• Nuclear, Particle, Astroparticle and Cosmology (NUPAC) Seminars

March 24, 2026 2:00 PM
PAIS 3205

Host:

Michael Gold

Presenter:

Tensor Elmikawy (UNM)

Neutrinos are in a unique position in particle physics: they are electrically neutral, extremely light, and seldomly interact. Their observed flavor oscillations demonstrate that neutrinos possess non-zero mass, a fact that cannot be accommodated within our Standard Model and therefore points toward physics beyond it. One of the most powerful probes of this new physics is neutrinoless double-beta decay (0νββ), a hypothetical nuclear transition in which two electrons are emitted without accompanying neutrinos. Observation of this process would violate total lepton number by two units and establish neutrinos as Majorana particles, thereby providing insight into the origin of neutrino mass and potentially connecting particle physics to a pressing cosmological issue: matter–antimatter asymmetry of the universe.

This talk presents the theoretical motivation and experimental search for 0νββ within the LEGEND (Large Enriched Germanium Experiment for Neutrinoless ββ Decay) effort. After introducing the role of neutrinos in the Standard Model, and the problem of neutrino mass, the discussion turns to the experimental Work. The LEGEND-200 operating high-purity germanium detectors enriched in ⁷⁶Ge within an ultra-low-background liquid argon (LAr) environment. Recent results establish a new lower limit on the half-life of 0νββ decay,T^0ν_1/2 > 10²⁶ yr, demonstrating the experiment’s sensitivity to extremely rare processes.

A central component of the analysis is understanding and suppressing backgrounds, and isolating signal events near the Q_ββ = 2039 keV region of interest. Detailed Monte Carlo simulations based on Geant4, implemented through the REMAGE code and developed largely in C++, are used to model the physics processes, and detector geometry. These simulations are the bridge between theoretical predictions and experimental observables.

The talk also highlights ongoing work at the University of New Mexico, including improvements beyond the legacy BACON cryostat model and studies of xenon-doped liquid argon to enhance scintillation light yield and veto efficiency. Finally, the talk outlines future directions toward the discovery level sensitivity experiment, LEGEND-1000. Together, the combination of theoretical motivation, and simulation makes the search for neutrinoless double-beta decay a powerful pathway to uncovering physics beyond the Standard Model.