Theoretical status of epsilon'/epsilon

TL;DR

This paper reviews the theoretical understanding of epsilon'/epsilon, compares it with recent experiments, and discusses the main uncertainties, especially in hadronic matrix element calculations, which affect the accuracy of theoretical predictions.

Contribution

It provides a comprehensive review of the theoretical status of epsilon'/epsilon and highlights the dominant uncertainties in hadronic matrix elements affecting predictions.

Findings

Theoretical predictions are generally below experimental measurements.

Hadronic matrix element uncertainties are the main source of theoretical error.

Discussions on possible reasons for discrepancies between theory and experiment.

Abstract

The present theoretical status of the parameter for direct CP violation epsilon'/epsilon in the Standard Model is reviewed and compared with most recent experimental measurements of the same quantity. After collecting the basic expressions for epsilon'/epsilon, the situation of hadronic matrix element calculations is summarised. The matrix elements constitute the dominant source of uncertainty for theoretical determinations of epsilon'/epsilon. For central values of the input parameters, the numerical analysis then yields results which are generally below the experimental data. Possible reasons for these findings are discussed.