Title: Test of light-lepton universality in τ-decays with Belle II
 

Speaker: Paul Feichtinger, Austrian Academy of Sciences, Vienna

Abstract: Lepton flavor universality is an intrinsic property of the Standard Model that can be tested with high precision. At the same time, several New Physics models predict a violation of lepton universality. In this seminar, I will present a test of muon-electron universality by measuring the ratio of the leptonic branching fractions of the τ lepton. The measurement is based on a data sample collected with the Belle II detector at the SuperKEKB electron-positron collider in Tsukuba, Japan. The sample corresponds to an integrated luminosity of 362 fb-1 at a center-of-mass energy of 10.58 GeV. I will focus on the main experimental challenges, such as understanding and reducing the different sources of systematic error, particularly those associated with lepton identification. The result is the most precise measurement of muon-electron universality in tau decays from a single experiment.