Search For Neutrinoless Double Beta Decay Research Articles

Demonstration of event position reconstruction based on diffusion in the NEXT-white detector

Noble element time projection chambers are a leading technology for rare event detection in physics, such as for dark matter and neutrinoless double beta decay searches. Time projection chambers typically assign event position in the drift direction using the relative timing of prompt scintillation and delayed charge collection signals, allowing for reconstruction of an absolute position in the drift direction. In this paper, alternate methods for assigning event drift distance via quantification of electron diffusion in a pure high pressure xenon gas time projection chamber are explored. Data from the NEXT-White detector demonstrate the ability to achieve good position assignment accuracy for both high- and low-energy events. Using point-like energy deposits from 83m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{83\ extrm{m}}$$\\end{document}Kr calibration electron captures (E∼45\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E\\sim 45$$\\end{document} keV), the position of origin of low-energy events is determined to 2 cm precision with bias <1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$< 1~$$\\end{document}mm. A convolutional neural network approach is then used to quantify diffusion for longer tracks (E≥1.5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E\\ge ~1.5$$\\end{document} MeV), from radiogenic electrons, yielding a precision of 3 cm on the event barycenter. The precision achieved with these methods indicates the feasibility energy calibrations of better than 1% FWHM at Qββ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{\\beta \\beta }$$\\end{document} in pure xenon, as well as the potential for event fiducialization in large future detectors using an alternate method that does not rely on primary scintillation.

Radon concentration measurement with a high-sensitivity radon detector at the Yemilab

The radiation emitted from radon is a critical background in rare event search experiments conducted at the Yemi Underground Laboratory (Yemilab) in Jeongseon, Korea. A Radon Reduction System (RRS) has been developed and installed in Yemilab to reduce radon concentration in the air. The RRS primarily provides a purified air of 50 m3/h to the cleanroom used to assemble crystal detectors in the AMoRE, a neutrinoless double beta decay search experiment. RRS can reduce the radon level by a factor of 300, so a high-sensitivity radon detector was required. A highly sensitive radon detector was constructed using a 70 L chamber with a large PIN photodiode to measure radon concentration in the purified air. The radon detector shows an excellent resolution of 72 keV (FWHM) for 6.003 MeV alphas from 218Po decay and a sensitivity down to 23.8 ± 2.1 mBq/m3 with a boil-off N2 gas sample. The radon concentration level from the RRS measured by the radon detector was below 0.29 Bq/m3 with a reduction factor of about 300.

Searching for Two-Neutrino and Neutrinoless Double Beta Decay of ^{134}Xe with the PandaX-4T Experiment.

^{134}Xe is a candidate isotope for neutrinoless double beta decay (0νββ) search. In addition, the two-neutrino case (2νββ) allowed by the standard model of particle physics has not yet been observed. With the 656-kg natural xenon in the fiducial volume of the PandaX-4T detector, which contains 10.4% of ^{134}Xe, and its initial 94.9-day exposure, we have established the most stringent constraints on 2νββ and 0νββ of ^{134}Xe half-lives, with limits of 2.8×10^{22} yr and 3.0×10^{23} yr at 90%confidence level, respectively. The 2νββ (0νββ) limit surpasses the previously reported best result by a factor of 32 (2.7), highlighting the potential of large monolithic natural xenon detectors for double beta decay searches.

Demonstration of neutrinoless double beta decay searches in gaseous xenon with NEXT

The NEXT experiment aims at the sensitive search of the neutrinoless double beta decay in 136Xe, using high-pressure gas electroluminescent time projection chambers. The NEXT-White detector is the first radiopure demonstrator of this technology, operated in the Laboratorio Subterráneo de Canfranc. Achieving an energy resolution of 1% FWHM at 2.6 MeV and further background rejection by means of the topology of the reconstructed tracks, NEXT-White has been exploited beyond its original goals in order to perform a neu- trinoless double beta decay search. The analysis considers the combination of 271.6 days of 136Xe-enriched data and 208.9 days of 136Xe-depleted data. A detailed background modeling and measurement has been developed, ensuring the time stability of the radiogenic and cosmogenic contributions across both data samples. Limits to the neutrinoless mode are obtained in two alternative analyses: a background-model-dependent approach and a novel direct background-subtraction technique, offering results with small dependence on the background model assumptions. With a fiducial mass of only 3.50 ± 0.01 kg of 136Xe-enriched xenon, 90% C.L. lower limits to the neutrinoless double beta decay are found in the T1/20ν\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {T}_{1/2}^{0\ u } $$\\end{document} > 5.5 × 1023− 1.3 × 1024 yr range, depending on the method. The presented techniques stand as a proof-of-concept for the searches to be implemented with larger NEXT detectors.

Energy calibration of germanium detectors for the Majorana Demonstrator

The Majorana Demonstrator was a search for neutrinoless double-beta decay (0νββ) in the 76Ge isotope. It was staged at the 4850-foot level of the Sanford Underground Research Facility (SURF) in Lead, SD. The experiment consisted of 58 germanium detectors housed in a low background shield and was calibrated once per week by deploying a 228Th line source for 1 to 2 hours. The energy scale calibration determination for the detector array was automated using custom analysis tools. We describe the offline procedure for calibration of the Demonstrator germanium detectors, including the simultaneous fitting of multiple spectral peaks, estimation of energy scale uncertainties, and the automation of the calibration procedure.

A compact dication source for Ba2+ tagging and heavy metal ion sensor development

We present a tunable metal ion beam that delivers controllable ion currents in the picoamp range for testing of dry-phase ion sensors. Ion beams are formed by sequential atomic evaporation and single or multiple electron impact ionization, followed by acceleration into a sensing region. Controllability of the ionic charge state is achieved through tuning of electrode potentials that influence the retention time in the ionization region. Barium, lead, and cadmium samples have been used to test the system, with ion currents identified and quantified using a quadrupole mass analyzer. Realization of a clean Ba2+ ion beam within a bench-top system represents an important technical advance toward the development and characterization of barium tagging systems for neutrinoless double beta decay searches in xenon gas. This system also provides a testbed for investigation of novel ion sensing methodologies for environmental assay applications, with dication beams of Pb2+ and Cd2+ also demonstrated for this purpose.

Impact of nuclear matrix element calculations for current and future neutrinoless double beta decay searches

Nuclear matrix elements (NME) are a crucial input for the interpretation of neutrinoless double beta decay data. We consider a representative set of recent NME calculations from different methods and investigate the impact on the present bound on the effective Majorana mass mββ by performing a combined analysis of the available data as well as on the sensitivity reach of future projects. A crucial role is played by the recently discovered short-range contribution to the NME, induced by light Majorana neutrino masses. Depending on the NME model and the relative sign of the long- and short-range contributions, the current 3σ bound can change between mββ< 40 meV and 600 meV. The sign-uncertainty may either boost the sensitivity of next-generation experiments beyond the region for mββ predicted for inverted mass ordering or prevent even advanced setups to reach this region. Furthermore, we study the possibility to distinguish between different NME calculations by assuming a positive signal and by combining measurements from different isotopes. Such a discrimination will be impossible if the relative sign of the long- and short-range contribution remains unknown, but can become feasible if mββ ≳ 40 meV and if the relative sign is known to be positive. Sensitivities will be dominated by the advanced 76Ge and 136Xe setups assumed here, but NME model-discrimination improves if data from a third isotope is added, e.g., from 130Te or 100Mo.

Large low background kTon-scale liquid argon time projection chambers

We find that it is possible to increase sensitivity to low energy physics in a third or fourth Deep Underground Neutrino Experiment (DUNE)-like module with careful controls over radiopurity and targeted modifications to a detector similar to the DUNE Far Detector design. In particular, sensitivity to supernova and solar neutrinos can be enhanced with improved MeV-scale reach. A neutrinoless double beta decay search with 136Xe loading appears feasible. Furthermore, sensitivity to Weakly-Interacting Massive Particle (WIMP) Dark Matter becomes competitive with the planned world program in such a detector, offering a unique seasonal variation detection that is characteristic of the nature of WIMPs.

Enhanced light signal for the suppression of pile-up events in Mo-based bolometers for the 0nu beta beta decay search.

Random coincidences of events could be one of the main sources of background in the search for neutrino-less double-beta decay of ^{100}Mo with macro-bolometers, due to their modest time resolution. Scintillating bolometers as those based on Li_2MoO_4 crystals and employed in the CROSS and CUPID experiments can eventually exploit the coincident fast signal detected in a light detector to reduce this background. However, the scintillation provides a modest signal-to-noise ratio, making difficult a pile-up pulse-shape recognition and rejection at timescales shorter than a few ms. Neganov–Trofimov–Luke assisted light detectors (NTL-LDs) offer the possibility to effectively increase the signal-to-noise ratio, preserving a fast time-response, and enhance the capability of pile-up rejection via pulse shape analysis. In this article we present: (a) an experimental work performed with a Li_2MoO_4 scintillating bolometer, studied in the framework of the CROSS experiment, and utilizing a NTL-LD; (b) a simulation method to reproduce, synthetically, randomly coincident two-neutrino double-beta decay events; (c) a new analysis method based on a pulse-shape discrimination algorithm capable of providing high pile-up rejection efficiencies. We finally show how the NTL-LDs offer a balanced solution between performance and complexity to reach background index sim 10^{-4} counts/keV/kg/year with 280 g Li_2MoO_4 (^{100}Mo enriched) bolometers at 3034 keV, the Q_{beta beta } of the double-beta decay, and target the goal of a next generation experiment like CUPID.

Search for Majorana neutrinos

AbstractWhether there exist elementary particles having Majorana nature is a fundamental open question that has persisted since the 1930s. The only practical experiments to test the Majorana nature of neutrinos is the search for neutrinoless double-beta decay, which has been a major challenge for nuclear and particle physicists. In the 2000s, a number of experiments using advanced technologies were planned, some of which have already achieved significant improvements in the search sensitivity. In this article, the current status of the neutrinoless double-beta decay searches is summarized, reviewing the progress of KamLAND-Zen, which recorded the world’s best sensitivity in the effective Majorana neutrino mass limit.

Identification and simulation of surface alpha events on passivated surfaces of germanium detectors and the influence of metalisation

Events from alpha interactions on the surfaces of germanium detectors are a major contribution to the background in germanium-based searches for neutrinoless double-beta decay. Surface events are subject to charge trapping, affecting their pulse shape and reconstructed energy. A study of alpha events on the passivated end-plate of a segmented true-coaxial n-type high-purity germanium detector is presented. Charge trapping is analysed in detail and an existing pulse-shape analysis technique to identify alpha events is verified with mirror pulses observed in the non-collecting channels of the segmented test detector. The observed radial dependence of charge trapping confirms previous results. A dependence of the probability of charge trapping on the crystal axes is observed for the first time. A first model to describe charge trapping effects within the framework of the simulation software SolidStateDetectors.jl is introduced. The influence of metalisation on events from low-energy gamma interactions close to the passivated surface is also presented.

A congestion-aware and fault-tolerant readout network ASIC for a high-density electrode array targeting at neutrinoless double-beta decay search in a TPC

Abstract We present a distributed, self-organizing, fault-tolerant and congestion-aware readout network application specific integrated circuit (ASIC) for a high-density electrode array targeting at neutrinoless double-beta decay search in a time projection chamber (TPC). A sensor network is proposed to achieve the readout of the high-density electrode array. This network consists of approximately 1 × 105 single-electrode Topmetal-S sensors with a pitch of approximately 5~10 mm. Static routing is implemented in the first version of the sensor network, without the feature of congestion awareness, which means that only one deterministic path is available for a given packet. Because of the limited memory in each sensor, data will be lost when congestion occurs in this first version of the network. Therefore, the network should have congestion awareness to improve its memory occupancy and effective throughput. Accordingly, a 224 × 224 network with congestion awareness is emulated. The simulation results show that better performance of the sensor network can be achieved with less hardware. An ASIC named adaptive and fault-tolerant readout network chip (AFT-RNC) is implemented with 48.2% of the area of the first implementation.

A gaseous time projection chamber with Micromegas readout for low-radioactive material screening

PurposeLow-radioactive material screening is becoming essential for rare event search experiments, such as neutrinoless double beta decay and dark matter searches in underground laboratories. A gaseous time projection chamber (TPC) can be used for such purposes with large active areas and high efficiency.MethodsA gaseous TPC with a Micromegas readout plane of approximately \(20 \times 20\) \(\hbox {cm}^2\) is successfully constructed for surface alpha contamination measurements.ResultsWe have characterized the energy resolution, gain stability, and tracking capability with calibration sources.ConclusionWith the unique track-related background suppression cuts of the gaseous TPC, we have established that the alpha background rate of the TPC is (\(0.13\pm 0.03\))\(\times 10^{-6}\) Bq/\(\hbox {cm}^2\), comparable to the leading commercial solutions.

Xenon-doped liquid argon TPCs as a neutrinoless double beta decay platform

Searches for neutrinoless double-beta decay continue to expand our understanding of the lepton sector, with experiments now pursuing ton-scale target masses with sensitivity to $m_{\beta\beta}$ covering the allowed parameter space for the inverted neutrino mass ordering. Continued searches for this rare decay will require scalable detector technologies to achieve significant increases in the target mass beyond the ton scale, in order to probe the normal ordering region. This work explores the concept of searching for neutrinoless double-beta decay in a 10 kton scale liquid argon time projection chamber (LArTPC) located deep underground and doped with percent-level quantities of xenon. We discuss the design requirements, background mitigation and detector R&D needs, and considerations for deployment in a modified DUNE far detector module. We find that such a detector could reach $m_{\beta\beta}$ sensitivity at the 2-4 meV range with xenon doping at 2% if significant background reductions can be achieved.

A study of self-vetoing balloon vessel for liquid-scintillator detectors

KamLAND-Zen searches for neutrinoless double-beta decay with an ultra-pure liquid-scintillator (LS) filled with a custom-made clean nylon balloon. The primary backgrounds are radioactive impurities such as uranium and thorium series. To reduce them, we studied a self-vetoing balloon-shaped vessel for a future upgrade program, “KamLAND2-Zen”. We selected Polyethylene-Naphthalate (PEN) film which emit fluorescent light and performed the feasibility studies. Owing to its scintillation properties, 214Bi background could be identified in the KamLAND2-Zen. Moreover, thanks to the different waveforms between the LS and the PEN, we can apply the pulse-shape-discrimination for 212Bi-Po pileup background. We evaluated its background rejection efficiency as more than 90%. Resulting from these studies, it is possible to remove restrictions on fiducial volume in KamLAND2-Zen.

Majorana neutrino mass constraints in the landscape of nuclear matrix elements

We discuss up-to-date constraints on the Majorana neutrino mass $m_{\beta\beta}$ from neutrinoless double beta decay ($0\nu\beta\beta$) searches in experiments using different isotopes: KamLAND-Zen and EXO ($^{136}$Xe), GERDA and MAJORANA ($^{76}$Ge) and CUORE ($^{130}$Te). Best fits and upper bounds on $m_{\beta\beta}$ are explored in the general landscape of nuclear matrix elements (NME), as well as for specific NME values obtained in representative nuclear models. By approximating the likelihood of $0\nu\beta\beta$ signals through quadratic forms, the analysis of separate and combined isotope data becomes exceedingly simple, and allows to clarify various aspects of multi-isotope data combinations. In particular, we analyze the relative impact of different data in setting upper bounds on $m_{\beta\beta}$, as well as the conditions leading to nonzero $m_{\beta\beta}$ at best fit, for variable values of the NMEs. Detailed results on $m_{\beta\beta}$ from various combinations of data are reported in graphical and numerical form. Implications for future $0\nu\beta\beta$ data analyses and NME calculations are briefly discussed.

Muon track reconstruction in a segmented bolometric array using multi-objective optimization

Recent advances in segmented solid-state detector arrays for rare-event searches have allowed the technology to approach the ton-scale in detector mass and the scale of meters in size. Often focused around searches for neutrinoless double-beta decay or direct dark matter detection, such experiments also have the capability to search for exotic particles that leave track-like signatures across their volume. However, the segmented nature of such detector arrays often sets the spatial resolution and makes the problem of reconstructing track-like paths non-trivial. In this paper, we present an algorithm that improves reconstruction of track-like events in segmented detectors using multi-objective optimization — a computational technique that optimizes more than one cost function at a time without specifying a quantitative weighting between them. Such a technique allows the reconstruction of tracks through a detector and the determination of path-lengths through individual elements. When combined with the reconstructed energy depositions in each element this allows for a calculation of the stopping power of track-like particles and opens the door to searches for particles with abnormal stopping power like monopoles or lightly-ionizing particles (LIPs). Results are presented which evaluate the precision of the reconstruction tools as they currently stand against Monte Carlo generated data. The algorithm is presented in the context of the CUORE experiment, but has applications to other segmented calorimeter detectors.

Cosmogenic background study for a ^{100}Mo-based bolometric demonstration experiment at China JinPing underground Laboratory

We perform simulation study for a 10-kg ^{100}Mo-based bolometeric demonstration experiment for neutrinoless double-beta decay (0nu beta beta ) search at China JinPing underground Laboratory (CJPL). Cosmogenic production of radionuclides in ^{100}Mo-enriched lithium molybdate crystals and copper components of the detector system are studied using Geant4 toolkit based on the simulated cosmic ray data from the CRY library. Background energy spectra of the cosmogenic radionuclides including ^{56}Co, ^{82}Rb and ^{88}Y which are harmful for the ^{100}Mo-based 0nu beta beta experiment are investigated. We then evaluate the total cosmogenic background level in the ^{100}Mo 0nu beta beta search energy region of interest (ROI) for the demonstration experiment. After one year of cooling down underground, the residual background contribution is found to be 1.8 times 10^{-6} cts/kg/keV/yr and 3.3times 10^{-4} cts/kg/keV/yr from crystals and copper components, respectively. Furthermore, underground cosmogenic activation of copper and lithium molybdate crystal is calculated based on the simulation spectra of neutron and proton in CJPL. The underground cosmogenic background is found to be negligible in the ROI.

Luminescence and scintillation properties of ZnMo1-xWxO4 crystal

The luminescence and scintillation properties of ZnMo1-xWxO4 (x = 0, 0.0022, 0.0088) crystals grown by low thermal gradient Czochralski technique were studied in a temperature range of 10–300 K. The good optical transparency above the fundamental absorption of crystals were obtained for all the samples. The luminescence light yield enhancement and slowing of the decay time were observed with lowering the temperature for W doped samples under 4.42 eV excitation. Improvement in scintillation light yield with W doping in ZnMoO4 crystals was observed and found 76% that of ZnWO4 crystal at 10 K for 0.88 mol% W doped ZnMoO4 sample. An additional TSL band was observed for the W doped samples in the temperature range of 70–100 K. The enhancement in scintillation light yield at low temperature with W doping in ZnMoO4 crystal are quite encouraging to use it as a cryogenic phonon scintillation detector for the neutrinoless double beta decay search of 100Mo.

Alpha -event characterization and rejection in point-contact HPGe detectors

P-type point contact (PPC) HPGe detectors are a leading technology for rare event searches due to their excellent energy resolution, low thresholds, and multi-site event rejection capabilities. We have characterized a PPC detector’s response to alpha particles incident on the sensitive passivated and p^+ surfaces, a previously poorly-understood source of background. The detector studied is identical to those in the MajoranaDemonstrator experiment, a search for neutrinoless double-beta decay (0nu beta beta ) in ^{76}Ge. alpha decays on most of the passivated surface exhibit significant energy loss due to charge trapping, with waveforms exhibiting a delayed charge recovery (DCR) signature caused by the slow collection of a fraction of the trapped charge. The DCR is found to be complementary to existing methods of alpha identification, reliably identifying alpha background events on the passivated surface of the detector. We demonstrate effective rejection of all surface alpha events (to within statistical uncertainty) with a loss of only 0.2% of bulk events by combining the DCR discriminator with previously-used methods. The DCR discriminator has been used to reduce the background rate in the 0nu beta beta region of interest window by an order of magnitude in the MajoranaDemonstrator and will be used in the upcoming LEGEND-200 experiment.