A precise measurement of the tau lifetime

The tau lepton lifetime has been measured with the e+e - → τ+τ- events collected by the DELPHI detector at LEP in the years 1991-1995. Three different methods have been exploited, using both one-prong and three-prong τ decay channels. Two measurements have been made using events in which both taus decay to a single charged particle. Combining these measurements gave ττ(1 prong) = 291.8 ± 2.3stat ± 1.5sys fs. A third measurement using taus which decayed to three charged particles yielded τtau (3 prong) = 288.6± 2.4stat ± 1.3sys fs. These were combined with previous DELPHI results to measure the tau lifetime, using the full LEP1 data sample, to be τ τ = 290.9 ± 1.4stat ± 1.0sys fs. © Springer-Verlag / Società Italiana di Fisica 2004.