Strong final state interaction (FSI) effects can play a central role in the Standard Model prediction of weak K → 2π matrix elements. Here, I discuss how FSI's affect the direct CP violation parameter ε ′ /ε by solving the Omnès problem for the necessary K → 2π amplitudes. The main results of this analysis have been reported in a previous paper 1 and are further discussed in Refs. 2,3. The resu...

We discuss a new estimate of ε/ε in the kaon system. The present approach is based on the evaluation of the hadronic matrix elements of the ∆S = 1 effective quark lagrangian by means of the chiral quark model, with the inclusion of meson one-loop renormalization and NLO Wilson coefficients. The estimate here reviewed is fully consistent with the ∆I = 1/2 selection rule in K → ππ decays, which i...

We present a recent analysis of ε′/ε in the 1/Nc expansion. We show that the 1/Nc corrections to the matrix element of Q6 are large and positive, indicating a ∆I = 1/2 enhancement similar to the one of Q1 and Q2 which dominate the CP conserving amplitude. This enhances the CP ratio and can bring the standard model prediction close to the measured value for central values of the parameters. Seve...

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 sca...

“I’ve never touched the hard stuff, only smoked grass a few times with the boys to be polite, and that’s all, though ten is the age when the big guys come around teaching you all sorts to things. But happiness doesn’t mean much to me, I still think life is better. Happiness is a mean son of a bitch and needs to be put in his place. Him and me aren’t on the same team, and I’m cutting him dead. I...

CP violation in the neutral kaon system is known to be dominated by the mixing of K 0 and K 0. Direct CP violation in the 2 pion decays of neutral kaons has been a controversial subject over the last decade. A strong experimental effort has been devoted to the precise measurement of the direct CP violation parameter ℜe (ε ′ /ε). After 10 years of detector development, data collection and analys...