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### Why are mesons only made of a quark-antiquark pair? [duplicate]

Why can't we have a meson made of two quarks, why does there have to be the antiquark too?
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### About free quarks and confinement

I simply know that a single free quark does not exist. What is the reason that we can not get a free quark? If we can't get a free quark then what is single-top-quark?
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### Mathematically, what is color charge?

A similar question was asked here, but the answer didn't address the following, at least not in a way that I could understand. Electric charge is simple - it's just a real scalar quantity. Ignoring ...
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### Bound states in QCD: Why only bound states of 2 or 3 quarks and not more?

Why when people/textbooks talk about strong interaction, they talk only about bound states of 2 or 3 quarks to form baryons and mesons? Does the strong interaction allow bound states of more than 3 ...
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### Why are there 3 quarks in a proton? [closed]

A few quark related questions (I don't know much about them other than that there are 2 flavors concerning protons and neutrons). Why are there 3 quarks in a proton or neutron? Why not 2 or 4? Is ...
387 views

### The Makeup of the Pentaquark

Why is it that when they have the artist's rendition of the Pentaquark it shows two downs, two ups, and one anti-strange quark? Is this or is this just for show? Follow up to this question: if this ...
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### How many combination can quarks form?

How many different combinations can quarks produce? E.g. 2 up quarks + 1 down quark = proton. Is this value going to be infinite?
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### $SU(3)$ irreducible representations with tensor method

I am dealing with the tensor product representation of $SU(3)$ and I have some problems in understanding some decomposition. 1) Let's find the irreducible representation of $3\otimes\bar{3}$ we have ...
254 views

### Why does confinement apply only to quarks, and not to nucleons?

When energy is input in an attempt to break quark bonds one simply generates more quarks through hadronisation. The explanation my physics book gives for this is that "the strength of the strong ...
871 views

### Invariant tensors in a general representation and their physical meaning

I'm trying to use tensor methods to find invariant elements of representations. Specifically I'm looking at representations of $SU(5)$. I can show that the invariant element in $5\otimes\bar{5}$ (or ...
899 views

### Colorless charge in a baryon

In a baryon there are 3 quarks and in a meson there are one quark + one anti-quark. So color charge is colorless ( a color singlet state ) in a meson. But how is it colorless in a baryon?
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### $SU(3)$ Color Symmetry

I have following (maybe a bit general) question about the $SU(3)$-symmetry of color by quarks: If I consider the analogy to the $SU(2)$-symmetry of isospin $I$ crucially it concers the conservation ...
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### About the recent discovery of tetraquark boundstates

I am referring to this, http://home.web.cern.ch/about/updates/2014/04/lhcb-confirms-existence-exotic-hadron So how does this work if we stick to keeping quarks in the 3 dimensional fundamental ...
### Permitted bound states in extended QCD color group $SU(4)$
I'm very much curious about the possible quark combinations to form bound states in $SU(4)$ QCD. We already know Wilson has proven that only colorless combinations can arise in $SU(3)$ of these ...