Neutrino Oscillations

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Offline Supercryptid

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Neutrino Oscillations
« on: 31/05/2005 21:33:00 »
It is currently believed that neutrinos undergo "oscillations" of a sort, which allows them to transform from one flavor of neutrino into another (i.e. from an electron neutrino to a muon neutrino or tauon neutrino).

My question: doesn't this violate conservation of lepton number?

For example, take the decay of a muon into an electron, an electron antineutrino, and a muon neutrino. The lepton numbers before the decay are: muon number 1, electron number 0 and tauon number 0. After the decay, the lepton numbers are still the same: muon number 1, electron number 0, tauon number 0. This is conservation of lepton number. However, if that muon neutrino were to transform into a tau neutrino, then the scheme of lepton numbers would change into the following: muon number 0, electron number 0, tauon number 1.

In essence the transformation of one neutrino into another kind of neutrino would change the total universal content of a certain lepton number. Does this mean that lepton number is only approximately conserved, perhaps only in certain interactions or pathways?
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Offline gsmollin

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Re: Neutrino Oscillations
« Reply #1 on: 01/06/2005 21:10:13 »
No replies, because this is a tough one. I've been looking at it, but don't have a good answer. It appears that the oscillation requires a neutron; it does not happen in empty space. The neutron may supply the lepton.

That's not an answer, only a possibility.
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Offline DoctorBeaver

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Re: Neutrino Oscillations
« Reply #2 on: 01/06/2005 22:04:06 »
Forgive my ignorance, but don't you still end up with the value 1 even though it's somewhere else?
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Offline gsmollin

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Re: Neutrino Oscillations
« Reply #3 on: 02/06/2005 14:07:28 »
Well a muon and a tau are both leptons, so I suppose lepton number would be conserved. Is that good enough? I'm still looking.
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Offline chimera

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Re: Neutrino Oscillations
« Reply #4 on: 02/06/2005 20:35:16 »
Maybe this is helpful, this stuff is still a bit too new for me...

http://home.hockaday.org/HockadayNet/academic/physics/stuffglue/stuffglue.htm

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Offline gsmollin

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Re: Neutrino Oscillations
« Reply #5 on: 14/06/2005 17:42:18 »
This is still a mystery, to me. Neutrino oscillation is a violation of the standard model, so we can expect the standard model to be violated explaining it. In the standard model, total lepton number, as well as each of the electron, muon, and tau lepton numbers are all conserved. Neutrino oscillation is impossible, and the neutrinos all have zero rest mass.

If neutrino oscillation is allowed, the violation of the electron, tau, or muon lepton numbers has to happen, although total lepton number is still conserved, and the neutrino has rest mass.

Neutrino oscillation is being treated as the resolution of superimposed states, i.e., the neutrino contains all three states until it interacts with a W boson. I don't find this satisfying, but there it is.

There has been a lot of experimental work done detecting solar and atmospheric neutrinos, and it has made some good reading. It was gratifying to see the scientific community rise to the challenge of accepting a limitation of the standard model in the solar neutrino problem, and begin modifying theory based on the experimental data. I like physics because if that: At some point the BS has to answer to cold hard experimental results. Even the most cherished theory of particle physics can take a hit from observed data.

Here is a pretty short discussion of lepton number, with some reference to neutrino oscillation: http://en.wikipedia.org/wiki/Lepton_number
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