Talk:Pion

Why is there only one neutral pion?

To the layman, it seems odd that there is only one neutral pion — shouldn't there be one up+antiup and one down+antidown? Well, the math doesn't come out that way (short remarks above suggest earlier versions of the article explicitly described the $\pi ^{0}$ as an equal superposition of $u{\bar {u}}$ and $d{\bar {d}}$), but the article could do with an explicit explanation of how this comes about. (Possibly point 6 in the above todo list is a more technical way of saying the same thing.) 130.243.68.180 (talk) 18:12, 11 May 2018 (UTC)

I was about to ask this. I suspect it should be on or the other linear combination of the two. (That is, plus or minus.) Gah4 (talk) 01:13, 17 November 2022 (UTC)

The reason there's only one neutral Pion, is that the total isospin of a symmetric superposition of $u{\bar {u}}$ and $d{\bar {d}}$ is zero. When it is said that the charged Pions have a isospin of +1 and -1 and the neutral Pion has an isospin of 0, that is the projection of isospin in all directions. The total isospin of all three is 1 (or rather, square root of three divided by two). This is in perfect analogy with a particle with spin 1, which has three possible eigenvalues in the z component of spin, +1, -1, and 0, but always has total spin angular momentum of square root of three divided by two. Unfortunately I can't think of a simple non-technical way to explain this and why an antisymmetric superposition has total spin 1 and a symmetric superposition has total spin 0. So there sorta is a second neutral pion, but it actually isn't a pion, but a superposition of the eta and eta prime mesons. I guess point 6 is what I just described, but in representation theory terms (i.e. if you have a rank 2 tensor over a $\mathbb {C} ^{2}$ vector space, the trace is invariant under $SU(2)$, but the traceless component transforms like the triplet representation). --Lukflug (talk) 20:01, 22 November 2022 (UTC)

This one says that it is the ${\frac {u{\bar {u}}-d{\bar {d}}}{\sqrt {2}}}$. That seems like what I would expect, though I wasn't sure if it was the symmetric or antisymmetric case. Gah4 (talk) 06:09, 23 November 2022 (UTC)

The counterintuitive - sign is an artifact of the conjugate SU(2) representation acting on the antiquark. If you were composing spins, it would correspond to a + sign, of the spin triplet. The isoscalar, by contrast, has a + sign, corresponding to the - sign of the spin singlet. Cuzkatzimhut (talk) 14:25, 23 November 2022 (UTC)

Seems that there should be mention of the eta meson, a different linear combination, and the eightfold way describing how they come together. Gah4 (talk) 09:24, 30 September 2024 (UTC)

Correct information looks misleading

The information that π0 → 3γ decay is forbidden looks like it is a description of decay which takes place but forbidden and may be not correcly understood. It happens because the information on prohibited decay is mixed with information on real decay pathways. Probably, if this info would be given after real decay pathways, it would be great, as it is important.

The decay π0 → 3γ (as well as decays into any odd number of photons) is forbidden by the C-symmetry of the electromagnetic interaction. The intrinsic C-parity of the π0 is +1, while the C-parity of a system of n photons is (−1)n. Unsigned comment by User:81.211.8.86 .

Please sign your comments. What is your point? The decay is forbidden and impossible. Cuzkatzimhut (talk) 18:53, 22 May 2019 (UTC)

In many cases, forbidden means allowed using some other mechanism, often that is much slower. See Forbidden mechanism. Gah4 (talk) 19:55, 24 November 2022 (UTC)

What about spin?

Lack of spin 2600:100F:B1B8:A729:0:36:90BF:BF01 (talk) 22:02, 19 December 2023 (UTC)

Bibha Chowdhury Addition

Helped @Jonesey95 I had added credible sources and true sources that she and Debendra Observed the pion first in cosmic rays but my edit was unfairly removed without checking. I had given here PhD also.

This is very annoying and unfair MarsOlympus (talk) 02:56, 9 February 2026 (UTC)

Wikipedia has been Very biased towards Indian Scientists research.

There EXISTS an wikipedia of the two scientists too where their work has been clearly mentioned too citing 12 or so sources. Any "good" editor must check them before jumping to conclusions. MarsOlympus (talk) 02:58, 9 February 2026 (UTC)

https://www.nature.com/articles/148259a0

One of the many sources I could find. You are requested to go through it. MarsOlympus (talk) 13:01, 9 February 2026 (UTC)

Two more sources:

https://web.archive.org/web/20181206235038/https://copac.jisc.ac.uk/id/35205860?style=html

Wikipedia article:

https://en.wikipedia.org/wiki/Bibha_Chowdhuri

The Devs are requested to go through these please.... MarsOlympus (talk) 13:08, 9 February 2026 (UTC)

Please stop breaking the formatting of this page. I have left a help template for you; someone who is willing to take the time to understand what you want should stop by to assist you. – Jonesey95 (talk) 15:52, 9 February 2026 (UTC)

Hey there! Was informed that someone needed help at the Teahouse. What seems to be the issue? ArthurPlummer ( :) | talk | contribs) 00:31, 10 February 2026 (UTC)

Actually I wanted help to add to the List of discovery of the pions the names of Bibha Chowdhuri and Debendra Mohan Bose.

I have the sources which I added above,which are all credible, including from nature.from, reasearchgate, and including her PhD paper.

Also,there exists a wikipedia page on her (Bibha Chowdhuri) where you can get more info about her discovery.

She actually made the independent discovery first, but it went unnoticed.

I don't know how to properly add the references I gave link to above, if you could help me with that MarsOlympus (talk) 06:32, 10 February 2026 (UTC)

The help template hasn't made much difference. I've asked the folks at WikiProject Physics to contribute. Andy Mabbett (Pigsonthewing); Talk to Andy; Andy's edits 19:09, 11 February 2026 (UTC)

@MarsOlympus: I have inserted the new information correctly in the lead. This information will need to be incorporated into the History section now. –LaundryPizza03 (dc̄) 19:19, 11 February 2026 (UTC)

Strictly speaking, none of those three links are usable sources for the present purposes. Wikipedia is not a reliable source itself, and the other two are primary rather than secondary. Stepwise Continuous Dysfunction (talk) 19:30, 11 February 2026 (UTC)

The Telegraph source is secondary, and I have integrated the Chowdhuri & Bose study into the text using a different, more comprehensive secondary account used in Chowdhuri's article. –LaundryPizza03 (dc̄) 20:03, 11 February 2026 (UTC)

Thanks a lot♥️ MarsOlympus (talk) 04:15, 14 February 2026 (UTC)