Experimental Facilities : SLAC Linear Collider (SLC)

The Stanford Linear Collider (SLC) began construction in 1983 and was completed in 1989. This device was a novel kind of machine that serves both as a test bed for a new accelerator technique and as a facility to reach the energy region where the massive Z⁰ particle can be produced in quantity and in a simple environment.

The key elements of the SLC included:

• Extensive upgrades to the existing two-mile linear accelerator to produce 50 GeV beams of both electrons and positrons.
• Two small storage rings that are used to damp the beams down to suitable dimensions.
• Two long curving arcs of magnets that are used to transport the separate electron and positron beams from the end of the linac to a single collision point.
• An elaborate focusing system that reduces the sizes of the colliding beams down to dimensions much smaller than a human hair.
• The beams collide only once and then are not recycled. This tests the idea of a "linear collider", where beams from two head-to-head linear accelerators would collide, as a way to achieve very high energy electron-positron collisions.

In 1992 a polarized electron source was developed with very high intensity. The following year it was upgraded to generate highly polarized beams, which allow sensitive studies of the Z⁰ particle.

The first detector system used with the SLC (called MARK II) had been upgraded after earlier use at both SPEAR and PEP. A much more elaborate and complete detector system called the SLC Large Detector, or SLD, was installed in 1991.

The European community has chosen to achieve collisions between 50 GeV electron and positron beams through the use of the more conventional storage-ring technique at the CERN Laboratory near Geneva, Switzerland. Their Large Electron Positron collider (LEP) machine is a storage ring some 17 miles in circumference; it has the advantage of four interaction regions (rather than one at the SLC) and the possibility of a higher ultimate energy. The SLC, on the other hand, has a polarized electron beam and a collision spot with an area hundreds of times smaller than that of LEP, opening new physics areas to the SLC.

Research results from the SLC and LEP have already begun to prove the value of these colliders. The mass and other properties of the Z⁰ particle, which is a carrier of the weak force of subatomic physics, have been determined to unprecedented precision.

Even more important, this early work showed that there are only three kinds of neutrinos with mass less than 1/2 of the Z mesons.

This suggests, with high probability, that the universe is in fact made up of not more than the three known families of elementary particles (each with two kinds of leptons and two kinds of quarks).

The SLD no longer collects data on the production of the Z⁰ boson using a polarized electron beam and their subsequent decays, but analysis of the data continues. This has lead to the most precise measurement of a crucial parameter in particle physics theory as well as unique measurements on B mesons. Analysis of SLD data has shown a predicted preference for producing the Z⁰ when the beam is polarized with the spins rotating about the beam axis in a left-handed sense. This distinction at the most fundamental level between left- and right-handedness is one of the most intriguing phenomena in subatomic physics.

Learn more about the SLD experiment and results of years of data analysis