Angular analysis of $B^{+}\to \ddot{I}{}^{+}\ddot{I}{}^0$ decays reconstructed in 2019, 2020, and 2021 Belle II data

Abstract

We report on a Belle II measurement of the branching fraction ($\mathcal{B}$), longitudinal polarization fraction ($f_L$), and CP asymmetry (${\mathcal{A}}_{CP}$) of $B^{+}\to \ddot{I}{}^{+}\ddot{I}{}^0$ decays. We reconstruct $B^{+}\to \ddot{I}{}^{+}(\to \ddot{I}{€}^{+}\ddot{I}{€}^0(\to {\hat{I}}^3{\hat{I}}^3))\ddot{I}{}^0(\to \ddot{I}{€}^{+}\ddot{I}{€}^{-})$ decays in a sample of SuperKEKB electron-positron collisions collected by the Belle II experiment in 2019, 2020, and 2021 at the $\hat{I}\yen$(4S) resonance and corresponding to 190 fb${}^{-1}$ of integrated luminosity. We fit the distributions of the difference between expected and observed $B$ candidate energy, continuum-suppression discriminant, dipion masses, and decay angles of the selected samples, to determine a signal yield of $345\pm 31$ events. The signal yields are corrected for efficiencies determined from simulation and control data samples to obtain $\mathcal{B}(B^{+}\to \ddot{I}{}^{+}\ddot{I}{}^0)=[23.2_{-2.1}^{+2.2}(\mathrm{stat})\pm 2.7(\mathrm{syst})]\times 10^{-6}$, $f_L=0.943_{-0.033}^{+0.035}(\mathrm{stat})\pm 0.027(\mathrm{syst})$, and ${\mathcal{A}}_{CP}=-0.069\pm 0.068(\mathrm{stat})\pm 0.060(\mathrm{syst})$. The results agree with previous measurements. This is the first measurement of ${\mathcal{A}}_{CP}$ in $B^{+}\to \ddot{I}{}^{+}\ddot{I}{}^0$ decays reported by Belle II.