Measurement of B -> D^(*) tau nu using full reconstruction tags

TL;DR

This paper reports precise measurements of B meson decays involving tau leptons using full reconstruction tagging at Belle, providing important data for testing the Standard Model and probing new physics.

Contribution

First measurement of B -> D^(*) tau nu decays using full reconstruction tags at Belle, improving precision and methodology over previous partial reconstruction approaches.

Findings

Measured branching fractions for B -> D^(*) tau nu decays with detailed uncertainties.

Results consistent with Standard Model predictions within errors.

Provides data to constrain new physics models affecting semileptonic B decays.

Abstract

We present measurements of B -> D^* tau nu and B -> D tau nu decays using 604.5 fb^-1 of data collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. Events are tagged by fully reconstructing one of the B mesons in hadronic modes. We obtain Br(B^+ -> D^0-bar tau^+ nu) = (1.51 +0.41/-0.39 +0.24/-0.19 +/- 0.15)%, Br(B^+ -> D^*0-bar tau^+ nu) = (3.04 +0.69/-0.66 +0.40/-0.47 +/- 0.22)%, Br(B^0 -> D^- tau^+ nu) = (1.01 +0.46/-0.41 +0.13/-0.11 +/- 0.10)%, Br(B^0 -> D^*- tau^+ nu) = (2.56 +0.75/-0.66 +0.31/-0.22 +/- 0.10)%, where the first error is statistical, the second is systematic, and the third is due to the uncertainty in the branching fraction for the normalization mode.