What is the highest order contribution in the Feynman diagram for K decay?

[nonequilibrium]

Looking at, say, the decay [itex]K^+ \to \pi^+ + \pi^+ + \pi^- + \gamma[/itex], 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...

 

[LightHero]

The answer to your first question is yes, the drawing is one of the highest order contributions. The reasoning behind it is mostly solid, although there are other possible contributions that could have higher orders. As for the third question, it depends on the process being studied. For simple processes such as the one you described, it is usually possible to make an educated guess of the most important contributions. However, for more complex processes, it is usually necessary to use algorithms or computer programs to identify the highest order Feynman diagrams.