Measurements of branching fractions and CP-violating charge asymmetries in multibody charmless $B$ decays reconstructed in 2019-2020 Belle II data

Abstract

We report on measurements of branching fractions ($\mathcal{B}$) and CP-violating charge asymmetries (${\mathcal{A}}_{\mathrm{CP}}$) of multibody charmless $B$ decays reconstructed by the Belle II experiment at the SuperKEKB electron-positron collider. We use a sample of collisions collected in 2019 and 2020 at the $\hat{I}\yen (4S)$ resonance and corresponding to $62.8$ fb${}^{-1}$ of integrated luminosity. We use simulation to determine optimized event selections. The $\hat{I}”E$ and $M_{\mathrm{bc}}$ distributions of the resulting samples are fit to determine signal yields of approximately 690, 840, and 380 decays for the channels $B^{+}\to K^{+}{K}^{-}{K}^{+}$, $B^{+}\to K^{+}\ddot{I}{€}^{-}\ddot{I}{€}^{+}$, and $B^0\to K^{+}\ddot{I}{€}^{-}\ddot{I}{€}^0$, respectively. These yields are corrected for efficiencies determined from simulation and control data samples to obtain $\mathcal{B}(B^{+}\to K^{+}{K}^{-}{K}^{+})=[35.8\pm 1.6(\mathrm{stat})\pm 1.4(\mathrm{syst})]\times 10^{-6}$, $\mathcal{B}(B^{+}\to K^{+}\ddot{I}{€}^{-}\ddot{I}{€}^{+})=[67.0\pm 3.3(\mathrm{stat})\pm 2.3(\mathrm{syst})]\times 10^{-6}$, $\mathcal{B}(B^0\to K^{+}\ddot{I}{€}^{-}\ddot{I}{€}^0)=[38.1\pm 3.5(\mathrm{stat})\pm 3.9(\mathrm{syst})]\times 10^{-6}$, ${\mathcal{A}}_{\mathrm{CP}}(B^{+}\to K^{+}{K}^{-}{K}^{+})=-0.103\pm 0.042(\mathrm{stat})\pm 0.020(\mathrm{syst})$, ${\mathcal{A}}_{\mathrm{CP}}(B^{+}\to K^{+}\ddot{I}{€}^{-}\ddot{I}{€}^{+})=-0.010\pm 0.050(\mathrm{stat})\pm 0.021(\mathrm{syst})$, and ${\mathcal{A}}_{\mathrm{CP}}(B^0\to K^{+}\ddot{I}{€}^{-}\ddot{I}{€}^0)=0.207\pm 0.088(\mathrm{stat})\pm 0.011(\mathrm{syst})$. Results are consistent with previous measurements and demonstrate detector performance comparable with the best Belle results.