The charge asymmetry in " . o seml-leptomc K L decays has been measured in a high statistics experiment using multiwire proportional chambers. The asymmetry 6 = (N+-N-)/ (N++N-), where N + and N-are the partial decay rates for K~ ~ n-~+z, and K~ "--" rr+~-ff-, respectively, is found to be ti~ = (3.41 -+ 0.18) × 10 -3 for the Ke3 mode, and 8~ = (3.13 +-0.29) × 10 -3 for the K~u 3 mode. Assuming CPT invariance and the absence of AS = -AQ transitions, these results lead to a value of the real part

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... of the CP-violation parameter e, Re e --(1.67 -+ 0.08) × 10 -3. The charge asymmetry in the semi-leptonic decay modes of the long-lived neutral kaon is, apart from the two-pion decay of the long-lived kaon, the only manifestation of CP non-invariance observed up to now. A measurement of this effect is important to the understanding of the phenomenon of CP violation, as it can be related to e, the CP mixing amplitude in the neutral K-meson state N+-N -