Golden Jubilee Photos: Peering inside protons

At first many doubted the results from CERN's BCDMS experiment, which ran from 1978 to 1985 and was a crucial early test of quantum chromodynamics, or QCD. This theory, which was still in its infancy at that time, describes the strong force that governs protons and neutrons.

BCDMS slammed muons, heavier cousins of electrons, into the simplest atoms: hydrogen, with a lone proton in its nucleus, and deuterium, with a proton and neutron. When the muons showed a type of collision called deep inelastic scattering, they revealed the inner workings of protons and neutrons: the quarks and gluons.

However, the measurements from BCDMS at lower energies didn't fit with those from other CERN experiments, the EMC muon experiment and the CDHS neutrino experiment. These were some of the pre-eminent experiments of the time on deep inelastic scattering, and BCDMS was the odd man out. But gradually, later experiments, including NMC at CERN, accumulated evidence that vindicated BCDMS.

Even though the work at BCDMS has been continued and bolstered by later experiments, including COMPASS at CERN, its results have not been superseded. They're still some of the most precise measurements of deep inelastic scattering and key supports for the theory of QCD.