Charmonium and Charmonium-like (?) States

TL;DR

Recent advances in heavy quark spectroscopy have led to the discovery of new charmonium states, challenging existing QCD models and prompting diverse theoretical explanations.

Contribution

This paper critically reviews recent experimental discoveries of charmonium-like states and discusses their implications for quantum chromodynamics and theoretical modeling.

Findings

Identification of several new heavy quark states

Challenges to existing QCD models

Proposals of new theoretical explanations

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.