Paper detail

Measurement of B(B-->X_s γ), the B-->X_s γ photon energy spectrum, and the direct CP asymmetry in B-->X_{s+d} γ decays

The photon spectrum in B --> X_s γ decay, where X_s is any strange hadronic state, is studied using a data sample of (382.8\pm 4.2) \times 10^6 e^+ e^- --> Υ(4S) --> BBbar events collected by the BABAR experiment at the PEP-II collider. The spectrum is used to measure the branching fraction B(B --> X_s γ) = (3.21 \pm 0.15 \pm 0.29 \pm 0.08)\times 10^{-4} and the first, second, and third moments <E_γ> = 2.267 \pm 0.019 \pm 0.032 \pm 0.003 GeV,, <(E_γ- <E_γ>)^2> = 0.0484 \pm 0.0053 \pm 0.0077 \pm 0.0005 GeV^2, and <(E_γ- <E_γ>)^3> = -0.0048 \pm 0.0011 \pm 0.0011 \pm 0.0004 GeV^3, for the range E_γ> 1.8 GeV, where E_γ is the photon energy in the B-meson rest frame. Results are also presented for narrower E_γ ranges. In addition, the direct CP asymmetry A_{CP}(B --> X_{s+d} γ) is measured to be 0.057 \pm 0.063. The spectrum itself is also unfolded to the B-meson rest frame; that is the frame in which theoretical predictions for its shape are made.