Three-prong τ decays with charged kaons

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 x 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-ντ) = (1.63 ± 0.21 ± 0.17) x 10-3, B(τ- → K-π+π-ντ)=(2.14 ± 0.37 ± 0.29) x 10-3, B (τ- → K-K+π-π0ντ) = (0.75 ± 0.29 ± 0.15) x 10-3, and B(τ- → K-π+π-π0ν τ) = (0.61 ± 0.39 ± 0.18) x 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-ντ is 0.19 x 10-3. A study of intermediate states occurring in the K-K+π-ντ and K-π+π-ντ decays is also presented.