Underwater neutrino testing in Lake Superior, Lake Vermilion to begin this fall

Underwater neutrino testing in Lake Superior, Lake Vermilion to begin this fall Novel underwater detection experiment will continue Minnesota’s legacy of neutrino research From October 2026 through approximately April 2027, a team of university and government researchers will conduct experimental testing to observe neutrino interactions in Lake Superior and Lake Vermilion. The goal of the Experimental Neutrino Detector (END) project is to develop a complete baseline system capable of detecting and distinguishing a beam of neutrinos generated at Fermi National Accelerator Laboratory (Fermilab) from the cosmic background neutrinos and other noise sources in shallow bodies of water. END will place underwater neutrino detectors on the lakebed in the path of the Fermilab neutrino beamline as it passes through Lake Superior near Two Harbors, Minnesota, on its way north to previously established neutrino detector sites at Soudan (Lake Vermilion) and Ash River, Minnesota. Neutrinos are among the most abundant particles in the universe, a billion times more abundant than the particles that make up stars, planets and people. Unimaginably large numbers of neutrinos from the first moments of the universe are still present today. Though a trillion naturally occurring neutrinos from the sun and other bodies in the galaxy pass through us each second, they interact so rarely with other particles that they are very difficult to detect. That is why researchers strive to create intense beams packed with as many neutrinos as they can produce and to build large, precise detectors that can spot them when they interact. For more about neutrinos, watch this video from the University of Minnesota Duluth (UMD). Unique opportunity in Minnesota The END experiment aims to take advantage of the fact that the existing Fermilab NuMI (Neutrinos at the Main Injector) beam runs through Lake Superior and through Lake Vermilion. The experiment aims to learn about and prove the concept for using natural waters to observe very rare events from neutrino beams and distinguish them from cosmic rays and other backgrounds before this beamline is decommissioned later in 2027. Scientists have successfully observed natural neutrinos in large bodies of water or ice in the IceCube (Antarctica), Baikal (Siberia), and KM3Net (Mediterranean) experiments. Artificially produced neutrino beams have also been studied in many experiments, including MINOS and NOvA further north in Minnesota. However, due to technological limitations, no one has observed laboratory produced neutrinos in a large natural body of water. The END detectors deployed in Lake Superior will use underwater photosensors developed by the KM3Net collaboration, currently used in two sites deep in the Mediterranean Sea. Unlike the deep-sea experiments in the Mediterranean — where sensors are deployed in long vertical strings — the shallower Lake Superior experimentation design involves attaching sensors to underwater frames that are placed on the lake floor. The Lake Vermilion detectors will utilize a different neutrino detection technology. These detectors will be large metal cylinders lined with printed plastic scintillators which emit light when struck by muons, enabling the detection of neutrinos that interact in the surrounding environment. Preparation and deployment of sensors In September, construction is expected to begin on five 10m (33ft.) tall metal frames at Berth 11 on the Clure Terminal Expansion pier in Duluth. Once the frames are constructed, 18 spherical neutrino detectors — called Digital Optical Modules (DOM) — will be mounted to each frame. Each DOM has a diameter of 43cm (17in.), about the size of an inflated beach ball. In November, the R/V Neil Armstrong, a 73m (238ft.)-long research vessel from the Woods Hole Oceanographic Institution (WHOI) is scheduled to arrive at Berth 11. The R/V Neil Armstrong has a shipboard crane with capacity to hoist the frames and mounted sensors onto the ship’s deck and ferry them to a point several miles offshore Two Harbors aligned with the Fermilab neutrino beam. The frames will be lowered by ship-board crane and placed on the lakebed. The R/V Neil Armstrong will then lay fiberoptic cables connecting each frame to shore where the cables will terminate at a temporary hut with fiber transmission equipment near the Two Harbors water treatment plant. The R/V Neil Armstrong will be located offshore from the water treatment plant as it makes cable-laying trips from the deployment site to shore. A different type of neutrino detector will be deployed to the bottom of Lake Vermilion near Tower, Minnesota. Ten tanks, each measuring 2.5m (8ft.) tall and 6.4m (21ft.) long, will contain two flat panel neutrino detectors per tank. Clump weights will be deployed to the lake floor in the fall of 2026 to allow them to settle. Later, the tanks will be towed by a barge into position and attached to the weights where they will sit on the lakebed aligned with the Fermilab neutrino beam. Deployment of these detectors is expected to begin in mid to late October and take roughly one month, followed by several months of data collection. The detectors will be removed in late Spring/early summer of 2027 as lake conditions permit. Fermilab is working closely with local contractors, state agencies, lake authorities, and Minnesota residents, whose support and collaboration are essential to the success of this effort. The END preparations and testing period are not expected to impact daily life for local populations, cause noise pollution, or interfere with local businesses or recreational lake activity. How detection works When a neutrino from the NuMI beam occasionally strikes an atom in water, the resulting visible particles travel approximately 10m (33ft.) and stop. This creates a faint blue light as the particles pass through the clear Lake Superior water, which the photosensors detect and relay back to shore via an underwater fiber optic cable. END will operate at night, as enough daylight reaches the lake floor to overwhelm the faint particle flashes. It is estimated that END will detect several NuMI beam neutrinos per day of beam operations. The particles travelling through the water can also be detected using scintillators, as will be demonstrated with the Lake Vermilion experiment. Particles produced by neutrinos interacting with the water will travel through the plastic scintillator panels inside the pods on the lake floor. These particles will cause the scintillator to produce flashes of light that can be collected and detected by photosensors. The path the particle takes through the panels can be tracked and used to discriminate those particles from background events. Because the panels will be in light-tight containers and therefore not bothered by sunlight, these detectors will operate 24 hours a day. Sponsorship The END project is sponsored by the Defense Advanced Research Projects Agency (DARPA) in close cooperation with the Department of Energy (DoE) Office of Science, Fermi National Accelerator Laboratory, and Brookhaven National Laboratory. Conducting the research is a team comprising scientific experts from the University of Minnesota Duluth, University of Wisconsin, Drexel University, and Woods Hole Oceanographic Institution.