A Search for B+ -> tau+ nu

TL;DR

This paper reports a search for the rare decay B+ -> tau+ nu using data from the BABAR detector, setting an upper limit on its branching fraction and estimating the product of the decay constant and CKM matrix element.

Contribution

First measurement setting an upper limit on B+ -> tau+ nu decay and estimating f_B |V_ub| using BABAR data.

Findings

Branching fraction upper limit < 1.7 x 10^-4 at 90% CL

Measured f_B |V_ub| = (7.2^{+2.0}_{-2.8} +- 0.2) x 10^-4 GeV

No significant signal observed

Abstract

We present a search for the decay B+ -> tau+ nu using 383x10^6 BBbar pairs collected at the Y(4S) resonance with the BABAR detector at the SLAC PEP-II B-Factory. A sample of events with one reconstructed semileptonic B decay (B- -> D0 l nu X)) is selected, and in the recoil a search for B+ -> tau+ nu is performed. The tau is identified in the following channels: tau+ -> e nu nubar, tau+ -> mu nu nubar, tau+ -> pi+ nu, and tau+ -> pi+ pi0 nu. We measure a branching fraction of B(B+ -> tau+ nu)=(0.9 +- 0.6(stat.) +- 0.1(syst.)) x 10^-4. In the absence of a significant signal, we calculate an upper limit at the 90% confidence level of B(B+ -> tau+ nu) < 1.7 x 10^-4. We calculate the product of the B meson decay constant f_B and |V_ub| to be f_B x |V_ub| = (7.2^{+2.0}_{-2.8}(stat.) +- 0.2 (syst.)) x 10^-4 GeV.