Measurement of the inclusive semileptonic $B$ meson branching fraction in 62.8 fb$^{-1}$ of Belle II data

Abstract

We report a measurement of the branching fraction of inclusive semileptonic $B$ meson decays $B\to X_c\ell\nu\ell$ in $\Upsilon(4S)\to B\bar B$~data recorded by the Belle II experiment at the SuperKEKB asymmetric-energy $e^+e^-$ collider and corresponding to 62.8 fb$^{-1}$ of integrated luminosity. Only a charged lepton (electon or muon) is reconstructed and the signal yield is determined from a fit to the lepton momentum distribution in the center-of-mass frame of the colliding beams. Averaging the result in the electron and muon channels, we find ${\cal B}(B\to X_c\ell\nu_\ell) = (9.75\pm 0.03(\text{stat})\pm 0.47(\text{sys}))\%$.