Measurement of Michel parameters in leptonic τ decays at Belle

We present a study of Michel parameters in leptonic τ decays using experimental information collected at the Belle detector. Michel parameters are extracted in the unbinned maximum likelihood fit of the (τ∓→ℓ∓νν; τ±→π±π0ν) (ℓ=e, μ) events in the full nine-dimensional phase space. We exploit the spin-spin correlation of tau leptons to extract ξρξ and ξρξδ in addition to the ρ and η parameters. Sensitivity of the method and systematic effects will be discussed.