A Mixed Phase Model and the 'Softest Point' Effect
  Particularities of the statistical mixed phase model for describing the deconfinement phase transition and physics constraints on the model parameters, are discussed. The modifications proposed concern an improved treatment of hadron-hadron interactions within the nonlinear mean-field model of nuclear matter and an inclusion of the one-gluon exchange correction into the quark-gluon sector of the mixed phase thermodynamic potential. It is shown that the mixed phase model successfully reproduces both the available lattice data on the QCD deconfinement transition and thermodynamic characteristics of hadron systems evaluated within the modern models. The 'softest point' of the equation of state resulting in a possible formation of a long-lived fireball in nuclear collisions (the 'softest point' effect) is analyzed. The obtained results are confronted with the data on the two-phase model. Some manifestation of the mixed phase formation and deconfinement transition is estimated in fireball expansion dynamics. We discuss experimental possibilities of observing the softest point effect as a signal of the deconfinement phase transition. 
E.G.Nikonov, A.A.Shanenko and V.D.Toneev