Measurement of the ratio Gamma (KL--> pi + pi -)/ Gamma (KL--> pi l nu ) for KL with 65 GeV/c laboratory momentum.

We have measured the ratio GAMMA(K/sub L/..--> pi../sup +/..pi../sup -/)/GAMMA(K/sub L/..--> pi..l..nu.. ) to be (3.13 +- 0.14) x 10/sup -3/ for K/sub L/ with a mean laboratory momentum of 65 GeV/c. This value corresponds to the CP-nonconservation parameter Vertical Bareta/sub +/-Vertical Bar = (2.28 +- 0.06) x 10/sup -/ 3, and is consistent with the world average Vertical Bareta/sub +/-Vertical Bar = (2.274 +- 0.022) x 10 /sup -3/ which is derived from measurements with K/sub L/ laboratory momenta less than 10 GeV/c. In this experiment we find no evidence for an energy dependence of Vertical Bareta/sub +/-Vertical Bar.