A pair of heavy quarks，a new type of matter

The discovery of the J/ψ particle not only promoted the widespread acceptance of the Standard Model in theory, but also opened the door for subsequent research on charmonium and charmonium-like states. The Beijing Spectrometer Ⅲ experiments on charmonium and charmonium-like particles include but are not limited to searching for new particles, determining the internal structure of particles, measuring their mass and width, studying their transitions and decays, and exploring new production and decay processes. A number of important physics results have been achieved. This article focuses on representative work at the Beijing Spectrometer Ⅲ on charmonium and charmonium-like particles, including the precise measurement of resonance parameters for the η_c(1S) particle, the discovery of the D-wave spin triplet ψ(1³D₂), the direct production of the χ_c1(1P) from electron-positron annihilation, the discovery of charged tetraquark particles, and a series of cutting-edge studies on vector charmonium-like particles and the neutral X(3872) particle. These experimental results enrich our understanding of the world of fundamental particles, helping us to delve deeper into the understanding of strong interaction and the composition of matter in the universe.