Test of the quantum-theoretical behavior of theK0−K¯0system

The magnitude of the $K_S-K_L$ interference term in the ${\pi }^{+}{\pi }^{-}$ decay mode of regenerated $K^0\text{'}\mathrm{s}$ has been studied. The data at each momentum are consistent with the general expectations of quantum theory and with the conventional phenomenology of $\mathrm{CP}$ violation. The ratio of the measured amplitude of the interference to its predicted value is $k=0.95\mathrm{}\pm 0.034$ using our data alone. When additional data from other experiments are used, $k=0.97\mathrm{}\pm 0.02$.