Collisions at high energy.

Collisions at high energy

The Tevatron collider at the Fermi National Accelerator Laboratory in Batavia, Ill., flings protons against antiprotons at collision energies adding up to 1.8 trillion electron-volts. Completed last year and billed as the world's most powerful particle accelerator, the collider is starting to provide data for researchers, who sift through the debris from head-on collisions in search of exotic subatomic particles (SN: 9/28/85, p.202; 3/22/86, p.180).

The researchers are looking for evidence of the "top" quark, a rapidly decaying subatomic particle and the only member of the quark family not yet detected. A reported sighting in 1984 could not be confirmed, and particle physicists now suspect the top quark has a mass, expressed in energy terms, of at least 100 billion electron-volts -- roughly 100 times a proton's mass. The Fermilab collider is the only operating particle accelerator able to reach this energy range. Even so, only about 1 in a billion proton-antiproton collisions provides enough energy to create such a massive particle. Earlier this month, collider operators raised the collision rate to 50,000 collisions per second, significantly increasing the chances of discovering the top quark.

In West Germany last month, for the first time, operators of the new 30-billion-electron-volt electron-proton collder at the Deutsches Elektronen-Synchrotron stored an electron beam in the accelerator's recently completed electron ring. The next step is to install special superconducting magnets designed for accelerating protons. Both proton and electron rings should be ready for collision experiments in 1990. This facility, located in Hamburg and known as the Hadron Electron Ring Accelerator, will be the world's first high-energy electron-proton collider.