New results on direct CP violation in charged kaon decays by NA48/2

TL;DR

This paper reports a highly precise measurement of direct CP violation in charged kaon decays, achieving sensitivity at the 10^{-4} level, and significantly improving the accuracy over previous results.

Contribution

The paper presents the first measurement of the charge asymmetry parameter in $K^{ o} o o o$ decays with an order of magnitude better precision than prior studies.

Findings

Measured $A_g = (1.8 imes 10^{-4}) \

Result is consistent with no CP violation within uncertainties.

Achieved sensitivity at the $10^{-4}$ level with over 45 million events.

Abstract

The NA48/2 result, based on the data collected during the 2003 run, on direct CP violation in $K^{\pm}\to\pi^{\pm}\pi^0\pi^0$ decay is presented. The main goal of the experiment is to reach a sensitivity at level of $10^{-4}$ in the measurement of the charge asymmetry parameter $A_g=(g^+-g^-)/(g^++g^-)$, where $g$ is the \emph{linear slope} of the Dalitz plot in the $K\to 3\pi$ decay. Thanks to the simultaneous collection of the two kaon charges and to the high resolution of the main sub-detectors, the systematics uncertainties are kept under the statistical error level. The experimental procedure, the analysis technique and the main systematics are discussed to present the final result $$ A_g=(1.8\pm2.6)\times 10^{-4} $$ This result based on more than $45\cdot10^6$ events, correspondig to one half of the whole two year data taking, is about an order of magnitude more precise with respect to the previous measurement.