Abstract
The parameter ε_{K} describes CP violation in the neutral kaon system and is one of the most sensitive probes of new physics. The large uncertainties related to the charm-quark contribution to ε_{K} have so far prevented a reliable standard-model prediction. We show that Cabibbo-Kobayashi-Maskawa unitarity enforces a unique form of the |ΔS=2| weak effective Lagrangian in which the short-distance theory uncertainty of the imaginary part is dramatically reduced. The uncertainty related to the charm-quark contribution is now at the percent level. We present the updated standard-model prediction ε_{K}=2.16(6)(8)(15)×10^{-3}, where the errors in parentheses correspond to QCD short-distance, long-distance, and parametric uncertainties, respectively.
Highlights
Introduction.—CP violation in the neutral kaon system, parametrized by εK, is one of the most sensitive precision probes of new physics
The large uncertainties related to the charm-quark contribution to εK have so far prevented a reliable standard-model prediction
We show that Cabibbo-Kobayashi-Maskawa unitarity enforces a unique form of the jΔS 1⁄4 2j weak effective Lagrangian in which the short-distance theory uncertainty of the imaginary part is dramatically reduced
Summary
Þ and f1 1⁄4 jλuj þ ..., where the ellipsis denotes real terms that are suppressed by powers of the Wolfenstein parameter λ. The splitting of the imaginary part among f2 and f3 is not unique. The choice f2 1⁄4 2ReðλtλÃuÞ and f3 1⁄4 jλuj is convenient in the particle data group (PDG) phase convention.
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