CP Violation Results from the NA48 experiments

The main goal of the NA48 experiments at the CERN SPS has been the search for direct CP violation (CPV) in kaon decays. In this article two selected results will be presented. In the neutral kaon sector, NA48 determined +minus, related to the param eters of indirect and direct CPV (+minus = +), from data collected during a dedicated run in 1999 with a pure KL beam. Using a sample of 47000 KL+minus and 5 million KLplusmne, we extract |+minus| = (2.223plusmn0.012)times10minus3. In the charged kaon dec ays, NA48/2 has measured the asymmetry Ag = (g+minusgminus)/(g++gminus). of the linear slope parameter g in the Dalitz plot of Kplusmn3 decays from data collected in 2003 and 2004. Any non-zero value of Ag would be evidence for direct CPV. A new technique of asymmetry measurement, involving simultaneous K+ and Kminus beam and a large data sample allowed a result of unprecedented precision. The charge asymmetry parameter was measured to be Agc align=middle = (minus1.5plusmn2.1)times10minus4 with 3.11times1 09 Kplusmnplusmn+minus decays, and Agn align=middle = (1.8plusmn1.8)times10minus4 with 9.13times107 Kplusmnplusmn00 decays. The results are compatible with the SM predictions, i.e. no evidence for direct CP violation at the order of 10minus4 has been foun d.