Status of $\epsilon'$ /$\epsilon$ in the Standard Model

A recent lattice prediction of $\epsilon'$ /$\epsilon$, with a 2.1 σ deviation from the experimental value, has triggered several studies of possible contributions from physics beyond the Standard Model. We have recently updated the SM prediction, including all known short-distance and long-distance contributions, our result $^{1}$Re($\epsilon'$ /$\epsilon$) = (15±7)·10$^{−4}$ is in complete agreement with the experimental measurement. In addition, we emphasize on the importance of the long-distance re-scattering of the final pions in $K$ → $\pi\pi$ for a correct prediction of $\epsilon'$ /$\epsilon$.