Neutrinoless Double Beta Decay Of 136Xe Research Articles

Concept of KamLAND2 DAQ system

The KamLAND-Zen experiment is searching for neutrinoless double-beta decay of 136Xe. We are preparing for the upgrade of the KamLAND detector, KamLAND2. It is designed to improve the discrimination power of two-neutrino double-beta decay and cosmic-ray muon spallation backgrounds. Data acquisition of all neutrino events from nearby supernova is also an important issue of the KamLAND2 experiment and the data rate is a key factor to design a new DAQ system. High speed sampling will be realized with RFSoC on the front-end electronics. Data is read out from FEE to DAQ computers via 10 GbE, and FairMQ is one of the candidates for KamLAND2 DAQ software. In the KamLAND DAQ, the whole trigger system is implemented in hardware, while the KamLAND2 DAQ adopts hardware trigger for photon detection and software trigger to extract physics events. A simulation study of the software trigger is proceeding in order to detect low energy events using timing and charge information.

The EXO-200 detector, part II: auxiliary systems

The EXO-200 experiment searched for neutrinoless double-beta decay of 136Xe with a single-phase liquid xenon detector. It used an active mass of 110 kg of 80.6%-enriched liquid xenon in an ultra-low background time projection chamber with ionization and scintillation detection and readout. This paper describes the design and performance of the various support systems necessary for detector operation, including cryogenics, xenon handling, and controls. Novel features of the system were driven by the need to protect the thin-walled detector chamber containing the liquid xenon, to achieve high chemical purity of the Xe, and to maintain thermal uniformity across the detector.

Demonstration of background rejection using deep convolutional neural networks in the NEXT experiment

Convolutional neural networks (CNNs) are widely used state-of-the-art computer vision tools that are becoming increasingly popular in high-energy physics. In this paper, we attempt to understand the potential of CNNs for event classification in the NEXT experiment, which will search for neutrinoless double-beta decay in 136Xe. To do so, we demonstrate the usage of CNNs for the identification of electron-positron pair production events, which exhibit a topology similar to that of a neutrinoless double-beta decay event. These events were produced in the NEXT-White high-pressure xenon TPC using 2.6 MeV gamma rays from a 228Th calibration source. We train a network on Monte Carlo-simulated events and show that, by applying on-the-fly data augmentation, the network can be made robust against differences between simulation and data. The use of CNNs offers significant improvement in signal efficiency and background rejection when compared to previous non-CNN-based analyses.

DARWIN: direct dark matter search with the ultimate detector

DARk matter WImp search with liquid xenoN (DARWIN) is a future experiment for the direct detection of dark matter based on a multi-ton liquid xenon time projection chamber. The main goal of DARWIN is to reach an unprecedented sensitivity to WIMP (Weakly Interacting Massive Particle)-nuclear recoil cross sections for a large WIMP mass range, down to the level where the irreducible background from neutrino interactions with the target is dominant. This ultra-low background experiment will also have competitive sensitivity to test other dark matter hypotheses such as dark photons and superWIMPs and to detect other rare events like solar neutrinos, neutrinoless double-beta decay of 136Xe, solar axions and neutrinos from galactic supernovae. In this paper we present the design of the DARWIN detector and the estimated WIMP sensitivity based on the expected backgrounds. Other rare event searches are also discussed.

DARWIN: towards the ultimate dark matter detector

DARk matter WImp search with liquid xenoN (DARWIN) will be an experiment for the direct detection of dark matter using a multi-ton liquid xenon time projection chamber at its core. Its primary goal will be to explore the experimentally accessible parameter space for Weakly Interacting Massive Particles (WIMPs) in a wide mass-range, until neutrino interactions with the target become an irreducible background. The prompt scintillation light and the charge signals induced by particle interactions in the xenon will be observed by VUV sensitive, ultra-low background photosensors. Besides its excellent sensitivity to WIMPs above a mass of 5 GeV/c2, such a detector with its large mass, low-energy threshold and ultra-low background level will also be sensitive to other rare interactions. It will search for solar axions, galactic axion-like particles and the neutrinoless double-beta decay of 136Xe, as well as measure the low-energy solar neutrino flux with < 1% precision, observe coherent neutrino-nucleus interactions, and detect galactic supernovae. We present the concept of the DARWIN detector and discuss its physics reach, the main sources of backgrounds and the ongoing detector design and R&D efforts.

The LZ dark matter experiment

The LUX and ZEPLIN collaborations have merged to construct a 7 tonne two-phase Xe dark matter detector, known as LUX-ZEPLIN or LZ. Chosen as one of the Generation 2 suite of dark matter direct detection experiments, LZ will probe spin-independent WIMP-nucleon cross sections down to 2 × 10-48 cm2 at 50 GeV/c2 within 3 years of operation, covering a substantial range of theoretically-motivated dark matter candidates. Along with dark matter interactions with Xe nuclei, LZ will also be sensitive to solar neutrinos emitted by the pp fusion process in the sun, neutrinos emitted by a nearby supernova and detected by coherent neutrino-nucleus scattering, certain classes of axions and axion-like particles, and neutrinoless double-beta decay of 136Xe. The design of LZ is presented, along with its expected backgrounds and projected sensitivity.

Characterisation of NEXT-DEMO using xenon Kα X-rays

The NEXT experiment aims to observe the neutrinoless doublebeta decay of 136Xe in a high-pressure xenon gas TPC usingelectroluminescence (EL) to amplify the signal fromionization. Understanding the response of the detector is imperativein achieving a consistent and well understood energy measurement. Theabundance of xenon K-shell X-ray emission during data taking has beenidentified as a multitool for the characterisation of the fundamentalparameters of the gas as well as the equalisation of the response ofthe detector.The NEXT-DEMO prototype is a ∼ 1.5 kg volume TPC filled withnatural xenon. It employs an array of 19 PMTs as an energy plane andof 256 SiPMs as a tracking plane with the TPC light tube and SiPMsurfaces being coated with tetraphenyl butadiene (TPB) which acts as awavelength shifter for the VUV scintillation light produced byxenon. This paper presents the measurement of the properties of thedrift of electrons in the TPC, the effects of the EL productionregion, and the extraction of position dependent correctionconstants using Kα X-ray deposits. These constants wereused to equalise the response of the detector to deposits left bygammas from 22Na.

First [formula omitted] results from EXO-200

We report on a search for neutrinoless double-beta decay of 136Xe with EXO-200. No signal is observed for a 136Xe exposure of 26.3 kg-yr, with a background of ∼1.5×10−3kg(enrLXe)−1yr−1keV−1 in the ±1σ region of interest. This sets a lower limit on the half-life of the neutrinoless double-beta decay T1/20νββ(136Xe)>1.6×1025yr (90% CL), corresponding to effective Majorana masses of less than 140–380 meV, depending on the matrix element calculation.

Micromegas-TPC operation at high pressure in xenon-trimethylamine mixtures

In this work we present a systematic study of Micromegas detectorsin high pressure gaseous Xenon using trimethylamine(TMA) as quencher gas. Gas gains and energy resolutions for 22.1 keV X-raysare measured for pressures between 1 and10 bar and various relative concentrations of TMA from 0.3 % to 15 %. Weobserve stable operation at all pressures, and a strongly enhanced gas gain,suggestive of Penning-like energy-transfer processes. The effect is present at all pressures and it is strongest at TMA concentrationsranging from 1.5 % to 3 %. Operating in this concentration range, the maximum gain reached values as high as ∼ 2 × 103 ( ∼ 5 × 102) at 1 (10)bar. Besides, the energy resolution achievable for 22.1 keV X-rays is substantiallybetter than the one previously obtained in pure Xe, going down to7.3 % (9.6 %) FWHM for 1 (10) bar. These results are of interest for calorimetric applications of high pressure gas Xe TPCs,in particular for the search of the neutrinoless double beta decay of136Xe. The resolutions achieved would extrapolate into 0.7 %(0.9 %) FWHM at the Qββ value of 136Xe for1 (10) bar.

Radiopurity control in the NEXT-100 double beta decay experiment: procedures and initial measurements

The ``Neutrino Experiment with a Xenon Time-ProjectionChamber'' (NEXT) is intended to investigate the neutrinoless doublebeta decay of 136Xe, which requires a severe suppression ofpotential backgrounds. An extensive screening and material selectionprocess is underway for NEXT since the control of the radiopuritylevels of the materials to be used in the experimental set-up is amust for rare event searches. First measurements based on GlowDischarge Mass Spectrometry and gamma-ray spectroscopy usingultra-low background germanium detectors at the LaboratorioSubterr'aneo de Canfranc (Spain) are described here. Activity resultsfor natural radioactive chains and other common radionuclides aresummarized, being the values obtained for some materials like copperand stainless steel very competitive. The implications of theseresults for the NEXT experiment are also discussed.

New gas mixtures suitable for rare event detectionusing a Micromegas-TPC detector

The aim of the presented work was to develop furthertechniques based on a Micromegas-TPC, in order to reach a high gasgain with good energy resolution, and to search for gas mixturessuitable for rare event detection. This paper focuses on Xenon,which is convenient for the search of neutrinoless double betadecay in 136Xe, and CF4, suitable for dark matter searchesand the study of solar and reactor neutrinos. Variousconfigurations of the Micromegas plane were investigated and aredescribed. Gains of 105 and energy resolutions of 35–65%at 6 keV have been achieved.

A linear RFQ ion trap for the Enriched Xenon Observatory

The design, construction, and performance of a linear radio-frequency ion trap (RFQ) intended for use in the Enriched Xenon Observatory (EXO) are described. EXO aims to detect the neutrinoless double-beta decay of 136Xe to 136Ba. To suppress possible backgrounds EXO will complement the measurement of decay energy and, to some extent, topology of candidate events in a Xe filled detector with the identification of the daughter nucleus ( 136Ba). The ion trap described here is capable of accepting, cooling, and confining individual Ba ions extracted from the site of the candidate double-beta decay event. A single trapped ion can then be identified, with a large signal-to-noise ratio, via laser spectroscopy.

Mass and Double-Beta-DecayQValue ofXe136

The atomic mass of 136Xe has been measured by comparing cyclotron frequencies of single ions in a Penning trap. The result, with 1 standard deviation uncertainty, is M(136Xe)=135.907 214 484 (11) u. Combined with previous results for the mass of 136Ba [Audi, Wapstra, and Thibault, Nucl. Phys. A 729, 337 (2003)10.1016/j.nuclphysa.2003.11.003], this gives a Q value (M[136Xe]-M[136Ba])c(2)=2457.83(37) keV, sufficiently precise for ongoing searches for the neutrinoless double-beta decay of 136Xe.