Bread, backpacks, and bosons — a summer at CERN

Caitlin Gainey and some of her Yale friends spent the summer in Europe hiking in the mountains, strolling through medieval villages — and searching for subatomic particle collisions that few humans have ever seen.

Gainey, a Yale College senior studying astrophysics, along with fellow Yale seniors Dawson Thomas, Matthew Murphy, and Alexandra Haslund-Gourley, conducted critical research at one of the world’s most important physics hubs — the Large Hadron Collider at CERN (the European Organization for Nuclear Research), located just outside Geneva, Switzerland. They were part of a science team led by Sarah Demers, a physics professor in Yale’s Faculty of Arts and Sciences.

The Large Hadron Collider — the world’s biggest particle accelerator, located in a giant underground compound — restarted in mid-summer after four years of upgrades. Physicists use the facility to test theories about the fundamental laws of physics, from the composition of space and time to the relationship between quantum mechanics and general relativity.

The Yale students’ job was to analyze test collisions of subatomic particles, look for specific particles such as Z bosons and J/Psi particles, and create visual displays of the collisions. The work involved an intensive amount of physics knowledge, computer coding, and graphics expertise.

Their visit coincided with the 10^th anniversary of the discovery of the Higgs boson, a fundamental particle on the order of an electron or quark, a landmark moment celebrated by CERN scientists in July. During the same month, CERN announced the discovery of three new particles — a pentaquark and two tetraquarks — using a more powerful accelerator beam.

Event displays created by the Yale students, which illustrated specific particle collisions, were a prominent part of the announcement.

“It was an exciting time to be at CERN, and these students were in the thick of it,” said Demers, a CERN associate research scientist, collaborator with the ATLAS experiment at LHC, and part of the international research team that discovered the Higgs boson (along with fellow Yale physicists Keith Baker and Paul Tipton).

“I’m incredibly impressed with what they accomplished,” she said.

Meet the team

The physics foursome from Yale College arrived in Switzerland in May, boasting a variety of science skills and research interests.

Haslund-Gourley, who hails from Santa Barbara, California, has been passionate about physics since grade school. She’d previously completed a physics internship at the Fermilab facility in suburban Chicago, and she hosts a science podcast, “Extended Office Hours,” on Spotify.

Thomas, who is from the Atlanta suburbs, studies physics and mathematics, with a special interest in using geometric and topological machine learning methods to explore particle physics.

Gainey, like Haslund-Gourley, grew up in Santa Barbara. She’d already worked at three science labs during her time at Yale — two of them were labs focused on astronomy research and one was working in particle physics. Her research interest is in applying data science techniques to both fields.

Murphy, a member of the Yale rowing team from Portland, Oregon, had no previous lab experience before he emailed Demers, his former professor in PHYS 200, to ask about research opportunities in her campus lab. She told him she could do that — or he could just come to Switzerland.

“This was my first time doing research,” Murphy said. “I didn’t know what to expect.”

They arrived at their rented apartment outside Geneva during a driving rainstorm the third week of May. Their digs were just a 10-minute train ride to CERN.

With Demers guiding the way, they quickly got to work.

‘This magical land’

The Yale undergrads entered the CERN scene amid a wave of activity. The Large Hadron Collider, first fired up in 2008, was starting its third extended run of particle collisions with a series of test collisions.

Their assignment was two-fold: pick out interesting collision “events” from the early data that would indicate whether the detector was working properly and develop visual displays of those events, showing particles and energy deposits from the accelerator.

They spent weeks learning about the workings of the Large Hadron Collider itself, and then familiarizing themselves with computing tools they would use to access test data and write code to identify collision event candidates.

“I remember sitting in the apartment with Dawson on a Friday night in the middle of June, writing code that wasn’t quite working,” Murphy said. “Then, suddenly, it began to work perfectly. It was awesome.”

“I felt so lucky,” said Haslund-Gourley. “I’d grown up always wanting to work at CERN, this magical land where physicists learn about the forces and particles that make up the universe.”

On July 5, the students were on hand for the first collisions using the collider’s “stable beam,” which reached a world-breaking energy level of 13.6 TeV (tera electron volts). They watched a livestream broadcast of collisions, listened to music — and waited to run their code.

“Once we started, it was a race against time, with some of the best physicists in the world reviewing everything we did,” Gainey said.

“It was an exciting kind of pressure,” Thomas said. “They needed the event displays as soon as possible.”

One of their first visualizations was used almost immediately in a scientific lecture for the 2022 International Conference on High Energy Physics. It was the first slide in the presentation, in fact.

“That was incredibly validating,” Haslund-Gourley said.

A job well done

By all accounts, the group’s work was successful.

“Our students identified the only publicly available candidates for event displays from ATLAS and they have been thanked and highlighted regularly in collaboration-wide presentations,” Demers said.

Aside from their assigned projects, the students said they enjoyed being immersed in an intense, scientific environment far from home. Haslund-Gourley, for example, said she felt inspired by the international nature of collaborations at CERN; Thomas was happy he got the chance to meet some of the physicists he idolized from “Particle Fever,” the 2013 film documentary that inspired him to pursue physics in the first place.

In their off-hours, the students hiked in the Jura mountains, toured rustic villages in France, and explored the sights in Vienna, Budapest, Munich, and Bern. There were ample opportunities to sample local cuisine, too.

“A lot of bread was consumed,” Gainey said.

As for the future, Gainey said she’ll continue her CERN work while at Yale this year, making it the basis of her senior project. Thomas, meanwhile, thinks he’s found a “serendipitous” way to bring topological machine learning methods to bear on particle physics.

Haslund-Gourley, for her part, was inspired by the data science and machine learning techniques used to process collision data at CERN and hopes to apply similar analysis techniques to neurological data.

And Murphy? After a summer at CERN, he says he’s got the research bug, big-time. “I never felt stressed,” he said. “We all just hung out, did our jobs, and made it work. I know I’ll continue to work at CERN for my thesis.”