Measurements of Charged Current Lepton Universality and $|V_{us}|$ using Tau Lepton Decays to $e^{-}{\bar{\nu }}_e{\nu }_{\tau }$, ${\mu }^{-}{\bar{\nu }}_{\mu }{\nu }_{\tau }$, ${\pi }^{-}{\nu }_{\tau }$, and $\K^- ν_τ$

Abstract

Using 467 $f{b}^{-1}$ of $e^{+}{e}^{-}$ annihilation data collected with the BaBar detector, we measure $\frac{\mathcal{B}({\tau }^{-}\to {\mu }^{-}{\bar{\nu }}_{\mu }{\nu }_{\tau })}{\mathcal{B}({\tau }^{-}\to e^{-}{\bar{\nu }}_e{\nu }_{\tau })}=(0.9796\pm 0.0016\pm 0.0036)$, $\frac{\mathcal{B}({\tau }^{-}\to {\pi }^{-}{\nu }_{\tau })}{\mathcal{B}({\tau }^{-}\to e^{-}{\bar{\nu }}_e{\nu }_{\tau })}=(0.5945\pm 0.0014\pm 0.0061)$, and $\frac{\cal{B}(τ^- \to \K^- ν_τ)}{\cal{B}(τ^- \to e^- \barν_e ν_τ)} = (0.03882 \pm 0.00032 \pm 0.00057)$, where the uncertainties are statistical and systematic, respectively. From these precision $\tau$ measurements, we test the Standard Model assumption of $\mu$-$e$ and $\tau$-$\mu$ charge current lepton universality and provide determinations of $|V_{us}|$ experimentally independent of the decay of a kaon and which we compare with the value predicted from the unitarity of the Cabibbo-Kobayashi-Maskawa matrix.

7 pages, 1 encapsulated postscript figures, Phys. Rev. Lett 105, 051602 (2010)