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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Final results on the $$0\nu \beta \beta $$ decay half-life limit of $$^{100}$$Mo from the CUPID-Mo experiment

Abstract The CUPID-Mo experiment to search for 0 $$\nu \beta \beta $$ ν β β decay in $$^{100}$$ 100 Mo has been recently completed after about 1.5 years of operation at Laboratoire Souterrain de Modane (France). It served as a demonstrator for CUPID, a next generation 0 $$\nu \beta \beta $$ ν β β decay experiment. CUPID-Mo was comprised of 20 enriched $$\hbox {Li}_{{2}}$$ Li 2 $$^{100}$$ 100 $$\hbox {MoO}_4$$ MoO 4 scintillating calorimeters, each with a mass of $$\sim 0.2$$ ∼ 0.2 kg, operated at $$\sim 20$$ ∼ 20 mK. We present here the final analysis with the full exposure of CUPID-Mo ( $$^{100}$$ 100 Mo exposure of 1.47 $$\hbox {kg} \times \hbox {year}$$ kg × year ) used to search for lepton number violation via 0 $$\nu \beta \beta $$ ν β β decay. We report on various analysis improvements since the previous result on a subset of data, reprocessing all data with these new techniques. We observe zero events in the region of interest and set a new limit on the $$^{100}$$ 100 Mo 0 $$\nu \beta \beta $$ ν β β decay half-life of $$T_{1/2}^{0\nu }$$ T 1 / 2 0 ν $$> {1.8}\times 10^{24}$$ > 1.8 × 10 24 year (stat. + syst.) at 90% CI. Under the light Majorana neutrino exchange mechanism this corresponds to an effective Majorana neutrino mass of $$\left $$ m β β $$<~{(0.28{-}0.49)} $$ < ( 0.28 - 0.49 ) eV, dependent upon the nuclear matrix element utilized.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Status of the MAJORANA DEMONSTRATOR: A search for neutrinoless double-beta decay

If neutrinos are Majorana particles, i.e. fermions that are their own antiparticles, then neutrinoless double-beta (0νββ) decay is possible. In such a process, two neutrons can simultaneously decay into two protons and two electrons without emitting neutrinos. Neutrinos being Majorana particles would explicitly violate lepton number conservation, and might play a role in the matter–antimatter asymmetry in the universe. The MAJORANA DEMONSTRATOR experiment is under construction at the Sanford Underground Research Facility in Lead, SD and will search for the neutrinoless double-beta (0νββ) decay of the 76 Ge isotope. The goal of the experiment is to demonstrate that it is possible to achieve a sufficiently low background rate in the 4 keV region of interest (ROI) around the 2039 keV Q-value to justify building a tonne-scale experiment. In this study, we discuss the physics and design of the MAJORANA DEMONSTRATOR, its approach to achieving ultra-low background and the status of the experiment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Searching for Neutrinoless Double-Beta Decay of 130 Te with CUORE

Neutrinoless double-beta (0 ν β β ) decay is a hypothesized lepton-number-violating process that offers the only known means of asserting the possible Majorana nature of neutrino mass. The Cryogenic Underground Observatory for Rare Events (CUORE) is an upcoming experiment designed to search for 0 ν β β decay of 130 Te using an array of 988 TeO 2 crystal bolometers operated at 10 mK. The detector will contain 206 kg of 130 Te and have an average energy resolution of 5 keV; the projected 0 ν β β decay half-life sensitivity after five years of livetime is 1.6 × 10 26 y at 1 σ (9.5 × 10 25 y at the 90% confidence level), which corresponds to an upper limit on the effective Majorana mass in the range 40–100 meV (50–130 meV). In this paper, we review the experimental techniques used in CUORE as well as its current status and anticipated physics reach.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

CUORE and CUORE-0 experiments

Neutrino oscillation experiments proved that neutrinos have mass and this enhanced the interest in neutrinoless double-beta decay (0vββ). The observation of this very rare hypothetical decay would prove the leptonic number violation and would give us indications about neutrinos mass hierarchy and absolute mass scale. CUORE (Cryogenic Underground Observatory for Rare Events) is an array of 988 crystals of TeO 2 , for a total sensitive mass of 741 kg. Its goal is the observation of 0vββ of 130 Te. The crystals, placed into the a dilution cryostat, are operated as bolometers at a temperature close to 10 mK. CUORE commissioning phase has been concluded recently in Gran Sasso National Laboratory, Italy, and data taking is expected to start in spring 2017. If target background rate is reached (0.01counts/day/keV/kg), the sensibility of CUORE will be, in five years of data taking, T 1/2 10 26 years (1σ CL). In order to test the quality of materials and optimize the construction procedures, the collaboration realized CUORE-0, that took data from spring of 2013 to summer 2015. Here, after a brief description of CUORE, I report its commissioning status and CUORE-0 results.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Results from the CUORE experiment

Neutrinoless double beta decay (0νββ) is a rare, second-order nuclear transition that occurs only if neutrinos are massive Majorana particles or through new physics beyond Standard Model. This process explicitly violates the lepton number (L) by two units and, therefore, the observation of 0νββ would demonstrate that L is not a symmetry of nature. Combined with flavour mixing and cosmological measurements, it can provide unique contraints on neutrino mass scale and establish whether neutrinos are Dirac or Majorana particles. The Cryogenic Underground Observatory for Rare Events (CUORE) is an experiment located at the LNGS searching for 0νββ decay of 130 Te. CUORE exploits the bolometric technique to reach high resolution around the Q-value (2527.5 keV). It consists of an array of 988 natural TeO 2 cubic crystals grouped into 19 towers. With a total active mass of 742 kg (~206 kg of 130 Te), CUORE is operated at very low temperature with a new 3 He/ 4 He refrigerator. Data taking started at the beginning of 2017. After a brief introduction on the detector and the way data analysis is performed, I describe CUORE first results for the search of the 0νββ decay that were published in March 2018.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Task I: Dark Matter Search Experiments with Cryogenic Detectors: CDMS-I and CDMS-II Task II: Experimental Study of Neutrino Properties: EXO and KamLAND

Dark Matter Search - During the period of performance, our group continued the search for dark matter in the form of weakly interacting massive particles or WIMPs. As a key member of the CDMS (Cryogenic Dark Matter Search) collaboration, we completed the CDMS II experiment which led the field in sensitivity for more than five years. We fabricated all detectors, and participated in detector testing and verification. In addition, we participated in the construction and operation of the facility at the Soudan Underground Laboratory and played key roles in the data acquisition and analysis. Towards the end of the performance period, we began operating the SuperCDMS Soudan experiment, which consists of 15 advanced Ge (9 kg) detectors. The advanced detector design called iZIP grew out of our earlier DOE Particle Detector R&D program which demonstrated the rejection of surface electrons to levels where they are no longer the dominant source of background. Our group invented this advanced design and these larger detectors were fabricated on the Stanford campus in collaboration with the SLAC CDMS group and the Santa Clara University group. The sensitivity reach is expected to be up to 5 times better than CDMS II after two years of operation. We will check the new limits on WIMPs set by XENON100, and we expect improved sensitivity for light mass WIMPs beyond that of any other existing experiment. Our group includes the Spokesperson for SuperCDMS and continues to make important contributions to improvements in the detector technology which are enabling the very low trigger thresholds used to explore the low mass WIMP region. We are making detailed measurements of the charge transport and trapping within Ge crystals, measuring the diffusive trapping distance of the quasiparticle excitations within the Al phonon collector fins on the detector surface, and we are contributing to the development of much improved detector Monte Carlos which are essential to guide the detector design and optimize the analysis. Neutrino Physics – In the period of performance the neutrino group successfully completed the construction of EXO-200 and commissioned the detector. Science data taking started on Jun 1, 2011. With the discovery of the 2-neutrino double-beta decay in 136-Xe and the first measurement of the 0-neutrino mode resulting in the most stringent limit of Majorana masses, our group continues to be a leading innovator in the field of neutrino physics which is central to DOE-HEP Intensity Frontier program. The phenomenon of neutrino oscillations, in part elucidated by our earlier efforts with the Palo Verde and KamLAND experiments, provides the crucial information that neutrino masses are non-zero and, yet, it contains no information on the value of the neutrino mass scale. In recent times our group has therefore shifted its focus to a high sensitivity 0-neutrino double beta decay program, EXO. The 0-neutrino double beta decay provides the best chance of extending the sensitivity to the neutrino mass scale below 10 meV but, maybe more importantly, it tests the nature of the neutrino wave function, providing the most sensitive probe for Majorana particles and lepton number violation. The EXO program, formulated by our group several years ago, plans to use up to tonnes of the isotope 136-Xe to study the 0-neutrino double beta decay mode. The EXO-200 detector is the first step in this program and it represents the only large US-led and based experiment taking data. The EXO-200 isotope enrichment program broke new grounds for the enterprise of double beta decay. The detector design and material selection program paid off, resulting in a background that is among the very best in the field. The “first light" of EXO-200 was very exciting with the discovery -in the first month of data- of the rarest 2-neutrino double beta decay mode ever observed. The lower limit on the 0-neutrino double beta decay half-life, published in Phys. Rev. Lett. and based on the first 120 days of data is the second best but, when translated into a Majorana mass scale, it is one of the most stringent constraint we have on neutrino masses. Indeed, such a limit was the first result to contradict a claim of discovery in 76-Ge for most nuclear matrix elements calculations. As we continue data taking and plan some modest upgrades to EXO-200 our group is also very active in the design of nEXO, a 5 tonne detector based on the technology demonstrated by EXO-200. Over the years we have made it a tradition to explore the frontier and not to be shy about looking in new directions and re-inventing ourselves to best take advantage of the precious few opportunities provided by Nature. We have also cultivated a number of young people at all levels and, by now, many of the undergraduates, graduate students and postdocs educated by this group have leading positions in academia and industry around the world.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Investigation of Neutrino Properties with Bolometric Detectors

Neutrino mass and mixing are amongst the major discoveries of the past decade. The particle nature of neutrinos and the hierarchy of mass eigenstates, however, are unknown. Neutrinoless double beta-decay (0νββ) is the only known mechanism to test whether neutrinos are their own antiparticles. The observation of 0νββ would imply lepton number violation and show that neutrinos have Majorana mass. This report describes research activities performed at the University of Wisconsin in 2011-2014 aimed at the search for 0νββ with CUORE-0 and CUORE with the goal of exploring the inverted mass hierarchy region and probing an effective neutrino mass of ~40- 120 meV.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Characterization of Backgrounds for EXO

Neutrinos are fundamental particles that are all around us in nature. While neutrinos do not make up the building blocks of matter, they are an important byproduct of the fusion process that makes the sun burn. Because neutrinos are so light in mass, they almost exclusively interact with the weak force in nature. As such, they provide a unique probe for understanding the weak force. The heaviest mass of the neutrino is still so much lighter than all the other charged quarks and leptons that it hints at the possibility that their mass is produced by a different mechanism than the Higgs boson. How can we study these fleeting objects? This is the challenge for neutrino physicists, and we continue to push the limits of the experimental techniques further and further. Neutrinoless double beta decay is a unique probe of neutrinos that will attempt to answer the question of whether the neutrino is its own anti-particle (Majorana), what it's absolute mass is and if observed, we will see violation of lepton number which will lead the way to new physics. Discovering neutrinoless double beta decay will be exciting but still left to be answered will be what the mechanism is that causes the decay. Understanding this mechanism will also give us more insight into the weak force or new forces at work in the universe. The current experiments are attempting to measure the decay half-life at the level of 1025-1026 years. In order to do this (and better in the future), it is critical to eliminate as many radioactive background processes as possible by shielding from external radioactivity and reducing the internal radioactivity of the detector. This report discusses measurements performed to study potential backgrounds due to neutrons interacting with 136Xe that could affect experiments such as EXO-200 (Enriched Xenon Observatory - 200 kg) and nEXO (next Enriched Xenon Observatory) and KamLAND-Zen.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

DUNE’s Potential to Search for Neutrinoless Double Beta Decay

Neutrinoless double beta decay is a forbidden process by the standard model due to a violation of lepton number and could be piece of the matter/anti-matter asymmetry puzzle. Its rarity makes it very difficult to search for, but if found could aid in figuring out the mass hierarchy. The idea is to take advantage of DUNE's size and capabilities to attempt to detect the decay by doping the liquid argon with Xenon, a candidate isotope for this decay. Thus, we need to know whether this search is feasible within DUNE’s framework

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Research in Neutrinoless Double-Beta Decay (Final Report)

The research objective of the supported work was to search for neutrinoless double-beta decay in 76 Ge and investigate and identify backgrounds to a double-beta decay search. Understanding the neutrino mass generation mechanism, the absolute neutrino mass scale, the neutrino mass spectrum, and the possible Majorana nature of neutrinos are some of the future discoveries of the next generation neutrino experiments. The Majorana collaboration operated the Demonstrator experiment comprising 44 kg (30 kg enriched in 76 Ge) of Ge detectors in total split between two modules contained in a low background shield at the Sanford Underground Research Facility in Lead, South Dakota. Observation of 0νββ would have profound implications for the Standard Model of particle physics by demonstrating that neutrinos are Majorana particles, that lepton number is not conserved, and it would provide a measure of the effective Majorana neutrino mass. The decay rate of 0νββ is incredibly small and may only produce a few signature events in a detector per year. Therefore, observation of this rare process demands a careful study and implementation of signal processing, detector design, and new levels of background suppression.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

A cross-frontier quest to reveal the origin of the Universe

We still don't know much about our Universe. Various fundamental symmetry tests to reveal the origin of the Universe include: multi-species EDM searches, Lepton Flavor Violation, CPV/LNV/LFV searches at colliders, and Lepton Number Violation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

The Wavelength Shifting Plate on the LEGEND Experiment

Majorana-type neutrinos lead to a neutrinoless double beta decay with the emission of only two electrons. (Lepton Number Violation). LEGEND experiment is proposed to search for this transition from ⁷⁶Ge to ⁷⁶Se. The goal is to reach the half-life sensitivity of about 10²⁸ years in a 5 kton٠year exposure of a detector with 1 ton of isotopic ⁷⁶Ge mass.

Bae, Wonseok↗
DOE OSTI2024

The Mu2e Experiment and Progress in the Year 2024

The Mu2e Experiment is a search for Charged Lepton Flavor Violation (CLFV) in the process of a coherent neutrinoless mu- N -> e- N transition. This process is allowed under the Standard Model in the presence of neutrino mixing; albeit, at unobservable rates (branching ratio below 10-50). The sensitivity of the Mu2e experiment is a factor of 104 improvement over the current limit. This search both compliments and extends current searches for muon to electron+gamma at MEG and new physics searches at the LHC. Another interesting process that Mu2e will search for is the neutrionless conversion of stopped negative muons into positrons: mu- N -> e+ N'. This process violates both lepton flavor and lepton number (LNV) and would provide proof that neutrinos are Majorana particles. Progress has been made in many areas in preparation for beam. A description of the Mu2e Experiment and a synopsis of this experiment s progress in the year 2024 towards data collection will be presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

r -process Nucleosynthesis from Three-dimensional Magnetorotational Core-collapse Supernovae

Here, we investigate r -process nucleosynthesis in 3D general-relativistic magnetohydrodynamic simulations of rapidly rotating strongly magnetized core collapse. The simulations include a microphysical finite-temperature equation of state and a leakage scheme that captures the overall energetics and lepton number exchange due to postbounce neutrino emission and absorption. We track the composition of the ejected material using the nuclear reaction network SkyNet. Our results show that the 3D dynamics of magnetorotational core-collapse supernovae (CCSN) are important for their nucleosynthetic signature. We find that production of r -process material beyond the second peak is reduced by a factor of 100 when the magnetorotational jets produced by the rapidly rotating core undergo a kink instability. Our results indicate that 3D magnetorotationally powered CCSNe are robust r -process sources only if they are obtained by the collapse of cores with unrealistically large precollapse magnetic fields of the order of 10 13 G. Additionally, a comparison simulation that we restrict to axisymmetry results in overly optimistic r -process production for lower magnetic field strengths.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Exploring Fundamentally Three-dimensional Phenomena in High-fidelity Simulations of Core-collapse Supernovae

The details of the physical mechanism that drives core-collapse supernovae (CCSNe) remain uncertain. While there is an emerging consensus on the qualitative outcome of detailed CCSN mechanism simulations in 2D, only recently have high-fidelity 3D simulations become possible. In this work, we present the results of an extensive set of 3D CCSN simulations using high-fidelity multidimensional neutrino transport, high-resolution hydrodynamics, and approximate general relativistic gravity. We employ a state-of-the-art 20 M ⊙ progenitor generated using Modules for Experiments in Stellar Astrophysics, and the SFHo equation of state. While none of our 3D CCSN simulations explode within ~500 ms after core bounce, we find that the presence of large-scale aspherical motion in the Si and O shells aid shock expansion and bring the models closer to the threshold of explosion. We also find some dependence on resolution and geometry (octant versus full 4π). As has been noted in other recent works, we find that the post-shock turbulence plays an important role in determining the overall dynamical evolution of our simulations. We find a strong standing accretion shock instability (SASI) that develops at late times. The SASI produces transient shock expansions, but these do not result in any explosions. We also report that for a subset of our simulations, we find conclusive evidence for the lepton-number emission self-sustained asymmetry, which until now has not been confirmed by independent simulation codes. Finally, both the progenitor asphericities and the SASI-induced transient shock expansion phases generate transient gravitational waves and neutrino signal modulations via perturbations of the protoneutron star by turbulent motions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Fast-pairwise Collective Neutrino Oscillations Associated with Asymmetric Neutrino Emissions in Core-collapse Supernovae

We present a linear stability analysis of the fast-pairwise neutrino flavor conversion based on a result of our latest axisymmetric core-collapse supernova (CCSN) simulation with full Boltzmann neutrino transport. In the CCSN simulation, coherent asymmetric neutrino emissions of electron-type neutrinos (νe) and their antiparticles ($\bar{v}$e), in which the asymmetries of νe and $\bar{v}$e are anticorrelated with each other, occur at almost the same time as the onset of aspherical shock expansion. We find that the asymmetric neutrino emissions play a crucial role on occurrences of fast flavor conversions. The linear analysis shows that unstable modes appear in both pre- and post-shock flows; for the latter, they appear only in the hemisphere of higher $\bar{v}$e emissions (the same hemisphere with stronger shock expansion). We analyze the characteristics of electron–lepton number (ELN) crossing in depth by closely inspecting the angular distributions of neutrinos in momentum space. The ELN crossing happens in various ways, and the property depends on the radius: in the vicinity of neutron star, $\bar{v}$e (νe) dominates over ve ($\bar{n}$e) in the forward (backward) direction; at the larger radius, the ELN crossing occurs in the opposite way. We also find that the non-radial ELN crossing occurs at the boundary between no ELN crossing and the radial one, which is an effect of genuine multi-dimensional transport. Our findings indicate that the collective neutrino oscillation may occur more commonly in CCSNe and suggest that the CCSN community needs to accommodate these oscillations self-consistently in the modeling of CCSNe

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Ab-initio General-relativistic Neutrino-radiation Hydrodynamics Simulations of Long-lived Neutron Star Merger Remnants to Neutrino Cooling Timescales

Abstract We perform the first 3D ab-initio general-relativistic neutrino-radiation hydrodynamics of a long-lived neutron star merger remnant spanning a fraction of its cooling timescale. We find that neutrino cooling becomes the dominant energy loss mechanism after the gravitational-wave dominated phase (∼20 ms postmerger). Electron flavor antineutrino luminosity dominates over electron flavor neutrino luminosity at early times, resulting in a secular increase of the electron fraction in the outer layers of the remnant. However, the two luminosities become comparable ∼20–40 ms postmerger. A dense gas of electron antineutrinos is formed in the outer core of the remnant at densities ∼10 14.5 g cm −3 , corresponding to temperature hot spots. The neutrinos account for ∼10% of the lepton number in this region. Despite the negative radial temperature gradient, the radial entropy gradient remains positive, and the remnant is stably stratified according to the Ledoux criterion for convection. A massive accretion disk is formed from the material squeezed out of the collisional interface between the stars. The disk carries a large fraction of the angular momentum of the system, allowing the remnant massive neutron star to settle to a quasi-steady equilibrium within the region of possible, stable, rigidly rotating configurations. The remnant is differentially rotating, but it is stable against the magnetorotational instability. Other MHD mechanisms operating on longer timescales are likely responsible for the removal of the differential rotation. Our results indicate the remnant massive neutron star is thus qualitatively different from a protoneutron stars formed in core-collapse supernovae.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

A DG-IMEX Method for Two-moment Neutrino Transport: Nonlinear Solvers for Neutrino–Matter Coupling

Neutrino-matter interactions play an important role in core-collapse supernova (CCSN) explosions as they contribute to both lepton number and/or four-momentum exchange between neutrinos and matter, and thus act as the agent for neutrino-driven explosions. Due to the multiscale nature of neutrino transport in CCSN simulations, an implicit treatment of neutrino-matter interactions is desired, which requires solutions of coupled nonlinear systems in each step of the time integration scheme. In this paper we design and compare nonlinear iterative solvers for implicit systems with energy coupling neutrino-matter interactions commonly used in CCSN simulations. Specifically, we consider electron neutrinos and antineutrinos, which interact with static matter configurations through the Bruenn 85 opacity set. The implicit systems arise from the discretization of a nonrelativistic two-moment model for neutrino transport, which employs the discontinuous Galerkin (DG) method for phase-space discretization and an implicit-explicit (IMEX) time integration scheme. In the context of this DG-IMEX scheme, we propose two approaches to formulate the nonlinear systems — a coupled approach and a nested approach. For each approach, the resulting systems are solved with Anderson-accelerated fixedpoint iteration and Newton’s method. The performance of these four iterative solvers has been compared on relaxation problems with various degree of collisionality, as well as proto-neutron star deleptonization problems with several matter profiles adopted from spherically symmetric CCSN simulations. Here, numerical results suggest that the nested Anderson-accelerated fixed-point solver is more efficient than other tested solvers for solving implicit nonlinear systems with energy coupling neutrino-matter interactions.

79 ASTRONOMY AND ASTROPHYSICS↗