A Search for B- -> tau- nu-bar Recoiling Against a Fully Reconstructed B

TL;DR

This paper reports a search for the rare B- -> tau- nu-bar decay using data from the BaBar experiment, setting upper limits on its branching ratio and combining results from different analysis channels.

Contribution

The study introduces a new search method for B- -> tau- nu-bar decays with improved background suppression and combines independent measurements to tighten upper limit constraints.

Findings

No evidence for B- -> tau- nu-bar decay was found.

Set a 90% C.L. upper limit of BR < 7.7x10^(-4).

Combined analysis yields an upper limit of BR < 4.1x10^(-4).

Abstract

We present a search for the B- ->tau- nu-bar decay in a data sample of 82 fb^(-1) collected at the Y(4S) resonance with the BaBar detector at the SLAC PEP-II asymmetric B Factory. Continuum and combinatorial backgrounds are suppressed by selecting a sample of events with one completely reconstructed B. The decay products of the other B in the event are analyzed to search for a B- -> tau- nu-bar decay. The tau lepton is identified in the following decay channels: tau->e, tau->mu, tau->pi, tau->pi pi0 nu, tau->pi pi pi nu. We find no evidence for a signal and set a 90% C.L. upper limit of BR(B->tau nu) < 7.7x10^(-4). We combine this result with another BaBar measurement searching for B- -> tau- nu-bar decays in a sample with one B meson reconstructed in semi-leptonic channels. The two samples are statistically independent. We obtain a combined 90% C.L. upper limit of BR(B->tau nu) < 4.1x10^(-4). All results are preliminary.