Measurement of the Semileptonic Decays B --> D tau nubar and B --> D* tau nubar

TL;DR

This paper reports preliminary measurements of branching fractions for B meson decays to D or D* mesons with tau neutrinos, providing data that could indicate physics beyond the Standard Model.

Contribution

First measurement of B --> D(*) tau nu branching fractions using BaBar data, with results consistent with Standard Model expectations within uncertainties.

Findings

Branching fractions measured with significances up to 6.2 sigma.

Results are compatible with Standard Model predictions.

Data set includes 232 million Upsilon(4S) decays.

Abstract

We present preliminary measurements of branching fractions for the semileptonic decays B --> D tau nubar and B --> D* tau nubar, which are potentially sensitive to non--Standard Model amplitudes. The data sample comprises 232x10^6 Upsilon(4S) --> BBbar decays collected with the BaBar detector at the PEP-II e+e- storage ring. We obtain B(B- --> D0 tau nubar) = (0.63 +/- 0.38 +/- 0.10 +/- 0.06)%, B(B- --> D*0 tau nubar) = (2.35 +/- 0.49 +/- 0.22 +/- 0.18)%, B(B0bar --> D+ tau nubar) = (1.03 +/- 0.35 +/- 0.14 +/- 0.10)%, and B(B0bar --> D*+ tau nubar) = (1.15 +/- 0.33 +/- 0.04 +/- 0.04)%, where the uncertainties are statistical, systematic, and normalization, respectively. By combining B- and B0bar results, we also obtain the branching fractions B(B --> D tau nubar) = (0.90 +/- 0.26 +/- 0.11 +/- 0.06)% and B(B --> D* tau nubar) = (1.81 +/- 0.33 +/- 0.11 +/- 0.06)% (quoted for the B- lifetime), with significances of 3.5 sigma and 6.2 sigma.