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

TL;DR

This study examines how proton-antiproton annihilation and regeneration affect proton yields in late-stage heavy-ion collisions, revealing that regeneration partially offsets annihilation losses across various energies and collision centralities.

Contribution

It introduces a microscopic approach that explicitly models 5-body back-reactions, demonstrating their significant role in proton yield regeneration in heavy-ion collisions.

Findings

Back-reaction occurs in 15-20% of annihilations.

Regeneration recovers about half of the lost (anti-)proton yield.

Back-reaction effects are consistent across different energies and centralities.

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 5-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 allows to treat arbitrary multi-particle reactions. It is used to account for the regeneration of (anti-)protons via $5\pi\rightarrow p\bar{p}$. Our results show that a back-reaction happens for a fraction of 15-20\% of all annihilations. Within a viscous hybrid approach Au+Au/Pb+Pb collisions from $\sqrt{s_{NN}}=17.3$ GeV$-5.02$ TeV are investigated and the quoted fraction is independent of the beam energy or centrality of the collision. Taking the back-reaction into account results in regeneration of half of the (anti-)proton yield that is lost due to annihilations at midrapidity. We also find that, concerning the multiplicities, treating the back-reaction as a chain of 2-body reactions is equivalent to a single 5-to-2 reaction.