In physics, subatomic particles are the particles composing nucleons and atoms. There are two types of subatomic particles: elementary particles, which are not made of other particles, and composite particles. Particle physics and nuclear physics study these particles and how they interact.
Elementary particles of the Standard Model include:
Composite subatomic particles (such as protons or atomic nuclei) are bound states of two or more elementary particles. For example, a proton is made of two up quarks and one down quark, while the atomic nuclei of helium-4 is composed of two protons and two neutrons. Composite particles include all hadrons. These, in turn, are composed of baryons (e.g., protons and neutrons) and mesons (e.g., pions and kaons).
There are hundreds of known subatomic particles. Most are either the result of cosmic rays interacting with matter, or have been produced by scattering processes in particle accelerators.