How do you know what interaction a particle decays by? Watch

qujpzf
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#1
Report Thread starter 7 years ago
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Hey, I'm revising for my AS physics exam (AQA unit 1) and this question is in the textbook:

"State whether the strong or the weak interaction acts when
a) a muon decays
b) a K meson decays
c) Pi mesons are produced"

The answer in the back is
a) weak
b) weak
c) strong

Is it right to assume that if you are producing particles, it's always by strong force?
and that particles always decay by weak force?
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goonerjack
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Report 7 years ago
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It's not as simple as that, and actually decays produce particles too. Weak interactions involve the W+/- and Z bosons, strong interactions involve gluons. Have you learnt about Feynman diagrams?
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qujpzf
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Report Thread starter 7 years ago
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Hi, thanks for answering

We have learnt about Feynman diagrams, and I had a look at some (though I haven't seen any with gluons on them)

I think I get the first 2 now:
Muons are leptons so can't be affected by the strong force, therefore it must be a weak interaction
K mesons have a strange quark that decays - so it must be weak interaction if its changing flavour

But I still don't understand what's happening to produce a Pi meson and couldn't find a Feynman diagram for it
In the textbook it says you can produce it by colliding protons, but I still don't understand why it isn't weak interaction
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goonerjack
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It's difficult to understand fully without seeing the Feynman diagrams for the process, but the strong interaction governs the quark/quark-gluon vertex. So for the production of pions from protons, the quarks in the proton won't change flavour, instead they interact via the strong interaction to produce gluon(s) which then produce pions.
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