Neutrinoless Double Beta Decay (2212.11099v1)

Abstract: This White Paper, prepared for the Fundamental Symmetries, Neutrons, and Neutrinos Town Meeting related to the 2023 Nuclear Physics Long Range Plan, makes the case for double beta decay as a critical component of the future nuclear physics program. The major experimental collaborations and many theorists have endorsed this white paper.

• The paper demonstrates that detecting neutrinoless double beta decay could confirm neutrinos as Majorana fermions and reveal physics beyond the Standard Model.
• It details methodologies employed by CUPID, LEGEND, and nEXO, highlighting innovations in detector design and background noise reduction.
• The study proposes a collaborative, ton-scale experimental roadmap with enhanced theoretical modeling to refine constraints on neutrino mass.

Neutrinoless Double Beta Decay: Analysis and Prospects

The exploration of neutrinoless double beta decay (\BBz) has taken on imperative significance in advancing our understanding of neutrinos and the fundamental symmetries of nature. This paper delineates the scientific underpinning and the projected path forward in the pursuit of detecting \BBz, thus unveiling new facets of nuclear physics and influencing cosmological models.

Scientific Context and Motivation

Neutrinoless double beta decay is a hypothetical nuclear process wherein two neutrons within a nucleus transform into two protons and two electrons without the emission of neutrinos. This decay modality challenges the lepton number conservation principle imbedded in the Standard Model, flagging the occurrence of physics beyond the conventional framework. The detection of \BBz would provide evidence for neutrinos being Majorana fermions, potentially having profound implications on neutrino mass mechanisms, cosmology, and the observed asymmetry between matter and antimatter in the universe.

Current Experimental Landscape

The paper outlines three frontrunner experimental collaborations with significant U.S. involvement aimed at exploring the inverted mass hierarchy range in \BBz:

1. CUPID (CUORE Upgrade with Particle ID): Situated at Gran Sasso National Laboratory, CUPID aims to detect \BBz in $^{100}$Mo using an array of scintillating crystal bolometers. The anticipated sensitivity sets a robust foundation for probing new physics scenarios.
2. LEGEND (Large Enriched Germanium Experiment for Neutrinoless Double Beta Decay): This experiment employs high-purity germanium detectors enriched in $^{76}$Ge, utilizing advanced reduction techniques in background noise to push sensitivity limits exponentially higher within the context of inverted mass ordering.
3. nEXO (next Enriched Xenon Observatory): Utilizing a Xenon time projection chamber, nEXO is poised to host a substantial amount of enriched $^{136}$Xe, aiming for significant spatial resolution and event discrimination to enhance decay event detectability.

Theoretical Implications and Future Outlook

From a theoretical standpoint, \BBz research is crucial in validating the Majorana nature of neutrinos and in unraveling potential interactions at play. As experimental setups scale to ton-level mass and sensitivity, the imperative shifts to aligning theoretical modeling, using effective field theory (EFT) to interpolate nuclear matrix elements more precisely. Embedding lattice QCD inputs into calculations offers one viable pathway toward achieving theoretical accuracies consistent with experimental constraints.

Considering these theoretical and experimental developments, the roadmap posited by the paper prioritizes the simultaneous deployment of \BBz experiments to ensure mutual verification across multiple isotopes and methodologies. This ensures robustness in observational claims, steering clear of systematic inaccuracies that could skew interpretations.

Conclusion and Recommendations

This white paper strongly advocates for the timely execution of ton-scale \BBz experiments across multiple isotopes, acknowledging the collaborative and international efforts required to mount such expansive scientific endeavors. Concurrently, it notes the necessity of a vibrant research ecosystem encompassing theory and diverse experimental approaches that push boundaries beyond current mass ordering scales. These efforts, propelled by substantial U.S. participation, collectively aim to procure a more comprehensive understanding of fundamental symmetries and potentially alter our grasp of mass origins, neutrino properties, and the universe's evolutionary dynamics.

As the field endeavors to capitalize on existing discoveries and addresses burgeoning experimental and theoretical challenges, this concerted approach in \BBz research underscores an ambitious yet methodical stride toward elucidating fundamental physical principles.