Studies of \(τ^{-}→ηK^{-}ν_{τ}\) and \(τ^{-}→ηπ^{-}ν_{τ}\) at BABAR and a Search for a Second-Class Current

Abstract

We report on analyses of tau lepton decays \(τ^{−}→ηK^{−}ν_{τ}\) and \(τ^{−}→ηπ^{−}ν_{τ}\), with \(η→π^{+}π^{−}π^{0}\), using \(470 fb^{−1}\) of data from the BABAR experiment at PEP-II, collected at center-of-mass energies at and near the \(Υ(4S)\) resonance. We measure the branching fraction for the \(τ^{−}→ηK^{−}ν_{τ}\) decay mode, \(ℬ(τ^{−}→ηK^{−}ν_{τ})=(1.42±0.11(stat)±0.07(syst))×10^{−4}\), and report a 95% confidence level upper limit for the second-class current process \(τ^{−}→ηπ^{−}ν_{τ}\), \(ℬ(τ^{−}→ηπ^{−}ν_{τ})<9.9×10^{−5}\).