Physicists Narrow Search for Higgs Boson

UA particle physicist Erich Varnes is part of an experiment that just announced a new finding about the elusive Higgs boson.
March 16, 2009
The DZero detector records particles emerging from high-energy proton-antiproton collisions produced by the Tevatron. Tracing the particles back to the center of the collision, scientists understand the subatomic processes that take place at the core of proton-antiproton collisions. Scientists search for the tiny fraction of collisions that might have produced a Higgs boson. (Click to enlarge)
The DZero detector records particles emerging from high-energy proton-antiproton collisions produced by the Tevatron. Tracing the particles back to the center of the collision, scientists understand the subatomic processes that take place at the core of proton-antiproton collisions. Scientists search for the tiny fraction of collisions that might have produced a Higgs boson. (Click to enlarge)
The Fermilab accelerator complex accelerates protons and antiprotons close to the speed of light. The Tevatron produces about ten million proton-antiproton collisions per second, maximizing the chance for discovery. Two experiments, CDF and DZero, search for new subatomic particles and forces unveiled by the collisions. (Click to enlarge)
The Fermilab accelerator complex accelerates protons and antiprotons close to the speed of light. The Tevatron produces about ten million proton-antiproton collisions per second, maximizing the chance for discovery. Two experiments, CDF and DZero, search for new subatomic particles and forces unveiled by the collisions. (Click to enlarge)
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The haystack just got smaller for physicists searching for the Higgs boson.

The Higgs boson is the only subatomic particle predicted by theory that physicists have not yet found, so just reducing the search area is an achievement.

The Higgs has been estimated to have an energy between 114 and 185 giga-electronvolts, or GeV. Now researchers have eliminated the middle of the range, from 160 to 170 GeV, as possible energies for the Higgs.

"We're ruling out part of the mass of the Higgs," said Erich Varnes, a UA associate professor of physics. "That's the first time our experiments have been able to do that."

In the subatomic world of particle physics, the scientists sometimes talk as if energy and mass are interchangeable – which is just what Einstein's famous E=Mc2 equation says.

"Particle physics is trying to understand how the universe works on its most basic level," Varnes said. "No one has seen a Higgs boson – that's one of the frontiers of our field."

Finding the Higgs boson, first postulated by British physicist Peter Higgs in the 1960s, would be key validation of what's known as the Standard Model, physicists' explanation of how the universe works.

"It's the missing piece of the puzzle," Varnes said.

The UA's Varnes has a leadership role on the 550-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 Tevatron, a 4-mile circular tunnel, is located at Fermilab in Batavia, Ill.

The new constraints on the Higgs were announced recently 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.

DZero is an international experiment conducted by 550 physicists from 90 institutions in 18 countries. CDF is an international experiment of 602 physicists from 63 institutions in 15 countries.

While Varnes' was not directly involved in analyzing the data for this new finding, his work is critical to all the DZero results. As co-leader for algorithms and computing, he ensures that the computing tools – both the hardware and the software – are up to the task of analyzing the massive amounts of data generated by the experiments.

UA professor of physics Kenneth Johns also made a contribution to this finding. Johns led the design and construction of the Level1 muon trigger electronics being used in the Dzero experiment. Muons are one of the particles thrown off during the high-energy collisions within the collider.

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 LHC, a high-energy particle collider 17 miles in circumference, is located under the Franco-Swiss border.

Varnes, Johns and several other physics professors at the UA are also involved with the LHC. The UA physicists work on the LHC's ATLAS experiment.

Both colliders are designed to slam subatomic particles together at nearly the speed of light and then observe what kinds of energy and particles spew from the collision. Fermilab's Tevatron smashes protons and anti-protons together, whereas the collisions within the LHC will be between two protons.

Assuming the Higgs exists, creating one will be a rare event, which is why it hasn't yet been observed, Varnes said.

The energy of collisions at the LHC will be seven times higher than those at the Tevatron because the LHC is so much larger. The LHC will also have more collisions, increasing the likelihood of observing the Higgs, he said.

Finding the Higgs boson will help confirm that what physicists call the Standard Model is an accurate explanation of how the universe works.

The Higgs won't be the end of the investigation, Varnes said.

"Even though this picture we have explains everything we see so far," he said. "When we take that theory and try to translate it out to higher energies, things don't seem to work very well.

"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."

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