Simple question about particle physics

Does the neutrino produced always match the lepton?

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Simple question about particle physics

#1  Postby Little Idiot » Dec 11, 2017 10:00 am

Let's say K0 decays to π- and muon+ the neutrino is a muon neutrino.

Is it the case that the lepton must always match the neutrino?

So for example when an electron is produced the neutrino must be an electron neutrino and so on.

Thanks for any clarification.
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Re: Simple question about particle physics

#2  Postby DavidMcC » Dec 11, 2017 1:12 pm

Whilst it doesn't seem to be explicitly stated anywhere that I can find, it may be an unstated assumption that they do, perhaps even by definition of the neutrino as the particle that is produced along with the relevant partner.
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Re: Simple question about particle physics

#3  Postby Greyman » Dec 11, 2017 5:06 pm

Lepton flavour appears to be a proximately conserved quality. While there is evidence that a neutrino's flavour oscillates over time as it travels, there do not appear to be any lepton number violations during particle interactions.

As far as I know, to date, anyway.
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Re: Simple question about particle physics

#4  Postby Little Idiot » Dec 12, 2017 6:09 am

DavidMcC wrote:Whilst it doesn't seem to be explicitly stated anywhere that I can find, it may be an unstated assumption that they do, perhaps even by definition of the neutrino as the particle that is produced along with the relevant partner.


Thanks for the response David.
Like you, I've never come across it explicitly stated, that's why I was wondering is it so trivially obvious that it doesn't 'need' stating.
I'm teaching this stuff to some pretty bright students, and I don't want to present it as a fact if its not. But if it is a fact, its too important to skip over.
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Re: Simple question about particle physics

#5  Postby Little Idiot » Dec 12, 2017 6:10 am

Greyman wrote:Lepton flavour appears to be a proximately conserved quality. While there is evidence that a neutrino's flavour oscillates over time as it travels, there do not appear to be any lepton number violations during particle interactions.

As far as I know, to date, anyway.


Does that mean 'yes, (as far as you know)' to my original question about neutrinos?
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Re: Simple question about particle physics

#6  Postby DavidMcC » Dec 12, 2017 12:16 pm

Little Idiot wrote:
Greyman wrote:Lepton flavour appears to be a proximately conserved quality. While there is evidence that a neutrino's flavour oscillates over time as it travels, there do not appear to be any lepton number violations during particle interactions.

As far as I know, to date, anyway.


Does that mean 'yes, (as far as you know)' to my original question about neutrinos?

As far as I can tell, he was expanding on my simple, direct answer, because he said nothing to contradict it. Therefore, assume that neutrinos do, indeed, match the flavour of the muon/electron that they were produced with, in spite of flavour oscillations.
EDIT: If you want to play safe, you can always try waiting for Greyman to explicitly agree.
FURTHER EDIT: I still think it is pretty safe to assume that a muon neutrino is produced alongside a muon, and an electron neutrino alongside an electron, BY DEFINITION.
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Re: Simple question about particle physics

#7  Postby Greyman » Dec 12, 2017 2:53 pm

Little Idiot wrote:
Greyman wrote:Lepton flavour appears to be a proximately conserved quality. While there is evidence that a neutrino's flavour oscillates over time as it travels, there do not appear to be any lepton number violations during particle interactions.

As far as I know, to date, anyway.
Does that mean 'yes, (as far as you know)' to my original question about neutrinos?
Yes. That is what I said.
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Re: Simple question about particle physics

#8  Postby DavidMcC » Dec 12, 2017 4:47 pm

Greyman wrote:
Little Idiot wrote:
Greyman wrote:Lepton flavour appears to be a proximately conserved quality. While there is evidence that a neutrino's flavour oscillates over time as it travels, there do not appear to be any lepton number violations during particle interactions.

As far as I know, to date, anyway.
Does that mean 'yes, (as far as you know)' to my original question about neutrinos?
Yes. That is what I said.

In your erminology, does lepton number variation include wrong neutrino flavours? I ask, because that was Little Idiot's question. He didn't ask about flavour oscillations, as such, you added that without explanation.
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Re: Simple question about particle physics

#9  Postby Little Idiot » Dec 16, 2017 10:45 am

So much for a simple question bringing a simple answer, eh?

Thanks to David and Greyman who have answered 'yes, probably' to the OP.
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Re: Simple question about particle physics

#10  Postby Blip » Dec 16, 2017 2:24 pm


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Re: Simple question about particle physics

#11  Postby newolder » Jan 28, 2018 11:55 am

This Symmetry Magazine article, "How heavy is a neutrino?" explains a bit more on how neutrinos are modelled in today's thinking...
...
Neutrinos come in three flavors: electron, muon and tau. When a neutrino hits a neutrino detector, a muon, electron or tau particle is produced. When you catch a neutrino accompanied by an electron, you call it an electron neutrino, and so on.

Knowing this, you might be forgiven for thinking that there are three types of neutrinos: electron neutrinos, muon neutrinos and tau neutrinos. But that’s not quite right.

That’s because every neutrino is actually a quantum superposition of all three flavors. Depending on the energy of a neutrino and where you catch it on its journey, it has a different likelihood of appearing as electron-flavored, muon-flavored or tau-flavored.
...
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Re: Simple question about particle physics

#12  Postby DavidMcC » Jan 31, 2018 3:18 pm

newolder wrote:...
...

That’s because every neutrino is actually a quantum superposition of all three flavors. Depending on the energy of a neutrino and where you catch it on its journey, it has a different likelihood of appearing as electron-flavored, muon-flavored or tau-flavored.
...

Yes, but I thought that neutrino flavour was defined not by what it is at any given moment, but by what kind of lepton it started off in association with. Am I right?
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Re: Simple question about particle physics

#13  Postby newolder » Jan 31, 2018 3:42 pm

DavidMcC wrote:
newolder wrote:...
...

That’s because every neutrino is actually a quantum superposition of all three flavors. Depending on the energy of a neutrino and where you catch it on its journey, it has a different likelihood of appearing as electron-flavored, muon-flavored or tau-flavored.
...

Yes, but I thought that neutrino flavour was defined not by what it is at any given moment, but by what kind of lepton it started off in association with. Am I right?

The first sentence in that snippet gives the current thinking.

The earlier piece of the quote you snipped has:
Neutrinos come in three flavors: electron, muon and tau. When a neutrino hits a neutrino detector, a muon, electron or tau particle is produced. When you catch a neutrino accompanied by an electron, you call it an electron neutrino, and so on.
...

A particular flavour at a particular time is determined by measurement.

IOW, "What they started out as..." is a quantum superposition of the three flavors (or mass states, as per article). ("If quantum mechanics does not seem weird then you haven't grasped quantum mechanics." - Someone or other (probably Feynman) at some time, somewhere.)
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