Deep sub-threshold $\Xi^-$ production in Ar+KCl reactions at 1.76A GeV

TL;DR

This study reports the first observation of deep sub-threshold $ ext{Xi}^-$ hyperon production in heavy-ion collisions at 1.76A GeV, revealing a higher-than-expected production ratio that challenges existing models.

Contribution

It provides the first experimental evidence of $ ext{Xi}^-$ production below threshold energies in heavy-ion reactions, with detailed measurements challenging current theoretical predictions.

Findings

$ ext{Xi}^-$ production ratio is significantly higher than models predict.

First experimental measurement of sub-threshold $ ext{Xi}^-$ hyperon production.

High-statistics data enabled precise decay channel analysis.

Abstract

We report first results on a deep sub-threshold production of the doubly strange hyperon $\Xi^-$ in a heavy-ion reaction. At a beam energy of 1.76A GeV the reaction Ar+KCl was studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18/GSI. A high-statistics and high-purity $\Lambda$ sample was collected, allowing for the investigation of the decay channel $\Xi^- \to \Lambda \pi^-$. The deduced $\Xi^-/(\Lambda+\Sigma^0)$ production ratio of $(5.6 \pm 1.2 ^{+1.8}_{-1.7})\cdot 10^{-3}$ is significantly larger than available model predictions.