A circular tunnel, between 160 and 574 feet below Switzerland and France, is ringed with electromagnets chilled to -271.3oC—colder than outer space. Through the tunnel fly particle beams, controlled by the electromagnets and traveling on a collision course at close to the speed of light. The job of making them collide is, according to the organization that manages the tunnel, “akin to firing two needles 10 kilometers (6.2 miles) apart with such precision that they meet halfway.”
But meet they do, and the resulting collisions may just tell us how our universe formed.
And at the heart of it all is a small group of Ducks.
Physicists James Brau, David Strom, Eric Torrence, and Stephanie Majewski divide their time between the University of Oregon’s Brau-led Center for High Energy Physics in Eugene and the ATLAS detector at CERN’s Large Hadron Collider (LHC) in Switzerland. The 7000-ton ATLAS detector, 330 feet below the Swiss village of Meyrin, is aiding researchers in their quest to understand nothing less than what makes our universe tick.
“Our group joined ATLAS in 2005, so we’re fairly recent comers to the collaboration compared to some groups who’ve been there since day one,” said Torrence. “The plan for it started in the early 80s. These very large, complex, and expensive experiments take a very long lead time to get to the stage where you can consider building them, and there’s a very long construction process before you get to the point where you are taking data and trying to find something.”
Brau, Torrence, Strom, and Majewski all previously conducted research at the SLAC national accelerator laboratory at Stanford University—in particular on the BaBar experiment, where physicists are studying the difference between matter and antimatter—and their time there played a key role in their hiring at CERN.
“I was a graduate student at Stanford University, and I was working on the BaBar Experiment at the time, which was using the accelerator at SLAC, just down the road from Stanford,” said Majewski. “That’s what I did my graduate work on. As I finished up grad school, the LHC was almost ready to turn on, so I hurried to finish up and try to get a post-doc on one of the experiments at either ATLAS or CMS.”
“When BaBar was coming to a conclusion… we wanted to be involved in a running experiment, and what was closest to our interest was going on at CERN,” said Torrence. “We’d done a lot of work on trigger systems, particularly at BaBar, and historically David, myself, and Jim had a lot of history and background in trigger systems. We promised that we’d come in and work.”
3D model of a proton collision in the LHC.
A trigger system, the particular area of expertise among the University of Oregon’s CERN researchers, makes it possible for physicists to analyze the data produced by the LHC. Beams, composed of bunches of protons, cross in the LHC at a rate of 40 million times per second, with each collision producing multiple interactions—and almost none of the information produced is of use to a physicist. A trigger system provides a snapshot of approximately 500 events per second, making sure to keep the information physicists need.
“If you don’t trigger on an event, you won’t see it later, and nobody will ever find anything,” said Torrence.
Torrence was recently named the Deputy Data Preparation Coordinator at ATLAS, while Strom, the deputy project leader for the Trigger Data Acquisition (TDAQ) team, was the trigger coordinator when the Higgs boson was discovered on July 4, 2012. The 2013 Nobel Prize in physics was awarded to two theoretical physicists—including one of the particle’s two namesakes, Peter Higgs—in recognition of the discovery.
"I started getting excited by [the potential discovery of the Higgs boson] by the end of 2011, when it was clear there was a hint of signal in our data," said Strom. "The significance of the signal was slowly growing. It wasn't as if one woke up one morning and said, 'Oh, now I know the Higgs is there.' As we got more data we became progressively more confident we had discovered something.
"At the time of the 4th of July announcement, I was very busy making sure that our trigger strategy was working, so there was a certain amount of relief in knowing that we hadn't missed anything and all of our hard work had paid off. Remember that of the billion or so interactions we get each second we can only save about 500. Over the course of the 2012 run we saved about three billion events. In the most convincing channel—the Higgs to four leptons—the final sample only had 10 or 20 events. An enormous amount of work by students and post-docs—including many from the University of Oregon—went in to making sure the detectors and trigger were always working and that none of the events got lost."
Nicknamed “the God particle,” the Higgs boson gives particles their mass, and may help physicists understand not only the origin of the universe, but the future of the universe as well.
The Large Hadron Collider.
One of the mysteries of the universe that particle physicists at CERN hope to solve is that of dark matter, something that cannot be seen but whose gravity affects visible matter nonetheless. That’s where Majewski comes in. One of the newest members of the department led by Philip H. Knight Professor of Natural Science Brau, Majewski is taking data provided by Torrence and Strom and is looking for evidence of Supersymmetry, the theory, linked to dark matter, that each particle has a “super” partner.
“As of now there are theories or hints that something like that exists,” said Majewski. “For example, dark matter is a hint that something like Supersymmetry exists. One of the beautiful aspects of Supersymmetry is that the lightest Supersymmetric particle could be stable. And in this case it would make a very good dark matter candidate, so that’s a nice connection there and that’s pretty compelling.”
The LHC is currently shut down, giving researchers like Majewski time to sift through the data produced in 2012 while they plan for a restart in 2015 and a major electronics upgrade in 2018.
When the LHC restarts, the Duck physicists will once again be heavily involved, key members of the approximately 3,000-researcher-strong ATLAS project.
After all, it takes a lot of grey matter to search for dark matter.