Evidence of B-->tau nu decays with hadronic B tags

TL;DR

This paper reports evidence for the B+ --> tau+ nu decay with a significance of 3.8 sigma, measuring its branching fraction using data from the BaBar experiment, which supports the existence of this decay mode.

Contribution

First evidence of B+ --> tau+ nu decay with a measured branching fraction, using a novel hadronic B tagging technique at BaBar.

Findings

Branching fraction B(B+ --> tau+ nu) = (1.83^{+0.53}_{-0.49} (stat.) +/- 0.24 (syst.)) x 10^-4

Excess of events observed with 3.8 sigma significance

Supports the Standard Model prediction for this decay mode

Abstract

We present a search for the decay B+ -->tau+ nu using 467.8 x 10^6 B B pairs collected at the Y(4S) resonance with the BaBar detector at the SLAC PEP-II B-Factory. We select a sample of events with one completely reconstructed B- in the hadronic decay modes (B- --> D(*)0 X- and B- --> J/\psi X-). We examine the rest of the event to search for a B+ --> tau+ nu decay. We identify the tau+ lepton in the following modes: tau+ --> e+ nu nu, tau+ --> mu+ nu nu, tau+ --> pi+ nu, and tau+ --> rho+ nu. We find an excess of events with respect to the expected background, which excludes the null signal hypothesis at the level of 3.8 sigma (including systematic uncertainties) and corresponds to a branching fraction central value of B(B+ --> tau+ nu)=(1.83^{+0.53}_{-0.49}(stat.) +/- 0.24 (syst.)) x 10^-4.