First Observation of the Decay τ^- → K*^-η ν_τ

The decay τ^-→ K^*- η ν τ has been observed with the CLEO II detector. The K^*- is reconstructed in two decay channels, K^*-→ K_Sπ^-→π⁺π^- and K^*-→ K^-π⁰. The η is reconstructed from the decay η → γγ. The measured branching fraction isB(τ^-→ K^*-π η ν_τ)=(2.9 ± 0.8 ±0.4) × 10^-44. We also measure the inclusive branching fractions without requiring the K^* resonance, B(τ^-→ K_Sπ^- η ν_τ)=(1.10 ± 0.35 ±0.11) × 10^-4 and B(τ^-→ K^-π⁰ η ν_τ)=(1.77 ± 0.56 ±0.71) × 10^-4. The results indicate that the K^*- resonance dominates the K_Sπ^- mass spectrum.