First Search for CP Violation in Tau Lepton Decay
  Using the CLEO II detector we have performed the first search for $CP$ violation in tau lepton decay. CP violation in lepton decay does not occur in the minimal standard model but can occur in extensions such as the multi-Higgs doublet model. It appears as a characteristic difference between the $\tau^+$ and $\tau^-$ decay angular distributions for the semi-leptonic decay modes such as $\tau^- \to K^0 \pi^- \nu$. We define an observable asymmetry to exploit this and find no evidence for any CP violation. 
S. Anderson, et al. (CLEO Collaboration)