Measurement of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mfrac><mml:mrow><mml:mrow><mml:msup><mml:mrow><mml:mi>ε</mml:mi></mml:mrow><mml:mrow><mml:mo>′</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:mrow><mml:mrow><mml:mi>ε</mml:mi></mml:mrow></mml:mfrac></mml:math>in the Neutral Kaon System

A measurement of the ratio of the $\mathrm{CP}$-nonconservation parameters, $\frac{{\ensuremath{\epsilon}}^{\ensuremath{'}}}{\ensuremath{\epsilon}}$, 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 ${K}_{L}\ensuremath{\rightarrow}2{\ensuremath{\pi}}^{0}$ events were reconstructed leading to the result $\frac{{\ensuremath{\epsilon}}^{\ensuremath{'}}}{\ensuremath{\epsilon}}=\ensuremath{-}0.0046\ifmmode\pm\else\textpm\fi{}0.0053\ifmmode\pm\else\textpm\fi{}0.0024$ (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.