Talk:Neutrino

History of search for mass should be separate

When describing the mass of the neutrino, it is not necessary to tell the whole history of the search for the mass. It's best to describe some of the most recent estimates and some details, and put the history of the search in another section or another page. -- Thomas Barlow.

"Pauli postulated what is now called the electron neutrino" -- shouldn't that be "electron antineutrino"?

This note seems inaccurate: "More specifically, Pauli postulated what is now called the electron neutrino."

Per https://en.wikipedia.org/wiki/Beta_decay Pauli did that in 1930, presumably for beta minus decay, since beta plus decay wasn't discovered until 1934. That article also says, "In beta minus (β−) decay, a neutron is converted to a proton, and the process creates an electron and an electron antineutrino; while in beta plus (β+) decay, a proton is converted to a neutron and the process creates a positron and an electron neutrino."

Consequently, wouldn't it be more accurate to say that Pauli postulated what is now called the electron antineutrino? — Preceding unsigned comment added by 76.10.180.57 (talk) 19:49, 16 April 2022 (UTC)

Neil Turok on massless neutrinos

@Eric Kvaalen inserted a statement that the mass of the lightest neutrino "may even be zero" [1]. First on the procedure: I think that after one revert it should be up to the inserting user to justify their addition. Nevertheless, here's the justification for my revert: The quote from Neil Turok's interview that is given as a reference is rather vague and incidental. The interview appears to (it is behind a paywall and not accessible to me) and the quote taken from the interview does discuss Turok's theory on parallel universes, not neutrinos as such (if neutrino is massless, then that supports his theory). It does not say why Turok thinks that a massless remains a viable option and why we should take his statement seriously (other than because he is a respected cosmologist). This may be a very particular view point, the reader of our article cannot know. As this addition is in the lead section (which should be treated very sensitively with respect to statements that may not reflect the general state of knowledge on the subject) I think it should go. If there are more specific statements in Turok's interview that can be further supported by published literature, then the statement can stay. --Wrongfilter (talk) 17:21, 28 January 2023 (UTC)

@Wrongfilter: Thank you for your explanation. I added a couple more sentences from the interview. Yes indeed, I think that we should take his statement seriously because he is a respected cosmmologist, one of the leaders in the field. The interview is about his theory (his and Latham Boyle's) that there is a "universe" going backwards in time from the Big Bang, it's not about parallel "universes". But that's not important. At the end, he is asked "What observations would persuade people?" and he starts his answer with "Number one: show that the lightest neutrino is massless. If dark matter is composed of stable, right-handed neutrinos – as in our mirror universe picture – then this must also be true. Fortunately, within three to five years, large-scale galaxy surveys will make that measurement. If they find that it’s massless, then we’ll really be on a good road."

The article says that he will release the final paper in their series on the mirror universe later this week. I think that paper will probably also say something about this, and will provide a better reference.

I don't really understand this business of neutrino masses, but there is some explanation in the article "Sterile neutrino". It seems to me however that we don't know that the electron neutrino has mass. We know that there is a difference between its mass and that of the other neutrinos, because otherwise there would be no neutrino oscillation, but that doesn't mean that the electron neutrino mass is non-zero. (Two gamma-ray photons can collide and produce an electron-positron pair even though the photons are massless. I think that is similar.)

Eric Kvaalen (talk) 19:22, 28 January 2023 (UTC)

Nothing in the existing theory of neutrinos prohibits one of the flavors from being massless — indeed, “the” neutrino was presumed to be massless from the outset — so it shouldn’t be controversial to state that, but of course it ought to be referenced. The Turok angle given in the disputed edit is, technically, WP:SYNTH because the reasoning is “Turok et al have a theory that depends on a massless flavor of neutrino, and we trust Turok et al are not tendering baseless physical theories because their work is WP:RELIABLE”. However, in a formal paper describing their work, Turok et al state,

In particular, current experimental constraints allow for the possibility that one of the three right-handed neutrinos, $\nu _{R}$, is exactly stable. (Note that at most one of the heavy right-handed neutrinos can be stable since, for every heavy right-handed neutrino that is stable, there is a corresponding light left-handed neutrino that is massless, and we know observationally that at most one of the light neutrinos is massless.

In other words, this is known. Strebe (talk) 19:40, 28 January 2023 (UTC)

Thanks, that works as a proper reference. --Wrongfilter (talk) 20:47, 28 January 2023 (UTC)

Yeah, thanks. While I agree that "the" neutrino was originally thought to be massless, that was before neutrino oxcillation was discovered. So for a layman like me it's not entirely obvious that the electron neutrino may still be massless. By the way, I disagree with the "synthesis" policy, or at least with the way people often interpret it. It is used to prohibit any statement, not backed up by an explicit reference, no matter how obvious, that indicates the use of a little intelligence on the part of the "editor". For instance, a couple months ago I calculated the mass percentages of the components of the earth's atmosphere, from the molar percentages, and this was reverted (see Talk:Atmosphere of Earth). Eric Kvaalen (talk) 10:06, 1 February 2023 (UTC)

There is no "mass of an electron neutrino". All the flavor eigenstates (electron/muon/tau neutrino) are superpositions of the mass eigenstates. The lightest of these mass eigenstates could be massless. We don't know because mixing only gives access to differences and measurements of the absolute masses are not precise enough yet. Concerning WP:SYNTH, there is a wide range of interpretations among users. Some even "change their mind" from discussion to discussion based on what they prefer at that moment. --mfb (talk) 11:39, 1 February 2023 (UTC)

Just to clarify the history. Originally (~1930s), as stated in the article, the neutrino was postulated that the neutrino had a similar mass to the electron. It was found to be less than this, and by the time the neutrino was incorporated into the Standard Model was it thought to be massless (~1960s). Then when neutrino oscillation was discovered, at least some neutrino mass eigenstates were non-zero (~1990s). Dja1979 (talk) 18:21, 1 February 2023 (UTC)

References

Should the following apparently-redundant paragraph be removed from the article?

The resulting positron annihilation with electrons in the detector material created photons with an energy of about 0.5 MeV. Pairs of photons in coincidence could be detected by the two scintillation detectors above and below the target. The neutrons were captured by cadmium nuclei resulting in gamma rays of about 8 MeV that were detected a few microseconds after the photons from a positron annihilation event.

HOTmag (talk) 09:20, 23 October 2024 (UTC)

Why do you think that paragraph is redundant? --Wrongfilter (talk) 09:57, 23 October 2024 (UTC)

Because this paragraph is about electron-positron annihilation rather than about neutrinos, so I can't see how this paragraph has anything to do with our article dealing with neutrinos.

It seems that a user had copied this paragraph from an irrelevant source and inserted it by mistake into our article, because they probably confused "neutrons" (mentioned in this paragraph) with "neutrinos" (not mentioned). HOTmag (talk) 10:57, 23 October 2024 (UTC)

It explains how the positron and the neutron created in the reaction are detected to distinguish the signature of this particular reaction from all the background processes that are going on. It's a valid and necessary description of the Cowan–Reines neutrino experiment (see there for more details). --Wrongfilter (talk) 11:21, 23 October 2024 (UTC)

Thank you for this clarification. HOTmag (talk) 12:11, 23 October 2024 (UTC)

I agree that the entire paragraph including the quoted content is confusing. It starts with "Antineutrinos were first detected..." which is confusing since we've not yet learned about detecting neutrinos. It includes sentence ending in a colon, then "In the Cowan and Reines experiment, instead of an outgoing neutrino..." which is again is unclear where that comes from.

The section has no sources so I can't fix it. Maybe we should just delete it. Johnjbarton (talk) 16:32, 23 October 2024 (UTC)

Neutrino mass needs to be updated. (Where did 0.120 eV/c² come from?)

The KATRIN project is no longer in the "planning stages". They published a value for the mass of the electron antineutrino in the 2025-04-11 issue of Science: m_ν < 0.45 eV/c² (8.0×10⁻³⁷ kg) at 90% confidence level. I propose that this value replace the current one: m_ν < 0.120 eV/c².

I could not find the value of m_ν < 0.120 eV/c² anywhere in the 2016 Mertens paper, so I don't know why that's identified as the source. Their paper is a review of the experimental techniques and does not state an upper mass limit.

The PDG reference by Olive does report a mass, but it's m_ν < 0.2 eV/c² not m_ν < 0.120 eV/c². So where did our current fact come from? 2603:7000:9501:3A00:B959:14C6:342:2E9E (talk) 02:00, 8 May 2025 (UTC)

The value of <0.120eV/c2 is the cosmological limit quoted in the Mertens' source cited in the infobar. That value is listed in the intro to Mertens comes from a 2015 paper:

• Palanque-Delabrouille, N., Yeche, C., Baur, J., Magneville, C., Rossi, G., Lesgourgues, J., ... & Weinberg, D. (2015). Neutrino masses and cosmology with Lyman-alpha forest power spectrum. Journal of Cosmology and Astroparticle Physics, 2015(11), 011.

Neither the Mertens source nor the one it cites is appropriate in my opinion. Mertens is essential an outline of the KATRIN value proposition and the 2015 paper is a primary source. Similarly the recent KATRIN value is not appropriate, as it is a primary source.

The appropriate source is the Particle Data Group review for 2024. One of the values they cite is the <0.8eV/c2 from Akers which is the 2021 KATRIN team result, also used as the point of comparison in the recent KATRIN Science article. The Science article is from a large team with a track record published in a top journal and thus could be discussed in the article.

The real problem here is "one of the values". In my opinion our infobar should reflect what is known. The number of types of neutrinos is at least 3. The mass of "the neutrino" is only known to be greater than zero. Different techniques come up with different values for a combination of three neutrinos. The cosmological limit is tighter than any measurement but requires assuming the cosmology. This is discussed in the article.

I changed the reference to cite the 2024 PDG memo and note that this is the cosmological limit. I think ">0" would also be a valid choice. Johnjbarton (talk) 03:55, 8 May 2025 (UTC)

"Similarly the recent KATRIN value is not appropriate, as it is a primary source."

Never heard that before. 2603:7000:9501:3A00:65D2:72F:CE89:4BE6 (talk) 12:00, 8 May 2025 (UTC)

References

Less than one millionth of electron mass

It seems interesting that the neutrino mass is less than one millionth of the electron mass, which is 9.1 x 10^-31 kg or 0.5 Mev/c². Any opinions on the best way to make the comparison in the article? Dirac66 (talk) 22:17, 11 June 2025 (UTC)

Well my cheeky answer is "by citing a good source". The significance of particular comparisons are best from sources IMO. In this case the issues are confounded by the unconventional type of the evidence. I guess most sources would focus on "not zero, that's all we really know" and that is what we should reflect.

Would this comparison to the electron be significant? For readers aware of the history of the electron maybe it would be. For other readers? Any way just my 2 cents. Johnjbarton (talk) 23:11, 11 June 2025(UTC)

Thanks, that suggests a way to rephrase my question. I'll ask now: what (if anything) does the literature say about the significance (or importance) of a mass which is now known to be non-zero but so small relative to the electron? And yes, the answer needs a good source (which I don't have). Dirac66 (talk) 00:43, 12 June 2025 (UTC)

Sounds like this is what you are looking for:

• The neutrino masses are at least five orders of magnitude smaller than the mass of any other fermion of the standard model, which may point to a different underlying mass-creation mechanism. The determination of the neutrino mass would, thus, shed light on the fundamental open question of the origin of particle masses. Despite the smallness of their masses, neutrinos play a crucial role in the evolution of large-scale structures of our cosmos due to their high abundance in the Universe.
• "Direct neutrino-mass measurement with sub-electronvolt sensitivity." Nature Physics 18, no. 2 (2022): 160-166.

This source also has references for theoretical arguments and for the cosmological limit. Johnjbarton (talk) 02:19, 12 June 2025 (UTC)

Yes, this source looks very good, and I note that it is even open-access. Would you like to write a short paragraph to make the point about the 5 (or 6?) orders of magnitude and refer to this Nature Physics article? Dirac66 (talk) 01:19, 15 June 2025 (UTC)

I edited the mass section, please check. Johnjbarton (talk) 02:37, 15 June 2025 (UTC)

Looks good, thanks. Two minor suggestions: 1) Ref. 38 is ref. 11 repeated with a more complete list of authors, so we could combine their footnotes. 2) I think we should identify the next lightest fermion as the electron, using a link to Elementary particle#Mass which has a simple table. Dirac66 (talk) 18:16, 15 June 2025 (UTC)