We report the first observation of the radiative decay B-0 -> phi K-0 gamma using a data sample of 772 x 10(6) B (B) over bar pairs collected at the Gamma(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. We observe a signal of 37 +/- 8 events with a significance of 5.4 standard deviations including systematic uncertainties. The measured branching fraction is B(B-0 ->phi K-0 gamma) = (2.74 +/- 0.60 +/- 0.32) x 10(-6), where the uncertainties are statistical and systematic, respectively. We also report the first measurements of time-dependent CP-violation parameters: S-phi K0s gamma = +0.74(-1.05)(+0.72)(stat)(-0.024)(+0.10)(syst) and A phi(0)(Ks)gamma = +0.35 +/- 0.58(stat)(-0.10)(+0.23)(syst). Furthermore, we measure B(B+ -> phi K+gamma) = (2.48 +/- 0.30 +/- 0.24) x 10(-6), A(CP) = -0.03 +/- 0.11 +/- 0.08, and find that the signal is concentrated in the M-phi K mass region near threshold.
Robert Dalang, Carsten Hao Ye Chong
Mohamed Farhat, Davide Bernardo Preso, Armand Baptiste Sieber
Olivier Schneider, Yiming Li, Mingkui Wang, Chao Wang, Tagir Aushev, Sun Hee Kim, Donghyun Kim