The Advanced Mo-based Rare Process Experiment (AMoRE) collaboration has made significant progress in the search for neutrinoless double beta decay, a phenomenon that, if detected, could provide key insights into fundamental particle physics.
Highlights
Conducted at the Yangyang Underground Laboratory in Korea, the experiment utilizes molybdate scintillating crystals at extremely low temperatures to capture potential decay signals.
While no definitive evidence of the process was observed, the study established a new upper limit on the half-life of molybdenum-100, refining parameters for future research.
Neutrinoless Double Beta Decay
Neutrinoless double beta decay, if confirmed, would indicate that neutrinos and antineutrinos are the same particle, offering insights into the asymmetry between matter and antimatter in the universe.
The AMoRE collaboration used multiple kilograms of molybdenum-100 in the form of scintillating crystals designed to detect potential signals from this rare nuclear process. This approach represents one of the most sensitive attempts to observe neutrinoless double beta decay.
According to Yoomin Oh, a corresponding author of the study, neutrinos remain among the least understood elementary particles in the Standard Model of physics.
Although their existence was proposed by Wolfgang Pauli nearly a century ago, many of their properties, including their mass, remain unknown. A deeper understanding of neutrinos could help address fundamental questions in cosmology and particle physics.
AMoRE-I Achieves Record Sensitivity
Although neutrinoless double beta decay was not detected, AMoRE-I set a new benchmark for sensitivity in molybdenum-100 measurements.
The experiment achieved an exposure of 8.02 kg·year (or 3.89 kg of $^{100}$Mo·year), with a total background rate near the Q-value of 0.025 ± 0.002 counts/keV/kg/year.
This led to a new half-life constraint for $^{100}$Mo neutrinoless double beta decay at $T^{0\nu}_{1/2} > 3.0 \times 10^{24}$ years (90% confidence level).
The effective Majorana mass was constrained to a range of 210–610 meV, depending on nuclear matrix element calculations.
AMoRE-II: Next Phase of the Experiment
Building on AMoRE-I, the next phase, AMoRE-II, is set to be conducted at Yemi Underground Laboratory (Yemilab), a newly developed research facility in Korea. The upgraded experiment aims to enhance sensitivity and further refine search parameters.
Features of AMoRE-II
- Increased Detector Mass: AMoRE-II will utilize approximately 100 kg of $^{100}$Mo in the form of enriched molybdate crystals, significantly expanding the experiment’s detection capabilities.
- Lower Background Noise: The experiment is designed to achieve a background level of $10^{-4}$ counts/keV/kg/year, a crucial factor in improving half-life sensitivity.
- Advanced Detection System: AMoRE-II will deploy an array of 423 Li$_2$$^{100}$MoO$_4$ crystals, each coupled with metallic magnetic calorimeters operating at millikelvin temperatures. These enhancements aim to minimize background interference and improve detection precision.
- Deep Underground Shielding: Yemilab, situated approximately 1,000 meters underground, provides natural shielding from cosmic rays, reducing background noise and enhancing the experiment’s ability to detect rare decay events.
Data collection for them is expected to begin within the next year. Researchers anticipate that the experiment will contribute significantly to the ongoing search for physics beyond the Standard Model.
By setting more precise constraints on neutrinoless double beta decay, AMoRE-II could influence theoretical research and shape the direction of future experimental investigations into the properties of neutrinos.
