Test of lepton universality in Upsilon(1S) decays at BaBar

The BABAR Collaboration, P. del Amo Sanchez

The ratio $R_{\tau \mu }({\rm Y}(1S))={\Gamma }_{{\rm Y}(1S)\to {\tau }^{+}{\tau }^{-}}/{\Gamma }_{{\rm Y}(1S)\to {\mu }^{+}{\mu }^{-}}$ is measured using a sample of $(121.8\pm 1.2)\times 10^6$ ${\rm Y}(3S)$ events recorded by the BABAR detector. This measur…