ARLINGTON - Scientists from the CDF (Collider Detector at Fermilab) and DZero collaborations at the U.S. Department of Energy's Fermilab have combined data from the two Tevatron particle accelerator experiments to advance the quest for the long-sought Higgs boson. The University of Texas at Arlington High Energy Physics Group has worked on DZero for 15 years. Participants are physics professors Kaushik De, Andrew White, Andrew Brandt, and Jaehoon Yu and postdoctoral scientists Mark Sosebee, Armen Vartapetian, Barry Spurlock and the late Jia Li, recently killed in an accident. Several graduate students also worked on the DZero, included Venkatesch Kaushik, who earned his doctorate in December 2007 and Heather Brown, who has worked on the DZero detector for the past two years.
The results of the CDF and DZero experiments indicate that Fermilab researchers have for the first time excluded, with 95 percent probability, a mass for the Higgs of 170 GeV. This value lies near the middle of the possible mass range for the particle established by earlier experiments. This result not only restricts the possible masses where the Higgs might lie, but it also demonstrates that the Tevatron experiments are sensitive to potential Higgs signals.
"These results mean that the Tevatron experiments are very much in the game for finding the Higgs," said Pier Oddone, director of Fermilab.
Combining results from the two collider experiments effectively doubles the data available for analysis by experimenters and allows each experimental group to cross check and confirm the other's results. In the near future, the Fermilab experimenters expect to test more and more of the available mass range for the Higgs.
The Standard Model of Particles and Forces--the theoretical framework for particle physics--predicts the existence of a particle, the Higgs boson, which interacts with other particles of matter to give them mass. The mechanism by which particles acquire different mass values is unknown and finding evidence for the existence of the Higgs boson would address this fundamental mystery of nature.
The CDF and DZero experiments each comprise some 600 physicists from universities and laboratories from across the nation and around the world. Currently, Fermilab's plans call for the Tevatron experiments to continue operating through 2010. In that time, both groups expect to double their analysis data sets, improving their chances to observe the Higgs.
Scientists expect operations to begin at the Large Hadron Collider at CERN, in Europe, sometime later this year. Observation of the Higgs is also a key goal for LHC experiments.
The Tevatron accelerator and the experiments are operating at peak performance. The Tevatron continues to break records for luminosity, the number of high-energy proton-antiproton collisions it produces. The more luminosity the Tevatron delivers, the more chances experimenters have to see the Higgs. Moreover, by continually improving their experimental techniques, the CDF and DZero physicists have been able to boost their sensitivity to the Higgs and other phenomena by more than the margin afforded by the increased data alone.
"The Fermilab collider program is running at full speed," said Dennis Kovar, associate director of the Office of Science for High Energy Physics at the U.S. Department of Energy. "In the past year alone, the two experiments have produced 77 doctorates and 100 publications that advance the state of our knowledge across the span of particle physics at the energy frontier."
The new Higgs results are among the approximately 150 results that the two experiments presented at the International Conference on High Energy Physics in Philadelphia held July 29-Aug. 5.
"The discovery of the Higgs boson would answer one of the big questions in physics today," said Joseph Dehmer, director of the Division of Physics for the National Science Foundation. "We have not heard the last from the Tevatron experiments."
The DZero public Web page for CDF/DZero combination which provided first direct Higgs exclusion since LEP era can be visited at http://www-d0.fnal.gov/Run2Physics/WWW/results/prelim/HIGGS/H64/
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