Measurements of B --> {pi, eta, eta'} l nu Branching Fractions and Determination of |Vub| with Semileptonically Tagged B Mesons

TL;DR

This paper measures branching fractions of B meson decays to pseudoscalar mesons and leptons, and determines the CKM matrix element |Vub| using data from the BABAR detector, providing insights into semileptonic B decays and quark mixing.

Contribution

It presents new measurements of B --> P l nu branching fractions and a determination of |Vub| with semileptonically tagged B mesons, utilizing a large data set and recent form factor calculations.

Findings

Measured B(B0 --> pi- l+ nu) = (1.54 +/- 0.17 +/- 0.09) x 10^-4

Evidence for B+ --> eta l+ nu decay with branching fraction (0.64 +/- 0.20 +/- 0.03) x 10^-4

Determined |Vub| = (4.0 +/- 0.5 +/- 0.2 +0.7-0.5) x 10^-3

Abstract

We report measurements of branching fractions for the decays B --> P l nu, where P are the pseudoscalar charmless mesons pi-, pi0, eta and eta', based on 348 fb-1 of data collected with the BABAR detector, using B0 and B+ mesons found in the recoil of a second B meson decaying as B --> D(*) l nu. Assuming isospin symmetry, we combine pionic branching fractions to obtain B(B0 --> pi- l+ nu) = (1.54 +/- 0.17(stat) +/- 0.09(syst)) x 10-4; we find 3.2 sigma evidence of the decay B+ --> eta l+ nu and measure its branching fraction to be (0.64 +/- 0.20 (stat) +/- 0.03 (syst)) x 10-4, and determine B(B+ --> eta' l+ nu) < 0.47 x 10-4 to 90% confidence level. Using partial branching fractions for the pionic decays in ranges of the momentum transfer and a recent form factor calculation, we obtain the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element |Vub| = (4.0 +/- 0.5(stat) +/- 0.2(syst) +0.7-0.5(theory)) x 10-3.