Current Status of Indirect CP Violation in Neutral Kaon System

In the standard model (SM), the CP violation is introduced through a single phase in the CKM matrix. The neutral kaon system is one of the most precise channels to test how the SM theory describes the experiment data such as $\epsilon_K$ accurately. The indirect CP violation is parametrized into $\epsilon_{K}$, which can be calculated directly using lattice QCD. In this calculation, the largest uncertainty comes from two sources: one is $\hat{B}_K$ and the other is $V_{cb}$. We use the lattice results of $\hat{B}_K$ and exclusive $V_{cb}$ to calculate the theoretical estimate of $\epsilon_K$, which turns out to be $3.1\sigma$ away from its experimental value. Here, the error is evaluated using the standard error propagation method.