Iowa State Scientists Involved In Discovery Of Top Quark


Two international teams of physicists announced Thursday, 
March 2, that they have discovered the subatomic particle 
called the "top quark," the last undiscovered quark predicted 
to exist by current scientific theory. 

The teams, which make up the CDF and DZero experimental 
collaborations at Fermi National Accelerator Laboratory, near 
Chicago, described the observations of the top quark produced 
in high-energy collisions between protons and antiprotons. 

Iowa State has five researchers -- two faculty members, two 
students and a post-doctoral researcher -- who are part of 
the DZero collaboration. The Iowa State physicists are E. 
Walter Anderson, professor of physics and astronomy; John 
Hauptman, associate professor of physics and astronomy; 
graduate students Michael Wendling and Myungyun Pang; and 
post-doctoral researcher Jay Wightman. Each team is made up 
of about 450 scientists.

The quark-smashing experiments were carried out at Fermilab's 
Tevatron accelerator. Fermilab is a U.S. Department of Energy 
facility located 30 miles west of Chicago.

"For physicists, this is clearly the discovery of the 
decade," said Anderson. "This is nature at its most 
fundamental level."

"This is the last piece of a jigsaw puzzle that has been 
slowly put together by physicists worldwide over the past 30 
years," added Hauptman. "Iowa State participants played a big 
role, an essential role, in this discovery."

Scientists have been searching for the top quark since the 
discovery of the fifth quark, called "bottom," in 1977. The 
recent discovery reaffirms the quark theory of the structure 
of matter called the standard model, Anderson explained.

The theory predicts the existence of six quarks, called "up," 
"down," "charm," "strange," "bottom" and "top." The elusive 
top quark was the last to surrender its secrets to 
physicists. 

Quarks are the basic building blocks of all matter. The 
proton, for example, is made up of two "up" and one "down" 
quark, and the neutron is made up of one "up" and two "down" 
quarks. Together with the electron and its neutrino, they 
make up all that we see on Earth and in the nearby universe, 
said Hauptman.

The top quark is 40 times more massive than the next lighter 
quark (bottom). Presumably, these heavier quarks have not 
existed since the Big Bang creation of the universe some 15 
billion years ago, Hauptman said. 

The physicists discovered the top quark by measuring its 
final decay products in the DZero detector at Fermilab. 
Hauptman said that the Iowa State researchers developed a 
data analysis filtering technique used in the experiment. The 
technique helped the physicists sort out background data and 
hone in on authentic top quark data. 

Over a year's time the Fermilab team had data from some 20 
million particle collisions. Through the use of ISU's 
modified "least squares constrained fit" technique, a data 
analysis package that applies Einstein's theories of 
relativity, the physicists were able to pick out 11 possible 
top quark events from the 20 million particle collisions. 

"After analyzing these 11 events, we were able to go back and 
determine a mass for the top quark of about 200 GeV 
(gigaelectron volts) or about 40 times the mass of the next 
lighter quark," Hauptman said.

The two collaborations included scientists from Brazil, 
Canada, Colombia, France, Italy, Japan, Korea, Mexico, 
Poland, Russia, Taiwan, and the U.S.

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contact:  Skip Derra, News Service, (515) 294-4917
updated:  3-3-95