Evolution of antibaryon abundances in the early Universe and in heavy-ion collisions

TL;DR

This paper models antibaryon production and annihilation in an expanding universe and heavy-ion collisions, showing how expansion rates influence residual antibaryon abundances and explaining observed deviations from thermal models.

Contribution

It introduces a simplified kinetic model for antibaryon evolution that accounts for different expansion rates and net-baryon-to-entropy ratios, bridging early universe and heavy-ion collision conditions.

Findings

Residual antibaryon abundances are highly sensitive to expansion time scales.

The model explains deviations in antiproton-to-pion ratios observed at LHC energies.

Chemical freeze-out of antibaryons occurs at lower temperatures than mesons at high energies.

Abstract

We study the kinetics of antibaryon production and annihilation in an expanding system, assuming that it is spatially homogeneous and chemically equilibrated at the initial stage. By solving simplified rate equations for (anti)baryon abundances we study the deviations from chemical equilibrium at late stages. The calculations are done for different expansion rates and net-baryon-to-entropy ratios, covering the conditions from early Universe to heavy-ion collisions. Our analysis includes both stable (anti)baryons and resonances. We conclude that residual antibaryon abundances are very sensitive to the time scales of expansion. Our calculations naturally explain noticeable deviations of antiproton-to-pion and proton-to-pion ratios observed in nuclear collisions at the LHC energy from the thermal model predictions. We conclude that at high bombarding energies the chemical freeze-out of (anti)baryons should occur at lower temperatures as compared to mesons.