Contributions of hyperon-hyperon scattering to subthreshold cascade production in heavy ion collisions

Using a gauged flavor SU(3)-invariant hadronic Lagrangian, we calculate the cross sections for the strangeness-exchange reactions YY to N\Xi (Y=\Lambda, \Sigma) in the Born approximation. These cross sections are then used in the Relativistic Vlasov-Uehling-Uhlenbeck (RVUU) transport model to study \Xi production in Ar+KCl collisions at incident energy of 1.76A GeV and impact parameter b=3.5 fm. We find that including the contributions of hyperon-hyperon scattering channels strongly enhances the yield of \Xi, leading to the abundance ratio \Xi^{-}/(\Lambda+\Sigma^{0})=3.38E-3, which is essentially consistent with the recently measured value of $(5.6 \pm 1.2_{-1.7}^{+1.8})\times 10^{-3}$ by the HADES collaboration at GSI.