We analyze hadrochemical freeze-out in central Pb + Pb collisions at CERN SPS energies, employing the hybrid version of the Ultrarelativistic Quantum Molecular Dynamics model, which describes the transition from a hydrodynamic stage to hadrons by the Cooper-Frye mechanism, and matches to a final hadron-resonance cascade. We fit the results both before and after the cascade stage using the statistical model to assess the effect of the cascade phase. We observe a strong effect on antibaryon yields except anti-$\Omega$, resulting in a shift in $T$ and ${\mu }_B$ of the freeze-out curve. We discuss indications of a similar effect in SPS and RHIC data, and propose a method to recover the bulk hadron freeze-out conditions.

• Received 8 February 2012

DOI:https://doi.org/10.1103/PhysRevC.85.044921