Direct CP violation and the ΔI = 1/2 rule in K → ππ decay in the Standard Model

Christopher Kelly

doi:10.1051/epjconf/202225801003

Abstract

We discuss the RBC & UKQCD collaborations’ recent [1] lattice calculation of ϵ′, the measure of direct CP-violation in kaon decays. This result significantly improves on our previous 2015 calculation, with nearly 4× the statistics and more reliable systematic error estimates. We discuss how our results demonstrate the Standard Model origin of the ΔI = 1/2 rule, and present our plans for future calculations.

Highlights

We discuss the RBC & UKQCD collaborations’ recent [1] lattice calculation of ✏0, the measure of direct CP-violation in kaon decays
In this document we present the results of an updated calculation [1] published in 2020, where we have reduced our statistical error by a factor of two and dramatically improved our understanding and confidence in the systematic error resulting from the contribution of excited ⇡⇡ states – resolving the phase-shift discrepancy – alongside several other important systematic error sources
For Q2, the dominant contribution to ReA0, we find good with tahgereaedmdietinotnbaeltwopeeernataolrlso.fHthoewfietvsefrorfotm0r iQn 6≥, 4, we see improved the dominant contribution to statistical errors ImA0, we see a clear pattern of excited state contamination in the one and two-operator fit results, the latter converging later than the former as we would expect

Summary

Introduction

Direct CP-violation (CPV) in the decays of neutral kaons into two pions is highly suppressed in the Standard Model, making it an ideal probe for new sources of CPV. Beyond the Standard Model CPV processes appear necessary to explain the predominance of matter over antimatter in the observable Universe assuming that baryogeneses is responsible for this phenomenon. Measurements of these processes provide a new, horizontal band constraint on the CKM matrix unitarity triangle in the ⇢ − ⌘ plane, as illustrated in Fig. 1 where we compare the constraint from our calculation versus those of other sources. We discuss our ongoing e↵orts to further refine our calculation over the coming years

Summary of the calculations

Results of the updated calculation

Conclusions and outlook