Short answers, pulled from the story.
SPEAR stands for Stanford Positron Electron Accelerating Ring. It is a particle physics facility at the SLAC National Accelerator Laboratory that began running in 1972, colliding electrons and positrons to study the resulting subatomic particles.
Two Nobel Prizes in Physics came from work at SPEAR. The discovery of the meson was recognized with the 1976 Nobel Prize in Physics, and the discovery of the tau lepton was awarded the 1995 Nobel Prize in Physics.
The Mark I detector was used at SPEAR to collect data from electron-positron collisions. It recorded the particles produced when electrons and positrons annihilated at an energy of 3.
SPEAR2 is the name given to the SPEAR facility after it was converted from a particle collider into a dedicated synchrotron radiation source. It no longer collides particles but instead provides synchrotron light for the Stanford Synchrotron Radiation Lightsource beamlines.
A major upgrade completed in 2004 gave the ring its current name, SPEAR3. The upgrade enhanced the synchrotron radiation capabilities of the facility to better serve the researchers who use the SSRL beamlines.
Experiments at SPEAR during the 1970s identified many charmonium states, a family of particles formed from a charm quark and its antiquark. These discoveries were part of the broader body of particle physics research that made the facility prominent in that era.