MEASUREMENT OF THE MASS OF THE TAU-LEPTON

A data-driven energy scan in the immediate vicinity of the tau pair pr oduction threshold has been performed using the Beijing Spectrometer a t the Beijing Electron-Positron Collider. Approximately 5 pb(-1) of da ta, distributed over 12 scan points, have been collected. A previous m ass value for the tau lepton, obtained using only the e 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 f rom the ee, e mu eh, mu mu, mu h, and hh final states, where h denotes a charged ir or K. A maximum likelihood fit to the tau pair productio n cross section data yields the value m(tau) = 1776.96(-0.21-0.17)(+0. 18+0.25) MeV.