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

Abstract

The mass of the $\tau$-lepton has been measured in the decay modes $\tau \to 3\pi \nu_\tau$ and $\tau \to 3\pi \pi^0\nu_\tau$ using a pseudomass technique. The preliminary result is $1776.71\pm 0.25 {(stat)} \pm 0.62 {(syst)}$ MeV. The preliminary value of an upper limit on the relative mass difference between positive and negative $\tau$ leptons is $|(M_{\tau^+}-M_{\tau^-})|/M_{\mathrm{average}}$ is $5.0 \times 10^{-4}$ at 90% CL.