Observation of Radiative B Meson Decays into Higher Kaonic Resonances

We have studied radiative B meson decays into higher kaonic resonances decaying into a two-body or three-body final state, using a data sample of 21.3 fb$^{-1}$ recorded at the $\Upsilon(4S)$ resonance with the Belle detector at KEKB. For the two-body final state, we extract the $B \to K_2^{*}(1430)^0 \gamma$ component from an analysis of the helicity angle distribution, and obtain ${\cal B}(B^0 \to K_2^{*}(1430)^0 \gamma) = (1.26\pm 0.66\pm 0.10)\times 10^{-5}$. For the three-body final state, we observe a $B \to K\pi\pi\gamma$ signal that is consistent with a mixture of $B \to K^* \pi \gamma$ and $B \to K \rho \gamma$. This is the first time that $B \to K^* \pi \gamma$ and $B \to K \rho \gamma$ have been observed separately. We find their branching fractions to be ${\cal B}(B \to K^* \pi \gamma; M_{K^*\pi}<2.0 GeV/c^2) = (5.6\pm 1.1\pm 0.9)\times 10^{-5}$ and ${\cal B}(B \to K \rho \gamma; M_{K\rho} < 2.0 GeV/c^2) = (6.5\pm 1.7^{+1.1}_{1.2})\times 10^{-5}$, respectively.