Classification of microscopic particles
The composition of a large number of elementary particles is divided into three categories:
The first category: pure single particles, neutrinos, electrons, large uniform particles, quarks.
The second type: particles synthesized by two elementary particles, such as π meson, W, Z boson.
The third category: particles composed of three basic particles, such as: neutrons, protons and other hadrons.
The large unified particles in the first type of particles cannot exist in a free state. They must coexist with each other to form a pion and a W boson.
The quarks in the first category can not exist alone, they must exist in three to form hadrons such as protons and neutrons.