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Electron - positron annihilation

  1. Sep 20, 2010 #1
    Apologies if this question is already covered. I searched, but couldnt get info from pf. when electron-positron annihilation happens..what is emitted ? as per wiki, its gamma rays but on cern website i read that muon pairs(muon and anti muons) are emitted. which one is correct ?
  2. jcsd
  3. Sep 20, 2010 #2
    It depends on the energy of the electron and positron. If they are low energy, the only things that can be created are photons; at higher energies there is some probability that muon-pairs will be produced, and at even higher energies even more massive particles can be produced.

    As soon as the energy of the electron-positron pair exceeds the rest mass energy of a particle-anti-particle pair, I think there is some probability that it will be created.
  4. Sep 20, 2010 #3
    If photons are created in annihilation, there wont be electric charge created in photons...but for Muon pairs, we have a positive and a negative muon. How can this be possible ?
  5. Sep 20, 2010 #4


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    Staff: Mentor

    The total charge is conserved in both cases.
  6. Sep 20, 2010 #5
    There are numerous quantities you have to conserve; charge is one of them---which means that if a charged species is created (e.g. a muon, q = -e) another particle will also be created with the opposite charge (e.g. an antimuon, q = +e). Similarly, 'lepton number' needs to be conserved, energy, angular momentum (e.g. spin) etc etc.
  7. Sep 21, 2010 #6
    dont we have charge conservation for that particular charges ? like instead of sum total...how about total no of negative (or positive) charges should remain the same pre & post the event ?
  8. Sep 21, 2010 #7
    Nope. It's experimentally very well established that only the total charge is conserved.
    Examples include:
    pair production
    electron capture
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