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

We present a possible explanation for the deep sub-threshold, $ϕ$ and $Ξ^-$ 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 $ϕ$ and $Ξ^-$ hadrons we propose new decay channels for high mass baryon resonances. These new decay channels are constrained by elementary $\mathrm{p+p}\rightarrow \mathrm{p+p+}ϕ$ cross sections, and $Ξ^-$ production in p+Nb. Based on the fits to the elementary reactions one obtains a satisfactorily description of $ϕ$ and $Ξ^-$ production in deep sub-threshold Ar+KCl reactions as well as the observed nuclear transparency ratio in proton induced $ϕ$ 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.