Measurement ofε′εin the Neutral Kaon System

A measurement of the ratio of the $\mathrm{CP}$-nonconservation parameters, $\frac{{\epsilon }^{\prime }}{\epsilon }$, in the $K^0{\overline{K}}^0$ system was performed through a study of two-pion decays with and without a regenerator. To reduce systematic effects, $K_L$ and $K_S$ decays were recorded simultaneously with a double beam. Over 3100 $K_L\to 2{\pi }^0$ events were reconstructed leading to the result $\frac{{\epsilon }^{\prime }}{\epsilon }=-0.0046\mathrm{}\pm 0.0053\pm 0.0024$ (the first error is statistical, the second systematic). The measurement agrees with previous less precise determinations but, because of theoretical uncertainties, is not able to test decisively the Kobayashi-Maskawa mechanism.