Precision Measurement of the $B\ensuremath{\rightarrow}{X}_{s}\ensuremath{\gamma}$ Photon Energy Spectrum, Branching Fraction, and Direct $CP$ Asymmetry ${A}_{CP}(B\ensuremath{\rightarrow}{X}_{s+d}\ensuremath{\gamma})$

Precision Measurement of the $B \to X_{s} γ$ Photon Energy Spectrum, Branching Fraction, and Direct $C P$ Asymmetry $A_{C P} (B \to X_{s + d} γ)$

J. P. Lees et al. (BABAR Collaboration)

Phys. Rev. Lett. 109, 191801 – Published 9 November 2012

Abstract

The photon spectrum in the inclusive electromagnetic radiative decays of the $B$ meson, $B \to X_{s} γ$ plus $B \to X_{d} γ$ , is studied using a data sample of $(382.8 \pm 4.2) \times 10^{6} Υ (4 S) \to B \bar{B}$ decays collected by the BABAR experiment at SLAC. The spectrum is used to extract the branching fraction $B (B \to X_{s} γ) = (3.21 \pm 0.33) \times 10^{- 4}$ for $E_{γ} > 1.8 GeV$ and the direct $C P$ asymmetry $A_{C P} (B \to X_{s + d} γ) = 0.057 \pm 0.063$ . The effects of detector resolution and Doppler smearing are unfolded to measure the photon energy spectrum in the $B$ meson rest frame.