Collision Course

Members of the Tufts ATLAS team at CERN under the Big European Bublle Chamber (BEBC), particle detectors used in the 1970s for measurements at CERN. Clockwise from top: Raphael Osorio, A15, Noah Kurinsky, A14, Lesya Horyn, A15, Professor Hugo Beauchemin, postdoctoral associate Evelin Meoni, and graduate student Hyungsuk Son. (Photo: Genevieve Du Paul)

Assistant Professor of Physics Hugo Beauchemin and members of the Tufts ATLAS Group—part of an international collaboration comprising thousands of physicists and students—spent the past summer at the European Organization for Nuclear Research (CERN) in Geneva, Switzerland. A scientific laboratory, CERN currently houses the Large Hadron Collider (LHC), the world's largest and most powerful particle accelerator.

"The LHC takes the building blocks of nature, the smallest elements we call particles, and brings them to very high energy before colliding them," explains Beauchemin. "It's like a large microscope, but instead of shedding light onto a small object, we use a probe, a tiny particle, which we throw at another particle at high energy, and we are able to see smaller particles interact."

The ATLAS team at CERN in front of the building housing the ATLAS control room, where the data-taking of ATLAS is controlled. The detector is located about 80m underneath the building. (Photo: Genevieve Du Paul)

The ATLAS Group, in which Tufts has participated since the project's inception in 1996, is named for one of the two general-purpose detectors built on the ring of the LHC; ATLAS measures the interactions brought about by the LHC. The current group includes Beauchemin; professors Krzysztof Sliwa and Austin Napier, who specialize in experimental high energy physics; postdoctoral associate Evelin Meoni; graduate students Hyungsuk Son and Jeffrey Wetter; undergraduates Lesya Horyn, A15, Raphael Osorio, A15, Noah Kurnisky, A14 (recipients of Tufts International Research Program grants), and George Wojcik, A15, who was accepted into the 2014 US-CERN Summer Student program.

"We are trying to understand our world and the whole universe from the point of view of the possible interactions of the fundamental particles," explains Beauchemin. "To do this, we attempt to answer questions about the origin of the mass carried by things and why we 'see' only 5% of the energy composing our universe." None of these questions, adds Beauchemin, finds an answer in The Standard Model (SM), the current theory that describes the possible interactions with all particles known to date. "While being the most successful theory we have in physics, the Standard Model cannot be the end of the story," explains Beauchemin. "It does not account for the dark matter inferred from astrophysical observations, nor does it makes sense of gravity at the particle level, two of the most fundamental problems in high energy physics." 

Near the ATLAS control room, Professor Beauchemin introduces the team to a display on evidence for dark matter from astrophysical observations, the subject of one of Professor Beauchemin's research projects that students are working on. (Photo: Genevieve Du Paul)

By colliding tiny particles at unprecedented energies with the accelerators, and studying the product of these collisions with the detectors, the investigators look for deviations with respect to the Standard Model, taking precise measurements of the aspects of the Standard Model that are not accurately known. "I use collision data to look for extra dimensions of space, and for dark matter particles, the discovery of which would explain many of the current mysteries about the universe," says Beauchemin. 

The research requires writing computer programs to perform these measurements, and both graduate and undergraduate students are required to adapt, refine and debug the programs in order to perform data analysis. "The process of analyzing data is not an easy one," says Beauchemin. "We first used simulation to determine which physics quantity is the most sensitive to the new physics of interest, such as dark matter and extra dimensions," says Beauchemin. Then, they must measure these quantities in data and compare them to the theoretical predictions. "To do so, we have to remove something called 'background data', events which look like what we want to measure, but are of a different nature, therefore polluting our results if we don't remove them," he says. "The biggest challenge is to remove them properly without making the results biased."

Beauchemin selected students who expressed interest in research or who were already participating in other research projects at Tufts to work at CERN. "Many students were interested in doing a project with me after they learned what I was working on," he says. I am very keen to do research with undergrads because it is very important for their education. They do very good work, so their work is useful to me as well. It's a win-win situation."

There is a great collegiality among members of the Tufts ATLAS team. "The undergraduate students have rapidly found their place in our group," says Beauchemin, "an essential foundation on which to build ambitious projects."

Lesya Horyn, A15, is a recipient of the Steven J. Eliopoulos and Joyce J. Eliopoulos Summer Scholar Award. "I was originally drawn to high energy physics because it is a wonderful marriage of what I love about physics and the skills I have enjoyed honing throughout my undergraduate career, " says Horyn. "I'm hoping to go to graduate school for a Ph.D. in experimental high energy physics next year, so working on a project in the field, particularly at CERN, is an incredible opportunity."

George Wojcik, A15, a participant in the 2014 US-CERN Summer Student program, in front of the ATLAS detector

George Wojcik, A15, was excited about his work with CERN research physicist David d'Enterria, who is investigating measurement of the direct coupling of the Higgs boson, an elementary particle discovered at CERN in 2012, to the electron with a high-luminosity, high-precision machine. The team plans to publish their findings in this fall.

For Wojcik, CERN provided the opportunity to learn by examining the many different approaches to problem solving to which he was exposed. "Having experts such as the original software programmers on hand made the experience 'colossally useful,'" says Wojcik. "When I ran into a problem I lacked the general knowledge to solve, they were readily available to talk." Beyond the technical learning, Wojcik enjoyed working with researchers from Swaziland, Singapore, India, the Czech Republic, and visiting Albert Einstein's house in Bern. "Einstein lived there during his 'miracle year,'" says Wojcik, "during which he published his papers on the photoelectric effect, special relativity, Brownian motion, and mass-energy equivalence."

Geneva provides an incredible research opportunity for the students, says Beauchemin. "Our experience allows us to collaborate with many experts on different matter relevant to our work," says Beauchemin. Along with participating in the experiment, data taking and service activities, students can attend the CERN summer student lecture programs where experts in the field explain particle physics in simple and accessible terms. "It is really a unique experience for them," says Beauchemin, "and always enriching for me to participate in a large scale international collaboration."