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SFU physicists find first evidence of rare single top quark

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Dugan O’Neil 604.291.5623
Stuart Colcleugh 604.291.3219

Fermi National Accelerator Laboratory:
SFU high energy physics group:

December 15, 2006

Simon Fraser University’s high-energy physics group has detected for the first time ever the elusive, singly produced top quark, a subatomic discovery that may hold important clues to the fundamental nature of the universe.

Top quarks, which were discovered 11 years ago, are part of a family of quarks that comprise one of the two basic constituents of matter (the other being leptons).

They existed shortly after the Big Bang that created the universe, but no longer occur naturally and must be created experimentally in massive high-energy particle accelerators that recreate the conditions of the early universe.

Until now, however, scientists had never observed top quarks alone. They had always been accompanied by their anti-matter partners, seen through processes that simultaneously produced pairs of top and anti-top quarks.

The SFU group’s discovery of single top quarks could lead to a better understanding of how the universe works and how objects acquire mass.

“We’re pretty excited about it,” says SFU physicist Dugan O'Neil, who presented the group’s evidence Dec. 8 to a packed audience at the U.S. Fermi National Accelerator Lab in Batavia, IL, where the SFU team first made the discovery at Fermilab’s Tevatron Collider high-energy accelerator.

“It is certainly one of the most exciting particle physics results of the year and one of the most interesting new measurements to come out of the Tevatron in the last five years.”

The discovery is the culmination of years of intense international effort by more than 50 physicists working as part of DZero, an international experiment conducted by more than 600 physicists from 20 countries and 90 institutions. The Canadian participants include SFU, the University of Alberta, McGill University and York University.

Working with others in the DZero collaboration, the SFU physicists started from a million billion proton-antiproton collisions produced by the Tevatron, the world's most powerful particle collider, and used sophisticated analysis techniques to detect about 60 collisions, each containing a single-top-quark candidate.

The SFU DZero group consists of O’Neil, physicists Michel Vetterli and Yann Coadou, and grad students Dag Gillberg and Zhiyi Liu.

Electronic photos available upon request