Reading about the muon [1]: "... the muon is not thought to be composed of any simpler particles; that is, it is a fundamental particle ... Muon decay almost always produces at least three particles, which must include an electron of the same charge as the muon and two types of neutrinos".If the muon is not composed of other particles, how can it end up as a set of other particles?
[1] https://en.wikipedia.org/wiki/Muon