Charmonium and Charmonium-like (?) States

Abstract

The last few years have witnessed a renaissance in the spectroscopy of heavy quarks. Several long elusive states have now been firmly identified, and several unexpected states have been reported by the high luminosity experiments at Belle, Babar, CLEO, and Fermilab. These discoveries have posed important theoretical questions for our understanding of QCD, and a variety of theoretical models have been proposed. These developments are critically discussed.