Neutrinoless Double-Beta Decay: Status and Prospects (1902.04097v1)

Abstract: Neutrinoless double-beta decay is a forbidden, lepton-number-violating nuclear transition whose observation would have fundamental implications for neutrino physics, theories beyond the Standard Model and cosmology. In this review, we summarize the theoretical progress to understand this process, the expectations and implications under various particle physics models, as well as the nuclear physics challenges that affect the precise predictions of the decay half-life. We will also provide a synopsis of the current and future large-scale experiments that aim at discovering this process in physically well-motivated half-life ranges.

• The paper presents an in-depth review of theoretical frameworks and experimental techniques used to study neutrinoless double-beta decay.
• It details advanced nuclear matrix element calculations and highlights breakthroughs like GERDA’s background suppression and bolometer innovations.
• The review outlines future prospects with projects such as LEGEND and nEXO, aiming for decay half-life sensitivities near 10^28 years.

Overview of "Neutrinoless Double-Beta Decay: Status and Prospects"

The paper authored by Dolinski et al. presents a comprehensive review of the current status and future prospects of investigating neutrinoless double-beta decay ($0\nu\beta\beta$). This process, if observed, would offer groundbreaking insights into the physics beyond the Standard Model (SM), particularly concerning the Majorana nature of neutrinos and lepton-number violation.

Theoretical Considerations

Neutrinoless double-beta decay is a forbidden nuclear transition that violates lepton number conservation, a global symmetry in the SM. The experimental confirmation of $0\nu\beta\beta$ decay would imply that neutrinos are Majorana particles, capable of revealing information about the absolute neutrino mass scale and the mechanism of mass generation. Several theoretical models accommodate $0\nu\beta\beta$ decay, addressing scenarios ranging from light neutrinos to heavy TeV-scale particles, thus probing a wide spectrum of beyond-SM physics.

A notable focus in $0\nu\beta\beta$ theoretical investigations is understanding the underpinning nuclear physics to predict the half-life of the decay accurately. Advanced nuclear matrix element (NME) calculations, utilizing various methods, strive to reduce uncertainties; however, significant challenges remain. The notion of "quenching" of the axial vector coupling constant $g_A$ in nuclear media is scrutinized, which impacts the predicted decay rates substantially.

Experimental Landscape and Progress

On the experimental frontier, rigorous efforts are underway to detect $0\nu\beta\beta$ decay across different isotopes using varied technologies. Key isotopes include $^{76}$Ge, $^{136}$Xe, and $^{130}$Te, investigated through techniques such as semiconductor detectors and bolometers. The choice of isotopes and detector technologies is crucial to balancing factors like detector energy resolution, background suppression, and source mass scalability.

GERDA and the {\sc Majorana Demonstrator} have delivered leading $T_{1/2}^{0\nu}$ sensitivities through enhancements in material purity and innovative detector designs like point-contact HPGe detectors. For instance, GERDA has achieved an unprecedented background index, setting a limit on $T_{1/2}^{0\nu}$ at $8.0 \times 10^{25}$ years.

Efforts like CUORE, which deploys bolometers based on TeO$_2$ crystals, exhibit remarkable progress, emphasizing the critical role of energy resolution and active background discrimination. The collaboration's focus on reducing alpha-induced background via scintillating bolometers points to the innovative strategies aimed at extending $T_{1/2}^{0\nu}$ sensitivities further.

Future Outlook and Scientific Ramifications

Upcoming projects like LEGEND, CUPID, and nEXO exemplify the forward momentum in $0\nu\beta\beta$ research, targeting $T_{1/2}^{0\nu}$ sensitivities on the order of $10^{28}$ years. These experiments are pivotal in pushing the boundaries of our understanding of lepton-number violation and laying the groundwork for new physics.

The prospect of observing $0\nu\beta\beta$ decay directly implicates profound cosmological and particle physics ramifications. It could elucidate the matter-anti-matter asymmetry in the Universe and potentially validate models that incorporate new physics beyond SM neutrinos, including connections to baryogenesis.

In summary, the review by Dolinski et al. offers a detailed examination of $0\nu\beta\beta$ decay research, highlighting the theoretical motivations and the experimental innovations driving the quest to discover and understand this elusive process. The findings and methodologies discussed set the stage for pivotal discoveries that could redefine fundamental concepts in physics.