Physicists are on the cusp of making significant strides toward answering some of the most fundamental questions about the origins of the universe. At the heart of this research lies the study of neutrinos—tiny, elusive particles that pass through virtually everything at nearly the speed of light. These particles are abundant in the universe, yet their behavior remains one of the biggest mysteries in modern physics. Researchers like University of Cincinnati Professor Alexandre Sousa are at the forefront of global efforts to explore the behavior of neutrinos, with the goal of unlocking deeper insights into the nature of reality itself.
Neutrinos, although small and nearly undetectable, are the most abundant particles with mass in the universe. They are produced through processes such as nuclear fusion in stars, radioactive decay in Earth’s crust, and even in particle accelerators in laboratories. As they travel through space, neutrinos can oscillate or switch between three different types or “flavors”—electron, muon, and tau neutrinos. This phenomenon has intrigued scientists for decades, as it suggests that neutrinos possess properties that do not align with the predictions made by the Standard Model of particle physics.
While neutrinos were once thought to be massless, experimental evidence has shown that they do, in fact, have mass, albeit an incredibly tiny one. But some unexpected findings have led physicists to consider the possibility of an entirely new type of neutrino—a so-called sterile neutrino. Unlike the three known flavors of neutrinos, a sterile neutrino would interact only with gravity and not with the weak nuclear force, strong nuclear force, or electromagnetic force. This characteristic has made sterile neutrinos a focal point for research, as their existence could potentially reveal new physics beyond the Standard Model.
In a recent white paper published in the Journal of Physics G: Nuclear and Particle Physics, Sousa and his colleagues, including UC Professors Jure Zupan and Adam Aurisano, outline the directions of neutrino research in the coming decade. The paper is part of the Snowmass 2021/2022 exercise, which brings together particle physicists every ten years to plan future research priorities in the field. In their white paper, the authors discuss several key experiments and the potential for discovering new phenomena in neutrino physics.
One of the central questions driving neutrino research is the matter-antimatter asymmetry in the universe. According to the Big Bang theory, the universe should have produced equal amounts of matter and antimatter. Yet, the universe today is predominantly made up of matter, with only trace amounts of antimatter present. This imbalance remains one of the greatest unsolved mysteries in cosmology and particle physics. Neutrinos could hold the key to understanding this asymmetry, as their behavior may provide insights into why the universe is made primarily of matter.
Sousa is actively involved in one of the most ambitious neutrino experiments in the world—the Deep Underground Neutrino Experiment (DUNE). DUNE is being conducted by the Fermi National Accelerator Laboratory (Fermilab) and represents a massive international collaboration. The experiment aims to investigate neutrino properties by sending a beam of neutrinos through the Earth to detectors located deep underground. These detectors are placed far below the surface to shield them from cosmic rays and background radiation, which could interfere with the delicate measurements needed to study neutrinos.
The DUNE experiment is set to begin in 2029, with initial tests using atmospheric neutrinos. But by 2031, the experiment will take a major step forward when Fermilab shoots a high-energy neutrino beam 800 miles through the Earth, from Illinois to the South Dakota site. This powerful beam will allow researchers to conduct groundbreaking experiments, testing hypotheses about neutrino behavior and exploring the potential existence of sterile neutrinos. DUNE is poised to be the most advanced neutrino experiment ever conducted, with some of the brightest minds in physics collaborating to unlock the mysteries of these elusive particles.
In addition to DUNE, several other high-profile neutrino experiments are currently underway. One of these is the NOvA experiment, also conducted at Fermilab, which focuses on neutrino oscillations—the process by which neutrinos change flavor as they travel. The NOvA experiment has already made significant contributions to the field, including the most precise measurements of neutrino mass to date. Sousa and Aurisano are actively involved in this project, which complements the research being done at DUNE by focusing on different aspects of neutrino behavior.
Another major project on the horizon is the Hyper-Kamiokande (Hyper-K) neutrino observatory in Japan. Expected to begin operations in 2027, Hyper-K will search for sterile neutrinos and conduct experiments that could lead to groundbreaking discoveries in particle physics. When combined with the findings from DUNE, Hyper-K has the potential to revolutionize our understanding of neutrinos and the fundamental forces that govern the universe.
The next decade in neutrino research is poised to deliver exciting and potentially transformative discoveries. Multibillion-dollar projects like DUNE, NOvA, and Hyper-K represent the cutting edge of particle physics, and their success could lead to answers to some of the most profound questions in science. What is the nature of dark matter and dark energy? Why does the universe contain more matter than antimatter? Could there be entirely new particles, like sterile neutrinos, that defy current theories?
For researchers like Sousa, these questions are more than just theoretical curiosities—they are deeply tied to our understanding of the universe and our place in it. By studying neutrinos, scientists hope to answer fundamental questions about the origins of the universe, the forces that govern its evolution, and the nature of matter itself. As Sousa put it, “Neutrinos seem to hold the key to answering these very deep questions.”
The global collaboration on neutrino research is an inspiring example of how science can unite people from all over the world in the pursuit of knowledge. With thousands of scientists, engineers, and students involved in these experiments, neutrino physics is a truly international endeavor. In the coming years, as new data from DUNE, Hyper-K, and other experiments become available, the world will be watching closely, eager to see how these tiny, elusive particles will help answer some of the most profound questions about the universe.
Source: University of Cincinnati