New forms of matter, 1974–1976.

In November 1974, Burton Richter at SLAC and Samuel Ting at Brookhaven were leading two very different experiments, one studying e+e− annihilation, the other the e+e− pairs produced in proton-beryllium collisions. Their simultaneous discovery of a new resonance with a mass of 3.1 GeV so profoundly altered particle physics that the period is often referred to as the “November Revolution.” Word of the discoveries spread throughout the high energy physics community on November 11 and soon much of its research was directed towards the new particles.

Ting led a group from MIT and Brookhaven measuring the rate of production of e+e− pairs in collisions of protons on a beryllium target. The experiment was able to measure quite accurately the invariant mass of the e+e− pair. This made the experiment much more sensitive than an earlier one at Brookhaven led by Leon Lederman. That experiment differed in that μ−μ+ pairs were observed rather than e+e− pairs. Both these experiments investigated the Drell–Yan process whose motivation lay in the quark–parton model.

The Drell–Yan process is the production of e+e− or μ+μ+ pairs in hadronic collisions. Within the parton model, this can be understood as the annihilation of a quark from one hadron with an antiquark from the other to form a virtual photon. The virtual photon materializes some fraction of the time as a charged-lepton pair.