A new multiwire proportional chamber (MWPC) was designed and constructed for precision studies of neutron beta decay angular correlations. Its design has several novel features, including the use of low pressure neopentane as the MWPC gas and an entrance window made of thin Mylar sheet reinforced with Kevlar fibers. In the initial off-line performance tests, the gas gain of neopentane and the position resolution were studied.
Gas Electron Multiplication technology is finding more and more applications in beam instrumentation and at CERN these detectors have recently been adapted for use in transverse profile measurements at several of our facilities. In the experimental areas of CERN's Antiproton Decelerator, low energy Gas Electron Multipliers successfully replaced all Multwire Proportional Chambers in 2012 and another detector type has now been developed for high energy applications in the experimental areas of the SPS, totaling a potential of more than a hundred profile detectors to be replaced by GEM detectors …
A numerical method of determining the wire sag in a multiwire proportional chamber used in RICH (ALICE) by solving the second order differential equation which governs the wire stability has been presented. The three point Finite Difference Method (FDM) has generated a tridiagonal matrix equation relating the deflection of wire segments to the force acting on it. The precise estimates of electrostatic force has been obtained from accurate field computation using a nearly exact Boundary Element Method (neBEM) solver.
The DeeMe experiment to search for muon-to-electron conversions with a sensitivity 10--100 times better than those achieved by previous experiments is in preparation at the Japan Proton Accelerator Research Complex. The magnetic spectrometer used by the DeeMe experiment consists of an electromagnet and four multiwire proportional chambers (MWPCs). The newly developed MWPCs are operated with a high voltage (HV) switching technique and have good burst-hit tolerance. In this article, the final designs of the MWPCs, amplifiers for readout, and HV switching modules are described. Additionally, some…
A new experiment, called DeeMe, which is designed to search for $μ$-e conversions with a sensitivity of $\mathcal{O}(10^{-14})$, is in preparation at the Japan Proton Accelerator Research Complex (J-PARC). It utilizes a high-quality pulsed proton beam from the Rapid Cycling Synchrotron at J-PARC. The detector for DeeMe must tolerate large pulses of prompt charged particles whose instantaneous hit rate is as large as 70 GHz/mm$^2$ in a time width of 200 ns and detect a single electron that arrives with delayed timing on the order of microseconds. A special wire chamber has been developed with a…
A prototype multiwire proportional chamber (MWPC) was developed to demonstrate the feasibility of constructing a radiopure time projection chamber with MWPC track readout to assay materials for alpha- and beta-emitting surface contaminants for future rare-event-search experiments as well as other scientific fields. The design features and assembly techniques described here are motivated by the position and energy resolution required to reconstruct alpha and beta tracks while efficiently rejecting backgrounds. Results from a test setup using an $^{55}$Fe x-ray source indicate excellent operatio…
Sensitivities of current directional dark matter search detectors using gas time projection chambers are now constrained by target mass. A ton-scale gas TPC detector will require large charge readout areas. We present a first demonstration of a novel ThGEM-Multiwire hybrid charge readout technology which combines the robust nature and high gas gain of Thick Gaseous Electron Multipliers with lower capacitive noise of a one-plane multiwire charge readout in SF$_6$ target gas. Measurements performed with this hybrid detector show an ion drift velocity of $139~\pm~12~\text{ms}^{-1}$ in a reduced d…
The PandaX-III (Particle And Astrophysical Xenon Experiment III) experiment will search for Neutrinoless Double Beta Decay (NLDBD) of 136Xe at the China Jin-Ping underground Laboratory II (CJPL-II). In the first phase of the experiment, a high pressure gas Time Projection Chamber (TPC) will contain 200 kg, 90% 136Xe enriched gas operated at 10 bar. Microbulk Micromegas, a fine pitch micro-pattern gas detector, will be used for charge readout and enable us to reconstruct tracks of NLDBD events with good energy and spatial resolution. With simulation, we demonstrate excellent background suppress…
We introduce a novel particle detection concept for large-volume, fine granularity particle detection: The Ion Fluorescence Chamber (IFC). In electronegative gases such as SF$_6$ and SeF$_6$, ionizing particles create ensembles of positive and negative ions. In the IFC, positive ions are drifted to a chemically active cathode where they react with a custom organic turn-on fluorescent monolayer encoding a long-lived 2D image. The negative ions are sensed electrically with course resolution at the anode, inducing an optical microscope to travel to and scan the corresponding cathode location for …
In this work, we present a new approach for fast tracking on multiwire proportional chambers with neural networks. The tracking networks are developed and adapted for the first-level trigger at hadron collider experiments. We use Monte Carlo samples generated by Geant4 with a custom muon chamber, which resembles part of the thin gap chambers from the ATLAS experiment, for training and performance evaluations. The chamber has a total of seven gas gaps, where the first and last gas gaps are displaced by ~1.5 m. Each gas gap has 50 channels with a size of 18-20 mm. Two neural network models are d…
Xenon time projection chambers (TPCs) have become a well-established detection technology for neutrinoless double beta decay searches in $^{136}$Xe. I discuss the motivations for this choice. I describe the status and prospects of both liquid and gaseous xenon TPC projects for double beta decay.
Searching for the Neutrinoless Double Beta Decay (NLDBD) is now regarded as the topmost promising technique to explore the nature of neutrinos after the discovery of neutrino masses in oscillation experiments. PandaX-III (Particle And Astrophysical Xenon Experiment III) will search for the NLDBD of $^{136}$Xe at the China Jin Ping underground Laboratory (CJPL). In the first phase of the experiment, a high pressure gas Time Projection Chamber (TPC) will contain 200 kg, 90% $^{136}$Xe enriched gas operated at 10 bar. Fine pitch micro-pattern gas detector (Microbulk Micromegas) will be used at bo…
Multi-channel wire gas electron multipliers (MWGEM) with gaps between the electrodes of 1 and 3mm were investigated. The chamber of the MWGEM was filled with pure commercial neon gas at pressure of 0.4 or 1.0 bar and irradiated by alpha-particles (Pu-239) or beta-particles (Ni-63). The following maximal coefficients of electrons proportional multiplication have been obtained: 6 \times 10^3 (alpha, d=3mm, P=1bar, 20% streamers); 1.2 \times 10^3 (beta-, d=3mm, P=1bar, 50% streamers); 6 \times 10^3 (alpha, d=3mm, P=0.4bar, 20% streamers); 10^5 (beta-, d=3mm, P=0.4bar, 50% streamers). For the case…
The nuclear fission process that occurs in the core of nuclear reactors results in unstable, neutron rich fission products that subsequently beta decay and emit electron anti-neutrinos. These reactor neutrinos have served neutrino physics research from the initial discovery of the neutrino to current precision measurements of neutrino mixing angles. The prediction of the absolute flux and energy spectrum of the emitted reactor neutrinos hinges upon a series of seminal papers based on measurements performed in the 1970s and 1980s. The steadily improving reactor neutrino measurement techniques a…
This article reviews the application of high pressure gas xenon (HPXe) time projection chambers to neutrinoless double beta decay experiments. First, the fundamentals of the technology and the historical development of the field are discussed. Then, the state of the art is presented, including the prospects for the next generation of experiments with masses in the ton scale.
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…
As part of the T-REX project, a number of R&D and prototyping activities have been carried out during the last years to explore the applicability of gaseous Micromegas-read TPCs in rare event searches like double beta decay (DBD), axion research and low-mass WIMP searches. In both this and its companion paper, we compile the main results of the project and give an outlook of application prospects for this detection technique. While in the companion paper we focus on axions and WIMPs, in this paper we focus on the results regarding the measurement of the DBD of $^{136}$Xe in a high pressure Xe …
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 extrapolati…
The next-generation Enriched Xenon Observatory (nEXO) is a proposed experiment to search for neutrinoless double beta ($0νββ$) decay in $^{136}$Xe with a target half-life sensitivity of approximately $10^{28}$ years using $5\times10^3$ kg of isotopically enriched liquid-xenon in a time projection chamber. This improvement of two orders of magnitude in sensitivity over current limits is obtained by a significant increase of the $^{136}$Xe mass, the monolithic and homogeneous configuration of the active medium, and the multi-parameter measurements of the interactions enabled by the time projecti…
We report on measurements of relative beta-decay rates of Na-22, Cl-36, Co-60, Sr-90, Cs-137 monitored for more than one year. The radioactive samples are mounted in an automated sample changer that sequentially positions the five samples in turn, with high spatial precision, in front of each of four Geiger-Müller tubes. The sample wheel, detectors, and associated electronics are housed inside a sealed chamber held at constant absolute pressure, humidity, and temperature to isolate the experiment from environmental variations. The statistical uncertainty in the count rate approaches a few time…
NEXT (Neutrino Experiment with a Xenon TPC) is a neutrinoless double-beta (ββ0ν) decay experiment that will operate at the Canfranc Underground Laboratory (LSC). It is an electroluminescent high-pressure gaseous xenon Time Projection Chamber (TPC) with separate read-out planes for calorimetry and tracking. Energy resolution and background suppression are the two key features of any neutrinoless double beta decay experiment. NEXT has both good energy resolution (<1% FWHM) at the Q value of $^{136} $Xe and an extra handle for background identification provided by track reconstruction. With the b…
High pressure gas detectors offer advantages for the detection of rare events, where background reduction is crucial. For the neutrinoless double beta decay of 136Xe a high pressure xenon gas Time Projection Chamber (TPC) combines a good energy resolution and a detailed topological information of each event. The ionization topology of the double beta decay event of 136Xe in gaseous xenon has a characteristic shape defined by the two straggling electron tracks ending up in two higher ionization charge density blobs. With a properly pixelized readout, this topological information is invaluable t…
Searches of new physics beyond the Standard Model (SM) performed at low energy frontiers are complementary to experiments carried out at high energy colliders. Among the methods for testing the SM and beyond at low energies are the precision spectrum shape and correlation coefficient measurements in nuclear and neutron beta decay. In order to study tiny effects in beta spectrum shape, a special spectrometer was built. It consists of a 3D low pressure gas tracker (drift chamber with hexagonal cells, signal readout at both wire ends) and plastic scintillators for triggering data acquisition and …
Experimental updates on development of accelerator-driven ion source at TRIUMF to benchmark Ba-tagging techniques for future neutrinoless double beta decay searches
TRIUMF（特柳姆夫国家粒子加速器中心）；Department of Physics and Astronomy, McMaster University（麦克马斯特大学物理与天文系）；Department of Physics and Physical Oceanography, University of North Carolina at Wilmington（北卡罗来纳大学威尔明顿分校物理与物理海洋学系）；Department of Physics, McGill University（麦吉尔大学物理系）；Department of Physics and Astronomy, University of Victoria（维多利亚大学物理与天文系）
The neutron lifetime, $τ$ = 880.2 $\pm$ 1.0 sec , is an important parameter for particle physics and cosmology. There is, however, an 8.4 sec (4.0$\,σ$) deviation between the measured value of the neutron lifetime using two methods : one method counts neutrons that survive after some time, while the other counts protons resulting from neutron beta decay. A new method is being implemented at J-PARC / MLF / BL05 using a pulsed cold neutron beam. A Time Projection Chamber (TPC) records both the electrons from neutron beta decay and protons from the neutron-$^3$He capture reactions in order to est…
We have built and operated a crystalline/vapor xenon TPC, with the goal of improving searches for dark matter. The motivation for this instrument is the fact that beta decays from the radon decay chain to the ground state presently limit the state-of-the-art liquid/vapor xenon experiments. In contrast, a crystalline xenon target has the potential to tag and reject radon-chain backgrounds, due to the time and energy signature of their decays. The present article is the first demonstration of a crystalline/vapor xenon TPC with electroluminescence (gas gain) for the electron signal readout. It al…
We present a new neutrinoless double beta decay concept: the high pressure selenium hexafluoride gas time projection chamber. Combining techniques pioneered in high pressure xenon gas such as topological discrimination, with the high Q-value afforded by double beta decay isotope $^{82}$Se, a promising new detection technique is outlined. Lack of free electrons in SeF$_6$ mandates the use of an ion TPC. The microphysics of ion production and drift, which have many nuances, are explored. Background estimates are produced suggesting such a detector may achieve background indices of better than 1 …
Liquid Xe TPCs are among the most popular choices for double beta decay and WIMP dark matter searches. Gaseous Xe has intrinsic advantages when compared to Liquid Xe, specifically, tracking capability and better energy resolution for double beta decay searches. The performance of gaseous Xe can be further improved by molecular additives such as trimethylamine(TMA), which are expected to (1) cool down the ionization electrons, (2) convert Xe excitation energy to TMA ionizations through Penning transfer, and (3) produce scintillation and electroluminescence light in a more easily detectable wave…
We propose a novel charge sensing concept for high-pressure Time Projection Chamber (TPC) to search for Neutrinoless Double-Beta Decay (NLDBD) with ton-scale isotope mass and beyond. A meter-sized plane, tiled with an array of CMOS integrated sensors called Topmetal that directly collect charge without gas avalanche gain, is to be deployed into a high-pressure gaseous TPC with working gases containing suitable NLDBD candidate isotopes such as Xe-136 and Se-82. The Topmetal sensor has an electronic noise <30 e- per pixel, which allows the detector to reach <1% FWHM energy resolution at the NLDB…
We propose a novel detection concept for neutrinoless double-beta decay searches. This concept is based on a Time Projection Chamber (TPC) filled with high-pressure gaseous xenon, and with separated-function capabilities for calorimetry and tracking. Thanks to its excellent energy resolution, together with its powerful background rejection provided by the distinct double-beta decay topological signature, the design discussed in this Letter Of Intent promises to be competitive and possibly out-perform existing proposals for next-generation neutrinoless double-beta decay experiments. We discuss …
The gaseous Xenon(Xe) time projection chamber (TPC) is an attractive detector technique for neutrinoless double beta decay and WIMP dark matter searches. While it is less dense compared to Liquid Xe detectors, it has intrinsic advantages in tracking capability and better energy resolution. The performance of gaseous Xe can be further improved by molecular additives such as trimethylamine(TMA), which is expected to (1) cool down the ionization electrons, (2) convert Xe excitation energy to TMA ionizations through Penning transfer, and (3) produce scintillation and electroluminescence light in a…
Long-lived alpha and beta emitters in the $^{222}$Rn decay chain on detector surfaces may be the limiting background in many experiments attempting to detect dark matter or neutrinoless double-beta decay. Removal of tens of microns of material via electropolishing has been shown to be effective at removing radon daughters implanted into material surfaces. Some applications, however, require the removal of uniform and significantly smaller thicknesses. Here, we demonstrate that electropolishing < 1 $μ$m from stainless-steel plates reduces the contamination efficiently, by a factor > 100. Examin…
In this work, we present the concept for large low-background experiments in which an unusual gas mixture gas serves as a seamless, high-QE, near-100\%-coverage photodetector for scintillation or \cerenkov photons. We fill a large time projection chamber with a VUV scintillating gas, plus an unusually small admixture dopant gas with a low ionization threshhold (and a high ionization yield), akin to a highly-underquenched Penning mixture. Scintillation photons travel far from a primary ionization site before converting into photoionization electrons. Using standard TPC methods, we can separatel…
A high pressure xenon gas time projection chamber with electroluminescent amplification (EL HPGXe TPC) searching for the neutrinoless double beta ($0νββ$) decay offers: excellent energy resolution ($0.5-0.7\%$ FWHM at the $Q_{ββ}$), by amplifying the ionization signal with electroluminescent light, and tracking capabilities, as demonstrated by the NEXT collaboration using two kg-scale prototypes. The NEXT collaboration is building an EL HPGXe TPC capable of holding 100 kg (NEXT-100) of xenon isotopically enriched in ${{}^{136}\rm Xe}$. The installation and commissioning of the NEXT-100 detecto…
Several efforts are ongoing for the development of spherical gaseous time projection chamber detectors for the observation of rare phenomena such as weakly interacting massive particles or neutrino interactions. The proposed detector, thanks to its simplicity, low energy threshold and energy resolution, could be used to observe the $β\beta0ν$ process i.e. the neutrinoless double beta decay. In this work, a specific setup is presented for the measurement of $β\beta0ν$ on 50~kg of $^{136}$Xe. The different backgrounds are studied, demonstrating the possibility to reach a total background per yea…
We present a new detection scheme for rejecting backgrounds in neutrino less double beta decay experiments. It relies on the detection of Cherenkov light emitted by electrons in the MeV region. The momentum threshold is tuned to reach a good discrimination between background and good events. We consider many detector concepts and a range of target materials. The most promising is a high-pressure 136Xe emitter for which the required energy threshold is easily adjusted. Combination of this concept and a high pressure Time Projection Chamber could provide an optimal solution. A simple and low cos…
A new method to tag the barium daughter in the double beta decay of $^{136}$Xe is reported. Using the technique of single molecule fluorescent imaging (SMFI), individual barium dication (Ba$^{++}$) resolution at a transparent scanning surface has been demonstrated. A single-step photo-bleach confirms the single ion interpretation. Individual ions are localized with super-resolution ($\sim$2~nm), and detected with a statistical significance of 12.9~$σ$ over backgrounds. This lays the foundation for a new and potentially background-free neutrinoless double beta decay technology, based on SMFI co…
The PandaX-III experiment will search for neutrinoless double beta decay of $^{136}$Xe with high pressure gaseous time projection chambers at the China Jin-Ping underground Laboratory. The tracking feature of gaseous detectors helps suppress the background level, resulting in the improvement of the detection sensitivity. We study a method based on the convolutional neural networks to discriminate double beta decay signals against the background from high energy gammas generated by $^{214}$Bi and $^{208}$Tl decays based on detailed Monte Carlo simulation. Using the 2-dimensional projections of …
We report the Neutrino-less Double Beta Decay (NLDBD) search results from PandaX-II dual-phase liquid xenon time projection chamber. The total live time used in this analysis is 403.1 days from June 2016 to August 2018. With NLDBD-optimized event selection criteria, we obtain a fiducial mass of 219 kg of natural xenon. The accumulated xenon exposure is 242 kg$\cdot$yr, or equivalently 22.2 kg$\cdot$yr of $^{136}$Xe exposure. At the region around $^{136}$Xe decay Q-value of 2458 keV, the energy resolution of PandaX-II is 4.2%. We find no evidence of NLDBD in PandaX-II and establish a lower limi…
Large detectors employing xenon are a leading technology in existing and planned searches for new physics, including searches for neutrinoless double beta decay ($0νββ$) and dark matter. While upcoming detectors will employ target masses of a ton or more, further extending gas or liquid phase Xe detectors to the kton scale would enable extremely sensitive next-generation searches for rare phenomena. The key challenge to extending this technology to detectors well beyond the ton scale is the acquisition of the Xe itself. We describe the motivation for extending Xe time projection chambers (TPCs…
Enhancing Neutrinoless Double-Beta Decay Sensitivity of Liquid-Xenon Time Projection Chamber with Augmented Convolutional Neural Network
Columbia University（哥伦比亚大学）；Nikhef and the University of Groningen, Van Swinderen Institute（NIKHEF与格罗宁根大学范斯温德伦研究所）；Kamioka Observatory, Institute for Cosmic Ray Research, and Kavli Institute for the Physics and Mathematics of the Universe (WPI), University of Tokyo（东京大学神冈观测站、宇宙线研究所及Kavli宇宙物理数学研究所（WPI））；Physik-Institut, University of Zürich（苏黎世大学物理研究所）；LPNHE, Sorbonne Université, CNRS/IN2P3（索邦大学LPNHE，CNRS/IN2P3）；Institut für Kernphysik, University of Münster（明斯特大学核物理研究所）；INFN-Laboratori Nazionali del Gran Sasso and Gran Sasso Science Institute（意大利国家核物理研究所大萨索国家实验室与大萨索科学研究所）；Department of Physics, Enrico Fermi Institute & Kavli Institute for Cosmological Physics, University of Chicago（芝加哥大学费米研究所与Kavli宇宙物理研究所物理系）；Max-Planck-Institut für Kernphysik（马克斯·普朗克核物理研究所）；New York University Abu Dhabi - Center for Astro, Particle and Planetary Physics（纽约大学阿布扎比分校天体、粒子与行星物理中心）；SUBATECH, IMT Atlantique, CNRS/IN2P3（IMT大西洋学院SUBATECH，CNRS/IN2P3）
NEXT (Neutrino Experiment with a Xenon TPC) is a neutrinoless double beta decay experiment located at the Laboratorio Subterráneo de Canfranc (LSC, Spain). Its aim is to demonstrate that the neutrino is a Majorana particle by detecting the neutrinoless double beta decay process in xenon gas enriched in the $^{136}$Xe isotope. The detector technology used in NEXT is that of radiopure high pressure time projection chambers with electroluminescence amplification, which provide excellent energy resolution better than 1$\%$ FWHM in the energy region of interest, topological reconstruction that allo…
The Neutrino Experiment with a Xenon TPC (NEXT) seeks to discover the neutrinoless double beta ($ββ0ν$) decay of $^{136}$Xe using a high-pressure xenon gas time projection chamber with electroluminescent amplification. The observation of $ββ0ν$ decay would prove that neutrinos are Majorana particles and that lepton number is not conserved. The NEXT detector concept offers several features of great value for $ββ0ν$-decay searches, including excellent energy resolution, tracking for the active suppression of backgrounds and scalability to large source masses. The initial phase of the NEXT projec…
Radio-frequency (RF) carpets with ultra-fine pitches are examined for ion transport in gases at atmospheric pressures and above. We develop new analytic and computational methods for modeling RF ion transport at densities where dynamics are strongly influenced by buffer gas collisions. An analytic description of levitating and sweeping forces from phased arrays is obtained, then thermodynamic and kinetic principles are used to calculate ion loss rates in the presence of collisions. This methodology is validated against detailed microscopic SIMION simulations. We then explore a parameter space …
For identification and 3D-tracking of low-energy electrons a new type of gas-based detector was designed that minimizes scattering and energy loss. The current version of the detector is a combination of a plastic scintillator, serving as a trigger source and energy detector, and a hexagonally structured multi-wire drift chamber (MWDC), filled with a mixture of helium and isobutane gas. The drift time information is used to track particles in the plane perpendicular to the wires, while a charge division technique provides spatial information along the wires. The gas tracker was successfully us…
We demonstrate that the application of an external magnetic field could lead to an improved background rejection in neutrinoless double-beta (0nbb) decay experiments using a high pressure xenon (HPXe) TPC. HPXe chambers are capable of imaging electron tracks, a feature that enhances the separation between signal events (the two electrons emitted in the 0nbb decay of 136Xe) and background events, arising chiefly from single electrons of kinetic energy compatible with the end-point of the 0nbb decay (Qbb ). Applying an external magnetic field of sufficiently high intensity (in the range of 0.5-1…
NEXT-100 is an electroluminescent high-pressure xenon gas time projection chamber that will search for the neutrinoless double beta ($ββ0 ν$) decay of Xe-136. The detector possesses two features of great value for $ββ0 ν$ searches: energy resolution better than 1\% FWHM at the $Q$ value of Xe-136 and track reconstruction for the discrimination of signal and background events. This combination results in excellent sensitivity, as discussed in this paper. Material-screening measurements and a detailed Monte Carlo detector simulation predict a background rate for NEXT-100 of at most $4\times10^{-…
NEXT (Neutrino Experiment with a Xenon TPC) aims to observe the neutrinoless double beta decay of \ensuremath{{}^{136}\rm Xe} in a high-pressure gas xenon Time Projection Chamber using electroluminescence to amplify the signal from ionization. The two main advantages of this technology are a high energy resolution and the possibility of reconstructing electron tracks. NEXT-100 is an electroluminescent, asymmetric TPC which will host 100 kg of the \ensuremath{{}^{136}\rm Xe} isotope at 15 bar of pressure. On one side, a sparse array of photomultipliers records both the primary scintillation sig…
Searching for neutrinoless double beta decays ($β\beta0ν$) is the only practical way to establish if the neutrinos are their own antiparticles. Due to the smallness of neutrino masses, the lifetime of $β\beta0ν$ is expected to be at least ten orders of magnitude smaller than the noise associated with the natural radioactive chains. A positive identification of $β\beta0ν$ decays requires, ultimately, finding a signal that cannot be mimicked by radioactive backgrounds. This signal could be the observation of the daughter atom in the decay, since no known background processes induce a Z+2 transfo…
The measurement of the internal $^{222}$Rn activity in the NEXT-White detector during the so-called Run-II period with $^{136}$Xe-depleted xenon is discussed in detail, together with its implications for double beta decay searches in NEXT. The activity is measured through the alpha production rate induced in the fiducial volume by $^{222}$Rn and its alpha-emitting progeny. The specific activity is measured to be $(38.1\pm 2.2~\mathrm{(stat.)}\pm 5.9~\mathrm{(syst.)})$~mBq/m$^3$. Radon-induced electrons have also been characterized from the decay of the $^{214}$Bi daughter ions plating out on t…
The DARWIN observatory is a proposed next-generation experiment to search for particle dark matter and for the neutrinoless double beta decay of $^{136}$Xe. Out of its 50$\,$t total natural xenon inventory, 40$\,$t will be the active target of a time projection chamber which thus contains about 3.6 t of $^{136}$Xe. Here, we show that its projected half-life sensitivity is $2.4\times10^{27}\,$yr, using a fiducial volume of 5t of natural xenon and 10$\,$yr of operation with a background rate of less than 0.2$~$events/(t$\cdot$yr) in the energy region of interest. This sensitivity is based on a d…
