On final conditions in high energy heavy ion collisions
  Motivated by the recent experimental observations, we discuss the freeze-out properties of the fireball created in central heavy ion collisions. We find that the freeze-out conditions, like temperature, velocity gradient near center of the fireball, are similar for different colliding systems and beam energies. This means that the transverse flow is stronger in the collisions of heavy nuclei than that of the light ones. 
Yu.M. Sinyukov, S.V. Akkelin, and N. Xu