A Hydrodynamic Description of Heavy Ion Collisions at the SPS and RHIC

Abstract

A hydrodynamic + cascade model of relativistic heavy ion collisions is presented and compared to available hadronic data from the SPS to RHIC. The model consistently reproduces the radial and elliptic flow data for different particles, collision energies, and impact parameters. Three ingredients are essential to the success: (a) a reasonable EOS exhibiting the hard and soft features of the QCD phase transition, (b) thermal hadronization at the phase boundary, and (c) subsequent hadronic rescattering. Some features of the RHIC data are readily explained: (i) the observed elliptic flow and its dependence on $p_{T}$ and mass, (ii) the anomalous $\bar{p}/\pi^{-}$ ratio for $p_{T} \approx 2.0$ GeV, (iii) the difference in the slope parameters measured by the STAR and PHENIX collaborations, and (iv) the respectively strong and weak impact parameter dependence of the $\bar{p}$ and $\phi$ slope parameters. For an EOS without the hard and soft features of the QCD phase transition, the broad consistency with the data is lost.