Exclusive b → sγ decays at Belle

We report results on two exclusive b -> s gamma decays, namely B-s(0) -> phi gamma and B-s(0) -> gamma gamma at Belle. For this study, we have used 121.4 fb(-1) of Upsilon(5S) data collected with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. Calculations within the Standard Model framework predict the B-s(0) -> phi gamma branching fraction to be in the range (3.9-4.3) x 10(-5) and the B-s(0) -> gamma gamma branching fraction to be in the range (0.18 - 2.45) x 10(-6). The B-s(0) -> phi gamma branching fraction is measured as (3.6 +/- 0.5 +/- 0.3 +/- 0.6) x 10(-5), where the first uncertainty is statistical, the second is systematic and the last one is due to the uncertainty in the fraction of B-s((*))(B) over bar ((*))(s) in b (b) over bar events. This result agrees with the theoretical predictions and other experimental results. We observe no statistically significant signal for B-s(0) -> gamma gamma and have thus set a 90% confidence-level upper limit on its branching fraction at 3.1 x 10(-6). This improves on the previous result by a factor of about 3 and is the most stringent limit till date.