Study of tau- -> K_S pi- nu_tau decay at Belle

We present a study of the decay tau- -> K_S pi- nu_tau using a 351 fb^-1 data sample collected with the Belle detector. The analysis is based on 53110 lepton-tagged signal events. The measured branching fraction B(tau- -> K_S pi- nu_tau)=(0.404 +- 0.002(stat.) +- 0.013(syst.))% is consistent with the world average value and has better accuracy. An analysis of the K_S pi- 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 tau decay: M(K*(892)-)=(895.47 +- 0.20(stat.) +- 0.44(syst.) +- 0.59(mod.)) MeV/c2, Gamma(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.

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