Observation of the decay K/sub L/$sup 0$ $Yields$ $mu$$sup +$$mu$$sup -$

An experiment performed at the Brookhaven National Laboratory alternating-gradient synchrotron has yielded six events above negligible background which satisfy criteria for the decay K/sub L//sup o/ yields mu /sup +/ mu / sup -/. The K/sub L//sup o/ flux, measured by means of the decay K/sub L// sup o/ yields pi + pi , leads to a value for the branching ratio GAMMA (K/sub L/ /sup o/ yields mu + mu -)/ GAMMA (K/sub L/ yields all)=11x10/s up -9/. (auth)