Fundamental Component of Matter Detected

The CDF detector, about the size of a 3-story house, records "debris" emerging from each high-energy proton-antiproton collision produced by the Fermilab Tevatron acelerator. (Courtesy of Fermilab.)

Michigan State University scientists and colleagues around the world took a step closer to understanding the universe with the discovery of a fundamental building block of nature. The recent discovery of a single top quark at the U.S. Department of Energy’s Fermi National Accelerator Laboratory near Chicago is a major breakthrough in understanding matter and energy.

“The discovery of single top quark production fills in a major piece of the puzzle in particle physics and solidifies our understanding of the basic components of matter,” said MSU assistant physics professor Reinhard Schwienhorst.

Quarks are believed the smallest bits of matter and interact to form particles such as protons. Before, top quarks were only known to be produced in pairs. By producing a single top quark, scientists have recorded the most massive of elementary particles and perhaps have paved the way for discovery of the Higgs boson. Sometimes referred to as the “God Particle,” the Higgs boson is the theoretical building block of the Standard Model of the universe and could explain how massless elementary particles acquire mass.

“The discovery of a single top quark production marks a milestone in physics,” Schwienhorst added. “We anticipate upcoming research at the Large Hadron Collider in Europe to take these findings to the next step and either evolve our understanding of particle physics or overturn the model completely.”

Schwienhorst and colleagues periodically work with the LHC at the European Centre for Nuclear Research, or CERN, in Switzerland. A number of MSU scientists contributed to development of the world’s most powerful collider there, and researchers will return to apply what they learned about detecting the single top quark to seek the Higgs boson.

MSU physics professor Chien-Peng Yuan pioneered study of heavy top quarks and their relationship to the Higgs boson. He proposed the relevant strategies for discovering single top quarks in 1989. Those were discovered six years later at Fermilab by two groups of scientists combing through data from proton-antiproton collisions with a mass close to Yuan’s estimate. Since then Yuan has continued to theorize about top quarks and has collaborated closely with his MSU colleagues.

Scientists involved in the Fermilab project have been working in two groups, each exceeding 600 physicists: the DZero and the Collider Detector at Fermilab collaborations. Schwienhorst co-led the DZero team and MSU doctoral student Jorge Benitez was particularly active in that group, updating hardware and collecting and analyzing data. He also conducted theoretical work with Yuan, and even relocated to Fermilab. “The research we conduct at DZero is unique – there is no other place in the world that conducts such complex, high-energy experiments,” Benitez said.

MSU associate professor Kirsten Tollefson led a different group of nearly 150 collider detector team physicists. “MSU is one of only a handful of institutions that have faculty members on both the CDF and DZero experiments, and that can make life in the department very interesting,” Tollefson said. “For the last three years, the two groups have been in direct competition with each other over which experiment would be the first to see single top quarks. Both experiments have been close for a while, and it was pretty amazing that we each came out with papers on the same day stating the discovery.

“When you are trying to discover something that is so rare it only appears once in 20 billion collisions, it’s nice to have confirmation from two experiments.” Tollefson added.

MSU’s contributions to this discovery ranged from Yuan’s pioneering theoretical work to usage of a large computer cluster in the Department of Physics and Astronomy to conduct data analysis. MSU also hosted a conference with all DZero physicists in 2007.