Measurement of the branching fraction and $CP$ asymmetry of $B^0\to \ddot{I}{€}^0\ddot{I}{€}^0$ decays using $198\times 10^6$ $B\overline{B}$ pairs in Belle II data

Abstract

We report measurements of the branching fraction and $CP$ asymmetry in $B^0\to \ddot{I}{€}^0\ddot{I}{€}^0$ decays reconstructed at Belle II in an electron-positron collision sample containing $198\times 10^6$ $B\overline{B}$ pairs. We measure a branching fraction $\mathcal{B}(\Bpipi) = (1.38 \pm 0.27 \pm 0.22) \times 10^{-6}$ and a $CP$ asymmetry $\Acp(\Bpipi) = 0.14 \pm 0.46 \pm 0.07$, where the first uncertainty is statistical and the second is systematic.