Charged Current Lepton Universality and |Vus| using τ Lepton Decays at BaBar

Using a data sample corresponding to an integrated luminosity of L = 467 fb − 1 , collected with the BaBar detector at the SLAC PEP-II e + e − storage ring, we present preliminary measurements of B ( τ → μ ν ν ¯ ) B ( τ → e ν ν ¯ ) = ( 0.9796 ± 0.0016 ± 0.0035 ) , B ( τ → π ν ) B ( τ → e ν ν ¯ ) = ( 0.5945 ± 0.0014 ± 0.0061 ) , B ( τ → K ν ) B ( τ → e ν ν ¯ ) = ( 0.03882 ± 0.00032 ± 0.00056 ) , and B ( τ → K ν ) B ( τ → π ν ) = ( 0.06531 ± 0.00056 ± 0.00093 ) , where the uncertainties are statistical and systematic, respectively. From the branching ratio B ( τ → K ν ) B ( τ → π ν ) , | V u s | is determined to be 0.2255 ± 0.0023 . The branching ratio B ( τ → μ ν ν ¯ ) B ( τ → e ν ν ¯ ) enables a precision test of the Standard Model assumption of charged current lepton universality, | g μ g e | = 1.0036 ± 0.0020 . The branching ratios B ( τ → K ν ) B ( τ → e ν ν ¯ ) , and B ( τ → π ν ) B ( τ → e ν ν ¯ ) provide additional tests of charged current lepton universality, | g τ g μ | = 0.9859 ± 0.0057 in non-strange and | g τ g μ | = 0.9836 ± 0.0087 in strange decays.