Studies of τ−→ηK−ντ and τ−→ηπ−ντ at BABAR and a search for a second-class current

Abstract

We report on analyses of tau lepton decays τ − → η K − ν τ and τ − → η π − 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 ( 4 S ) resonance. We measure the branching fraction for the τ − → η K − ν τ decay mode, B ( τ − → η K − 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 − → η π − ν τ , B ( τ − → η π − ν τ ) < 9.9 × 10 − 5 .