Measurement of the branching fraction for $B^0\to \ddot{I}{€}^0\ddot{I}{€}^0$ decays reconstructed in 2019-2020 Belle II data

Abstract

We report the first reconstruction of the $B^0\to \ddot{I}{€}^0\ddot{I}{€}^0$ decay mode at Belle II using samples of 2019 and 2020 data that correspond to 62.8 fb${}^{-1}$ of integrated luminosity. We find $14.0_{-5.6}^{+6.8}$ signal decays, corresponding to a significance of 3.4 standard deviations and determine a branching ratio of $\mathcal{B}(B^0\to \ddot{I}{€}^0\ddot{I}{€}^0)=[0.98_{-0.39}^{+0.48}\pm 0.27]\times 10^{-6}$. The results agree with previous determinations and contribute important information to an early assessment of detector performance and Belle II's potential for future determinations of $\hat{I}\pm /\ddot{I}{•}_2$ using $B\to \ddot{I}€\ddot{I}€$ modes.

19 pages, 4 figures. Supporting material for Moriond 2021 conference