Inside Rensselaer
Volume 7, No. 13, September 13, 2013

photomultiplier tubes in the Daya Bay detector

The Daya Bay Neutrino Experiment is designed to provide new understanding of neutrino oscillations that can help answer some of the most mysterious questions about the universe. Shown here are the photomultiplier tubes in the Daya Bay detectors. Image courtesy of Roy Kaltschmidt

Results from Daya Bay: Tracking the Disappearance of Ghostlike Neutrinos

The international Daya Bay Collaboration, which includes researchers from Rensselaer Polytechnic Institute, has announced new results about the transformations of elusive, ghostlike neutrinos, particles that carry invaluable clues about the makeup of the early universe. The latest findings include their first data on how neutrino oscillation—in which neutrinos mix and change into other “flavors,” or types, as they travel—varies with neutrino energy, allowing scientists to measure a key difference in neutrino masses known as “mass splitting.”

The new results are based on four times the data, with twice the precision, of the first Daya Bay results released last year, which established the value of the third and final neutrino “mixing angle.” Mass splitting represents the frequency of neutrino oscillation. Mixing angles, another measure of oscillation, represent the amplitude. Both are crucial for understanding the nature of neutrinos.

Understanding the subtle details of these neutrino oscillations and other properties of these shape-shifting particles may help answer some of the most mysterious questions about the universe.

Rensselaer researchers and students, led by Professor of Physics, Applied Physics, and Astronomy James Napolitano, have led the design, installation, and commissioning of the large-scale water purification system needed to shield the antineutrino detectors from cosmic ray and radioactive backgrounds.

“After more than a year of careful calibrations and detailed study, we are releasing results that show the antineutrino spectrum shape is completely consistent with the rate at which they transform,” Napolitano said. “Electron antineutrinos indeed ‘disappear’ with the appropriate dependence on distance and, separately, with energy, as predicted by the phenomenology known as ‘neutrino oscillations.’”

From Rensselaer, Physics Professor Paul Stoler, research engineer James Wilhelmi, doctoral student Neill Raper, and a large group of undergraduate students all contributed to the project.

The Daya Bay Experiment is located close to the Daya Bay and Ling Ao nuclear power plants in China, 55 kilometers northeast of Hong Kong. The Daya Bay Collaboration includes more than 200 scientists from six regions and countries.

For additional background information on the Daya Bay Neutrino Experiment, visit the experiment’s website at



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Inside Rensselaer
Volume 7, Number 13, September 13, 2013
Rensselaer Polytechnic Institute
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