We use the data on the decays $D\to \pi \pi$ and $D\to \mathrm{KK}$ as a test vehicle for evaluating the effects of penguin diagrams in exclusive heavy meson decays. Evaluating $\Gamma (D\to {\pi }^{+}{\pi }^{-})$ and $\Gamma (D\to K^{+}{K}^{-})$, we find good agreement between our theoretical $\mathrm{SU}\mathrm{}\left(2L\right)\mathrm{}\times \mathrm{U}\mathrm{}\left(1\right)\mathrm{}\times \mathrm{SU}{\mathrm{}\left(3\right)\mathrm{}}^c$-based predictions and observation. Contributions from penguin diagrams are small and SU(3) flavor breaking effects account for the large value of $\frac{\Gamma (D\to K^{+}{K}^{-})}{\Gamma (D\to {\pi }^{+}{\pi }^{-})}$. Implications for $B$ decays are discussed briefly.

• Received 11 June 1992

DOI:https://doi.org/10.1103/PhysRevLett.70.2533