U.S. to Conduct Underwater Neutrino Detection Tests in Lake Superior and Vermilion Lake

From October 2026 to approximately April 2027, a team of researchers from U.S. universities and government agencies will conduct underwater neutrino tests in Lake Superior and Vermilion Lake. The project, named the Experimental Neutrino Detector (END), aims to validate a baseline detection system in natural water bodies to identify the NuMI neutrino beam produced by Fermi National Accelerator Laboratory and distinguish it from cosmic-ray backgrounds and other noise in shallow-water environments.

END will place underwater neutrino detectors on the lakebed of Lake Superior where the Fermilab neutrino beamline passes through—near Two Harbors, Minnesota. The beamline will continue northward to previously established neutrino detector sites at Soudan Lake (Vermilion Lake) and Ash River in Minnesota. Image credit: University of Minnesota Duluth

The END project will leverage the NuMI beam's passage through the lake region of northern Minnesota by deploying underwater detectors on the lakebed near Two Harbors in Lake Superior. The beam path continues northward, passing through Vermilion Lake in the Soudan area—where neutrino detection stations were previously established—and Ash River, Minnesota. The research team hopes to complete the technical validation of detecting neutrinos produced by the laboratory in natural water bodies before the NuMI beam is retired in 2027.

Neutrinos are elementary particles that are extremely abundant in the universe yet exceedingly difficult to detect. Their probability of interacting with other particles is extremely low, so researchers typically require high-intensity neutrino beams and large-volume, high-sensitivity detectors to capture their rare interactions. Previously, experiments such as IceCube, Baikal, and KM3Net have observed natural neutrinos in large water bodies or ice sheets, while experiments like MINOS and NOvA have studied artificial neutrino beams; however, observing laboratory-produced neutrinos in large natural water bodies remains to be validated.

According to the plan, the Lake Superior detector will employ underwater optical sensors developed by the KM3Net collaboration. Unlike the deep-sea Mediterranean experiment where sensors are deployed along long vertical strings, Lake Superior's relatively shallow depth means sensors will be mounted on metal frames placed on the lakebed. Starting in September, the research team will construct five metal frames approximately 10 meters tall at Pier 11 of the Clure Public Marine Terminal in Duluth, with each frame carrying 18 spherical Digital Optical Modules (DOMs), each approximately 43 centimeters in diameter.

In November, the Woods Hole Oceanographic Institution's research vessel *Neil Armstrong* is scheduled to arrive on site to load the frames and sensors onto the deck and transport them to the lake area near Two Harbors aligned with the Fermilab neutrino beam. The detection frames will be placed on the lakebed and connected via underwater fiber-optic cables to temporary shore-based equipment located near the Two Harbors water treatment plant.

A different type of neutrino detector will be deployed in Vermilion Lake. Researchers plan to place 10 large water tanks on the lakebed near Tower, Minnesota, with each tank approximately 2.5 meters tall and 6.4 meters long, housing two flat-panel neutrino detectors inside. In fall 2026, ballast weights will first be placed on the lakebed, after which barges will tow the tanks into position and secure them so the detectors align with the NuMI beam. Deployment is expected to begin in mid-to-late October, taking approximately one month, followed by several months of data collection; equipment will be removed in late spring to early summer of 2027 once lake conditions permit.

In terms of detection principles, when neutrinos in the NuMI beam occasionally interact with atoms in the water, visible particles are produced. As these particles travel through the clear lake water, they generate faint blue light, which the optical sensors in Lake Superior will capture and transmit back to shore via underwater fiber-optic cables. The research team estimates that during NuMI beam operation, END could detect several neutrino events per day originating from the beam. The Vermilion Lake experiment, by contrast, uses plastic scintillator panels to detect flashes of light produced when particles pass through, distinguishing background events through particle path information; since the detectors are housed in light-tight containers, they can operate around the clock.

The project is funded by the U.S. Defense Advanced Research Projects Agency (DARPA) and conducted in collaboration with the U.S. Department of Energy Office of Science, Fermi National Accelerator Laboratory, and Brookhaven National Laboratory. Participating teams include researchers from the University of Minnesota Duluth, the University of Wisconsin, Drexel University, and the Woods Hole Oceanographic Institution. Project representatives stated that the preparation and testing phases of END are not expected to affect the daily lives of local residents, nor will they cause noise pollution or interfere with local businesses or recreational activities on the lakes.