Direct CP Violating Asymmetry in B0 -> K+pi- Decays

TL;DR

This paper reports the first significant observation of direct CP violation in B0 -> K+pi- decays, measuring an asymmetry of approximately -13% with high statistical significance.

Contribution

The study provides the first measurement of direct CP violation in B0 -> K+pi- decays using a large data sample from BaBar, confirming the presence of CP asymmetry.

Findings

Measured CP asymmetry of -0.133 with statistical and systematic uncertainties.

Observed a 4.2 sigma significance for direct CP violation.

Collected 227 million B meson decays at BaBar.

Abstract

We present a measurement of the direct CP violating asymmetry in the decay B0 -> K+pi- using 227 x 10^6 Y(4S) -> BBbar decays collected with the BaBar detector at the PEP-II asymmetric-energy e+e- collider at SLAC, we observe a total signal yield of n(K-pi+) + n(K+pi-) = 1606 +- 51 decays and measure the asymmetry [n(K-pi+)-n(K+pi-)]/[n(K-p+-)+n(K+pi-)] = -0.133+-0.030 (stat) +- 0.009 (syst). The probability of observing such an asymmetry in the absence of direct CP violation is 1.3 x 10^-5, corresponding to 4.2 standard deviations.