Speaker
Description
$K\to\pi\pi$ decay amplitudes and the measure of its direct CP violation, $\varepsilon'$, are expected to play a key role in searching for new physics beyond the Standard Model because of the highly suppressed value of $\varepsilon'$. While, NA48 and KTeV experiments gave a well-resolved result, Re$(\varepsilon'/\varepsilon) = 16.6(2.3)\times10^{-4}$, there have been tremendous obstacles to reaching this level of precision in theoretical calculations. One lattice group, the RBC and UKQCD collaborations, is now overcoming these difficulties after a few decades of their efforts and further improving the precision. In this talk, we will mainly discuss the past challenges, current status, remaining challenges and future prospects of lattice QCD calculations of $\varepsilon'$. Since understanding two-pion system in a finite box is essential for lattice calculation of $K\to\pi\pi$ decay, $\pi\pi$ scattering will also be discussed.
