Classification of Particles

In physics experiments, particles of known spin were smashed together in order to produce other particles. Since physicists knew the total spin of the particles going into the collision, they used conservation of angular momentum to determine the spin of the particles produced. They found that the spin of all particles were either integer values of (0, 1, 2, 3,...) or half integer values of (1/2, 3/2, 5/2,...).

Most of the newly discovered particles were part of a common class of particles called hadrons. Hadrons were classified as either mesons, with integer values of spin, or baryons, with half-integer values of spin.