Search for B s 0 → γ γ and a measurement of the branching fraction for B s 0 → φ γ

Abstract

We search for the decay Bs0→γγ and measure the branching fraction for Bs0→φγ using 121.4 fb-1 of data collected at the (5S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. The Bs0→φγ branching fraction is measured to be (3.6±0.5(stat)±0.3(syst)±0.6(fs))×10-5, where fs is the fraction of Bs(∗)B¯s(∗) in bb¯ 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 Bs0→γγ and set a 90% confidence-level upper limit on its branching fraction at 3.1×10-6. This constitutes a significant improvement over the previous result.