PNNL

Abstract

We report the first observation of the radiative decay B°? fK°? using a data sample of 772 × 106 BB¯ pairs collected at the (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°? fK°?) = (2.74±0.60±0.32)×10-6 , where the uncertainties are statistical and systematic, respectively. We also report the first measurements of time-dependent CP violation parameters: S *K0 S = +0.74+0.72 -1.05(stat)+0.10 -0.24(syst) and A *K0 S = +0.35 ± 0.58(stat)+0.23 -0.10(syst). Furthermore, we measure B(B+ ! K+ ) = (2.48 ± 0.30 ± 0.24) × 10-6, ACP = -0.03 ± 0.11 ± 0.08 and find that the signal is concentrated in the M K mass region near threshold.