Observation of Large CP Violation in the Neutral B Meson System

TL;DR

This paper reports the first observation of large CP violation in the neutral B meson system, measuring sin 2phi_1 with high significance using data from the Belle detector.

Contribution

It provides the first experimental evidence of CP violation in the neutral B meson system, confirming a key prediction of the Standard Model.

Findings

Measured sin 2phi_1 = 0.99 ± 0.14 (stat) ± 0.06 (syst)

Observed CP violation with high statistical significance

Supports the Standard Model's description of CP violation

Abstract

We present a measurement of the Standard Model CP violation parameter sin 2phi_1 based on a 29.1 fb^{-1} data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. One neutral B meson is fully reconstructed as a J/psi Ks, psi(2S) Ks, chi_c1 Ks, eta_c Ks, J/psi K_L or J/psi K^{*0} decay and the flavor of the accompanying B meson is identified from its decay products. From the asymmetry in the distribution of the time intervals between the two B meson decay points, we determine sin 2phi_1 = 0.99 +- 0.14(stat) +- 0.06(syst). We conclude that we have observed CP violation in the neutral B meson system.