Searches for , and Properties of , New Charmonium - like states

Although the Standard Model of elementary particles is well established, strong interactions are not yet fully under control. We believe QCD is the field theory capable of describing them, but we are not yet capable, in most cases, to make exact predictions. Systems that include heavy quark-antiquark pairs (quarkonia) are an ideal and unique laboratory to probe both the high energy regimes of QCD, where an expansion in terms of the coupling constant is possible, and the low energy regimes, where non-perturbative effects dominate. Recently, this field has experienced a rapid expansion with a wealth of new data coming in from diverse sources: data on quarkonium formation from dedicated experiments (BES at BEPC, KEDR at VEPP4M CLEO-c at CESR), clear samples produced by high luminosity B-factories (PEP-II and KEKB), and very large samples produced from gluon-gluon fusion in pp̄ annihilations at the Tevatron (CDF and D0 experiments).