Double the Data: Neutrino Hunters Nearing Long-Sought Answer in Fundamental Physics
A presentation at the Neutrino 2024 conference in Milan in June 2024 included twice the data since the team comprising Fermilab’s NuMI Off-axis νe Appearance (NOvA) experiment had last presented its findings, meaning that NOvA is well on its way to meeting the high threshold of certainty required to declare a discovery.
By reaching such a high-level threshold, the results are overwhelmingly likely to be evidence of a new phenomenon, not just noise or statistical fluctuations.
While such a declaration wasn’t made in June, the NOvA team—which includes Illinois Tech faculty members Professor Emeritus of Physics Dan Kaplan, Chair and Professor in the Department of Physics Pavel Snopok, Associate Professsor of Physics Yagmur Torun, graduate student Robert Chico (PHYS ’25), and alumni Yiding Yu (PHYS ’24) and Brinden “Bear” Carlson (PHYS ’21)—is quickly approaching the levels of precision necessary to make a definitive statement on the ordering of neutrino masses.
Theoretical models of physics predict two possibilities for neutrino mass ordering—normal and inverted. In the normal ordering, there are two light neutrinos and one heavier neutrino; in inverted, there is one light neutrino and two heavier ones. NOvA’s newest data continues to suggest—consistent with its previous results—that the normal ordering is favored, but more data is needed before the team can definitely make such a declaration.
NOvA sends a stream of neutrinos from a 300-ton underground detector at Fermilab in Batavia, Illinois, to the experiment’s 14,000-ton detector in Ash River, Minnesota, where they’re received and measured. By measuring neutrinos and antineutrinos at both locations, physicists can understand more about neutrino oscillation, or the phenomenon that sees neutrinos change type as they travel.
Physicists are working to determine neutrino mass hierarchy, crucial for understanding neutrino properties and behavior. Neutrinos come in three types: muon, electron, and tau. They oscillate, changing types, with unknown factors governing these oscillations.
Knowledge of the mass hierarchy will also help answer the question of whether neutrinos are their own antiparticles. Particles and antiparticles have opposite charges. Because neutrinos have no electric charge, it is possible that neutrinos and antineutrinos are fundamentally the same.
NOvA physicists compare muon neutrino and antineutrino oscillations to determine the mass hierarchy. The normal hierarchy favors neutrino oscillations, while the inverted hierarchy favors antineutrino oscillations. Clarifying neutrino properties will reveal if they are their own antiparticles and will shed light on the universe’s makeup.
Resolving this mystery will eliminate incorrect theoretical models and deepen our understanding of the cosmos.
The neutrino detector uses 344,000 cells that are filled with liquid scintillator to capture energy bursts when neutrinos strike an atom and release a burst of charged particles. Scientists study the resulting light patterns to understand neutrino properties and determine what kind of neutrino caused the interaction.
While a declaration of discovery has not yet been made by NOvA, the experiment is slated to continue through 2027. By then, the team hopes to double its current antineutrino data set, as well as maximize the experiment’s sensitivity.
Photo: Illinois Tech faculty members (from left to right) Daniel Kaplan, Pavel Snopok, Yagmur Torun, and alumnus Yiding Yu at the NOvA Far Detector in Ash River, Minnesota.
