The Exotic XYZ Charmonium-like Mesons

TL;DR

This paper reviews recent discoveries of charmonium-like mesons, highlighting their potential exotic nature beyond conventional models, and discusses experimental evidence and theoretical predictions for these states.

Contribution

It provides a comprehensive overview of the properties, production mechanisms, and evidence for exotic charmonium-like states, emphasizing their significance in hadronic physics.

Findings

Evidence suggests some new states are exotic hadrons.

Conventional models do not fully explain these states.

Experimental measurements are ongoing to clarify their nature.

Abstract

Charmonium, the spectroscopy of c\bar{c} mesons, has recently enjoyed a renaissance with the discovery of several missing states and a number of unexpected charmonium-like resonances. The discovery of these new states has been made possible by the extremely large data samples made available by the B-factories at the Stanford Linear Accelerator Center and at KEK in Japan, and at the CESR e^+e^- collider at Cornell. Conventional c\bar{c} states are well described by quark potential models. However, many of these newly discovered charmonium-like mesons do not seem to fit into the conventional c\bar{c} spectrum. There is growing evidence that at least some of these new states are exotic, i.e. new forms of hadronic matter such as mesonic-molecules, tetraquarks, and/or hybrid mesons. In this review we describe expectations for the properties of conventional charmonium states and the predictions for molecules, tetraquarks and hybrids and the various processes that can be used to produce them. We examine the evidence for the new candidate exotic mesons, possible explanations, and experimental measurements that might shed further light on the nature these states.