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

The mass of the $tau$-lepton has been measured in the decay modes $tau to 3pi u_tau$ and $tau to 3pi pi^0 u_tau$ using a pseudomass technique. The preliminary result is $1776.71pm 0.25 {(stat)} pm 0.62 {(syst)}$ 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.