Scientists working on the Short-Baseline Near Detector (SBND) at Fermi National Accelerator Laboratory have identified the detector’s first neutrino interactions.
The SBND collaboration has been planning, prototyping, and constructing the detector for nearly a decade. After a few months of carefully turning on each of the detector subsystems, they achieved their long-awaited goal.
“It isn’t every day that a detector sees its first neutrinos,” said David Schmitz, co-spokesperson for the SBND collaboration and associate professor of physics at the University of Chicago. “We’ve all spent years working toward this moment and this first data is a very promising start to our search for new physics.”
SBND completes Fermilab’s Short-Baseline Neutrino (SBN) Program and will play a critical role in solving longstanding mysteries in particle physics. The construction was an international effort involving 250 physicists and engineers from Brazil, Spain, Switzerland, the United Kingdom, and the United States.
The Standard Model is currently the best theory explaining fundamental particles and forces but remains incomplete. Over the past 30 years, multiple experiments have observed anomalies hinting at a potential new type of neutrino.
Neutrinos are abundant yet difficult to study due to their weak interactions with matter. They come in three types: muon, electron, and tau. These particles can oscillate between these types as they travel.
Previous experiments showed discrepancies in expected versus observed neutrino counts. “That could mean that there's more than the three known neutrino flavors,” explained Fermilab scientist Anne Schukraft. “Unlike the three known kinds of neutrinos, this new type wouldn’t interact through the weak force.”
Fermilab's Short Baseline Neutrino Program aims to search for such oscillations using SBND as its near detector and ICARUS as its far detector. A third detector called MicroBooNE also contributed by recording particle collisions until 2021.
The SBN Program's design allows precise measurement comparisons between near-source and post-oscillation neutrinos without assumptions about initial beam composition. “Understanding anomalies seen by previous experiments has been a major goal in the field for the last 25 years,” said Schmitz.
Beyond searching for new neutrinos alongside ICARUS, SBND offers an extensive physics program due to its proximity to Fermilab’s beamline—seeing 7,000 interactions per day. This data will help future experiments like DUNE better understand complex argon-neutrino interactions.
“We will collect 10 times more data on how neutrinos interact with argon than all previous experiments combined,” said Ornella Palamara, Fermilab scientist and co-spokesperson for SBND.
SBND may also detect other phenomena outside of standard particle models potentially linked to dark matter—a major unsolved question in physics. Lightweight theoretical particles might be produced in Fermilab’s beam providing insight into these dark sector models.
“These neutrino signatures are only the beginning for SBND,” added Palamara. The collaboration will continue operating and analyzing millions of collected interactions over several years.
“Seeing these first neutrinos is just the start,” she concluded.
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