Heavy Ion Tea

Physics in the Vicinity of Phase Transition
Reinhard Stock (Frankfurt University)

Abstract: I will discuss possible effects of a QCD critical point and/or an adjacent 1st order transition on the process of hadron chemical freezeout and its analysis. For example, the dynamical focusing of the expansion trajectory, schematically discussed by Nonaka et al. in a hydro model, should lead to a reshuffling of the freezeout points in the T,mu(B)-plane that get determined by statistical model analysis. Furthermore, these points appear to disentangle from the lattice parton-hadron coexistence line . If chemical freezeout is not the consequence of a coincident phase transition one would expect a sequential decoupling of hadronic species, in order of their total inelastic cross sections. There are no clear indications at present for such behaviour but we need much more precise data at these low SPS energies to settle this questions.