A Search for B+ --> tau+ nu Recoiling Against B- --> D0 l- nubar X

TL;DR

This paper reports a search for the rare decay B+ to tau+ nu using data from the BaBar experiment, measuring its branching fraction and setting an upper limit, which constrains the product of decay constant and CKM matrix element.

Contribution

First measurement of the B+ to tau+ nu decay branching fraction using recoil technique at BaBar, providing limits and constraints on fundamental parameters.

Findings

Measured branching fraction: (0.88^{+0.68}_{-0.67} (stat) ± 0.11 (syst)) × 10^{-4}

Upper limit on branching fraction: < 1.8 × 10^{-4} at 90% CL

Calculated f_B · |V_ub|: (7.0^{+2.3}_{-3.6} (stat)^{+0.4}_{-0.5} (syst)) × 10^{-4} GeV

Abstract

We present a search for the decay $B^{+} \to \tau^{+} \nu_{\tau}$ using 288 fb-1 of data collected at the $\Upsilon(4S)$ resonance with the BaBar detector at the SLAC PEP-II $B$-Factory. A sample of events with one reconstructed semileptonic B decay is selected, and in the recoil a search for $B^{+} \to \tau^{+} \nu_{\tau}$ signal is performed. The $\tau$ is identified in the following channels: {\tau^+ \to e^+ \nu_e \nutb}, {\tau^+ \to \mu^+ \nu_{\mu} \nutb}, {\tau^+ \to \pi^+ \nutb} and {\tau^+ \to \pi^+ \pi^0 \nutb}. We measure a branching fraction of $\mathcal{B}(B^{+} \to \tau^{+} \nu_{\tau})=(0.88^{+0.68}_{-0.67}({stat.}) \pm 0.11 ({syst.})) \times 10^{-4}$ and extract an upper limit on the branching fraction, at the 90% confidence level, of $\mathcal{B}(B^{+} \to \tau^{+} \nu_{\tau}) < 1.8 \times 10^{-4}$. We calculate the product of the $B$ meson decay constant and $|\Vub|$ to be $f_{B}\cdot|\Vub| = (7.0^{+2.3}_{-3.6}({stat.})^{+0.4}_{-0.5}({syst.}))\times10^{-4}$ GeV \.