With the apparent discovery of the top quark, the last of the subatomic particles believed to be the building blocks of matter, MIT scientists have now been involved in tracking down four of the six quarks predicted by leading scientific theory.
Last Tuesday an international team of physicists, including 18 from MIT, announced the first direct evidence for the top quark. Physicists had already identified the so-called up, down, charm, strange, and bottom quarks, but the Standard Model of particle physics, scientists' leading theory for the nature of matter, predicted a sixth-the top quark.
At a seminar here on the day of the announcement Assistant Professor Paraskevas Sphicas of physics, who led the MIT group, emphasized that "the [new] data provide evidence for, but don't firmly establish the existence of, the top [quark]. In order to confirm it we need more data." (Further experiments over the coming year at DOE's Fermi National Accelerator Laboratory, where the work was conducted, are expected to provide that data.)
Nevertheless, Professor Sphicas said, "the Standard Model seems to be surviving another test."
Professor Robert J. Birgeneau, dean of the School of Science, noted in an introduction to the seminar that of the six quarks predicted by the Standard Model, "four are known because of MIT direct discoveries or MIT collaborations."
In the late 1960s, J.A. Stratton Professor of Physics Henry W. Kendall, Institute Professor Jerome I. Friedman, and Professor Richard Taylor of the Stanford Linear Accelerator Center (SLAC) set the stage for the quark hunt by discovering the first quarks-the up and the down. They shared the 1990 Nobel prize for physics for that work.
Then in independent experiments Samuel C.C. Ting, the Thomas Dudley Cabot Professor of Physics, and Professor Burton Richter (MIT SB '52 and PhD in physics) of SLAC uncovered the first evidence-through the "J/psi" particle-of the charm quark. The two shared the Nobel prize for physics in 1976 for that achievement.
"And fortunately today we're able to make an announcement of the apparent discovery of the top quark," Dean Birgeneau said. The MIT group that contributed to the new evidence includes three faculty members: Institute Professor Jerome Friedman (who has done it again, said Dean Birgeneau), Professor Sphicas, and Professor Lawrence Rosenson of physics. The three hold appointments in the Laboratory for Nuclear Science (LNS) and the Department of Physics.
Six LNS staff members and nine physics graduate students were also involved in the work.
A version of this article appeared in the May 4, 1994 issue of MIT Tech Talk (Volume 38, Number 31).
