Weakly Interacting Massive Particles Mass Research Articles

Design and construction of the DEAP-3600 dark matter detector

The Dark matter Experiment using Argon Pulse-shape discrimination (DEAP) has been designed for a direct detection search for particle dark matter using a single-phase liquid argon target. The projected cross section sensitivity for DEAP-3600 to the spin-independent scattering of Weakly Interacting Massive Particles (WIMPs) on nucleons is 10−46cm2 for a 100 GeV/c2 WIMP mass with a fiducial exposure of 3 tonne-years. This paper describes the physical properties and construction of the DEAP-3600 detector.

A direct dark matter search in XMASS-I

A search for dark matter using an underground single-phase liquid xenon detector was conducted at the Kamioka Observatory in Japan, particularly for Weakly Interacting Massive Particles (WIMPs). We have used 705.9 live days of data in a fiducial volume containing 97kg of liquid xenon at the center of the detector. The event rate in the fiducial volume after the data reduction was (4.2±0.2)×10−3day−1kg−1keVee−1 at 5keVee, with a signal efficiency of 20%. All the remaining events are consistent with our background evaluation, mostly of the “mis-reconstructed events” originated from 210Pb in the copper plates lining the detector's inner surface. The obtained upper limit on a spin-independent WIMP-nucleon cross section was 2.2×10−44cm2 for a WIMP mass of 60GeV/c2 at the 90% confidence level, which was the most stringent limit among results from single-phase liquid xenon detectors.

Dark Matter Search Results from a One Ton-Year Exposure of XENON1T.

We report on a search for weakly interacting massive particles (WIMPs) using 278.8days of data collected with the XENON1T experiment at LNGS. XENON1T utilizes a liquid xenon time projection chamber with a fiducial mass of (1.30±0.01) ton, resulting in a 1.0ton yr exposure. The energy region of interest, [1.4,10.6] keV_{ee} ([4.9,40.9] keV_{nr}), exhibits an ultralow electron recoil background rate of [82_{-3}^{+5}(syst)±3(stat)] events/(ton yr keV_{ee}). No significant excess over background is found, and a profile likelihood analysis parametrized in spatial and energy dimensions excludes new parameter space for the WIMP-nucleon spin-independent elastic scatter cross section for WIMP masses above 6 GeV/c^{2}, with a minimum of 4.1×10^{-47} cm^{2} at 30 GeV/c^{2} and a 90%confidence level.

Materials Informatics for Dark Matter Detection

Dark Matter particles are commonly assumed to be weakly interacting massive particles (WIMPs) with a mass in the GeV to TeV range. However, recent interest has shifted toward lighter WIMPs, which are more difficult to probe experimentally. A detection of sub‐GeV WIMPs will require the use of small gap materials in sensors. Using recent estimates of the WIMP mass, we identify the relevant target space toward small gap materials (100 to 10 meV). Dirac Materials, a class of small‐ or zero‐gap materials, emerge as natural candidates for sensors for Dark Matter detection. We propose the use of informatics tools to rapidly assay materials band structures to search for small gap semiconductors and semimetals, rather than focusing on a few preselected compounds. As a specific example of the proposed strategy, we use the organic materials database (https://omdb.diracmaterials.org) to identify organic candidates for sensors: the narrow band gap semiconductors BNQ‐TTF and DEBTTT with gaps of 40 and 38 meV, and the Dirac‐line semimetal (BEDT‐TTF)·Br which exhibits a tiny gap of ≈50 meV when spin‐orbit coupling is included. We outline a novel and powerful approach to search for dark matter detection sensor materials by means of a rapid assay of materials using informatics tools.

First Results from the DEAP-3600 Dark Matter Search with Argon at SNOLAB.

This Letter reports the first results of a direct dark matter search with the DEAP-3600 single-phase liquid argon (LAr) detector. The experiment was performed 2km underground at SNOLAB (Sudbury, Canada) utilizing a large target mass, with the LAr target contained in a spherical acrylic vessel of 3600kg capacity. The LAr is viewed by an array of PMTs, which would register scintillation light produced by rare nuclear recoil signals induced by dark matter particle scattering. An analysis of 4.44 live days (fiducial exposure of 9.87ton day) of data taken during the initial filling phase demonstrates the best electronic recoil rejection using pulse-shape discrimination in argon, with leakage <1.2×10^{-7} (90%C.L.) between 15 and 31 keV_{ee}. No candidate signal events are observed, which results in the leading limit on weakly interacting massive particle (WIMP)-nucleon spin-independent cross section on argon, <1.2×10^{-44} cm^{2} for a 100 GeV/c^{2} WIMP mass (90%C.L.).

DAMA/LIBRA-phase2 in WIMP effective models

The DAMA/LIBRA collaboration has recently released updated results from their search for the annual modulation signal expected from Dark Matter (DM) scattering in their NaI detectors. We have fitted the updated DAMA result for the modulation amplitudes in terms of a Weakly Interacting Massive Particle (WIMP) signal, parameterizing the interaction with nuclei in terms of the most general effective Lagrangian for a WIMP particle spin up to 1/2, systematically assuming dominance of one of the 14 possible interaction terms, and assuming for the WIMP velocity distribution a standard Maxwellian. We find that most of the couplings of the non-relativistic effective Hamiltonian can provide a better fit compared to the standard Spin Independent interaction case, and with a reduced fine-tuning of the three parameters (WIMP mass, WIMP-nucleon effective cross-section and ratio between the WIMP-neutron and the WIMP-proton couplings). Moreover, effective models for which the cross section depends explicitly on the WIMP incoming velocity can provide a better fit of the DAMA data at large values of mχ compared to the standard velocity-independent cross-section due to a different phase of the modulation amplitudes. All the best fit solutions are in tension with exclusion plots of both XENON1T and PICO60.

Novel constraints on mixed dark-matter scenarios of primordial black holes and WIMPs

We derive constraints on mixed dark-matter scenarios consisting of primordial black holes (PBHs) and weakly interacting massive particles (WIMPs). In these scenarios, we expect a density spike of the WIMPs that are gravitationally bound to the PBHs, which results in an enhanced annihilation rate and increased indirect detection prospects. We show that such scenarios provide strong constraints on the allowed fraction of PBHs that constitutes the dark matter, depending on the WIMP mass mχ and the velocity-averaged annihilation cross-section ⟨σv⟩. For the standard scenario with mχ = 100 GeV and ⟨σv⟩ = 3 × 10−26 cm3/s, we derive bounds that are stronger than all existing bounds for PBHs with masses 10−12 M⊙ ≲ MBH ≲ 104 M⊙, where M⊙ is the solar mass, and mostly so by several orders of magnitude.

Limits on Light Weakly Interacting Massive Particles from the First 102.8 kg×day Data of the CDEX-10 Experiment.

We report the first results of a light weakly interacting massive particles (WIMPs) search from the CDEX-10 experiment with a 10kg germanium detector array immersed in liquid nitrogen at the China Jinping Underground Laboratory with a physics data size of 102.8kg day. At an analysis threshold of 160eVee, improved limits of 8×10^{-42} and 3×10^{-36} cm^{2} at a 90%confidence level on spin-independent and spin-dependent WIMP-nucleon cross sections, respectively, at a WIMP mass (m_{χ}) of 5 GeV/c^{2} are achieved. The lower reach of m_{χ} is extended to 2 GeV/c^{2}.

Optimizing EDELWEISS detectors for low-mass WIMP searches

The physics potential of EDELWEISS detectors for the search of low-mass Weakly Interacting Massive Particles (WIMPs) is studied. Using a data-driven background model, projected exclusion limits are computed using frequentist and multivariate analysis approaches, namely profile likelihood and boosted decision tree. Both current and achievable experimental performance are considered. The optimal strategy for detector optimization depends critically on whether the emphasis is put on WIMP masses below or above $\sim$ 5 GeV/c$^2$. The projected sensitivity for the next phase of the EDELWEISS-III experiment at the Modane Underground Laboratory (LSM) for low-mass WIMP search is presented. By 2018 an upper limit on the spin-independent WIMP-nucleon cross-section of $\sigma_{SI} = 7 \times 10^{-42}$ cm$^2$ is expected for a WIMP mass in the range 2$-$5 GeV/c$^2$. The requirements for a future hundred-kilogram scale experiment designed to reach the bounds imposed by the coherent scattering of solar neutrinos are also described. By improving the ionization resolution down to 50 eV$_{ee}$, we show that such an experiment installed in an even lower background environment (e.g. at SNOLAB) should allow to observe about 80 $^8$B neutrino events after discrimination.

Low-mass dark matter search with CDMSlite

The SuperCDMS experiment is designed to directly detect weakly interacting massive particles (WIMPs) that may constitute the dark matter in our Galaxy. During its operation at the Soudan Underground Laboratory, germanium detectors were run in the CDMSlite mode to gather data sets with sensitivity specifically for WIMPs with masses <10 GeV/c2. In this mode, a higher detector-bias voltage is applied to amplify the phonon signals produced by drifting charges. This paper presents studies of the experimental noise and its effect on the achievable energy threshold, which is demonstrated to be as low as 56 eVee (electron equivalent energy). The detector-biasing configuration is described in detail, with analysis corrections for voltage variations to the level of a few percent. Detailed studies of the electric-field geometry, and the resulting successful development of a fiducial parameter, eliminate poorly measured events, yielding an energy resolution ranging from ∼9 eVee at 0 keV to 101 eVee at ∼10 keVee. New results are derived for astrophysical uncertainties relevant to the WIMP-search limits, specifically examining how they are affected by variations in the most probable WIMP velocity and the Galactic escape velocity. These variations become more important for WIMP masses below 10 GeV/c2. Finally, new limits on spin-dependent low-mass WIMP-nucleon interactions are derived, with new parameter space excluded for WIMP masses ≲3 GeV/c2.26 MoreReceived 6 July 2017DOI:https://doi.org/10.1103/PhysRevD.97.022002© 2018 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDark matterParticle astrophysicsParticle dark matterPhysical SystemsWeakly interacting massive particlesTechniquesDark matter detectorsGravitation, Cosmology & AstrophysicsParticles & Fields

Limits on light WIMPs with a 1 kg-scale germanium detector at 160 eVee physics threshold at the China Jinping Underground Laboratory**Supported by the National Key Research and Development Program of China (2017YFA0402200, 2017YFA0402201), the National Natural Science Foundation of China (11175099, 11275107, 11475117, 11475099, 11475092, 11675088), the National Basic Research Program of China (973 Program) (2010CB833006). We thank the support

We report results of a search for light weakly interacting massive particle (WIMP) dark matter from the CDEX-1 experiment at the China Jinping Underground Laboratory (CJPL). Constraints on WIMP-nucleon spin-independent (SI) and spin-dependent (SD) couplings are derived with a physics threshold of 160 eVee, from an exposure of 737.1 kg-days. The SI and SD limits extend the lower reach of light WIMPs to 2 GeV and improve over our earlier bounds at WIMP mass less than 6 GeV.

Deformed shell model study of event rates for WIMP-73Ge scattering

The event detection rates for the Weakly Interacting Massive Particles (WIMP) (a dark matter candidate) are calculated with [Formula: see text]Ge as the detector. The calculations are performed within the deformed shell model (DSM) based on Hartree–Fock states. First, the energy levels and magnetic moment for the ground state and two low-lying positive parity states for this nucleus are calculated and compared with experiment. The agreement is quite satisfactory. Then the nuclear wave functions are used to investigate the elastic and inelastic scattering of WIMP from [Formula: see text]Ge; inelastic scattering, especially for the [Formula: see text] transition, is studied for the first time. The nuclear structure factors which are independent of supersymmetric model are also calculated as a function of WIMP mass. The event rates are calculated for a given set of nucleonic current parameters. The calculation shows that [Formula: see text]Ge is a good detector for detecting dark matter.

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.

Halo-independent determination of the unmodulated WIMP signal in DAMA: the isotropic case

We present a halo-independent determination of the unmodulated signal corresponding to the DAMA modulation if interpreted as due to dark matter weakly interacting massive particles (WIMPs). First we show how a modulated signal gives information on the WIMP velocity distribution function in the Galactic rest frame from which the unmodulated signal descends. Then we describe a mathematically-sound profile likelihood analysis in which the likelihood is profiled over a continuum of nuisance parameters (namely, the WIMP velocity distribution). As a first application of the method, which is very general and valid for any class of velocity distributions, we restrict the analysis to velocity distributions that are isotropic in the Galactic frame. In this way we obtain halo-independent maximum-likelihood estimates and confidence intervals for the DAMA unmodulated signal. We find that the estimated unmodulated signal is in line with expectations for a WIMP-induced modulation and is compatible with the DAMA background+signal rate. Specifically, for the isotropic case we find that the modulated amplitude ranges between a few percent and about 25% of the unmodulated amplitude, depending on the WIMP mass.

Dark matter searches with the Super-Kamiokande detector

A search for dark matter as WIMPs (Weakly Interacting Massive Particles) using neutrino data collected with the Super-Kamiokande detector in years 1996-2014 has been performed. No excess of ν’s from possible dark matter sources such as Sun, Earth and Galactic Center was found compared to the expected atmospheric ν background. Event samples including both electron and muon ν’s covering a wide range of neutrino energies were used, with sensitivity to WIMP masses down to tens of GeV.

Neutrino physics with DARWIN

DARWIN (DARk matter WImp search with liquid xenoN) will be a multi-ton dark matter detector with the primary goal of exploring the entire experimentally accessible parameter space for weakly interacting massive particles (WIMPs) over a wide mass-range. With its 40 tonne active liquid xenon target, low-energy threshold and ultra-low background level, DARWIN can also search for other rare interactions. Here we present its sensitivity to low-energy solar neutrinos and to neutrinoless double beta decay. In a low-energy window of 2-30 keV a rate of 105/year, from pp and 7Be neutrinos can be reached. Such a measurement, with 1% precision will allow testing neutrinos models. DARWIN could also reach a competitive half-life sensitivity of 8.5 · 1027 y to the neutrinoless double beta decay (0νββ) of 136Xe after an exposure of 140 t×y of natural xenon. Nuclear recoils from coherent scattering of solar neutrinos will limit the sensitivity to WIMP masses below 5 GeV/c2, and the event rate from 8B neutrinos would range from a few to a few tens of events per tonne and year, depending on the energy threshold of the detector. Deviations from the predicted but yet unmeasured neutrino flux would be an indication for physics beyond the Standard Model

Optical response of highly reflective film used in the water Cherenkov muon veto of the XENON1T dark matter experiment

The XENON1T experiment is the most recent stage of the XENON Dark Matter Search, aiming for the direct detection of dark matter candidates, such as the Weakly Interacting Massive Particles (WIMPs). The projected sensitivity for the spin-independent WIMP-nucleon elastic scattering cross-section is σ ≈ 2 × 10−47 cm2 for a WIMP mass of mχ = 50 GeV/c2. To reach its projected sensitivity, the background has to be reduced by two orders of magnitude compared to its predecessor XENON100. This requires a water Cherenkov muon veto surrounding the XENON1T TPC, both to shield external backgrounds and to tag muon-induced energetic neutrons through detection of a passing muon or the secondary shower induced by a muon interacting in the surrounding rock. The muon veto is instrumented with 84 8'' PMTs with high quantum efficiency (QE) in the Cherenkov regime and the walls of the watertank are clad with the highly reflective DF2000MA foil by 3M. Here, we present a study of the reflective properties of this foil, as well as the measurement of its wavelength shifting (WLS) properties. Furthermore, we present the impact of reflectance and WLS on the detection efficiency of the muon veto, through the use of a Monte Carlo simulation carried out with the Geant4 toolkit. The measurements yield a specular reflectance of ≈100% for wavelengths larger than 400 nm, while ≈90% of the incoming light below 370 nm is absorbed by the foil. Approximately 3–7.5% of the light hitting the foil within the wavelength range 250 nm ⩽ λ ⩽ 390 nm is used for the WLS process. The intensity of the emission spectrum of the WLS light is slightly dependent on the absorbed wavelength and shows the shape of a rotational-vibrational fluorescence spectrum, peaking at around λ ≈ 420 nm. Adjusting the reflectance values to the measured ones in the Monte Carlo simulation originally used for the muon veto design, the veto detection efficiency remains unchanged. Including the wavelength shifting in the Monte Carlo simulation leads to an increase of the efficiency of approximately 0.5%.

Multidimensional effective field theory analysis for direct detection of dark matter

The scattering of dark matter particles off nuclei in direct detection experiments can be described in terms of a multidimensional effective field theory (EFT). A new systematic analysis technique is developed using the EFT approach and Bayesian inference methods to exploit, when possible, the energy-dependent information of the detected events, experimental efficiencies, and backgrounds. Highly dimensional likelihoods are calculated over the mass of the weakly interacting massive particle (WIMP) and multiple EFT coupling coefficients, which can then be used to set limits on these parameters and choose models (EFT operators) that best fit the direct detection data. Expanding the parameter space beyond the standard spin-independent isoscalar cross section and WIMP mass reduces tensions between previously published experiments. Combining these experiments to form a single joint likelihood leads to stronger limits than when each experiment is considered on its own. Simulations using two nonstandard operators (3 and 8) are used to test the proposed analysis technique in up to five dimensions and demonstrate the importance of using multiple likelihood projections when determining constraints on WIMP mass and EFT coupling coefficients. In particular, this shows that an explicit momentum dependence in dark matter scattering can be identified.

Capture and decay of electroweak WIMPonium

The spectrum of Weakly-Interacting-Massive-Particle (WIMP) dark matter generically possesses bound states when the WIMP mass becomes sufficiently large relative to the mass of the electroweak gauge bosons. The presence of these bound states enhances the annihilation rate via resonances in the Sommerfeld enhancement, but they can also be produced directly with the emission of a low-energy photon. In this work we compute the rate for SU(2) triplet dark matter (the wino) to bind into WIMPonium—which is possible via single-photon emission for wino masses above 5 TeV for relative velocity v < O(10−2) —and study the subsequent decays of these bound states. We present results with applications beyond the wino case, e.g. for dark matter inhabiting a nonabelian dark sector; these include analytic capture and transition rates for general dark sectors in the limit of vanishing force carrier mass, efficient numerical routines for calculating positive and negative-energy eigenstates of a Hamiltonian containing interactions with both massive and massless force carriers, and a study of the scaling of bound state formation in the short-range Hulth'{e}n potential. In the specific case of the wino, we find that the rate for bound state formation is suppressed relative to direct annihilation, and so provides only a small correction to the overall annihilation rate. The soft photons radiated by the capture process and by bound state transitions could permit measurement of the dark matter's quantum numbers; for wino-like dark matter, such photons are rare, but might be observable by a future ground-based gamma-ray telescope combining large effective area and a low energy threshold.

First search for dark matter annihilations in the Earth with the IceCube detector

We present the results of the first IceCube search for dark matter annihilation in the center of the Earth. Weakly interacting massive particles (WIMPs), candidates for dark matter, can scatter off nuclei inside the Earth and fall below its escape velocity. Over time the captured WIMPs will be accumulated and may eventually self-annihilate. Among the annihilation products only neutrinos can escape from the center of the Earth. Large-scale neutrino telescopes, such as the cubic kilometer IceCube Neutrino Observatory located at the South Pole, can be used to search for such neutrino fluxes. Data from 327 days of detector livetime during 2011/2012 were analyzed. No excess beyond the expected background from atmospheric neutrinos was detected. The derived upper limits on the annihilation rate of WIMPs in the Earth and the resulting muon flux are an order of magnitude stronger than the limits of the last analysis performed with data from IceCube’s predecessor AMANDA. The limits can be translated in terms of a spin-independent WIMP–nucleon cross section. For a WIMP mass of 50 GeV this analysis results in the most restrictive limits achieved with IceCube data.