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Wayne State physicists play major role in Fermilab discovery on Higgs mass

March 17, 2009

DETROIT—The Higgs particle is a keystone in the theoretical framework known as the Standard Model of particles and their interactions. According to the Standard Model, the Higgs boson explains why some elementary particles have mass and others do not.
Fermilab announced Friday that the territory where the Higgs boson may be found continues to shrink. Wayne State researchers Robert Harr, Ph.D., associate professor of physics and resident of Grosse Pointe Woods, and Shalhout Shalhout of Detroit, a WSU doctoral student who received his B.S. and M.S. in physics from WSU, both were major contributors in this discovery.

"Our theory of particle physics only works for massless particles,” said Harr. “The Standard Model of particle physics introduces a mechanism to endow particles with mass, and the Higgs boson is the material embodiment of this mechanism. The model has been experimentally confirmed in all aspects except for the Higgs boson. Discovering the Higgs would be a fabulous confirmation of the model.”
The latest analysis of data from the CDF and DZero collider experiments at the U.S. Department of Energy's Fermilab now excludes a significant fraction of the allowed Higgs mass range established by earlier measurements. Those experiments predict that the Higgs particle should have a mass between 114 and 185 GeV/c2. Now the CDF and DZero results carve out a section in the middle of this range and establish that it cannot have a mass in between 160 and 170 GeV/c2.

Harr and Shalhout collaborate on the CDF experiment with support from the Department of Energy. “Our work focuses on the low end of the allowed mass range,” said Harr. “We’re working diligently to extract everything we can from the data we’ve worked so hard to acquire.
“The outstanding performance of the Tevatron and CDF and DZero together have produced this important result,” said Dennis Kovar, associate director of the Office of Science for High Energy Physics at the U.S. Department of Energy. “We're looking forward to further Tevatron constraints on the Higgs mass."

So far, the Higgs particle has eluded direct detection. Searches at the Large Electron Positron collider at the European laboratory CERN established that the Higgs boson must weigh more than 114 GeV/c2. Calculations of quantum effects involving the Higgs boson require its mass to be less than 185 GeV/c2. The observation of the Higgs particle is also one of the goals of the Large Hadron Collider experiments at CERN, which plans to record its first collision data before the end of this year.

The success of probing the Higgs territory at the Tevatron has been possible thanks to the excellent performance of the accelerator and the continuing improvements that the experimenters incorporate into the analysis of the collider data. To increase their chances of finding the Higgs boson, the CDF and DZero scientists combine the results from their separate analyses, effectively doubling the data available.
“A particle collision at the Tevatron collider can produce a Higgs boson in many different ways, and the Higgs particle can then decay into various particles,” said CDF co-spokesperson Rob Roser, of Fermilab. “Each experiment examines more and more possibilities. Combining all of them, we hope to see a first hint of the Higgs particle.”

So far, CDF and DZero each have analyzed about three inverse femtobarns of collision data---the scientific unit that scientists use to count the number of collisions. Each experiment expects to receive a total of about 10 inverse femtobarns by the end of 2010, thanks to the superb performance of the Tevatron. The collider continues to set numerous performance records, increasing the number of proton-antiproton collisions it produces.

The Higgs search result is among approximately 70 that the CDF and DZero collaborations presented at the annual conference on Electroweak Physics and Unified Theories known as the Rencontres de Moriond, held March 7-14. In the past year, the two experiments have produced nearly 100 publications and about 50 Ph.D.s that have advanced particle physics at the energy frontier.

Notes for editors:
Fermilab, the U.S. Department of Energy's Fermi National Accelerator Laboratory located near Chicago, operates the Tevatron, the world's highest-energy particle collider. The Fermi Research Alliance LLC operates Fermilab under a contract with DOE.

CDF is an international experiment of 602 physicists from 63 institutions in 15 countries. DZero is an international experiment conducted by 550 physicists from 90 institutions in 18 countries. Funding for the CDF and DZero experiments comes from DOE's Office of Science, the National Science Foundation, and a number of international funding agencies. 
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Wayne State University is one of the nation’s pre-eminent public research universities in an urban setting, ranking in the top 50 in R & D expenditures of all public universities by the National Science Foundation. Through its multidisciplinary approach to research and education, and its ongoing collaboration with government, industry and other institutions, the university seeks to enhance economic growth and improve the quality of life in the city of Detroit, state of Michigan and throughout the world.