SPEAR

SPEAR (originally Stanford Positron Electron Accelerating Ring)^[1][a] was a particle physics collider at the SLAC National Accelerator Laboratory.^[2] 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 (awarded the 1976 Nobel Prize in Physics), many charmonium states, and the discovery of the τ⁻
lepton (awarded the 1995 Nobel Prize in Physics).^{[citation needed]}

After its use as a particle collider had been superseded, the facility built for SPEAR was converted to a dedicated synchrotron radiation source for the Stanford Synchrotron Radiation Lightsource (SSRL) beamlines, known as SPEAR2.^[3] A major upgrade of the ring completed in 2004 gave it the current name SPEAR3.^[4]