Updated Standard Model Prediction for ε′/ε

Abstract

A recent lattice evaluation of ε′/ε, finding a 2.1 σ deviation from the experimental value, has revived the old debate about a possible ε′/ε anomaly. The unfounded claims of a too low Standard Model prediction are based on incorrect estimates that neglect the long-distance re-scattering of the final pions in K → 2π. In view of the current situation, we have recently updated the Standard Model calculation, including all known short- and long-distance contributions. Our result, Re(ε′/ε)=(15±7)⋅10−4 [H. Gisbert and A. Pich, “Direct CP violation in K0→ππ: Standard Model Status”, Rept. Prog. Phys. 81 (2018) no. 7, 076201 arXiv:1712.06147 [hep-ph].], is in complete agreement with the experimental measurement.