  We characterize a system of hard spheres with a simple collision rule that
breaks time reversal symmetry, but conserves energy. The collisions lead to an
a-chiral, isotropic, and homogeneous stationary state, whose properties are
determined in simulations and compared to an approximate theory originally
developed for elastic hard spheres. In the nonequilibrium fluid state,
velocities are correlated, a phenomenon known from other nonequilibrium
stationary states. The correlations are long-ranged decaying like $1/r^d$ in
$d$ dimensions. Such correlations are expected on general grounds far from
equilibrium and had previously been observed in driven or non-stationary
systems.
