Matter-Antimatter Asymmetry in Neutral Kaons

  • Sept. 30, 2021, 2:30 pm US/Central
  • Zachary Polonsky, U. Cincinnati

The parameter $\epsilon_K$ is an important measure of the imbalance between matter and antimatter in the neutral kaon ($K^0$ and $\bar{K}^0$) system. In particular, $\epsilon_K$ 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 $\epsilon_K$, 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 worth-while. We present the two-loop electroweak contributions from the top quark to $\epsilon_K$. In the traditional normalization of the weak Hamiltonian, this results in a -1\% shift in the top quark contribution.