Measurement of branching fractions, CP asymmetry, and isospin asymmetry for $\mathbf{B}\to \ddot{\mathbf{I}}{\hat{\mathbf{I}}}^3$ decays using Belle and Belle II data

Abstract

We present measurements of $B^{+}\to \ddot{I}{}^{+}{\hat{I}}^3$ and $B^0\to \ddot{I}{}^0{\hat{I}}^3$ decays using a combined data sample of $772\times 10^6$ $B\overline{B}$ pairs collected by the Belle experiment and $387\times 10^6$ $B\overline{B}$ pairs collected by the Belle II experiment in $e^{+}{e}^{-}$ collisions at the $\hat{I}\yen (4S)$ resonance. After an optimized selection, a simultaneous fit to the Belle and Belle II data sets yields $114\pm 12$ $B^{+}\to \ddot{I}{}^{+}{\hat{I}}^3$ and $99\pm 12$ $B^0\to \ddot{I}{}^0{\hat{I}}^3$ decays. The measured branching fractions are $(13.1_{-1.9-1.2}^{+2.0+1.3})\times 10^{-7}$ and $(7.5\pm 1.3_{-0.8}^{+1.0})\times 10^{-7}$ for $B^{+}\to \ddot{I}{}^{+}{\hat{I}}^3$ and $B^0\to \ddot{I}{}^0{\hat{I}}^3$ decays, respectively, where the first uncertainty is statistical and the second is systematic. We also measure the isospin asymmetry $A_{\mathrm{I}}(B\to \ddot{I}{\hat{I}}^3)=(10.9_{-11.7-7.3}^{+11.2+7.8})\%$ and the direct CP asymmetry $A_{CP}(B^{+}\to \ddot{I}{}^{+}{\hat{I}}^3)=(-8.2\pm 15.2_{-1.2}^{+1.6})\%$.

12 pages, 4 figures