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Are muons elementary particles?

  1. Apr 1, 2012 #1

    I've been reading that muons are supposedly leptons (elementary particles), in the past confused for mesons (hadronic particles). They are clearly not mesons, which are composed of a quark and an antiquark. But i've also read that muons decay to an electron and two neutrinos of different types.

    So my question is simple, aren't leptons supposed to be elementary particles, not composed of any other particles? If muons are composed of an electron and neutrinos, how can a muon be a lepton? What am i missing?

    Thank you for you answers. Cheers, Val.
  2. jcsd
  3. Apr 1, 2012 #2


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    muons and taus are leptons. They happen to decay as you described. There is a similar situation with quarks, where top, bottom, charm, and strange will decay into up and down.

    This is the way things are defined.

  4. Apr 1, 2012 #3


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    Muons are not composed of an electron and two neutrinos. In a muon decay, they are transformed into other particles.

    In a similar way, neutrons can decay into proton+electron+neutrino, electrons and positrons can annihilate to give two photons. Collisions of electrons and positrons can produce muons and so on.
  5. Apr 1, 2012 #4
    OK, I get it! Thank you! :) I thought decay was different than composition i just wasn't sure what the difference was. Cheers, Val.
  6. Apr 1, 2012 #5
    There are three classes of leptons; electron, muon and tau. Each class of leptons has four particles (two are antiparticles), two charged particles e+ and e-, μ+ and μ-, and τ+ and τ-, and two neutrals each (neutrino and antineutrino). Each class is conserved in decays and interactions. So when a μ- decays, it has to emit a muon neutrino, an e-, and an electron antineutrino. However, when a π- [pi-] decays to a μ-, it also has to emit a muon antineutrino.
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