First observation of the decay τ−→ϕK−ντ

We present the first observation of τ lepton decays to hadronic final states with a ϕ-meson. This analysis is based on 401 fb−1 of data accumulated at the Belle experiment. The branching fraction obtained is B(τ−→ϕK−ντ)=(4.05±0.25±0.26)×10−5.