Measurement of the B→Xsγ branching fraction and photon energy spectrum using the recoil method

Abstract

We present a measurement of the branching fraction and photon-energy spectrum for the decay B → X s γ using data from the BABAR experiment. The data sample corresponds to an integrated luminosity of 210 fb − 1 , from which approximately 680 000 B ¯¯¯ B events are tagged by a fully reconstructed hadronic decay of one of the B mesons. In the decay of the second B meson, an isolated high-energy photon is identified. We measure B ( B → X s γ ) = ( 3.66 ± 0.85 stat ± 0.60 syst ) × 10 − 4 for photon energies E γ above 1.9 GeV in the B rest frame. From the measured spectrum we calculate the first and second moments for different minimum photon energies, which are used to extract the heavy-quark parameters m b and μ 2 π . In addition, measurements of the direct C P asymmetry and isospin asymmetry are presented.