Charmonium, exotic hadrons and hadron structure

TL;DR

Understanding hadron structure in the presence of multiquark dynamics requires moving beyond quenched quark models. The paper surveys QCD-inspired potential models for heavy quarkonia, extensions to light hadrons via the hadronic interaction picture built on Goldstone-boson and vector-meson exchanges, and unquenched quark dynamics with quark-antiquark pair creation, combining to explain a diverse set of near-threshold exotics as hadronic molecules or mixed states. It presents substantial evidence for sizable penta-quark components in the proton and discusses iconic exotics such as $X(3872)$, $Z_c(3900)$, and $P_c$ within a unified molecular/threshold-framed picture, supported by coupled-channel analyses. The results underscore the importance of unquenched dynamics and threshold effects for a coherent multiquark spectroscopy and motivate a broad, multi-facility experimental program to map the landscape of exotic hadrons and their strange and beauty partners.

Abstract

To celebrate the 50th anniversary of the discovery of the J/ψ, the first charmonium state observed, I start with a brief review of major progresses on the QCD inspired quark potential model originated from charmonium spectrum.Then I show the importance of unquenching dynamics, multiquark components and exotic multiquark states for understanding hadron structure and hadron spectrscopy. The J/ψ and charmonium-like states have played an important role in this aspect.

Figures (2)

• Figure 1: Meson exchange between $q\bar{q}$ (left) and $qq$ (right).
• Figure 2: The spectrum of the $D_s$ mesons with the unquenched quark model Hao:2022vwt. Red dots with error bars denote the experimental values from PDG and the model calculations are depicted as black lines.