Experimental measurement of K/subL/$sup 0$$Yields$$mu$$sup +$$mu$$sup -$
Using a spark-chamber magnet spectrometer and applying very stringent requirements to eliminate background contamination, we find three events of the rare process K/subL/$sup 0$$Yields$$mu$$sup +$$mu$$sup -$ corresponding to a branching ratio relative to K/subL/$sup 0$$Yields$$pi$$sup +$$pi$$sup -$ of 4.2/ sup +5.1//sub -2.6/ x 1$pi$$sup -6$. Using the branching ratio (K/subL/$sup 0$$Yields$$pi$$sup +$$pi$$sup -$)/(K/subL/$sup 0$$Yields$all) =0.21%, we calculate the branching ratio to be 8.8/sup +10.7//sub -5.5/ x 10$sup -9$ (90% confidence level) for the K/subL/$sup 0$$Yields$$mu$$sup +$$mu$$sup -$ decay. (AIP)