Deep sub-threshold $\Xi$ and $\Lambda$ production in nuclear collisions with the UrQMD transport model

Understand

We present results on deep sub threshold hyperon production in nuclear collisions, with the UrQMD transport model.

• Introducing anti-kaon+baryon and hyperon+hyperon strangeness exchange reactions we obtain a good description of experimental data on single strange hadron production in Ar+KCl reactions at $E_{lab}=1.76$ A GeV.
• We find that the hyperon strangeness exchange is the dominant process contributing to the $\Xi^-$ yield, however remains short of explaining the $\Xi^-/\Lambda$ ratio measured with the HADES experiment.
• We also discuss possible reasons for the discrepancy with previous studies and the experimental results, finding that many details of the transport simulation may have significant effects on the final $\Xi^-$ yield.