Neutrinoless Decay Hunt Persists with New Limits

Context:

Published on March 17, 2025, this article from The Hindu details the latest findings from the AMoRE experiment in South Korea, which failed to detect neutrinoless double beta decay after two years of searching. This ultra-rare subatomic process, pivotal for understanding neutrino properties and cosmic mysteries, remains elusive, prompting continued global research efforts as of March 27, 2025.

Key Information Points:

• AMoRE Experiment: The Advanced Molybdenum-based Rare process Experiment (AMoRE) in South Korea reported no evidence of neutrinoless double beta decay after two years, as published on March 11, 2025, in Physical Review Letters.
• Neutrino Significance: Neutrinos, the second-most abundant particles after photons, are key to unraveling universe mysteries, produced during the Big Bang, stellar explosions, and nuclear fusion (e.g., 60 billion neutrinos per square centimeter hit Earth from the Sun each second).
• Detection Challenge: Neutrinos’ weak interaction with matter makes them hard to study, yet essential for understanding subatomic processes and unresolved cosmic questions.
• Neutrino Mass Mystery: Known to exist in three flavors with known mass differences, their absolute masses remain unknown; detecting neutrinoless double beta decay could reveal if neutrinos are Majorana particles and provide mass clues.
• Beta Decay Basics: In standard beta decay, an unstable nucleus emits an electron and an antineutrino (e.g., actinium-227 to thorium-227) or a positron and neutrino, releasing excess energy.
• Double Beta Decay: A rare process where two beta decays occur simultaneously, typically emitting two electrons and two antineutrinos; neutrinoless double beta decay (0vββ) omits neutrinos, suggesting they are their own antiparticles.
• Majorana Hypothesis: If neutrinos are Majorana particles (self-antiparticles), 0vββ could occur, offering insights into their mass and nature.
• Experimental Setup: AMoRE-I, at the Yemilab underground facility (1 km deep) in South Korea, uses 1 kg of molybdenum-100 crystals cooled to near absolute zero (-273.135°C) with sensitive detectors to spot energy releases from decays.
• Findings: After two years (ended December 2023), AMoRE-I set the strictest limits yet on 0vββ half-life in molybdenum-100—beyond 2 trillion trillion years—ruling out prior tentative claims from a Soviet-U.S. team in 1995.
• Global Efforts: Other experiments like GERDA (Germany), CUORE (Italy), and KamLAND-Zen (Japan) also seek 0vββ using germanium-76, tellurium-130, and xenon-136, respectively, with no confirmed detections yet.
• Next Phase: AMoRE-II, starting late 2025, will use 100 kg of molybdenum-100 to enhance detection chances, aiming to probe deeper into this rare process.
• Implications: Confirming 0vββ could reshape particle physics, clarify neutrino masses, and explain matter-antimatter asymmetry in the universe.

Key Terms:

• Neutrinoless Double Beta Decay (0vββ): Rare nuclear process omitting neutrinos, hinting at their Majorana nature.
• Neutrinos: Subatomic particles, abundant yet weakly interacting, key to cosmic insights.
• Majorana Particles: Particles that are their own antiparticles, potentially neutrinos.
• Beta Decay: Nuclear process releasing energy via electron and antineutrino emission.
• AMoRE Experiment: South Korean project searching for 0vββ using molybdenum-100.
• Half-Life: Time for half a radioactive sample to decay, a measure of decay rarity.
• Yemilab: Underground facility in South Korea hosting AMoRE, shielded from cosmic interference.

Link To The Original Article – https://www.thehindu.com/sci-tech/science/new-finding-forces-search-for-ultra-rare-decay-process-to-continue/article69281791.ece