Influence of anisotropic Λ/Sigma creation on the Xi^- mutiplicity in subthreshold proton-nucleus collisions

We present an analysis of $\Xi^-$ baryon production in subthreshold proton--nucleus ($p+A$) collisions in the framework of a BUU type transport model. We propose a new mechanism for $\Xi$ production in the collision of a secondary $\Lambda$ or $\Sigma$ hyperon and a nucleon from the target nucleus. We find that the $\Xi^-$ multiplicity in $p+A$ collisions is sensitive to the angular distribution of hyperon production in the primary $N+N$ collision. Using reasonable assumptions on the unknown elementary cross sections we are able to reproduce the $\Xi^-$ multiplicity and the $\Xi^-/(\Lambda+\Sigma^0)$ ratio obtained in the HADES experiment in $p$+Nb collisions at $\sqrt{s_{NN}} = $ 3.2 GeV energy.