon in granular gases, chain structures
of head-on collisions caused by the boundary heated mechanism form a network in
an Airbus micro-gravity experiment and horizontal vibrated one in the
laboratory, which differ markedly from the grazing-collision-dominant in
randomly driven granular fluid. This new order property is an orientation
correlation between the relative position and the relative velocity of any
particle pair, which weakens the collision frequency and leads a long range
boundary effect. By the histogram of the relative position and the relative
velocity, we find this position-velocity correlation is not only at limits of
very small relative velocities but also large ones, which means the breakdown
of molecular chaos assumption is not limited to a small portion of the phase
space. Through a simple anisotropic angular distribution model of the relative
position and the relative velocity, we could modify classical uniform angular
integration results of mean field values taking the effect of the observed
collision chain structure explicitly into account.
