Speaker
Summary
Semi-leptonic B decays B -> D() tau nu have been of interest because of the high sensitivity to the New Physics.
Recent indication of a discrepancy of R(D) and R(D) (branching ratio of B → D() tau nu over B → D() l nu where l + e, mu) from the Standard Model prediction can be a hint for the New Physics effect.
In this talk, the new measurement of R(D) and R(D) based on semileptonically tagged B\to D^{()} \tau^+ \nu decays as well as the first measurement of the D^ polarization in B\to D^\tau^+\nu decays are presented.
This talk also covers new Belle search for the purely leptonic decay B \to \mu^+ \nu.
The analyses are based on the full data set recorded by the Belle detector at the KEKB e^+ e^- collider containing 772 million B\bar{B} pair events.
