Measurement of the mass of the τ lepton

Abstract

A data-driven energy scan in the immediate vicinity of the \ensuremath{\tau} pair production threshold has been performed using the Beijing Spectrometer at the Beijing Electron-Positron Collider. Approximately 5 ${\mathrm{pb}}^{\mathrm{\ensuremath{-}}1}$ of data, distributed over 12 scan points, have been collected. A previous mass value for the \ensuremath{\tau} lepton, obtained using only the e\ensuremath{\mu} final state, has been published. In this paper, the final BES result on the mass measurement is presented. The analysis is based on the combined data from the ee, e\ensuremath{\mu}, eh, \ensuremath{\mu}\ensuremath{\mu}, \ensuremath{\mu}h, and hh final states, where h denotes a charged \ensuremath{\pi} or K. A maximum likelihood fit to the \ensuremath{\tau} pair production cross section data yields the value ${\mathit{m}}_{\mathrm{\ensuremath{\tau}}}$=1776.${96}_{\mathrm{\ensuremath{-}}0.21}$ -0.${17}^{+0.18\phantom{\rule{0ex}{0ex}}+0.25}$ MeV. \textcopyright{} 1995 The American Physical Society.