Sub-threshold φ and Xi^- production by high mass resonances with UrQMD

We present a possible explanation for the deep sub-threshold, $\phi$ and $\Xi^-$ production yields measured with the HADES experiment in Ar+KCl reactions at $E_{\mathrm{lab}}=1.76$ A GeV and present predictions for Au+Au reactions at $E_{\mathrm{lab}}=1.23$ A GeV. To explain the surprisingly high yields of $\phi$ and $\Xi^-$ hadrons we propose new decay channels for high mass baryon resonances. These new decay channels are constrained by elementary $\mathrm{p+p}\rightarrow \mathrm{p+p+}\phi$ cross sections, and $\Xi^-$ production in p+Nb. Based on the fits to the elementary reactions one obtains a satisfactorily description of $\phi$ and $\Xi^-$ production in deep sub-threshold Ar+KCl reactions as well as the observed nuclear transparency ratio in proton induced $\phi$ production in cold nuclear matter. The results implicate that no new medium effects are required to describe the rare strange particle production data in low energy nuclear collisions.