Studies of tau- -> eta.K-.nu and tau- -> eta.pi-.nu at BaBar and a search for a second-class current

Abstract

We report on analyses of tau lepton decays ${\tau }^{-}\to \eta K^{-}{\nu }_{\tau }$ and ${\tau }^{-}\to \eta {\pi }^{-}{\nu }_{\tau }$, with $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$, using 470 fb${}^{-1}$ of data from the Babar experiment at PEP-II, collected at center-of-mass energies at and near the ${\rm Y}(4S)$ resonance. We measure the branching fraction for the ${\tau }^{-}\to \eta K^{-}{\nu }_{\tau }$ decay mode, $\Br(τ^- \to ηK^- ν_τ) = (1.42\pm0.11\text{(stat)}\pm0.07\text{(syst)})\times10^{-4}$, and report a 95% confidence level upper limit for the second-class current process ${\tau }^{-}\to \eta {\pi }^{-}{\nu }_{\tau }$, $\Br(τ^- \to ηπ^- ν_τ) < 9.9\times10^{-5}$.

11 pages, 4 figures