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

TL;DR

This paper measures the photon energy spectrum, branching fraction, and CP asymmetry in B --> X_s gamma decays using BABAR data, providing detailed moments and unfolded spectrum for theoretical comparison.

Contribution

It presents the first measurement of the photon energy moments and the unfolded spectrum in B --> X_s gamma decays, along with the branching fraction and CP asymmetry.

Findings

Branching fraction B(B --> X_s gamma) = (3.21 ± 0.15 ± 0.29 ± 0.08)×10^{-4}

Photon energy moments <E_gamma>, <(E_gamma - <E_gamma>)^2>, <(E_gamma - <E_gamma>)^3> measured

CP asymmetry A_CP = 0.057 ± 0.063

Abstract

The photon spectrum in B --> X_s {\gamma} 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^- --> \Upsilon(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 \gamma) = (3.21 \pm 0.15 \pm 0.29 \pm 0.08)\times 10^{-4} and the first, second, and third moments <E_\gamma> = 2.267 \pm 0.019 \pm 0.032 \pm 0.003 GeV,, <(E_\gamma - <E_\gamma>)^2> = 0.0484 \pm 0.0053 \pm 0.0077 \pm 0.0005 GeV^2, and <(E_\gamma - <E_\gamma>)^3> = -0.0048 \pm 0.0011 \pm 0.0011 \pm 0.0004 GeV^3, for the range E_\gamma > 1.8 GeV, where E_{\gamma} is the photon energy in the B-meson rest frame. Results are also presented for narrower E_{\gamma} ranges. In addition, the direct CP asymmetry A_{CP}(B --> X_{s+d} \gamma) 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.