After SPEAR and several other machines around the world had demonstrated the great power of electron-positron colliding beams to produce important new physics results, the next logical step was to increase the energy of such colliders substantially. Both the American and European particle physics communities undertook such a step with the construction of the PETRA storage ring at the DESY laboratory in Hamburg, Germany and the PEP storage ring at SLAC. PEP, the Positron-Electron Project, was a collaborative effort of SLAC and the Lawrence Berkeley Laboratory. Completed in 1980, PEP was used for a decade to support the research activities of several hundred physicists and graduate students.
The PEP tunnel is about 800 meters in diameter and can produce The PEP storage ring produced electron-positron collisions up to center-of-mass energies of about 30 GeV. The PEP physics program did important work measuring the lifetimes of certain elementary particles, studying how the quarks that are initially produced in the collision then fragment or evolve into the various kinds of particles that are actually observed in the detection apparatus, and testing the theory (called Quantum Chromodynamics or QCD) that is presently believed to describe the strong force that binds quarks together. Of particular interest was the observation, made first at PEP, that the B quark had a much longer lifetime than had been anticipated.
PEP is currently being reconfigured as PEP-II, the SLAC Asymmetric B Factory.