Baryon-antibaryon annihilation and reproduction in relativistic heavy-ion collisions

TL;DR

This paper extends the quark rearrangement model for baryon-antibaryon annihilation to include strangeness in heavy-ion collisions, demonstrating detailed balance and comparing results with experimental data to explore signals of chiral symmetry restoration.

Contribution

The study introduces a strangeness sector extension to the PHSD model, deriving transition probabilities and implementing reaction channels, improving the description of strange antibaryon spectra in heavy-ion collisions.

Findings

Reaction channels impact antibaryon rapidity spectra.

Strangeness channels improve agreement with experimental data.

No clear signals of chiral symmetry restoration in strange antibaryon spectra.

Abstract

The quark rearrangement model for baryon-antibaryon annihilation and reproduction ($B\bar B\leftrightarrow 3M$) - incorporated in the Parton-Hadron-String Dynamics (PHSD) transport approach - is extended to the strangeness sector. A derivation of the transition probabilities for the three-body processes is presented and a strangeness suppression factor for the invariant matrix element squared is introduced to account for the higher mass of the strange quark compared to the light up and down quarks. In simulations of the baryon-antibaryon annihilation and reformation in a box with periodic boundary conditions we demonstrate that our numerical implementation fulfills detailed balance on a channel-by-channel basis for more than 2000 individual $2 \leftrightarrow 3$ channels. Furthermore, we study central Pb+Pb collisions within PHSD from 11.7$A$ GeV to 158$A$ GeV and investigate the impact of the additionally implemented reaction channels in the strangeness sector. We find that the new reaction channels have a visible impact essentially only on the rapidity spectra of antibaryons. The spectra with the additional channels in the strangeness sector are closer to the experimental data than without for all antihyperons. Due to the chemical redistribution between baryons/antibaryons and mesons we find a slightly larger production of antiprotons thus moderately overestimating the available experimental data. We additionally address the question if the antibaryon spectra (with strangeness) from central heavy-ion reactions at these energies provide further information on the issue of chiral symmetry restoration and deconfinement. However, by comparing transport results with/without partonic phase as well as including/excluding effects from chiral symmetry restoration we find no convincing signals in the strange antibaryon sector for either transition due to the strong final-state interactions.