Search For Double Beta Decay Research Articles

Fluorescence imaging of individual ions and molecules in pressurized noble gases for barium tagging in 136Xe

The imaging of individual Ba2+ ions in high pressure xenon gas is one possible way to attain background-free sensitivity to neutrinoless double beta decay and hence establish the Majorana nature of the neutrino. In this paper we demonstrate selective single Ba2+ ion imaging inside a high-pressure xenon gas environment. Ba2+ ions chelated with molecular chemosensors are resolved at the gas-solid interface using a diffraction-limited imaging system with scan area of 1 × 1 cm2 located inside 10 bar of xenon gas. This form of microscopy represents key ingredient in the development of barium tagging for neutrinoless double beta decay searches in 136Xe. This also provides a new tool for studying the photophysics of fluorescent molecules and chemosensors at the solid-gas interface to enable bottom-up design of catalysts and sensors.

Measurement of energy resolution with the NEXT-White silicon photomultipliers

The NEXT-White detector, a high-pressure gaseous xenon time projection chamber, demonstrated the excellence of this technology for future neutrinoless double beta decay searches using photomultiplier tubes (PMTs) to measure energy and silicon photomultipliers (SiPMs) to extract topology information. This analysis uses 83mKr data from the NEXT-White detector to measure and understand the energy resolution that can be obtained with the SiPMs, rather than with PMTs. The energy resolution obtained of (10.9 ± 0.6)%, full-width half-maximum, is slightly larger than predicted based on the photon statistics resulting from very low light detection coverage of the SiPM plane in the NEXT-White detector. The difference in the predicted and measured resolution is attributed to poor corrections, which are expected to be improved with larger statistics. Furthermore, the noise of the SiPMs is shown to not be a dominant factor in the energy resolution and may be negligible when noise subtraction is applied appropriately, for high-energy events or larger SiPM coverage detectors. These results, which are extrapolated to estimate the response of large coverage SiPM planes, are promising for the development of future, SiPM-only, readout planes that can offer imaging and achieve similar energy resolution to that previously demonstrated with PMTs.

Generative models for simulation of KamLAND-Zen

The next generation of searches for neutrinoless double beta decay (0νββ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0 \ u \\beta \\beta $$\\end{document}) are poised to answer deep questions on the nature of neutrinos and the source of the Universe’s matter–antimatter asymmetry. They will be looking for event rates of less than one event per ton of instrumented isotope per year. To claim discovery, accurate and efficient simulations of detector events that mimic 0νββ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0 \ u \\beta \\beta $$\\end{document} is critical. Traditional Monte Carlo (MC) simulations can be supplemented by machine-learning-based generative models. This work describes the performance of generative models that we designed for monolithic liquid scintillator detectors like KamLAND to produce accurate simulation data without a predefined physics model. We present their current ability to recover low-level features and perform interpolation. In the future, the results of these generative models can be used to improve event classification and background rejection by providing high-quality abundant generated data.

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.

New studies on the radiopurity and performances of Cs2ZrCl6 crystal scintillators

In this work, we present new studies by using different materials and procedures to improve the performances and radiopurity of Cs2ZrCl6 (CZC) crystal scintillators. In particular, measurements of three new CZC crystals as scintillators were performed over 97.7 days live-time in the low-background DAMA/CRYS set-up deep underground at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N. They allow us to derive elements for improvements towards a possible future use of this kind of detectors in the search for neutrino-less double beta decay of 94,96Zr and rare single beta decay of 96Zr.

Background study of the AMoRE-pilot experiment

We report a study on the background of the Advanced Molybdenum-Based Rare process Experiment (AMoRE), a search for neutrinoless double beta decay (0νββ) of 100Mo. The pilot stage of the experiment was conducted using ∼1.9 kg of 48deplCa100MoO4 crystals at the Yangyang Underground Laboratory, South Korea, from 2015 to 2018. We compared the measured β/γ energy spectra in three experimental configurations with the results of Monte Carlo simulations and identified the background sources in each configuration. We replaced several detector components and enhanced the neutron shielding to lower the background level between configurations. A limit on the half-life of 0νββ decay of 100Mo was found at T1/20ν≥3.0×1023 years at 90% confidence level, based on the measured background and its modeling. Further reduction of the background rate in the AMoRE-I and AMoRE-II are discussed.

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.

Testing realistic SO(10) SUSY GUTs with proton decay and gravitational waves

We present a comprehensive analysis of a supersymmetric SO(10) grand unified theory, which is broken to the Standard Model via the breaking of two intermediate symmetries. The spontaneous breaking of the first intermediate symmetry, B−L, leads to the generation of cosmic strings and right-handed neutrino masses and further to an observable cosmological background of gravitational waves and generation of light neutrino masses via type-I seesaw mechanism. Supersymmetry breaking manifests as sparticle masses below the B−L breaking but far above the electroweak scale due to proton decay limits. This naturally pushes the B−L breaking scale close to the grand unified theory scale, leading to the formation of metastable cosmic strings, which can provide a gravitational wave spectrum consistent with the recent pulsar timing arrays observation. We perform a detailed analysis of this model using two-loop renormalization group equations, including threshold corrections, to determine the symmetry-breaking scale consistent with the recent pulsar timing arrays signals such as NANOGrav 15-year data and testable by the next-generation limits on proton decay from Hyper-K and JUNO. Simultaneously, we find the regions of the model parameter space that can predict the measured quark and lepton masses and mixing, baryon asymmetry of our Universe, a viable dark matter candidate and can be tested by a combination of neutrinoless double beta decay searches and limits on the sum of neutrinos masses. Published by the American Physical Society 2024

Selection and purification of Li2CO3 precursor for bolometric double beta decay experiments

This paper describes the preparation of radiopure lithium carbonate powder for the needs of low-background research, in particular, AMoRE-II, the second phase of a search for the neutrinoless double-beta decay (0νDBD) of the 100Mo isotope using over 100 kg of 100Mo contained in 200 kg of ultra-pure Li2100MoO4 bolometric crystals. About 150 kg of pure Li2CO3 powder is required to synthesize the crystals. The desired radiopurity for the lithium powder is 40K below 100 mBq/kg, and Th/U and Ra are at a few mBq/kg. Several commercially available powders were tested with ICP-MS and HPGe detectors at the Center for Underground Physics (CUP) of the Institute for Basic Science in Korea. The lowest purity of the tested products was 99.99%. The results of the powders’ radioassay at CUP showed that none of the tested products were suited for the 0νDBD search application. A special purification technology had to be developed to remove the original contamination of the powder with potassium (K), thorium (Th), uranium (U), and radium (Ra). Lithium carbonate crystallization via carbonization technique was inefficient in removing radiochemical impurities. Lithium formate fractional recrystallization effectively removed Ra, K, and Th, but the synthesis of the final lithium carbonate product had a low yield and required the introduction of additional chemicals. The analysis results of raw and purified powders, the decontamination efficiency, and plans are described in the article.

First Study of the PIKACHU Project: Development and Evaluation of High-Purity Gd3Ga3Al2O12:Ce Crystals for 160Gd Double Beta Decay Search

Abstract Uncovering neutrinoless double beta decay (0ν2β) is crucial for confirming neutrinos’ Majorana characteristics. The decay rate of 0νββ is theoretically uncertain, influenced by nuclear matrix elements that vary across nuclides. To reduce this uncertainty, precise measurement of the half-life of neutrino-emitting double beta decay (2ν2β) in different nuclides is essential. We have launched the PIKACHU (Pure Inorganic scintillator experiment in KAmioka for CHallenging Underground sciences) project to fabricate high-purity Ce-doped Gd3Ga3Al2O12 (GAGG) single crystals and use them to study the double beta decay of 160Gd. Predictions from two theoretical models on nuclear matrix element calculations for 2ν2β in 160Gd show a significant discrepancy in estimated half-lives, differing by approximately an order of magnitude. If the lower half-life estimation holds true, detecting 2ν2β in 160Gd could be achievable with a sensitivity enhancement slightly more than an order of magnitude compared to prior investigations using Ce-doped Gd2SiO5 (GSO) crystal. We have successfully developed GAGG crystals with purity levels surpassing previous standards through refined purification and selection of raw materials. Our experiments with these crystals indicate the feasibility of reaching sensitivities exceeding those of earlier studies. This paper discusses the ongoing development and scintillator performance evaluation of High-purity GAGG crystals, along with the anticipated future prospects of the PIKACHU experiment.

Experimental and theoretical multichannel study of direct nuclear reactions: A tool to provide data driven information on neutrino-less double-beta decay

The search for neutrino-less double beta decay has attracted much interest in the last years due to the extraordinary consequences that could derive from its observation. In the view to provide experimental information on the nuclear matrix elements involved in the expression of neutrino-less double beta decay half-life, the NUMEN project is measuring cross-sections of double charge exchange and other quasi-elastic nuclear reactions using the MAGNEX magnetic spectrometer. In particular, the newly proposed multichannel approach, applied both to the experimental and theoretical analysis, will be discussed.

Status and prospects of the PandaX-III experiment

The PandaX-III experiment searches for neutrinoless double beta decay of 136Xe with a high-pressure xenon gaseous time projection chamber (TPC). Thermal-bonding Micromegas modules are used for charge collection. Benefitting from the excellent energy resolution and imaging capability, the background rate can be significantly suppressed through the topological information of events. The technology is successfully demonstrated by a prototype detector. The final detector has been constructed. In this paper, we will report the status of the PandaX-III experiment, including the construction and commissioning of the final detector, and the Micromegas-based TPC performance test in the prototype detector.

Constraints on the Decay of ^{180m}Ta.

^{180m}Ta is a rare nuclear isomer whose decay has never been observed. Its remarkably long lifetime surpasses the half-lives of all other known β and electron capture decays due to the large K-spin differences and small energy differences between the isomeric and lower-energy states. Detecting its decay presents a significant experimental challenge but could shed light on neutrino-induced nucleosynthesis mechanisms, the nature of dark matter, and K-spin violation. For this study, we repurposed the Majorana Demonstrator, an experimental search for the neutrinoless double-beta decay of ^{76}Ge using an array of high-purity germanium detectors, to search for the decay of ^{180m}Ta. More than 17kg, the largest amount of tantalum metal ever used for such a search, was installed within the ultralow-background detector array. In this Letter, we present results from the first year of Ta data taking and provide an updated limit for the ^{180m}Ta half-life on the different decay channels. With new limits up to 1.5×10^{19} yr, we improved existing limits by 1-2 orders of magnitude which are the most sensitive searches for a single β and electron capture decay ever achieved. Over all channels, the decay can be excluded for T_{1/2}<0.29×10^{18} yr.

R2D2 TPC: first Xenon results

Radial time projection chambers (TPC), already employed in the search for rare phenomena such as light Dark Matter candidate, could provide a new detection approach for the search of neutrinoless double beta decay (ββ0ν). The assessment of the performances of such a detector for ββ0ν search is indeed the goal of the Rare Decays with Radial Detector (R2D2) R&D. Promising results operating a spherical TPC with argon up to 1 bar have been published in 2021. Supplementary measurements were recently taken extending the gas pressure range up to 3 bar. In addition, a comparison between two detector geometries, namely spherical (SPC for spherical proportional counter) and cylindrical (CPC for cylindrical proportional counter), was performed. Using a relatively simple gas purification system the CPC detector was also operated with xenon at 1 bar: an energy resolution of 1.4% full-width at half-maximum was achieved for drift distances up to 17 cm. Much lower resolution was observed with the SPC. These results are presented in this article.

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.

Search for two-neutrino double-beta decay of 136Xe to the excited state of 136Ba with the complete EXO-200 dataset* *EXO-200 is supported by DOE and NSF in the United States, NSERC in Canada, SNF in Switzerland, IBS in Korea, DFG in Germany, and CAS in China. EXO-200 data analysis and simulation uses resources of the National Energy Research Scientific Computing Center

A new search for two-neutrino double-beta (2νββ) decay of 136Xe to the excited state of 136Ba is performed with the full EXO-200 dataset. A deep learning-based convolutional neural network is used to discriminate signal from background events. Signal detection efficiency is increased relative to previous searches by EXO-200 by more than a factor of two. With the addition of the Phase II dataset taken with an upgraded detector, the median 90% confidence level half-life sensitivity of 2νββ decay to the state of 136Ba is yr using a total 136Xe exposure of 234.1 kg yr. No statistically significant evidence for 2νββ decay to the state is observed, leading to a lower limit of yr at 90% confidence level, improved by 70% relative to the current world's best constraint.

Tellurium-loaded organic scintillators

The R&D results of new tellurium-loaded liquid and plastic scintillators (TeLS and TePS) for the experiments on the search for neutrinoless double beta decay are presented. Linear alkylbenzene and polystyrene are used as a scintillation base for TeLS and TePS, respectively. Diphenyltellurium di-2-ethylhexanoate and a complex compound of diphenyltellurium oxide and di-(2-ethylhexyl)phosphoric acid are proposed as tellurium-containing additives. The transparency, light yield and long-term stability of the organic scintillators are discussed.

NEXT-CRAB-0: a high pressure gaseous xenon time projection chamber with a direct VUV camera based readout

The search for neutrinoless double beta decay (0νββ) remains one of the most compelling experimental avenues for the discovery in the neutrino sector. Electroluminescent gas-phase time projection chambers are well suited to 0νββ searches due to their intrinsically precise energy resolution and topological event identification capabilities. Scalability to ton- and multi-ton masses requires readout of large-area electroluminescent regions with fine spatial resolution, low radiogenic backgrounds, and a scalable data acquisition system. This paper presents a detector prototype that records event topology in an electroluminescent xenon gas TPC via VUV image-intensified cameras. This enables an extendable readout of large tracking planes with commercial devices that reside almost entirely outside of the active medium. Following further development in intermediate scale demonstrators, this technique may represent a novel and enlargeable method for topological event imaging in 0νββ.

Reduction of radioactive impurities in liquid scintillator by using metal scavengers

Development of radio-purification for the large-volume liquid scintillator detector is a key to enhance search sensitivities in neutrino physics. In this paper, we describe laboratory studies on the radio-purification of the liquid scintillator detector by using the metal scavenger, aiming at the improved search for the neutrinoless double beta decay in KamLAND-Zen. In the purification tests, the 210Pb reduction efficiency was evaluated. Based on the purification performance in small-scale system, we designed a large adsorption column for the metal scavenging applicable to the KamLAND purification system. We produced the column and constructed a purification test bench, and confirmed the 212Pb reduction efficiency, the process speed, the LS contamination and quality changes, and the stability of chemical components in the Xe-LS. We found that the metal scavenging is a practical method for the large-volume LS purification, and will be effective to reduce metallic radioactive elements.