Talk:Baryon

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[edit] Elementary

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)

[edit] Include table?

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

[edit] Number of baryons

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)

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

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)

[edit] baryons, mesons, and hadrons

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 bosans. Are bosons Hadrons or are hadrons bosons, etc....

Kingdon 16:21, 10 May 2007 (UTC)

[edit] In cosmology

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)