Observation of B+→K+ηγB+→K+ηγ

We report measurements of radiative B decays with KηγKηγ final states, using a data sample of 253 fb−1253 fb−1 recorded at the ϒ(4S)ϒ(4S) resonance with the Belle detector at the KEKB e+e−e+e− storage ring. We observe B+→K+ηγB+→K+ηγ for the first time with a branching fraction of (8.4±1.5(stat)−0.9+1.2(syst))×10−6 for MKη<2.4 GeV/c2MKη<2.4 GeV/c2, and find evidence of B0→K0ηγB0→K0ηγ. We also search for B→K3∗(1780)γ.