Measurements of the τ lepton lifetime

The precision of τ lifetime measurements have increased remarkably in the last several years. The techniques which lead to these results are summarized and compared, together with results obtained by different experiments from use of these methods. By combining the recent, and previous lifetime values an updated world average lifetime of ττ = (291.7 ± 1.6) fs is obtained, which is in good agreement with the prediction derived from the τ electronic branching ratio through the assumption of τ-μ lepton universally