Measurement of the branching fractions of the<i>τ</i>lepton using a tagged sample of<i>τ</i>decays

The branching fractions for the major decay modes of the \ensuremath{\tau} lepton are measured from a sample of tagged \ensuremath{\tau} decays selected from ${\ensuremath{\tau}}^{+}$${\ensuremath{\tau}}^{\mathrm{\ensuremath{-}}}$ pairs produced in ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ annihilation. The decay products of one member of the ${\ensuremath{\tau}}^{+}$${\ensuremath{\tau}}^{\mathrm{\ensuremath{-}}}$ pair are used to identify the event. The opposite member of the pair is then included in the sample if it satisfies an invariant-mass cut and a charged-multiplicity cut. In this way, we attempt to select an unbiased sample of \ensuremath{\tau} decays. The sample is divided into categories based on charged- and neutral-particle multiplicities, and charged-particle identification. The branching fractions are measured simultaneously, with an unfold technique and a maximum-likelihood fit, with the sum of the branching fractions constrained to be unity.The branching fractions for the decay modes ${\ensuremath{\tau}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\ensuremath{\nu}}_{\ensuremath{\tau}}$ ${K}^{\mathrm{\ensuremath{-}}}$ and ${\ensuremath{\tau}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\ensuremath{\nu}}_{\ensuremath{\tau}}$ ${K}^{\mathrm{*}\mathrm{\ensuremath{-}}}$ are fixed at the world averages in the fit. The following branching fractions are measured: B(${\ensuremath{\tau}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\ensuremath{\nu}}_{\ensuremath{\tau}}$${e}^{\mathrm{\ensuremath{-}}}$\ensuremath{\nu}${\ifmmode\bar\else\textasciimacron\fi{}}_{e}$) =(19.1\ifmmode\pm\else\textpm\fi{}0.8\ifmmode\pm\else\textpm\fi{}1.1)%, B(${\ensuremath{\tau}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\ensuremath{\nu}}_{\ensuremath{\tau}}$ ${\ensuremath{\mu}}^{\mathrm{\ensuremath{-}}}$ \ensuremath{\nu}${\ifmmode\bar\else\textasciimacron\fi{}}_{\ensuremath{\mu}}$)=(18.3\ifmmode\pm\else\textpm\fi{}0.9\ifmmode\pm\else\textpm\fi{}0.8)%, B(${\ensuremath{\tau}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\ensuremath{\nu}}_{\ensuremath{\tau}}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$) =(10.0\ifmmode\pm\else\textpm\fi{}1.1 *1,4)%, B(${\ensuremath{\tau}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\ensuremath{\nu}}_{\ensuremath{\tau}}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${\ensuremath{\pi}}^{0}$) =(25.8\ifmmode\pm\else\textpm\fi{}1.7\ifmmode\pm\else\textpm\fi{}2.5)%, B(${\ensuremath{\tau}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\ensuremath{\nu}}_{\ensuremath{\tau}}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$(n${\ensuremath{\pi}}^{0}$, n&gt;1))=(12.0\ifmmode\pm\else\textpm\fi{}1.4\ifmmode\pm\else\textpm\fi{}2.5)%, B(${\ensuremath{\tau}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\ensuremath{\nu}}_{\ensuremath{\tau}}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$) =(6.7 \ifmmode\pm\else\textpm\fi{}0.8\ifmmode\pm\else\textpm\fi{}0.9)%, and B(${\ensuremath{\tau}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\ensuremath{\nu}}_{\ensuremath{\tau}}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ (n${\ensuremath{\pi}}^{0}$,n&gt;0) )=(6.1\ifmmode\pm\else\textpm\fi{}0.8\ifmmode\pm\else\textpm\fi{}0.9)%.The total branching fraction to one charged pion plus at least one neutral hadron is measured to be (37.8\ifmmode\pm\else\textpm\fi{}1.2\ifmmode\pm\else\textpm\fi{}1.0)%. Limits on allowed decay modes involving the \ensuremath{\eta} meson are discussed.