Measurement of the branching fraction and $CP$ asymmetry in $B^0\to \ddot{I}{€}^0\ddot{I}{€}^0$ decays, and an improved constraint on $\ddot{I}{•}_2$

Abstract

We measure the branching fraction and $CP$ violation asymmetry in the decay $B^0\to \ddot{I}{€}^0\ddot{I}{€}^0$, using a data sample of $752\times 10^6$ $B\bar{B}$ pairs collected at the $\hat{I}\yen (4S)$ resonance with the Belle detector at the KEKB $e^{+}{e}^{-}$ collider. The obtained branching fraction and direct $CP$ asymmetry are $\mathcal{B}(B\to \ddot{I}{€}^0\ddot{I}{€}^0)=[1.31\pm 0.19\text{(stat.)}\pm 0.19\text{(syst.)}]\times 10^{-6}$ and $A_{CP}=+0.14\pm 0.36\text{(stat.)}\pm 0.10\text{(syst.)},$ respectively. The signal significance, including the systematic uncertainty, is 6.4 standard deviations. We combine these results with Belle's earlier measurements of $B^0\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}$ and $B^{\pm }\to \ddot{I}{€}^{\pm }\ddot{I}{€}^0$ to exclude the $CP$-violating parameter $\ddot{I}{•}_2$ from the range $15.5^{\circ }<\ddot{I}{•}_2<75.0^{\circ }$ at 95\% confidence level.

8 pages, 2 figures