Subthreshold Ξ- Production in collisions of p (3.5GeV)+Nb

Abstract

Results on the production of the double strange cascade hyperon Ξ- are reported for collisions of p(3.5GeV)+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 Ξ- production is observed in proton-nucleus interactions. Assuming a Ξ- phase-space distribution similar to that of Λ hyperons, the production probability amounts to PΞ-=[2.0±0.4(stat)±0.3(norm)±0.6(syst)]×10-4 resulting in a Ξ-/(Λ+Σ0) ratio of PΞ-/PΛ+Σ0=[1.2±0.3(stat)±0.4(syst)]×10-2. Available model predictions are significantly lower than the measured Ξ- yield.