Beta- decay


by Edi
Tags: beta, decay
Edi
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#1
Jul17-09, 03:22 PM
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How can a down quark emit a W- when decaying if the boson is much heavier than the quark or even the whole neutron?

Actually, the three quarks together make ~10 MeV, but the neutron is said to be ~939 MeV, so there is 929 MeV missing, i though that W- bosons made it up, but then i realized that the bosons mass is said to be ~80 GeV, witch is much more than missing. And gluons are said to be massless.
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jtbell
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Jul17-09, 04:49 PM
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The W- is a virtual particle in this case. Virtual particles are "off the mass shell," that is, they don't satisfy the mass-energy-momentum relationship for real particles, [itex]E^2 = (pc)^2 + (mc^2)^2[/itex]. Alternatively, people sometimes say that virtual particles can very briefly violate conservation of energy by "hiding" behind the uncertainty principle.
humanino
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Jul17-09, 05:29 PM
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Quote Quote by Edi View Post
Actually, the three quarks together make ~10 MeV, but the neutron is said to be ~939 MeV, so there is 929 MeV missing
[...]
And gluons are said to be massless.
The W has nothing to do with the nucleon mass. The virtual gluons binding together the three quarks hold pretty much 90% of the nucleon mass in the form of energy. It is possible to describe the situation in a different manner : we can say that individual quarks whose bare mass (at high energy) is a few MeV dress up inside the hadrons to obtain a constituent mass around 350 MeV. This picture is supported by relativistic bound state equations, namely calculating the propagator using Dyson-Schwinger methods.


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