New QCD estimate of the kaon penguin matrix elements and epsilon'/epsilon
Abstract
Firstly, we use the recent ALEPH/OPAL data on the V-A spectral functions for fixing the continuum threshold with which the first and second Weinberg sum rules should be satisfied in the chiral limit. Then, we predict the values of the low-energy constants m_{pi^+}-m_{pi^0}, L_{10}, and test the values of the electroweak kaon penguin matrix elements _{2\pi} obtained from DMO-like sum rules. Secondly, we use the data on the tau-total hadronic width R_{tau,V/A} for extracting _{2pi}, in the MS \bar-scheme, and propose some new sum rules for _{2pi} in the chiral limit, which require more accurate data for the spectral functions near the \tau-mass. Thirdly, we show that the S_2\equiv(\bar uu+\bar dd) component of the I=0 scalar meson, with its parameters fixed from QCD spectral sum rules, enhances the matrix element _{2pi}. Finally, using our previous determinations, we deduce the CP-violating ratio: \epsilon'/\epsilon = (24.2\pm 8.0) 10^{-4}, in the Standard Model (SM), which is in good agreement with the present measurements.Keywords
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