Neutrinos are elusive particles that can traverse nearly all matter without interaction, making them the most prevalent particles in the universe. Despite their abundance, scientists continue to grapple with understanding their properties. A recent study that integrates findings from two prominent neutrino experiments in the United States and Japan offers significant advancements in our knowledge of these mysterious particles.
Neutrinos are generated in extreme environments, such as the core of the sun and during supernova explosions, and they exist in three distinct types, or “flavors.” These particles are capable of changing from one flavor to another in a phenomenon known as oscillation. This latest research provides critical insights into the mass differences between neutrino types, addressing a significant question that has puzzled physicists.
As fundamental particles, neutrinos are not composed of smaller constituents, categorizing them as essential components of the universe. Notably, they possess no electric charge, distinguishing them from other particles like protons and electrons. Understanding neutrinos is crucial because they may hold the key to unraveling several cosmic mysteries, including the origins of matter in the universe, the nature of dark matter and dark energy, and the processes that occur during supernovae.
The NOvA experiment transmits an underground beam of neutrinos approximately 500 miles from the Fermi National Accelerator Laboratory near Chicago to a detector located in Ash River, Minnesota. Meanwhile, the T2K experiment sends a neutrino beam about 185 miles through the Earth”s crust from its source in Tokai, Japan, to another detector in Kamioka. Both experiments focus on neutrino oscillation but utilize varying energies, distances, and detector designs.
By merging nearly a decade of observations from both NOvA and T2K, researchers have made notable progress in understanding neutrinos, as detailed in a study published recently in the journal Nature. “Initially, there were concerns about the compatibility of the T2K and NOvA results. We have found that they are indeed very compatible,” stated Kendall Mahn, a physicist at Michigan State University and a co-spokesperson for the T2K team.
One of the longstanding challenges in neutrino research is determining the masses of the three neutrino types and identifying which is the lightest, a concept known as “neutrino mass ordering.” “Although we still need to wait before we can determine which neutrino is the lightest, this study has measured the small mass gap between two of the three neutrinos with remarkable precision—less than 2% uncertainty—making it one of the most accurate measurements recorded,” commented Zoya Vallari, a physicist at Ohio State University and a member of the NOvA collaboration.
The two experiments are also investigating whether neutrinos and their counterparts, known as antineutrinos, oscillate differently. This inquiry is particularly significant as it may shed light on a fundamental mystery in physics: the dominance of matter over antimatter in the universe. According to Vallari, “At the moment of the Big Bang, matter and antimatter should have existed in equal proportions and annihilated one another. However, matter prevailed, and our existence stems from that imbalance.”
Addressing these essential questions about the universe requires extremely precise measurements and statistical validation. Vallari notes that another generation of large-scale neutrino experiments is on the way. The DUNE experiment, led by Fermilab, is currently under construction in Illinois and South Dakota. Additionally, the Hyper-Kamiokande project is underway in Gifu Prefecture, Japan. Other initiatives, such as the JUNO project in China and telescopes like KM3NeT and IceCube that detect cosmic neutrinos, are also in progress.
“Neutrinos possess unique characteristics, and there remains much to learn about them,” Mahn remarked.
