Strangeness Balance in HADES Experiments and the Xi- Enhancement

TL;DR

This study analyzes strangeness production in Ar+KCl collisions at 1.76A GeV using a statistical model, finding good agreement for some particle ratios but significantly underestimating Xi baryon production, suggesting alternative production mechanisms.

Contribution

It introduces a minimal statistical model that explicitly conserves strangeness in each event and incorporates in-medium potentials to describe particle ratios in heavy-ion collisions.

Findings

Successfully describes K-/K+, Lambda/K+, Sigma/K+ ratios with in-medium potentials.

Underestimates Xi-/Lambda/K+ ratio by a factor of 8 compared to experimental data.

Discusses possible direct reaction mechanisms for Xi production.

Abstract

HADES data on a strangeness production in Ar+KCl collisions at 1.76A GeV are analyzed within a minimal statistical model. The total negative strangeness content is fixed by the observed K^+ multiplicities on event-by-event basis. Particles with negative strangeness are assumed to remain in chemical equilibrium with themselves and in thermal equilibrium with the environment until a common freeze-out. Exact strangeness conservation in each collision event is explicitly preserved. This implies that Xi baryons can be released only in events where two or more kaons are produced. An increase of the fireball volume due to application of a centrality trigger in HADES experiments is taken into account. We find that experimental ratios of K-/K+, Lambda/K+ and Sigma/K+ can be satisfactorily described provided in-medium potentials are taken into account. However, the calculated Xi-/Lambda/K+ ratio proves to be significantly smaller compared to the measured value (8 times lower than the experimental median value and 3 times lower than the lower error bar). Various scenarios to explain observed Xi enhancement are discussed. Arguments are given in favor of the Xi production in direct reactions. The rates of the possible production processes are estimated and compared.