Limit on the tau neutrino mass

Abstract

A limit on the tau neutrino mass ${\mathit{M}}_{\ensuremath{\nu}\mathrm{\ensuremath{\tau}}}$ is obtained from a study of tau decays in the reaction ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\mathrm{\ensuremath{\tau}}}^{+}$${\mathrm{\ensuremath{\tau}}}^{\mathrm{\ensuremath{-}}}$ at center-of-mass energies \ensuremath{\sim}10.6 GeV. The result is based on an end-point analysis of the invariant mass spectrum of the decay products in the decay modes ${\mathrm{\ensuremath{\tau}}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}3${\mathit{h}}^{\mathrm{\ensuremath{-}}}$2${\mathit{h}}^{+}$${\ensuremath{\nu}}_{\mathrm{\ensuremath{\tau}}}$ and ${\mathrm{\ensuremath{\tau}}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}2${\mathit{h}}^{\mathrm{\ensuremath{-}}}$${\mathit{h}}^{+}$2${\mathrm{\ensuremath{\pi}}}^{0}$${\ensuremath{\nu}}_{\mathrm{\ensuremath{\tau}}}$. The data sample used in this analysis contains 1.77\ifmmode\times\else\texttimes\fi{}${10}^{6}$ tau pairs, corresponding to an integrated luminosity of 1.92 ${\mathrm{fb}}^{\mathrm{\ensuremath{-}}1}$, and is substantially larger than previous data samples used to place a limit on ${\mathit{M}}_{\ensuremath{\nu}\mathrm{\ensuremath{\tau}}}$. The limit obtained for both five-hadron modes together is 32.6 MeV at 95% C.L.