If you’re from the Bay Area or know it well,
you’ve likely noticed the long building under 280 near Stanford. If you’re like me, you may not have always known what it is.
This is the SLAC Linear particle accelerator. Today, I’m gonna take you through how
this accelerator came to be in this spot and how it’s helped make many important
discoveries in particle physics. In the 40s and 50s, researchers like
Robert Hofstadter, WKH Panofsky, and Edward Ginzton made huge developments
in linear electron accelerators, or linacs. These were essential in pursuing the
relatively new field of high energy physics. Here, you can see on the map of
the area where Stanford physicists set out to build a 2 mile long
electron accelerator in 1956. It was called “M” for monster,
poking fun at its ambitious size. At the time, it was the biggest US
Government funded science project. In 1964, US Atomic Energy Commision
Chairman Glenn T Seaborg said that “High energy physics is one of the leading intellectual developments of our age.
It is not only very exciting but experimentation in this field will probably
lead to some of the most important theoretical and perhaps then the most practical
developments of our age." SLAC’s linac was completed in 1966 and in May of that year its first
electron beams bounded through the tunnel, The accelerator sped up electrons
to nearly the speed of light, which helped them achieve huge amounts of energy.
The electrons were smashed into targets in the building on the right and their results
were captured by large detectors. Richard Taylor co-led the team
that designed these experiments which would go on to reveal
signs of an inner structure within the protons and neutrons
that make up the atomic nucleus. This work was crucial to other major
discoveries both at SLAC and other labs beyond. Richard Taylor and his collaborators
over at MIT (Jerome Friedman and Henry Kendall) went on to share
the 1990 Nobel Prize of Physics. You can see them together here. While the linac was a huge step for experiments that used fixed targets, physicists were looking for other ways to work.
You can see their solution here - a figure-eight beam storage ring on Stanford’s campus that would be able to generate collisions with increased energy by colliding
positrons and electrons head on. Encouraged by these experiments,
SLAC scientists proposed adding a circular ring at the end of the linac to
create these head-on particle collisions. In 1972, SLAC completed the construction of SPEAR, the Stanford Positron Electron Accelerating Ring. And right away the project started colliding its high-energy beams into one another in an attempt to discover new subatomic particles. In 1974, SPEAR scientists found an inconsistency in the data. But it wasn’t just a glitch or an error. It actually turned out to be evidence that their collisions had discovered a new subatomic particle! Pretty nuts. At the same time, a team of scientists over at MIT had discovered that same particle independent of the SLAC group. The MIT group had used Brookhaven National Lab’s proton-proton collider. So they had used a different method to discover the same thing. The discovery of this new subatomic
particle, dubbed J/psi at the time, confirmed the original theory of its existence. Today the particle has been
renamed a “charmed quark”. SLAC’s Burton Richter, pictured here on the left,
and MIT’s Samuel CC Ting pictured on the right shared the 1976 Nobel Prize in
physics for the J/psi’s discovery. SLAC researchers kept improving
their particle colliders, building several more to continue
their research on particle physics and improve the ways we understand
accelerators and particle collisions. In 1975, SLAC’s Martin Perl
proved another particle existed, the tau lepton.
You can think of the tau Lepton as the electron’s heavier cousin and the first
known member of a third family of particles. This chart shows how particle
families are categorized. As a result, Martin Perl shared
the 1995 Nobel Prize in Physics. Perl’s discovery inspired other scientists
to seek out two more quarks and a neutrino, rounding out the third particle family.
By 2000, only 44 years after the original linac was built, all three had been
discovered at other laboratories. As SLAC’s particle physics research pioneered
important discoveries, SLAC expanded its mission. The main accelerator became one of the
most advanced tools in X-ray science and SPEAR became Stanford Synchrotron
Radiation Lightsource, or SSRL. These facilities now support
30 experimental stations and around 2,000 visiting researchers every year. Now, SLAC’s research has branched out
into fields like cosmology, materials and environmental sciences, biology, sustainable chemistry and energy research,
scientific computing, and much more. Now, this is only the first
part of SLAC’s history. To recap, we explored the early years
of SLAC and the lab’s contributions to the field of particle physics.
In the next videos, we’ll look at SLAC’s more current history and dive into some of the
lab’s more well known research and experiments.
