Rapidity dependent momentum anisotropy at RHIC
  In Au+Au collisions at RHIC, elliptic flow was found to rapidly decrease as a function of rapidity. We argue that the origin of this phenomenon is incomplete thermalization of the initial fireball outside the midrapidity region and show that it can be quantitatively related to the analogous effect at midrapidity in peripheral collisions and in collisions at lower beam energies. 
Ulrich Heinz and Peter F Kolb