Abstrakt
We determine the Cabibbo-Kobayashi-Maskawa matrix-element magnitude vertical bar V-cb vertical bar using (B) over bar (0) -> D*(+)l(-)(nu) over bar (l) decays reconstructed in 189 fb(-1) of collision data collected by the Belle II experiment, located at the SuperKEKB e(+)e(-) collider. Partial decay rates are reported as functions of the recoil parameter w and three decay angles separately for electron and muon final states.
We obtain vertical bar V-cb vertical bar using the Boyd-Grinstein-Lebed and Caprini-Lellouch-Neubert parametrizations, and find vertical bar V-cb vertical bar(BGL) = (40.57 +/- 0.31 +/- 0.95 +/- 0.58) x 10(-3) and vertical bar V-cb vertical bar(CLN) = (40.13 +/- 0.27 +/- 0.93 +/- 0.58) x 10(-3) with the uncertainties denoting statistical components, systematic components, and components from the lattice QCD input, respectively. The branching fraction is measured to be B((B) over bar (0) -> D*(+)l(-)(nu) over bar (l)) = (4.922 +/- 0.023 +/- 0.220)%.
The ratio of branching fractions for electron and muon final states is found to be 0.998 +/- 0.009 +/- 0.020. In addition, we determine the forward-backward angular asymmetry and the D*(+) longitudinal polarization fractions.
All results are compatible with lepton-flavor universality in the Standard Model.