# ICHEP 2020

28 July 2020 to 6 August 2020
virtual conference
Europe/Prague timezone

## $\tau-\mu$ lepton flavor universality in $\Upsilon(3S)$ decays at the $BABAR$ experiment

29 Jul 2020, 18:16
15m
virtual conference

#### virtual conference

Talk 05. Quark and Lepton Flavour Physics

### Speaker

Alexei Sibidanov (University of Victoria)

### Description

We report on a precision measurement of the ratio $R_{\tau\mu} = BF(\Upsilon(3S)\to\tau^+\tau^-)/BF(\Upsilon(3S)\to\mu^+\mu^-)$ using data collected with the BABAR detector at the SLAC PEP-II $e^+e^-$ collider. The measurement is based on a 28 ${\mathrm{fb^{-1}}}$ data sample collected at a center-of-mass energy of 10.355 ${\mathrm{GeV}}/c^2$ which corresponds to a sample 122 million $\Upsilon(3S)$ mesons. In order to estimate backgrounds from direct dilepton production we use 2.6 ${\mathrm{fb^{-1}}}$ of data collected 30 MeV below the $\Upsilon(3S)$ resonance mass and 86 ${\mathrm{fb^{-1}}}$ of data collected near the $\Upsilon(4S)$ resonance. The ratio is measured to $R_{\tau\mu} = 0.9662 \pm 0.0084 \pm 0.0135$ and is in agreement with the Standard Model prediction. Its uncertainty is almost order of magnitude smaller than the only previous measurement reported by the CLEO collaboration.

Secondary track (number) 03. Beyond the Standard Model

### Primary author

Alexei Sibidanov (University of Victoria)