Measurements of the $τ$ Mass and Mass Difference of the $τ^{+}$ and $τ^{-}$} at BaBar

Abstract

We present the result from a precision measurement of the mass of the $τ$ lepton, $M_τ$, based on $423 fb^{-1}$ of data recorded at the $Υ(4S)$ resonance with the BaBar detector. Using a pseudomass endpoint method, we determine the mass to be $1776.68 \pm 0.12 (stat) \pm 0.41 (syst) MeV$. We also measure the mass difference between the $τ^+$ and $τ^-$, and obtain $(M_{τ^{+}}-M_{τ^{-}})/M^τ_{AVG} = (-3.4 \pm 1.3 (stat) \pm 0.3 (syst)) \times 10^{-4}$, where $M^τ_{AVG}$ is the average value of $M_{τ^+}$ and $M_{τ^-}$.