Search for the decay $B_s^0\to {\pi }^0{\pi }^0$ at Belle

We report the results of the first search for the decay $B_s^0\to {\pi }^0{\pi }^0$ using $121.4\mathrm{f}{\mathrm{b}}^{-1}$ of data collected at the $\mathrm{{\rm Y}}(5\mathrm{S})$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We observe no signal and set a 90% confidence level upper limit of $7.7\times {10}^{-6}$ on the $B_s^0\to {\pi }^0{\pi }^0$ decay branching fraction.