1. The problem statement, all variables and given/known data The question is to draw possible Feynman diagrams of the following decay. Sigma(plus) ----> proton + photon 2. Relevant equations Quark content of sigma(plus) is uus Quark content of proton is uud 3. The attempt at a solution I know that the decay has to proceed by the weak interaction. After all strangeness is not conserved. So the the strange quark in the sigma plus must first decay into a W(minus) and an up quark. The W- will then produce a down quark plus and an anti-up quark. With this I will now have the uud for the proton...which is good but I will have an up quark and an anti up quark left over. These can annihilate each other to form 2 photons but not one (due to conservation of momentum). I can see no way of getting rid of this "extra" photon. Do you think its a typo?