Observation of the decays $B^{+}\to \hat{I}{\pounds }_c(2455{)}^{++}\bar{\hat{I}}{ž}_c^{\prime -}$ and $B^0\to \hat{I}{\pounds }_c(2455{)}^0\bar{\hat{I}}{ž}_c^{\prime 0}$

Abstract

We report the first observation of the decays $B^{+}\to \hat{I}{\pounds }_c(2455{)}^{++}\bar{\hat{I}}{ž}_c^{\prime -}$ and $B^0\to \hat{I}{\pounds }_c(2455{)}^0\bar{\hat{I}}{ž}_c^{\prime 0}$, with significances of $6.4\ddot{I}ƒ$ and $5.3\ddot{I}ƒ$, respectively, including systematic uncertainties. This analysis is based on data samples containing $771.6\times 10^6$ $\hat{I}\yen (4S)$ decays collected with the Belle detector at the KEKB collider and $520.6\times 10^6$ $\hat{I}\yen (4S)$ decays collected with the Belle~II detector at the SuperKEKB collider. The branching fractions are measured to be $\mathcal{B}(B^{+}\to \hat{I}{\pounds }_c(2455{)}^{++}\bar{\hat{I}}{ž}_c^{\prime -})=(1.68\pm 0.31\pm 0.12_{-0.54}^{+1.49})\times 10^{-3}$ and $\mathcal{B}(B^0\to \hat{I}{\pounds }_c(2455{)}^0\bar{\hat{I}}{ž}_c^{\prime 0})=(1.28\pm 0.32\pm 0.10_{-0.21}^{+0.30})\times 10^{-3}$, where the first and second uncertainties are statistical and systematic, respectively, and the third arises from the uncertainties in the absolute branching fractions of $\bar{\hat{I}}{ž}_c^{-}$ and $\bar{\hat{I}}{ž}_c^0$ decays. This result represents the first observation of $B$-meson decays into a pair of charmed baryon-antibaryon states belonging to the same $SU(3)$ flavor sextet.