SPEAR
SPEAR, the Stanford Positron Electron Accelerating Ring, helped reshape our understanding of the fundamental building blocks of matter. Tucked inside the SLAC National Accelerator Laboratory, this ring-shaped machine began colliding electrons and positrons in 1972. What came out of those collisions stunned the physics world. Over the course of one decade, experiments at SPEAR produced two separate Nobel Prize-winning discoveries, probing a realm of particles that had never been seen before. How did a single facility rack up that kind of achievement? And what became of the machine once it had done its most celebrated work? Those are the questions this documentary sets out to answer.
When SPEAR fired up in 1972, it brought electrons and positrons together at an energy of 3, directing the resulting debris into a sophisticated detector called the Mark I. Positrons are the antimatter counterparts of electrons, and when these two particles meet, they annihilate in a burst of energy. That energy then re-emerges as new particles, giving physicists a window onto the subatomic world. The Mark I detector was designed to capture as much of that debris as possible, logging the identities, energies, and trajectories of the particles that emerged. Each run of the collider was, in effect, a controlled experiment in creating new matter from pure energy.
The 1970s at SPEAR produced a run of discoveries that is almost without parallel in the history of a single accelerator. Physicists working with the facility identified a new particle called the meson, a find recognized with the 1976 Nobel Prize in Physics. But the Nobel committee would return to work done at SPEAR again. The discovery of the tau lepton, a heavier relative of the electron and muon, earned the 1995 Nobel Prize in Physics. Two separate Nobel Prizes, two separate decades of recognition, both traceable to experiments run at the same ring inside SLAC. Beyond those headline discoveries, researchers also mapped out many charmonium states, a family of particles built from a charm quark and its antiquark, adding crucial data to the emerging picture of how quarks bind together.
Particle colliders have a natural lifespan. Newer, more powerful machines eventually overtake them, and the physics they can reach becomes available elsewhere. When SPEAR's days as a collider were done, the facility was not dismantled. Instead it was repurposed into something quite different: a dedicated synchrotron radiation source, renamed SPEAR2. Synchrotron radiation is the intense light that charged particles emit as they are bent around a curved path, and it turns out to be extraordinarily useful for fields ranging from materials science to biology. The Stanford Synchrotron Radiation Lightsource, known as SSRL, runs its beamlines off this radiation, and the converted SPEAR facility became the engine behind that work.
A major upgrade to the ring was completed in 2004, and with it came a new name: SPEAR3. The upgrade was aimed at improving the quality and intensity of the synchrotron light the ring produces, making it more useful for the researchers who rely on the SSRL beamlines. The original mission of probing the subatomic world through particle collisions had given way entirely to a role as a precision scientific instrument for a very different community of users. The same infrastructure that once delivered Nobel-caliber discoveries in physics now serves chemists, biologists, and materials scientists extracting information from the interaction of X-rays and matter.
Common questions
What is SPEAR at SLAC and what does the name stand for?
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.
What Nobel Prizes were awarded for discoveries made at SPEAR?
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.
What detector was used at SPEAR to collect experimental data?
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.
What is SPEAR2 and how does it differ from the original SPEAR collider?
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.
When was SPEAR3 created and what was the purpose of the upgrade?
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.
What charmonium discoveries were made at SPEAR during the 1970s?
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.