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Quarkonium states are bound states of a quark-antiquark pair but so do the mesons. What is the difference between a quarkonium (e.g., charmonium, and bottomonium) and a meson then? Why use a separate name for $c\bar{c}$ and $b\bar{b}$ bound states other than some meson state?

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  • $\begingroup$ I've removed a comment that answered the question. Please post answers as answers. $\endgroup$ – rob Jan 15 '20 at 16:18
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    $\begingroup$ -1 The opening lines of Wikipedia answers your question: en.wikipedia.org/wiki/Quarkonium Quarkonium is a flavorless meson whose constituents are a heavy quark and its own antiquark, making it a neutral particle and the antiparticle of itself. $\endgroup$ – SRS Jan 15 '20 at 16:56
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Quarkonium states are a type of meson state. There are other meson states, e.g charged mesons.

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  • $\begingroup$ This looks more a comment than an answer. $\endgroup$ – Deschele Schilder Jan 16 '20 at 22:07
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    $\begingroup$ @descheleschilder It was originally a comment but got deleted for being an answer. $\endgroup$ – bemjanim Jan 16 '20 at 22:36
  • $\begingroup$ Your history shows it was an answer the first time. $\endgroup$ – Deschele Schilder Jan 17 '20 at 8:25
  • $\begingroup$ it was a comment. $\endgroup$ – bemjanim Jan 17 '20 at 8:31
  • $\begingroup$ But look here: physics.stackexchange.com/posts/525170/timeline $\endgroup$ – Deschele Schilder Jan 17 '20 at 8:45
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I'll answer in the most simple way:

Quarkonium (like positronium in the electromagnetic case) consists of two anti-particles (like an electron and a positron in positronium). The quarks inside quarkonium are anti-particles of each other.

The properties of one quark are opposite (anti) to the properties of the other. Which is to say, the colors and electric charge. In mesons, you have indeed two anti-particles but the charges don't have to be opposite (in contrast to their color). After all, there exists charged mesons.

So charmonium or bottomonium, in wich all charges have to be opposite, are different from the corresponding mesons, in which only the colors have to be opposite.

So you could say, both are special kinds of mesons.

See also this Wikipedia article.

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  • $\begingroup$ Your second paragraph is badly messed up. At valence level the constituiends of the meson do have to have opposite color (because mesons are unconfined and must be colorless), but they are not required to be opposite in electric charge (which is why some mesons are non-neutral). $\endgroup$ – dmckee --- ex-moderator kitten Jan 15 '20 at 17:25
  • $\begingroup$ For a bound system to be colorless as a whole the colors must also be the opposite. $\endgroup$ – mithusengupta123 Jan 16 '20 at 13:01
  • $\begingroup$ @dmckee---ex-moderatorkitten Kitten? What are constitui ends? $\endgroup$ – Deschele Schilder Jan 16 '20 at 22:06
  • $\begingroup$ @mithusengupta123 You're right. I edited. $\endgroup$ – Deschele Schilder Jan 16 '20 at 22:08

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