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K-Long and K-Short pion decay cross sections

  1. Apr 30, 2015 #1
    In the text-book example of CP violation in the kaon system, the usual statement is that the KS decays much faster than the KL because the phase space is larger for a decay into two pions, compared to three pions. (See, for example, Griffiths or "Modern Particle Physics" by Thomson.)

    I was wondering if that is the only large contribution. Doesn't a third pion add at least two gluon vertices to the highest-order Feynman diagram? Can this be neglected in comparison with the phase space?
  2. jcsd
  3. Apr 30, 2015 #2


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    The point with strong interactions is that they are ... well ... strong. Adding gluon vertices does not supress the amplitudes by a large amount as adding EM vertices does.
  4. May 3, 2015 #3
    OK, thanks. So there is a contribution, but it's much smaller than the phase space suppression?
  5. May 3, 2015 #4


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    Yes, and it is not even clear if that contribution is smaller or larger than one.
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