2025/06/18 by Belle II Collaboration, Adachi, I., Adamczyk, K. +407
#FOS: Physical sciences #High Energy Physics - Experiment (hep-ex)
paper · doi:10.48550/arxiv.2506.15256
We present a determination of the Cabibbo-Kobayashi-Maskawa matrix element |Vcb| from the decay B→ Dℓν_ℓ using a 365~fb-1 e+e-→Υ(4S)→ B B 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+ν_ℓ and B+→ D0(→ K+π-)ℓ+ν_ℓ, 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 4-velocities of the B and D mesons. We measure the total decay branching fractions to be B(B0→ D-ℓ+ν_ℓ)=(2.06 ± 0.05 (stat.) ± 0.10 (sys.))% and B(B+→ D0ℓ+ν_ℓ)=(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.