Observation of the Decay Xi^0 --> Sigma^+ mu^- nu(bar)
  The Xi^0 muon semi-leptonic decay has been observed for the first time with nine identified events using the KTeV beam line and detector at Fermilab. The decay is normalized to the Xi^0 beta decay mode and yields a value for the ratio of decay rates of $(1.8^{+0.7}_{-0.5}(stat.)\pm0.2(syst.))\times 10^{-2}$. This is in agreement with the SU(3) flavor symmetric quark model. 
KTeV Collaboration: E. Abouzaid, T. Alexopoulos, M. Arenton, R. F.   Barbosa, A. R. Barker, L. Bellantoni, A. Bellavance, E....