Learn more about childbirth – Science News, February 13, 1971
Experiments in which protons and neutrons were bombarded with high-energy electrons gave indications that protons and neutrons are not amorphous masses but composed of distinct subparticles. Subparticles have been named partons, and whether or not they correspond to hypothetical quarks remains a debatable question.
The so-called partons seen in experiments at the Stanford Linear Accelerator Center were indeed quarks, a discovery that won three researchers the 1990 Nobel Prize in Physics (SN: 27/10/90, p. 263). Predicted by physicists Murray Gell-Mann and George Zweig in 1964, quarks are the building blocks of most ordinary matter in the universe. Quarks were originally thought to be of three varieties: top, bottom, and odd. But particle collision experiments revealed three additional types: charm, down, and up (SN: 4/30/94, p. 276). Quarks usually come in pairs or trios. Recently, physicists have glimpsed more elaborate tetraquarks and pentaquarks (SN: 8/1/20, p. 14).