First observation of radiative B-0 -> phi K-0 gamma decays and measurements of their time-dependent CP violation

Abstract

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.