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Quark question

  1. Apr 16, 2005 #1


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    As far as I've heard, there are 6 "flavors" of quarks, which are divided up into three "colors". There are also antiquarks. So this means thet there's a total of 6*3= 36 quarks. Do all of these quarks have a name? just wondering.

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  2. jcsd
  3. Apr 17, 2005 #2

    Using smilies to represent quarks.... :approve: That's very creative, really.

    However there are no 36 quarks. We have debated this issue many times here and i don't feel like repeating myself. I urge you to look at the very first post of the 'elementary particles presented' thread. You will find a link there that explains quasi everything about flavours and colours in a very amusing manner. If you browse through this thread, you will find answers to questions like :
    1) how were quarks discovered
    2) why eight gluons
    3) why can't you see a single quark


  4. Apr 18, 2005 #3

    Meir Achuz

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    Many physicists do consider that there are 36 quarks, as you counted them.
    It is a matter of taste whether you call a red u a different particle than a blue u, or whether you say they are two different states of the same particle. For instance, the proton and neutron can be considered as two different particles or two different isospin states of the same particle. SU(3) is not generically different than SU(2).
  5. Apr 18, 2005 #4


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    While I defer to Meir Achuz's likely greater knowledge, I normally think of their being 6 quarks (up, down, top, bottom, strange, charm) which can couple to gluons, which come in a variety of color combinations. Add anti-particles and keep in mind that quarks themselves come in three groups of two (which are themselves paired to three kinds of electrons and three kinds of neutrios), and there you are.

    Thus, you would typically say that a particular fermion was comprised of three quarks and three gluons, and identify each. You also wouldn't necessarily identify the gluons with a particular quark, on the theory they are exchanged.

    I'm interested in knowing the arguments that there really are only three groups of two, rather than four or an infinite number, myself. Also, I'm interested in knowing an answer to a related question. Would the discovery of, e.g., a "fourth order neutrino" (presumably the lowest energy possible next order neutrion-electron-quark) would contradict M theory, as it might break the wonderful SU(3) kind of patterns?
  6. Apr 18, 2005 #5


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    I don't understand your post, three groups of 2? Huh?
    Are you talking about 3 generations of particles plus their anti particles?

    To be really complete (though not quite fundamental)

    You have 3 generations of quarks that transform as doublets (for instance the first generation has two eigenstates of isospin) so 6 flavors in all + their antiparticles (so multiply by two). You kinda/sorta want to also note that they come in two chiralities (this is true b/c they acquire mass).

    The same is true for the lepton fields, you have three generations which transform as doublets (electron vs neutrino), again with their antiparticles.

    The standard model doesn't really know anything about 'generations' outside of reality conditions on the CKM matrix. You have to explain that *somehow*, and no one really is quite sure why it seems to be the case.

    You can cook up models that have very heavy fourth generation partners for instance but they nearly always break experimental bounds on W decays and nucleosynthesis.

    3 generations is what we are left with, and its actually very interesting b/c very few standard model extensions really explain 'why' 3 and nothing else. It turns out that one of the few potential solutions is large extra dimensions, where one sees that number is related topologically to the euler characteristic of the space.
  7. Apr 24, 2005 #6
    You missed out the three colours of quarks. To QCD, a red quark is as different from a blue quark as an electron is from a neutrino in the weak theory.

    As for the three generations, like you say, there is no real explanation yet, but it's interesting to note that at least three generations are required to cancel some of the infinities in the theory, and also to produce CP violation. It doesn't work with only two generations.
    Last edited: Apr 24, 2005
  8. Apr 24, 2005 #7


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    Can you expand on this?
  9. Apr 25, 2005 #8


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    Some links on fourth generation neutrinos:

    Bibliography of the literature on the issue:
    http://www.nu.to.infn.it/Fourth_Generation/ [Broken]

    This paper (Could there be a Fourth Generation?) is among the most interesting of those listed and dates to 2002:

    Discussion of a possible 50 GeV 4th generation neutrino and its connection to string theory in a 1999 paper:
    http://arxiv.org/PS_cache/astro-ph/pdf/9903/9903086.pdf [Broken]

    This has 18 citations: http://citebase.eprints.org/cgi-bin/citations?id=oai:arXiv.org:astro-ph/9903086 [Broken]

    2002 paper on constraints: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002hep.ph....3207H&db_key=PRE

    1997 abstract discussing observational limits on 4th generation neutrinos:

    More contraints in a 1993 abstract: http://arxiv.org/PS_cache/hep-ph/pdf/9301/9301286.pdf [Broken]

    Physics Forums Archives: https://www.physicsforums.com/archive/topic/t-11254_Is_there_any_evidence_for_a_4th_family_of_particles?.html [Broken]

    Recent MiniBoone searchers for 4th Gen neutrinos mentioned:
    http://www.mppmu.mpg.de/common/cc_neutrino.html [Broken]

    Power point style summary with lots of graphs (from 2000):
    Last edited by a moderator: May 2, 2017
  10. Apr 25, 2005 #9
    I apologise, that was a mistake. I was getting mixed up between the GIM mechanism, which predicted the charm quark through loop diagrams, and the cancellation of anomalies between quarks and leptons. Sorry!

    The other thing was correct, though- without a third generation you can't have CP violation.
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