Measurement of the B --> K^* gamma Branching Fractions and Asymmetries

Abstract

We report measurements of the radiative decay B --> K^*γ. The analysis is based on a data sample containing 85.0*10^6 B meson pairs collected by the Belle detector at the KEKB storage ring. We measure branching fractions of Br(B^0 --> K^{*0}γ) = (4.01 \pm 0.21 \pm 0.17)*10^{-5} and Br(B^+ --> K^{*+}γ) = (4.25 \pm 0.31 \pm 0.24)*10^{-5}, where the first and second errors are statistical and systematic, respectively. The isospin asymmetry between B^0 and B^+ decay widths is measured to be Δ_{0+} = +0.012 \pm 0.044 \pm 0.026. We search for a partial rate asymmetry between CP conjugate modes, and find A_{cp}(B --> K^*γ) = =0.015 \pm 0.044 \pm 0.012.