Observation of the Decay B−→D(*)+sK−ℓ−¯νℓ

Abstract

We report the observation of the decay B − → D ( * ) + s K − ℓ − ¯ ν ℓ based on 342 fb − 1 of data collected at the Υ ( 4 S ) 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 − → D ( * ) + s K − ℓ − ¯ ν ℓ with a significance greater than 5 standard deviations (including systematic uncertainties) and measure its branching fraction to be B ( B − → D ( * ) + s K − ℓ − ¯ ν ℓ ) = [ 6.13 + 1.04 − 1.03 ( stat ) ± 0.43 ( syst ) ± 0.51 ( B ( D s ) ) ] × 10 − 4 , where the last error reflects the limited knowledge of the D s branching fractions.