Search for $B_{s}^{0}rightarrowgammagamma$ and a measurement of the branching fraction for $B_{s}^{0}rightarrowphigamma$

We search for the decay $B_{s}^{0}rightarrowgammagamma$ and measure the branching fraction for $B_{s}^{0}rightarrowphigamma$ using 121.4~$textrm{fb}^{-1}$ of data collected at the $Upsilon(mathrm{5}S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. The $B_{s}^{0}rightarrowphigamma$ branching fraction is measured to be $(3.6 pm 0.5 (mathrm{stat.}) pm 0.3 (mathrm{syst.}) pm 0.6 (f_{s})) times 10^{-5}$, where $f_{s}$ is the fraction of $B_{s}^{(*)}bar{B}_{s}^{(*)}$ in $bbar{b}$ events. Our result is in good agreement with the theoretical predictions as well as with a recent measurement from LHCb. We observe no statistically significant signal for the decay $B_{s}^{0}rightarrowgammagamma$ and set a $90%$ confidence-level upper limit on its branching fraction at $ 3.1 times 10^{-6}$. This constitutes a significant improvement over the previous result.