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

Abstract

Results on the production of the double-strange cascade hyperon $\hat{\mathrm{I}}{ž}^{-}$ 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 $\hat{\mathrm{I}}{ž}^{-}$ production is observed in proton-nucleus interactions. Assuming a $\hat{\mathrm{I}}{ž}^{-}$ phase-space distribution similar to that of $\hat{\mathrm{I}}›$ hyperons, the production probability amounts to $P_{\hat{\mathrm{I}}{ž}^{-}}=(2.0\pm 0.4(\mathrm{stat})\pm 0.3(\mathrm{norm})\pm 0.6(\mathrm{syst}))\times 10^{-4}$ resulting in a $\hat{\mathrm{I}}{ž}^{-}/(\hat{\mathrm{I}}›+\hat{\mathrm{I}}{\pounds }^0)$ ratio of $P_{\hat{\mathrm{I}}{ž}^{-}}/P_{\hat{\mathrm{I}}›+\hat{\mathrm{I}}{\pounds }^0}=(1.2\pm 0.3(\mathrm{stat})\pm 0.4(\mathrm{syst}))\times 10^{-2}$. Available model predictions are significantly lower than the estimated $\hat{\mathrm{I}}{ž}^{-}$ yield.

6 pages, 3 figures