Search for $B$ decays to final states with the ${\eta }_c$ meson

We report a search for $B$ decays to selected final states with the ${\eta }_c$ meson: $B^{\pm }\to K^{\pm }{\eta }_c{\pi }^{+}{\pi }^{-}$, $B^{\pm }\to K^{\pm }{\eta }_c\omega$, $B^{\pm }\to K^{\pm }{\eta }_c\eta$ and $B^{\pm }\to K^{\pm }{\eta }_c{\pi }^0$. The analysis is based on $772\times {10}^6$ $B\bar{B}$ pairs collected at the $\mathrm{{\rm Y}}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We set 90% confidence level upper limits on the branching fractions of the studied $B$ decay modes, independent of intermediate resonances, in the range $(0.6-5.3)\times {10}^{-4}$. We also search for molecular-state candidates in the $D^0{\bar{D}}^{\ast 0}-{\bar{D}}^0{D}^{\ast 0}$, $D^0{\bar{D}}^0+{\bar{D}}^0{D}^0$ and $D^{\ast 0}{\bar{D}}^{\ast 0}+{\bar{D}}^{\ast 0}{D}^{\ast 0}$ combinations, neutral partners of the $Z(3900{)}^{\pm }$ and $Z(4020{)}^{\pm }$, and a poorly understood state $X(3915)$ as possible intermediate states in the decay chain, and set 90% confidence level upper limits on the product of branching fractions to the mentioned intermediate states and decay branching fractions of these states in the range $(0.6-6.9)\times {10}^{-5}$.