Nucleons and pions have been thought of as elementary particles for a long time. It took over 30 years of trial and error to realize they are composites made of quarks. During the process, there were two turning points. One was the discovery of the strange particles, which began in the late 1940s, and the other that of charmed particles in 1974. By the time the charmed particles were discovered, particle taxonomy was fairly advanced and the significance of the discovery was immediately recognized, creating a turbulent but transient transformation of the particle view referred to as "the November revolution". On the other hand, the characteristics of the strange particles have been a central riddle, something researchers had to pursue for a long time. In retrospect, when the characteristics of the strange particles were understood, the essence of the quark model was already in hand. The process was slow and did not create a fever like that of the charmed particles, but was far more important in its contribution to the progress of particle physics.
14.1 S U(3) Symmetry
Historically, the discovery of strange particles added to isospin another conserved internal quantum number, the strangeness S. Just as isospin (S U(2) symmetry) was introduced when the equality of both the mass and the properties of the proton and neutron was noticed, the near equality (m p ' m n ' m ฮ ) of three basic elements of the Sakata model [339] led to S U(3) symmetry, known as IOO symmetry [212] at the time of introduction. Based on the Sakata model and S U(3), the meson octet was successfully explained. The discovery of the โฆ particle firmly established the validity of S U(3). However, one misplacement of p, n, ฮ as the three basic elements, hindered the Sakata model and the "eightfold way" took over, which, in turn, led to the quark model. With the discovery of the charmed particles, S U(3) was extended to S U( 4), but all the essential features of so-called flavor symmetry are contained in S U(3) and the quark model. In this chapter we explain that static properties of the hadrons, including the mass and magnetic moment, are well reproduced by the quark model. We defer discussions of the dynamic