Do solar neutrinos really change flavor?

  1. Perhaps I'm simply missing something, but it seems to me that the "evidence" to support the belief that neutrinos change "flavor" is very weak at best. From my perspective, the current arguement amounts to "we don't recieve every item we sent, so one of them must have changed into a toad".

    What am I missing?
  2. jcsd
  3. SpaceTiger

    SpaceTiger 2,969
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    The fact that we detect the "toads" in exactly the amounts predicted by theory. The total flux of tau and mu neutrinos coming from the sun is consistent with the previously missing flux of electron neutrinos, as determined by the Sudbury Neutrino Observatory. Even if the numbers didn't add up just right, I think we'd have a tough explaining any significant solar flux of mu and tau neutrinos in the absence of oscillations.
  4. jtbell

    Staff: Mentor

    Yay! Now I know what to answer if anyone ever asks me what the "[itex]\tau[/itex]" in "[itex]\tau[/itex]-neutrino" means. :rofl:
  5. EL

    EL 780
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    At you can read some more:

    See also SNO:s homepage for more details:
  6. Hurkyl

    Hurkyl 15,987
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    If I remember the history, it went like this:

    (1) We wondered if neutrinos had mass. The theory said that if they had mass, then they would change flavors. This is obviously silly, so we decided neutrinos had no mass.

    (2) We count the electron-neutrinos coming from the sun, and find there aren't enough! Ack!

    (3) We revisit the hypothesis that neutrinos have mass, and find out that the observed number of electron-neutrinos is consistent with neutrinos changing flavors. So, we posulate that neutrinos do have mass, and thus change flavors.

    (4) We eventually manage to count the number of tau- and mu-neutrinos, and it agrees with the hypothesis that neutrinos have mass.
  7. Well, the total neutrino count when we add up *all* types of neutrinos is at least "in the ballpark". Theory however suggested that they should all be the same kind of neutrino, and that isn't what we found. Now they claim that neutrinos "change", but how do they change? What causes this change? What exactly is changing? The wavelength? The energy state? How are they changing exactly, and where in the process do they change?

    The anology here that comes to mind is predicting from a model that you will only see red light in quantity X. Instead we see white light in with red making up only 1/3 of the light. Someone then claims that red light turns to blue and yellow between here and there. I find that a bit hard to swallow without some clear evidence that this actually occurs.

    Here's the problem I have in a nutshell with the nuetrino studies to date: Where is the actual evidence that they change flavors?

    In other words if we were to shoot 10 of one kind of neutrino at a detector and it were to count 3 of one kind of neutrino, 4 of another, 3 of another flavor at the other end then we would have clear evidence that neutrinos change flavor in mid flight. If however one neutrino simply gets "lost" along the way, we cant' simply assume that it transformed itself into another kind of neutrino. QM insists that nothing is entirely predictable, and if a neutrino does have mass, then it can be scattered too. The current studies seem to be trying to correlate a "missing" (potentially scattered neutrino) with a nuetrino of a different flavor *without* first detecting that kind of neutrino in it's place. Even if we do recieve multiple kinds of neutrinos, we can't automatically *assume* they are began as one type of neutrino. How do we know for instance that there aren't a plethora of different flavored neutrinos being produced in the areas where Rhessi sees neutron capture and position/electron annihilation signatures?
    Last edited: May 1, 2006
  8. :smile:

    Ok, I admit, it was a goofy choice of words. :)
  9. SpaceTiger

    SpaceTiger 2,969
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    See here:

    Neutrinos, can you explain them to me?

    I'm sure there are also some nice sources in the High Energy forum if you do an archive search.

    Similar (though not identical) flavor-mixing behavior is exhibited by quarks and has been under investigation for quite some time.

    That's exactly what happened with the sun. It produced only electron neutrinos (the total number was predicted by theory) and on earth, we found the right number of neutrinos, but found that some of them had changed flavor. Or are you saying that it's a coincidence that the total number of neutrinos matches up with our theories of stellar structure?

    That's unlikely, IMO, but there is more evidence. We also have neutrino detectors placed near nuclear reactors that are detecting neutrino oscillation signatures consistent with those inferred from the sun. See, for example, KAMLand.
  10. nrqed

    nrqed 3,106
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    I'd like to add a comment regarding (1) above.
    Actually, the masslessness of the neutrinos in the Standard Model is more than just the fact that flavor changing seemed "silly" :shy:

    It is much more than that. In th Standard Model, with one Higgs particle, neutrinos can not be massive! Pure and simple. Mass terms are forbidden by the theory. Since the Standard Model was so successful (predictions of the W+- and Z_0 and a huge number of other spectacular confirmations), I guess that there was a natural prejudice against neutrino masses (that went beyond not liking flavour changing).

  11. Neutrinos are not my field of expertise, so bear with me a bit:

    So if I understand you correctly, the other neutrinos are *more* massive, and *less* stable. If that is so, then how do they get "more massive", and why wouldn't the stability of the electron neutrino make it revert back?

    I'm saying it's a leap of faith to suggest that the sun only manufacturers one type of neutrino in one particular way. This is expecially true since Rhessi records neutron capture events in the solar atmosphere and it records positron electron anihillation signatures at the bases of the coronal loops. I see no reason to "assume" that *every* neutrino we see coming from the sun began it's life as an electron-neutrino.

    I'm going to have to chew on that link for awhile before I comment.
  12. Hurkyl

    Hurkyl 15,987
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    But you should make sure you aren't assuming otherwise. :tongue:

    I really cannot imagine that physicists would merely assume that (essentially) every neutrino we see coming from the sun began it's life as an electron-neutrino. I would be quite surprised if the assertion is backed by anything less than decades of effort spent trying to model how the sun works.
  13. Point noted. Then again, in a very real way we could say that we see evidence to suggest that there could be multiple processes involved in solar neutrino creation. If other neutrino types posess a greater mass, where do they acquire their mass along the way? If there are stable and less stable forms of neutrinos, why wouldn't most of them revert to the more stable version and be found in this arrangement in greater abundance?

    I personally haven't seen a single solar observation that favors only a single solar model to the exclusion of all other solar models. It therefore seems premature to simply *assume* that neutrinos acquire mass. Again that analogy about light seems to apply. While I might sypathize with the fact that total light output is *around* what was expected, the light is not all red, and we cannot assume all the light from the sun began as a red wavelength.
  14. SpaceTiger

    SpaceTiger 2,969
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    The point was that "electron-type" neutrinos don't have definite mass because they're not a mass eigenstate. The same is true of the other flavors. All neutrinos are stable (as far as we know), so that's not a concern.

    As Hurkyl said, the word "assume" is not doing this justice. The neutrino production rates are calculated in great detail, using all nuclear reactions available at the solar center. As energetic as the center of the sun is, it isn't energetic enough to produce significant quantities of muons or tau particles (along with their associated neutrinos) in its nuclear reactions.
  15. I think a better way to explain the "assumption" is that all neutrinos are "assumed" to be produced by fusion reactions at the core to fit with contemporary gas model theory.

    Yet z-pinch forces in plasma are known to create temperatures more than twice the temperatures of what we might find at the core according to contemporary gas model theory. In fact the plasma in the coronal loops shows every sign of being a very "hot" plasma that is driven by electricity. The coronal loops are the areas of the corona where we find evidence of neutron capture, and the base of these loops show areas that are experiencing positron/electron annihilation.

    As I said, there is a core "assumption" in astronomy that gas model theory must be right, *therefore* neutrinos must somehow change flavors. I've yet to see any hard evidence to support the concept that neutrinos actually do change flavor.

    There seems to be a strong *desire* to explain these various neutrinos in a way that *fits* somehow with gas model theory, but I see no evidence that neutrinos were all originally emitted exactly the same way, from exactly the same processes on the sun.

    It also seems to me (assuming I'm understanding your arguements correctly) that muon and tau neutrinos are actually more energetic than electron neutrinos. Something here doesn't seem to add up. If it requires *more* energy to make these other kinds of neutrinos, how did they gain this excess energy? How do they come to contain this excess energy without violating the conservation of energy laws in the process?
  16. SpaceTiger

    SpaceTiger 2,969
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    It's called a prediction, those things that good theories make.

    Discussion of this belongs in the IR forum.

    It looks more like you don't understand it, as in statements like this:

    The misunderstandings are extensive and it's clear that you're talking way beyond your depth. Your questions have been answered, so I'm locking this thread. If you want to understand neutrino oscillations, I suggest doing some reading or posing some more pedagogical questions in the High Energy forum.
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