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Physicists are closing in on the subatomic particle known as the Higgs boson, according to new research from an international team that includes two University of Arizona physicists.
The Higgs boson may have a mass between 115 to 135 giga-electron volts, or GeV, according to the new finding from the Tevatron particle accelerator at Fermilab in Batavia, Ill.
The Higgs boson is the only subatomic particle predicted by theory that physicists have not yet found, so every bit of progress in the search arena is an achievement.
Finding the Higgs boson, first postulated by British physicist Peter Higgs in the 1960s, would be a key validation of what's known as the Standard Model – physicists' explanation of how the universe works.
"The Higgs can only be in one place," said Erich Varnes, a UA associate professor of physics involved with this latest finding. "It's a particle that has one mass."
"Particle physics is trying to understand how the universe works on its most basic level," he said. "No one has seen a Higgs boson – that's one of the frontiers of our field."
Xiaowen Lei, who received her doctorate in physics from the UA and is now a postdoctoral researcher in the UA physics department, had a key role in this new finding.
Lei and Varnes were among a team of 12 people looking for a particular signature of the Higgs boson: the production of a kind of particle called bottom, or b, quarks.
For clues to the Higgs' existence, Lei and her colleagues sifted through 10 years of data gathered by the Tevatron's DZero experiment from 2001 to 2011. The Tevatron particle accelerator smashed protons and anti-protons together.
Theory predicts that, if Higgs bosons exist, a proton-anti-proton collision can create a Higgs boson and a particle called a Z-boson. The Higgs boson could then decay into a pair of b-quarks – which is why detecting pairs of b-quarks is important in the search for the Higgs.
One of Lei's key contributions is improving the computer software to better distinguish b-quarks from other kinds of quarks, Varnes said.
She said, "If we improve our ability to detect a b-quark by 5 percent, we improve our ability to detect the Higgs by 10 percent."
The researchers aren't ready to declare the Higgs found. That requires more statistical analysis, both of the data from the Tevatron and the data from other particle colliders. Varnes said about the existence of the Higgs boson, "It's a definite ‘maybe.'"
The UA's Varnes has a leadership role on the 540-member Dzero team, one of the two experiments at the Tevatron particle collider that were involved in the finding. The other experiment is dubbed CDF.
The new constraints on the Higgs were announced today at the annual conference on Electroweak Physics and Unified Theories, known as the Rencontres de Moriond, held in La Thuile, Italy.
The U.S. Department of Energy, the National Science Foundation, and a number of international funding agencies fund the Tevatron's DZero and CDF experiments at DOE's Fermi National Accelerator Laboratory.
The Tevatron shut down in the fall of 2011. Researchers are still analyzing the reams of data the experiments generated.
Finding the Higgs boson also is one of the goals of the Large Hadron Collider experiments at CERN. The LHC, the largest particle collider in the world at 17 miles in circumference, is located under the Franco-Swiss border.
Varnes and four other faculty members in UA's physics department are part of the team working on the LHC's ATLAS experiment.
"There's more going on than we know about. We're interested to look at what's going on in the universe that we don't know about," Varnes said. "So if we don't find the Higgs boson, that might lead us to a better understanding of what else is out there."