Measurement of the Branching Fraction and Photon Energy Moments of B→Xsγ and CP(B→Xs+dγ)

Abstract

The photon spectrum in B → X s γ decay, where X s is any strange hadronic state, is studied using a data sample of 88.5 × 10 6 e + e − → Υ ( 4 S ) → B ¯¯¯ B decays collected by the BABAR experiment at the Stanford Linear Accelerator Center. The partial branching fraction, Δ B ( B → X s γ ) = ( 3.67 ± 0.29 ( stat ) ± 0.34 ( syst ) ± 0.29 ( model ) ) × 10 − 4 , the first moment ⟨ E γ ⟩ = 2.288 ± 0.025 ± 0.017 ± 0.015 GeV , and the second moment ⟨ E 2 γ ⟩ = 0.0328 ± 0.0040 ± 0.0023 ± 0.0036 GeV 2 are measured for the photon energy range 1.9 GeV < E γ < 2.7 GeV . They are also measured for narrower E γ ranges. The moments are then fit to recent theoretical calculations to extract the heavy quark expansion parameters m b and μ 2 π and to extrapolate the partial branching fraction to E γ > 1.6 GeV . In addition, the direct C P asymmetry A C P ( B → X s + d γ ) is measured to be − 0.110 ± 0.115 ( stat ) ± 0.017 ( syst ) .