Measurement of the mass of the τ-lepton

The mass of the τ-lepton has been measured in the decay mode τ→3πντ using a pseudomass technique. The obtained result, based on 414 fb−1 of data collected by the Belle detector, is Mτ=(1776.71±0.13(stat.)±0.35(sys.)) MeV/c2. The value of an upper limit on the relative mass difference between positive and negative τ leptons is |(Mτ+−Mτ−)|/Mτ is 2.8×10−4 at 90% confidence level.