ε′/ε in the Standard Model

providing clear evidence for a non-zero ε/ε value. The theoretical status is instead more debated (see ref. [2] for a brief review). One of the problems that had to be faced during the past years has been that, while CP violation is born at a scale say O(MW ), the observables that enter in the game have to be estimated at a scale of O(MK) (see fig. 1). Changing the order of magnitude of the scales one considers, different physical effects appear and have to be disentangled. In this picture, the physics is described by a chain of different effective field theories, with different particle content, which match each other at the corresponding boundary (heavy threshold). This procedure permits to perform an explicit summation of large logarithms t ≡ ln (M/m), where M and m refer to any scale appearing in the evolution.