How did quarks appear in the theory of elementary particles? (towards the 60^th anniversary of the great discovery)

The article examines the history of the emergence of the concept of quarks and the quark model in the theory of elementary particles in 1963–1964. Quarks have a fractional electric charge and only exist inside strongly interacting particles (hadrons), thus being a completely new form of matter. The development of this model led to a modern theory of strong interactions, called quantum chromodynamics (QCD), which is included in the standard model that is the modern theory of elementary particles and fundamental interactions in the microcosm. It is shown that this discovery was made almost simultaneously and independently by the American theorists M. Gell-Mann and G. Zweig (the term “quark” was coined by Gell-Mann while Zweig used the word “ace” which, however, did not become common). There has been an earlier anticipation of the quark model in the work of Israeli scientists Y. Ne’eman and H. Goldberg. All of these physicists proceeded from the symmetry of the strong interaction, discovered by Gell-Mann and Ne’eman in 1961 and called the “eightfold way” by Gell-Mann. Their approaches differed in the understanding of the problem of the reality of quarks: Ne’eman and his co-author did not believe in the reality of fractionally charged particles; Zweig believed that they could exist in a free form while Gell-Mann was closest to the modern understanding, believing that they only exist inside hadrons. Some features of the process of the discovery of quarks (the phenomena of missed opportunities, simultaneous and independent discoveries, the invasion of metaphysics into physics, etc.) are noted. The article is accompanied by a brief dictionary of special terms used in the article.