Relative Size of SU(3) Symmetry-Breaking Effects and Penguin Diagrams

We use the data on the decays D→ππ and D→KK as a test vehicle for evaluating the effects of penguin diagrams in exclusive heavy meson decays. Evaluating Γ(D→π⁺π^-) and Γ(D→K⁺K^-), we find good agreement between our theoretical SU(2L)×U(1)×SU(3)ᶜ-based predictions and observation. Contributions from penguin diagrams are small and SU(3) flavor breaking effects account for the large value of Γ(D→K⁺K^-)Γ(D→π⁺π^-). Implications for B decays are discussed briefly.