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 $p\overline{p}\leftrightarrow \overline{n}\pi$ (with $\overline{n}=5\mathrm{}–6$) 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 ${\mu }_{\pi }\simeq 60–80\mathrm{MeV}$, 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 $\overline{p}/p$ ratio in $\mathrm{Pb}\left(158A\mathrm{GeV}\right)+\mathrm{Pb}$ collisions.