First Search for the Flavor Changing Neutral Current Decay $D^0\to \gamma \gamma$

Using $13.8{\mathrm{f}\mathrm{b}}^{-1}$ of data collected at or just below the ${\rm Y}(4S)$ 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 $\mathcal{B}(D^0\to \gamma \gamma )/\mathcal{B}(D^0\to {\pi }^0{\pi }^0)<0.033$ and $\mathcal{B}(D^0\to \gamma \gamma )<2.9\times {10}^{-5}$.

Figure 1

The $Q$ distributions for $D^{*+}\to D^0{\pi }^{+}$ where $D^0\to {\pi }^0{\pi }^0$ (a) and $D^0\to \gamma \gamma$ (b). The circles are from data and the solid curves are the fit to the data. The histograms are from the normalized Monte Carlo expectations.