Strong Enhancement of ${ϵ}^{\mathrm{\prime }}\mathrm{/}ϵ$ Through Final State Interactions

We quantify the important effect of strong final state interactions in the weak $K\to 2\pi$ amplitudes, using the measured $\pi$–$\pi$ phase shifts with J=0 and $I=0,2$. The final rescattering of the two pions provides a strong enhancement of the $\mathrm{\Delta }I=1\mathrm{/}2$ amplitude, which so far has been neglected in the theoretical predictions of ${ϵ}^{\mathrm{\prime }}\mathrm{/}ϵ$. This correction increases the Standard Model prediction of ${ϵ}^{\mathrm{\prime }}\mathrm{/}ϵ$ to values in good agreement with the experimental measurements.