Experimental review of exotic states discoveries in the last 20 years

The traditional quark model posits that hadrons are primarily composed of two quarks (mesons) or three quarks (baryons). However, the existence of exotic hadrons, such as tetraquarks, pentaquarks, and hybrid states, extends beyond this framework. Studying these exotic states helps refine the classification of hadrons and unveils the diversity of hadronic structures. Furthermore, the study of exotic hadron states provides crucial insights into the non-perturbative properties of Quantum Chromodynamics in the low-energy regime. By investigating the composition, mass, and decay properties of these states, we can delve deeper into the complex interactions between quarks and gluons. Since the discovery of the X(3872), the study of exotic hadron states has seen tremendous progress both experimentally and theoretically. In this report, I will present some of the significant experimental advancements in the field of exotic hadron states over the past two decades.