Stopping and the K/pi horn
  We propose a non-equilibrium hadronic model to interpret the observed excitation function of kaon-to-pion ratios in nuclear collisions at AGS and SPS energies. The crucial assumption of our model is that due to stronger stopping at lower energies the lifetime of the fireball is prolonged because the system has to build up the longitudinal expansion from internal pressure. 
Boris Tomasik and Evgeni E. Kolomeitsev