SU(3) and quarks

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  • #1
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Main Question or Discussion Point

Can anyone please explain to me how quarks are the fundamental representation of SU(3)?

Why is a proton exactly uud and not another combination of quarks?

What is a multiplet?

Thank you for answers :)
 

Answers and Replies

  • #2
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Hi,

I'll pick the short one :smile:
Why is a proton exactly uud and not another combination of quarks?
This is not true : the valence part of the proton, which determines its quantum numbers (so its unique identity) is exactly uud, but there is more to the proton. There is an infinite tower of additional Fock state, or if you will as much vacuum fluctuations as you can wish for if you look "close enough" (at short distances).
 
  • #3
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but why is it not lets say just u or uuudd? Those combinations also correspond to the protons isospin so why just uud? the baryon number and charge seems to be defined after knowing that it is the combination of 3 quarks which determine the proton state.
 
  • #4
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but why is it not lets say just u or uuudd? Those combinations also correspond to the protons isospin so why just uud? the baryon number and charge seems to be defined after knowing that it is the combination of 3 quarks which determine the proton state.
We always proceed by trials and errors. You can not expect that we knew historically about quarks before we knew about protons. Given quarks, the minimal combination considering all quantum numbers is uud. That is what we call valence part of the wavefunction.
 
  • #5
malawi_glenn
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uuudd does not satisfy colour neutrality.
 
  • #6
blechman
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uuudd does not satisfy colour neutrality.
true. if one of the d's is a dbar, then it's a pentaquark, those mythical particles that we thought we found a few years back.
 
  • #7
malawi_glenn
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true. if one of the d's is a dbar, then it's a pentaquark, those mythical particles that we thought we found a few years back.
also one u must be u-bar in order to maintain colour neutrality.
 
  • #8
blechman
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also one u must be u-bar in order to maintain colour neutrality.
no - you can have the color combination r+g+b+c+cbar (where c is any color). that's the pentaquark.
 
  • #9
malawi_glenn
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ah yeah of course, stupid me.. and I supposed to be a Hadron Physicsits:P
 
  • #10
Can anyone please explain to me how quarks are the fundamental representation of SU(3)?

Why is a proton exactly uud and not another combination of quarks?

What is a multiplet?

Thank you for answers :)
Which SU(3) are you referring to? SU(3)_c (color) or SU(3)_f (flavor)? It makes a difference...
 

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