Updated Standard Model Prediction for $\varepsilon'/\varepsilon$

TL;DR

This paper updates the Standard Model prediction for /, incorporating all known contributions, and finds it consistent with experimental results, addressing previous claims of a discrepancy.

Contribution

The paper provides a revised Standard Model calculation of / that includes long-distance effects, resolving prior misconceptions and aligning theory with experiment.

Findings

Updated prediction / = (15 1 7) 7 10^{-4}

Standard Model prediction now agrees with experimental data

Addresses previous neglect of long-distance re-scattering effects

Abstract

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