Semi-hard scattering of partons at SPS and RHIC: A study in contrast
  We analyze the contribution of pQCD based semi-hard parton (re)scattering to the reaction dynamics of relativistic heavy-ion collisions at SPS and RHIC. While such processes are able to account for the measured yield of high momentum direct photons at SPS energies, the conditions necessary for jet-quenching are not fulfilled. The situation changes dramatically at RHIC energies. 
Steffen A. Bass, Berndt M\"uller, Dinesh K.Srivastava