Search For Double Beta Decay Research Articles

Low temperature luminescence and scintillation properties of NaLa(MoO4)2 crystal grown by the vertical Bridgman method

Scheelite related rare-earth double molybdate with the formula of NaLa(MoO4)2 is a promising scintillator for investigating the neutrinoless double beta decay process. In this study, NaLa(MoO4)2 crystal was grown by the vertical Bridgman method using spontaneous crystallization. The as-grown NaLa(MoO4)2 crystal exhibited yellow and dark blue in color (from top to the bottom). The powder x-ray diffraction and optical transmission spectra of the crystal were measured at room temperature. The temperature dependence of the luminescence and scintillation properties were measured under the excitations of 4.42 eV UV light from a LED source and β-particles from a90Sr source in 10–300 K range, respectively. The transmittance of the annealed NaLa(MoO4)2 crystal sample with the thickness of 10 mm was about 65–72% above the fundamental absorption edge. The light yield under UV and β-particles excitations were found to be enhanced upon cooling and exhibited maximum intensity at 10 K. The luminescence light yield of NaLa(MoO4)2 crystal was estimated to be about half of that of CaMoO4 crystal and 18 times as much as that of Li2MoO4 crystal at 10 K. The scintillation light yield of NaLa(MoO4)2 crystal reached the maximum at 10 K and was 70% of Li2MoO4 crystal. The shortest average decay time of 6.12 μs was obtained at 250 K, which was further slowed down upon cooling of the crystal and the longest average decay time of 442.77 μs was found to be at 10 K. Considering the possibility of crystal growth with large volume and high quality, the luminescence and scintillation properties of NaLa(MoO4)2 crystal revealed that this scintillation material may be a promising candidate as a cryogenic detector for investigating the neutrinoless double beta decay (0νββ) search.

A distributed readout network ASIC for high-density electrode array targeting at neutrinoless double-beta decay search in a Time Projection Chamber

We present a distributed, self-organizing and fault-tolerant readout network Application Specific Integrated Circuit (ASIC) for the high-density electrode array targeting at neutrinoless double-beta decay search in Time Projection Chamber (TPC). A meter-sized plane tiled by approximately 1×105 single-electrode Topmetal-S sensors with a pitch of 5∼10 mm is utilized to realize charge readout plane in a ton-scale high-pressure gaseous TPC. A sensor network is proposed under the premise of ensuring the tightness and radioactive purity of the high-pressure TPC. As a node of the network, each sensor not only generates and transmits its own data but also forwards the data from its adjacent sensors. Therefore, a Readout and Data-Routing Circuit (RDRC) is integrated into each sensor. To realize the RDRC, a distributed readout network ASIC is fabricated in a 130 nm CMOS Technology. A routing algorithm called Fault-Tolerance XY (FT-XY) is implemented to avoid the faulty sensors from disabling large sections of the network. A single ASIC and a 3 × 3 network have been tested. The test results show that the throughput of the 3 × 3 network reaches 110.52 Mbit/s.

Neutron background measurement for rare event search experiments in the YangYang underground laboratory

Several experiments have been conducted in the YangYang Underground Laboratory in the Republic of Korea such as the search for dark matter and the search for neutrinoless double beta decay, which require an extremely low background event rate due to the detector system and the environment. In underground experiments, neutrons have been identified as one of the background sources. The neutron flux in the experimental site needs to be determined to design a proper shielding system and for precise background estimation. We measured the neutron spectrum with a Bonner sphere spectrometer, with Helium-3 (3He) proportional counters. The neutron flux at the underground laboratory was so low that the radioactive decays from the radioisotopes contained in the detector created a significant background interference to the neutron measurement. Using Monte Carlo simulations, the intrinsic α background distribution due to the radioactive isotopes in the detector materials, was estimated. The neutron count rate of each Bonner sphere was measured from the pulse height spectrum of the 3He proportional counter, after subtracting the α particle background. The neutron flux and the energy spectrum were determined using the unfolding technique. The total neutron flux measured was (4.46 ± 0.66) × 10−5 cm−2 s−1, and the thermal and fast neutron flux (in the range 1–10 MeV) were (1.44 ± 0.15) × 10−5 cm−2 s−1 and (0.71 ± 0.10) × 10−5 cm−2 s−1, respectively.

A resistive ACHINOS multi-anode structure with DLC coating for spherical proportional counters

The spherical proportional counter is a gaseous detector used in a variety of applications, including direct dark matter and neutrino-less double beta decay searches. The ACHINOS multi-anode structure is a read-out technology that overcomes the limitations of single-anode read-out structures for large-size detectors and operation under high pressure. A resistive ACHINOS is presented, where the 3D printed central component is coated in a Diamond-Like Carbon (DLC) layer. The production and testing of the structure, in terms of stability and resolution, is described.

Searching for New Physics in Two-Neutrino Double Beta Decay.

Motivated by nonzero neutrino masses and the possibility of new physics discovery, a number of experiments search for neutrinoless double beta decay. While hunting for this hypothetical nuclear process, a significant amount of two-neutrino double beta decay data have become available. Although these events are regarded and studied mostly as the background of neutrinoless double beta decay, they can also be used to probe physics beyond the standard model. In this Letter, we show how the presence of right-handed leptonic currents would affect the energy distribution and angular correlation of the outgoing electrons in two-neutrino double beta decay. Consequently, we estimate constraints imposed by currently available data on the existence of right-handed neutrino interactions without having to assume their nature. In this way, our results complement the bounds coming from the nonobservation of neutrinoless double beta decay as they limit also the exotic interactions of Dirac neutrinos. We perform a detailed calculation of two-neutrino double beta decay under the presence of exotic (axial-) vector currents, and we demonstrate that current experimental searches can be competitive to existing limits.

Controlling T c of iridium films using the proximity effect

A superconducting Transition-Edge Sensor (TES) with low-Tc is essential in high resolution calorimetric detection. With the motivation of developing sensitive calorimeters for applications in cryogenic neutrinoless double beta decay searches, we have been investigating methods to reduce the Tc of an Ir film down to 20 mK. Utilizing the proximity effect between a superconductor and a normal metal, we found two room temperature fabrication recipes for making Ir-based low-Tc films. In the first approach, an Ir film sandwiched between two Au films, a Au/Ir/Au trilayer, has a tunable Tc in the range of 20–100 mK depending on the relative thicknesses. In the second approach, a paramagnetic Pt thin film is used to create the Ir/Pt bilayer with a tunable Tc in the same range. We present a detailed study of fabrication and characterization of Ir-based low-Tc films and compare the experimental results to the theoretical models. We show that Ir-based films with a predictable and reproducible critical temperature can be consistently fabricated for use in large scale detector applications.

Search for Double Beta Decay of 106Cd with an Enriched 106CdWO4 Crystal Scintillator in Coincidence with CdWO4 Scintillation Counters

Studies on double beta decay processes in 106Cd were performed by using a cadmium tungstate scintillator enriched in 106Cd at 66% (106CdWO4) with two CdWO4 scintillation counters (with natural Cd composition). No effect was observed in the data that accumulated over 26,033 h. New improved half-life limits were set on the different channels and modes of the 106Cd double beta decay at level of limT1/2∼1020−1022 yr. The limit for the two neutrino electron capture with positron emission in 106Cd to the ground state of 106Pd, T1/22νECβ+≥2.1×1021 yr, was set by the analysis of the 106CdWO4 data in coincidence with the energy release 511 keV in both CdWO4 counters. The sensitivity approaches the theoretical predictions for the decay half-life that are in the range T1/2∼1021−1022 yr. The resonant neutrinoless double-electron capture to the 2718 keV excited state of 106Pd is restricted at the level of T1/20ν2K≥2.9×1021 yr.

Применение современных конструкционных материалов, методик и детекторов для низкофоновых экспериментов

Good examples of the key tasks of modern non-accelerator physics are the searches for dark matter and neutrinoless double beta decay. The essential requirement for such an experiment is the requirement of a minimal background level. The ways to reduce it are quite obvious and widely used in the ongoing experiments. So, the experiments are located in the underground laboratories, a careful selection of structural materials is carried out, and various techniques for active background suppression are used. However, in order to advance in new generation projects in addition to a serious increase in the detector mass, the significant reduction of the background level (which is already pretty low) is required. Very important irremovable background sources are the structural materials close to the detector(s). In this regard, it is extremely important not only to constantly search for new low-background materials, but also to ensure that radioactive contaminants cannot be introduced at the stage of the required parts production. In this article the results of the successful using of structural parts produced by modern methods from novel low-background materials during the preparation of the new generation ultra-low-background experiment searching for neutrinoless double beta decay are presented.

Projected sensitivity of the LUX-ZEPLIN experiment to the 0νββ decay of Xe136

The LUX-ZEPLIN (LZ) experiment will enable a neutrinoless double beta decay search in parallel to the main science goal of discovering dark matter particle interactions. We report the expected LZ sensitivity to $^{136}$Xe neutrinoless double beta decay, taking advantage of the significant ($>$600 kg) $^{136}$Xe mass contained within the active volume of LZ without isotopic enrichment. After 1000 live-days, the median exclusion sensitivity to the half-life of $^{136}$Xe is projected to be 1.06$\times$10$^{26}$ years (90% confidence level), similar to existing constraints. We also report the expected sensitivity of a possible subsequent dedicated exposure using 90% enrichment with $^{136}$Xe at 1.06$\times$10$^{27}$ years.

Purification and recovery of 100MoO3 in crystal production for AMoRE experiment

The AMoRE collaboration searches for the neutrinoless double-beta decay of 100Mo with ultra-radiopure molybdate crystals operated as low-temperature scintillating bolometers. For such a rare event search experiment, the techniques for investigating and reducing radioactive background contaminants in detector materials are extremely crucial. This paper discusses techniques for deep purification of enriched molybdenum for growing the crystals and the recovery of 100MoO3 from the residual melt left after growing lithium molybdate crystals. The purities of enriched molybdenum trioxide powders before and after the purification and that of the recovered powder were tested with ICP-MS; results of these tests are presented.

Front-End Electronics for the SiPM-Readout Gaseous TPC for Neutrinoless Double-Beta Decay Search

We have developed a dedicated front-end-electronics board for a high-pressure xenon gas time projection chamber for a neutrinoless double-beta decay search. The ionization signal is readout by detecting electroluminescence photons with SiPM's. The board readout the signal from 56~SiPM's through the DC-coupling and record the waveforms at 5 MS/s with a wide dynamic range up to 7,000 photons/200 ns. The SiPM bias voltages are provided by the board and can be adjusted for each SiPM. In order to calibrate and monitor the SiPM gain, additional auxiliary ADC measures 1 photon-equivalent dark current. The obtained performance satisfies the requirement for a neutrinoless double-beta decay search.

Development of Tin-Based Single Crystal Scintillator for Double-Beta Decay Experiments

124Sn is one of the potential candidate isotopes for the study of $2\nu \beta \beta $ and $0\nu \beta \beta $ decay having a $\text{Q}_{ \boldsymbol {\beta \beta } }$ value of 2.228 MeV and natural isotopic abundance of 5.8%. 124Sn-loaded-liquid scintillator has been investigated for $2\nu \beta \beta $ and $0\nu \beta \beta $ decay search. Since $2\nu \beta \beta $ has not been experimentally observed from 124Sn isotope, unlike some of the isotopes subject to double-beta decay (DBD), it is necessary to study this element. However, lower light yield, chemical instability, and lower Sn-loading capability are some of the limitations of the liquid and plastic scintillators. The current investigation has been carried out to develop a single crystal of tetraphenyltin (TPSn) for the $2\nu \beta \beta $ and $0\nu \beta \beta $ decay search experiments. The TPSn powder for crystal growing was purified by recrystallization. The single crystals were grown using two-zone vertical Bridgman and slow solvent-evaporation techniques. Purified powder, diphenyloxazole (PPO), 1, 4-bis(2-methylstyryl) benzene (bis-MSB), and anthracene-doped Bridgman-grown crystal and anthracene-doped solvent-evaporation grown crystals showed X-ray induced emission peaking at 475 nm. The anthracene-doped crystal grown by solvent evaporation method showed scintillation under $\alpha $ -particles excitation from 241Am source. Two decay components, 16 ns with 68.7% and 132 ns with 31.3% relative contributions, were observed under $\alpha $ -particles excitation. This article suggests that after crystal growth optimization, TPSn can be a promising candidate for the DBD search of 124Sn.

Theia: an advanced optical neutrino detector

New developments in liquid scintillators, high-efficiency, fast photon detectors, and chromatic photon sorting have opened up the possibility for building a large-scale detector that can discriminate between Cherenkov and scintillation signals. Such a detector could reconstruct particle direction and species using Cherenkov light while also having the excellent energy resolution and low threshold of a scintillator detector. Situated deep underground, and utilizing new techniques in computing and reconstruction, this detector could achieve unprecedented levels of background rejection, enabling a rich physics program spanning topics in nuclear, high-energy, and astrophysics, and across a dynamic range from hundreds of keV to many GeV. The scientific program would include observations of low- and high-energy solar neutrinos, determination of neutrino mass ordering and measurement of the neutrino CP-violating phase delta , observations of diffuse supernova neutrinos and neutrinos from a supernova burst, sensitive searches for nucleon decay and, ultimately, a search for neutrinoless double beta decay, with sensitivity reaching the normal ordering regime of neutrino mass phase space. This paper describes Theia, a detector design that incorporates these new technologies in a practical and affordable way to accomplish the science goals described above.

ADC Nonlinearity Correction for the Majorana Demonstrator

Imperfections in analog-to-digital conversion (ADC) cannot be ignored when signal digitization requirements demand both wide dynamic range and high resolution, as is the case for the Majorana Demonstrator <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">76</sup> Ge neutrinoless double-beta decay search. Enabling the experiment's high-resolution spectral analysis and efficient pulse shape discrimination required careful measurement and correction of ADC nonlinearities. A simple measurement protocol was developed that did not require sophisticated equipment or lengthy data-taking campaigns. A slope-dependent hysteresis was observed and characterized. A correction applied to digitized waveforms prior to signal processing reduced the differential and integral nonlinearities by an order of magnitude, eliminating these as dominant contributions to the systematic energy uncertainty at the double-beta decay Q value.

Alternative renormalizable SO(10) GUTs and data fitting

The alternative renormalizable minimal SO(10) model is composed of the Yukawa couplings with 10⊕120 Higgs fields, whereas the right-handed (RH) neutrino Majorana masses are generated via the Witten mechanism. The gauge coupling unification is achieved together with a unique pattern of the fermion masses and mixing at the grand unification scale due to additional contributions of vector-like quarks to the standard model renormalization group equations. We perform the fitting of the model to the experimental data of charged fermion masses and the CKM matrix. The best fit point is obtained with large pulls for mc, ms, mb, and mτ. For the modifications to the minimal model by adding either 10′ or 120′, a large deviation for the tau mass rules out all these models. In the case with the bottom and vector-like quark mixing, the mass matrices are well fitted the charged fermions but the bound on the light neutrino mass scale excludes this scenario. To ameliorate this deficit, we consider the two-step symmetry breaking scenario, SO(10)→SU(5)→SU(3)C×SU(2)L×U(1)Y, with the SO(10) breaking at the Planck scale leading to the radiatively generated RH neutrino Majorana masses being at the ordinary seesaw scale. For this case, we find the best fit point with χ2=7.8 consistent with experimental results including the neutrino sector. The largest deviation is 2.3σ corresponding to the strange quark mass. Hence, a more precise determination of the strange quark mass can test this model. For the best fit point, we find the effective Majorana neutrino mass of mββ=0.22 meV and the sum of light neutrino masses as Σ=0.078 eV, which are consistent with the current constraints from the search for the neutrinoless double beta decay and the CMB anisotropy measurement.

Design and performance of a high-pressure xenon gas TPC as a prototype for a large-scale neutrinoless double-beta decay search

Abstract A high-pressure xenon gas time projection chamber, with a unique cellular readout structure based on electroluminescence, has been developed for a large-scale neutrinoless double-beta decay search. In order to evaluate the detector performance and validate its design, a 180 L size prototype is being constructed and its commissioning with partial detector has been performed. The obtained energy resolution at 4.0 bar is 1.73 $\pm$ 0.07% (FWHM) at 511 keV. The energy resolution at the $^{136}$Xe neutrinoless double-beta decay $Q$-value is estimated to be between 0.79 and 1.52% (FWHM) by extrapolation. Reconstructed event topologies show patterns peculiar to the track endpoint that can be used to distinguish $0\nu\beta\beta$ signals from gamma-ray backgrounds.

PbMoO4 Synthesis from Ancient Lead and Its Single Crystal Growth for Neutrinoless Double Beta Decay Search

A powder synthesis of PbMoO4 (PMO) from ancient lead (Pb) and deeply purified commercial MoO3 powders was performed using a wet chemistry technique to achieve the low radioactivity scintillator for neutrinoless double beta decay search in 100Mo. The synthesized powders were used to grow single crystals of PbMoO4 by the Czochralski technique in an Ar environment. The luminescence and scintillation properties were measured with excitations using UV, X- and γ-rays in the temperature range of 10–300 K. Annealing of the grown PMO crystal in an air atmosphere significantly enhanced the scintillation light yield compared to that measured before annealing. The scintillation light yield of grown PMO crystal at 10 K was found to be 127% to that of a reference PMO crystal under 662 keV γ-rays excitation from a 137Cs source. The background measurement of the grown crystal performed at 50 K shows a lower internal activity from 210Pb compared to that of reference PMO (grown from modern Pb) crystal. These preliminary performances show that the PMO crystal grown from ancient Pb and deeply purified MoO3 powders has a great potential to be used as a cryogenic scintillator for the neutrinoless double beta decay search in 100Mo.

The CROSS Experiment: Rejecting Surface Events by PSD Induced by Superconducting Films

Neutrinoless double beta ($0\nu\beta\beta$) decay is a hypothetical rare nuclear transition ($T_{1/2}>10^{26}$ y). Its observation would provide an important insight about the nature of neutrinos (Dirac or Majorana particle) demonstrating that the lepton number is not conserved. This decay can be investigated with bolometers embedding the double beta decay isotope ($^{76}$Ge, $^{82}$Se, $^{100}$Mo, $^{116}$Cd, $^{130}$Te...), which perform as low temperature calorimeters (10 mK) detecting particle interactions via a small temperature rise read out by a dedicated thermometer. CROSS (Cryogenic Rare-event Observatory with Surface Sensitivity) aims at the development of bolometric detectors (Li$_{2}$MoO$_{4}$ and TeO$_{2}$) capable of discriminating surface $\alpha$ and $\beta$ interactions by exploiting superconducting properties of Al film deposited on the crystal surface. We report in this paper the results of tests on prototypes performed at CSNSM (Orsay, France) that showed the capability of a-few-$\mu$m-thick superconducting Al film deposited on crystal surface to discriminate surface $\alpha$ from bulk events, thus providing the detector with the required surface sensitivity capability. The CROSS technology would further improve the background suppression and simplify the detector construction with a view to future competitive double beta decay searches.

A new neutrinoless double beta decay experiment: R2D2

The search for neutrinoless double beta decay could cast light on one critical piece missing in our knowledge i.e. the nature of the neutrino mass. Its observation is indeed the most sensitive experimental way to prove that neutrino is a Majorana particle. The observation of such a potentially rare process demands a detector with an excellent energy resolution, an extremely low radioactivity and a large mass of emitter isotope. Nowadays many techniques are pursued but none of them meets all the requirements at the same time. The goal of R2D2 is to prove that a spherical high pressure TPC could meet all the requirements and provide an ideal detector for the 0vββ decay search. In the presented talk the R2D2 goal and preliminary results are presented as well as the project roadmap.

First results of KamLAND-Zen 800

KamLAND-Zen is a neutrinoless double beta decay (0vββ) search experiment using xenon 136 and ultra-low background environment of KamLAND (Kamioka Liquid scintillator Anti-Neutrino Detector). KamLAND-Zen collaboration has prepared the KamLAND-Zen 800 project with almost 750 kg of xenon and cleaner container for xenon loaded liquid scintillator. The container production was started in May 2017 and KamLAND-Zen 800 data acquisition was started in January 2019. In this paper, we will describe the KamLAND-Zen 800 project and report on the detector condition, data quality, the first analysis results, and the prospects.