A new measurement of direct CP violation in the neutral kaon system

Abstract A new measurement of the ratio of the CP -violating amplitudes for K L → 2 π 0 and K L → π + π − is reported. The measured value for R = ∣ η 00 / η +- ∣ 2 is 0.9878±0.0026±0.0030, where the first error is the statistical uncertainty and the second is the estimate of the systematic uncertainty. This gives a value for the parameter describing direct CP violation: Re ϵ '/ ϵ = (2.0 ± 0.7) × 10 −3 .