Quark Model

The quark model proposes that protons, neutrons and related particles called hadrons are not fundamental but are built from smaller, fractionally charged constituents. Murray Gell-Mann and, independently, George Zweig proposed the idea in 1964, with Gell-Mann naming the constituents quarks. The model went untested for four years until 1968, when deep inelastic electron-proton scattering experiments at the Stanford Linear Accelerator Center found direct evidence of point-like structures inside the proton, confirming the theory and establishing quarks as real physical constituents of matter rather than a bookkeeping device. The quark model became a cornerstone of the Standard Model of particle physics.