Measurement of the τ lepton polarization and R(D~*) in the decay B → D~*τ~ ?ν_τ with one-prong hadronic τ decays at Belle

摘要

With the full data sample of 772 × 10~6 BB pairs recorded by the Belle detector at the KEKB electronpositron collider, the decay B → D~*τ~? ν_τ is studied with the hadronic τ decays τ~? → π~?ν_τ and τ~? → ρ~?ν_τ. The τ polarization P_τ(D~*) in two-body hadronic τ decays is measured, as well as the ratio of the branching fractions R(D~*) = B(B → D~*τ~? ν_τ)=B(B → D~*?~? ν_?), where ?~? denotes an electron or a muon. Our results, P_τ(D~*) = ?0.38 ± 0.51(stat)_(?0.16)~(+0.21) (syst) and R(D~*) = 0.270 ± 0.035(stat)_(?0.025)~(+0.028) (syst), are consistent with the theoretical predictions of the standard model. The polarization values of P_τ(D~*) > +0.5 are excluded at the 90% confidence level.