Background study of the AMoRE-pilot 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.

The Korea Invisible Mass Search (KIMS) collaboration has performed experiments on dark matter searches and double beta decay searches at the Yangyang underground laboratory. Recent results of KIMS as well as the status of the R&D on various detectors are presented. For the WIMP search KIMS ruled out the recoil of 127I of DAMA signal region unambiguously and set the most stringent limit on spin dependent WIMP interactions in the case of pure proton coupling. New limits on neutrino-less double beta decays of 112Sn, 124Sn, 64Zn is also reported.

The LEGEND Collaboration is searching for neutrinoless double-beta (0νββ) decay by operating high-purity germanium detectors enriched in ^{76}Ge in a low-background liquid argon environment. Building on key technological innovations from the GERmanium Detector Array (GERDA) experiment and the MAJORANA DEMONSTRATOR experiment, LEGEND-200 has performed a first 0νββ decay search based on 61.0kg yr of data. Over half of this exposure comes from our highest performing detectors, including newly developed inverted-coaxial detectors, and is characterized by an estimated background level of 0.5_{-0.2}^{+0.3} cts/(keV ton yr) in the 0νββ decay signal region. A combined analysis of data from GERDA, the MAJORANA DEMONSTRATOR, and LEGEND-200, characterized by a 90%confidence level exclusion sensitivity of 2.8×10^{26} yr on the half-life of 0νββ decay, reveals no evidence for a signal and sets a new observed lower limit at T_{1/2}^{0ν}>1.9×10^{26} yr (90% confidence level). Assuming the decay is mediated by Majorana neutrinos, this corresponds to an upper limit on the effective Majorana mass in the range m_{ββ}<75-200 meV, depending on the adopted nuclear matrix element.

Cuoricino was a cryogenic bolometric detector operating in Gran Sasso Underground Laboratory, Italy, from March 2003 to June 2008. With its 40.7 kg of 130TeO2 in the form of an array of 62 crystals it has set the currently best lower limit on the halflife of 130Te neutrinoless double beta decay, T1/2 > 2.94 · 1024 y at 90 % CL. It has moreover proven the feasibility of the CUORE experiment, whose aim is to be sensitive to values of the effective neutrino mass as low as few tens of meV. We will report on the latest results from Cuoricino and on the status of the CUORE project.

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·yr, or equivalently 22.2 kg·yr of 136Xe exposure. At the region around 136Xe 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 limit for decay half-life of 2.1 yr at the 90% confidence level, which corresponds to an effective Majorana neutrino mass eV. This is the first NLDBD result reported from a dual-phase xenon experiment.

The primary goal of the GERmanium Detector Array (GERDA) experiment at the Laboratori Nazionali del Gran Sasso of INFN is the search for the neutrinoless double beta decay of 76Ge. High-purity germanium detectors made from material enriched in 76Ge are operated directly immersed in liquid argon, allowing for a substantial reduction of the background with respect to predecessor experiments. The first 5.04 kg yr of data collected in Phase I of the experiment have been analyzed to measure the half-life of the neutrino-accompanied double beta decay of 76Ge. The observed spectrum in the energy range between 600 and 1800 keV is dominated by the double beta decay of 76Ge. The half-life extracted from GERDA data is T2ν1/2 = (1.84+0.14−0.10) × 1021 yr.

A search for the neutrinoless double beta decay of $^{136}$Xe was conducted with the xenon-loaded liquid scintillator detector KamLAND-Zen 800 using 970 kg$\\cdot$year of $^{136}$Xe exposure. No significant signal excess from the expected background was observed from the energy spectrum fitting, and we set a lower limit on the half-life of \n2.0 $\\times$ 10$^{26}$ years at a 90% confidence level.\nA combined fit of the KamLAND-Zen 400 and 800 data sets gives a lower limit of the half-life of 2.3 $\\times$ 10$^{26}$ years at a 90% confidence level. It corresponds to the upper limits on the effective Majorana neutrino mass of 36 - 156 meV with various nuclear matrix element calculations.\nIt is the first test for inverted mass ordering.

The evidence for the existence of dark matter from astrophysical observations is strong. However, there has not been a conclusive direct detection of dark matter that does not rely on gravitational interaction with visible matter. One experiment, DAMA, claims to have observed an annual modulation signal in a sodium-iodide-based detector consistent with that expected from dark matter. COSINE-100 and ANAIS-112, two leading sodium-iodide dark matter experiments, were designed to test DAMA’s claim directly using the same target material. COSINE-100, located at Yangyang Underground Laboratory in South Korea, and ANAIS-112, located at Canfranc Underground Laboratory, have been taking data since 2016 and 2017, respectively. The two experiments have similar sensitivity and have thus far published results independently. In this contribution, I will discuss our efforts to combine the data from the two experiments for increased search sensitivity and share its results.

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.

Neutrinoless double beta (0νββ) decay searches are currently among the major foci of experimental physics. The observation of such a decay will have important implications in our understanding of the intrinsic nature of neutrinos and shed light on the limitations of the Standard Model. The rate of this process depends on both the unknown neutrino effective mass and the nuclear matrix element (M0ν) associated with the given 0νββ transition. The latter can only be provided by theoretical calculations, hence the need of accurate theoretical predictions of M0ν for the success of the experimental programs. This need drives the theoretical nuclear physics community to provide the most reliable calculations of M0ν. Among the various computational models adopted to solve the many-body nuclear problem, the shell model is widely considered as the basic framework of the microscopic description of the nucleus. Here, we review the most recent and advanced shell-model calculations of M0ν considering the light-neutrino-exchange channel for nuclei of experimental interest. We report the sensitivity of the theoretical calculations with respect to variations in the model spaces and the shell-model nuclear Hamiltonians.

Evaluation of the spin wave green's functions for rutile structure Heisenberg antiferromagnets with exchange between ions both on the same and opposite sublattices

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.