New results from the KIMS experiment

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

The AMoRE (Advanced Mo-based Rare process Experiment) is an experimental search for neutrinoless double beta decay of \(^{100}\)Mo using enriched in \(^{100}\)Mo and depleted in \(^{48}\)Ca calcium molybdate (\(^{48\rm{depl}}\)Ca\(^{100}\)MoO\(_4\)) scintillating crystals at low temperature aiming to investigate the inverted hierarchy of the neutrino mass pattern. The AMoRE uses metallic magnetic calorimeter sensors to read out scintillation and phonon signals from the crystals at milli-Kelvin temperature, which provide an excellent energy resolution (~10 keV FWHM at 2615 keV) and very efficient particle discrimination to suppress background caused by U/Th contamination of the crystal scintillators and near materials. The AMoRE experiment is intended to reach zero-background level in the region of interest, near the energy of \(^{100}\)Mo double beta decay 3034 keV. Monte Carlo simulations using the GEANT4 code and measurements of radioactive contamination of the \(^{48\rm{depl}}\)Ca\(^{100}\)MoO\(_4\) crystal scintillators, detectors and shielding materials are in progress. Currently, the AMoRE pilot experiment with five \(^{48\rm{depl}}\)Ca\(^{100}\)MoO\(_4\) detectors (total mass ~1.5 kg) is running at the YangYang underground laboratory (Korea). The first phase of the AMoRE experiment, using ~5 kg of \(^{48\rm{depl}}\)Ca\(^{100}\)MoO\(_4\) detectors, is scheduled to start at the end of 2017. Preparations for the first phase experiment and R&D for the second phase experiment with ~200 kg of molybdate crystal scintillators is ongoing.

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.

Liquefied-noble-gas (LNG) detectors offer, in principle, very good energy resolution for both neutrons and gamma rays, fast response time (hence high-count-rate capabilities), excellent discrimination between neutrons and gamma rays, and scalability to large volumes. They do, however, need cryogenics. LNG detectors in sizes of interest for fissionable material detection in cargo are reaching a certain level of maturity because of the ongoing extensive R&}D effort in high-energy physics regarding their use in the search for dark matter and neutrinoless double beta decay. The unique properties of LNG detectors, especially those using Liquid Argon (LAr) and Liquid Xenon (LXe), call for a study to determine their suitability for Non-Intrusive Inspection (NII) for Special Nuclear Materials (SNM) and possibly for other threats in cargo.Rapiscan Systems Laboratory, Yale University Physics Department, and Adelphi Technology are collaborating in the investigation of the suitability of LAr as a scintillation material for large size inspection systems for air and maritime containers and trucks. This program studies their suitability for NII, determines their potential uses, determines what improvements in performance they offer and recommends changes to their design to further enhance their suitability. An existing 3.1 liter LAr detector (microCLEAN) at Yale University, developed for R&}D on the detection of weakly interacting massive particles (WIMPs) was employed for testing. A larger version of this detector (15 liters), more suitable for the detection of higher energy gamma rays and neutrons is being built for experimental evaluation. Results of measurements and simulations of gamma ray and neutron detection in microCLEAN and a larger detector (326 liter CL38) are presented.

Position sensitive detectors based on gaseous scintillation proportional counters with Anger-type readout are being used in several research areas such as neutron detection, search for dark matter and neutrinoless double beta decay. Design and optimization of such detectors are complex and time consuming tasks. Simulations, while being a powerful tool, strongly depend on the light transfer models and demand accurate knowledge of many parameters, which are often not available. Here we describe an alternative approach based on the experimental evaluation of a detector using an isotropic point-like light source with precisely controllable light emission properties, installed on a 3D positioning system. The results obtained with the developed setup at validation conditions, when the scattered light is strongly suppressed show good agreement with simulations.

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Large-scale, precision xenon doping of liquid argon

The recent results from the HEIDELBERG-MOSCOW experiment have demonstrated the large potential of double beta decay to search for new physics beyond the Standard Model. To increase by a major step the present sensitivity for double beta decay and dark matter search much bigger source strengths and much lower backgrounds are needed than used in experiments under operation at present or under construction. We present here a study of a project proposed recently [1], which would operate one ton of ‘naked’ enriched GErmanium-detectorsinliquid NItrogenas shielding in an Underground Setup (GENIUS). It improves the sensitivity to neutrino masses to 0.01 eV. A ten ton version would probe neutrino masses even down to 10−3 eV. The first version would allow to test the atmospheric neutrino problem, the second at least part of the solar neutrino problem. Both versions would allow in addition significant contributions to testing several classes of GUT models. These are especially tests of R-parity breaking supersymmetry models, leptoquark masses and mechanism and right-handed W-boson masses comparable to LHC. The second issue of the experiment is the search for dark matter in the universe. The entire MSSM parameter space for prediction of neutralinos as dark matter particles could be covered already in a first step of the full experiment with the same purity requirements, but using only 100 kg of 76Ge or even of natural Ge making the experiment competitive to LHC in the search for supersymmetry. The layout ofthe proposed experiment is discussed and the shielding and purity requirements are studied using GEANT Monte Carlo simulations. As a demonstration of the feasibility of the experiment first results of operating a ‘naked’ Ge detector in liquid nitrogen are presented.

Background study of the AMoRE-pilot experiment

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.

The response of a 19 kg active mass liquid argonscintillation detector to gamma, alpha and neutron radiation and itscharacteristic scintillation photon time distribution has been studiedin the framework of the Gerda double beta decay research anddevelopment program. The achieved photo-electron yield of 1.24 pe/keVwas stable during the two years of operation. The detector exhibitsexcellent energy resolution of 8.7/17.2 keV (σ) for gammaenergies of 60/239 keV. Radon was loaded into the liquid argon tostudy alpha energy quenching and decay time correlation of itsprogenies. A robust pulse shape analysis method was used to identifyand discriminate amongst the different radiation types. 60 keV gammasignals could be discriminated against neutron recoils of the samevisible energy with a miss-identification probability of < 5 · 10−4 limited by statistics and ambient backgrounds. Xenon dopingof liquid argon increased the photo-electron yield and improved thespectroscopic performance of the detector leading to an energyresolution of 7.2/15.4 keV (σ) for 60/239 keV. Thediscrimination power improved slightly with the addition of xenon up to concentrations of 300 ppm. Applications for background identification anddiscrimination in double beta decay search with 76Ge crystals, aswell as for Dark Matter search with liquid argon are discussed.

The NEMO 3 experiment searches for neutrinoless double beta decay and makes precision measurements of two-neutrino double beta decay in seven isotopes. The latest two-neutrino half-life results are presented, together with the limits on neutrinoless half-lives and the corresponding effective Majorana neutrino masses. Also given are the limits obtained on neutrinoless double beta decay mediated by Rp-violating SUSY, right-hand currents and different Majoron emission modes.

A search for double beta decay of 116Cd and 196Hg was made in the Solotvina underground laboratory operating at 1000 m w.e.

We report on a search for double beta decay of ^{130}hbox {Te} to the first 0^{+} excited state of ^{130}hbox {Xe} using a 9.8,hbox {kg}cdot hbox {yr} exposure of ^{130}hbox {Te} collected with the CUORE-0 experiment. In this work we exploit different topologies of coincident events to search for both the neutrinoless and two-neutrino double beta decay modes. We find no evidence for either mode and place lower bounds on the half-lives: T^{0nu }_{0^+_1}>7.9cdot 10^{23}hbox {yr} and T^{2nu }_{0^+_1}>2.4cdot 10^{23}hbox {yr} (90%,hbox {CL}). Combining our results with those obtained by the CUORICINO experiment, we achieve the most stringent constraints available for these processes: T^{0nu }_{0^+_1}>1.4cdot 10^{24}hbox {yr} and T^{2nu }_{0^+_1}>2.5cdot 10^{23}hbox {yr} (90%,hbox {CL}).

The Enriched Xenon Observatory (EXO) is an experimental program which aims to observe the neutrinoless double beta decay of Xe-136. The existence of this process requires neutrinos to be Majorana particles and in its simplest interpretation the rate of decay provides a measurement of the absolute neutrino mass. The first stage of the experiment, EXO-200, features 200 kg of liquid xenon, enriched to 80% in Xe-136. The detector, located at the Waste Isolation Pilot Plant in New Mexico, has been in operation for about one and a half years, and the two-neutrino double beta decay of Xe-136 has been measured. Its half life of T1/22νββ = 2.23±0.017(stat)±0.22(sys)×1021 yr makes it the slowest process ever measured directly. No evidence for neutrinoless decay has been found with an exposure of 32.5 kg-yr. A lower limit for the half life has been set to T1/20νββ(136Xe)>1.6×1025 yr (90% CL), corresponding to effective Majorana masses of less than 140-380 meV, depending on the matrix element calculation.