Getting to the Heart of the Matter

Hunting an elusive particle at the world’s best-known atom smasher

It’s been called the single biggest machine on Earth: the Large Hadron Collider, an atom smasher on the Franco-Swiss border that crashes proton beams together inside a circular 17-mile tunnel, enabling breakthroughs in particle physics and our understanding of all matter in the universe.

But when the LHC is running, says Taylor Contreras, it doesn’t make a sound.

She should know—the senior in physics spent six weeks this summer with the group housing the collider, the European Organization for Nuclear Research, or CERN.

Physics student Taylor Contreras made time for a Skype interview during her stay at CERN, the Geneva-based home of the Large Hadron Collider. On an internship this summer, she searched for a theoretical particle that can’t be explained within our current understanding of matter. Nuclear Research or CERN.

Contreras is a member of a team run by UO physicist Stephanie Majewski that is studying dark matter and other topics through data collected by ATLAS, one of the detectors at the collider. Majewski’s is one of several UO groups involved in experiments at CERN.

Thanks to a research internship through Duke University and the National Science Foundation, Contreras joined the team on-site in the hunt for a new particle. She spent much of her time analyzing data that scientists running the collider churned out, and also enjoyed the thrill of being at the epicenter of one of the world’s largest international research projects.

“It’s really inspiring—this is where physics is happening,” said Contreras, interviewed via Skype while at CERN. “It gives me a realistic view of what working here would be like. I would love to work here.”

Q: What does your typical day look like?

TAYLOR CONTRERAS: I’m living with three other students in a hotel apartment in Saint-Genis-Pouilly, France—it’s about a 10-minute bus ride to CERN. In the mornings, there are lectures by some of the scientists—today there was an astroparticle lecture that really interested me. After lunch, I typically work on my research for the rest of the day, until 5 p.m. or so. On Wednesdays, our research team has a group meeting at 6 p.m. to give updates on our work. In the evenings, I just go back to the hotel and make dinner, maybe work on my research if there are lingering questions that are still bugging me from the day.

Q: How close is your work space to the Large Hadron Collider? Can you see the scientists who run it?

TC: Most of the CERN building is conference rooms and computer rooms and labs where scientists are working on hardware and the detectors that collect data inside the collider. I’m in a regular office and the collider is about 500 feet underground. They schedule tours but when it’s running, they don’t let anyone down there. There are monitors in most buildings that show live data as it’s being collected.

I did get to go down and see the control room for the ATLAS detector—but only through glass from the outside. Access is very carefully controlled. There are monitors everywhere and the room is packed with computers. I was there with Johan Bonilla, a UO graduate student, who helped me interpret some of the data displayed on the monitors.

There were other graduate students inside the control room, monitoring the detector. They go through a lot of clearance—it’s awesome that even at the graduate-student level, they can work directly with the detector. I want to be doing that someday.

Q: Tell us more about the goal of your project.

TC: I’m part of the search for a new particle that can’t be explained within our current understanding of fundamental particles and forces.

When particles break up in the collisions inside the LHC, researchers capture the data on the components that are released. With the particle we are searching for, one possible product is the release of one photon and two quarks, which are all elementary particles. If we see these elementary particles in a collision in the detector, we can find out what the mass of the parent particle was. If the parent particle has a mass that is different from any particle we know of, then we have evidence for a new particle.

Q: There are lots of leading physicists at CERN. Have you had any valuable meetings with anyone?

TC: I definitely enjoyed meeting with physics professor Marjorie Shapiro (of the University of California at Berkeley). She gave me a good understanding of all the different components that go into the ATLAS project. There’s the hardware team, which includes people who make parts of the detector itself, and there’s the software team, which includes computer programming and the analysis of data.

I love computer programming, so the software is very interesting to me. But I’m intrigued by the hardware as well. I told professor Shapiro that I’d never had any experience in hardware but she said I should pursue that if it’s interesting to me—it’s important to have experiences in all of these areas.

Also, I ran into a problem with my research and I got some help from one of the scientists at CERN. You have to include a variable in your data to account for something called “missing energy,” and I was confused about how you do that. Professor Al Goshaw, my adviser in the Duke internship, referred me to Cong Geng, a postdoc at CERN from the University of Michigan. I emailed him and then we had a discussion about why my research looked the way it did.

This “missing energy” is energy that isn’t detected, but we believe exists based on imbalances we find in the data. It’s a really complicated calculation. Geng looked through my work and we were able to find the bug and he helped me learn more about how the calculations worked. After I got that running, the project started going well. I think it’s going to wrap up nicely in the next two weeks.

I like to work through things for myself but there’s a point where I really should ask for help—especially when there are experts on site. That’s what’s great about being here. We get access to these world-class scientists for all our research needs.


—Matt Cooper