Search for Nonspectator Decays of theD0

The weak hadronic decay $D^0\to {\overline{K}}^0{K}^{+}{K}^{-}$ is observed in a data sample of 9.3 ${\mathrm{pb}}^{-1\mathrm{}}$ collected with the Mark III detector at the $\psi \mathrm{}\left(3770\right)\mathrm{}$ resonance. An analysis of the $K^{+}{K}^{-}$ subsystem suggests that while the decay proceeds in part through the ${\overline{K}}^0\phi$ channel, providing evidence for the presence of nonspectator amplitudes in $D^0$ decays, a significant fraction of the decays occurs through both higher- and lower-mass $K^{+}{K}^{-}$ systems. A limit is set on the decay $D^0\to {\overline{K}}^0{K}^0$, also thought to proceed by nonspectator processes.