Measurements of the branching fraction, isospin asymmetry, and lepton-universality ratio in $B\to J/\psi K$ decays at Belle II

Belle II Collaboration, F. Abudinén, I. Adachi +591

We report a study of $B\to J/\psi ({\ell }^{+}{\ell }^{-})K$ decays, where $\ell$ represents an electron or a muon, using $e^{+}{e}^{-}$ collisions at the ${\rm Y}(4S)$ resonance. The data were col…