The SPEAR Storage Ring

Stanford University has a long history of involvement in the development and use of colliding-beam storage rings for particle physics research. The first such machine at Stanford was a small electron-electron collider, shaped like a figure eight, located on the main campus. A collaborative effort between physicists from Princeton and Stanford Universities, this project produced the first physics results ever obtained with the colliding-beam technique. The next in the succession of Stanford colliders was the SPEAR machine at SLAC, completed in 1972. SPEAR consists of a single ring some 80 meters in diameter, in which counter-rotating beams of electrons and positrons were circulated at energies up to 4 GeV. In terms of the rich harvest of discoveries it has yielded, it has been the most cost-effective machine ever built in the field of high energy physics. In 1990, the machine was dedicated to synchrotron radiation research.

Two of these achievements stand out in particular. The first was the 1974 discovery of a particle called the psi that is made up of a combination of a quark and an antiquark of an entirely new kind. Before that time only three types of quarks were known, but the discovery of this new quark (called charm) served as convincing evidence that the basic idea of the quark substructure of matter was in fact valid. This work was recognized by the award of the 1976 Nobel Prize in Physics to Burton Richter of SLAC, an award he shared with Samuel C. C. Ting of MIT for the simultaneous discovery of this new particle at Brookhaven National Laboratory.

The second revolutionary discovery made at SPEAR was that of a new particle called the tau, which turned out to be the third in the sequence of electrically charged elementary particles called leptons. The first lepton discovered was the electron, found in 1897; the second was the muon (1937); and the third was the tau, discovered at SPEAR in 1976. Martin Perl of SLAC was awarded the Wolf Prize in 1982 and the Nobel Prize in Physics in 1995 for its discovery.

SPEAR also produces intense beams of synchrotron radiation -- ultraviolet and x-ray photons emitted by the circulating electron beams -- that have found extensive use for basic and applied research in such fields as materials science and medicine.

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Last modified 14 December 1995 by Henniss.