How can you tell what force mediates an interaction?

[malcomson]

Doing some examples I came across the question:


Can the following processes occur and if not, why not? Draw Feynman diagrams for
the allowed processes.

one of which was

K(-) (u(bar) , s) + p → K(+) (u , s(bar)) + Σ(-) (d,d,s)



I thought that the strange quark could emit a W(-) and change to a up quark, that W boson could then change an up quark from the proton to a down quark.

At he same time the anti-up from the kaon could annihilate with the second up from the proton to create a gluon that then creates a strange anti-strange pair that go back into their respective particles.



The answers say

"not allowed, strong interation that violates strangeness conservation"


My question is - how can you tell it has to be via the strong interaction? Is there something I'm missing?

 

[Meir Achuz]

I think they were just implicitly considering strong interactions.

 

[malcomson]

It would be nice if that were the case, but there were weak EM and hybrid interactions in the other parts of the question.

There is the possibility that there's a mistake in the answers - they were handwritten by my lecturer, but I'd discounted that as me being arrogant.

Thanks for the reply, I'm quite heartened that you didn't point out some mistake I've made (I have an exam on it in a week and thought I didn't understand something).