Measurements of the branching fraction and spectral function in the decay τ−→π−π+π−π0ντ

We report a measurement of the branching fraction in the τ−→π−π+π−π0ντ decay using a data sample accumulated with the Belle detector at the KEKB asymmetric-energy e+e− collider. The branching fraction is measured to be B(τ−→π−π+π−π0ντ)=(4.38±0.02±0.12)% where the first uncertainty is statistical and the second is systematic. This is an initial step of the high-statistics measurement of the spectral function in the τ−→π−π+π−π0ντ decay.