Measurement of the mass of the τ lepton

A data-driven energy scan in the immediate vicinity of the {τ} pair production threshold has been performed using the Beijing Spectrometer at the Beijing Electron-Positron Collider. Approximately 5 pb^-1 of data, distributed over 12 scan points, have been collected. A previous mass value for the {τ} lepton, obtained using only the e{μ} 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{μ}, eh, {μ}{μ}, {μ}h, and hh final states, where h denotes a charged {π} or K. A maximum likelihood fit to the {τ} pair production cross section data yields the value m_τ=1776.96_-0.21 -0.17^+0.180ex0ex+0.25 MeV. {} 1995 The American Physical Society.