Measurement of the Branching Fraction and Photon Energy Moments of B->X_s gamma and A_{cp}(B->X_(s+d) gamma)

TL;DR

This paper measures the photon energy spectrum, branching fraction, and CP asymmetry in B -> X_s gamma decays using BaBar data, providing key parameters for testing the Standard Model and extracting heavy quark parameters.

Contribution

It presents the first measurement of photon energy moments and the partial branching fraction for B -> X_s gamma, along with a new determination of the CP asymmetry, using a large data sample.

Findings

Partial branching fraction: (3.67 +- 0.29(stat.) +- 0.34(sys.) +- 0.29(model)) x 10^-4

Photon energy moments measured and fitted to theoretical models

CP asymmetry measured as -0.110 +- 0.115(stat.) +- 0.017(sys.)

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 88.5 million e+e- -> Upsilon(4S) -> BBbar decays collected by the BaBar experiment at SLAC. The partial branching fraction, Delta B(B -> X_s gamma)=(3.67 +- 0.29(stat.) +- 0.34(sys.) +- 0.29(model)) times 10^-4, the first moment <E_gamma>=2.288 +- 0.025 +- 0.017 +- 0.015 GeV and the second moment <E_gamma^2> - <E_gamma>^2 =0.0328 +- 0.0040 +- 0.0023 +- 0.0036 GeV^2 are measured for the photon energy range 1.9 GeV < E_gamma < 2.7 GeV. They are also measured for narrower E_gamma ranges. The moments are then fit to recent theoretical calculations to extract the Heavy Quark Expansion parameters, m_b and mu_pi^2, and to extrapolate the partial branching fraction to E_gamma>1.6 GeV. In addition, the direct CP asymmetry A_CP(B -> X_(s+d) gamma) is measured to be -0.110 +- 0.115(stat.) +- 0.017(sys.).