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.
Highlights
Lattice quantum-chromo-dynamics calculations suggest that at vanishing baryon chemical potential there is a crossover phase transition from hadronic to partonic degrees of freedom [1,2,3,4,5,6] for the deconfinement phase transition as well as for the restoration of chiral symmetry
The Hadron-String Dynamics (HSD) transport approach has been further extended in the last 15 years (a) to the formation of an initial partonic phase with quark and gluon quasiparticle properties that are fitted to lattice QCD results in thermodynamic equilibrium, (b) to a dynamical hadronization scheme on the basis of covariant transition rates, (c) to incorporate further hadronic reactions in the strangeness sector with full baryon-antibaryon symmetry, and (d) to employ essential aspects of chiral symmetry restoration in the hadronic phase [14]. Whereas the latter developments are important for the lower Super Proton Synchrotron (SPS) energy regime to account for the strangeness enhancement seen experimentally in heavy-ion collisions, the formation of a partonic phase is mandatory to understand the physics at higher SPS, Relativistic Heavy-Ion Collider (RHIC) and Large Hadron Collider (LHC) energies
The most recent version including the effects from chiral symmetry restoration [14] (PHSD3.3) and nonperturbative charm dynamics as well as extended 2 ↔ 3 reactions. We found that both rates differ only slightly for times 6 fm/c but the huge rates at the first few fm/c are essentially missing in PHSD4.0
Summary
The HSD transport approach has been further extended in the last 15 years (a) to the formation of an initial partonic phase with quark and gluon quasiparticle properties that are fitted to lattice QCD results in thermodynamic equilibrium, (b) to a dynamical hadronization scheme on the basis of covariant transition rates, (c) to incorporate further hadronic reactions in the strangeness sector with full baryon-antibaryon symmetry, and (d) to employ essential aspects of chiral symmetry restoration in the hadronic phase [14] Whereas the latter developments are important for the lower Super Proton Synchrotron (SPS) energy regime to account for the strangeness enhancement seen experimentally in heavy-ion collisions, the formation of a partonic phase is mandatory to understand the physics at higher SPS, Relativistic Heavy-Ion Collider (RHIC) and Large Hadron Collider (LHC) energies. VI while more technical details are described in the appendices
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