Measurement of the mass of the $τ$-lepton and an upper limit on the mass difference between $τ^+$ and $τ^-$

Abstract

The mass of the $τ$ lepton has been measured in the decay mode $τ\to 3πν_τ$ using a pseudomass technique. The result obtained from $414 \mathrm{fb}^{-1}$ of data collected with the Belle detector is $M_τ= (1776.61\pm 0.13 {(stat.)} \pm 0.35 {(sys.)})$ MeV/$c^2$. The upper limit on the relative mass difference between positive and negative $τ$ leptons is $|M_{τ^+}-M_{τ^-}|/M_τ < 2.8 \times 10^{-4}$ at 90% confidence level.

9 pages, 3 figures. Submitted to Phys. Rev. Lett