Search for the decay $B^0\to {\hat{I}}^3{\hat{I}}^3$ using Belle and Belle II data

Abstract

We report the result of a search for the rare decay $B^0\to {\hat{I}}^3{\hat{I}}^3$ using a combined dataset of $753\times 10^6$ $B\bar{B}$ pairs collected by the Belle experiment and $387\times 10^6$ $B\bar{B}$ pairs collected by the Belle II experiment from decays of the $\hat{\mathrm{I}}\yen (4S)$ resonance produced in $e^{+}{e}^{-}$ collisions. A simultaneous fit to the Belle and Belle II data sets yields $11.0_{-5.5}^{+6.5}$ signal events, corresponding to a 2.5$\ddot{I}ƒ$ significance. We determine the branching fraction $\mathcal{B}(B^0\to {\hat{I}}^3{\hat{I}}^3)=(3.7_{-1.8}^{+2.2}(\mathrm{stat})\pm 0.5(\mathrm{syst}))\times 10^{-8}$ and set a 90% credibility level upper limit of $\mathcal{B}(B^0\to {\hat{I}}^3{\hat{I}}^3)<6.4\times 10^{-8}$.

Published in PRD(L)