Talk:List of baryons

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This is the discussion/talk page for: List of baryons.

Let's bring this to Featured List/Article status[edit]

edit·history·watch·refresh Stock post message.svg To-do list for List of baryons:


Here are some tasks awaiting attention:

Let's get to work folks.Headbomb (talk) 17:47, 20 April 2008 (UTC)

Nomination will be this week end, if I can find references for the list. You may find them for me and I won't complain one bit. If you have objections, let it be known. Headbomb (ταλκ · κοντριβς) 01:59, 10 May 2008 (UTC)

Since there were no objections in the last week, I've nominated the list nominated! Thanks to everyone that worked on this so far, and thanks in advance to those who will continue to do so. Headbomb (ταλκ · κοντριβς) 06:20, 16 May 2008 (UTC)

List of suggested improvements that remains to be done (or to be thrown away)[edit]

  • Add references for section on Isospin and quark content. (Moved the section to [Isospin]) Headbomb
  • Decide what stays here and what goes on the baryon page. (I think we chopped enough fat) Headbomb
  • Possible diagram update/removal. (Diagrams were integrated in overview text). Headbomb
  • List the remainder of the baryons you can make from six quarks, possibly excluding the t-quark because they do not hadronize (Did not list baryons containing t quarks). Headbomb
  • Add some well-known resonances. Wing gundam
  • (Decided to remove the resonances from here and expand the Sigma, Xi... pages to contain them instead. Headbomb (talk · contribs) 02:58, 23 April 2008 (UTC))
  • List exotic baryons. v
  • Find decay mode references for the Delta(1232)s. (PDG reference contains them, albeit in a cryptic way.) Headbomb
  • Verify that decays listed are correct. Headbomb
  • The significance of * and primes in the particle symbols are explained in the overview, but I am not sure I got it right (need to find references) (Rewrote section and gave a source that used this way of doing things Headbomb (ταλκ · κοντριβς) 06:03, 16 May 2008 (UTC)) Headbomb
  • Define or clarify what "common decay" means. Headbomb
  • Clarify what is the criterion for inclusion in the lists. Headbomb
  • Update the Delta baryon, Lambda baryon, Sigma baryon, Nucleon, Xi baryon and Omega baryon pages to be consistent with this list, and vice-versa. Headbomb

List Progress Overview[edit]

Bold means currently not in the list. Blanks could be particles, or could be forbidden states. x are forbidden states. See Rules for making baryons - Take 3 down this page.

Particles and Isospins
Makeup Isospin 0 Isospin 1/2 Isospin 1 Isospin 3/2
uuu x x x Delta++
uud x Proton x Delta+
uus x x Sigma+ x
uuc x x Sigma C++ x
uub x x Sigma B+ x
uut x x Sigma T++ x
udd x Neutron x Delta0
uds Lambda0 x Sigma0 x
udc Lamba C+ x Sigma C+ x
udb Lambda B0 x Sigma B0 x
udt Lambda T+ x Sigma T+ x
uss x Xi0 x x
usc x Xi C+ x x
usb x Xi B0 x x
ust x Xi T+ x x
ucc x Xi CC++ x x
ucb x Xi CB+ x x
uct x Xi CT++ x x
ubb x Xi BB0 x x
ubt x Xi BT+ x x
utt x Xi TT++ x x
ddd x x x Delta0
dds x x Sigma- x
ddc x x Sigma C0 x
ddb x x Sigma B- x
ddt x x Sigma T0 x
dss x Xi- x x
dsc x Xi C0 x x
dsb x Xi B- x x
dst x Xi T0 x x
dcc x Xi CC+ x x
dcb x Xi CB0 x x
dct x Xi CT+ x x
dbb x Xi BB- x x
dbt x X BT0 x x
dtt x Xi TT+ x x
sss Omega- x x x
ssc Omega C0 x x x
ssb Omega B- x x x
sst Omega T0 x x x
scc Omega CC+ x x x
scb Omega CB0 x x x
sct Omega CT+ x x x
sbb Omega BB- x x x
sbt Omega BT0 x x x
stt Omega TT+ x x x
ccc Omega CCC++ x x x
ccb Omega CCB+ x x x
cct Omega CCT++ x x x
cbb Omega CBB0 x x x
cbt Omega CBT+ x x x
ctt Omega CTT++ x x x
bbb Omega BBB- x x x
bbt Omega BBT0 x x x
btt Omega BTT+ x x x
ttt Omega TTT++ x x x

Created by Headbomb (talk) 17:39, 21 April 2008 (UTC)
Last updated by Headbomb (talk · contribs) 00:58, 27 April 2008 (UTC)

Rules for making baryons[edit]

I'm kinda confused about how baryons are made up. All I can find is that baryons are made of up three quarks. Since there are 6 kinds of quarks, shouldn't there be 6^3=729 distinct baryons (going by quark composition)? Not only that, but the delta+ and the proton have the same quark make-up, the only difference are the different spin states. Wouldn't this mean that there are even more distinct particles since we have to keep tract of the spin alignments of the baryons with u and d quarks? Headbomb 20:43, 21 March 2008 (UTC)

Don't you mean 6^3=216 baryons? I don't know the answer. SkyLined (talk) 20:50, 21 March 2008 (UTC)

Alright I've looked into this. It seems (from what I can gather) that I was on the right track. It looks like 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? Headbomb 21:41, 22 March 2008 (UTC)

It's far more complicated than that. Saying that the quark content of a baryon is xyz is shorthand that hides a lot of detail. For the uds system, there are three orthonormal states: ½(usd - sud + dsu - sdu), 1/sqrt(6)(uds - usd - dus + sud - sdu + dsu), and 1/sqrt(12)(usd - sud + sdu - dsu + 2dus - 2uds). Counting hadrons is most easily done with SU(n) multiplets, but I don't fully understand them, so I can't explain it. In addition there are all the excited states as well. Finally, it's a bit academic to count the top quark in these calculations—it will decay to W+b long before it has a chance to hadronize.Mjamja (talk) 13:40, 18 April 2008 (UTC)
Yes, I've read a bit on the topic since, and the update by Wing Gundam help me understand things better. Isospin is what matters when differentiating particles of the same quark makeup. Now to understand what the hell Isospin is...
In any cases, for baryons made of 3 quarks of 6 flavors, there are (6+5+...)+(5+4+3+...)+(2+1)+(1)=56 distinct quark makeup. And while counting the t-quark baryons may be academic, I'm trying to understand the rules for making baryons are, rather than what baryons may be found in nature.

Also would be interesting if someone updated the list of baryons to take into account all the possibilities, with placeholders for the undiscovered particles Headbomb 22:12, 22 March 2008 (UTC)

I don't think it's scientific to declare a baryon before one is actually observed in an acclerator... Wing gundam (talk) 17:25, 17 April 2008 (UTC)

Are you saying is that we should not write about anything that is predicted/expected/suspected to exist but which has not been proven through laboratory testing? That doesn't sound very scientific to me ;) -- SkyLined (talk) 08:08, 24 April 2008 (UTC)
I agree in a certain way to wing gundam: Probably we should have different tables for observed and predicted (and not yet observed) SM baryons.. Tatonzolo (talk) 12:41, 24 April 2008 (UTC)
You are right in that it should be clear which particles have been proven to exist and which are predicted to exist, but have not been seen. Having two tables is a valid option, but putting everything into one table and marking them in some way is a valid alternative. I think the choice between these two options is a trade off between making it clear which baryons are similar (=one table, putting simililar baryons close together) and making it clear which baryons have been proven to exist (=two tables, seperating proven and non-proven baryons). I prefer one table, with a clear marker to indicate which particles are proven and which are not, but I have no argument other than personal preference. If we go with that option, we should put a remark ABOVE the table, so people know what to expect, rather than as a footer (which may not get read). -- SkyLined (talk) 14:27, 24 April 2008 (UTC)
concerning the clarity of the Baryon table I would suggest to make some "multilines" for the names, having Delta repeated lots of times is not beatiful, and possibly the p/n/n+ and n/n/N0 notations are quite unused... this was on the aesthetical side.. on practical side it would be useful to group the Baryons "a-la PDG" grouping them by flavour quantum numbers.. The mass scale for the Baryons would be mmore understandable to the less experts and the resonances would be better fitted... Tatonzolo (talk) 15:13, 24 April 2008 (UTC)
I think dividing them into unobserved and observed tables would clutter up the page and we'd lose part of the benefits of grouping particles together in the table. Also unobserved particles have daggers next to names to indicate exactly that, and have their masses, decay, lifetimes, and references missing. We could always add (unobserved) next to their names, I guess (removing daggers). Or we could add the move dagger note at the top of the table, (this option gets my vote for now).
Also I've list the p/p+/N+ because even though they are rarely used, they are still used. Perhaps we could add a note that p and n are the most commonly used symbols, with p+ and n0 trailing behind. As a side note, I've used p+ and n0 everywhere to indicate the charge in decays and whatnot, so it's easier to see charge conservation.Headbomb (talk · contribs) 16:40, 24 April 2008 (UTC)


Take 3[edit]

Alright. I think I have it.

u and d quarks each carry isospin 1/2. This is why isospin can be either 3/2 (3 aligned u and/or d quarks), 1 (2 aligned u and/or d quarks), 1/2 (2 aligned u with one unaligned d, 2 aligned d with one unaligned u, or 1 u or d quarks) or 0 (unaligned u and d quarks, or 0 u or d quarks). Three unaligned u or three unaligned d is forbidden by Pauli, and so is two unaligned u or two unaligned d.

Isospin 3/2 baryons are the 4 Deltas (uuu, uud, udd, ddd) Isopin 1 baryons are the 12 Sigmas (uus, uuc, uub, uut, uds, udc, udb, udt, dds, ddc, ddb, ddt) Isospin 1/2 baryons are the two nucleons (uud, udd), and the 20 Xis (uss, usc, usb, ust, ucc, ucb, uct, ubb, ubt, utt, dss, dsc, dsb, dst, dcc, dcb, dct, dbb, dbt, dtt). Isospin 0 baryons are the Lambda (uds, udc, udb, udt) and the 20 Omega (sss, ssc, ssb, sst, scc, scb, sct, sbb, sbt, stt, ccc, ccb, cct, cbb, cbt, ctt, bbb, bbt, btt, ttt).

And thus there are 62 triquark baryons. Headbomb (talk · contribs) 00:53, 27 April 2008 (UTC)

wrong. again. (don't mean to be harsh, but...). isospin is a number unique to baryons. however, the biggest mistake i notice is that you're listing baryons containing top quarks, which don't even exist! (see the note i left on your talk). There are no true rules for 'baryon making', whatever the hell that even is. The list, at this moment, is actually complete, provided no-one attempts to stuff it with theorical baryons, some of which may not exist. Really, the only thing this article needs is to lose some dead fat.
For example, the section "Relation between isospin and up and down quark content" is completely irrelevent to the present subject matter, by which i mean to say an explication of the fine details of isospin has no place in a list of baryons. On a side note, yet equally valid point, this section is full of gross errors in its basic understanding of particle physics, making elementary mistakes of comprehension in its explanation of isospin. This is meaningless, however, as it already does not belong on a list. The section currently labeled overview suffices to perform its function of acting as a legend, and, in truth, i think it looked much better before it was even split from the introductory paragraph. This is, after all, a LIST.Wing gundam (talk) 02:16, 29 April 2008 (UTC)

Well, I know that PDG lists that u quarks have isospin 1/2 and that d quarks have isospin -1/2, so isospin cannot be unique to baryons. Especially considering that the pi mesons form an isospin triplet. As for t quarks, I've sort of giving them a "magnetic monopole" treatment (see my talk page). I'm not opposed to not listing them, but it would be nice to know where they would fit, were they to have a bigger lifetime.
And there must be a rule for what baryons can exist, else they wouldn't show patterns such as [1]. Stuff like SU(3)xSU(2)xU(1) or SU(6) represents something and obey some rules. I'm trying to figure what the hell those rules are, and there are no books out there that seem to care to explain things to people that don't know Lie algebra, and the books on Lie algebra aren't written to be understood. At least tell me where I'm wrong, or how I'm wrong. All I know is with the rules I gave, I can reproduce every baryon diagram I encountered, and I can "predict" every baryon listed in the PDG. I can think of no reason why
Ξ
bb
(observed) could exist and that
Ξ0
cb
(unobserved) could not. Headbomb (talk · contribs) 15:11, 29 April 2008 (UTC)

Perhaps I can offer a historical explanation of Isospin to help in general understanding. Mesons and Baryons occur in multiplets. Members of the same multiplet have similar masses and differ in charge number by unit steps. Also the interactions of different members of a multiplet do not depend strongly on their charge. For these reasons each member of a given multiplet can be regarded as a different charge state of a single particle which has an extra degree of freedom in an internal space -- isospin space. The number of possible orientations of a particle in isospin space is 2I + 1. Thus the isospin quntum number of a particle may be determined simply by finding out how in how many charge states it can exist.--Vectorboson (talk) 20:30, 1 May 2008 (UTC)

Also, on the issue of rules for a baryon to exist. The first rule is that it will exist unless there is a reason it cannot. In the case of a baryon containing the top quark, calculations have been done to estimate the time it takes for a baryon to form and the result is that it takes longer for a baryon to form than it takes for the top quark to decay (about 10 to -24 seconds). --Vectorboson (talk) 20:30, 1 May 2008 (UTC)

Old rules vs. new rules[edit]

[copied from Vectorboson's talk page]

With my old rules, I could make every baryons out there with no extra baryons. The rules were quarks of the same flavor must have their isospin aligned, and quarks of different flavor can, but need not, have their isospin aligned. See Talk:List of baryons#List Progress Overview for the list of particles and their corresponding isospin values it gave me.

Now if I go with the PDG rules; that I and Iz are additive numbers and that I = 1⁄2 for u and d quarks and that Iz = 1⁄2 for u and −1⁄2 for d, then I can't account for nucleons (can't get isospin 1⁄2 with three u or d quarks, and Lambda's (can't get isospin 0 with a u and d quark).

So what am I missing? Headbomb (talk · contribs) 00:20, 4 May 2008 (UTC)

First, I-spin is NOT additive, Iz IS additive-- so forget about I-spin for a minute and concentrate on Iz. When constructing composite particles, Iz is the additive quantum number. A proton has two up quarks and one down quark -- the Iz values add to 1/2. The neutron has two down quarks and one up quark-- the Iz values add to -1/2. I-spin doesn't have a direction in real space, so I-spin CANNOT "align" as can spin.
Lambda's have one up and one down quark (total Iz = 0) plus another quark with Iz = 0 -- total lambda Iz then = 0.
Did that help?--Vectorboson (talk) 01:01, 4 May 2008 (UTC)

I'm fine with Iz, it's the isospin itself I have a problem with (BTW PDG lists the Isospin as an additive number, table 14.1 PDG quark model, if that's a mistake we'll need a reference for the article).

I thought isospin was a vector, just like spin is, and that as such it had a length (I) and a direction that could only be probed on one of the component (Iz by convention, sometimes noted I3) because the components did not commute.Headbomb (talk · contribs) 01:23, 4 May 2008 (UTC)

I noticed that JRSpriggs tried to bring tensor algebra and possibly some group theory in this, so just as a note, I don't get tensor algebra, tensor products, lie algebra, group theory etc... at ALL. So any attempt to explains things going these way will be lost on me.Headbomb (ταλκ · κοντριβς) 13:45, 4 May 2008 (UTC)

Certainly, the mathematical formalism for dealing with isospin parallels that of real spin and that is what led to its unfortunate name. But emphasize that any rotations and projections you imagine are NOT in x-y-z space but in some internal space. I will try and find you a reference for only the z-component of isospin being additive.--Vectorboson (talk) 15:10, 4 May 2008 (UTC)
Now some thoughts about the latest changes to this section. It is factually correct, and I like the table idea, but it should express the POINT of isospin. Each isospin singlet, doublet, triplet or other multiplet is, as far as the strong interactions are concerned, the same particle in a different electric-charge state.
In presentation, these multiplets should be shown together (perhaps, each should have its own table?). Adjacent states always differ by one unit of electric charge. And the number of states defines the isospin with this relationship
I = 1/2(NumStates -1 )
And according to the generalized Gell-Mann / Nishijima relationship, the z-component of isospin is
Iz = Q – 1/2( BaryonNum + S+ C + B + T)
So for example, the delta particle comes in 4 charge states, so it has isospin equal to 3/2
And
Iz of Delta++ = +3/2
Iz of Delta+ = +1/2
Iz of Delta0 = -1/2
Iz of Delta- = -3/2
At this point let’s emphasize what spin (and parity) has to do with this.
If we consider three-quark combinations of the up and the down quark. Since the quarks have spin = ½ (real spin, NOT isospin) the three-quark combinations can have spin =1/2 or spin = 3/2.
The Delta baryon has spin = 3/2 while the nucleons have spin = ½. So REAL spin is used to help classify to which family a charge state belongs.
Also, let’s point out that since the quarks have a color charge, and inside a baryon, the three quarks all have different color, so the Pauli Exclusion Principle is not violated. Historically, it was the delta++ with its three up quarks – all in the same spin state – that made us realize there were three colors in the strong force.--Vectorboson (talk) 15:10, 4 May 2008 (UTC)

Yes that's fine an all, but that still hasn't answer the question. What are the rules of baryon making? Why can't there be a I=0 uus baryon? Why can't there be a uuu baryon with I=1/2?

Perhaps if I ask my question different.

In terms of quark content (u is numbers of u quarks, d is number of d quarks etc...) The rule for charge of a particle is

The rule for the baryon number of a particle is

The rule for the z component of isospin of a particle contains at least this term

And because I strongly suspect that there should be some symmetry with the above equations, I think that the full equation is

Writing this in terms of quantum numbers B (as given above), Iz (as given above), S (
s
− s), C (c −
c
), B*prime; (
b
− b), T (t −
t
) is a bit tricky since u and d quark content dependance is not explicit, but really isn't all that hard to do since since you can get from B, Iz, S, C, B, and T to u and d quark content with simple algebra. I'll remark that the Iz looks rather artificial detracts from the fundamental understanding of things; it really looks to me as nothing more than a historical leftover from the particle zoo. It would seem infinitely more natural to have defined U (u −
u
) and D (
d
− d) quantum number, and while we're at that, we might as well have defined positive U,D,S,C,B,T quantum numbers to reflect the quark content, rather than quark for u-type and antiquark for d-type quark, but I disgress. Anyway, when that's done, you end up with

(Gell-Mann–Nishijima formula‎)

or in terms of the hypercharge (Y=S+C+B′+T)

Now in all of this, we never tackled isospin (either its length or the vector). So what is it? What's the rule in terms of quark content? What does the axis represent? What does isospin 3/2 mean? What does isospin 1/2 mean?Headbomb (ταλκ · κοντριβς) 16:31, 5 May 2008 (UTC)

After friggin' around with combinations of three quarks (uds, udc, udb, udt, scb, sct) I finally got what isospin was. And all I have to say is ... wow. That people still use it is beyond me. It's completely useless, and it's completely counter intuitive once you understand the quark model. Altough I shouldn't rejoice too quickly because I can't make the Lambdas fit.

Expect an update from me soon. Headbomb (ταλκ · κοντριβς) 21:05, 5 May 2008 (UTC)


You are being very harsh with history. Working from the bottom of your last entries toward the top... ANY conserved quantum number was (and is) a valuable insight into clues about how things work. Before we knew about quarks, we knew that Isospin and z-component were both conserved by the strong interactions. That explained branching ratios of decays and explained the symmetries in experiments where we collided pi+ with neutrons and pi- with protons. Your criticism is much like asking why do we need Newton's ideas now that we have Einstein's. That helped us understand that nucleons and other hadrons had a symmetry in an inner space that could be mathematically dealt with with a rotational formalism -- that was BIG! Internal symmetries are actually much easier to deal with than external symmetries which must be MEASURED to know. Now that we know about quarks, the only thing that has changed is that instead of referring to nucleons, isospin applies directly to quarks.

Your criticism about what "inner-space" or "axis" we are talking about and what does isospin 3/2 or 1/2 MEAN is actually to answer. When we predicted which particles should exist, we needed a scheme -- a grouping -- that showed which discovered particles fit in where and which missing particles we needed to search for. The diagrams that demonstrate these families are among the detritus that you have already rejected for inclusion in this article...
http://www.fnal.gov/pub/inquiring/physics/discoveries/images/Baryon%20Chart_MR.jpg
The formalism is beautiful and perfect and it does still need isospin much as the periodic table still needs the spdf nomenclature that defines energy shells

Finally your first questions "Why can't there be a I=0 uus baryon? Why can't there be a uuu baryon with I=1/2?" are also easily answered. As I indicated before, START by adding up the Iz components and you will get your answers. A uus baryon would have z-component = 1/2+1/2+0 = 1 ...so it CANNOT be part of an I=0 family. Similarly a uuu baryon has Iz=3/2 so it CANNOT be part of an I=1/2 grouping.--Vectorboson (talk) 23:05, 5 May 2008 (UTC)


I applaud this (and any) effort to explain difficult science in layman's terms. But while it is usually possible to explain the "facts" this way, it is often impossible to explain how we know what we know without resorting to difficult mathematical formalism. The Pauli Exclusion Principle for example is easily stated in words, but trying to explain why an anti-symmetric wave function vanishes for fermions and what that has to do with the matter is much more difficult. This article describes the general quark content of the baryons, but it does not address the mixing ratios of the various quark states involved or the symmetrization of the wave function which, by the way MUST take into account the internal symmetries of the quarks.--Vectorboson (talk) 23:19, 5 May 2008 (UTC)

I am not harsh with history. The way I finally figured out was by going through history and putting myself through the minds of those who didn't have the c,b,t quarks to work around with. It made sense back then to think that the neutron and proton were "variation of the same particle". It made sense to think that all deltas were the same particle, and that the different charges were the result of being in different states. Isospin had merits back then, and whoever came up with it gave nature a hell of a good shot and deserve a pat on the back for coming with a simple way of organizing particles and interpreting the meaning of the organization with the current knowledge at the time. However now, in light of the quark model, it doesn't make sense to think of the proton and neutron as the same particle, and isospin doesn't help to understand how particles are related. So I am harsh towards this generation of particle physicists because they did not have re-written the formalism in a more natural and comprehensible way.

BTW, that image was brought here by me because it had more particle than the baryon decuplet, and contained it. I felt it had a greater value than the decuplet image so I don't know why you refer to it as a "detritus that I rejected for inclusion". I would prefer figure 14.4 in the PDG review of the quark model containing udsc over the .jpg we just talked about, and make figures containing different mix of quarks to show that the pyramid and the decahedron work with any selection of 4 quarks. But you do not need isospin to make it, or understand it. It is simply every combination of quarks that is allowed in a certain spin state. The base of the udsc pyramid are made by choosing three quarks (let's say uds) and trying every combination to get a baryon decuplet. The first floor is made by imposing a c quark, and trying every combination of two uds and one c quark. Second floor is made by imposing two c quarks , and the tip is made by the remaining ccc baryon. It is a very beautiful figure and I would very much like to have a poster with all the six quarks arranged in such a fashion, but I don't know how to project 6D into a 3D. The pyramid is a clever way of showing 4D into 3D (on a 2D screen no less using a volume with perspective), but I don't know if you could show 6D into 3D. For the meantime I think I'll have to settle for a poster of what's on my talk page right now (6 octets (missing the Lambdas) and 6 decuplets corresponding to groups of uds, udc, udb, udt, scb, sct) Headbomb (ταλκ · κοντριβς) 00:00, 6 May 2008 (UTC)

And I also object to your characterization of my criticism of isospin as being analogous to a criticism of Newton. Newton is an approximation of Einstein that applies at low gravity and at low speeds, so it is worth more than simply being an old way of understanding things, it is also useful and connects with the everyday world. The meaning of "speed, energy, momentum" etc.. isn't hidden in Newton.

Isospin however, hides the true nature of things in favor of a artificial constructs. It is very unnatural to express charge in terms of baryon number and projection of isospin rather than in terms of quark content. It is equally unnatural to classify particles in groups of isospin rather than in groups of quark content. Doing so is neither an "approximation" of reality nor does it help anyone to understand anything even approximetaly. An equivalent analogy of me criticizing the concept of isospin would be someone else criticizing the classification of the the chemical characteristics of elements in terms of atomic mass, neutron number and a new quantity called "chemi-spin" that would be defined in a Chemispin (C)= Atomic number(A) - number of electrons + 12" fashion rather than dealing in terms of electronic configurations directly.

Imagine the kind of mess we'd be dealing in chemistry if we spoke of Element A=71/N=40/C=14 that shows similarity to Element A=69/N=38/C=14 rather than speaking of Gallium-69++ and Gallium-71++. We could rewrite all the classification of chemistry using linear combinations of any number of quantities and it would work. But what a damn mess it would be. Headbomb (ταλκ · κοντριβς) 01:20, 6 May 2008 (UTC)

Take 4[edit]

Isospin: Definition the greatest value of |Iz| within a group of specific non u and d quark content and of specific spin state.

Example 1: Baryons of spin 1/2 and with a single bottom quark as non-u/d quark content. There are three particle in this group, uub (Iz=1), udb (Iz = 0), ddb (Iz = -1). The greatest |Iz| is 1, and thus these three particles have isospin 1. Isospin 1 particles containing a bottom and a mix of two u or d quark content are bottom Sigmas.

Example 2: Baryons of spin 1/2 with no non-u/d quarks. There are two particle in this group, uud (Iz=1/2), udd (Iz = -1/2). The greatest |Iz| is 1/2, and thus these two particles have isospin 1/2. Isospin 1/2 particles made of a mixture of three u or d quarks are nucleons.

Example 3: Baryons of spin 3/2 with no non-u/d quarks. There are four particle in this group, uuu (Iz=3/2), uud (Iz=1/2), udd (Iz = -1/2), ddd (Iz=-3/2). The greatest |Iz| is 3/2, and thus these four particles have isospin 3/2. Isospin 3/2 particles made of a mixture of three u or d quarks are Deltas.

Still can't figure out the Lambdas. Headbomb (ταλκ · κοντριβς) 23:27, 5 May 2008 (UTC)

But you are almost there! -- What's hard to figure -- all the lamdas have Iz=0 and are singlet states. so by your own rules (please don't put your definitions on the article page), the lambda's are I=0.--Vectorboson (talk) 00:48, 6 May 2008 (UTC)

I can tell the difference between a proton and a delta (different spin state), and I understand why they have different isospin (Pauli removes uuu and ddd from spin 1/2, so isospin is reduced by 1). However, I can't tell the difference between a sigma0 and a lambda0, both are uds, and both have spin 1/2.Headbomb (ταλκ · κοντριβς) 01:24, 6 May 2008 (UTC)

Since the sigma decays into a lambda electromagnetically, you can think of the sigma as an excited state of the lambda if that helps.--Vectorboson (talk) 22:49, 6 May 2008 (UTC)

Not really. I agree that there is something different about the lambda, since it has a different mass, and different decay products. What I'm asking is why does it exist in the first place? Why are there two uds in spin j=1/2+ states, but not two uud in spin j=1/2+ state? Headbomb (ταλκ · κοντριβς) 23:28, 6 May 2008 (UTC)

I think moving the isospin section to the isospin page is a great idea. --Vectorboson (talk) 22:49, 6 May 2008 (UTC)

Yeah, it didn't really belong here and it's a good addition to the isospin page. Headbomb (ταλκ · κοντριβς) 23:28, 6 May 2008 (UTC)

Not sure I wanna answer your question about why there are two uds particles in spin j=1/2 octet... but here goes. The wave functions in the baryon octet are pretty complicated considering that all of the quantum numbers must combine in a normalized wave function symmetric under interchange of any two quarks. It turns out there are two independent ways to do this with a quark content of uds. One with isospin 0 and one with isospin 1. --Vectorboson (talk) 15:32, 7 May 2008 (UTC)

By now you're going to expect this question :P. How would you write the two ways (Dirac notation doesn't scare me BTW, so if you need to use that, go ahead)? Headbomb (ταλκ · κοντριβς) 16:49, 7 May 2008 (UTC)

Baryon wavefunctions[edit]

Alright, I decided I'd give a shot at writing wave functions. Since the color charge is always anti-symmetric under interchange of any two quarks, then the non-color part of the wave function needs to be symmetric. I got this for the uds decuplet. + means spin 1/2, - means spin -1/2.

Decuplet[edit]











Octet[edit]

For the octet it is trickier, I got to this, but I'm not confident I got the right wavefunctions, especially for the Lambda0/Sigma0 or if I assigned the correct wavefunctions to the correct particle (I got inspired from this image [2]).

Also I don't quite understand how you'd tell the excited state from the fundamental state by looking at the ± sign. I also noticed that there were other particles with a ± in the wavefunction, would I be correct in saying that the
Λ0
is to the
Σ0
in the uds octet what the
Ξ′+
c
is to the
Ξ+
c
in the usc octet?

or more concisely



You're gaining on it! I like your decuplet wave functions (there is a typo on the sigma-star-minus (it is dds) line that needs fixing and also the cascade*-). So far I don't like your octet wave functions. Starting with the proton, these are all mixtures of mixed symmetry spin and mixed symmetry isospin (or flavour if you prefer) states. These mixed symmetry states come about naturally when combining the quarks.

For example the mixed symmetry (symmetric for 1-2 interchange) isospin state 1/SQRT(6)(2ddu-udd-dud) joins the mixed symmetry spin -- and then you combine the mixed assymetric parts and finally join them all together into a proton to get...

proton = 1/SQRT(18) { 2(u+u+d-) + 2(d-u+u+) + 2(u+d-u+) - (u+u-d+) - (d+u-u+) - (u+d+u-) - (u-u+d+) - (d+u+u-) - (u-d+u+) }

Then you can use ladder operators to get the other states in the octet (TEDIOUS!) (sorry about the formatting) --Vectorboson (talk) 21:34, 8 May 2008 (UTC)

Here is a good discussion... http://www.hep.phy.cam.ac.uk/~thomson/partIIIparticles/handouts/Handout8_2007.pdf --Vectorboson (talk) 00:41, 9 May 2008 (UTC)

Footnote [a][edit]

Can you tell me what footnote "a" means (about precision in mass units vs. MeV) please?--Vectorboson (talk) 22:49, 6 May 2008 (UTC)

From what I gather, it simply means that it is easier to calibrate the instruments in atomic mass unit than it is to calibrate in MeV/c^2.Headbomb (ταλκ · κοντριβς) 23:28, 6 May 2008 (UTC)

Resonance[edit]

"This is not always the case, as with Ξ0c (J=1/2) and Ξ0c (J=1/2), where the J=1/2 state is marked by Ξ′0c, the prime in this case also indicating a resonance, but of the same spin."

Is that sentence really what is meant? Or is this better?

"This is not always the case, as with
Ξ0
c
(J=1/2) and
Ξ∗0
c
(J=1/2), where the prime indicates a resonance, but of the same spin."Headbomb (talk) 04:31, 20 April 2008 (UTC)

I changed the sentence to what I felt was more accurate.Headbomb (talk) 17:25, 20 April 2008 (UTC)

I have removed the resonances from the list, and expanded the Sigma baryon,Xi baryon... pages to contain them instead.Headbomb (talk · contribs) 03:00, 23 April 2008 (UTC)

The resonances you removed represented unique particles of the 10+8+8'+4 20-plet, with the same difference as Delta+'s and protons, which is why they were explicitly left, and identified with a prime.Wing gundam (talk) 02:23, 29 April 2008 (UTC)

If you remember what they were, you can find them in the Sigma baryon, Xi baryons, etc... pages to save you the trouble of retyping all the code.Headbomb (talk · contribs) 04:14, 29 April 2008 (UTC)

Isospin, decay mode, resonance listings[edit]

I'm preparing to add a separate column for isospin, if there are no objections. I'm also going to list the mass after every particle's symbol which requires it, per PDG guidelines. I also strongly recommend against listing high energy resonances of baryons, say, for the Sigma0 J=1/2 and Sigma0 J=3/2, as in fact there exist numerous other values of J, even if they do not exist in any pyramid-like table. 68.10.32.199 (talk) 17:19, 17 April 2008 (UTC)

I suggest we include all baryons with 3 or 4 star status in the PDG, since this is the definitive source for information like this. That would mean lots of Ns, Δs, Λs and Σs, but none of the double and triple charm and bottom states that have not been observed.Mjamja (talk) 13:40, 18 April 2008 (UTC)
You understand that the majority of these are isomers, right? i.e. theyre not actual "distinct" baryons. though difficult to describe, they're basically energized variants of their ground states. Don't think of these resonances as separate baryons; rather, imagine them as 'energized variations' of a representative particle.
If we are attempting to make a list of baryons, which has the potential to become grossly over-complicated by including minor variations of almost every entry, and terribly confusing to anyone who isn't an expert on particle physics, I think it would be better to include only the aforementioned representative particle, although a few exceptions are necessary:
From the article, "Recursively, for each baryon group (Nucleon, Delta, Sigma, etc) and for each possible quark content structure possible within the group, data for the ground resonance state of the arrangement has been included. ... Currently, certain other well known resonances, namely those populating the decuplet of the primary SU(3) and the 20-plets of the SU(4) groups, are included below."Wing gundam (talk) 07:02, 19 April 2008 (UTC)

Oops forgot to log in. I'm also going to add a † marker and a note below the table to denote particles not yet observed. Wing gundam (talk) 17:22, 17 April 2008 (UTC)

According to Isospin#SU(2), "... isospin is described by two numbers, I, the total isospin, and I3, the component of the spin vector in a given direction. The proton and neutron both have I=1/2, as they belong to the doublet. The proton has I3=+1/2 or 'isospin-up' and the neutron has I3=−1/2 or 'isospin-down'.". Please make clear in each instance in the article where you mention isospin whether you are talking about the total isospin or the component. JRSpriggs (talk) 14:54, 29 April 2008 (UTC)

It is always the modulus of the isospin (I) we're talking about, except when isospin projection are mentionned (Iz), but I guess that could be clarified.Headbomb (talk · contribs) 15:06, 29 April 2008 (UTC)

Spin vs. Total angular momentum[edit]

I wondered if the J given was spin or rather total angular momentum. Upon browsing the PDG archives, I found particles with J=5/2 and J=7/2, which to my understanding would be impossible to achieve by spin alone (three quarks, so spin can be at most 3/2). Someone edited it to total angular moment a while ago, but I changed it because the particle were given in their fundamental state (aka J=S+L where L = 0). Should we keep J ( equal to S+L) or change it to S? Headbomb (ταλκ · κοντριβς) 02:31, 6 May 2008 (UTC)

J=(S+L) --Vectorboson (talk) 22:49, 7 May 2008 (UTC)

I'll edit in consequence.Headbomb (ταλκ · κοντριβς) 22:55, 7 May 2008 (UTC)

Name of bottom Sigmas[edit]

Yes, they decay strongly, so their masses should be in the names. However, resonances are often grouped together, and for the name an approximate of the average mass value is chosen. They will probably end up as being
Σ
b
(5810), but as of now the values that goes in the brackets hasn't been decided and I would really be surprised if these two particles ended as
Σ
b
(5808) and
Σ
b
(5815).Headbomb (ταλκ · κοντριβς) 14:44, 6 May 2008 (UTC)

Diagram Updates[edit]

I think it would be a good idea if we could fit something like theses diagram somewhere in the article

http://www.fnal.gov/pub/inquiring/physics/discoveries/images/Baryon%20Chart_MR.jpg
http://www.regenerating-universe.org/images/Baryon.gif
Headbomb (talk) 18:03, 20 April 2008 (UTC)

On second thought, the more I look at them, the less I see a need for them. They already are in the baryon article.Headbomb (talk) 07:02, 21 April 2008 (UTC)

Node-count limit exceeded[edit]

Anyone know how to fix this?? Headbomb (ταλκ · κοντριβς) 21:17, 9 May 2008 (UTC)

Problem was fixed by a mysterious force who's more than welcomed to identify itself. Headbomb (ταλκ · κοντριβς) 01:17, 10 May 2008 (UTC)

Sections[edit]

As per Headbomb's request when my edit was reverted, here's my objection to the sections as they are. First, "Overview" doesn't overview the article. It explains the columns. Hence "Explanation" is a better term (but I'll admit not ideal). Second, the "List of baryons" section. _The whole article_ is the list of baryons: why is it restricted to a single section? It's also regarded as bad form to include the name of the article in the sections. A better way is to have sections for each sub-section of the list; see e.g. List of space telescopes. Having it that way also brings the two introductions to the page together (we currently have one at the top, and one at the start of the "List of Baryons" section. I was going to rewrite the introduction to merge the two, but didn't have time this morning. Mike Peel (talk) 16:10, 10 May 2008 (UTC)

I felt that "overview" summed up the things necessary to understand the list: it explains mostly what the symbols mean, the classification, and the rules of both. Aka it's about everything "around" the list. It could be expanded to give an overview of the spin 1/2 baryons, and spin 3/2 baryons and to elaborate a little on the significance of isospin (there used to be a section here but I moved it to the isospin page), and explain some of the quantities (such as rest mass, bottomness etc...). In all cases "explanation" is a horrible title.
The reason why I put the three lists into one section is that this way, the general comments about the list themselves that pertains to all of them (stars, daggers etc...) is in the "list" section, separate from the overview/intro, while comments that pertain to specific list are in that specific list's subsection (see pentaquarks).
I'm not married to this version of things, but I wanted you to get the reasons I did things the way I did.
BTW, the rest were excellent edits. Headbomb (ταλκ · κοντριβς) 20:57, 10 May 2008 (UTC)
Hmm... I get your reasoning, but I think that things could still be improved a bit. How about:
  1. Introduction
  2. Triquarks
  1. J=1/2
  2. J=3/2
  1. Pentaquarks
  2. References
  3. Further reading
  4. See also
... where Introduction is the current Overview section, Triquarks is the current "List of Baryons" section with Pentaquarks moved into its own section. See also is further down to incorporate the navigation box at the bottom (with redundant links removed), although I'm not sure if that's the standard wikipedia ordering...
Acceptable? Mike Peel (talk) 21:18, 10 May 2008 (UTC)

Well the order of things as far as references/see also/further reading was done according to the MoS, so I don't see why that should be changed that'll fly by the Featured Article reviewers, but I like the idea of having the See-Also and the Infobox next to each other. Concerning the See Also links, I'm a bit worried that things in the infobox get less visibility (if they don't end up next to each other) (good idea to include the lists of baryons/mesons/particles/particle discoveries in it BTW) than in the See Also section. If we clean up the see also section, I think it's the nucleon/sigma/xi... pages that should go because they are link a billion times each in the article. How about a See Also with: Eightfold Way (physics), Isospin, List of Mesons, List of Particles, Physics Portal, Timeline of particle discoveries? Hyperons (these classes should really be dropped for smarter ones) could also be included since it's not in the infobox.Headbomb (ταλκ · κοντριβς) 03:38, 11 May 2008 (UTC)

How about doing something a bit more radical: getting rid of the whole of the see also section? We have links throughout the article, and the navigation box at the bottom, which should cover all of them. I can see the point in such a section in a printed encyclopaedia, but we're _not_ a printed encyclopaedia, are we?
A link to Portal:Physics is not in the Wikipedia:Featured list criteria (and I've not seen it used in other featured lists), and because it's rather off topic I don't think it's needed. Perhaps if Portal:Particle Physics existed, then it would be good to link to it, but probably only in the navigation box at the bottom.
(Note: in general a box at the top right giving important statistics about the article is an infobox, whereas a box giving links is a navigation box or navbox.)
Thanks, Mike Peel (talk) 07:28, 11 May 2008 (UTC)

MMM... I wonder where I saw this then. Perhaps it was in on an editor's personal reviewing checklist.Headbomb (ταλκ · κοντριβς) 02:28, 12 May 2008 (UTC)

Empty table cells[edit]

Why are there empty table cells? Are these values that are known, but haven't been filled in yet, or values that haven't been measured yet, or values that can't be measured? Mike Peel (talk) 21:23, 10 May 2008 (UTC)

They are values that aren't yet measured. At least according to the PDG review of 2006, and very quick Google searches.Headbomb (ταλκ · κοντριβς) 00:36, 11 May 2008 (UTC)

I'd like to quickly point out that there is a new review coming out soon (as in this year) since the PDG does a review every two years.Headbomb (ταλκ · κοντριβς) 03:24, 11 May 2008 (UTC) There'll probably be some new entries in that one.Headbomb (ταλκ · κοντριβς) 03:24, 11 May 2008 (UTC)

How about we fill them in with "Unknown" for now, then? Or alternatively, a dash (—)? When I was getting List of space telescopes to featured list status, empty boxes were one of the things that were identified as an issue. Mike Peel (talk) 07:30, 11 May 2008 (UTC)

I say go with "Unknown".Headbomb (ταλκ · κοντριβς) 02:25, 12 May 2008 (UTC)

I've marked them "Unknown". Headbomb (ταλκ · κοντριβς) 06:09, 16 May 2008 (UTC)

h-bar[edit]

The article states:

It comes in increments of 1⁄2 ℏ. The ℏ is often dropped because it is the "fundamental" unit of spin, much like the e is often dropped when speaking of the charge of particles since e is the "fundamental" unit of charge.

The comparison to e is highly misleading. The h-bar can be "dropped" by simply defining it to be one (using units where it is exactly equal to one -- and these are the units used almost universally in particle physics. See Geometrized unit system and natural units) By contrast, e is only "dropped" when you're slightly tipsy and sharing a beer with friends. e is equal to 1 over sqrt(137), the fine structure constant, and can never be defined to be one. Its ommited only to save space in some table, where an asterisk/footnote explains that its been omitted. linas (talk) 01:18, 31 May 2008 (UTC)

BTW, please link h-bar to Plank's constant. linas (talk) 01:24, 31 May 2008 (UTC)

I agree. I'll fix that later today. Headbomb (ταλκ · κοντριβς) 16:25, 31 May 2008 (UTC)

isospin section is .. "strange".[edit]

The discussion of isospin is ... strange. Isopspin was proposed long before "delta baryons" and certainly before strange particles were discovered. Thus, just mentioning these in the section on isospin is ... confusing. Having pictures of the baryon octet and decuplet in the "isospin" section is wrong. Isopsin only has singlets, doublets and triplets, it does not have octets or decuplets.

I suggest entirely removing the isospin section, since the modern concept of flavour supplants it completely.linas (talk) 01:36, 31 May 2008 (UTC)

I figured out what makes me nervous about this section. Its the mixture of history together with technical description of the quantum number. If the sentences that talk about the history are cut, then the section is OK, I guess. In other words, its OK to say that the deltas for a isospin quadruplet, and that the next line down in the decuplet is an isospin triplet of sigmas, and the next one is an isospin doublet of xi's, and finally an isospin singlet omega. But I find the attempted summary of the history to be misleading, by this I mean the section "Observation of baryons prior to the development of the quark model...although this wasn't known at the time)"
The core idea that is trying to be grasped here is that of symmetry, a very important concept that should be reviewed in this article. I note the word itself is never used in this article, except to talk about "symmetry breaking", which of course begs the question "what's the symmetry"? and why did they think it was a symmetry if it was broken? These are the break-through ideas/discoveries. Once the idea of symmetry was clear, the idea of quarks became much easier. (although maybe I'm rewriting history here, too?) linas (talk) 02:33, 31 May 2008 (UTC)

I wrote this from scratch. Litteraly. I've locked myself in a room, and place myself in 1960 where there were only UDS baryons around, but no knowledge of quarks, then quarks were discovered, then the c quark was discovered etc...

I believe I got the significance of these quantities right, but the history could be a load of hoo-haa. What is given is given as examples more than history. Isospin was not devised for the Deltas in the sense that the Deltas lead to the concept of isospin, but rather that isospin was constructed to describe groups of particles of the same mass such as the Deltas. Headbomb (ταλκ · κοντριβς) 05:59, 31 May 2008 (UTC)

Symmetry[edit]

At the risk of repeating myself, I say again: "SYMMETRY". The section on flavour once again delves into a fractured history. I suggest the following article layout:

  • Introduction
  • Symmetry, what it is, what it means, its central importance to everything as the number-one-primary-leading conceptual breakthrough about particles and particle classification. Review historical ideas here ("observed that the mass was the same...", etc.) In particular, flavour symmetry which is SU(6), the historical SU(3) eightfold way, isospin SU(2) before that; quarks as constituents of particles. Mention that quarks belong to the fundamental representation of SU(6) flavor symmetry, and that the baryons belong to the .. damn, where's the articles when you need them? I wanted to say adjoint representation, but its more complicated than that.
  • Isospin (without the sentences that "physics once believed...discovered..etc.") Focus on telling the reader how to interpret the table...
  • Flavour (without the historical comments "As other quarks where discovered" etc.) also remove sentences "Since only the u and d mass are similar...etc. ... ...referred to as symmetry breaking.", since this whole idea is discussed in the symmetry section. Get rid of the "It was noted ...", and just say "It is.." Get rid of the historical "it was later generalized by.." and just say "it is given by..."
  • Classification (as it stands)
  • List (as it stands)

I think that would clarify the article immensely. linas (talk) 03:08, 31 May 2008 (UTC)

I'm iffy about including a section on symmetry since it's not required to understand anything in the tables themselves. Historical parts aren't meant to be about historic events and chronology of concepts, but rather back then, this was the understanding, and in that picture, this was the interpretation. I'll give this a better, more thorough reply tomorrow, since it's 3AM and I'm tired as hell. Headbomb (ταλκ · κοντριβς) 06:04, 31 May 2008 (UTC)

I'm simply trying to suggest a way of making the article clearer, and more accurate. Right now, its occasionally confusing and misleading in its claims and structure. There's talk of life before quarks, life after quarks, life with and without strangeness. Its sort of all mushed up into a ball that's not quite right. I'd like to see all that mushiness and prevarication stripped out.
Talking about baryons without talking about symmetry is like talking about the periodic table of elements, and avoiding any discussion of periodicity. The most important property of the table of elements is that its periodic, even if lithium, sodium and potassium do not weigh the same: they are in the same column for a reason. Comprehending that reason, and comprehending the general outlines of the periodic table of elements is critical. Likewise with the baryons. Split the article into two: one which deals with how to read the table, and only that, and an introductory part which talks about the general outlines and shape of the table. Don't mush these distinct conversations into one. linas (talk) 16:17, 3 June 2008 (UTC)

There's a mention of symmetry, and there's an explanation of what it means and how it's broken. I don't see what more is needed, but then again I don't see what a section about symmetry would cover exactly. Headbomb (ταλκ · κοντριβς) 16:25, 3 June 2008 (UTC)

Ideas to help article obtain FL status[edit]

I can tell that there has been a lot of work on this article and that it is well done. I hope it receives a FL standing. I have a few suggestions that may help with that, although some of them may take a lot more work.

  1. Focus entire article more on tables
  • Longer table headings (if possible) Isospin is more comprehensible then I when you have only seen it for the first time 5 minutes ago.
  • Link from table headings to section in article prior to table. Don't link to other articles since it takes longer to load. Link to section in article that explains the column. This section should have a main article tag that links to the appropriate web page.
  • The structure of the article could go something like this: Introduction 1. Content 1.1 Particle name (include naming conventions) 1.2 Particle symbol (Include something about nomenclature-short. Then link this to classification 2. below) 1.3 Quark content (main|quark discussion about 3 types of quarks and that baryons are made of 3 (or 5) quarks 1.4 Rest mass (main|... include something about units used )... 2. Classification (keep this intact) 3. List of Baryons
  • Cut out anything that does not relate directly to quantities in the list. Be ruthless. Focus on the list.
  1. For every section use the proton and neutron as an example
  2. Focus on the familiar first in the introduction. Say that protons and neutrons are baryons in the second sentence if possible. (You may want to try mentioning how they compare with mesons and leptons. If it is not possible to do in one clear sentence then forget about it.)

Just a few thoughts that may help in the long run. I am new to the requirements for FL standing. I personally don't know if any of these things are necessary to become a FL. Most are probably not, which is why I am putting it here. I will see if I can get to the FL review page after I have thought about which if any of my ideas are valid enough to mention.

Good Luck

TStein (talk) 17:04, 19 June 2008 (UTC)

I'll read this more carefully tonight, as these are good comments. I'll say this for now:
  • The structure of the article is the way it is because I don't want to introduce a concept that depends on something that's introduced later. Isospin can't precede spin, flavour quantum numbers can't precede isospin etc... Particle names/symbols is the last thing in there because you need all the rest to understand why the symbols are the way they are (and I hate particle physicists for not cleaning this unnatural and convoluted way of naming things). I'm open to change in the structure, but not if it compromises understanding.
Headbomb {ταλκWP Physics: PotW} 17:21, 19 June 2008 (UTC)

Featured list has been achieved![edit]

Thanks to all who helped! Headbomb {ταλκWP Physics: PotW} 13:42, 1 July 2008 (UTC)

Lifetimes[edit]

Many of the particles didn't have their lifetimes listed, so I "extracted them" using

And uncertainties with

as the PDG did for Browman 74 in [3]. Headbomb {ταλκκοντριβςWP Physics} 04:03, 18 November 2008 (UTC)

Yes, this is correct and uncontroversial. I just made it so that a link to decay width or resonance width will go to a page explaining this. --Steve (talk) 18:54, 17 December 2008 (UTC)

The accurate decay rates (lifetimes) are calculated using quantum theory (i.e. Fermi's Golden Rule for the first order perturbation treatment). The uncertainty principle (if that is where the formula comes from) is an approximation that in only a good approximation because the decay has a poisson distribution (i.e mean = standard deviation = uncertainty). I think it is best to only state experimentally verified decay rates (lifetimes). Also if gamma is the decay rate than hbar/gamma does not have the units of time. I am not sure how that formula is derived. — Preceding unsigned comment added by 131.252.127.172 (talk) 00:48, 11 April 2017 (UTC)

Parity section rewrite[edit]

The section describes the term "parity" as symmetry or antisymmetry of the wavefunction with respect to inversion about the origin. (About what origin? Who knows...) That's one use of the term, but it's not the definition used in particle physics. Here's my proposed rewrite of that section. (No references right now, but they should be easy to find, and I can do that later.) Here goes, as a first draft and starting point:

If the universe were reflected in a mirror, the laws of physics would be almost, but not quite, identical: Certain radioactive decays distinguish "left" from "right", a phenomenon called parity violation. Parity violations are associated with the weak force, one of the four forces in the universe; the other three forces, gravity, the electromagnetic force, and the strong force, do not distinguish left from right.
Based on this, one might think that if the wavefunction for each particle (more precisely, the quantum field for each particle type) were simultaneously mirror-reversed mathematically, then these new set of wavefunctions and fields would perfectly satisfy the laws of physics (apart from the weak force). It turns out that this is not quite true: In order for the equations to be satisfied, the wavefunctions of certain types of particles have to be multiplied by (-1), in addition to being mirror-reversed. Such particle types are said to have negative parity or odd parity, while the other particles are said to have positive parity or even parity.
It turns out that all baryons have positive parity, while antibaryons (their antiparticles) have negative parity.

Thoughts? --Steve (talk) 04:35, 17 December 2008 (UTC)

Yes that makes more than what I wrote. How about this?:

If the universe were reflected in a mirror, most of the laws of physics would be identical – things behave the same way regardless of what we call "left" and what we call "right". This concept of mirror reflection is called parity (symbol P). Gravity, the electromagnetic force, and the strong interaction all behave in the same way regardless of whether or not the universe is reflected in a mirror, and thus are said to conserve parity (P-symmetry). However, the weak interaction does distinguish "left" from "right", a phenomenon called parity violation (P-violation).
Based on this, one might think that if the wavefunction for each particle (more precisely, the quantum field for each particle type) were simultaneously mirror-reversed, then the new set of wavefunctions would perfectly satisfy the laws of physics (apart from the weak interaction). However, because of the nature of the wavefunction, it turns out that this is not quite true. The square of the wavefunction is what is important, not the wavefunction itself, and this leads to two possible types of wavefunctions – even and odd. In order for the equations to be satisfied, the wavefunctions of certain types of particles have to be multiplied by −1, in addition to being mirror-reversed. Such particle types are said to have negative parity or odd parity, while the other particles are said to have positive parity or even parity.

(Also could you check the lifetime section just above and tell me whether or not I should be shunned and beaten for extracting lifetimes in this manner?) Headbomb {ταλκκοντριβςWP Physics} 07:09, 17 December 2008 (UTC)

I still don't think you quite have the idea. Even and odd functions are irrelevant here. For example, the shape of my body is neither perfectly symmetric nor perfectly antisymmetric, yet my mirror reflection appears to perfectly satisfy the laws of physics. It's not a matter of comparing the original directly to the reflection. What matters is that the reflection of one particle interacts with the reflection of each other particle in a way that's quantitatively consistent with the laws of physics. It's just like pseudovectors. When I'm driving forward in a car, the angular momentum of the wheels points left. If you naively reflect the universe (and everything in it) in a mirror that flips the left and right sides of the car, then mirror-Steve would be driving forward in his mirror-car, and he would be appalled that the mirror-angular-momentum-vector points right, when it's supposed to point left according to the laws of physics. To do it correctly, you need to reflect everything in the universe in a mirror, and multiply pseudovectors like angular momentum by -1. It's the same idea for parity.
As you suggest, it's easy enough to show that the "reflected wavefunction" has to agree with the reflection of the wavefunction, up to possibly a global phase factor, 1 or -1; otherwise the "reflected particle" has an observably-different position/momentum from the reflection of the particle. (You can actually come up with convoluted theories where you need to multiply the field by i, but luckily our universe is simpler than that.) But again, this is very different from even/odd functions. Does that help? --Steve (talk) 20:14, 17 December 2008 (UTC)
OK, a couple more suggestions.
  • What confused me before was that the Ls discussed in this article are the orbital angular momentum of the quarks around each other within the baryon, not the orbital angular momentum of the baryon itself through space. I think that each of the couple times you use "L" in the article, you should say something like "L is the orbital angular momentum of the quarks with respect to each other", rather than just "L is the orbital angular momentum".
  • In principle, I assume the quarks can have any value of L, and in fact I'm surprised that they have any definite value at all. Due to spin-orbit coupling of the quarks, shouldn't the "L=0, S=3/2, J=3/2" baryons" actually have a tiny amount of L=2,S=3/2,J=3/2 in order to be an actual energy eigenstate? This confuses me. At any rate, it would be nice to say whether or not L is a good quantum number precisely or only approximately (both in this case and for the many baryons not covered in this article), since this is interesting, relevant, and not obvious.
  • Another point is that maybe you should use the term "intrinsic parity" to distinguish what you're discussing from spatial parity. The intrinsic parity of a proton is always +1, regardless of where it is or how it's moving, but spatial parity can be anything, or more often, no definite value at all. The intrinsic parity of an antiproton is likewise always -1. When you were originally talking about even and odd functions, that's spatial parity. Confusingly, what counts as "intrinsic parity" for a proton might be partly determined by "spatial parity" from the quark point of view, just as what counts as "spin" for a proton might be partly determined by "orbital angular momentum" from the quark of view.
  • Might be worth mentioning that the assignments of intrinsic parity is (at least in the case of baryons) a convention, albeit one that all physicists have unanimously agreed on, thank god. Here is a source explaining this.
Here's another source I found after a quick search. I can give more sources in a couple weeks. --Steve (talk) 22:58, 20 December 2008 (UTC)
  • Bullet 1: Yes that could be indeed clarified.
  • Bullet 2: Hum I don't understand the details of LS coupling, but wouldn't J = 7/2 here, per J = L + S?
  • Bullet 3: Yes, but I wasn't wrong to talk about spatial parity in the first place? Why bring it back? Does spatial parity play a part in things?
  • Bullet 4: Hmmm... I don't know if it's worth mentioning here, but it should at least be mentioned in the parity article it it's not already mentioned.
Headbomb {ταλκκοντριβςWP Physics} 03:21, 21 December 2008 (UTC)
Bullet 2: The rule is that J is somewhere between |L-S| and L+S. See Angular momentum#Addition of quantized angular momenta. There may be other problems though.
Bullet 3: I was merely suggesting saying e.g. "the intrinsic parity of a baryon is..." instead of "the parity of a baryon is..."
Bullet 4: I agree. On that note, I may try to improve the relevant parts of the parity (physics) article at some point, now that I'm warmed up. :-) --Steve (talk) 03:56, 21 December 2008 (UTC)
Bullet 2: Yes of course. Then I think you are right. I think there is a degeneracy. I'll expand the section in consequence, but the opinion of someone working in baryon spectroscopy would be nice to have.
Bullet 3: Oh, ok. That's reasonable enough I suppose, much like "intrinsic spin" is often appropriate. Headbomb {ταλκκοντριβςWP Physics} 05:42, 21 December 2008 (UTC)

(unindent) Alright, I've clarified. Is this better/clear/accurate? Headbomb {ταλκκοντριβς – WP Physics} 06:51, 21 December 2008 (UTC)

Looks good. I would only add that the an antibaryon with L=0 has negative parity, since this article implicitly covers both the baryons and the antibaryons. It would also be nice to have a source confirming that L=0 corresponds to "ground state".
Also, on second thought, I think I was confused before. It wouldn't be surprising at all for L to be a good quantum number for a baryon. In particular, spin-orbit coupling doesn't get in the way of that. (What you put in the article is fine, but my idle speculation above was probably off. Sorry.) --Steve (talk) 18:47, 21 December 2008 (UTC)

New untheorized particle?[edit]

Hi, sorry if this has been discussed but I'm not exactly a particle expert. I came across this article awhile ago [4] and was browsing this page to see any mention of it.

Is there anything in this article about this already? I'm hesitant to edit the page because of my ignorance of the topic. Perhaps someone who is a little more experienced in this could shed some light on it, and maybe even include this in the main article? -- Chupon (talk) 15:47, 23 April 2009 (UTC)

See Y(4140). It's a kind of meson (possibly a tetraquark or two regular mesons bunched up together, see Mahajan, Namit (2009). "Y(4140): Possible options". arXiv:0903.3107Freely accessible [hep-ph].  More than one of |author1= and |last= specified (help) for an analysis of the possible options). Still thanks for the interest/pointing it out.Headbomb {ταλκκοντριβς – WP Physics} 16:53, 23 April 2009 (UTC)

2010 update[edit]

The 2010 PDG values are out. I've updated the list accordingly. I'll do list of mesons later on this week. Headbomb {talk / contribs / physics / books} 22:22, 7 August 2010 (UTC)

List is massively incomplete[edit]

List is nowhere near complete. See http://pdg.lbl.gov/2010/tables/rpp2010-qtab-baryons.pdf for starters. Mollwollfumble (talk) 19:23, 5 April 2011 (UTC)

Have added a new table, which includes about 100 other Baryons that had previously been missed. Mollwollfumble (talk) —Preceding undated comment added 04:10, 9 April 2011 (UTC).
Again no it's not incomplete, these are resonances of already mentioned baryons. I'm not sure these are good additions to the list. Several of these entries are unreliable and unconfirmed, etc... Headbomb {talk / contribs / physics / books} 04:41, 9 April 2011 (UTC)

Xi-sub-b[edit]

Are any changes to this article called for because of the observation of a new particle, the neutral Xi-sub-b (Ξb0)? See http://www.sciencedaily.com/releases/2011/07/110720162045.htm -- Jo3sampl (talk) 16:16, 2 August 2011 (UTC)

I'd wait for something more than a press release only citing an arXiv preprint, but let's hear other people's opinions too. A. di M.plédréachtaí 16:45, 2 August 2011 (UTC)

According to PDG (http://pdg.lbl.gov/2011/listings/rpp2011-list-xib-zero-xib-minus.pdf), Xi-sub-b minus have mass 5790.5 ± 2.7 Mev/c^2. Xi sub b 0 have mass 5945.0±3.7 MeV/c^2 according to recent results from CMS (http://arxiv.org/pdf/1204.5955.pdf), this is however exited state. --91.213.255.7 (talk) 01:26, 28 April 2012 (UTC)

Charmed Chi prime isospin I value in table seems to be wrong[edit]

Shouldn't the charmed chi prime isospin value be zero rather than 1/2? Ohwilleke (talk) 22:55, 19 February 2014 (UTC)

If it's a Xi, it's isospin 1/2 (charmed Xi prime = quark content either usc or dsc). Headbomb {talk / contribs / physics / books} 23:59, 19 February 2014 (UTC)

Accessibility of lists of baryons[edit]

The lists of baryons appear not to be accessible to blind people, but I don't know enough about baryons to fix them (the tables, not the baryons).

J P = 1⁄2+ baryons table:

Some items have both the 1/2 and the plus sign in red, some have just the plus sign in red. Do the ones that have just the plus sign in red have the part not in red established? Or is it a markup error?

Text color is not accessible to blind people, so a symbol needs to be added, such as a ‡. If J and P are independent of one another, then if both were red, then the symbol would need to be added to each. But if it was a markup error, then only one symbol is needed.

If it was a markup error, then we don't even need the J P column to contain 1/2+. We just need it to contain a Y for established or N for not established, since the entire table is of J P = 1/2+ baryons.

The same thing goes for the JP = 3⁄2+ baryons table.

Until those symbols are added, these tables are not accessible to blind people.

The names of the baryons do not appear sufficient to this non-scientist. There are several cases where two or three baryons appear to share a name. Why is the + or 0 or - not part of the name to distinguish them?

Baryon resonance particles:

Are all particles in the same table row related, with the particle in the first column the "master" particle that describes the table? Or are the columns side-by-side to save space? If the latter, then the table is not accessible, and there needs to be some other way to achieve such a layout than putting unrelated particles into the same table row.

The marking of non-established JP values solely with red text is unambiguously not accessible, so I am adding the {{AccessibilityDispute}} template to this page.

Wikipedia accessibility guidelines can be found at WP:ACCESSIBILITY.

Thisisnotatest (talk) 08:04, 26 January 2015 (UTC)

I'll be happy to make the accessibility improvements if someone would answer my questions so that I don't change the meaning of this page. Thisisnotatest (talk) 05:01, 27 January 2015 (UTC)

External links modified[edit]

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double charmed Xi ccd[edit]

I suggest removing the mass and lifetime from the table. One experiment claimed that it had found the particle, with properties largely different from predictions. Several other experiments didn't find anything like the claimed properties. Now LHCb measured ccu, with a mass that makes the ccd claim even less plausible. The LHCb paper serves as reference that the older claims from SELEX are very unlikely. --mfb (talk) 00:29, 7 July 2017 (UTC)

Did that. The discovery claim is still accessible via the footnote. --mfb (talk) 12:15, 9 July 2017 (UTC)

Templates[edit]

What's going on with the templates on this page? Are they massively screwed up and half of them only show as links for anyone else? It's hard to believe no one would at least be distracted by the huge barnstar at the top of the page, is it my browser screwing something up and hitting some sort of limit for rendering templates, or is that an issue with the page no one's bothered fixing because of how huge the tables are? --Jessietail (talk) 11:05, 8 March 2018 (UTC)

Category:Pages where template include size is exceeded - too many templates on the page. This looks like a recent development, so I wonder what changed. We can probably replace all instances of Template:Subatomic particle, that should help a lot. --mfb (talk) 11:47, 8 March 2018 (UTC)
Yes, that template is doing too much work. See sub-templates. A module containing all the data is needed. I could fix that later but I'm a bit busy now. Johnuniq (talk) 09:45, 15 March 2018 (UTC)
I fixed the problem using Module:Particles. I'll document what it does a little later although the change I made should be reasonably clear. It has to use the somewhat ugly #invoke because using a template to call the module would double the expansion size. Before my edit, the post‐expand include size was 2,097,152 bytes which is the limit. After that limit is reached all further templates fail. After my edit, the expand size was 1,415,550 bytes. I only changed some of the {{Subatomic particle}} templates and will do more later. Johnuniq (talk) 00:45, 18 March 2018 (UTC)
I finished replacing the {{Subatomic particle}} templates. The expand size is now 559,986 bytes. That means the article is displayed correctly and editing it will be faster. Johnuniq (talk) 04:22, 18 March 2018 (UTC)