Observation of radiative B -> phi K gamma decays

Abstract

The radiative decay $B\to \varphi K\gamma$ is observed for the first time. The branching fraction for the charged $B^{-}\to \varphi K^{-}\gamma$ decay mode is measured to be $\mathcal{B}(B^{-}\to \varphi K^{-}\gamma )=(3.4\pm 0.9\pm 0.4)\times 10^{-6}$. The photon energy distribution for the $B^{-}\to \varphi K^{-}\gamma$ decay is presented. The signal for the neutral ${\bar{B}}^0\to \varphi {\bar{K}}^0\gamma$ decay mode is not statistically significant and an upper limit, $\mathcal{B}({\bar{B}}^0\to \varphi {\bar{K}}^0\gamma )<8.3\times 10^{-6}$ at $90$, is set. The analysis is based on a dataset of 90 fb${}^{-1}$ collected by the Belle experiment at the $e^{+}{e}^{-}$ asymmetric collider KEKB.

9 pages, 2 pages (7 eps files)