Search for Neutrinoless Double-β Decay in ^{76}Ge with the Majorana Demonstrator

Area of Science:

• Nuclear physics
• Particle physics
• Astroparticle physics

Background:

• Neutrinoless double-beta decay is a hypothesized rare nuclear process.
• Observing this decay would indicate neutrinos are Majorana particles.
• The Majorana Demonstrator searches for this decay in Germanium-76.

Purpose of the Study:

• To search for neutrinoless double-beta decay in Germanium-76.
• To establish a lower limit on the half-life of this decay.
• To constrain the effective Majorana neutrino mass.

Main Methods:

• Utilized an array of high-purity Germanium detectors.
• Operated the Majorana Demonstrator at the Sanford Underground Research Facility.
• Collected data during construction, commissioning, and initial operations.

Main Results:

• Achieved an energy resolution of 2.5 keV FWHM at Qββ.
• Recorded 9.95 kg yr of enriched Germanium exposure with no candidate events.
• Established a lower limit on the half-life of 1.9×10^25 yr (90% C.L.).

Conclusions:

• Constrained the effective Majorana neutrino mass to below 240-520 meV.
• Achieved a low background rate of 4.0 counts/(FWHM yr) in the lowest background configuration.
• The results advance the search for physics beyond the Standard Model.