Determination of

We present a determination of the Cabibbo-Kobayashi-Maskawa matrix element |Vcb| from the decay B → Dℓνℓ using a 365 fb^-1 e⁺e^- → ϒ(4S) → BB¯ data sample recorded by the Belle II experiment at the SuperKEKB collider. The semileptonic decay of one B meson is reconstructed in the modes B⁰ → D⁻(→ K⁺π⁻π⁻)ℓ⁺νℓ and B⁺ → D¯⁰( → K⁺π⁻)ℓ⁺νℓ, where ℓ denotes either an electron or a muon. Charge conjugation is implied. The second B meson in the ϒ(4S) event is not reconstructed explicitly. Using an inclusive reconstruction of the unobserved neutrino momentum, we determine the recoil variable w = vB·vD, where vB and vD are the four-velocities of the B and D mesons. We measure the total decay branching fractions to be B(B⁰ → D⁻ℓ⁺νℓ) = (2.06 ± 0.05(stat) ± 0.10(sys))% and B(B⁺ → D¯⁰ℓ⁺νℓ) = (2.31 ± 0.04(stat) ± 0.09(sys))%. We probe lepton flavor universality by measuring B(B → Deνe)/B(B → Dμνμ) = 1.020 ± 0.020(stat) ± 0.022(sys). Fitting the partial decay branching fraction as a function of w and using the average of lattice QCD calculations of the B → D form factor, we obtain |Vcb| = (39.2 ± 0.4(stat) ± 0.6(sys) ± 0.5(th)) × 10⁻³.

Duke Scholars

Author Anselm G. Vossen Physics