Study of τ−→KSπ−ντ decay at Belle

We present a study of the decay τ−→KSπ−ντ using a 351 fb−1 data sample collected with the Belle detector. The analysis is based on 53,110 lepton-tagged signal events. The measured branching fraction B(τ−→KSπ−ντ)=(0.404±0.002(stat.)±0.013(syst.))% is consistent with the world average value and has better accuracy. An analysis of the KSπ− invariant mass spectrum reveals contributions from the K∗(892)− as well as other states. For the first time the K∗(892)− mass and width have been measured in τ decay: M(K∗(892)−)=(895.47±0.20(stat.)±0.44(syst.)±0.59(mod.))MeV/c2, Γ(K∗(892)−)=(46.2±0.6(stat.)±1.0(syst.)±0.7(mod.))MeV. The K∗(892)− mass is significantly different from the current world average value.