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Homework Help: Feynman diagram interpretation - 2 electrons in and 2 electrons out

  1. Feb 9, 2009 #1
    1. The problem statement, all variables and given/known data
    Hello :smile:

    The question is from "Advanced Physics" by Adams and Allday. It is from section 9 "The Physics of Particles", "Practice Exam Questions". It is question 11, part c. The level of this study is between school and University.

    Figure 9.5 represents a simple particle interaction. State the nature of the interaction and describe what happens to the particles involved. State three properties of the exchange particle.

    [Figure 9.5 is in the attachment]

    2. Relevant equations

    3. The attempt at a solution
    The particles in the interaction are leptons (electrons) so it must be a weak force interaction.

    It looks like nothing happens to the particles involved!!! The same particles are present before and after the interaction (possibly at different energies).

    It is not clear which way the exchange particle moves and there is no transfer of charge.

    Because there is no transfer of charge and the weak force is acting, I guess the only unidentified particle must be the uncharged weak force exchange particle, the Z0.

    I further guess that the directionless nature of the reaction means the exchange particle must be one that is its own anti-particle; again the Z0.

    I don't like guessing -- it means lack of understanding :frown:

    Illumination gratefully received.

    As for the three properties, I don't think we are required to recall actual figures so how about: massive (hence very unstable), uncharged, own anti-partcle?



    Attached Files:

  2. jcsd
  3. Feb 9, 2009 #2

    Tom Mattson

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    Nope. The squiggly line represents a photon. W and Z bosons are represented by straight dashed lines.

    When two billiard balls collide, the same balls are present before and after the interaction. Does that mean that nothing happens to them??

    You don't need to know the direction of motion of the exchange particle. But you're right, there is no transfer of charge.
  4. Feb 9, 2009 #3
    Thanks Tom :-)

    Duh! I didn't consider that it might be an electromagnetic force interaction! We've been so focussed on weak and strong I missed the obvious.


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