Updated Standard Model Prediction for ${\epsilon }^{\prime }/\epsilon$

Abstract

A recent lattice evaluation of ${\epsilon }^{\prime }/\epsilon$, finding a 2.1 $\sigma$ deviation from the experimental value, has revived the old debate about a possible ${\epsilon }^{\prime }/\epsilon$ 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 $K\to 2\pi$. In view of the current situation, we have recently updated the Standard Model calculation, including all known short- and long-distance contributions. Our result, $\text{Re}\left({\epsilon }^{\prime }/\epsilon \right)=(15\pm 7)\cdot 10^{-4}$, is in complete agreement with the experimental measurement.

8 pages, 3 figures, talk given at 21th International Conference in Quantum Chromodynamics (QCD 18), 2 - 6 July 2018, Montpellier - FR