Talk:Baryon

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Elementary[edit]

My references say that baryons are elementary particles, they consist of quarks and cannot be broken down. Mesons also fit this description.

Two web sources for you to examine - [1] and [2]

Also my dictionary says: Hadron Pronunciation: (had'ron), [key] —n. Physics.
any elementary particle that is subject to the strong interaction. Hadrons are subdivided into baryons and mesons. Cf. quark.

All the sources I've seen don't call baryons as elementary particles, because they are composites, even if they can't be physically ripped apart. I would guess the usage varies, and so suggest that they not be called elementary.

Give some citations - I'm sure we can sort it out. I've given three, but I acknowledge that they are all quoting generalist literature. By the way, the link to boson simply redirects to particle physics... surely they deserve their own article. - MMGB

Elementary refers to any particle which is not composed of smaller particles. "Broken down" is not meant in a physical sense. There are exactly 16 elementary particles known to date: 6 quarks, 6 leptons, and 4 gauge bosons (not including antiparticles or gluon flavors). The jury is still out on the Higgs boson and the graviton. See http://www.neutron.anl.gov/hyper-physics/Particles.html for a good diagram -- Xaonon

Well I guess this is a case where infoplease got it wrong - some other sources I have checked confirm this position. If/When we have an article on elementary particles this confusion should be addressed directly.


Someone mentioned that mesons may be a superposition of quark-antiquark pairs, but I think it would be less confusing and more accurate to describe them as a pair where each of the quark and antiquarks may be in a superposition of states (colors and generations). Does this sound fair?



Does anyone know the mass of a baryon? Is it just the mass of a proton? or neutron? --PY

It varies between different types of baryon. If a specific baryon is a proton, then it has the mass of a proton; if a neutron, then it has the mass of a neutron; and so on. -- Paul A


PY, I believe that you are assuming that the baryon is a particle when it is actually a classification of particles. There are dozens of different baryons, each with its own mass.


Keep in mind that there was not a general consensus that hadrons were made of quarks until the mid-1970s. Older references could well describe them as elementary particles simply because their constituents were undiscovered or not generally accepted; even today they are sometimes called elementary particles because of a kind of language inertia. But we probably shouldn't call them that. --Matt McIrvin 00:29, 1 Oct 2004 (UTC)

Include table?[edit]

This article lacks a table summarising the properties of the mentioned baryons. Obviously a comprehensive table of known baryons would be a bit too large for the article. :) But something like this might be nice: http://hyperphysics.phy-astr.gsu.edu/hbase/particles/baryon.html

A mention of the quantum numbers associated with baryons would be nice as well. (Baryon number, strangeness etc.)


Here's a first attempt, perhaps someone can check that there are no errors in it? (Either of fact or of format :) ). It includes all of the baryons mentioned in the article, in the order mentioned.

Various Baryons
Particle Symbol Makeup Rest mass
MeV/c2
B S C Mean lifetime
s
Proton p uud 938.3 +1 0 0 Stable1
Neutron n ddu 939.6 +1 0 0 920
Delta Δ++ uuu 1232 +1 0 0 .6×10-23
Delta Δ+ uud 1232 +1 0 0 .6×10-23
Delta Δ0 udd 1232 +1 0 0 .6×10-23
Delta Δ- ddd 1232 +1 0 0 .6×10-23
Lambda Λ0 uds 1115.7 +1 -1 0 2.60×10-10
Lambda Λ+c udc 2285 +1 0 1 2.0×10-13
Sigma Σ+ uus 1189.4 +1 -1 0 0.8×10-10
Sigma Σ0 uds 1192.5 +1 -1 0 6×10-20
Sigma Σ- dds 1197.4 +1 -1 0 1.5×10-10
Xi Ξ0 uss 1315 +1 -2 0 2.9×10-10
Xi Ξ- dss 1321 +1 -2 0 1.6×10-10
Omega Ω- sss 1672 +1 -3 0 0.82×10-10

1at least 1030


It looks fine to me, except that some numbers aren't being written in proper scientific notation. Instead of 0.6×10-23, for example, it should be 6x10-24. I would edit it myself, but I haven't quite had the time to thoroughly look through the editing system.

The numbers are written that way so you can more easily compare the decay times of related particles. Tho in the case you cited (the Deltas), none of the related particles seem to have made the table, so there's no reason that one should be in a funny format. -- Xerxes 14:52, 2005 Mar 10 (UTC)

After reading your post, I edited the scientific notation of the Deltas.

Are you sure that the neutron has a half-life of nine hundred and twenty seconds? That seems awfully short. Didn't someone have to build a really, really big detector to try to determine the half-life, because it was extremely long? [...] Okay, I looked it up, and neutrons do decay that quickly, but only when not bound inside nuclei. Should this be mentioned? I was led to the impression that we should all be big masses of Hydrogen-1 by now. grendel|khan 23:23, 2005 Mar 11 (UTC)


Thank you to the author of this article. You did a great job explaining in detail the topic; yet not too esoteric that someone without a strong background in physics won't understand the information (such as I). --jorgekluney

Number of baryons[edit]

Baryons are made from 3 quarks, any quarks. Since there are 6 different quarks, then we have 6^3 combinations of 3 quarks. However, from the Delta+ and the proton, each with quark composition u/u/d, it looks like the spin orientation have to be taken into account. Since each quark can be in +1/2 or -1/2 isospin state, then we have 12 different quarks/quarkstates possible for each of the three quarks, which gives us 12^3 different combinations of three quarks. If we remove the degeneracies (such as ssd (3/2),sds(3/2),dss(3/2)), then we have 364 (12+11+10...+11+10+9...+10+9+8+...3+2+1+2+1+1) distinct combination of quarks/quarkstates.

Now I'm not sure of this, but I think that it is the modulus of the spin that is important, so particles with spin -3/2 and -1/2 really are the same than the particles with spin 3/2 and spin 1/2. Removing these degeneracies leaves us with half the particles, and thus there are 182 distinct baryons that can be made from three quarks.

Did I understand it correctly? It would also be interesting if someone updated the list of baryons to take into account all the possibilities, with placeholders for the undiscovered particles Headbomb 22:11, 22 March 2008 (UTC)

bottom baryons, charmed baryons, where are they?[edit]

The article makes no mention of baryons with heavy quark content. See for example the summary page from the Review of Particle Physics ( W.-M. Yao et al., Journal of Physics G 33, 1 (2006) ) [3]. Erkcan 16:48, 24 July 2006 (UTC)

Sorry, it does mention at the very bottom, but the description mentions nucleons and hyperons only. Erkcan 16:51, 24 July 2006 (UTC)

Charmed baryons also have their own page -- I'll add a link to it. I'm not convinced that it should be a separate page (as opposed to a section within this one) but since it's nearly empty it's a moot point for now. As far as the ordering within this page goes, I think that introducing the light baryons and the octet+decuplet first and bringing up heavy flavours later is the right thing to do; isospin and strangeness are complicated enough without adding a third dimension right off the bat. Do you have any thoughts on what a heavy baryon section should cover? I had trouble coming up with a middle ground between "very vague" and "painful detail". Physicsdog 07:41, 27 July 2006 (UTC)

I also think that charmed and bottom baryons should be a section here. As for what should go in that section, I haven't got a good suggestion yet. As for the ordering within the page, I have no objection to your logic, but the current description (at the very top) seems to be misleading: It reads as if baryons = nucleons + hyperons. Just few sentences below it again says baryons = nucleons + lambda, omega, xi, delta. I understand that we might not want to go into c and b baryons right away, but IMHO the article looks somewhat inconsistent at the moment. Erkcan 16:04, 28 July 2006 (UTC)

baryons, mesons, and hadrons[edit]

I moved the following text from the article to here:

-- Here it says Baryons and Mesons are known as Hadrons, but then it says mesons are a type of bosons. Are bosons Hadrons or are hadrons bosons, etc....

Kingdon 16:21, 10 May 2007 (UTC)

In cosmology[edit]

In cosmology, it seems that baryonic matter can refer to both protons and electrons:

[Electrons and protons] are often grouped together and called baryons, nomenclature which is obviously ridiculous (electrons are leptons, not baryons) but nonetheless common.
-Dodelson, Modern Cosmology

Is this a common enough practice to mention in the article? --Starwed (talk) 11:47, 28 February 2008 (UTC)

Strangeness Convention[edit]

Please note that the diagrams (black-and-white, with pink circles for the states) in the "isospin" and the "baryons" page show the value of the strangeness opposite of the standard convention (which in turn is followed in the "mesons" page and the table above, under the "Include Table?" heading. For example, the Omega- baryon has strangeness -3, but is in the diagram on the "baryons" and the "isospin" pages is shown to have strangeness "3", with the strangeness axis oriented downward. I do not know enough about this wiki editing system to edit the figures and fix this. Tristan (talk) 02:42, 3 October 2009 (UTC)

Hadron overhaul[edit]

Please give input at Talk:Hadron#Hadron overhaul. Thanks. Headbomb {ταλκκοντριβς – WP Physics} 02:01, 24 January 2010 (UTC)

Delta parity[edit]

The article states that the intrinsic parity of a baryon is (-1)^L and therefore the parity of all ground state baryons is positive. It would be useful if some expert on the subject added some scattering process where the relative parity between a Nucleon and a Delta becomes determined. Otherwise the statement seems a little bit unsubstantiated. Kotika98 (talk) 14:34, 6 July 2010 (UTC)

Delta spin[edit]

The Delta (Δ++ (uuu)) has the spin of all three quarks aligned. What is the particle formed when one of the quarks is anti-parallel to the others? It should have spin 1/2, yet doesn't appear in the octet. Why is that? --Michael C. Price talk 10:02, 19 October 2010 (UTC)

First Sentence[edit]

"A baryon be a composite particle made of three quarks." What are we, pirates? Hahaha. Fixing it now, but it was too funny not to point out. Bugbrain 04 (talk) 00:49, 28 January 2011 (UTC)

Baryons have no gluons[edit]

I'm glad that this article makes no mention of the fanciful claim that Baryons might possibly contain gluons that would then contribute to their total masses, like say the proton article does. Hcobb (talk) 15:18, 9 January 2012 (UTC)

If emission and absorption of (virtual) gluons by quarks would not take place in baryons, they wouldn't be stable. And the analysis of the structure functions obtained from deep inelastic scattering of electrons and neutrinos by nucleons shows that 1/2 of the nucleon momentum is carried by particles that interact neither electromagnetically nor weakly (like quarks do). So why do you consider identifying these particles with the gluons fanciful? Impulseigenzustand (talk) 04:09, 16 July 2013 (UTC)

a single quark has a spin vector of length 1⁄2[edit]

I know what the author of this wants to say, but it is not correct. The quantum number S is 1/2, the length of the vector is ħ*sqrt(S(S+1)) != S. Impulseigenzustand (talk) 04:16, 16 July 2013 (UTC)

Why does Pauli exclusion principle prohibit nucleon with charge +2 ?[edit]

The parenthetical remark in the following fragment of the article confused me:

In the "isospin picture", the four Deltas and the two nucleons were thought to be the different states of two particles. However in the quark model, Deltas are different states of nucleons (the N++ or N are forbidden by Pauli's exclusion principle). Isospin, although conveying an inaccurate picture of things, is still used to classify baryons, leading to unnatural and often confusing nomenclature.

As I understood the rest of the article, the difference between Δ (Delta-particles) and N (nucleons) is their spin. In a Δ the spins of the quarks are aligned to give S = 3/2, while in an N one quark has an opposite spin to the other quarks, giving S = 1/2. So the quarks are more similar in a Δ, leading to the question why does Pauli apply to N and not to Δ? Perhaps this needs to be clarified somewhere. -- Jitse Niesen (talk) 10:19, 14 August 2013 (UTC)

I'm not really sure what your background is, but Pauli, in a more formal way, means that baryons need to be overall antisymmetric with respect to the exchange of any two of its constituents. The degrees of liberty involved are space, color, flavour, and spin. For spin = 1/2 (as in nucleons), the spatial part is symmetrical. Color is always antisymmetrical (rgb - rbg - grb + gbr + brg - bgr) [exchange the first letter with the second letter, and you obtain the same thing with a - sign [grb - brg - rgb + bgr + rbg - gbr)]. Spin and flavour are individually of mixed symmetry, and together symmetrical (very long term, so I won't bother writing it down).
If you wanted a N++, its flavour part would necessarily be symmetrical (uuu), which means spin would need to be symmetrical. But you cannot make an symmetrical spin 1/2 part, you can only make those with mixed symmetries. So you cannot have uuu (analogue of the Δ++) or ddd (analogue of the Δ), or sss (which would be the analogue of the Ω), or any baryons with the same three quarks in a spin-1/2 configuration.
If you need to read more on it, I would suggest ISBN 978-0471164333 and ISBN 978-0471164357 (to get how spin and symmetries work), and then ISBN 978-3527406012 for how that works with light baryons and mesons. I would recommend my own thesis [G. Landry, (2013), "Symétries et nomenclature des baryons: Proposition d'une nouvelle nomenclature", (Université de Moncton).], as it directly tackles this stuff in more details than you would usually encounter, but it's a thesis, which can be annoying to obtain, and it's in French, which you may not understand. Headbomb {talk / contribs / physics / books} 21:45, 14 August 2013 (UTC)

Thanks. That's very helpful in pointing out the right direction. I did one university course on quantum mechanics a dozen years ago, which covered some of this stuff, but not in great detail and I forgot most of it. My mistake was in supposing that the Pauli principle has the narrow meaning of "no two in the same state", while - as I now saw, rather embarrassingly, in the second (!) sentence of Pauli exclusion principle - it refers to the anti-symmetry of the wave function. -- Jitse Niesen (talk) 11:34, 15 August 2013 (UTC)

Note that "no two in the same state" follows from antisymmetry. Take for example, the following antisymmetric state
\frac{1}{\sqrt{2}}\left( |ud \rangle - | du \rangle \right)
What happens if you substitute u for d (or vice-versa)? This becomes 0 (i.e. it's a forbidden state). Headbomb {talk / contribs / physics / books} 15:10, 15 August 2013 (UTC)

Binding energy and mass[edit]

The success of the isospin model is now understood to be the result of the similar masses of the u and d quarks.

Isn't most of the mass of baryons the mass-energy of strong interaction? --130.233.162.130 (talk) 12:42, 8 November 2013 (UTC)

Yes, but the reason why the proton (N+) and neutron (N0) [for example] have similiar masses of roughly 939 MeV/c2 is because the up and down quarks have similar masses. If you change the proton's down quark to a strange quark (uud → uus), you get a Σ+ baryon which is much more massive (roughly 1190 MeV/c2), in great part because the strange quark is more massive than the down quarks. Headbomb {talk / contribs / physics / books} 12:58, 8 November 2013 (UTC)

Star Trek use of the word baryons/baryon[edit]

Does any science-minded person who knows Star Trek well know whether it uses the word baryons/baryon in a similar or same way as current science? (It has been said that Star Trek (by some point) often tried to accurately use real science (as known then) mixed with Star-Trek-universe science.) The more info (and in layman's terms) about its use of this, the better. Thanks! Misty MH (talk) 02:40, 17 February 2014 (UTC)