Self-Contained Determination of the Phase ofη+−

In a single $K^0$ regeneration experiment, all the parameters needed to specify the phase of the $\mathrm{CP}$-noninvariant parameter ${\eta }_{+-}$ have been measured concurrently. The $K_{\pi 2}$ data have given the ${\eta }_{+-}$ phase relative to the phase of the $K_1^0$ regeneration, while the regeneration phase has been measured directly using the $K_{e3\mathrm{}}$ charge asymmetry. Incorporated in the latter measurement is an experimentally determined correction for the effects of incoherent regeneration. The experiment yields $\arg {\eta }_{+-}=36.2\mathrm{}°\pm 6.1°$.