G. Adhikari, E. Barbosa de Souza, N. Carlin, J. J. Choi, S. Choi, M. Djamal, A. C. Ezeribe, L. E. Franca, C. Ha, I. S. Hahn, E. J. Jeon, J. H. Jo, W. G. Kang, M… 展开作者
G. Adhikari, E. Barbosa de Souza, N. Carlin, J. J. Choi, S. Choi, M. Djamal, A. C. Ezeribe, L. E. Franca, C. Ha, I. S. Hahn, E. J. Jeon, J. H. Jo, W. G. Kang, M. Kauer, H. Kim, H. J. Kim, K. W. Kim, S. K. Kim, Y. D. Kim, Y. H. Kim, Y. J. Ko, E. K. Lee, H. S. Lee, J. Lee, J. Y. Lee, M. H. Lee, S. H. Lee, D. S. Leonard, B. B. Manzato, R. H. Maruyama, R. J. Neal, S. L. Olsen, B. J. Park, H. K. Park, H. S. Park, K. S. Park, R. L. C. Pitta, H. Prihtiadi, S. J. Ra, C. Rott, K. A. Shin, A. Scarff, N. J. C. Spooner, W. G. Thompson, L. Yang, G. H. Yu
This paper describes the liquid scintillator veto system for the COSINE-100 dark matter experiment and its performance. The COSINE-100 detector consists of eight NaI(Tl) crystals immersed in 2200~L of linear alkylbenzene-based liquid scintillator. The liquid scintillator tags between 65 and 75\% of the internal $^{40}$K background in the 2--6 keV energy region. We also describe the background model for the liquid scintillator, which is primarily used to assess its energy calibration and threshold.
Scintillator doped with a high neutron-capture cross-section material can be used to detect neutrons via their resulting gamma rays. Examples of such detectors using liquid scintillator have been successfully used in high-energy physics experiments. However, a liquid scintillator can leak and is not as amenable to modular or complex shapes as a solid scintillator. Polystyrene-based scintillators from a variety of gadolinium compounds with varying concentrations were polymerized in our laboratory. The light output, emission spectra, and attenuation length of our samples were measured and light …
We report the performance of an active veto system using a liquid scintillator with NaI(Tl) crystals for use in a dark matter search experiment. When a NaI(Tl) crystal is immersed in the prototype detector, the detector tags 48% of the internal K-40 background in the 0-10 keV energy region. We also determined the tagging efficiency for events at 6-20 keV as 26.5 +/- 1.7% of the total events, which corresponds to 0.76 +/- 0.04 events/keV/kg/day. According to a simulation, approximately 60% of the background events from U, Th, and K radioisotopes in photomultiplier tubes are tagged at energies o…
AMoRE-II is the second phase of the Advanced Molybdenum-based Rare process Experiment aiming to search for the neutrino-less double beta decay of 100Mo isotopes using ~ 200 kg of molybdenum-containing cryogenic detectors. The AMoRE-II needs to keep the background level below 10-5 counts/keV/kg/year with various methods to maximize the sensitivity. One of the methods is to have the experiment be carried out deep underground free from the cosmic ray backgrounds. The AMoRE-II will run at Yemilab with ~ 1,000 m depth. However, even in such a deep underground environment, there are still survived c…
A simulation of neutrons traversing a shield beneath the COMET scintillator strip cosmic-veto counter is accomplished using the Geant4 toolkit. A Geant4 application is written with an appropriate detector construction and a possible spectrum of neutron's energy. The response of scintillator strips to neutrons is studied in detail. A design of the shield is optimized to ensure the time loss concerned with fake veto signals caused by neutrons from muon captures is tolerable. Materials of shield layers are chosen, and optimum thicknesses of the layers are computed.
The NUCLEUS experiment aims at measuring the coherent elastic scattering of nuclear reactor antineutrinos off nuclei using cryogenic calorimeters. Operating at an overburden of 3m.w.e., muon-induced backgrounds are expected to be dominant. It is therefore essential to develop an efficient muon veto, with a detection efficiency of more than 99%. This will be realized in NUCLEUS through a compact cube assembly of plastic scintillator panels. In order to prevent a large unshielded area where the cryostat intersects the shielding arrangement without unnecessarily increasing the induced detector de…
At upcoming medium baseline reactor neutrino experiments the spallation 9Li background will be somewhat larger than the inverse beta decay reactor neutrino signal. We use new FLUKA simulations of spallation backgrounds to optimize a class of veto strategies and find that surprisingly the optimal veto for the mass hierarchy determination has a rejection efficiency below 90%. The unrejected background has only a modest effect on the physics goals. For example $Δχ^2$ for the hierarchy determination falls by 1.4 to 3 points depending on the muon tracking ability. The optimal veto strategy is essen…
A sandwich detector composed of scintillator and steel-covered lead layers was introduced in the fixed-target COMPASS experiment at CERN for vetoing events not completely covered by the two-stage magnetic spectrometer. Wavelength shifting fibres glued into grooves in the scintillator tiles serve for fast read-out. Minimum ionizing particles impinging on the $2 \textrm{m} \times 2 \textrm{m}$ detector outside of a central hole, sparing the spectrometer's entry, are detected with a probability of 98%. The response to charged particles and photons is modeled in detail in Monte Carlo calculations.…
A computer model of a scintillator strip veto counter was built in order to verify the efficiency of the cosmic muon veto for the COMET experiment. To tune the model, experimentally measured data were utilized. Three different geometrical configuration of the counter were considered. For one of the configurations the simulation gave the inefficiency of the cosmic muon registration being below 0.0001, which meets requirements of the experiment.
Long lead-scintillator sandwich modules developed for the BNL experiment KOPIO are described. The individual 4 m long module consists of 15 layers of 7 mm thick extruded scintillator and 15 layers of 1 mm lead absorber. Readout is implemented via WLS fibers glued into grooves in a scintillator with 7 mm spacing and viewed from both ends by the phototubes. Time resolution of 300 ps for cosmic MIPs was obtained. Light output stability monitored for 2 years shows no degradation beyond the measurement errors. A 4 m long C-bent sandwich module was also manufactured and tested.
COSINE-100 is a dark matter direct detection experiment designed to test the annual modulation signal observed by the DAMA/LIBRA experiment. COSINE-100 consists of 8 NaI(Tl) crystals with a total mass of 106 kg, a 2200 L liquid scintillator veto, and 37 muon detector panels. We present details of the data acquisition system of COSINE-100, including waveform storage using flash analog-to-digital converters for crystal events and integrated charge storage using charge-sensitive analog-to-digital converters for liquid scintillator and plastic scintillator muon veto events. We also discuss several…
Validation of the COSINE-100U NaI(Tl) Encapsulation for Low-Temperature Operation in Liquid Scintillator
Institute for Basic Science (IBS)（基础科学研究院）；Chung-Ang University（中央大学）；University of Science and Technology (UST)（科学技术大学）；Jeju National University（济州国立大学）；Kyungpook National University（庆北国立大学）
Neutrons are a particularly dangerous background for direct WIMP dark matter searches; their nuclear recoils with the target nucleus are often indistinguishable from nuclear recoils produced by WIMP-nuclear collisions. In this study, we explore the concept of a liquid scintillator neutron veto detector that would allow direct dark matter detectors to potentially reject neutrons with greater than 99% efficiency. Here we outline the construction and testing of a small prototype detector and the potential implications of this technology for future dark matter detectors.
The discovery of scintillation in the blue regime from polyethylene naphthalate (PEN), a commonly used high-performance industrial polyester plastic, has sparked considerable interest from the physics community as a new type of plastic scintillator material. This observation in addition to its good mechanical and radiopurity properties makes PEN an attractive candidate as an active structure scintillator for low-background physics experiments. This paper reports on investigations of its potential in terms of production tests of custom made tiles and various scintillation light output measureme…
In this study, the conceptual design and physics simulations of a near-field Water-based Liquid Scintillator (WbLS) detector placed 100 meters from the Akkuyu Nuclear Power Plant (ANPP), currently under construction and aiming at being Turkey's first nuclear power plant, is presented. The ANPP is an excellent opportunity for neutrino studies and the development of an R&D program for neutrino detectors in Turkey. The Reactor Neutrino Experiments of Turkey (RNET) program includes a compact and portable detector with a 2.5-ton volume of WbLS and a ~30% photo-coverage, and the program is planned t…
Results are presented on R&D efforts to design and build large size veto panels, optimized for underground low background experiments, in the most efficient and economical way using commercially available components. A variety of plastic scintillators, photomultiplier tubes, wavelength shifting fibers, and light reflector combinations were tested. Results of these studies and performance of a 2.2 meter long panel are presented.
Scintillating NaI(Tl) crystals are used for various rare decay experiments, such as dark matter searches. The hygroscopicity of NaI(Tl) crystal makes the construction of crystal detectors in these experiments challenging and requires a tight encapsulation to prevent from air contact. More importantly, in a low radioactivity measurement, identification of external radiations and surface contamination is crucial to characterize the origin of total crystal radioactivities. Studies for NaI(Tl) crystal encapsulation with active organic scintillator vetoes have been performed to mitigate the above-m…
Neutron veto detector based on liquid scintillator containing hydrogen atoms is an integral part of any underground experiment for dark matter search. So far, a flammable mixture of liquid hydrocarbons was used as a liquid scintillator in such detectors. A safe alternative might be a liquid scintillator based on liquid argon doped with methane. In this work, we have studied the primary scintillations in pure liquid argon and its mixtures with methane, the CH4 content varying from 100 ppm to 5%. The primary scintillations have for the first time been observed in liquid argon doped with methane,…
The SABRE (Sodium Iodide with Active Background REjection) experiment will search for an annually modulating signal from dark matter using an array of ultra-pure NaI(Tl) detectors surrounded by an active scintillator veto to further reduce the background. The first phase of the experiment is the SABRE Proof of Principle (PoP), a single 5 kg crystal detector operated in a liquid scintillator filled vessel at Laboratori Nazionali del Gran Sasso (LNGS). The SABRE-PoP installation is underway with the goal of running in 2018 and performing the first in situ measurement of the crystal background, t…
The Outer-Edge Veto (OEV) counter subsystem for extra-photon detection from the backgrounds for the? $K^0_L\rightarrowπ^0ν\barν$ decay is located at the outer edge of the endcap CsI calorimeter of the KOTO experiment at J-PARC. The subsystem is composed of 44 counters with different cross-sectional shapes. All counters are made of lead and scintillator plates and read out through wavelength-shifting fibers. In this paper, we discuss the design and performances of the OEV counters under heavy load ($\sim8$ tons/m$^2$) in vacuum. For 1-MeV energy deposit, the average light yield and time resolut…
Organic liquid scintillators are used in a wide variety of applications in experimental nuclear and particle physics. Boron-loaded scintillators are particularly useful for detecting neutron captures, due to the high thermal neutron capture cross section of $^{10}$B. These scintillators are commonly used in neutron detectors, including the DarkSide-50 neutron veto, where the neutron may produce a signal when it scatters off protons in the scintillator or when it captures on $^{10}$B. Reconstructing the energy of these recoils is complicated by scintillation quenching. Understanding how nuclear…
The JSNS$^{2}$ (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) experiment will search for neutrino oscillations over a 24 m short baseline at J-PARC. The JSNS$^{2}$ inner detector will be filled with 17 tons of gadolinium-loaded liquid scintillator (LS) with an additional 31 tons of unloaded LS in the intermediate $γ$-catcher and outer veto volumes. JSNS$^{2}$ has chosen Linear Alkyl Benzene (LAB) as an organic solvent because of its chemical properties. The unloaded LS was produced at a refurbished facility, originally used for scintillator production by the RENO experime…
COSINE is a dark matter search experiment based on an array of low background NaI(Tl) crystals located at the Yangyang underground laboratory. The assembly of COSINE-100 was completed in the summer of 2016 and the detector is currently collecting physics quality data aimed at reproducing the DAMA/LIBRA experiment that reported an annual modulation signal. Stable operation has been achieved and will continue for at least two years. Here, we describe the design of COSINE-100, including the shielding arrangement, the configuration of the NaI(Tl) crystal detection elements, the veto systems, and t…
The SABRE (Sodium iodide with Active Background REjection) experiment aims to detect an annual rate modulation from dark matter interactions in ultra-high purity NaI(Tl) crystals in order to provide a model independent test of the signal observed by DAMA/LIBRA. It is made up of two separate detectors; SABRE South located at the Stawell Underground Physics Laboratory (SUPL), in regional Victoria, Australia, and SABRE North at the Laboratori Nazionali del Gran Sasso (LNGS). SABRE South is designed to disentangle seasonal or site-related effects from the dark matter-like modulated signal by using…
KATANA - the Krakow Array for Triggering with Amplitude discrimiNAtion - has been built and used as a trigger and veto detector for the S$π$RIT TPC at RIKEN. Its construction allows operating in magnetic field and providing fast response for ionizing particles, giving the approximate forward multiplicity and charge information. Depending on this information, trigger and veto signals are generated. The article presents performance of the detector and details of its construction. A simple phenomenological parametrization of the number of emitted scintillation photons in plastic scintillator is p…
The High Energy cosmic-Radiation Detector (HERD) facility is planned to go onboard China's Space Station, planned to be operational starting in around 2025 for about 10 years. The main scientific objectives of HERD are the search for signals of dark matter annihilation products, precise cosmic electron/positron spectrum and measurements of anisotropy up to 10 TeV, precise cosmic ray spectrum and composition measurements up to the knee energy (1 PeV), and high energy $γ$-ray monitoring and survey. HERD consists of a 3D cubic crystals calorimeter (CALO) surrounded by microstrip silicon trackers …
The LUX-ZEPLIN experiment will search for dark matter particle interactions with a detector containing a total of 10 tonnes of liquid xenon. Surrounding the liquid xenon cryostat is an outer detector veto system with the primary aim of vetoing neutron single-scatter events in the liquid xenon that could mimic a weakly interacting massive particle (WIMP) dark matter signal. The outer detector consists of approximately 17 tonnes of gadolinium-loaded liquid scintillator confined to 10 acrylic tanks surrounding the cryostat and 228,000 litres of water as the outermost layer. It will be monitored b…
The NUCLEUS experiment aims to measure coherent elastic neutrino nucleus scattering of reactor anti-neutrinos using cryogenic calorimeters. Operating at an overburden of 3 m.w.e., muon-induced backgrounds are expected to be one of the dominant background contributions. Besides a high efficiency to identify muon events passing the experimental setup, the NUCLEUS muon veto has to fulfill tight spatial requirements to fit the constraints given by the experimental site and to minimize the induced detector dead-time. We developed highly efficient and compact muon veto modules based on plastic scint…
The SABRE (Sodium Iodide with Active Background Rejection) experiment will search for an annually modulating signal from dark matter particles in our Galaxy using an array of ultra-pure NaI(Tl) detectors surrounded by an active scintillator veto to further reduce their intrinsic background. The first phase of the experiment is the SABRE Proof of Principle (PoP), a single 5kg crystal detector operated in a liquid scintillator filled vessel at Laboratori Nazionali del Gran Sasso (LNGS). The PoP installation is underway with the goal of running in 2018 and performing the first in situ measurement…
The Daya Bay Antineutrino Detector gas system is designed to protect the liquid scintillator targets of the antineutrino detectors against degradation and contamination from exposure to ambient laboratory air. The gas system is also used to monitor the leak tightness of the antineutrino detector assembly. The cover gas system constantly flushes the gas volumes above the liquid scintillator with dry nitrogen to minimize oxidation of the scintillator over the five year lifetime of the experiment. This constant flush also prevents the infiltration of radon or other contaminants into these detecti…
We present new results on the radiopurity of a 3.4-kg NaI(Tl) crystal scintillator operated in the SABRE proof-of-principle detector setup. The amount of potassium contamination, determined by the direct counting of radioactive $^{40}$K, is found to be $2.2\pm1.5$ ppb, lowest ever achieved for NaI(Tl) crystals. With the active veto, the average background rate in the crystal in the 1-6 keV energy region-of-interest (ROI) is $1.20\pm0.05$ counts/day/kg/keV, which is a breakthrough since the DAMA/LIBRA experiment. Our background model indicates that the rate is dominated by $^{210}$Pb and that a…
The COSINE-100 dark matter search experiment has started taking physics data with the goal of performing an independent measurement of the annual modulation signal observed by DAMA/LIBRA. A muon detector was constructed by using plastic scintillator panels in the outermost layer of the shield surrounding the COSINE-100 detector. It is used to detect cosmic ray muons in order to understand the impact of the muon annual modulation on dark matter analysis. Assembly and initial performance test of each module have been performed at a ground laboratory. The installation of the detector in Yangyang …
The JUNO observatory is a medium baseline experiment in construction in China. A large liquid scintillator volume detects the antineutrinos issued from nuclear reactors. The liquid scintillator detector is instrumented with 17000 large photomultiplier tubes. Two veto systems are added to reduce the backgrounds. The front-end electronics system performs analog signal processing (the underwater electronics) and after about 100 m cables, the back-end electronics system, outside water, consists of the DAQ and the trigger. One of the main challenges of the whole electronics system is the fast data …
We report on the design and performance of the LUX-ZEPLIN (LZ) "Screener", a small liquid scintillator detector consisting of $\approx 23$ kg of LAB-based gadolinium-loaded liquid scintillator (GdLS) to be used in the LZ Outer Detector. The Outer Detector will be filled with 17.3 tonnes of GdLS and will surround the central liquid xenon time projection chamber of LZ. Its primary function will be to veto neutron single-scatter events in the liquid xenon which could mimic a WIMP dark matter signal. To meet the requirements for the Outer Detector, the radioimpurity levels in the GdLS must be kept…
Cosmic muon interactions are important contributors to backgrounds in underground detectors when searching for rare events. Typically neutrons dominate this background as they are particularly difficult to shield and detect in a veto system. Since actual background data is sparse and not well documented, simulation studies must be used to design shields and predict background rates. This means that validation of any simulation code is necessary to assure reliable results. This work studies the validation of the FLUKA simulation code, and reports the results of a simulation of cosmogenic backgr…
DarkSide-50 is a detector for dark matter candidates in the form of weakly interacting massive particles (WIMPs). It utilizes a liquid argon time projection chamber (LAr TPC) for the inner main detector. The TPC is surrounded by a liquid scintillator veto (LSV) and a water Cherenkov veto detector (WCV). The LSV and WCV, both instrumented with PMTs, act as the neutron and cosmogenic muon veto detectors for DarkSide-50. This paper describes the electronics and data acquisition system used for these two detectors.
A large effort has been carried out to characterize the background of sodium iodide crystals within the ANAIS (Annual modulation with NaI Scintillators) project. In this paper, the background models developed for three 12.5-kg NaI(Tl) scintillators produced by Alpha Spectra Inc. and operated at the Canfranc Underground Laboratory are presented together with an evaluation of the background prospects for the full experiment. Measured spectra from threshold to high energy in different conditions are well described by the models based on quantified activities. At the region of interest, crystal bu…
We present studies on electron backscattering from the surface of plastic scintillator beta detectors. By using a setup of two detectors coaxial with a strong external magnetic field - one detector serving as primary detector, the other as veto-detector to detect backscattering - we investigate amount and spectrum of unrecognized backscattering, i.e. events where only one detector recorded a trigger signal. The implications are important for low energy particle physics experiments.
Nuclear recoil events produced by neutron scatters form one of the most important classes of background in WIMP direct detection experiments, as they may produce nuclear recoils that look exactly like WIMP interactions. In DarkSide-50, we both actively suppress and measure the rate of neutron-induced background events using our neutron veto, composed of a boron-loaded liquid scintillator detector within a water Cherenkov detector. This paper is devoted to the description of the neutron veto system of DarkSide-50, including the detector structure, the fundamentals of event reconstruction and da…
In the published cosmogenic background study for a ton-sized DarkSide dark matter search, only prompt neutron backgrounds coincident with cosmogenic muons or muon induced showers were considered, although observation of the initiating particle(s) was not required. The present paper now reports an initial investigation of the magnitude of cosmogenic background from $β$-delayed neutron emission produced by cosmogenic activity in DarkSide. The study finds a background rate for $β$-delayed neutrons in the fiducial volume of the detector on the order of < 0.1 event/year. However, detailed studies a…
Development and Initial Performance of an Upgraded NaI(Tl) Crystal Encapsulation for COSINE-100U
Kyungpook National University（庆北国立大学）；Chung-Ang University（中央大学）；Institute for Basic Science（基础科学研究院）；University of Science and Technology（科学技术大学）；Seoul National University（首尔国立大学）；Jeju National University（济州国立大学）；Carnegie Mellon University（卡内基梅隆大学）
In the case of underground experiments for neutrino physics or rare event searches, the background caused by cosmic muons contributes significantly and therefore must be identified and rejected. We proposed and optimized a new detector using liquid scintillator with wavelenghth-shifting fibers which can be employed as a veto detector for cosmic muons background rejection. From the prototype study, it has been found that the detector has good performances and is capable of discriminating between muons induced signals and environmental radiation background. Its muons detection efficiency is grea…
The Backward Angle Neutron Detector (BAND) of CLAS12 detects neutrons emitted at backward angles of $155^\circ$ to $175^\circ$, with momenta between $200$ and $600$ MeV/c. It is positioned 3 meters upstream of the target, consists of $18$ rows and $5$ layers of $7.2$ cm by $7.2$ cm scintillator bars, and read out on both ends by PMTs to measure time and energy deposition in the scintillator layers. Between the target and BAND there is a 2 cm thick lead wall followed by a 2 cm veto layer to suppress gammas and reject charged particles. This paper discusses the component-selection tests and the …
The solar neutrino experiment Borexino, which is located in the Gran Sasso underground laboratories, is in a unique position to study muon-induced backgrounds in an organic liquid scintillator. In this study, a large sample of cosmic muons is identified and tracked by a muon veto detector external to the liquid scintillator, and by the specific light patterns observed when muons cross the scintillator volume. The yield of muon-induced neutrons is found to be Yn =(3.10+-0.11)10-4 n/(μ (g/cm2)). The distance profile between the parent muon track and the neutron capture point has the average valu…
The JUNO liquid scintillator-based experiment, construction of which is on-going in Jiangmen (China), will start operations in 2020 and will detect anti-neutrinos from nearby reactors; but also solar neutrinos via elastic scattering on electrons. Its physics goals are broad; its primary aim to measure the neutrino mass ordering demands to collect large statistics, which requires JUNO's 20 kt sensitive mass, and achieve an unprecedented energy resolution (3$\%/\sqrt{E}$). Thanks to these characteristics, JUNO is in a very good position to contribute to the solar neutrino studies in the line of …
This paper describes the design, fabrication, commissioning and use of a CALibration source Insertion System (CALIS) in the DarkSide-50 direct dark matter search experiment. CALIS deploys radioactive sources into the liquid scintillator veto to characterize the detector response and detection efficiency of the DarkSide-50 Liquid Argon Time Projection Chamber, and the surrounding 30 t organic liquid scintillator neutron veto. It was commissioned in September 2014 and has been used successfully in several gamma and neutron source campaigns since then. A description of the hardware and an excerpt…
It is generally inferred from astronomical measurements that Dark Matter (DM) comprises approximately 27\% of the energy-density of the universe. If DM is a subatomic particle, a possible candidate is a Weakly Interacting Massive Particle (WIMP), and the DarkSide-50 (DS) experiment is a direct search for evidence of WIMP-nuclear collisions. DS is located underground at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy, and consists of three active, embedded components; an outer water veto (CTF), a liquid scintillator veto (LSV), and a liquid argon (LAr) time projection chamber (TPC). Thi…
We report the first results of DarkSide-50, a direct search for dark matter operating in the underground Laboratori Nazionali del Gran Sasso (LNGS) and searching for the rare nuclear recoils possibly induced by weakly interacting massive particles (WIMPs). The dark matter detector is a Liquid Argon Time Projection Chamber with a (46.4+-0.7) kg active mass, operated inside a 30 t organic liquid scintillator neutron veto, which is in turn installed at the center of a 1 kt water Cherenkov veto for the residual flux of cosmic rays. We report here the null results of a dark matter search for a (142…
SABRE (Sodium-iodide with Active Background REjection) is a direct dark matter search experiment based on an array of radio-pure NaI(Tl) crystals surrounded by a liquid scintillator veto. Twin SABRE experiments in the Northern and Southern Hemispheres will differentiate a dark matter signal from seasonal and local effects. The experiment is currently in a Proof-of-Principle (PoP) phase, whose goal is to demonstrate that the background rate is low enough to carry out an independent search for a dark matter signal, with sufficient sensitivity to confirm or refute the DAMA result during the follo…
