Anti-Baryon Puzzle in Ultra-Relativistic Heavy-Ion Collisions

R. Rapp; E. V. Shuryak

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Anti-Baryon Puzzle in Ultra-Relativistic Heavy-Ion Collisions

R. Rapp·E. V. Shuryak

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Abstract

The evolution of (non-strange) antibaryon abundances in the hadronic phase of central heavy-ion collisions is studied within a thermal equilibrium framework, based on the well-established picture of subsequent chemical and thermal freezeout. Due to large annihilation cross sections, antiprotons are, a priori, not expected to comply with this scheme. However, we show that a significant regeneration of their abundance occurs upon inclusion of the inverse reaction of multipion fusion, $n_ππ\to p\bar p$ (with $n_π$=5-6), necessary to ensure detailed balance. Especially at SPS energies, the build-up of large pion-chemical potentials between chemical and thermal freezeout reinforces this mechanism, rendering the $\bar p/p$ ratio in reasonable agreement with the observed one (reflecting chemical freezeout). Explicit solutions of the pertinent rate equation, which account for chemical off-equilibrium effects, corroborate this explanation.

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R. Rapp, E. V. Shuryak. 2002-02-19. Anti-Baryon Puzzle in Ultra-Relativistic Heavy-Ion Collisions. https://arxiv.org/abs/nucl-th/0202059

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