When Wolfgang Amadeus Mozart composed his famous duet
Papageno-Papagena for the Magic Flute,
he must have been inspired by some magic knowledge
on the properties of mesons.
How this charming couple of a quark (Papageno) and
his equally charming antiquark (Papagena) come at the stage,
resonate, create another handful Papagenos e Papagenas,
and subsequently disappear,
is right what happens in the interaction vertex
of a high-energy experiment:
The showing up of a quark-antiquark pair which resonates for a short while
and then disappears after creating a handful of other quark-antiquark pairs,
which in the form of light mesons, pions and kaons,
fly away from the interaction vertex, observed by distant detectors.
The latter processes happen in just a very small fraction of a second, but long enough for electronic devices to register their presence. Mozart, who was counting with human recording, allows the presence on stage of Papageno and Papagena for a few minutes. But from what we register, either in the concert hall, or in fast computers, is a duet, not a quartet, neither a sextet, or the company of a choir, but just Papageno and Papagena, which resonate on stage. This is the main lesson we learn from the recordings of the charmonium spectrum, just one quark and one antiquark which resonate in the interaction vertex.
How Mozart knew about all this, will remain a mystery forever, since he left us only his fabulous music.