Measurement of the relative B^- →D⁰/D^∗0/D^∗∗0μ^- ν̅_μ branching fractions using B^- mesons from B̅_s2^∗0 decays

The decay of the narrow resonance B̅_s2^∗0→B^-K⁺ can be used to determine the B^- momentum in partially reconstructed decays without any assumptions on the decay products of the B^- meson. This technique is employed for the first time to distinguish contributions from D⁰, D^∗0, and higher-mass charmed states (D^∗∗0) in semileptonic B^- decays by using the missing-mass distribution. The measurement is performed using a data sample corresponding to an integrated luminosity of 3.0 fb^-1 collected with the LHCb detector in pp collisions at center-of-mass energies of 7 and 8 TeV. The resulting branching fractions relative to the inclusive B^-→D⁰Xμ^-ν̅_μ are f_D0=ℬ(B^-→D⁰μ^-ν̅_μ)/ℬ(B^-→D⁰Xμ^-ν̅_μ)=0.25±0.06, f_D∗∗0=ℬ(B^-→(D^∗∗0→D⁰X)μ^-ν̅_μ)/ℬ(B^-→D⁰Xμ^-ν̅_μ)=0.21±0.07, with f_D∗0=1-f_D0-f_D∗∗0 making up the remainder.