Determination of the Branching Fraction for B --> Xc l nu Decays and of |Vcb| from Hadronic-Mass and Lepton-Energy Moments

Abstract

We determine the inclusive B --> Xc l nu branching fraction, the CKM matrix element |Vcb|, and other heavy-quark parameters from a simultaneous fit to moments of the hadronic-mass and lepton-energy distributions in semileptonic B-meson decays, measured as a function of the lower limit on the lepton energy, using data recorded with the BABAR detector. Using Heavy Quark Expansions (HQEs) to order 1/mb^3, we extract BR_cenu=(10.61 +- 0.16(exp) +- 0.06(HQE))% and |Vcb| = (41.4 +- 0.4(exp) +- 0.4(HQE) +- 0.6(th)) 10^-3. The stated errors refer to the experimental, HQE, and additional theoretical uncertainties.

Figures (2)

• Figure 1: The measured hadronic-mass (a-d) and electron-energy (e-h) moments as a function of the cut-off energy, $E_{cut}$, compared with the result of the simultaneous fit (line), with the theoretical uncertainties gambino indicated as shaded bands. The solid data points mark the measurements included in the fit. The vertical bars indicate the experimental errors; in some cases they are comparable in size to the data points. Moment measurements for different $E_{cut}$ are highly correlated.
• Figure 2: Fit results (crosses) with contours corresponding to $\Delta \chi^2=1$ for two pairs of the eight free parameters a) $m_b$ and b) $\mu_{\pi}^2$ versus $|V_{cb}|$, separately for fits using the hadronic-mass, the electron-energy, and all moments.