Precision Measurement of the B→Xsγ Photon Energy Spectrum, Branching Fraction, and Direct CP Asymmetry ACP(B→Xs+dγ)

Abstract

The photon spectrum in the inclusive electromagnetic radiative decays of the B meson, B → X s γ plus B → X d γ , is studied using a data sample of ( 382.8 ± 4.2 ) × 10 6 Υ ( 4 S ) → B ¯¯¯ B decays collected by the BABAR experiment at SLAC. The spectrum is used to extract the branching fraction B ( B → X s γ ) = ( 3.21 ± 0.33 ) × 10 − 4 for E γ > 1.8 GeV and the direct C P asymmetry A C P ( B → X s + d γ ) = 0.057 ± 0.063 . The effects of detector resolution and Doppler smearing are unfolded to measure the photon energy spectrum in the B meson rest frame.