Secondary phi meson peak as an indicator of QCD phase transition in   ultrarelativistic heavy ion collisions
  In a previous paper, we have shown that a double phi peak structure appears in the dilepton invariant mass spectrum if a first order QCD phase transition occurs in ultrarelativistic heavy ion collisions. Furthermore, the transition temperature can be determined from the transverse momentum distribution of the low mass phi peak. In this work, we extend the study to the case that a smooth crossover occurs in the quark-gluon plasma to the hadronic matter transition. We find that the double phi peak structure still exists in the dilepton spectrum and thus remains a viable signal for the formation of the quark-gluon plasma in ultrarelativistic heavy ion collisions. 
M. Asakawa and C. M. Ko