Measurement of Cabibbo-Suppressed Tau Lepton Decays and the Determination of |Vus|

Abstract

This work presents simultaneous branching fraction measurements of the decay modes τ- → K- nπ0ντ with n = 0,1,2,3 and τ- → π- nπ0ντ with n = 3,4. The analysis is based on a data sample of 427 x 106 τ+τ- pairs recorded with the BABAR detector, which corresponds to an integrated luminosity of 464.4 fb-1. The measured values are β(τ- → K-ντ ) = (6.57 ± 0.03 ± 0.11) x 10-3, β(τ- → K-π0ντ ) = (4.61 ± 0.03 ± 0.11) x 10-3, β(τ- {yields} K- π0π0ντ) = (5.05 ± 0.17 ± 0.44) x 10-4, β(τ- {yields} K-π0π0π0ντ ) = (1.31 ± 0.43 ± 0.40) x 10-4, β(τ0 → π0π0π0π0ντ) = (1.263 ± 0.008 ± 0.078) x 10-2 and β(τ0 → π0π0π0π0π0ντ) = (9.6 ± 0.5 ± 1.2) x 10-4, where the uncertainties are statistical and systematic, respectively. All measurements are compatible with the current world averages whereas the uncertainties are significantly smaller by a factor of up to five. The determination of β(τ0 → π-π0π0π0π0vτ) is the first measurement of this branching fraction. The measured branching fractions are combined with the current world averages. Using the new averages, an updated determination of |Vus| from hadronic τ decays yields |Vus| = 0.2146 ± 0.0025, which improves previous measurements by 19%. Its uncertainty is comparable to the one of the current world average from semileptonic kaon decays.