Three-prong τ decays with charged kaons

Abstract

Final states with charged kaons in three-prong τ decays are studied by exploiting the particle identification from the dE/dx measurement. The results are based on a sample of about 1.6 × 10⁵ detected τ pairs collected with the ALEPH detector between 1991 and 1995 around the Z peak. The following branching ratios have been measured: B(τ- → K−K⁺π−ν_τ) = (1.63 ± 0.21 ± 0.17) × 10⁻³, B(τ− → K⁻π⁺π⁻ν_τ) = (2.14 ± 0.37 ± 0.29) × 10⁻³, B(τ⁻ → K⁻K⁺π⁻π⁰ν_τ) = (0.75 ± 0.29 ± 0.15) × 10⁻³, and B(τ⁻ → K⁻π⁺π⁻π⁰ν_τ) = (0.61 ± 0.39 ± 0.18) × 10⁻³. The first two measurements are more precise than the current world averages, while the last two channels are investigated for the first time. The 95% C.L. upper limit on the branching ratio for the decay τ⁻ → K⁻K⁺K⁻ν_τ is 0.19 × 10⁻³. A study of intermediate states occurring in the K⁻K⁺π⁻ν_τ and K⁻π⁺π⁻ν_τ decays is also presented.