The standard model prediction for epsilon '/epsilon

We present a detailed analysis of epsilon'/epsilon within the Standard Mode l, taking into account the strong enhancement through final-state interacti ons identified by Pallante and Pich in Phys. Rev. Lett. 84 (2000) 2568 and Nucl. Phys. B 592 (2000) 294. The relevant hadronic matrix elements are fix ed at leading order in the 1/N-C expansion, through a matching procedure be tween the effective short-distance Lagrangian and its corresponding low-ene rgy description in Chiral Perturbation Theory. All large logarithms are sum med up, both at short and long distances. Two different numerical analyses are performed, using either the experimental or the theoretical value for e psilon, with compatible results. We obtain Re(epsilon'/epsilon) = (1.7 +/- 0.9) x 10(-3). The error is dominated by the uncertainty in the value of th e strange quark mass and the estimated corrections from unknown 1/N-C-suppr essed local contributions. A better estimate of the strange quark mass woul d reduce the uncertainty to about 30%. The Standard Model prediction agrees with the present experimental world average Re(epsilon'/epsilon) (1.93 +/- 0.24) x 10(-3). (C) 2001 Elsevier Science B.V. All rights reserved.