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Homework Help: How can a pi_0 meson decay into 2 photons?

  1. Jan 28, 2017 #1
    1. The problem statement, all variables and given/known data
    Earlier my teacher put this equation on the board,
    π_0 --> γ+γ
    It appears to work until you consider spin.

    2. Relevant equations
    a quick google search reveals that the spin of a photon is +1 and the spin of a pi meson is 0

    3. The attempt at a solution
    This appears to work for momentum, energy, charge, baryon number.....
    But π_0 has no spin and γ has a spin of +1.
    So in essence the atomic spin starts at 0 and finishes at +2.
    What am I missing?
  2. jcsd
  3. Jan 28, 2017 #2


    User Avatar
    2017 Award

    Staff: Mentor

    Two particles with spin 1 don't have to add to spin 2.
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