Evidence for the Quark: Deep Inelastic Scattering at SLAC

When Murray Gell-Mann proposed the quark model in 1964, it successfully organized the "particle zoo"—yet many physicists initially viewed quarks as mere mathematical tools rather than real, physical particles.

That changed between 1967 and 1973 during ground-breaking experiments at the Stanford Linear Accelerator Center (SLAC). By firing high-energy electrons into protons and neutrons in a process known as deep inelastic scattering, researchers observed large-angle deflection patterns—mirroring Rutherford's famous gold foil experiment, but at a subatomic scale.

This provided the first direct empirical evidence that protons are not fundamental point particles, but rather composite structures containing three distinct, point-like charged constituents: quarks.

Watch the video to explore how deep inelastic scattering works and how SLAC provided definitive proof for the physical existence of quarks.