Hi all, I have a question regarding to the branching ratio of neutral D-meson decay. Give three decays: 1. D --> negative kaon + positive pion 2. D --> positive pion + negative pion 3. D --> positive kaon + negative pion The one with highest branching ratio is 1. due to its non-cross generation mixing. However, my question is: why isn't 2 more likely since D-meson can decay into two photons and split into two pairs of quarks? It's because Intermediate photons are involved with EM interactions, which dominate over weak interactions (1 and 3 b/c they don't conserve strangeness). Thanks :\ O.