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 $P_{mathrm{Xi^-}}/ P_{mathrm{Lambda+Sigma^0}}=(1.2pm 0.3,mathrm{(stat)}pm0.4,mathrm{(syst)})times10^{-2}$. Available model predictions are significantly lower than the estimated $mathrm{Xi^-}$ yield.
Results on $Lambda$ hyperon production 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. The transverse mass distribut
ions in rapidity bins are well described by Boltzmann shapes with a maximum inverse slope parameter of about $90,$MeV at a rapidity of $y=1.0$, i.e. slightly below the center-of-mass rapidity for nucleon-nucleon collisions, $y_{cm}=1.12$. The rapidity density decreases monotonically with increasing rapidity within a rapidity window ranging from 0.3 to 1.3. The $Lambda$ phase-space distribution is compared with results of other experiments and with predictions of two transport approaches which are available publicly. None of the prese
Results on $Lambda$p femtoscopy are reported at the lowest energy so far. 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 $Lambda$ p correlations at small relative momenta. The experimental correlation function is compared to corresponding model calculations allowing the determination of the space-time extent of the $Lambda$p emission source. The $Lambda$p source radius is found slightly smaller than the pp correlation radius for a similar collis ion system. The present $Lambda$p radius is significantly smaller than that found for Au+Au/Pb+Pb collisio ns in the AGS, SPS and RHIC energy domains, but larger than that observed for electroproduction from He. Taking into account all available data, we find the $Lambda$p source radius to increase almost linearly with the number of participants to the power of one-third.
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.
