Dynamical Symmetry and Hadron Spectrum

Symmetry plays an important role in hadron physics. The predictions of baryon Ω− and dibaryon d∗ in the 1960s, which were confirmed by experiments, are based on the dynamical symmetry of quark systems. In this pedagogical article, the dynamical symmetry of hadrons is explored. The multiplets of color, spin, and flavor symmetries of two- to six-quark systems are discussed and the phase-consistent wave functions of these systems are presented. Based on the dynamical symmetry of the system, the mass formulas for these systems are constructed, which give a good description of the hadron spectra. Compared with quark–antiquark mesons and three-quark baryons, multi-quark systems have richer structures. It is expected that the symmetry can provide a good guide for exploring multi-quark systems (exotic hadrons) systematically.