First Search for<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="italic">CP</mml:mi></mml:math>Violation in Tau Lepton Decay

We have performed the first search for $\mathrm{CP}$ violation in tau lepton decay. $\mathrm{CP}$ 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 ${\ensuremath{\tau}}^{\ensuremath{-}}$ and ${\ensuremath{\tau}}^{+}$ decay angular distributions for the semileptonic decay modes such as ${\ensuremath{\tau}}^{\ensuremath{-}}\ensuremath{\rightarrow}{K}^{0}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\nu}$. We define an observable asymmetry to exploit this and find no evidence for any $\mathrm{CP}$ violation.