Measurement of τ decays involving η mesons

Abstract

The decay ${\mathrm{\ensuremath{\tau}}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\ensuremath{\nu}}_{\mathrm{\ensuremath{\tau}}}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$${\mathrm{\ensuremath{\pi}}}^{0}$\ensuremath{\eta} has been observed for the first time using the CLEO-II detector at the Cornell Electron Storage Ring. The measured branching ratio (0.17\ifmmode\pm\else\textpm\fi{}0.02\ifmmode\pm\else\textpm\fi{}0.02)%, agrees with the CVC (conserved vector current) prediction based on ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\eta} data. Upper limits on the branching ratios for other \ensuremath{\tau} decays to final states including \ensuremath{\eta} mesons are improved by an order of magnitude compared to previous measurements.