Analysis of ε′/ε in the 1/Nc expansion Original Research Article

We present a new analysis of the ratio ε′/ε which measures the direct CP violation in K→ππ decays. We use the 1/Nc expansion within the framework of the effective chiral Lagrangian for pseudoscalar mesons. The 1/Nc corrections to the hadronic matrix elements of all operators are calculated at leading order in the chiral expansion. Performing a simple scanning of the input parameters we obtain 1.5×10−4⩽ε′/ε⩽31.6×10−4. We also investigate, in the chiral limit, the 1/Nc corrections to the operator Q6 at next-to-leading order in the chiral expansion. We find large positive corrections which further enhance ε′/ε and can bring the standard model prediction close to the measured value for central values of the parameters. Our result indicates that at the level of the 1/Nc corrections a ΔI=1/2 enhancement is operative for Q6 similar to the one of Q1 and Q2 which dominate the CP-conserving amplitude.