Role of proton-antiproton regeneration in the late stages of heavy-ion collisions

Abstract

We investigate the long-standing question of the effect of proton-antiproton annihilation on the (anti-)proton yield, while respecting detailed balance for the five-body back-reaction for the first time in a full microscopic description of the late stages of heavy-ion collisions. This is achieved by employing a stochastic collision criterion in a hadronic transport approach (SMASH), which is used to account for the regeneration of (anti-)protons via $5\ensuremath{\pi}\ensuremath{\rightarrow}\mathrm{p}\overline{\mathrm{p}}$. We investigate $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Pb}+\mathrm{Pb}$ collisions from $\sqrt{{s}_{NN}}=17.3\phantom{\rule{4pt}{0ex}}\mathrm{GeV}\ensuremath{-}5.02$ TeV in a viscous hybrid approach. Our results show that back-reactions happen for a fraction of 15%--20% of all annihilations, independent of the beam energy or centrality of the system. The inclusion of the back-reaction results in the regeneration of half of the (anti-)proton yield lost to annihilations at midrapidity. We also find that, concerning the multiplicities, treating the back-reaction as a chain of two-body reactions is equivalent to a single 5-to-2 reaction.