Billions of neutrinos stream through our bodies every second, and yet we don’t fully understand them. 

As part of the international NOvA collaboration, William & Mary scientists are one step closer to unraveling the mysteries of neutrinos, with new results recently presented at the Neutrino 2024 conference.

Neutrinos are created every time atomic nuclei split or fuse. They travel through matter without leaving any trace, with an absolute mass so small that physicists cannot measure it yet.

“But we can tell that the three different neutrinos have different masses, and we can measure the differences between the masses,” said W&M Professor of Physics Patricia Vahle, spokesperson for the NOvA experiment at the U.S. Department of Energy’s Fermi National Accelerator Laboratory (Fermilab).

In its first large update since the COVID-19 pandemic, new NOvA results suggest there are two lighter neutrinos and a heavier one. This is what theory posits as the “normal” mass ordering versus a possible “inverted” ordering of two heavier neutrinos and a lighter one.  While the results are more precise than earlier measurements, the determination of the ordering is still not at the high threshold scientists require for certainty.

“Neutrinos are the most abundant matter particle in the universe, so even tiny masses add up,” said Vahle. “Knowing the ordering of the masses is critical for understanding this fundamental particle and could help us understand the evolution of the universe.”

At William & Mary, Vahle is one of three High Energy Physics faculty members, who all play critical roles in the study of neutrinos. With professors Mike Kordosky and Jeff Nelson, W&M has a long history of studying neutrinos and is involved in planning the next generation neutrino oscillation experiment, the Deep Underground Neutrino Experiment or DUNE, the largest experiment of its kind and one of the highest priorities for particle physics.

Vahle’s group has been working with the NOvA experiment since 2008. Current Ph.D. student Jozef Trokan-Tenorio was heavily involved in putting together the latest results; W&M undergraduates’ work over the years has fed into the infrastructure supporting NOvA measurements. 

W&M physicist Erika Catano-Mur, a postdoctoral research associate and co-leader of the analysis, described neutrinos as “fundamental but weird.” They are among the most abundant matter particles in the universe, but they are also extremely light and electrically neutral, only rarely and weakly interacting with other matter.

“Streams of neutrinos are being made in the sun all the time, in cosmic ray interactions in our atmosphere, in the nuclear power plant across the river,” said Vahle. “They are an intrinsic, fundamental part of what’s going on around us.”

The NOvA experiment generates an intense beam of neutrinos at Fermilab in Illinois.  Scientists measure the beam first in a near-detector at Fermilab, then again after the beam travels straight through the Earth to a far-detector in Minnesota. Differences in the measurements at each location prove that neutrinos are changing their type (or flavor), a phenomenon known as oscillation.

Catano-Mur, who is presenting results to the Fermilab community on Friday, June 28, said it is quite exciting to see where the field is, with all the potential for the next few years.” 

NOvA scientists, said Vahle, aim to double their dataset of antineutrinos by 2027. They hope to provide more conclusive evidence of the neutrino mass ordering and gain an even better understanding of their oscillation properties.

, Senior Research Writer