Tau decays with neutral kaons

Abstract.

The branching ratio of the $\tau$ lepton to a neutral kaon meson is measured from a sample of approximately 200,000 $\tau$ decays recorded by the OPAL detector at centre-of-mass energies near the $\mathrm{Z}^0$ resonance. The measurement is based on two samples which identify one-prong $\tau$ decays with $\mathrm{K^0_L}$ and $\mathrm{K^0_JS}$ mesons. The combined branching rat ios are measured to be \begin{eqnarray*} B({\tau^- \rightarrow \pi^-{\overline{\mathrm{K}}{}^0} {\nu_\tau} } ) & = & {{(9.33\pm0.68\pm0.49})\times 10^{-3}} , \\ B({\tau^- \rightarrow \pi^-{\overline{\mathrm{K}}{}^0} \mbox{\small $[ \geq 1\pi^0]$}{\nu_\tau} } ) & = & {{(3.24\pm0.74\pm0.66})\times 10^{-3}} , \\ B({\tau^- \rightarrow {\mathrm{K}^-} {\mathrm{K}{}^0} [\geq 0\pi^0]{\nu_\tau} } ) & = & {{(3.30\pm0.55\pm0.39})\times 10^{-3}} , \end{eqnarray*} where the first error is statistica l and the second systematic.