A non-zero value would violate $\mathit CPT$ invariance in $\Delta \mathit S$ = $\Delta \mathit Q$ amplitude. Re(y) is the following combination of ${{\mathit K}_{{{e3}}}}$ decay amplitudes: Re(y) = Re ${A( {{\overline{\mathit K}}^{0}} \rightarrow {{\mathit e}^{-}} {{\mathit \pi}^{+}} {{\overline{\mathit \nu}}_{{e}}} ){}^{*} - A( {{\mathit K}^{0}} \rightarrow {{\mathit e}^{+}} {{\mathit \pi}^{-}} {{\mathit \nu}_{{e}}} )\over A( {{\overline{\mathit K}}^{0}} \rightarrow {{\mathit e}^{-}} {{\mathit \pi}^{+}} {{\overline{\mathit \nu}}_{{e}}} ){}^{*} + A( {{\mathit K}^{0}} \rightarrow {{\mathit e}^{+}} {{\mathit \pi}^{-}} {{\mathit \nu}_{{e}}} )}$