SPEAR was a particle physics collider at the SLAC National Accelerator Laboratory. It began running in 1972, colliding electrons and positrons with an energy of 3 GeV, and collecting data about the resulting particles with the Mark I detector. During the 1970s, experiments at the accelerator played a key role in particle physics research, including the discovery of the J/ψ meson, many charmonium states, and the discovery of the τ− lepton.