Measurements of Direct CP Asymmetries in B to X_s gamma decays using Sum of Exclusive Decays

TL;DR

This paper reports a precise measurement of direct CP asymmetry in B to X_s gamma decays, confirming Standard Model predictions and providing new insights into Wilson coefficients through analysis of decay mode differences.

Contribution

First measurement of the isospin difference in CP asymmetry in B to X_s gamma decays, improving the world average and constraining Wilson coefficients.

Findings

Measured A_CP = +1.7% with uncertainties, consistent with Standard Model.

First measurement of Delta A_CP = +5.0%, indicating differences between charged and neutral B decays.

Provided confidence intervals on the imaginary part of Wilson coefficient ratios.

Abstract

We measure the direct CP violation asymmetry, A_CP, in B to X_s gamma and the isospin difference of the asymmetry, Delta A_CP, using 429 fb^-1 of data collected at Upsilon(4S) resonance with the BaBar detector at the PEP-II asymmetric-energy e+e- storage rings operating at the SLAC National Accelerator Laboratory. B mesons are reconstructed from 10 charged B final states and 6 neutral B final states. We find A_CP = +(1.7 +- 1.9 +- 1.0)%, which is in agreement with the Standard Model prediction and provides an improvement on the world average. Moreover, we report the first measurement of the difference between A_CP for charged and neutral decay modes, Delta A_CP = +(5.0 +- 3.9 +- 1.5)%. Using the value of Delta A_CP, we also provide 68% and 90% confidence intervals on the imaginary part of the ratio of the Wilson coefficients corresponding to the chromo-magnetic dipole and the electromagnetic dipole transitions.