Study of $B$ and $B_s$ Decays at Belle

We report results on the search for $B_s\to\eta^{\prime}\eta$ decay, and the searches for $B^0\to\textrm{invisible}$ and $B^0\to\textrm{invisible}+\gamma$ decays. The former result is based on a data sample of $121.4~\textrm{fb}^{-1}$ recorded at the $\Upsilon(5S)$ resonance while the later results are obtained from a $711~\textrm{fb}^{-1}$ of data sample collected at $\Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+e^-$ collider. We observe no significant signal for the decays and set upper limit on their branching fractions at 90\% confidence level of $\mathcal{B}(B_s\to\eta^{\prime}\eta)<7.1\times 10^{-5}$, $\mathcal{B}(B^0\to\textrm{invisible})<7.8\times 10^{-5}$ and $\mathcal{B}(B^0\to\textrm{invisible}+\gamma)<1.6\times 10^{-5}$.

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