The lifetime of the τ lepton is measured using the process e+e−→τ+τ−, where both τ leptons decay to 3πντ. The result for the mean lifetime, based on 711 fb−1 of data collected with the Belle detector at the ϒ(4S) resonance and 60 MeV below, is τ=(290.17±0.53(stat)±0.33(syst))×10−15 s. The first measurement of the lifetime difference betweenτ+ and τ− is performed. The upper limit on the relative lifetime difference between positive and negative τ leptons is |Δτ|/τ<7.0×10−3 at 90% C.L.
K. Belous et al. (Belle Collaboration). Measurement of the τ-lepton Lifetime at Belle. Phys. Rev. Lett. 112, 031801, Jan 2014. DOI: http://dx.doi.org/10.1103/PhysRevLett.112.031801