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Quarks .

  1. Sep 2, 2004 #1
    Neutrons and protons consist of quarks right? my question is ;has any one theory as to how are they aranged inside of protons/neutrons?. one orbits another or whatever?
  2. jcsd
  3. Sep 2, 2004 #2
    Protons and neutrons are indeed made up of quarks. You can imagine that protons and neutrons look like a boiling soup of fluctuations when you watch them very closely. But when you watch them from far away, they much more look like a billard ball. Almost.

    The situation is intricated, and difficult to understand. We do not fully undestand the structure of those guys, which constitute more than 99% of the ordinary mass around us. Doubtlessly, their structure is essentialy dynamical. It is the glue fluctuations which make up most of the mass, and also has an very important contribution to the spin.

    If you can wait at least one year, probably more, maybe much more, we will ultimately be able to contemplate a 3-dimensional view of the proton content. This will be provided by a recent formalism called "generalized parton distributions" wich allow (among other things) to access the energy-momentum tensor of the partons.

    Please note that the only other way known to access the full energy-momentum tensor is graviton scattering. You would have to wait much longer.
  4. Sep 2, 2004 #3

    As a matter of fact we have the dual abelian Higgs model based upon the dual superconductor as the QCD vacuum. This model includes the existence :yuck: of magnetic monopoles, which have not yet been found in reality. It states that a neutron is constituted out of three quarks each positioned at the corner of a tringle or at the endpoints of the Merceds-sign, hence the name Mercedes-structure...


  5. Sep 2, 2004 #4
    there are two types of quark in the universe (others can be created in particle accelerators but don't worry about them in the formation of protons and neutrons.)

    The two are up quarks and down quarks. An up quark has a charge of 2/3e and a down quark has a charge of -1/3e

    A proton therefore is made of 2 up quarks and a down quark, so it has total charge of 1e.

    A neutron is made of 1 up quark and a down quark, so it has zero charge.

    I don't know if there is specific arrangement inside nucleons, but just try to imagine the best way to fit three balls in the smallest space possible
  6. Sep 2, 2004 #5
    It's postulated that the interchange of gluons maintains the quarks together, but i've never understood completely how it works. If a gluon hits a quark it should push instead or pull it, right?
  7. Sep 2, 2004 #6
    Specific structure of quarks inside nucleons is something I answered to in my previous post.

    i would like to ealborate on these different quarks though. basically the are classified in the Standard Model into 3 generations

    First colum is the name,second colum is the force they feel, finally their electirc charge

    First family

    Up-quark ,spin ½ ,they feel Elektroweak, strong force charge 2/3
    Down-quark, spin ½,they feel Elektroweak,strong force, charge -1/3

    Second family

    Charm-quark, spin ½ they feel Elektroweak, strong force, charge 2/3
    Strange-quark, spin ½ they feel Elektroweak, strong force,charge1/3

    Third family
    Top-quark, spin ½, they feel Elektroweak, strong force charge 2/3
    Bottom-quark, spin ½,they feel Elektroweak, strong force, charge -1/3

    The quarks from the second and third family are much heavier than those of the first family, so they are much more difficult to make. remeber that mass and energy are equivalent, right ... A strange-quark is 20 times more heavy then a down-quark.

    Last edited: Sep 2, 2004
  8. Sep 2, 2004 #7

    Quarks are "glued" together by the stronf-force-mediating gluons. The rule for interquark interaction states that all colours involved must sum up to "white" or neutral. A gluon itself contains two colours so it can be neutral itself (e.g. red-antired-combination) or not. In the last case, gluons can interact with other gluons that carry no net neutral-colour. This is a big difference to the fotons from QED that never carry any charge.

    A red quark "emits" for example a red-anti-blue gluon that is then absorbed by a blue quark. This blue quark will become red and the original red quark will become blue. So the net-effect is the switching of two colours.

    Pay attention to the fact that this quark doesn't really generate a gluon and spits it out or absorbes it. I just state this in order to exemplify the ATTRACTIVE interaction due to colour-neutrality. This colour-confinement is one of the big unsolved problems in contemporary theoretical fysics. Why are quarks in the QCD-groundstate (and not only there) always found in triplets (baryons) or doublets (mesons, like pions that also mediate the residual strong force) ??? try to answer this question and you will get a Nobel Prize :biggrin:

  9. Sep 2, 2004 #8
    Quarks will not have the same colour as a nearby gluon due to the current algebra that has to be respected. Otherwise, quarks would not be confined and asymptotic freedom that caracterises the strong force in different energy-scales will not be respected.

    The very small distance scale of a neutronstar gives rise to enormous energies that would lead to deconfinement of quarks. They would constitute a gas. The thermodynamic properties of this gas is studied by many fysicists

    In this case quarks or more specifically the quark-interaction via gluons would become repulsive. This is not yet proven though...

  10. Sep 3, 2004 #9
    Here's a simpler problem that one can actually say things about. Forget about baryons since that's a three body problem, which isn't even solvable in classical mechanics, and think about mesons (two-quark objects). Also forget about the light quarks because the theory actually has difficulties with them due to the inherently relativistic structure. So consider the heavy quark mesons. One can approximate the interaction potential as a piece that falls off with the sep. distance and another that increases linearly with the sep. distance. Now this can be solved through the Schroedinger eqn, so you get a whole spectrum of states. Since the potential is actually radial, you get the same angular momentum states as in the hydrogen atom. So there are orbital quantum numbers in this case, yes, and one expects such numbers for baryons and lighter mesons too. But I hope you know enough not to associate this with classical orbits :smile:
  11. Sep 3, 2004 #10

    Actually , this is not really true zefram_c.
    Three quarks in a baryon can sit on the corners of a triangle. this is the delta-structure or triangle-structure. When this configuration is to be studied, You will get the best results when you look at the three quarks as three two-body-problems and not one three-body-problem.

    Which of the two configurations will occur??? Well following the Abelian Higgs model, that depends on the interquark-distance. Beneath 0.7fm the triangle-configuration is "dominant"

  12. Sep 3, 2004 #11
    Another question,maybe I missed the answer (sorry).What is the energy associated with quarks?Lets say, we take apart neutron, how much energy we are releasing?Are there energy levels inside comparable to quatntum levels of electrons?
  13. Sep 3, 2004 #12
    Sorry, you can't take a neutron apart. Quarks cannot exist on their own, they can only exist when joined together to make their "colour charge" as talked about above to be neutral

    So although we talk about neutrons being made from quakrks. we cannot observe isolated quarks
  14. Sep 7, 2004 #13


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    I've noticed that all the diagrams I see are of a triangular formation for baryons and a verticle linear formation for mesons. Though they probably have no idea how they are stuctured.
  15. Sep 9, 2004 #14
    Like I stated in previous posts, it really depends on the energyscales of the quarks. Keep in mind that quarks must obtain a linear potential in the low QCD-regime because of confinement. So when I say that energy determins the structure then you could also say that the interquarkdistance is a deciding factor.

    Quarks want to sit as close together as possible, yet they we not get too close because this linear potential is only dominant in low-energy-region of QCD. The reason for this is asymptotic freedom. The strong coupling constant get's bigger and bigger with decreasing energy. And low energy is equivalent with big interquark-distances because of Heisenberg-uncertainty

  16. Sep 9, 2004 #15
    why do some mesons have wavefunctions like
    Y (down) Y (antistrange) + Y (antidown) Y ( strange) / constant

    Is this because the strange and down quarks can change into one another as time passes? And how do we know this is really happening?

    Also when particle physicists say that the electric force = colour force at 10^-17 metres, what is the magnitude of the force at 10^-17 metres and
    was qed used to calculate the electric force at 10^-17 metres?
    Is there a table of electric force against distance for qed somewhere?
    Last edited: Sep 9, 2004
  17. Sep 9, 2004 #16
    Those are mesons (the neutral kaons) which have a strange content yet having zero net strange charge. The K-zero-short and K-zero-long are very similar particles with different lifetimes decaying respectively in two and three pions. Historically, it was a serious puzzle. See hyperphysics.
    Not really. The kaon is a quantum superposition of the two states, but there is no weak process transforming one flavor into another before the decay of those particles.

    Can somebody elaborate on that ?
  18. Sep 9, 2004 #17
    Could you tell me where you got this ??? it seems rather strange to me. are you sure they were not talking about COLOUR-electric charge in stead of just ordinary electric charge and force...

  19. Sep 9, 2004 #18
    This is to do with asymptotic freedom and the colour force getting weaker at shorter
    distances.I'll try to find the website where I orignially read it.
  20. Sep 9, 2004 #19

    Maybe (just a suggestion, ok ?) they are trying to say that at the given "small" distance the strong force coupling constant gets so weak that the electric-force (Coulomb-potential) get's more dominant when it comes to the main contribution to the energy of the "quarksystem". I mean, it is a well established fact that the linear potential between quarks in the dual Landau-Ginzburgmodel become extremely small in the short range and it is there that the Coulmb-potential "takes over".

    Still wondering how you got that number though... :uhh:

  21. Sep 9, 2004 #20
    I can't find the website where I read that number many months ago.
    When you say coulomb potential do you mean qed or kq1q2/r^2?
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