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

With the full data sample of 772 x 10(6) B (B) over bar pairs recorded by the Belle detector at the KEKB electron-positron collider, the decay (B) over bar -> D+ tau(-)(nu) over bar (tau) is studied with the hadronic tau decays tau(-) -> pi(-)nu(tau) and tau(-) -> rho(-)nu(tau). The tau polarization P-tau(D*) in two-body hadronic tau decays is measured, as well as the ratio of the branching fractions R(D*) = B((B) over bar -> D*tau(-) (nu) over bar (tau))/B((B) over bar -> D*l(-) (nu) over bar (l),where l(-) denotes an electron or a muon. Our results, P-tau (D*) = - 0.38 +/- 0.51(stat)(+0.21)(-0.16) (syst) and R(D*) = 0.270 +/- 0.035(stat)(+0.028)(-0.025)(syst), are consistent with the theoretical predictions of the standard model. The polarization values of P-tau(D*) > +0.5 are excluded at the 90% confidence level.