At the end of Section 20.3b we spoke very briefly about “colored” quarks and the resulting Yang–Mills field with gauge group SU(3). This was not, however, the first appearance of quarks. They appeared in the early 1960s in the form of “flavored” quarks, independently in the work of Gell–Mann and Zweig. Their introduction changed the whole course of particle physics, and we could not pass up the opportunity to present one of the most striking applications to meson physics, the relations among pion, kaon, and eta masses. This application involves only global symmetries, rather than the Yang–Mills feature of the colored quarks.

For expositions of particle physics for “the educated general reader” see, e.g., the little books ['t Hooft] and [Nam].

Flavored Quarks

The description to follow will be brief and very sketchy; the main goal is to describe the almost magical physical interpretations physicists gave to the matrices that appear. My guide for much of this material is the book [L–S,K], with minor changes being made to harmonize more with the mathematical machinery developed earlier in the present book. As to mass formulas, while there are more refined, technical treatments (see, e.g., [We, Chap. 19]) applying (sometimes with adjustments required) to more mesons and to “baryons,” the presentation given in Section C.f for the “0- meson octet” seems quite direct.