Measurement of the τ-lepton mass with the Belle II experiment

We present a measurement of the τ-lepton mass using a sample of about 175 million e⁺e^-→τ⁺τ^- events collected with the Belle II detector at the SuperKEKB e⁺e^- collider at a center-of-mass energy of 10.579 GeV. This sample corresponds to an integrated luminosity of 190 fb^-1. We use the kinematic edge of the τ pseudomass distribution in the decay τ^-→π^-π⁺π^-ν_τ and measure the τ mass to be 1777.09±0.08±0.11 MeV/c², where the first uncertainty is statistical and the second systematic. This result is the most precise to date.