University of Cincinnati Professor Alexandre Sousa helped outline the next 10 years of global research into the behavior of neutrinos, particles so tiny that they pass through virtually everything by the trillions every second at nearly the speed of light.
They are created by nuclear fusion reactions in the sun, radioactive decay in nuclear reactors or the Earth's crust or in particle accelerator labs. As they travel, they can transition between one of three types or "flavors" of neutrinos and back.
But unexpected experimental results made physicists suspect there might be another neutrino flavor, called a sterile neutrino because it appears immune to three of the four known "forces."
"Theoretically, it interacts with gravity, but it has no interaction with the others, weak nuclear force, strong nuclear force or electromagnetic force," Sousa said.
In a new white paper published in the Journal of Physics G, Sousa and his co-authors discuss experimental anomalies in neutrino exploration that have baffled researchers.
Their collective vision is articulated and confronted with science funding scenarios by the Particle Physics Project Prioritization Panel, or P5, whose final report issued in 2023 made direct recommendations to Congress about funding the projects.
"Progress in neutrino physics is expected on several fronts," co-author and UC Professor Jure Zupan said.
Besides the search for sterile neutrinos, Zupan said physicists are looking at several experimental anomalies - disagreements between data and theory - that they will be able to test in the near future with the upcoming experiments.
One question is why the universe has more matter than antimatter if the Big Bang created both in equal measure. Neutrino research could provide the answer, Sousa said.
"It might not make a difference in your daily life, but we're trying to understand why we're here," Sousa said. "Neutrinos seem to hold the key to answering these very deep questions."
Sousa is part of one of the most ambitious neutrino projects called DUNE or the Deep Underground Neutrino Experiment conducted by the Fermi National Accelerator Laboratory. Crews have excavated the former Homestake gold mine 5,000 feet underground to install neutrino detectors. It takes about 10 minutes just for the elevator to reach the detector caverns, Sousa said.
Researchers put detectors deep underground to shield them from cosmic rays and background radiation. This makes it easier to isolate the particles generated in experiments.
"With these two detector modules and the most powerful neutrino beam ever we can do a lot of science," Sousa said. "DUNE coming online will be extremely exciting. It will be the best neutrino experiment ever."
The paper was an ambitious undertaking, featuring more than 170 contributors from 118 universities or institutes and 14 editors, including Sousa.
"It was a very good example of collaboration with a diverse group of scientists. It's not always easy, but it's a pleasure when it comes together," he said.
Meanwhile, Sousa and UC Associate Professor Adam Aurisano are involved in another Fermilab neutrino experiment called NOvA that examines how and why neutrinos change flavor and back. In June, his research group reported on their latest findings, providing the most precise measurements of neutrino mass to date.
Another major project called Hyper-Kamiokande, or Hyper-K, is a neutrino observatory and experiment under construction in Japan.
"That should hold very interesting results, especially when you put them together with DUNE. So the two experiments combined will advance our knowledge immensely," Sousa said. "We should have some answers during the 2030s."
Research Report:White paper on light sterile neutrino searches and related phenomenology
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