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UCR Physicists Part of "Top Quark" Discovery

UC Riverside Scientists Take Part in Worldwide Physics Surprise

Collaboration Measures “Top Quark” in New Way, Finds Vital Differences

(June 16, 2004)

The DZero team, on a signed posterEnlarge

The DZero team, on a signed poster

RIVERSIDE, Calif. ( -- Nine UC Riverside scientists are among many around the world who worked together to uncover an important answer about the makeup of the universe. Now they are left with even harder questions.

The 642-member DZero collaboration last week announced its re-analysis of the top quark mass measurement, using a new method to increase the accuracy of its findings by 40 percent over older techniques. The report appears in the June 10 issue of the British science journal Nature. The news was announced June 9 from the U.S. Department of Energy's Fermi National Accelerator Laboratory in Batavia, Ill.

Important new findings often come from developing ways to measure things more accurately, said Ann Heinson, an associate research physicist at UCR and a member of DZero’s Top Quark Group.

“You rule out anomalies that way, by reducing the size of the errors,” she said. “That is how we make progress.”

High-energy physics focuses on what the world is, and what holds it together. Its Standard Model is a comprehensive theory that explains interactions of hundreds of particles. The Standard Model’s biggest, heaviest particle is the top quark, found in 1995 by two teams of physicists, one of which included UC Riverside scientists.

Having more precise information about a piece of the Standard Model -- the top quark -- gives scientists clues in their search for another missing puzzle piece, the Higgs boson, nicknamed “the God particle,” which many believe will solve long-standing mysteries about mass and inertia. But data from the top quark re-analysis indicate the knowledge physicists seek is farther away than they thought it was, authors of the paper say, and pursuit of it may require new technology.

Heinson and five other UC Riverside scientists are co-authors of the paper. They designed and built parts of the DZero detector and analyzed data for many years. The other UCR co-authors are Professor Stephen Wimpenny, who also led UCR’s 1995 top quark team, Associate Professor John Ellison, and postdoctoral researchers Suyong Choi, Ia Iashvili and Valentin Kuznetsov. Other UCR physicists who are part of the DZero Collaboration are Professor Robert Clare and graduate students Raymond Gelhaus and Philip Perea.

Heinson and Ellison are both on the University’s July 1 promotion list, as research physicist and professor, respectively.

Heinson takes special pride in the attention the Top Quark Group’s paper is getting from the scientific community, she said, because it was she who pushed to publish in high-profile Nature rather than one of the smaller physics journals to which the collaboration usually submits its findings.

“Nature requires interpretations of results -- in other words, why it’s interesting -- because you’re speaking to people in other scientific fields,” Heinson said.

One of the most interesting things about the new measurements is that they clear up inconsistencies in the Standard Model, authors contend.

“This is a remarkable achievement in the measurement of the top quark,” said Thomas Ferbel, professor of physics and astronomy at the University of Rochester, a principal author of the paper and mentor of Juan Estrada, the graduate student whose work led to the new method of measuring the mass of the top quark with unprecedented accuracy.

Raymond L. Orbach, a former chancellor of UC Riverside and now director of the Department of Energy's Office of Science, which funds Fermilab, said "These important results demonstrate how our scientists are applying new techniques to existing data, producing new estimates for the mass of the Higgs boson. We eagerly await the next round of results."

The University of California, Riverside ( is a doctoral research university, a living laboratory for groundbreaking exploration of issues critical to Inland Southern California, the state and communities around the world. Reflecting California's diverse culture, UCR's enrollment has exceeded 21,000 students. The campus opened a medical school in 2013 and has reached the heart of the Coachella Valley by way of the UCR Palm Desert Center. The campus has an annual statewide economic impact of more than $1 billion.

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