Heavy baryonic resonances, multistrange hadrons, and equilibration at energies available at the GSI Schwerionensynchrotron, SIS18

TL;DR

This study uses the UrQMD model to analyze particle production, especially multistrange hadrons, in nuclear collisions at 1.76 A GeV, revealing that apparent chemical equilibrium results from resonance decay rather than local equilibration.

Contribution

It demonstrates that multistrange hadron production occurs via secondary interactions and clarifies the origin of apparent chemical equilibrium in low-energy nuclear collisions.

Findings

Multistrange hadrons are produced through secondary interactions.

Apparent chemical equilibrium arises from resonance decay, not local multi-collision processes.

Centrality dependence can confirm the proposed production mechanism.

Abstract

We study the details and time dependence of particle production in nuclear collisions at a fixed target beam energy of $E_{\mathrm{lab}}= 1.76$ A GeV with the UrQMD transport model. We find that the previously proposed production mechanism for multi strange hadrons, $\phi$ and $\Xi$, are possible due to secondary interactions of incoming nuclei of the projectile and target with already created nuclear resonances, while the Fermi momenta of the nuclei play only a minor role. We also show how the centrality dependence of these particle multiplicities can be used to confirm the proposed mechanism, as it strongly depends on the number of participants in the reaction. Furthermore we investigate the time dependence of particle production in collisions of Ca+Ca at this beam energy, in order to understand the origins of the apparent chemical equilibration of the measured particle yields. We find that indeed the light hadron yields appear to be in equilibrium already from the very early stage of the collision while in fact no local equilibration, through multi collision processes, takes place. The apparent equilibrium is reached only through the decay of the resonances according to available phase space.