Measurement of the B¯→D*lν¯ branching fractions and ‖Vcb‖

Abstract

We study the exclusive semileptonic B meson decays ${\mathit{B}}^{\mathrm{-}}$→${\mathit{D}}^{\mathrm{*}0}$ ${\mathit{l}}^{\mathrm{-}}$ν¯ and B${\mathrm{¯}}^0$→${\mathit{D}}^{\mathrm{*}+}$ ${\mathit{l}}^{\mathrm{-}}$ν¯ using data collected with the CLEO II detector at the Cornell Electron-positron Storage Ring (CESR). We present measurements of the branching fractions scrB(B${\mathrm{¯}}^0$→${\mathit{D}}^{\mathrm{*}+}$ ${\mathit{l}}^{\mathrm{-}}$ν¯)= (0.5/${\mathit{f}}_{00}$)[4.49±0.32(stat.)±0.39 (syst.)]% and scrB(${\mathit{B}}^{\mathrm{-}}$→${\mathit{D}}^{\mathrm{*}0}$ ${\mathit{l}}^{\mathrm{-}}$(ν¯)= (0.5/${\mathit{f}}_{+\mathrm{-}}$)[5.13±0.54 (stat) ±0.64 (syst)]%, where ${\mathit{f}}_{00}$ and ${\mathit{f}}_{+\mathrm{-}}$ are the neutral and charged B meson production fractions at the Υ(4S) resonance, respectively. Assuming isospin invariance and taking the ratio of charged to neutral B meson lifetimes measured at higher energy machines, we determine the ratio ${\mathit{f}}_{+\mathrm{-}}$/${\mathit{f}}_{00}$=1.04±0.13 (stat) ±0.12 (syst) ±0.10 (lifetime); further assuming ${\mathit{f}}_{+\mathrm{-}}$+${\mathit{f}}_{00}$=1 we also determine the partial width Γ(B¯→${\mathit{D}}^{\mathrm{*}}$lν¯)=[29.9±1.9 (stat) ±2.7 (syst.) ±2.0 (lifetime)] ${\mathrm{ns}}^{\mathrm{-}1}$ (independent of ${\mathit{f}}_{+\mathrm{-}}$/${\mathit{f}}_{00}$).