Measurement of the tau lepton mass by the Beijing Spectrometer (BES) Collaboration

Abstract

The mass of the {tau} lepton has been measured at the Beijing Electron Positron Collider using the Beijing Spectrometer. A search near threshold for e{sup +}e{sup {minus}} {yields} {tau}{sup +}{tau}{sup {minus}} was performed. Candidate events were identified by requiring that one {tau} decay via {tau} {yields} e{nu}{bar {nu}}, and the other via {tau} {yields} {mu}{nu}{bar {nu}}. The mass value, obtained from a fit to the energy dependence of the {tau}{sup +}{tau}{sup {minus}} cross section, is m{sub {tau}} = 1776.9{sub -0.5}{sup +0.4} {plus_minus} 0.2 MeV.