Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Beta decay?

  1. Jul 25, 2015 #1
    Energy of beta ray and neutrino is equal Q=M(mass) of nucleous before-M of nucleous after,so it about 1Mev.But the mass of W boson is 80 MeV,so the least energy of electron and neutrino must be 80 MeV.
    Why there is the difference?Why does it seem that energy were not conservation?
     
  2. jcsd
  3. Jul 25, 2015 #2

    bcrowell

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The W is a virtual particle. It's "off shell," so it doesn't have to have an energy and momentum that are consistent with its mass.
     
  4. Jul 25, 2015 #3

    jtbell

    User Avatar

    Staff: Mentor

    Energy and momentum are both conserved at each vertex of a Feynman diagram, so one can calculate the energy and momentum of the virtual W from the energies and momenta of the outgoing (anti)neutrino and electron. However, because the W is virtual, ##\sqrt{E^2 - (pc)^2}## does not equal the mass of a real W. For a real W, ##\sqrt{E^2 - (pc)^2} = m_W c^2##.

    Particle physicists use the jargon that real (virtual) particles are "on (off) the mass shell," referring to the quantity ##\sqrt{E^2 - (pc)^2}##. Or as Ben said, just "on (off) shell" for short.
     
    Last edited: Jul 25, 2015
  5. Jul 25, 2015 #4
    I can understand your teaching! Thanks very much!
     
  6. Jul 26, 2015 #5

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Also, the mass of the W is 80 GeV.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Beta decay?
  1. Beta decay (Replies: 1)

  2. Beta decay and quarks (Replies: 5)

  3. Beta- decay (Replies: 2)

  4. Beta decay (Replies: 4)

  5. Beta+ Decay (Replies: 15)

Loading...