Search for Flavor Changing Neutral Current Charm Decays

We study the flavor changing neutral current process $c\rightarrow u \mu^+ \mu^-$ using a large data sample of $p \bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV recorded by the D\O\ detector operating at the Fermilab Tevatron. We observe a significant excess in the $D_s^+\rightarrow \pi^+ \mu^+\mu^-$ channel where the $\mu^+\mu^-$ system is consistent with production via the intermediate $\phi(1020)$ resonance. This mode is used to normalize our search for the quark level processes $D_s^+\rightarrow K^+ \mu^+ \mu^-$ and $D^+\rightarrow \pi^+ \mu^+\mu^-$.