Measurements of the Semileptonic Decays $\Bb\to D\ell\nub$ and $\Bb\to D^*\ell\nub$ Using a Global Fit to $D X\ell\nub$ Final States

TL;DR

This paper reports precise measurements of semileptonic B meson decays to D and D* mesons, using a global fit approach to extract branching fractions, form factors, and CKM matrix element products from a large dataset at BaBar.

Contribution

It introduces a comprehensive global fit method to analyze semileptonic B decays, providing improved determinations of branching fractions, form factors, and |V_cb| with reduced uncertainties.

Findings

Branching fraction for B- to D0 l nu: (2.34 ± 0.03 ± 0.13)%

Branching fraction for B- to D*0 l nu: (5.40 ± 0.02 ± 0.21)%

Product |V_cb| × form factor at zero recoil: (43.1 ± 0.8 ± 2.3)×10^{-3} for D and (35.9 ± 0.2 ± 1.2)×10^{-3} for D*

Abstract

Semileptonic $\bar{B}$ decays to $DX\ell\bar{\nu}$ ($\ell=e$ or $mu$) are selected by reconstructing $D0\ell$ and $D^+\ell$ combinations from a sample of 230 million $\Upsilon(4S) \to B\bar{B}$ decays recorded with the BaBar detector at the PEPII $e^+e^-$ collider at SLAC. A global fit to these samples in a 3-dimensional space of kinematic variables is used to determine the branching fractions $\mathcal{B}(B^- \to D0\ell\bar{\nu}) = (2.34 \pm 0.03 \pm 0.13) %$ and $\mathcal{B}(B^- \to D^{*0}\ell\bar{\nu}) = (5.40 \pm 0.02 \pm 0.21) %$,where the errors are statistical and systematic, respectively. The fit also determines form factor parameters in a HQET-based parameterization, resulting in $\rho_D2 = 1.20 \pm 0.04 \pm 0.07$ for $\bar{B} \to D\ell\bar{\nu}$ and $\rho_{D^*}2 = 1.22 \pm 0.02 \pm 0.07$ for $\bar{B} \to D^*\ell\bar{\nu}$ These values are used to obtain the product of the CKM matrix element $|V_{cb}|$ times the form factor at the zero recoil point for both $\bar{B} \to D\ell\bar{\nu}$ decays, $\mathcal{G}(1)|V_{cb}| = (43.1 \pm 0.8 \pm 2.3)\times 10^{-3}$, and for $\bar{B} \to D^*\ell\bar{\nu}$ decays, $\mathcal{F}(1)|V_{cb}| = (35.9 \pm 0.2 \pm 1.2)\times 10^{-3}$.