Measurement of the mass of the τ lepton

Abstract

The mass of the τ lepton has been measured at the Beijing Electron Positron Collider using the Beijing Spectrometer. A search near threshold for e+e−→τ+τ− was performed, requiring that one τ decay via τ→eνν, and the other via τ→μνν. The mass value, obtained from a fit to the energy dependence of the τ+τ− cross section, is mτ=1776.9+0.4−0.5±0.2 MeV.