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Why do gluons and W and Z bosons have a limited range?

  1. Dec 21, 2011 #1
    Why do the gluon and W and Z boson particles have a limited range of movement, 10-15m for the gluon and 10-18m for the W and Z bosons, when the photon particles, gravitational force, and other particles have no limit to the distance they can travel?
  2. jcsd
  3. Dec 21, 2011 #2
    W and Z bosons are exhange bosons. The appear do there job and disapear again. The uncertainty pricinciple governs this. high mass short range. Gluons are confined by their nature. I will let someone else explain that one. The energy "borrowed" to create this particle must be "paid" back with a set time. Given these particles travel at neary the speed of light the follow is can be said.

    Uncertainity principle states
    ΔxΔp ≥ h/(4*pi) or

    ΔEΔt ≥ h/(4*pi)

    ΔEΔt = mc^2Δt ≥ h/(4*pi)

    Virtual particles are travelling close to c so:

    Range ≈ cΔt ≥ h/(4*pi*m*c)

    Given the mass of a W boson is 80.4 Gev that works out to be 1.43E-25 kg. That gives a range of 1.2E-18 m. The same goes for the slightly ore massive Z boson.
    Last edited: Dec 21, 2011
  4. Dec 21, 2011 #3
    Gluons are massless so their confinement comes form another process. I do not understand QCD!
  5. Dec 23, 2011 #4


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    W and Z bosons are not always virtual. When they are created for example in the LHC, they have more than enough energy to put them on the mass shell. Even so they have an extremely short natural lifetime. The basic reason is that despite their large rest mass, they decay into lighter products. If you look up their properties at the Particle Data Group, you'll find that the W has a mass of 80 GeV and a width of 2 GeV. This corresponds to a range of about one-tenth of a fermi and a lifetime of 3 x 10-25 sec. Similarly the Z has a mass of 91 GeV and a width of 2.5 GeV.
    Last edited: Dec 23, 2011
  6. Dec 24, 2011 #5
    I think your reason is abit more exact and technical.

    Decay width = h/(2*pi*t1/2) where t1/2 is half life. Putting 2.5 Gev into this gives you 2.63E-25 s which is right. Tavelling at ~c the range with half life is 7.9E-17m.

    I am still trying to find an exact defination of decay width that makes sense though. there are no many explanations on the web and those that are present are very short an do explain in enough depth.

    What do you mean by the mass shell as well?
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