Branching fraction measurement of $B^{+}\to \omega {\ell }^{+}\nu$ decays

We present a measurement of the $B^{+}\to \omega {\ell }^{+}\nu$ branching fraction based on a sample of 467 million $B\overline{B}$ pairs recorded by the BABAR detector at the SLAC PEP-II $e^{+}{e}^{-}$ collider. We observe $1125\pm 131$ signal decays, corresponding to a branching fraction of $\mathcal{B}(B^{+}\to \omega {\ell }^{+}\nu )=(1.21\pm 0.14\pm 0.08)\times {10}^{-4}$, where the first error is statistical and the second is systematic. The dependence of the decay rate on $q^2$, the invariant mass squared of the leptons, is compared to QCD predictions of the form factors based on a quark model and light-cone sum rules.

Figure 1

Distribution of $\Delta E$ versus $m_{\mathrm{ES}}$ for true-$\omega$ signal MC. The 20 bins into which the plane is divided for the fit histogram are overlaid.

Figure 2

Fit to the distribution of $m_{3\pi }$ for data from the all-$q^2$ sample, with MC combinatorial-$\omega$ signal subtracted. The dashed (red) and dotted (blue) curves describe the fitted peaking and combinatorial background functions, respectively, and the solid (black) curve is their sum. The peak and sideband regions are also indicated.

Figure 3

Distributions of $m_{\mathrm{ES}}$ after the fit and the ratio of the data to the fitted predictions, for five separate $q^2$ bins and the full $q^2$ range, in the $\Delta E$ signal band, $-0.25<\Delta E\le 0.25\mathrm{GeV}$. The points represent data with statistical uncertainties, while the stacked histograms represent the sum of fitted source components, signal (white), true-$\omega$ $B\overline{B}$ (light gray), true-$\omega$ $q\overline{q}$ (dark gray), and combinatorial-$\omega$ background (diagonally thatched).

Figure 4

Partial branching fractions (points with error bars) with respect to $q^2$. The data are compared with the predictions from light-cone sum rules (LCSR) [8] and a quark-model calculation (ISGW2) [10]. The uncertainty band (shaded) is given for the LCSR calculation.