A photo of a student using a glove box to install tantalum discs in the Majorana Demonstrator detector array at the Sanford Underground Research Facility in Lead, S.D.
By Kim Catley

Deep under a mountain at the Gran Sasso National Laboratory in Italy, physics professor Graham Giovanetti has been contributing to an experiment that could unlock one of the biggest mysteries of the universe.

DarkSide-20k is a collaboration of more than 400 scientists, engineers and technicians, including Giovanetti and several of his students, that seeks to understand dark matter: material that has the gravitational pull to affect and shape the cosmos yet is invisible to telescopes and other astronomical instruments.

Contributors work from labs and universities on nearly every continent. Giovanetti is the only collaborator from a liberal arts college and is partnering with two project teams. Along with U.S.-based researchers, he is constructing the innermost chamber of the dark matter detector. He is also collaborating with researchers in the U.K. and Italy who are developing custom photosensors.

Once construction is complete in 2026, the experimental phase of DarkSide-20k will begin. One of the leading theories contends that dark matter consists of weakly interacting massive particles (WIMPs) that only interact with atoms through gravity or very rare collisions. DarkSide-20k aims to observe these collisions inside the detector, which is filled with 50 tons of liquefied argon. Giovanetti and the other project researchers will spend a decade monitoring the detector, hoping to see a collision between the dark matter and argon nuclei, which will produce a small burst of light. Even just a handful of collisions could provide insights into dark matter, which makes up 85% of the universe—“a transformative discovery,” says Giovanetti, whose work is supported by a $530,000 National Science Foundation grant and a three-year, $1.7-million sub-award as part of an $11.7 million grant to Princeton University.

Even with such a large collaboration, Giovanetti says he saw “opportunities for undergrads to make meaningful contributions to world-leading experiments. In addition, working side by side with undergraduates keeps me engaged directly in day-to-day activities in the lab, which is the part of experimental physics I most enjoy.”

Three of his students have traveled to the U.K. to help produce the custom photosensors using silicon chips that are sensitive enough to detect a single photon. The sensors eventually will be aggregated into larger panels that will cover the entire detector chamber.

Jason Lu ’26, a prospective physics and political science major, and Zoe Kane ’25, who is studying physics and math, spent last summer at Royal Holloway, University of London, where they tested nearly 50 silicon chips to assess their functionality, performance and quality. Kane says using cryogenics and other advanced lab equipment was an invaluable experience. “I was able to quickly pick up on how to use the equipment and not just follow instructions but use it intuitively and have a deep understanding of what I was doing,” she says. “It was a completely different experience from doing a lab in class.”

Michael Bedard ’24, a physics and math major, has spent the spring 2024 semester at the University of Oxford, where he processed image scans from the chips, looking for dust contamination. While he says it was easy to become hyper-focused on his small role, he would remind himself, “The tiles I’m handling will be installed inside a giant tub of [cryogenic liquid] under a mountain in Italy. Suddenly, everything falls into the proper perspective.”

In a related experiment, another team of Giovanetti’s students is working with the Majorana Demonstrator at the Sanford Underground Research Facility in Lead, S.D. Giovanetti, Alex Rouyer ’24 and William Zhang ’22 reconfigured the existing detector, located inside a clean room nearly a mile underground, to try to make the first measurement of the decay of tantalum-180m (Ta-180m). Their work was funded in 2023 by a $100,000 Cottrell Scholar Award from the Research Corporation for Science Advancement, which Giovanetti is also using to support prospective physics majors who might need additional preparation for introductory physics courses.

“Just like DarkSide-20k, the Ta-180m measurement is looking for a signal that is many, many orders of magnitude smaller than the huge particle background rate we find ourselves bathed in on Earth,” Giovanetti says. “It also turns out that the Ta-180m decay rate is sensitive to the presence of dark matter.”

Giovanetti’s exploration of dark matter will continue this summer when he returns to Italy to test the detector. Lu also plans to return to test the photosensor prototype using common electron interactions and to benefit from the guidance of DarkSide-20k collaborators and graduate students. “My mentors showed me that graduate school isn’t just about learning more,” Lu says. “It is just as much about empowering those that come after you to learn in your footsteps.”

For a full overview of the DarkSide-20k project, visit bit.ly/darkside20k.

Photo at top: William Zhang ’22 uses a glove box to install tantalum discs in the Majorana Demonstrator detector array at the Sanford Underground Research Facility in Lead, S.D. Photograph provided by Graham Giovanetti

Photo of writer Kim Catley in front of a kitchen pantry.
Kim Catley is a freelance writer based in Richmond, Va. She previously worked for the University of Richmond and Virginia Commonwealth University and is now a contributor to a number of university magazines.