$K^0_S$ production in $\tau$ decays

Abstract.

From a sample of about 160k $\mbox{Z}\!\!\to\!\!\tau^+\tau^-$ candidates collected with the ALEPH detector at LEP between 1991 and 1995, $\tau$ lepton decays involving $K^0_S\!\to\!\pi^+\pi^-$ are studied. The $K^0_SK^0_L$ associated production in $\tau$ decays is also investigated. The branching ratios are measured for the inclusive decay $B(\tau^-\!\!\to\!\!K^0_SX^-\nu_\tau)=(9.70\!\p m\!0.58\!\pm\!0.62)\times10^{-3}$, where $X^-$ can be anything, and for the exclusive decays \[ \begin{array}{rcl} B(\tau^-\!\!\to\!\!\overline{K}^0\pi^-\nu_\tau)&=& (8.55\!\pm\!1.17\! \pm\!0.66)\times10^{-3} ,\\ B(\tau^-\!\!\to\!\!\overline{K}^0\pi^-\pi^0\nu_\tau)&=& (2.94\!\pm\! 0.73\!\pm\!0.37)\times10^{-3},\\ B(\tau^-\!\!\to\!\!\overline{K}^0K^-\nu_\tau)&=& (1.58\!\pm\!0.42\!\pm\! 0.17)\times10^{-3},\\ B(\tau^-\!\!\to\!\!\overline{K}^0K^-\pi^0\nu_\tau)&=& (1.52\!\p m\!0.76\! \pm\!0.21)\times10^{-3}. \end{array} \] The decay $\tau^-\!\!\to\!\!K^0_SK^0_L\pi^-\nu_\tau$ is studied for the first time, giving a branching ratio \[ \begin{array}{rcl} B(\tau^-\!\!\to\!\!K^0_SK^0_L\pi^-\nu_\tau)&=& (1.01\!\pm\!0.23\!\pm\!0.13)\times10^{-3}. \end{array} \] The channels $\tau^- \!\!\!\to\!\!\! K^0_SK^0_S\pi^-\nu_\tau$, $\tau^- \!\!\!\to\!\!\! K^0_SK^0_S\pi^-\pi^0\nu_\tau$, $\tau^-\!\!\!\to\!\!\! K^0_SK^0_L\pi^-\pi^0\nu_\tau$, $\tau^- \!\!\!\to\!\!\! \overline{K}^0\pi^-\pi^0\pi^0\nu_\tau$, $\tau^- \!\!\!\to\!\!\! K^0K^-\pi^0\pi^0\nu_\tau$ and $\tau^- \!\!\!\to\!\!\! K^0h^+h^-h^-\nu_\tau$ are also investigated. In addition, mass spectra in the $K^0_Sh^-$ and $K^0_Sh^-\pi^0$ final states are analysed to provide information on the intermediate states produced in the decays.