Seeking the top quark.

Of the six types of quarks that physicists postulate as the constituents of matter, only the top quark remains unobserved. Particle physicists working with two detectors - called CDF and DO -- at Fermilab's Tevatron collider in Batavia, Ill., have observed three collisions of a proton and an antiproton that may have produced a top quark. However, these events also fit alternative scenarios that do not include creation of a top quark. Until they obtain additional evidence, the researchers refuse to draw any conclusion about the top quark's discovery

"This is not going to be a 'eureka' moment," says John Peoples, Fermilab director. "It's going to take time."

Analyzing accumulated data from billions of collisions that produced no top quark, physicists using the CDF detector now report 108 billion electron-volts (108 GeV) as the new lower limit on the top quark's mass. This result raises the limit from last year's reported value of 91 GeV (SN: 3/21/92, p.189).