"In particle physics, quarkonium (from quark + onium, pl. quarkonia) designates a flavorless meson whose constituents are a quark and its own antiquark. Examples of quarkonia are the J/\u03C8 meson (an example of charmonium, cc) and the \u03D2 meson (bottomonium, bb). Because of the high mass of the top quark, toponium does not exist, since the top quark decays through the electroweak interaction before a bound state can form."@en . . . .