Discovering Quarks at the SLAC

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© SLAC National Accelerator Laboratory historical photo index.

The first evidence for substructure in nucleons was discovered at the Stanford Linear Accelerator Center (SLAC). When accelerated electrons slammed into stationary protons in End Station A, it was clear that the electrons were deflected by three distinct scattering centers inside the proton—the first experimental evidence that quarks were real, rather than convenient mathematical constructs. (Unit: 1)