Talk:Meson

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Why were spin and discovery date removed from the table?

How can the quark "makeup" contain a root - we are talking about particles, no?

Yep, but the type of particle is just a property of its state. For something like an electron, there's really nothing else that matches the charge and the like, so you get a pure state. But an up-antiup and a down-antidown are just different versions of the same thing, so real states are mixes of them, somewhat like molecular orbitals.

Why is the subtraction then? --Kenny TM~ 12:55, Nov 25, 2004 (UTC)
That's a phase. If you have two possible values, that a quantum entity can have, you can superpose them with a different phase relative to each other. That's a bit hard to explain in an illustrative way but maybe this helps: If you want to use the formalism of quantum mechanics to calculate some property, and you now how to calculate the property for a basis state, the what should you do if you have a superposition of two basis states? Should you add the values, or subtract them, or what? Well, the phase and the \sqrt{2} shows you how to combine the individual values. So, we are not subtracting two quarks. The '-' is merely indicating that properties of the individual quark types have to be subtracted to get the value of the superposition. Simon A. 13:12, 25 Nov 2004 (UTC)

Actually, if you think about it, the "makeup" listings are only valid in the limit in which the up, down and strange have zero mass and the charm, bottom and top have infinite mass. Perhaps this should be clarified somehow? -- Xerxes 19:56, 2005 Feb 3 (UTC)

Is the "famously corrected" part correct? I thought the original word "mesotron" was from the Greek root meso- plus the ending from "neutron" and "electron". Was the actual "correction" more like pointing out that the suffix in "neutron" and "electron" is just -on, not -tron? -- Anonymous, 04:40, 17 June 2005 (UTC)


I think Heisenbergs pun should be elucidated. It believe it should read "there are is 'tr' in 'mesons'", and 'tr' is referring to the trace of some matrix. It isn't about Greek morphology at all. Baad 12:44, 31 October 2005 (UTC)

after a websearch, I think I was mistaken, and Heisenberg's comment was indeed about Greek morphology. meson would just be the Greek neuter form for "middle", meaning "the thing in the middle". The suffix -tron was mistakenly abstracted from the words electron and neutron which coincidentially both have a -tro- suffix. Baad 12:52, 31 October 2005 (UTC)

Contents

[edit] Names

Should the names of the mesons be redirected here, to the list of mesons or to another article? -- Kjkolb 09:08, 19 December 2005 (UTC)

The more important mesons ought to have standalone articles. I don't think it matters much if other mesons redirect to the list or here. The list has a link here at the top anyway. -- Xerxes 19:10, 19 December 2005 (UTC)

[edit] Too complicated

Perhaps a more simple article can be written? This uses too many words that are unknown to the reader, such as "quarks", "antiquarks" and "tetraquarks". If these are going to be in the article, then they should be explained. Scorpionman 23:02, 19 January 2006 (UTC)

A reader unfamiliar with these terms is invited to click on the appropriate links. No individual wiki page can be expected to give the reader a complete science education. -- Xerxes 01:58, 20 January 2006 (UTC)
The introduction could be re-written to be clearer to reader unfamiliar with the topic and the body could stay complicated. I may try to fix it. -Ravedave (help name my baby) 17:59, 26 September 2006 (UTC)

[edit] integral spin

I don't quite understand what u mean by integral. Doesn't that refer to the type of spin. Don't fermions have "half integer times h bar" integral spins as in (n/2)*(h bar) where n = 1,3,5..... In which case it would make more sense to say mesons are hadrons with integer integral "spins" or just integer "spin" ((n/2) * (h bar) where n = 2,4,6....

Alex

Integral spin means just that: integers. 0, 1, 2, etc. -- Xerxes 18:03, 5 June 2006 (UTC)

[edit] \mathrm{u}\, + \bar{\mathrm{u}}

How can a particle (like an up quark \mathrm{u}\,) and its antiparticle (an anti-up, \bar{\mathrm{u}}) coexist within a meson without annihilating each other? --HantaVirus 20:52, 9 August 2006 (UTC)

  • They are tightly bound in the same potential and thus very close to each other, but not in exactly the same position. Particle physics is not my forte, but I would wager that the lifetime is related to the amount of time it takes for the two quarks to "find" each other. Eldereft 01:51, 27 September 2006 (UTC)

[edit] article

Can someone work this information into the article? [1] it is beyond me how it might fit. -Ravedave (help name my baby) 18:02, 26 September 2006 (UTC)


[edit] way too complex

This article is way too complex even for an educated reader to understand.

For instance this sentence in the beginning of the article: "The valence quarks may exist in a superposition of flavor states; for example, the neutral pion is neither an up-antiup pair nor a down-antidown pair, but an equal superposition of both."

'equal superposition of both'? In English please...

"Flavorless mesons are mesons whose flavor quantum numbers are all equal to zero."

You mean, 'are all zero'. Making things more complicated than necessary is a BAD thing.

Apparently the 'charge conjugation parity' page is written by an equally techno-babbling professor. Stop making unreadable pages ffs.

Basically, anything below the heading 'flavorless mesons' is totally incomprehensible. This article needs a rewrite, BIGTIME. —The preceding unsigned comment was added by Crusty007 (talk • contribs) 23:06, 26 September 2006 (UTC)

You have some valid points but there's no need to be rude about it. The intro should be simplified, and I will work on it. It may not be possible to keep the entire article simple; this is a rather technical subject, and except for the most basic details it can't be conveyed accurately without using technical concepts and terms. -- SCZenz 23:55, 26 September 2006 (UTC)

[edit] Intro

Lets work on the intro here. Below is my version, which I think turned out quite well. Do mesons bind protons and neutrons or is that just what they were predicted to do? -Ravedave (help name my baby) 05:39, 27 September 2006 (UTC)


In particle physics, a meson is a subatomic particle that experiences the strong nuclear force. Mesons are not elementary particles, but composite particles consisting of an equal number of quarks and antiquarks. This equal number gives them a baryon number of zero. This seperates them from bosons, which have a baryon number not equal to zero because of their unequal number of quarks and anti-quarks. Both mesons and bosons are a type of hadron. All mesons are unstable and decay in nanoseconds.

Mesons were originally predicted as carriers of the force that bind protons and neutrons together by Hideki Yukawa in 1935. Yukawa was awarded the Nobel Prize in Physics for his theory of mesons. He originally named the particle the 'mesotron', but was famously corrected by Werner Heisenberg (whose father was a professor of Greek at the University of Munich) that there is no 'tr' in the Greek word 'mesos'.

When first described, the muon was identified with the meson family due to its similar mass and was named "mu meson". However, it did not show a strong attraction to nuclear matter and is actually a lepton. Cecil Frank Powell made the first experimental discovery of a true meson, the pion, in 1947.

[edit] leftovers

There are several modern theories in which nucleon-nucleon interactions are mediated by meson exchange. This is area fo study is called quantum hadrodynamics. All known mesons are believed to consist of a quark-antiquark pair — the so-called valence quarks — plus a "sea" of virtual quark-antiquark pairs and virtual gluons. The valence quarks may exist in a superposition of flavor states; for example, the neutral pion is neither an up-antiup pair nor a down-antidown pair, but an equal superposition of both. Pseudoscalar mesons (spin 0) have the lowest rest energy, where the quark and antiquark have opposite spin, and then the vector mesons (spin 1), where the quark and antiquark have parallel spin. Both come in higher-energy versions where the spin is augmented by orbital angular momentum. Searches for exotic mesons that have different constituents are ongoing.

[edit] Comments

The new intro looks good to me. To answer Ravedave's question... Yes, pions, to a good approximation, can be thought of as mediating the residual strong force—i.e., yes they cause the force between nucleons, as predicted by Yuakawa. Of course, that's not exactly what's going on, because really it's the quarks in the pions interacting with the quarks in the nucleons, but it's close enough that pion exchange is a good model. -- SCZenz 21:26, 3 October 2006 (UTC)

[edit] Bosons?

I'm confused as to how mesons can be bosons, and at the same time, be hadrons composed of quarks and antiquarks. Quarks are fermions, no? How can a meson be a fermion and a boson? I thought these were mutually exclusive categories. Please clarify, thanks.24.21.139.41 15:45, 12 May 2007 (UTC)

Mesons are bosons because they have an even number of fermions in their makeup.24.21.139.41 00:31, 14 May 2007 (UTC)
Bosons are any particle with an integer spin, so both force carriers and mesons have integer spin values, quarks on their own have a half spin as do leptons and baryons and so are all defined as fermions, this site might help: http://durpdg.dur.ac.uk/lbl/particleadventure/frameless/fermibos.html Murdochious (talk) 16:31, 15 February 2008 (UTC)

[edit] Sigma boson

It seems to me that the the sigma boson is worth mentioning, though it's more a broad resonance than a particle, because of its historical importance and since it is still the meson which "mediates" the nuclear force, if such a very rough interpretation of the nuclear force is made. I'm not an expert on this, so I guess someone else should write about it (If not, I will have to read this for example and still probably do some mistakes). Of course one should mention it's highly unstable and therefore not exactly a particle, and that mediation of nuclear force by mesons is only an approximate concept, etc. It should also be mentioned that the fact that the sigma is 0++ is responsible to the nuclear force being charge independent and to first approximation also spin independent; Correction to the latter (spin dependence) comes as far as I understand from mediating by the pion which is 0-+. Anyway I could also be wrong in some of these statesments, so somebody else please do the job.Dan Gluck 19:44, 3 June 2007 (UTC)

[edit] needs work

Two things at least are missing from this article and the result is an aimless feeling.

  • it says all mesons are unstable but doesn't say how they form
  • it says mesons were once thought to do the job that gluons do if I understand it correctly, but it doesn't say that nor does it say what mesons actually seem to do.

This page should also mention the eightfold path and say what good that path is toward understanding mesons, or else point to the article on the eightfold path 4.249.198.64 12:56, 22 July 2007 (UTC)