SPEAR (originally Stanford Positron Electron Asymmetric Rings, now simply a name) was a collider at the SLAC National Accelerator Laboratory. It began running in 1972, colliding electrons and positrons with an energy of . During the 1970s, experiments at the accelerator played a key role in particle physics research, including the discovery of the meson (awarded the 1976 Nobel Prize in physics), many charmonium states, and the discovery of the tau (awarded the 1995 Nobel Prize in physics). Today, SPEAR is used as a synchrotron radiation source for the Stanford Synchrotron Radiation Lightsource (SSRL). The latest major upgrade of the ring in that finished in 2004 rendered it the current name SPEAR3. References External links Brief explanation of the acronym in SLACspeak 25th Anniversary Info from SLAC SPEAR3 status Buildings and structures in San Mateo County, California Particle physics facilities Stanford University Particle accelerators