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How many tree-levels in various QED processes

  1. Nov 30, 2012 #1
    how many tree-level diagrams in various QED processes

    Why do Compton scattering, pair annihilation, Moller scattering and Bhabba scattering have two
    tree-level Feynman graphs to sum over, whereas electron-positron to muon-antimuon scattering and electron-muon to electron-muon scattering have only one tree-level Feynman graph?

    I suspect that it has something to do with identical particles, but I do not see how.

    any help appreciated
     
    Last edited: Nov 30, 2012
  2. jcsd
  3. Nov 30, 2012 #2

    mfb

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    Just look at the individual graphs - if the final particles are the same as the initial particles, you always have a simple photon exchange. Something you cannot have if the particles are different.
     
  4. Nov 30, 2012 #3
    thanks for answering mfb!

    But then why does "electron + photon --> electron + photon" (Compton scattering) have two Feynman diagrams at the tree level, but "electron + muon --> electron + muon" only one!
     
  5. Dec 1, 2012 #4

    mfb

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    Electrons and photons interact directly with each other, and you have two possible ways to connect incoming + outgoing photons to the electron.
    In electron/muon scattering, the single photon exchange is the only option.
     
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