Observation of the Decay B^{-} \rightarrow D_{s}^{(*)+} K^{-} \ell^{-} \bar{\nu}_{\ell}

TL;DR

This paper reports the first observation of the semileptonic decay of B- mesons into D_s(*)+ K- l- nu, measuring its branching fraction with high significance using data from the BABAR experiment.

Contribution

The study provides the first experimental evidence of the decay B- → D_s(*)+ K- l- nu, expanding understanding of B meson decay channels and testing theoretical models.

Findings

Decay observed with >5 sigma significance

Branching fraction measured as approximately 6.13 x 10^-4

Analysis based on 342 fb^-1 of data from BABAR

Abstract

We report the observation of the decay $B^{-} \rightarrow D^{(*)+}_{s} K^{-} \ell^{-} \bar{\nu}_{\ell}$ based on $342 \mathrm {\,fb}^{-1}}$ of data collected at the $\Y4S$ resonance with the BABAR detector at the PEP-II $e^{+}e^{-}$ storage rings at SLAC. A simultaneous fit to three $D^{+}_{s}$ decay chains is performed to extract the signal yield from measurements of the squared missing mass in the B meson decay. We observe the decay $B^{-} \rightarrow D^{(*)+}_{s} K^{-} \ell^{-} \bar{\nu}_{\ell}$ with a significance greater than five standard deviations (including systematic uncertainties) and measure its branching fraction to be $\BR(B^{-} \rightarrow D^{(*)+}_{s} K^{-} \ell^{-} \bar{\nu}_{\ell}) = [6.13^{+1.04}_{-1.03}(\mathrm{stat.})\pm0.43(\mathrm{syst.}) \pm 0.51(\BR(D_{s}))]\times10^{-4}$, where the last error reflects the limited knowledge of the $D_{s}$ branching fractions.