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A quick look on wikipedia (https://en.wikipedia.org/wiki/W_and_Z_bosons) will tell me that the rest mass of a $W$ boson is 2 orders of magnitude higher than that of a proton.

It seems weird that a particle would 'spit out' something 100x more massive than it - is it simply because weak interactions will only occur when a proton or neutron is at very high energy (so has a lot to get rid of as mass)?

Qmechanic
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Poo2uhaha
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  • Careful you are comparing it to the protons rest mass, not the invariant mass due to its momentum – Triatticus Apr 24 '20 at 21:47
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    "Spitting out" might well refer to emitting a virtual W, where your mental picture of the balance between mass and energy is useless and confusing. – Cosmas Zachos Apr 24 '20 at 21:52
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    Weak interactions don't only occur when a proton or neutron is at very high energy. A free neutron, even when it's sitting still, beta-decays into a proton, an electron, and an antineutrino (beta decay is a weak interaction: a down quark emits a virtual W boson and transforms to an up quark, and the virtual W boson decays into an electron and an electron antineutrino). – probably_someone Apr 24 '20 at 22:13
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    Yes that's true, but to just be bewildered strictly on the basis of the rest masses alone is an erroneous thought process – Triatticus Apr 25 '20 at 00:45

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Copied from https://www.open.edu/openlearn/science-maths-technology/particle-physics/content-section-8.1 (A W− boson is emitted with one unit of negative electric charge, so conserving electric charge in the process. The mass energy of the W− boson is about 80 GeV, so it cannot possibly emerge from the nucleus as there are only a few MeV of energy available. In accordance with the energy–time uncertainty principle it therefore rapidly decays to produce an electron and an electron antineutrino, setting the energy accounts straight. ) This is a little misleading as it suggests that the w-boson is actually 80Gev rather than 0.002 Gev which it is able to be BECAUSE of the energy-time uncertainty principle. So to clarify see also this (https://youtu.be/yOiABZM7wTU) regarding the probability of this and explaining why the weak force is weak. (From 6m50s).

Fergal O'Rourke
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The proton/neutron can emit a W boson that has more mass than itself because

A)the W boson can be a special W boson which is actually quite light. This W boson is heavy enough to turn into an electron/positron and neutrino/antineutrino in radioactive decay.

B)the W boson is a virtual particle that just borrows mass from the vacuum allowing for the conservation of energy to be violated for a split second-enough to allow radioactive decay- and allow these particles to be produced.

MiltonTheMeme
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    While a virtual boson may lie "off the mass shell" (that is, with $E^2-p^2\neq m^2$), it's not correct to suggest that such an object is a "special" or "quite light" version of the ordinary $W$. – rob May 07 '20 at 21:15
  • Why is it not correct to say that the W boson is special if it has less mass? – MiltonTheMeme May 07 '20 at 21:17
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    The distinction between an interaction being mediated by a massive field and a discrete, particle-like excitation of that field is a little more subtle than I can manage to explain in a comment. But there are no "special $W$ bosons." Identical particles are indistinguishable from each other. – rob May 07 '20 at 22:34
  • You may find it helpful to read this page (and the links there) about virtual particles: https://physics.stackexchange.com/q/230113/123208 – PM 2Ring May 08 '20 at 00:44