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I Quantum Chromodynamics

  1. Apr 4, 2016 #1

    Kyx

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    So, a particle made of quarks is only stable if the 'colours' of the quarks add up to white

    So, red + antired = white
    blue + antiblue = white
    green + antigreen = white
    red + blue + green = white
    red + antired + red + blue + green = white

    But what causes the 'colour'?
    And why do they have to add up to white?
     
  2. jcsd
  3. Apr 4, 2016 #2

    mfb

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    There is nothing (known) that "causes" color. Quarks just have them.
    Otherwise the strong interaction with other color charges is so strong that you do not have isolated hadrons.
     
  4. Apr 4, 2016 #3

    Kyx

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    So you would have a proton with a neutron as a new particle? like a preutron?
     
  5. Apr 4, 2016 #4

    Orodruin

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    Colour is merely a name we have put on something because it behaves similarly to how we perceive colours as being made up out of red, green, and blue. In reality, we are talking about three different directions in a three-dimensional complex vector space. Quarks carry a fundamental representation of the linear operators on this space. The rule "red+blue+green = white" are merely simplified mnemonics of the mathematical group theory structure, wherein three fundamental representations couple to make a singlet representation.

    It is not clear what you mean by this. The proton and neutron form an isospin doublet.
     
  6. Apr 4, 2016 #5

    Kyx

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    There must be a reason why they form protons and neutrons, and not a proton and a neutron together as its own particle. like red+blue+green+red+blue+green = white?
     
  7. Apr 4, 2016 #6

    Orodruin

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    There are particles consisting of a proton and a neutron, they are called deuterium nuclei and are also colour neutral (just as any nucleus is).
     
  8. Apr 4, 2016 #7

    Kyx

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    OK :)

    thx
     
  9. Apr 5, 2016 #8

    Garlic

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    I think what Kyx wanted to ask was, if a proton and neutron is combined, would they form a hexaquark hadron.
    Such hadrons can (they are allowed to) theoretically exist, but only at extreme high energies. They would have etremely short half lives.
    There are lots of particles that are allowed to exist, but most of them are too heavy (and energetic) that you wouldn't find them in nature.
    We can barely create such particles. I have red in the wiki that only one hexaquark hadron is detected so far.
     
  10. Apr 5, 2016 #9

    mfb

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    Only if you count the deuteron and similar states. Also, how do you distinguish a deuteron (or a possible excited state of it) from a different 6-quark state?

    There is quite clear evidence for 4-quark and 5-quark states now, but there you have the same interpretation question: is it a bound state of two mesons or a meson and a baryon respectively, or does that classification does not make sense?
     
  11. Apr 5, 2016 #10
    Does the shell model of nuclei, and the allowed spins and excited states of deuterons and other nuclei, clarify as to whether nucleons exist (and occupy states) in nuclei, or whether nuclei consist of quarks being direct members?
     
  12. Apr 5, 2016 #11

    mfb

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    Nucleons are a great model to describe nuclei. They are certainly not completely unordered n-quark states.
     
  13. Apr 5, 2016 #12

    ChrisVer

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    That's where they use some diagrams to distinguish it, but I have never understood how they use them.

    I want to say that there is/has to be a discriminant way to seperate them... a bound state for example would need two (color neutral) mesons bound by some yukawa interaction? While the tetraquark states should be colorful (qq) and colorful (q*q*) coming together into a colorless bound state with gluons.
     
  14. Apr 5, 2016 #13
  15. Apr 5, 2016 #14

    mfb

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    They certainly did not know about QCD. There are three animals in a circle, so what? The number three appears everywhere.
     
  16. Apr 5, 2016 #15
    but their ears form the gluons..

    ok fine back to real science, i won't pollute the thread any further
     
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