THE ANATOMY OF EPSILON'-EPSILON IN THE STANDARD MODEL

We perform a detailed renormalization group analysis of the ratio ε′ ε for 50 GeV < mt < 250 GeV including the contributions from the gluon penguin, photon penguin, Z0-penguin and neutral Higgs penguin diagrams as well as from π0-η-η′ mixing and current-current operators. The final result for the Wilson coefficient functions with full O(αQED) corrections taken into account can be written in a compact and transparent form. Using the constraints on mt and the phase δ coming from the data on ε and B0-B0 mixing, we investigate the dependence of the resulting ε′ ε ratio on the values of mt, ΛQCD, BK, ms(1 GeV), FB and the ratio Γ(b → u) Γ(b → c). The presence of Z0-diagrams suppresses strongly ε′ ε for large values of mt. For mt ≃ O(100 GeV) the standard model is milliweak wity typical values ε′ ε ≃ (1.0 ± 0.5) × 10-3. For mt ≃ O(220 GeV) it behaves like a superweak theory with | ε′ ε|≃0 and negative values for larger mt. These two distinct regions of mt, "milliweak" and "superweak" respectively, are the two regions of mt favoured by the data on ε{lunate} and B0-B0 mixing. © 1990.