Precision Measurement of the B to X_s \gamma Photon Energy Spectrum, Branching Fraction, and Direct CP Asymmetry A_{CP}(B to X_{s+d}\gamma

TL;DR

This paper measures the photon energy spectrum, branching fraction, and CP asymmetry in inclusive B meson decays to X_s gamma using a large data sample, providing precise experimental results relevant for testing the Standard Model.

Contribution

First measurement of the photon energy spectrum and CP asymmetry in B to X_s+d gamma decays with detailed unfolding of detector effects.

Findings

Branching fraction: (3.21 ± 0.33)×10^{-4} for E_gamma > 1.8 GeV

CP asymmetry: 0.057 ± 0.063

Photon spectrum unfolded to B meson rest frame

Abstract

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