Correlations of pions and kaons as a measure for delayed expansion due to the QCD phase transition

We study pion and kaon correlations in ultra-relativistic heavy ion collisions in a hydrodynamical model with transverse cylindrical and boost-invariant longitudinal symmetry. As a function of the initial energy density ε₀, the ratioR _out/R _side of the inverse widths of the two-particle correlation function in out- and side-direction reflects the behaviour of the lifetime of the system. The ratio shows an enhancement in the case of a delayed expansion caused by the QCD phase transition. We discuss how this time-delay signal depends on the average transverse momentum of the pair, and show that it appears particularly strong for pairs with large average transverse momentum,K _⊥～1 GeV and for initial energy densities ε₀ ? 10 ? 20 GeVfm^?3 GeVfm^?3, corresponding to nuclear collisions at RHIC.