Influence of anisotropic Λ/Σ creation on the Ξ− multiplicity in subthreshold proton-nucleus collisions

We present an analysis of Ξ− baryon production in subthreshold proton-nucleus (p+A) collisions in the framework of a BUU type transport model. We propose a new mechanism for Ξ production in the collision of a secondary Λ or Σ hyperon and a nucleon from the target nucleus. We find that the Ξ− 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 Ξ− multiplicity and the Ξ−/(Λ+Σ0) ratio obtained in the HADES experiment in p+Nb collisions at sNN= 3.2 GeV energy.