# Feynman diagram K decay

1. May 28, 2012

### nonequilibrium

Looking at, say, the decay $K^+ \to \pi^+ + \pi^+ + \pi^- + \gamma$, is it easy to say what the Feynman diagram is of highest contribution? I suppose it is not unique, but say we're satisfied with just one of highest order. Is there as it were a sort of flowchart one follows? For example, since strangeness is not conserved, we'll at least need one weak interaction. This will increase the number of quarks from 2 to 4. We need 2 more, for this we can use any of the interactions, hence we use the strong interaction, as it has the highest contribution. To get an outgoing photon, it seems best to simply attach a photon line to an arbitrary fermion line already present. This gives me the following drawing

Firstly, is this drawing indeed one of the highest order contributions? Secondly, is the reasoning solid? Thirdly, do you use some kind of flowchart/algorithm/step-by-step procedure to find such things? Or perhaps it's all computers? Or random guessing...

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