Measurement of the time-integrated mixing probability $\ddot{I}{‡}_d$ with a semileptonic double-tagging strategy and $34.6{\mathrm{fb}}^{-1}$ of Belle II collision data

Abstract

We present the first measurement of the time-integrated mixing probability $\ddot{I}{‡}_d$ using Belle II data collected at a center-of-mass (CM) energy of 10.58 GeV, corresponding to the mass of the $\hat{I}\yen$(4S) resonance, with an integrated luminosity of $34.6{\mathrm{fb}}^{-1}$ at the SuperKEKB $e^{+}{e}^{-}$ collider. We reconstruct pairs of B mesons both of which decay to semileptonic final states. Using a novel methodology, we measure $\ddot{I}{‡}_d=0.187\pm 0.010\text{ (stat.)}\pm 0.019\text{ (syst.)}$, which is compatible with existing indirect and direct determinations.

19 pages, 10 figures, conference note Moriond 2021