Measurement of the B --> X_s gamma Branching Fraction and Photon Energy Spectrum using the Recoil Method

TL;DR

This paper reports a precise measurement of the B --> X_s gamma decay rate and photon energy spectrum using the recoil method, providing insights into heavy-quark parameters and CP asymmetries.

Contribution

It introduces a novel measurement of the B --> X_s gamma branching fraction and photon spectrum using the recoil method with a large data sample.

Findings

Branching fraction BR(B --> X_s gamma) = (3.66 +- 0.85_{stat} +- 0.60_{syst}) x 10^{-4}

First and second moments of the photon energy spectrum calculated for different energy thresholds

Measurements of direct CP asymmetry and isospin asymmetry

Abstract

We present a measurement of the branching fraction and photon energy spectrum for the decay B --> X_s gamma using data from the BaBar experiment. The data sample corresponds to an integrated luminosity of 210 fb^{-1}, from which approximately 680 000 BB events are tagged by a fully reconstructed hadronic decay of one of the B mesons. In the decay of the second B meson, an isolated high--energy photon is identified. We measure BR(B --> X_s gamma) = (3.66 +- 0.85_{stat} +- 0.60_{syst}) x 10^{-4} for photon energies E_gamma above 1.9 GeV in the B rest frame. From the measured spectrum we calculate the first and second moments for different minimum photon energies, which are used to extract the heavy-quark parameters m_b and mu_{pi}^2. In addition, measurements of the direct CP asymmetry and isospin asymmetry are presented.