Measurement of the Ratio $\frac{\Gamma (K_L\to {\pi }^{+}{\pi }^{-})}{\Gamma (K_L\to \pi l\nu )}$ for $K_L$ with 65 GeV/c Laboratory Momentum

We have measured the ratio $\frac{\Gamma (K_L\to {\pi }^{+}{\pi }^{-})}{\Gamma (K_L\to \pi l\nu )}$ to be (3.13 ± 0.14) × ${10}^{-3\mathrm{}}$ For $K_L$ with a mean laboratory momentum of 65 GeV/c. This value corresponds to the $\mathrm{CP}$-nonconservation parameter $\left|{\eta }_{+-}\right|=(2.28\mathrm{}\pm 0.06)\times {10}^{-3\mathrm{}}$, and is consistent with the world average $\left|{\eta }_{+-}\right|=(2.274\mathrm{}\pm 0.022)\times {10}^{-3\mathrm{}}$ which is derived from measurements with $K_L$ laboratory momenta less than 10 GeV/c. In this experiment we find no evidence for an energy dependence of $\left|{\eta }_{+-}\right|$.