Precision measurement of the B→X sγ photon energy spectrum, branching fraction, and direct CP asymmetry A CP(B→ X s+dγ)

The photon spectrum in the inclusive electromagnetic radiative decays of the B meson, B→X sγ plus B→X dγ, is studied using a data sample of (382.8±4.2)×106Υ(4S) →BB̄ decays collected by the BABAR experiment at SLAC. The spectrum is used to extract the branching fraction B(B→X sγ)=(3. 21±0.33)×10 -4 for E γ>1.8GeV and the direct CP asymmetry A CP(B→X s+dγ)=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. © 2012 American Physical Society.