Ton-scale Detectors Research Articles

NEXT-White results and roadmap towards a ton-scale detector

The goal of the NEXT collaboration is the sensitive search of the neutrinoless double beta decay of 136Xe at the Laboratorio Subterráneo de Canfranc. A first large-scale prototype of a high-pressure gas-Xenon electroluminescent TPC, NEXT-White, was operated from 2016 to 2021. This 4–kg radiopure detector has proven the outstanding performance of the NEXT technology in terms of the energy resolution (<1% FWHM at 2.6 MeV) and the topology-based background rejection. After measuring the relevant backgrounds and their spatial origin, the NEXT-White data collected with 136Xe-enriched and 136Xe-depleted gas have been used to perform a measurement of the two-neutrino mode of the double beta decay. A novel technique based on a direct background subtraction yields a half-life of . This result is consistent with the half-life derived from a background-model-dependent approach. Scaling the technological solutions of NEXT-White, the NEXT-100 detector is being constructed during 2022 and will start the physics data taking in 2023. Holding 100 kg of 136Xe and with a background index below 5×10−4 counts/keV/kg/year, NEXT-100 will perform the first competitive search for the neutrinoless double beta decay within the NEXT roadmap. After 3 years of data taking, a sensitivity to the half-life of 6×1025 yr at 90% C.L. will be achieved. The design for a future ton-scale detector, NEXT-HD, is being carried out in paralel. Operating with low-difussion gas mixtures and a reduced background budget, NEXT-HD will reach sensitivities above 1027 yr. A promising R&D line aims at eventually equiping the NEXT techonlogy with 136Ba-tagging capabilities, opening the doors for a truly background-free experiment.

Performance study of charcoal-based radon reduction systems for ultraclean rare event detectors

The continuous emanation of radon due to trace amounts of uranium and thorium in detector materials introduces radon to the active detection volume of low-background rare event search detectors. 222Rn produces a particularly problematic background in the physics region of interest by the “naked” beta decay of its 214Pb daughter nucleus. While charcoal-based adsorption traps are expected to be effective for radon reduction in auxiliary circulation loops that service the warm components of current ton-scale detectors at slow flow rates (0.5-2 SLPM), radon reduction in the entire circulation loop at high flow rates \U0001d4aa(100s SLPM) is necessary to reach high sensitivity in future generation experiments. In this article we explore radon dynamics with a charcoal-based radon reduction system in the main circulation loop of time projection chamber detectors. We find that even for perfect radon traps, circulation speeds of 2,000 SLPM are needed to reduce radon concentration in a 10 ton detector by 90%. This is faster by a factor of four than the highest circulation speeds currently achieved in dark matter detectors. We further find that the effectiveness of vacuum swing adsorption systems, which have been employed very successfully at reducing atmospheric radon levels in clean-rooms, is limited by the intrinsic radon activity of the charcoal adsorbent in ultra-low radon environments. Adsorbents with significantly lower intrinsic radon activity than in currently available activated charcoals would be necessary to build effective vacuum swing adsorption systems operated at room temperature for rare event search experiments. If such VSA systems are cooled to about 190 K, this requirement relaxes drastically.

Development of Cryogenic Detectors for Neutrinoless Double Beta Decay Searches with CUORE and CUPID

Searching for neutrinoless double beta decay is a top priority in particle and astroparticle physics, being the most sensitive test of lepton number violation and the only suitable process to probe the Majorana nature of neutrinos. In order to increase the experimental sensitivity for this particular search, ton-scale detectors operated at nearly zero-background conditions with a low keV energy resolution at the expected signal peak are required. In this scenario, cryogenic detectors have been proven effective in addressing many of these issues simultaneously. After long technical developments, the Cryogenic Underground Observatory for Rare Events (CUORE) experiment established the possibility to operate large-scale detectors based on this technology. Parallel studies pointed out that scintillating cryogenic detectors represent a suitable upgrade for the CUORE design, directed towards higher sensitivities. In this work, we review the recent development of cryogenic detectors, starting from the state-of-the-art and outlying the path toward next-generation experiments.

New era of dark matter particle detection

The astronomical evidence of the existence of dark matter is overwhelming. However, the physical nature of dark matter is still unknown. It is widely believed that dark matter is some kind of new particles beyond the standard model of particle physics. Alternative candidates include the massive compact halo objects such as primordial black holes. Among all these candidates, the class of so-called weakly interacting massive particles (WIMPs) is the most natural and well theoretically motivated one. The WIMP scenario can naturally explain the abundance of dark matter in the universe via a canonical thermal production mechanism. It also gives a practical way of detecting those particles via various kinds of particle physics experiments. The direct detection method measures the momentum exchange when a dark matter particle scatters off a nucleus. The sensitivities of direct detection increase remarkably during the past 30 years since it was first proposed in the 1980s. China has operated two direct detection experiments, the CDEX and PandaX experiments, in the Jinping underground laboratory. Through the efforts of all the direct detection experiments, including CDEX and PandaX, the current upper limit about the spin-independent scattering cross section between the dark matter particle and the nucleon reaches the level of 10⁻⁴⁷ cm² which is only about two orders of magnitude higher than the neutrino-induced background. Although no convincing signal has been detected yet, such null results can constrain severely many kinds of theoretical models of dark matter. Several experiments are upgrading now, with the goal of a fiducial detector mass of several tons, which are expected to further improve the direct detection sensitivities. The indirect detection method is to search for the annihilation or decay products of dark matter in cosmic rays and gamma-rays, which is complimentary to the direct detection. The main indirect detection experiments in operation include the alpha magnetic spectrometer and the calorimeter electron telescope on the International Space Station, the Fermi gamma-ray space telescope, and China’s dark matter particle explorer. Several anomalies have been reported by the indirect detection experiments, such as the positron excess, the excess of the total electron plus positron spectrum, the gamma-ray excess in the Galactic center region. Interpretations of these excesses are still in debate. Nevertheless, these anomalies offer us targets for further investigation with increased statistics and improved understanding of the astrophysical backgrounds. Both the direct detection and indirect detection experiments will have significantly upgrading in the coming years. Particularly, China’s PandaX experiment is currently building a 4-ton scale detector which is expected to start to operate in 2021. The long-term plan of the CDEX experiment is also a ton-scale detector for multi-purpose studies including the dark matter searches. For the indirect detection, the HERD payload onboard the Chinese Space Station is in the prototype phase, and the next generation very large area gamma-ray space telescope is under design. On the ground we are building the large high-altitude air shower observatory for high-sensitivity sky survey in the very high energy gamma-ray band. All these efforts will make China play a significant or even leading role in the campaign of dark matter detection. We are looking forward to the breakthroughs in the exploration of the nature of dark matter.

The CUORE cryostat

The CUORE experiment (Cryogenic Underground Observatory for Rare Events) is a ton-scale detector, operating at a cryogenic temperature around 10 mK, searching for neutrinoless double-beta decay in 130Te and other rare events. The experiment cryogenic infrastructure, its subsystems and the cool-down procedure that allowed CUORE to obtained the first physics results will be presented.

High voltage insulation and gas absorption of polymers in high pressure argon and xenon gases

High pressure gas time projection chambers (HPGTPCs) are made with a variety of materials, many of which still await proper characterization in high pressure noble gas environments. As HPGTPCs increase in size toward ton-scale detectors, assemblies become larger and more complex, creating a need for detailed understanding of how structural supports and high voltage insulators behave. This includes identification of materials with predictable mechanical properties and without surface charge accumulation that may lead to field deformation or sparking. This paper explores the mechanical and electrical effects of high pressure gas environments on insulating polymers PTFE, HDPE, PEEK, POM and UHMW in argon and xenon, including studying gas absorption, swelling and high voltage insulation strength.

First Dark Matter Search Results from the XENON1T Experiment.

We report the first dark matter search results from XENON1T, a ∼2000-kg-target-mass dual-phase (liquid-gas) xenon time projection chamber in operation at the Laboratori Nazionali del Gran Sasso in Italy and the first ton-scale detector of this kind. The blinded search used 34.2 live days of data acquired between November 2016 and January 2017. Inside the (1042±12)-kg fiducial mass and in the [5,40] keV_{nr} energy range of interest for weakly interacting massive particle (WIMP) dark matter searches, the electronic recoil background was (1.93±0.25)×10^{-4} events/(kg×day×keV_{ee}), the lowest ever achieved in such a dark matter detector. A profile likelihood analysis shows that the data are consistent with the background-only hypothesis. We derive the most stringent exclusion limits on the spin-independent WIMP-nucleon interaction cross section for WIMP masses above 10 GeV/c^{2}, with a minimum of 7.7×10^{-47} cm^{2} for 35-GeV/c^{2} WIMPs at 90%C.L.

Status and prospects of the nMSSM after LHC Run-1

The new minimal supersymmetric standard model (nMSSM), a variant of the general next to minimal supersymmetric standard model (NMSSM) without $Z_3$ symmetry, features a naturally light singlino with a mass below 75 GeV. In light of the new constraints from LHC Run-1 on the Higgs couplings, sparticles searches and flavour observables, we define the parameter space of the model which is compatible with both collider and dark matter (DM) properties. Among the regions compatible with these constraints, implemented through NMSSMTools, SModelS and MadAnalysis 5, only one with a singlino lightest supersymmetric particle (LSP) with a mass around 5 GeV can explain all the DM abundance of the universe, while heavier mixed singlinos can only form one of the DM components. Typical collider signatures for each region of the parameter space are investigated. In particular, the decay of the 125 GeV Higgs into light scalars and/or pseudoscalars and the decay of the heavy Higgs into charginos and neutralinos, provide distinctive signatures of the model. Moreover, the sfermion decays usually proceed through heavier neutralinos rather than directly into the LSP, as the couplings to the singlino are suppressed. We also show that direct detection searches are complementary to collider ones, and that a future ton-scale detector could completely probe the region of parameter space with a LSP mass around 65 GeV.

Prospects for direct detection of dark matter in an effective theory approach

We perform the first comprehensive analysis of the prospects for direct detection of dark matter with future ton-scale detectors in the general 11-dimensional effective theory of isoscalar dark matter-nucleon interactions mediated by a heavy spin-1 or spin-0 particle. The theory includes 8 momentum and velocity dependent dark matter-nucleon interaction operators, besides the familiar spin-independent and spin-dependent operators. From a variegated sample of 27 benchmark points selected in the parameter space of the theory, we simulate independent sets of synthetic data for ton-scale Germanium and Xenon detectors. From the synthetic data, we then extract the marginal posterior probability density functions and the profile likelihoods of the model parameters. The associated Bayesian credible regions and frequentist confidence intervals allow us to assess the prospects for direct detection of dark matter at the 27 benchmark points. First, we analyze the data assuming the knowledge of the correct dark matter nucleon-interaction type, as it is commonly done for the familiar spin-independent and spin-dependent interactions. Then, we analyze the simulations extracting the dark matter-nucleon interaction type from the data directly, in contrast to standard analyses. This second approach requires an extensive exploration of the full 11-dimensional parameter space of the dark matter-nucleon effective theory. Interestingly, we identify 5 scenarios where the dark matter mass and the dark matter-nucleon interaction type can be reconstructed from the data simultaneously. We stress the importance of extracting the dark matter nucleon-interaction type from the data directly, discussing the main challenges found addressing this complex 11-dimensional problem.

Dark-matter harmonics beyond annual modulation

The count rate at dark-matter direct-detection experiments should modulate annually due to the motion of the Earth around the Sun. We show that higher-frequency modulations, including daily modulation, are also present and in some cases are nearly as strong as the annual modulation. These higher-order modes are particularly relevant if (i) the dark matter is light, O(10) GeV, (ii) the scattering is inelastic, or (iii) velocity substructure is present; for these cases, the higher-frequency modes are potentially observable at current and ton-scale detectors. We derive simple expressions for the harmonic modes as functions of the astrophysical and geophysical parameters describing the Earth's orbit, using an updated expression for the Earth's velocity that corrects a common error in the literature. For an isotropic halo velocity distribution, certain ratios of the modes are approximately constant as a function of nuclear recoil energy. Anisotropic distributions can also leave observable features in the harmonic spectrum. Consequently, the higher-order harmonic modes are a powerful tool for identifying a potential signal from interactions with the Galactic dark-matter halo.

Search for neutrino-less double beta decay with EXO-200 and prospects for Ba ion tagging

The Enriched Xenon Observatory collaboration searches for neutrino-less double beta decay in 136Xe. The first phase of the experiment, EXO-200 has started taking data in 2011 and has already produced important physics results like the first observation of the allowed two-neutrino double beta decay in 136Xe. A massive effort for material screening has accompanied the design of EXO-200 and has produced a detector with very low background due to the residual radioactivity. The most recent data analysis campaign has provided a strong limit for the neutrino-less double beta decay in 136Xe. For the next phase ton-scale detector, the collaboration is investigating the options for employing a Ba ion tagging technique to provide complete suppression of the radioactive background.

First operation and performance of a 200 lt double phase LAr LEM-TPC with a 40 × 76 cm2 readout

In this paper we describe the design, construction, and operation of afirst large area double-phase liquid argon Large Electron MultiplierTime Projection Chamber (LAr LEM-TPC). The detector has a maximumdrift length of 60 cm and the readout consists of a 40 × 76 cm2 LEM and 2D projective anode to multiply and collectdrifting charges. Scintillation light is detected by means ofcryogenic PMTs positioned below the cathode. To record both chargeand light signals, we have developed a compact acquisition system,which is scalable up to ton-scale detectors with thousands of chargereadout channels. The acquisition system, as well as the design andthe performance of custom-made charge sensitive preamplifiers, aredescribed. The complete experimental setup has been operated for afirst time during a period of four weeks at CERN in the cryostat ofthe ArDM experiment, which was equipped with liquid and gas argonpurification systems. The detector, exposed to cosmic rays, recordedevents with a single-channel signal-to-noise ratio in excess of 30 forminimum ionising particles. Cosmic muon tracks and theirδ-rays were used to assess the performance of the detector, andto estimate the liquid argon purity and the gain at differentamplification fields.

What can(not) be measured with ton-scale dark matter direct detection experiments

Direct searches for dark matter have prompted in recent years a great deal of excitement within the astroparticle physics community, but the compatibility between signal claims and null results of different experiments is far from being a settled issue. In this context, we study here the prospects for constraining the dark matter parameter space with the next generation of ton-scale detectors. Using realistic experimental capabilities for a wide range of targets (including fluorine, sodium, argon, germanium, iodine and xenon), the role of target complementarity is analysed in detail while including the impact of astrophysical uncertainties in a self-consistent manner. We show explicitly that a multi-target signal in future direct detection facilities can determine the sign of the ratio of scalar couplings fn/fp, but not its scale. This implies that the scalar-proton cross-section is left essentially unconstrained if the assumption fp ∼ fn is relaxed. Instead, we find that both the axial-proton cross-section and the ratio of axial couplings an/ap can be measured with fair accuracy if multi-ton instruments using sodium and iodine will eventually come online. Moreover, it turns out that future direct detection data can easily discriminate between elastic and inelastic scatterings. Finally, we argue that, with weak assumptions regarding the WIMP couplings and the astrophysics, only the dark matter mass and the inelastic parameter (i.e. mass splitting) may be inferred from the recoil spectra — specifically, we anticipate an accuracy of tens of GeV (tens of keV) in the measurement of the dark matter mass (inelastic parameter).

Searching for double beta decay with the Enriched Xenon Observatory

The Enriched Xenon Observatory (EXO) will search for neutrinoless double beta decay in 136Xe. The first phase of the experiment, EXO-200, uses 200 kg of liquid xenon enriched to 80% in 136Xe in an ultra-low background time projection chamber (TPC). EXO-200 is in the final stages of assembly at the WIPP site in Carlsbad, NM and will begin taking data in 2009 with two-year sensitivity to the half-life for neutrinoless double beta decay of 6.4 × 1025 years. According to nuclear matrix element calculations, this corresponds to an effective Majorana neutrino mass of 0.13 to 0.19 eV. The EXO collaboration is also performing R&D for simultaneous detection of the decay electrons and emerging Ba ion allowing essentially background free detection in a future, ton-scale detector. The status of EXO-200 and of the ion tagging technology in liquid xenon is described.

MOON for neutrino-less double beta decays

The MOON (Majorana/Mo Observatory Of Neutrinos) project aims at studies of the Majorana nature of the neutrino (ν) and the ν-mass spectrum by spectroscopic experiments of neutrino-less double beta decays (0νββ) with the ν-mass sensitivity of 〈m 〉 = 100−30 meV. The solid scintillator option of the MOON detector is a super ensemble of multi-layer modules, each being composed by PL scintillator plates and position-sensitive detector planes with good overall energy resolution of σ ≈ 2% at the Q ββ ≈ 3 MeV. Thin ββ source films are interleaved between the detector planes. High localization of the two β tracks enables one to select true signals and reject BG ones. The multi-layer structure of the detector makes it realistic to build a compact ton-scale detector. MOON with detector ≠ ββ source is used for studying 0νββ decays from 100Mo, 82Se and other ββ isotopes with large Q ββ . Real-time exclusive measurements of low energy solar neutrinos can be made by observing inverse β rays from solar-ν captures of 100Mo in delayed coincidence with the subsequent β decay of 100Tc.

Dark matter searches: Technology and backgrounds

The current status of direct dark matter searches is reviewed, with special emphasis on the effect of various backgrounds to the sensitivity attainable by this technology. The current leader in sensitivity is the Cryogenic Dark Matter Search, now operating at the Soudan Underground Laboratory in Minnesota. The next generation of larger and more sensitive detectors will require ever more radiopure materials and access to screening facilities to ensure rapid turn-around in decisions based on material selection and fabrication modification. Recent surveys collected from the DUSEL working groups point to a tripling in screening needs, many of which require an overburden. Low background counting facilities should be established at existing underground sites and integration of their complementary strengths would ensure that new techniques in dark matter, solar neutrino, and neutrinoless double beta decay have the resources they need to build ton-scale detectors.

Status of the ZEPLIN II experiment

ZEPLIN II is a 30-kg two-phase xenon detector designed for direct detection of cold dark matter in the form of WIMPs. Currently in the commissioning phase, it will begin operation in the Boulby Mine, UK later this year. ZEPLIN II is capable of discriminating between nuclear recoils and background events and has a design reach up to two orders of magnitude beyond current limits. It will also serve as a step in the development program for a next-generation ton-scale detector.

Dark matter search with the HDMS-experiment and the GENIUS project

We present a new Germanium Dark Matter Experiment. It consists of two HPGe-Detectors which are run in a unique configuration. The anticoincidence between the two detectors will further reduce the background that we achieve now in the Heidelberg-Moscow-Experiment and will allow to improve WIMP cross section limits to a level comparable to planned cryogenic experiments. This should also allow to test recently claimed positive evidence for dark matter by the DAMA experiment. We show first detector performances from the test period in the Heidelberg Low Level Laboratory and give a preliminary estimation for the background reduction efficiency. The HDMS experiment in being built up now in the Gran Sasso Underground Laboratory and will start taking data by the end of this year. For a substantial improvement of the WIMP-nucleon cross section limits, future dark matter experiments will have to be either massive direction-sensitive detectors or massive ton-scale detectors with almost zero background. A proposal for a high mass (1 ton) Ge experiment with a much further reduced background is the Heidelberg GENIUS experiment. GENIUS will be able to give a WIMP limit of the order 0.02 counts/day/kg and additionally to look for the annual modulation WIMP-signature by using raw data without subtraction.