Search for direct CP-violation in K+- --> 3pi decays by NA48/2

TL;DR

The NA48/2 experiment conducted a high-precision search for direct CP-violation in charged kaon decays to three pions, achieving unprecedented accuracy limited mainly by statistical uncertainties.

Contribution

This study provides the most precise measurement to date of CP-violation asymmetries in K+- --> 3pi decays, utilizing a novel double-beam system and advanced analysis methods.

Findings

Measured asymmetry in charged decays: A^c_g = (-1.3 +- 2.3) x 10^-4

Measured asymmetry in neutral decays: A^n_g = (2.1 +- 1.9) x 10^-4

Result limited by statistical uncertainties, with no significant CP-violation observed.

Abstract

A high precision search for direct CP-violation in K+- --> 3 pi decays was performed by the NA48/2 experiment at CERN SPS. The asymmetry in the Dalitz plot linear slopes A_g = (g^+ - g^-)/(g^+ + g^-) is measured to be A^c_g = (-1.3 +- 2.3)x10^-4 by studying ~3.1x10^9 K+- --> pi+- pi+ pi- decays and A^n_g = (2.1 +- 1.9)x10^-4 by studying ~91x10^6 K+- --> pi+- pi0 pi0 decays. The unique double- beam system, the design of the detectors and the method of analysis provide good control of the instrumental charge asymmetries and allow to keep the precision of the result limited by statistics, reaching accuracy one order of magnitude better than in previous experiments.