Updated analysis of epsilon '/epsilon in the standard model with hadronic matrix elements from the chiral quark model - art. no. 056009

We discuss the theoretical and experimental status of the CP violating rati o epsilon'/epsilon. We revise our 1997 standard-model estimate-based on had ronic matrix elements computed in the chiral quark model up to O(p(4)) in t he chiral expansion-by including an improved statistical analysis of the un certainties and updated determination of the Cabibbo-Kobayashi-Maskawa elem ents and other short-distance parameters. Using normal distributions for th e experimental input data we find Re epsilon'/epsilon = (2.2 +/- 0.8) x 10( -3), whereas a hat scanning gives 0.9 x 10(-3)<Re <epsilon>'/epsilon <4.8x1 0(-3). Both results are in agreement with the current experimental data, Th e key element in our estimate is, as before, the fit of the <Delta>I = 1/2 rule, which snows us to absorb most of the theoretical uncertainties in the determination of the model-dependent parameters in the hadronic matrix ele ments. Our semiphenomenological approach leads to numerical stability again st variations of the renormalization scale and scheme dependence of the sho rt- and long-distance components. The same dynamical mechanism at work in t he selection rule also explains the larger value obtained for epsilon'/epsi lon with respect to other estimates. A coherent picture of K-->pi pi decays is thus provided.