= Charmonium
{title2=$c\bar c$}
<Charmonium> is a family of <bound states> of a <charm quark> and its <antiquark>, with zero net charm. It differs from open-charm <D mesons>, which carry a charm <quark> together with a light <antiquark>.
The constituent spins and relative <orbital angular momentum> distinguish states such as the <J psi meson>, <eta c meson> and <chi c mesons>. Their level separations and radiative transitions test the interaction between heavy <quarks>. Decay can proceed through annihilation of the charm–anticharm pair, so net charm conservation does not imply that a charmonium state is stable. A valence <quark> label organizes the spectrum while additional gluonic and quark-pair contributions remain part of the interacting state.
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