First Search for the Flavor Changing Neutral Current Decay D^0 -> gamma   gamma
  Using 13.8 fb^{-1} of data collected at or just below the \Upsilon(4S) with the CLEO detector, we report the result of a search for the flavor changing neutral current process D^{0} \to \gamma\gamma.   We observe no significant signal for this decay mode and determine 90% confidence level upper limits on the branching fractions Br(D^{0}\to \gamma\gamma)/Br(D^{0}\to\pi^{0}\pi^{0}) < 0.033 and Br(D^{0}\to\gamma\gamma) < 2.9 \times 10^{-5}.'' 
CLEO Collaboration: T.E. Coan, et al