Description |
Charm and bottom quarks form quark/antiquark bound states called quarkonium. The low lying levels are well measured in experiments and provide an exacting test of theory. Many excited states have also been observed recently, but many have yet to be classified in quark-model language. Some could be exotic hybrid states including a valence gluon and some could be multiquark molecular states. Lattice QCD provides a theoretical framework for assisting in the discovery and classification. For low-lying levels we are now achieving impressive precision. I review the current state of the
art.
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