Measurement of the $B^0$ lifetime and flavor-oscillation frequency using hadronic decays reconstructed in 2019-2021 Belle II data

Abstract

We measure the $B^0$ lifetime and flavor-oscillation frequency using $B^0\to D^{(\ast )-}\ddot{I}{€}^{+}$ decays collected by the Belle II experiment in asymmetric-energy $e^{+}{e}^{-}$ collisions produced by the SuperKEKB collider operating at the $\hat{I}\yen (4S)$ resonance. We fit the decay-time distribution of signal decays, where the initial flavor is determined by identifying the flavor of the other $B$ meson in the event. The results, based on $33000$ signal decays reconstructed in a data sample corresponding to $190{\text{fb}}^{-1}$, are $\ddot{I}{„}_{B^0}=1.499\pm 0.013\pm 0.008\text{ps}$, $\hat{I}”m_d=0.516\pm 0.008\pm 0.005{\text{ps}}^{-1}$, where the first uncertainties are statistical and the second are systematic. These results are consistent with the world-average values.