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

Understand

The ratio $R_{\tau\mu}(\Upsilon(1S)) = \Gamma_{\Upsilon(1S)\to\tau^+\tau^-}/\Gamma_{\Upsilon(1S)\to\mu^+\mu^-}$ is measured using a sample of $(121.8\pm1.2)\times10^6$ $\Upsilon(3S)$ events recorded by the BABAR detector.

• This measurement is intended as a test of lepton universality and as a search for a possible light pseudoscalar Higgs boson.
• In the standard model (SM) this ratio is expected to be close to 1.
• Any significant deviations would violate lepton universality and could be introduced by the coupling to a light pseudoscalar Higgs boson.