Observation of B+ -> Dbar*0 tau+ nu_tau and Evidence for B+ -> Dbar^0 tau+ nu_tau at Belle

TL;DR

This paper reports the first evidence for the B+ -> Dbar0 tau+ nu_tau decay and measures the branching fractions of B+ -> Dbar*0 tau+ nu_tau and B+ -> Dbar0 tau+ nu_tau using data from the Belle experiment.

Contribution

The study provides the first evidence for the B+ -> Dbar0 tau+ nu_tau decay and precise measurements of branching fractions for both decay modes.

Findings

First evidence for B+ -> Dbar0 tau+ nu_tau decay.

Measured branching fraction for B+ -> Dbar*0 tau+ nu_tau: approximately 2.12%.

Measured branching fraction for B+ -> Dbar0 tau+ nu_tau: approximately 0.77%.

Abstract

We present measurements of B+ -> Dbar*0 tau+ nu_tau and B+ -> Dbar^0 tau+ nu_tau decays in a data sample of 657 x 10^6 BBbar pairs collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. We find 446^{+58}_{-56} events of the decay B+ -> Dbar*0 tau+ nu_tau with a significance of 8.1 standard deviations, and 146^{+42}_{-41} events of the decay B+ -> Dbar0 tau+ nu_tau with a significance of 3.5 standard deviations. The latter signal provides the first evidence for this decay mode. The measured branching fractions are B(B+ -> Dbar*0 tau+ nu_tau)=(2.12^{+0.28}_{-0.27} (stat) +- 0.29 (syst)) % and B(B+ -> Dbar0 tau+ nu_tau)=(0.77 +- 0.22 (stat) +- 0.12 (syst)) %.