# Talk:Top quark

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## Importance discussion

(Ironically, it is not of Top importance.)

Now it is :P, as are all all fundamental particles (or will all soon be). See Wikipedia:WikiProject Physics/Projects of the Week for reasons.Headbomb (ταλκ · κοντριβς) 22:41, 14 June 2008 (UTC)
I can't figure the logic by which you decided strange quarks are of Mid importance, but tops are of High importance. Surely the lighter strange quark is more relevant to real-world physics. Think strange quark stars or strangelets. The top is only relevant to beyond-the-Standard Model probing. -- Xerxes 17:16, 6 June 2006 (UTC)
I'm not sure what you mean by "real-world physics"? The top quark is a topic of active ongoing research. There isn't much new being studied or discovered when it comes to the lighter quarks (except maybe bottom). Bodhitha 15:11, 22 June 2006 (UTC)
The top quark is relatively new news and an active area of research. The strange quark, as far as I'm aware, is not. Quark stars and strangelets are entirely hypothetical, and I really don't know what you mean by "real-world" physics. It really doesn't have any properties more interesting than the up and down, and all the strange particles were discovered before quark theory. I wouldn't have rated the strange quark at all except that I was testing the rating system. -- SCZenz 19:18, 22 June 2006 (UTC)
Well put. The road of assigning importance to purely hypotheticals (quark stars, etc.) is a slippery slope. Bodhitha 19:47, 22 June 2006 (UTC)
I see no reason why active research should have any bearing on importance. There's no cutting edge research on atoms, anatomy or arithmetic, but these are crucial foundations of science. Encyclopedic importance should be inversely proportional to a subject's distance to the cutting edge. -- Xerxes 23:52, 22 June 2006 (UTC)
Maybe the key here is importance "within physics" as it states, not necessarily encyclopedic importance? Bodhitha 03:58, 23 June 2006 (UTC)
Xerxes, I don't think that's true even for print encyclopedias; they tend to have large, detailed articles on current issues which shrink over time as the editors put the subject into historical perspective. The fact of the matter is, for the next several decades at least, I anticipate that people are far more likely to look up the top quark than the strange quark. Thus on the much-shorter timescale on which Wikipedia changes, having this article up to standard is the most important—which is ultimately what these importance ratings are for. -- SCZenz 06:07, 23 June 2006 (UTC)
Also, don't forget that most of the interesting facts about the strange quarks are actually interesting facts about the kaon (probably High importance) or other particles, or about its relationship to the Eightfold way (High importance) or the quark model (Top importance). The strange has its thunder stolen, in a real sense, by hadronizing; there's not much left to say about the quark itself after all that. Some day the interesting facts about the top quark may perhaps be in the Supersymmetry article, once we understand that the top Yukawa coupling equals one exactly and it was telling us what new physics to look for the whole time, but that day has not yet arrived; the interesting info on the top quark all goes in this article in the meantime. -- SCZenz 06:17, 23 June 2006 (UTC)
Well, perhaps we should think of it this way: which of the elements of the periodic table would you omit if you had to choose one? or which of the five kingdoms of life? There are only six quarks. By what criterion could you choose one over the others? Maybe it's not really that important; I'm sure all six quark flavors will make it into whatever canonical edition is being cooked up. -- Xerxes 19:27, 23 June 2006 (UTC)
There are some very fundamental things that set aside the top quark from all 5 others. Among them are the fact that it is the only quark that you can study in "bare" form (since it decays before it ever hadronizes). It is also the *only* (known) fermion with a mass anywhere near the EWSB scale and as thus may offer unique insight into that mechanism. Bodhitha 22:24, 23 June 2006 (UTC)

## Electroweak symmetry breaking section

I have a rule of thumb about particle physics equations. If I can't make heads or tails out of it, despite being a grad student (albeit an experimentalist), it may be too complex for a general-use encyclopedia. And I have to say I don't understand the the Electroweak symmetry breaking section; in particular, I don't understand the purpose. Is the idea that the proximity of the top mass to a fixed point in the SM RGE is an argument for the MSSM or other supersymmetry model? If so, that should be made explicit, just for starters. One could also ask if we need all those equations, and if the top quark article is really the right place for that argument. -- SCZenz 02:13, 27 January 2006 (UTC)

I kinda like it, tho it certainly could use some clarification. There are also some fascinating things that have been postulated in so-called topcolor models, which use technicolor but have top quarks as techniquarks. -- Xerxes 04:31, 27 January 2006 (UTC)
A general discussion of the implications of the top quark mass for various physics models would be very appropriate here. But this is a lot of detail about one issue, and rather vague to boot. -- SCZenz 06:38, 27 January 2006 (UTC)

Sorry for the poor writing. I was just trying clarify what 'evidence for the MSSM' meant -- a bit of an oblique statement. The heaviness of the top disfavours many models of EWSB that involve a composite Higgs or technicolour models -- but that just means it favours an elementary Higgs. Some people claim that the proximity of the top quark's mass to its RG fixed point is evidence for the MSSM over the SM (both of which have elementary HIggs). I (or someone else) should explain that there is a basin of attraction around fixed points of RGs where couplings will flow to at low energies regardless of the initial value of the coupling. Therefore, if you believe that the top Yukawa is just a random number to start with at high energies then it is much more likely for it to be near the fixed point at low energies than some place else. There is certainly a lot that can be said explaining what a fixed point of an RG equation is -- but that probably belongs some place else.

I personally don't like blanket statements about whether a piece of experimental data supports or refutes some unproven theory unless the caveats are stated. To my knowledge this RG argument is the only way that the MSSM is preferred over the SM, and it is not amazingly strong evidence. Nonetheless it is interesting, especially with the (as yet unwritten) backstory that after the top was discovered, every theorist and their brother posted a paper claiming that they had predicted the top mass (through small modifications of this equation).

More concretely, I feel that the questions someone will come to the top quark page with is "what is it?" "why is it special?" "how did we discover it?" "what is the history behind the top?" "why do we care about it?"

• There was a set of predicitons for the top mass involving precision electroweak data which closely parallels the prediction of the charm mass. (this is not an RG argument and is the reason why 't Hooft and Veltmann won the Nobel Prize)
• Since there is an on going effort to measure the properties of the top quark, describing their SM predictions and possible deviations is possibly useful (and also motivations for why to expect such deviations).
• Also, driving EWSB from the top quark is a qualitative idea that is commonly used -- ie the quantum dynamics of the top quark yukawa coupling causes electroweak symmetry to break.
• I also feel that description of the experimental signature for top discovery is also important would be useful (ie 2 bjets + 2 leptons + MET, (or whichever the signal was))

Again, my regrets on the poor writing.

--jay 06:31, 28 January 2006 (UTC)

## A small problem with the wording

I'm uncomfortable with the wording. The article states "It was discovered in 1995 by the CDF and D0 experiments at Fermilab". Surely this should read "It was first observed...". Theorists predicted it before then, and as such it was expected to turn up at some high mass.

Apologies if I've missed a previous discussion on use of the word "discovered". I've had a look around and couldn't see anything conclusive.

86.15.240.245 04:26, 28 November 2006 (UTC)

## The top quark DOES hadronize

The top quark needs to stay with two other quarks or an antiquark. The strong force overrides the other three forces.--67.10.200.101 06:18, 30 June 2007 (UTC)

No, the top quark really does decays well before it has time to find the quarks that would make it color neutral. The decay width of the top quark is 1.5 GeV while the hadronization time scale is 1/0.2 GeV. See for instance "Jets from massive unstable particles: Top-mass determination" by Fleming, Hoang, Mantry, and Stewart (hep-ph/0703207) that exploits this property to argue that the theoretical uncertainty on the top quark mass is much less than that of other quarks -- the order of uncertainty is $\Lambda_{\text{QCD}}^2/\Gamma_{\text{top}}$. jay 07:04, 30 June 2007 (UTC)

## R Baryon

Someday I want an R baryon to appear, with three top quarks, a spin of 3/2, and a charge of +2. I know that it's not normally possible, but I do wish for a longer lifetime for the top quark.--Mathexpressions 03:44, 11 July 2007 (UTC)

## actuality

the t-Quark does have 172.5 ± 2.7 GeV by partical group ->http://pdg.lbl.gov/2007/listings/q007.pdf —Preceding unsigned comment added by 87.123.231.207 (talk) 04:43, 20 February 2008 (UTC)

Note that in the first paragraph of the paper you provide, it states, "Including the most recent unpublished top mass measurements from Run-II, the TEVEWWG reports an average top mass of 170.9 ± 1.1 ± 1.5 GeV". This newer figure has since been published, and is given correctly in this article. -David Schaich Talk/Cont 06:00, 20 February 2008 (UTC)

## Comparison of weight with other nuclei

• If you are going to say that the mass of the top quark is the same as the mass of a gold nuclei you need to at least say it grammatically correctly (what you wrote was not even a sentence). Also you need to explain how this can be true since it is completely counterintuitive since a quark is supposedly a more fundamental particle than a nucleus. Just a throwaway sentence does NOT work here and it looked like vandalism which is why I took it out. Therefore I would not recommend keeping that in the introduction since it is just confusing and the introduction is not a good place to explain it and it is just not necessary. But I am only an undergraduate so I will bow to you assuming you have a higher degree.149.159.112.163 (talk) 01:10, 12 June 2008 (UTC)
• Compare the mass of the top quark with the mass of a proton or neutron. You'll see the top quark is actually far heavier. That's because those two particles aren't made of top quarks, but rather the much lighter up and down quarks. "More fundamental" and "lighter" are not always necessarily the same.
As a side note, the comparison to gold is more traditional, and I think it's better because everyone knows about gold and knows it's a heavy metal. Not necessarily so with the others. -- SCZenz (talk) 02:33, 12 June 2008 (UTC)
• There are many "fundamental particles". Amongst them, are the quarks. Quarks are the building blocks of many composite particles. Protons, for example, are made of two ups and one down quark., Neutron in turn are made of one up and two down quarks. You could say quarks are to atoms what atoms are to molecules. Just like a molecule of water (H2O, weighs about 18 atomic mass unit on average) is lighter than a single uranium atom which weighs about 238 atomic mass unit. Just like a particle made of atoms is not automatically heavier than a particular atom, an atom made of quarks is not automatically heavier than a particular quark.
The mass of the top quark is about 170 900 MeV/c2, while the mass of protons and neutrons (sometimes they are called nucleons) is about 938 MeV/c2. If you divide 170 900 (mass of t quark) by 938 (mass of nucleon) you get 182.something (a.k.a. the t quark has the mass of 182 nucleons). If you look for stable atoms made of 182 nucleons, you end up somewhere around Tungsten-110 (74 proton + 110 neutron = 184 nucleons) or Tantalum-108 (73 proton + 108 neutron = 181 nucleons). A gold atom is slightly heavier with usually 197 nucleons.
The incredibly heavy mass of the T quark is the reason that it was discovered so late (1995) and that to this date, only the Fermilab can produce t-quarks. It just takes an incredibly amount of energy to create. I hope that clarifies things.Headbomb (ταλκ · κοντριβς) 02:51, 12 June 2008 (UTC)

And BTW, the 2+2=4 comment in the edit isn't meant to be condescending, it's just that the statement that t quarks have mass comparable to that of a tungsten atom comes down to a simple division. Headbomb (ταλκ · κοντριβς) 02:51, 12 June 2008 (UTC)

## Decay branching ratios

Decay branching ratios were just added to the infobox. Can this information be put in the article itself, along with the source? I don't see it in the PDG, but perhaps I'm just not looking in the right place. -David Schaich Talk/Cont 16:57, 27 July 2009 (UTC)

They were in the main text before (also without source), but where removed in my revision/expansion of the decay section. They are simply the magnitudes squared of the relevant CKM matrix elements (due to the high mass of the top, the masses of the decay products can be safely ignored.) The only branching ratio that has been measured is the t->b decay, which is in the text. The decay section should probably be expanded by a sentence or two about the theoretical values of the branching ratio. (with an appropriate source). (TimothyRias (talk) 09:18, 28 July 2009 (UTC)0

## Harari's quark model

See Talk:Quark#Harari's quark model. Headbomb {ταλκκοντριβς – WP Physics} 00:05, 22 February 2010 (UTC)

H. Harari actually COINED the names of the "top" and "bottom" quarks. Harari was the first to propose a model of six quarks and six leptons, naming the two new quarks “top” and “bottom” (names presently accepted by all), and predicting the existence of six leptons. In August 1975, at the Stanford International Particle Physics conference he presented, for the first time ever, the full synthesis accepted today as “the standard model” of six quarks and six leptons. Its seems that the authors of this page arent from the field of HEP Barak90 (talk) 10:21, 22 February 2010 (UTC)

## New reference

2010 PDG values have been posted, http://pdg.lbl.gov/2010/2010/tables/rpp2010-sum-quarks.pdf
I will wait a few more days before making the changes to mass. If there are no objections I'll apply the changes on Friday August 06, 2010 sometime between 0700 and 2200 UTC. Abyssoft (talk) 20:31, 2 August 2010 (UTC)

## Willenbrock reference

Added link to full text on arxiv. Someone may wish to remove the reference to the article as published in Prosper's book. It's better to refer to the version everyone can freely access electronically. --Biggus Dictus (talk) 18:03, 13 October 2011 (UTC)