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
$P_{mathrm{Xi^-}}=(2.0,pm0.4,mathrm{(stat)},pm
0.3,mathrm{(norm)},pm 0.6,mathrm{(syst)}) imes10^{-4}$ resulting in a
$mathrm{Xi^-/(Lambda+Sigma^0)}$ ratio of $P_{mathrm{Xi^-}}/
P_{mathrm{Lambda+Sigma^0}}=(1.2pm
0.3,mathrm{(stat)}pm0.4,mathrm{(syst)}) imes10^{-2}$. Available model
predictions are significantly lower than the estimated $mathrm{Xi^-}$ yield. |