Search for $B_{s}^{0}\rightarrow\gamma\gamma$ and a measurement of the branching fraction for $B_{s}^{0}\rightarrow\phi\gamma$

TL;DR

This study measures the branching fraction of $B_{s}^{0} ightarrow ext{phi} ext{gamma}$ and searches for the rare decay $B_{s}^{0} ightarrow ext{gamma} ext{gamma}$ using Belle data, providing results consistent with theory and setting new upper limits.

Contribution

First measurement of the $B_{s}^{0} ightarrow ext{phi} ext{gamma}$ branching fraction at Belle and improved upper limit for $B_{s}^{0} ightarrow ext{gamma} ext{gamma}$ decay.

Findings

Measured $B_{s}^{0} ightarrow ext{phi} ext{gamma}$ branching fraction as $(3.6 imes 10^{-5})$ with uncertainties.

No significant signal for $B_{s}^{0} ightarrow ext{gamma} ext{gamma}$ decay; set upper limit at $3.1 imes 10^{-6}$.

Results agree with theoretical predictions and LHCb measurements.

Abstract

We search for the decay $B_{s}^{0}\rightarrow\gamma\gamma$ and measure the branching fraction for $B_{s}^{0}\rightarrow\phi\gamma$ 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 $B_{s}^{0}\rightarrow\phi\gamma$ 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 $b\bar{b}$ 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 $B_{s}^{0}\rightarrow\gamma\gamma$ 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.