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Name: Tommy
Status: student
Grade: 9-12
Location: TX
Country: USA
Date: Spring 2012

I have read that the W+ and W- Bosons are the messenger particles for the weak interaction. Furthermore, I understand that they are very massive, requiring high energy accelerators to produce them. If, as in beta decay, a down quark decays into a W-, an electron and a neutrino, where does the mass come from to create a W-? Is this one of these "virtual particle" phenomena where the W- cannot be considered "real"?


First, it is not true that the down quark decays into a W-, an electron, and a neutrino. Charge does not balance. I will not get into specific decays. The Z particle, charge zero, serves the same function as W+ and W-, but works when a zero-charge particle decays.

W and Z particles have such huge mass so as to limit the probability of decay. The extreme energy (mc^2) of the mass does not exist in a resting neutron. By the rules of standard physics, beta decay cannot happen. According to quantum rules, it can. Slight variations in energy occur frequently, but last for a short time. Huge variations in energy happen once in a while, and last for a VERY short time. This is what beta decay is. The energy from before to after the decay (before: neutron, after: proton, electron, anti-neutrino) is balanced. The energy during the decay, when the W or Z particle is present, is not balanced. The more out of balance the energy is, the less likely it can happen. Also, the W or Z particle cannot exist long enough to be measured directly. It will decay into the proton, electron, and anti-neutrino long before any experiment can sight it.

Dr. Ken Mellendorf Physics Instructor Illinois Central College

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