Determination of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mo stretchy="false">|</mml:mo><mml:msub><mml:mi>V</mml:mi><mml:mrow><mml:mi>c</mml:mi><mml:mi>b</mml:mi></mml:mrow></mml:msub><mml:mo stretchy="false">|</mml:mo></mml:math> using <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mover accent="true"><mml:mi>B</mml:mi><mml:mo stretchy="false">¯</mml:mo></mml:mover><mml:mn>0</mml:mn></mml:msup><mml:mo stretchy="false">→</mml:mo><mml:msup><mml:mi>D</mml:mi><mml:mrow><mml:mo>*</mml:mo><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:msup><mml:mo>ℓ</mml:mo><mml:mo>−</mml:mo></mml:msup><mml:msub><mml:mover accent="true"><mml:mi>ν</mml:mi><mml:mo stretchy="false">¯</mml:mo></mml:mover><mml:mo>ℓ</mml:mo></mml:msub></mml:math> decays with Belle II

Abstract

We determine the Cabibbo-Kobayashi-Maskawa matrix-element magnitude |Vcb| using B0 → D∗+ℓ−νℓ 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 |Vcb| using the Boyd-Grinstein-Lebed and Caprini-Lellouch-Neubert parametrizations, and find |Vcb|BGL = (40.57±0.31±0.95±0.58)×10−3 and |Vcb|CLN = (40.13±0.27±0.93±0.58)× −3 with the uncertainties denoting statistical components, systematic components, and components from the lattice QCD input, respectively. The branching fraction is measured to be β(B0 → D∗+ ℓ− νℓ) = (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.