Strong Enhancement of $ε'/ε$ Through Final State Interactions

Abstract

We quantify the important effect of strong final state interactions in the weak $K\to2π$ amplitudes, using the measured $π$--$π$ phase shifts with J=0 and $I=0,2$. The final rescattering of the two pions provides a strong enhancement of the $ΔI =1/2$ amplitude, which so far has been neglected in the theoretical predictions of $ε'/ε$. This correction increases the Standard Model prediction of $ε'/ε$ to values in good agreement with the experimental measurements.