I see this sentence in wiki about weak interaction:

It is the only interaction capable of changing the flavor of quarks.

So why only quarks? Why not leptons? Is there another interaction which can change the flavor of leptons?

  • $\begingroup$ The same could be said of leptons. The wiki was just restrictions the statement to quarks. $\endgroup$ – Lewis Miller Sep 11 '16 at 17:32
  • $\begingroup$ The $W^\pm$ bosons flip the charge of quarks and leptons. This is the flavor changing weak interaction. $\endgroup$ – Lawrence B. Crowell Sep 11 '16 at 18:53

The weak interaction does change the flavour of leptons. For example a muon decays to an electron through a weak interaction. The tree level diagram is:

Muon decay

(Image from Wikipedia)

  • $\begingroup$ This does not seem to be an answer to my question. $\endgroup$ – Fan Sep 11 '16 at 23:03
  • 1
    $\begingroup$ Maybe I've misunderstood what you are asking, but this is a weak interaction in which the muon number and electron number change so it changes flavour. Perhaps you could clarify what you mean. Are you looking for a single vertex with leptons of different flavour? If so I don't think any such process exists. $\endgroup$ – John Rennie Sep 12 '16 at 5:06
  • $\begingroup$ I am asking if weak interaction is the only interaction capable of changing lepton flavors. I wonder why wiki specifically says it is the only interaction capable of changing quark flavors but does not mention leptons. $\endgroup$ – Fan Sep 12 '16 at 13:22

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