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

TL;DR

This paper reports a precise measurement of the tau lepton's mass using decay modes and sets an upper limit on the mass difference between tau+ and tau-, contributing to tests of lepton universality.

Contribution

The study introduces a pseudomass technique for tau mass measurement and provides the first upper limit on the tau mass difference between positive and negative leptons.

Findings

Tau mass measured as 1776.71 ± 0.25 (stat) ± 0.62 (syst) MeV.

Upper limit on mass difference is 5.0 × 10^{-4} at 90% CL.

Results support lepton universality and CPT symmetry.

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.