Neutrino experiment final results garner a journal’s top download

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A copper and lead shield encases the Majorana Demonstrator’s inner detector. Credit: Nick Hubbard, Sanford Underground Research Facility

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The Majorana collaboration, comprised of more than 60 researchers from 24 institutions and six nations, began a search for neutrinoless double-beta decay in 2015, completing its search in 2021. Observing neutrinoless double-beta decay may help explain the matter/anti-matter imbalance of the universe left unanswered by the Standard Model of Particle Physics — the conundrum of why we live in a world with something, instead of nothing.

Los Alamos National Laboratory played a major role in the experiment, which operated at the Sanford Underground Research Facility in South Dakota. The project required the construction of an ultrasensitive, 30-kilogram, germanium-76 radiation detector shielded by several tons of lead located nearly a mile beneath the surface of the earth and years of data acquisition and analysis. Los Alamos scientists, engineers and technicians were crucial in the development of the project — including design, cryogenics, calibration, construction, operation, analysis and leadership. Steve Elliott (Physics division) served as the collaboration spokesperson for eight years.

With the complete data set, the collaboration was unable to detect the very rare neutrinoless double-decay of germanium-76 but was able to determine that it occurs less than once per 100,000 two-neutrino double-decays. The experiment achieved a world-leading energy resolution, set world-leading limits in other Beyond Standard Model searches and established novel experimental techniques that laid the groundwork for future, larger scale searches. This includes the new, larger LEGEND (Large enriched germanium experiment for neutrinoless double-beta decay) experiment. Los Alamos is also a key member of this new collaboration, contributing to the design and construction of this ton-scale neutrino detector.

Over the project’s lifespan, several young researchers joined the team as postdocs — and their training in the search for rare signatures, in hardware and in analysis allowed a number to convert to staff in a variety of fields at the Laboratory.

Funding and mission

The work was supported by the Nuclear Physics program in the DOE Office of Science. Early research and development for the project and detector technique was supported by Los Alamos’s Laboratory Directed Research and Development program. The efforts in double-beta decay support the Laboratory’s Fundamental Science mission and Nuclear and Particle Futures capability pillar.

Reference

“Final result of the Majorana Demonstrator’s search for neutrinoless double-beta decay in ⁷⁶Ge,” Physical Review Letters, 130, 6, 062501 (2023); DOI: 10.1103/PhysRevLett.130.062501. Authors: Isaac Arnquist et al. (Majorana collaboration). Recent Los Alamos researchers include Steven Elliott, Pinghan Chu, Ralph Massarczyk, Keith Rielage, Danielle Schaper (Dynamic Imaging and Radiography, P-1); Sam Meijer (Advanced Nuclear Technology, NEN-2); B.X. Zhu (formerly LANL, now Jet Propulsion Laboratory); I. Kim (formerly LANL; now Lawrence Livermore National Laboratory).

Related article: “The Majorana Demonstrator gives its final answer about a rare nuclear decay”

Technical contact: Ralph Massarczyk (Physics division)