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Quarks, and gluons

  1. Nov 6, 2003 #1
    I’ve been trying to find specifics about quarks and gluons, and it seems like not a lot is known.

    If I’ve got things right Up quarks have a speculated mass between 1.5 and 4.5 MeV, and Down quarks a speculated mass of between 5 and 8.5 MeV. Gluons are considered to be massless. A proton is uud, and has a measured mass of 938, a neutron udd mass 940.

    The mass discrepancy between uud max 17.5 and a proton 938 is in the form of the strong nuclear binding force, or quark colour charge. All stable or maybe even legal particles made of quarks are colour neutral.

    An electron has no quarks, is considered indivisible, and has a mass of 0.51 MeV. So even if we add the mass of a proton and an electron we don’t get a neutron. There is some binding energy thus between the electron and the proton in a neutron that accounts for the mass discrepancy.

    I have never seen any accounts of the number of gluons in an up or down quark. Or of the number of gluons in a proton, or neutron, or in deuterium. Or even a probability distribution for the number of gluons that a particle has.

    Nor have I seen any suggestion about the speed gluons travel between quarks in the same hadron, or between quarks in a proton-neutron pair. I’ve read that gluons exchange often between quarks, but never found a hint of a frequency.

    The limit of the strong nuclear force is about 3x10E-15 metres.

    If you pull a proton-neutron apart to the limit of the strong force, you will add energy until the energy of pulling them to the limit of the force is enough to create a gluon anti-gluon pair, as the nuclear bond snaps, and a gluon goes to one of them, and an anti-gluon to the other.

    Its almost suggested that we can’t talk about a gluon outside a quark because it has colour, (and anti-colour) and colour neutrality is the law.



    However I notice that unstable particles involving the strong nuclear force have a life of about 10-23 s, so we could guess that gluons must travel within 10-23 s, between quarks.

    Could an electron have an anti-gluon ? Could a quark’s colour charge simply be it’s number of gluons, with 0, and 4 being colour neutral, and 1,2,3 the colours. Gluon exchanges would then certainly change a quark’s colour.

    Let’s say the Up quark, has 3 gluons, and the down 2. The protons have 5, and neutrons 3. A Deuterium atom would have 8, and Helium-4 16.

    If a multiple of four is a “good” number of gluons in a nucleus such a model would explain why Neutrons don’t bind, and why even numbers of neutrons and protons make the most stable nuclei, and release the most energy from fusion. Two neutrons have 6 gluons with is 4+2. Two protons have 10 gluons with is 2x4 + 2.

    Ok I want people to verify I’ve painted the known picture correctly, or correct it, and comment on my speculations.
     
  2. jcsd
  3. Nov 6, 2003 #2
  4. Nov 6, 2003 #3
    Okay.

    A neutron is not made out of a proton and an electron, binding energy or not. It is made out of quarks, just like a proton is.

    Quarks do not contain gluons; they are indivisible particles, just like electrons. They exchange gluons with each other, just like particles exchange photons and other gauge bosons.

    A static strong field doesn't contain any real gluons, just like a static electric field doesn't contain any real photons. When it comes to virtual gluon or photon exchange, particle number doesn't make sense: you sum over all possible ways that any number of gluons could be exchanged.

    Gluons, being massless particles, always travel at c. (But we can speak of them having an effectively slower speed in a medium, due to absorption and reemission, just like we can with photons.)

    This runs into the same kind of problems that gluon number does.

    Actually you create quark-antiquark pairs.

    Yes, gluons as well as quarks are confined.

    I don't know of any way of connecting a gluon effective propagation speed with the lifetime of a particle. For instance, in the case of mesons, the lifetime has to do with the probability that the quark and antiquark inside the meson will annihilate each other, not with how fast gluons are exchanged.

    No elementary (indivisible) particle "has" a gluon, in the sense of containing one. And electrons don't even interact via gluons.

    No.
     
    Last edited: Nov 6, 2003
  5. Nov 10, 2003 #4
    Ambitwitsor thankyou for your patient and very precise answers to what I realise came across as naive questions.

    I don’t really understand electromagnetism, strong, weak, gravity, or spin. However I know a little bit about each, and have since found the standard model chart from CPEPweb.org, actually through benzun_1999’s link.

    If I can explain what I’m after, I think fundamental particles want something.

    Want is a rather fuzzy term, but an electron and a positron want to be together because of gravity and electromagnetism. Two protons might want to be together depending on the colour flux compared to the electromagnetic flux.

    The gravity flux is largely irrelevant in calculating want involving small clusters of fundamental particles.

    Two protons have an additional not want. If they get to the weak barrier, one of the up quarks has to transmute to a down by creating a virtual anti Boson which decays to a positron and an electron neutrino. The positron is emitted as if the nucleus has absorbed an electron.

    P, P = P, N, e+, en_

    The apparent force on a particle is a function of the sum of the energy released by satisfying its wants. The mass energy is a function of the rest mass, and the extent to which its wants have been satisfied which is related to the mass energy of the various fluxes.

    He4 is more satisfied than deuterium H2, which is happier than H1, and two neutrons on a whole don’t want each other unless there are protons to mediate.

    So I think Up quarks have an intrinsic colour want of 3, and down quarks 2. In a stable non degenerate (dense star, electron or neutron degeneracy) nucleus the quarks have been satisfied to the extent that the “electromagnetic want” allows.

    Conceptually it is similar to chemical covalent bonding, between Nitrogen the up quark, and Oxygen the down quark. Helium4 is a U6D6 molecule, and a good one, Tritium is U4D5 pretty bad because up is better at bonding, hence decay to Helium3 U5D4.

    Deuterium is U3D3 also good, the first “real molecule” or nucleus, and its shape defines the shape of larger nuclei.

    He2 is U4D2 even better than H2 if you ignore electromagnetic repulsion which forces He2 or two protons to decay to deuterium.

    Using this model I can predict stable isotopes up to carbon, but don’t find one for Beryllium instead thinking B9 is better than Be9. This makes sense as I’m not considering electromagnetic want or repulsion, and B9 with 5 protons, and 4 neutrons is obviously electro magnetically unstable

    It also finds H1->H2->He3 a good path inside a star. He3->He4 also good.
    He3->Be7->B8->Be8->He4 an alternative way of getting to He4
     
  6. Nov 12, 2003 #5
    some quark math

    I would also recommend for you to take a look at the Particle Listings in the Physical Review D, which you can access at http://pdg.lbl.gov/. This will show you all of the quantum numbers, rest masses, and decay modes that are known for all particles which are known to exist or have been seen with a certain amount of confidence.

    I can see some of what you are saying, but I would not necessarily describe it as "want", but rather satisfying conservation of quantum numbers and acheiving the lowest possible available energy states.

    It is not possible to assign up quarks an arbitrary "color-charge" of 3 or any other number; it is not a quantity that can be defined numerically right now, but rather the colors for quarks come in a set of three colors and three anticolors: red, green, blue; anti-red, anti-green, anti-blue. Red + green + blue is white, and anti-red + anti-green + anti-blue is white; this explains the baryons (composites of three quarks) and anti-baryons (composites of three anti-quarks). Red + anti-red is white, green + anti-green is white, and blue + anti-blue is white; this explains the mesons (composites of a quark and an anti-quark). Hence, baryons always have half-integer spins and act as fermions, while mesons always have integer spins and act as bosons. Quarks each have spin 1/2 and have a baryon number of 1/3, while the anti-quarks also half spin 1/2 but have baryon number of -1/3. Hence, baryons have an intrinsic baryon number of 1, anti-baryons have intrinsic baryon number of -1, and mesons have an intrinsic baryon number of 0. Reactions between quarks, mesons, and baryons/anti-baryons will always proceed in a manner that conserves charge, baryon number, lepton number, and other quantum numbers, such as spin momentum number, angular momentum number, and radial excitation number.

    When you talk about the quark content of atomic nucleii, you are treading on tricky ground. If up and down quarks, the only constituents of non-hypernucleic atoms, are taken to intrinsically have opposite isospins, then it is somewhat true that they will tend to find stability in isoscalar arrangements (i.e. total isospin equal to zero), and hence equal numbers of up and down quarks. But you must understand that this is not always a solid rule; protons and neutrons do have only three valence quarks, but these reside in a "sea" of virtual quarks and anti-quarks. This fact can have interesting effects of all sorts in the nucleus. The Drell-Yan process is a clear example of how a valence quark in one proton can react with a "sea" anti-quark in another proton to generate muon pairs.

    Keep on reading and learning, and keep on thinking things through. You've got a good start, and you'll get it right in time.
     
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