(Whimsical names are common in particle physics, reflecting the personalities of modern physicists.) Originally, three quark types-or flavors-were proposed to account for the then-known mesons and baryons. Their quaint name was taken by Gell-Mann from a James Joyce novel-Gell-Mann was also largely responsible for the concept and name of strangeness. Quarks were first proposed independently by American physicists Murray Gell-Mann and George Zweig in 1963.
In this module we will discuss the quark substructure of hadrons and its relationship to forces as well as indicate some remaining questions and problems. Leptons, quarks, and carrier particles may be all there is. The third and perhaps final group of fundamental particles is the carrier particles for the four basic forces. Quarks are the second group of fundamental particles (leptons are the first). There is strong evidence that quarks are the fundamental building blocks of hadrons as seen in Figure 1. Keep in mind that all leptons seem to be fundamental, whereas no hadrons are fundamental.
This does not mean that fundamental particles are stable-some decay, while others do not. Note that an elementary or fundamental particle has no substructure (it is not made of other particles) and has no finite size other than its wavelength. Quarks have been mentioned at various points in this text as fundamental building blocks and members of the exclusive club of truly elementary particles.
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