Radiative B Meson Decays into K pi gamma and K pi pi gamma Final States

We report observations of radiative B meson decays into the K+pi-gamma and K+pi-pi+gamma final states. In the B0 -> K+pi-gamma channel, we present evidence for decays via an intermediate tensor meson state with a branching fraction of B(B0 -> K2*(1430)0gamma) = (1.3 +-0.5 (stat.) +- 0.1 (syst.)) X 10^{-5}. We measure the branching fraction B(B+ -> K+pi-pi+gamma) = (2.4 +- 0.5 (stat.) +0.4-0.2 (syst.)) X 10^{-5}, in which the B+ -> K*0pi+gamma and B+ -> K+rho0gamma channels dominate. The analysis is based on a dataset of 29.4 /fb recorded by the Belle experiment at the KEKB collider.