The final measurement of $\epsilon'\epsilon$ by NA48

TL;DR

This paper reports a precise measurement of direct CP violation in neutral kaon decays, combining data from multiple years to refine the value of Re(ε'/ε) and confirm its non-zero nature.

Contribution

The paper presents the final combined measurement of Re(ε'/ε) from the NA48 experiment, improving precision and confirming direct CP violation.

Findings

Re(ε'/ε) = (14.7 ± 2.2) × 10^{-4} from combined data

Consistent results across different data-taking periods

Confirmation of direct CP violation in neutral kaon decays

Abstract

The direct CP violation parameter Re($\epsilon'\epsilon$) has been measured from the decay rates of neutral kaons into two pions using the NA48 detector at the CERN SPS. The 2001 running period was devoted to collecting additional data under varied conditions compared to earlier years (1997-99). The 2001 data yield the result: Re($\epsilon\epsilon'$)=$(13.7\pm3.1)\times10^{-4}$. Combining this result with that published from the 1997,98 and 99 data, an overall value of Re($\epsilon'\epsilon$)=$(14.7\pm2.2)\times10^{-4}$ is obtained from the NA48 experiment.