epsilon'/epsilon and Chiral Dynamics

Abstract

The long-distance contributions to $K\to 2\pi$ amplitudes can be pinned down, using well established Chiral Perturbation Theory techniques. The strong S--wave rescattering of the two final pions generates sizeable chiral loop corrections, which have an important impact on the direct CP violation ratio epsilon'/epsilon. Including all large logarithmic corrections, both at short and long distances, the Standard Model Prediction for this observable is found to be Re(epsilon'/epsilon) = (1.7\pm 0.9) 10^{-3}, in good agreement with the most recent experimental measurements. A better estimate of the strange quark mass could reduce the theoretical uncertainty to 30%.