We report on a precision measurement of the ratio R^Υ(3S)_τμ = B[Υ(3S) → τ+τ−] / B[Υ(3S) → μ+μ−] using data collected with the BaBar detector at the SLAC PEP-II e+e− collider. The measurement is based on a 28 fb−1 data sample collected at a center-of-mass energy of 10.355 GeV corresponding to a sample of 122 million Υ(3S) mesons. The ratio is measured to be R^Υ(3S)_τμ = 0.966 ± 0.008 (stat) ± 0.014 (syst) and is in agreement with the Standard Model prediction of 0.9948 within 2 standard deviations. The uncertainty in R^Υ(3S)_τμ is almost an order of magnitude smaller than the only previous measurement.
|What is your topic?||Lepton universality and flavour violation|