Measurement of the CP Asymmetry in B -> X_s gamma

TL;DR

This paper measures the CP asymmetry in B -> X_s gamma decays to test for new physics beyond the Standard Model, using a novel reconstruction technique to reduce background contamination.

Contribution

It introduces a pseudo-reconstruction method for measuring CP asymmetry in B decays, minimizing contamination from b->d gamma processes.

Findings

Measured ACP = 0.002 ± 0.050 (stat) ± 0.030 (syst)

Analysis based on 140 fb^-1 data sample at Belle detector

Results consistent with Standard Model predictions

Abstract

Direct CP violation in the b->sgamma process is a sensitive probe of physics beyond the Standard Model. We report a measurement of the CP asymmetry in B -> X_s gamma, where the hadronic recoil system Xs is reconstructed using a pseudo-reconstruction technique. In this approach there is negligible contamination from b->dgamma decays, which are expected to have a much larger CP asymmetry. We find ACP = 0.002 +- 0.050(stat.) +- 0.030(syst.) for B -> Xs gamma events having recoil mass smaller than 2.1 GeV/c^2. The analysis is based on a data sample of 140 /fb recorded at the Upsilon(4S) resonance with the Belle detector at the KEKB e+e- storage ring.