Resolving the Antibaryon-Production Puzzle in High-Energy Heavy-Ion Collisions

We argue that the observed antiproton production in heavy-ion collisions at CERN-SPS energies can be understood if (contrary to most sequential scattering approaches) the backward direction in the process pp̅ ↔n̅ π (with n̅  =  5–6) is consistently accounted for within a thermal framework. Employing the standard picture of subsequent chemical and thermal freezeout, which induces an oversaturation of pion number with associated chemical potentials of μ_π≃60–80 MeV, enhances the backward reaction substantially. The resulting rates turn out to be large enough to maintain an antiproton abundance at thermal freezeout in accordance with the measured p̅ /p ratio in Pb(158A  GeV)+Pb collisions.