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How do the W and Z Gauge Bosons work in the weak nuclear force?

  1. Nov 10, 2014 #1
    I've seen explanations that when a neutrino with a W+ Boson comes near a neutron, it affects one of the bottom quarks and changes it to a up quark which effectively turns the neutron into a proton. The neutrino then turns into an electron.

    Source:

    (2:20 onwards)

    I've seen other explanations which say that a down quark in a neutron emits a W- Boson and changes into a up quark, effectively turning the neutron into a proton. And then the W- Boson decays into an electron and antineutrino.

    Source: http://atlas.physicsmasterclasses.org/en/zpath_radioactivity.htm

    So which is the correct explanation?
    And one more thing, I've searched many websites and I still can't find a good explanation for what exactly the Z boson does?
    I get that it is neutral, but that's it.

    Thanks to any help in advance. :)
     
  2. jcsd
  3. Nov 10, 2014 #2

    e.bar.goum

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    Both are correct, they're just describing different weak interactions. The first one is something called "charged current interaction", and can be shown schematically here: (time on the y axis)
    feynman03.jpg

    The second describes weak nuclear decay, schematically shown here:

    These are just two examples of weak interactions. The boson that carries the weak force for any given reaction is the one that conserves electrical charge. Hence W+ in the first example, W- in the second. If no charge is carried, you use the Z boson. For example, the scattering of a neutrino and an electron:

    feynman04.jpg

    Does this clear things up?
     
    Last edited by a moderator: Apr 18, 2017
  4. Nov 10, 2014 #3
    Hi,

    Thank you very much for the reply.
    I've never learned how Feynmann diagrams work but after doing some more research, I think I understand the first two interactions. :)
    I take it that both the first two interactions apply to both W+ and W- bosons? As in the first interaction can also happen with W- and the second can also happen with W+?
    Also, a question on the second interaction, if the W- Boson decays into an electron and anti-neutrino, then why isn't the arrow of the anti-neutrino the other way?

    m7colg.jpg


    And I still don't understand how the Z boson works exactly. Does it carry "no charge" between particles? Why does it need to carry no charge? Can't the electron and neutrino collide and then scatter by themselves?
    I'm still quite confused on the mechanics and purpose of the Z boson.
    Also, are there any other interactions? Or is it just these three?

    Sorry for all the questions, I'm just really interested in this stuff.
    Thanks again for the replies! :)
     
    Last edited: Nov 10, 2014
  5. Nov 10, 2014 #4

    e.bar.goum

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    No, the arrow of anti-particles go in the opposite direction to that of the particles - this is notation, and harks back to the fact that antiparticles look like particles travelling backwards in time.

    No, the choice of W+ or W- depends on the charge. You need to conserve charge at every vertex, so if you have a neutron turning into a proton, one unit of negative charge needs to be carried away by a W-, for a proton turning into a neutron, you need to carry away one unit of positive charge with the W+. So, with the above reactions, if instead you had a proton turning into a neutron, you'd have a W- in the first case, W+ in the second.


    Like I said, you need to conserve charge at each vertex.

    That's exactly what that diagram shows! Collisions occur through some mediating force, which must be carried by a gauge boson. In this case, the weak force, and W+/W-/Z0. When electrons scatter off of each other, the force is mediated by a photon, the gauge boson for the electromagnetic force.

    Many, many others! I alluded to a couple up at the top of this post, but there are many others beyond this! And I've only shown you the most simple version of the processes we've been discussing, too.
     
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