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W+ or W- in neutrino collisions

  1. Apr 18, 2014 #1
    All the Feynman diagrams I have seen so far for a neutron colliding with a neutrino have a w+ with an arrow from the neutrino to the neutron.
    Would it not also be possible with a W- leaving the neutron taking away negative charge for it to become a positive proton or is there some quantum rule I am not aware of that forbids this?

    Any help gratefully received.
  2. jcsd
  3. Apr 18, 2014 #2


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    Staff: Mentor

    The W in a Feynman diagram like that one is "virtual" and can be interpreted either as a W+ going one way, or a W- going the other way. There's no difference as far as I know.
  4. Apr 18, 2014 #3
    Hi jtbell,
    thanks for the rapid response,

    What confuses me is that for example in say beta minus decay. The proton turns to a neutron by emitting a W- and this W- decays to become an electron and a anti-electon neutrino. The electron in a sense is formed from the "negativness" of the W-. So in this type of decay it must be a W-.
    Also in electron capture it seems that the proton captures the electron by emitting a W+ to turn the electron into a neutrino, with this process happening to protons in a neucleus. Yet if a free electron and a proton collide via the weak interaction then a W- leaves the electron.

    So do you mean there is no difference in the initial and final states or do you mean its the same W we just assigne a sign to it.

    I hope this garbled rant makes sense
    confused of planet Earth
  5. Apr 18, 2014 #4


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    Staff: Mentor

    You can write the same process as W+, electron and antineutrino appearing out of nowhere, and then an interaction where the neutron "absorbs" the W+ and becomes a proton.
    That is an unconventional way to draw the Feynman diagram, but it is the same physics and does not change the calculation at all.
    It is the same process.
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