Measurement of the Direct CP Asymmetry in b -> s gamma Decays

TL;DR

This paper reports a measurement of the direct CP asymmetry in b -> s gamma decays using data from the BaBar detector, finding results consistent with the Standard Model and constraining possible new physics effects.

Contribution

First measurement of the direct CP asymmetry in inclusive b -> s gamma decays using a large data sample from BaBar, providing limits on new physics contributions.

Findings

Measured asymmetry A_CP = 0.025 ± 0.050(stat) ± 0.015(syst)

Allowed asymmetry range at 90% CL: -0.06 to +0.11

Results consistent with Standard Model predictions

Abstract

We describe a measurement of the direct CP asymmetry between inclusive b -> s gamma and bbar -> sbar gamma decays. This asymmetry is expected to be less than 0.01 in the Standard Model, but could be enhanced up to about 0.10 by new physics contributions. We use a sample of 89 million BB pairs recorded with the BaBar detector at PEP-II, from which we reconstruct a set of 12 exclusive b -> s gamma final states containing one charged or neutral kaon and one to three pions. We measure an asymmetry of A_CP(b -> s gamma) = 0.025 +/- 0.050(stat.) +/- 0.015(syst.), corresponding to an allowed range of -0.06 < A_CP(b -> s gamma) < +0.11 at 90% confidence level.