Subthreshold Xi- Production in Collisions of p(3.5 GeV)+Nb

TL;DR

This paper reports the first observation of subthreshold $ ext{ extmu}$Xi- hyperon production in proton-nucleus collisions at 3.5 GeV, revealing higher yields than existing models predict, with implications for hyperon production mechanisms.

Contribution

It provides the first experimental evidence of subthreshold $ ext{ extmu}$Xi- production in p+Nb collisions and compares the results with theoretical models, highlighting discrepancies.

Findings

First observation of subthreshold $ ext{ extmu}$Xi- production in p+Nb collisions.

Measured $ ext{ extmu}$Xi-/($ ext{ extmu}$Lambda + $ ext{ extmu}$Sigma0) ratio of approximately 1.2%.

Model predictions significantly underestimate the observed $ ext{ extmu}$Xi- yield.

Abstract

Results on the production of the double-strange cascade hyperon $\mathrm{\Xi^-}$ are reported for collisions of p\,(3.5~GeV)\,+\,Nb, studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18 at GSI Helmholtzzentrum for Heavy-Ion Research, Darmstadt. For the first time, subthreshold $\mathrm{\Xi^-}$ production is observed in proton-nucleus interactions. Assuming a $\mathrm{\Xi^-}$ phase-space distribution similar to that of $\mathrm{\Lambda}$ hyperons, the production probability amounts to $P_{\mathrm{\Xi^-}}=(2.0\,\pm0.4\,\mathrm{(stat)}\,\pm 0.3\,\mathrm{(norm)}\,\pm 0.6\,\mathrm{(syst)})\times10^{-4}$ resulting in a $\mathrm{\Xi^-/(\Lambda+\Sigma^0)}$ ratio of $P_{\mathrm{\Xi^-}}/\ P_{\mathrm{\Lambda+\Sigma^0}}=(1.2\pm 0.3\,\mathrm{(stat)}\pm0.4\,\mathrm{(syst)})\times10^{-2}$. Available model predictions are significantly lower than the estimated $\mathrm{\Xi^-}$ yield.