**Matter-Antimatter Asymmetry in Neutral Kaons**

Zachary Polonsky

Graduate Research Assistant

University of Cincinnati

The parameter ε* _{K}* is an important measure of the imbalance between matter and antimatter in the neutral kaon system. In particular, εK provides a sensitive probe of new physics and plays a critical role in the global fit of the Cabibbo-Kobayashi-Maskawa matrix. As one of the first discovered sources of CP violation, it has been extensively measured in experiment to per-mil precision. The theoretical calculation of ε

*, however, has historically been plagued by large perturbative errors arising from charm-quark corrections. These errors were larger than the expected magnitude of higher-order electroweak corrections in perturbation theory, rendering these contributions irrelevant. Recently, it was discovered that a simple re-parameterization of the theory drastically reduces perturbative errors, making these higher-order electroweak calculations worthwhile. We present the two-loop electroweak contributions from the top quark to εK. In the traditional normalization of the weak Hamiltonian, this results in a -1% shift in the top quark contribution.*

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