Hunting for Higgs

With the July 2012 global announcement that the Higgs boson, a subatomic particle, might have been found, the UA physicists involved in the hunt have much to celebrate.

Decades of work by researchers in the University of Arizona Department of Physics were rewarded by the recent announcement that the Higgs boson had likely been observed.

The Higgs boson, a key subatomic particle long predicted by theory, had not been detected until now.

“I’m excited – tremendously pleased,” said John Rutherfoord, Ph.D., a UA professor of physics who has been pursuing the Higgs boson for 28 years, most recently as part of an international group of physicists working on the Large Hadron Collider, or LHC.

This is the first new fundamental particle discovered by physicists since 2000.

The UA is the only institution in Arizona involved with the Large Hadron Collider, or LHC.

Physicists had hoped the LHC, the most powerful particle accelerator ever built, would be able to find the boson named for physicist Peter Higgs.

Into the ATLAS Instrument

The LHC smashes protons together in a 17-mile circular tunnel about 100 yards under the Franco-Swiss border and is operated by the European Organization for Nuclear Research, known as CERN.

“We have found a new boson – and evidence that it’s the Higgs is very strong,” Rutherfoord said.

So far, all indications are promising. The new particle has a mass of about 125-126 giga-electron volts – within the range where the physicists expected to see the Higgs boson.

Even so, Rutherford said more analyses must be done before the new boson is definitively declared to be the Higgs: “We just don’t have enough data to say with the degree of certainty that scientists like to have.”

He and other UA physicists built part of a massive instrument called ATLAS that is inside the LHC. In addition to Rutherfoord, the UA-ATLAS research team includes UA physics professors Elliott Cheu, Ph.D., Kenneth Johns, Ph.D., and Michael Shupe, Ph.D., and Erich Varnes, Ph.D., a UA associate professor of physics.

The team also includes research engineers and technicians, postdoctoral students, graduate students and undergraduates.

Physicists have developed “The Standard Model” to explain how the universe works. The Higgs boson is the only subatomic particle predicted by the model that physicists have not yet found.

Cheu said, “It’s a pretty good theory – with one problem. We’ve never seen the Higgs boson.”

He went on to say that if the newly observed boson really is the Higgs, that would be a key validation of the Standard Model.

The LHC has been regularly smashing protons together for two years, but the particle known as the Higgs boson is extremely hard to detect. Finding it requires analyzing the data generated by trillions of proton-proton collisions.

The UA's ATLAS team led the design, construction and installation of the Forward Calorimeter, an instrument within ATLAS that measures the position and the tremendous energies of the particles given off when the LHC’s proton beams collide. At 150-feet long, 82 feet in diameter and weighing more than 7,700 tons, ATLAS, shorthand for A Toroidal LHC Apparatus, is the world's largest-volume particle physics detector ever built.

Gleaning Answers from Mountains of Data

Approximately 700 physicists, engineers and graduate students from 44 U.S. institutions participate in the ATLAS collaboration. The U.S. Department of Energy and the National Science Foundation fund the U.S. participation in the Large Hadron Collider.

The whole ATLAS collaboration includes 3,000 physicists from 38 countries and 176 institutions.

The ATLAS detector and another detector called CMS – the Compact Muon Solenoid – have been accumulating more and more data the longer the LHC runs. And the researchers have become better and better at sifting through the mountains of data being generated.

“You don’t all of a sudden find it,” Rutherfoord said of the Higgs boson. “You accumulate data and you accumulate data and then finally you can say that you found it.”

Finding the Higgs is just one of the things the UA physicists expect to learn from the Large Hadron Collider. The collider may be able to help scientists learn more about dark matter or reveal other surprises that point the way to a better understanding of physics.

Rutherfoord said, “Dark matter is an extremely exciting possibility that we are hoping to discover."