WIMPs Research Articles

Low-mass WIMP searches with the EDELWEISS experiment

The EDELWEISS experiment is a direct search for Weakly Interacting Massive Particles (WIMP) dark matter using an array of twenty-four 860 g cryogenic germanium detectors equipped with a full charge and thermal signal readout. The experiment is located in the ultra-low radioactivity environment of the Modane underground laboratory in the Frejus tunnel. WIMP limits, background rejection factors and measurements of cosmogenic activation recorded in long exposures are used to assess the performance of the third generation of EDELWEISS detectors in view of the search for WIMPs in the mass range from 1 to 20 GeV/c2. The developments in progress to pursue this goal in the coming years are also presented.

Indirect Searches for Dark Matter Signatures at INO

Neutrino fluxes could arise due to annihilation of Weakly Interactive Massive Particles (WIMPs) in the center of the sun. We study the prospects of search for muon events due to such neutrinos at the upcoming Iron CALorimeter (ICAL) detector to be housed at India-based Neutrino Observatory (INO). Although the atmospheric neutrinos will pose a serious background to the signal neutrinos produced through WIMP annihilation, the former could be supressed significantly by using the directional property of signal neutrinos. For 50kt×10 years of ICAL running and WIMP masses (mχ) between 3-100 GeV, we perform a χ2 analysis and present expected exclusion regions in the σβख़ — mx and σβι — mx plane, where σβख़ and σβι are the WIMP-nucleon Spin-Dependent (SD) and Spin-Independent (SI) scattering cross-sections, respectively. For mx = 25 GeV, the expected 90 % C.L. exclusion limit on σβख़ are σβॄ < 7.82 x 10−41 cm2 for τ+τ− channel and σβख़ < 1.23 10−39 cm2 for 66 channel. For same m×, the expected 90 % C.L. exclusion limits on σβι are σβι < 8.97 × 10−43 cm2 for τ +τ− channel and σβι < 1.43×10−41 cm2 for 66 channel.

Dark Matter Searches at Super-Kamiokande

This work presents indirect searches for dark matter (DM) as WIMPs (Weakly Interacting Massive Particles) using neutrino data collected with the Super-Kamiokande detector from 1996 until 2016. The results of the search for WIMP-induced neutrinos from the Sun, the Earth’s core and the Milky Way are discussed. We looked for an excess of neutrinos related to a given source as compared to the expected atmospheric neutrino background. No excess of the WIMP-induced neutrinos is observed in any of the analyses. Limits on the WIMP-nucleon spin-dependent/-independent cross sections (Solar & Earth analysis) and on the WIMP self-annihilation cross section 〈σAV〉 (Galactic analysis) are derived assuming various annihilation modes and masses of the relic particles.

New Experiment NEWSdm for Direct Searches for Heavy Dark Matter Particles

NEWSdm [Nuclear Emulsions for WIMP (weakly interacting massive particles) Search—directional measurement] is a new international experiment in which a photoemulsion target is used for a direct detection of dark-matter particles. In this experiment, the detection method is based on fixing the directions of trajectories of recoil nuclei originating from the elastic interaction of target nuclei with dark-matter particles from the galactic halo. This distinguishes NEWSdm from standard low-background experiments aimed at searches for dark-matter particles and based on an analysis of annual modulations of the number of detected events. The detector, which is simultaneously a target, is a block of nuclear emulsions that have a uniquely high spatial resolution owing to the reduction of the size of AgBr grains to about $$10$$ nm. A resolution on this order of magnitude permits directional searches for dark-matter particles in cosmic space even at energies of recoil nuclei not higher than 30 keV.

Prototype of pulse digitizer and readout electronics for CDEX-10 in CJPL

The CDEX (China Dark matter Experiment) is currently in the stage to upgrade to approximately 10 kg HPGe (High Purity Germanium) detectors (CDEX-10) in CJPL (China Jinping Underground Laboratory) and aims to detect the WIMP (Weakly Interacting Massive Particles). Six analog signals and one inhibited signal are outputted from preamplifier by one HPGe detector (∼ 1 kg) of CDEX-10. The analog signals are conditioned with two 6 μs and one 12 μs shaping amplifiers, and three timing amplifiers respectively. The inhibited signal is used for trigger. The analog signals from shaping and timing amplifiers are digitized to obtain energy spectrum and rise-time distribution. The rise-time distribution is used to discriminate surface, bulk, and very bulk events, which can help to supress the background level in dark matter detection. Composed of commercial modules, the previous DAQ (Data Acquisition Systems) is insufficient in discriminating between bulk and very bulk events due to the limited sampling rate (100 MSPS). Besides, as number of channel increases, the system will be simplified by integrating the trigger logic in FPGA (Field Programmable Gate Array). In this paper, a prototype named RAIN4HPGe is designed with pulse digitizer and readout electronics, integrating 14-bit 100 MSPS ADCs (Analog-to-Digital Converters), 12-bit 1 GSPS ADCs, FPGA etc. . The RAIN1000Z1 readout module based on ZYNQ SoC (System on Chip) is used for readout over Gigabit Ethernet. Better energy resolution, e.g. improving from 558 eV to 474 eV @122 keV, can be achieved by RAIN4HPGe compared to previous DAQ (Data Acquisition Systems) with commercial solution. Moreover, the discrimination performance of bulk, and very bulk events has been improved by RAIN4HPGe with 1 GSPS ADC.

Latest results of the LUX dark matter experiment

LUX (Large Underground Xenon) was a dark matter experiment, which was housed at the Sanford Underground Research Facility (SURF) in South Dakota until late 2016, and previously set world-leading limits on Weakly Interacting Massive Particles (WIMPs), axions and axion-like particles (ALPs). This proceeding presents an overview of the LUX experiment and discusses the most recent analysis efforts, which are probing various dark matter models and detection techniques. In particular, studies of signals from inelastic scattering processes and of single scintillation photon events have improved the sensitivity of the experiment to low mass WIMPs. Additionally, a model-independent search for modulations in the LUX electron recoil rate is presented, demonstrating the most sensitive annual modulation search to date.

SIMPler realisation of scalar dark matter

With growing agony of not finding a dark matter (DM) particle in direct search experiments so far (for example in XENON1T), frameworks where the freeze-out of DM is driven by number changing processes within the dark sector itself and do not contribute to direct search, like Strongly Interacting Massive Particle (SIMP) are gaining more attention. In this analysis, we ideate a simple scalar DM framework stabilised by \U0001d4b53 symmetry to serve with a SIMP-like DM (χ) with additional light scalar mediation (ϕ) to enhance DM self interaction. We identify that a large parameter space for such DM is available from correct relic density and self interaction constraints coming from Bullet or Abell cluster data. We derive an approximate analytic solution for freeze-out of the SIMP like DM in Boltzmann equation describing 3DM → 2DM number changing process within the dark sector. We also provide a comparative analysis of the SIMP like solution with the Weakly Interacting Massive Particle (WIMP) realisation of the same model framework here.

NEWS-G, a Spherical Proportional Counter with low-Z target to search for sub-GeV Weakly Interacting Particles

Despite several large-scale direct detection experiments operating worldwide, dark matter remains elusive. Not favoured by supersymmetric theories, the low Weakly Interacting Massive Particle (WIMP) mass regime (less than few GeV) has been largely ignored. The NEWS-G project builds on the experience gathered with the operation of the SEDINE detector at the Laboratoire Souterrain de Modane (France). The goal is to construct a 140cm diameter low-background Spherical Proportional Counter (SPC) capable of holding up to 10 bar of gas and to be operated at the SNOLAB underground facility (Canada). The use of low-Z target materials such as Ne, He and H, together with a strict selection of low activity materials will provide sensitivity to WIMP masses down to 0.1 GeV/c2. The detector is expected to be deployed in 2018.

Annual modulation search by XMASS-I with 2.7 years of data

In this work, we conducted annual modulation search for dark matter with 2.7 years of data taking with the XMASS-I detector. A total exposure was 800 live days times 832 kg. When we assume Weakly Interacting Massive Particle (WIMP) dark matter elastically scattering on the xenon target, the exclusion upper limit of the WIMP-nucleon cross section was 1.9×10−41cm2 at 8 GeV/c2. For model independent case, without assuming any specific dark matter model, we did not find any modulation signal with a p-value of 0.11 in the 1-20 keV energy region for the null hypothesis.

CDEX Dark Matter Experiment: Status and Prospects

The China Dark Matter Experiment (CDEX) aims at direct searches of light Weakly Interacting Massive Particles (WIMPs) at the China Jinping Underground Laboratory (CJPL) with an overburden of about 2400m rock. Results from a prototype CDEX-1 994 g p-type Point Contact Germanium(pPCGe) detector are reported. Research programs are pursued to further reduce the physics threshold by improving hardware and data analysis. The CDEX-10 experiment with a pPCGe array of 10 kg target mass range is being tested. The evolution of CDEX program into “CDEX-1T Experiment” with ton-scale germanium detector arrays will also be introduced in this study.

Directional detection of Dark Matter with a nuclear emulsion based detector

The nature of Dark Matter is one of the fundamental questions to be answered. Direct Dark Matter searches are focussed on the development, construction, and operation of detectors looking for the scattering of Weakly Interactive Massive Particles (WIMPs) with target nuclei. The measurement of the direction of WIMP-induced nuclear recoils is a challenging strategy to extend dark matter searches beyond the neutrino floor and provide an unambiguous signature of the detection of Galactic dark matter. Current directional experiments are based on the use of gas TPC whose sensitivity is strongly limited by the small achievable detector mass. NEWSdm is an innovative directional experiment proposal based on the use of a solid target made by newly developed nuclear emulsion films and read-out systems achieving a position accuracy of 10 nm.

Supernova neutrino detection in XENONnT neutron and muon Vetoes

The current phase of the XENON Dark Matter Project, named XENONnT, will be operative in 2020 in the underground Laboratori Nazionali del Gran Sasso (LNGS). It is a multi-ton detector for direct search of Dark Matter, consisting of a double phase liquid-gas xenon Time Projection Chamber (TPC) which contains 5.9 tons of liquid xenon target mass, inserted in a cryostat surrounded by a tank containing 700 tons of water doped with Gd sulphate. Its aim, as that of its precursor XENON1T, is to detect elastic scattering of Weakly Interacting Massive Particles (WIMPs) off xenon nuclei. The presence of two Veto sub-systems, the muon Veto instrumented with 84 photomultiplier tubes (PMTs) and the neutron Veto with other 120 PMTs, allows to reduce the background for WIMPs search through muon and neutron tagging, while the presence of Gd sulphate increases the neutron capture cross section. Thanks to the large xenon target used and the presence of the two Vetoes, XENONnT will be able also to detect all flavours of Supernova neutrinos. Here the results from Monte Carlo simulations of XENONnT detection efficiency are presented for Supernova neutrinos through their inverse beta decay interactions in water of the two Veto sub-systems.

Constraints to Dark Matter Annihilation from High-Latitude HAWC Unidentified Sources

The Λ CDM cosmological framework predicts the existence of thousands of subhalos in our own Galaxy not massive enough to retain baryons and become visible. Yet, some of them may outshine in gamma rays provided that the dark matter is made of weakly interacting massive particles (WIMPs), which would self-annihilate and would appear as unidentified gamma-ray sources (unIDs) in gamma-ray catalogs. Indeed, unIDs have proven to be competitive targets for dark matter searches with gamma rays. In this work, we focus on the three high-latitude ( | b | ≥ 10 ) sources present in the 2HWC catalog of the High Altitude Water Cherenkov (HAWC) observatory with no clear associations at other wavelengths. Indeed, only one of these sources, 2HWC J1040+308, is found to be above the HAWC detection threshold when considering 760 days of data, i.e., a factor 1.5 more exposure time than in the original 2HWC catalog. Other gamma-ray instruments, such as Fermi-LAT or VERITAS at lower energies, do not detect the source. Also, this unID is reported as spatially extended, making it even more interesting in a dark matter search context. While waiting for more data that may shed further light on the nature of this source, we set competitive upper limits on the annihilation cross section by comparing this HAWC unID to expectations based on state-of-the-art N-body cosmological simulations of the Galactic subhalo population. We find these constraints to be particularly competitive for heavy WIMPs, i.e., masses above ∼25 (40) TeV in the case of the b b ¯ ( τ + τ − ) annihilation channel, reaching velocity-averaged cross section values of 2 × 10 − 25 ( 5 × 10 − 25 ) cm 3 ·s − 1 . Although far from testing the thermal relic cross section value, the obtained limits are independent and nicely complementary to those from radically different DM analyses and targets, demonstrating once again the high potential of this DM search approach.

Low-Energy Physics Reach of Xenon Detectors for Nuclear-Recoil-Based Dark Matter and Neutrino Experiments.

Dual-phase xenon detectors lead the search for keV-scale nuclear recoil signals expected from the scattering of weakly interacting massive particle (WIMP) dark matter, and can potentially be used to study the coherent nuclear scattering of MeV-scale neutrinos. New capabilities of such experiments can be enabled by extending their nuclear recoil searches down to the lowest measurable energy. The response of the liquid xenon target medium to nuclear recoils, however, is not well characterized below a few keV, leading to large uncertainties in projected sensitivities. In this work, we report a new measurement of ionization signals from nuclear recoils in liquid xenon down to the lowest energy reported to date. At 0.3keV, we find that the average recoil produces approximately one ionization electron; this is the first measurement of nuclear recoil signals at the single-ionization-electron level, approaching the physical limit of liquid xenon ionization detectors. We discuss the implications of these measurements on the physics reach of xenon detectors for nuclear-recoil-based WIMP dark matter searches and the detection of coherent elastic neutrino-nucleus scattering.

Inelastic dark matter nucleus scattering

Direct detection experiments aim at the detection of dark matter in the form of weakly interacting massive particles (WIMPs) by searching for signals from elastic dark matter nucleus scattering. Additionally, inelastic scattering in which the nucleus is excited is expected from nuclear physics and provides an additional detectable signal. In the context of a low-energy effective field theory we investigate the experimental reach to these inelastic transitions for xenon-based detectors employing a dual-phase time projection chamber. We find that once a dark matter signal is established, inelastic transitions enhance the discovery reach and we show that they allow a better determination of the underlying particle physics.

Search for Light Weakly-Interacting-Massive-Particle Dark Matter by Annual Modulation Analysis with a Point-Contact Germanium Detector at the China Jinping Underground Laboratory.

We present results on light weakly interacting massive particle (WIMP) searches with annual modulation (AM) analysis on data from a 1-kg mass p-type point-contact germanium detector of the CDEX-1B experiment at the China Jinping Underground Laboratory. Datasets with a total live time of 3.2yr within a 4.2-yr span are analyzed with analysis threshold of 250eVee. Limits on WIMP-nucleus (χ-N) spin-independent cross sections as function of WIMP mass (m_{χ}) at 90%confidence level (C.L.) are derived using the dark matter halo model. Within the context of the standard halo model, the 90%C.L. allowed regions implied by the DAMA/LIBRA and CoGeNT AM-based analysis are excluded at >99.99% and 98%C.L., respectively. These results correspond to the best sensitivity at m_{χ}<6 GeV/c^{2} among WIMP AM measurements to date.

Two-component dark matter with cogenesis of the baryon asymmetry of the Universe

We discuss the possibility of realising a two-component dark matter (DM) scenario where the two DM candidates differ from each other by virtue of their production mechanism in the early universe. One of the DM candidates is thermally generated in a way similar to the weakly interacting massive particle (WIMP) paradigm where the DM abundance is governed by its freeze-out while the other candidate is produced only from non-thermal contributions similar to freeze-in mechanism. We discuss this in a minimal extension of the standard model where light neutrino masses arise radiatively in a way similar to the scotogenic models with DM particles going inside the loop. The lepton asymmetry is generated at the same time from WIMP DM annihilations as well as partially from the mother particle for non-thermal DM. This can be achieved while satisfying the relevant experimental bounds, and keeping the scale of leptogenesis or the thermal DM mass as low as 3 TeV, well within present experimental reach. In contrast to the TeV scale thermal DM mass, the non-thermal DM can be as low as a few keV, giving rise to the possibility of a sub-dominant warm dark matter (WDM) component that can have interesting consequences on structure formation. The model also has tantalizing prospects of being detected at ongoing direct detection experiments as well as the ones looking for charged lepton flavour violating process like $\mu \rightarrow e \gamma$.

Z′ mediated WIMPs: dead, dying, or soon to be detected?

Although weakly interacting massive particles (WIMPs) have long been among the most studied and theoretically attractive classes of candidates for the dark matter of our universe, the lack of their detection in direct detection and collider experiments has begun to dampen enthusiasm for this paradigm. In this study, we set out to appraise the status of the WIMP paradigm, focusing on the case of dark matter candidates that interact with the Standard Model through a new gauge boson. After considering a wide range of Z′ mediated dark matter models, we quantitatively evaluate the fraction of the parameter space that has been excluded by existing experiments, and that is projected to fall within the reach of future direct detection experiments. Despite the existence of stringent constraints, we find that a sizable fraction of this parameter space remains viable. More specifically, if the dark matter is a Majorana fermion, we find that an order one fraction of the parameter space is in many cases untested by current experiments. Future direct detection experiments with sensitivity near the irreducible neutrino floor will be able to test a significant fraction of the currently viable parameter space, providing considerable motivation for the next generation of direct detection experiments.

Comparison between DAMA/LIBRA and COSINE-100 in the light of quenching factors

There is a long standing debate about whether or not the annual modulation signal reported by the DAMA/LIBRA collaboration is induced by Weakly Interacting Massive Particles (WIMP) in the galaxy's dark matter halo scattering from nuclides in their NaI(Tl) crystal target/detector. This is because regions of WIMP-mass vs. WIMP-nucleon cross-section parameter space that can accommodate the DAMA/LIBRA-phase1 modulation signal in the context of the standard WIMP dark matter galactic halo and isospin-conserving (canonical), spin-independent (SI) WIMP-nucleon interactions have been excluded by many of other dark matter search experiments including COSINE-100, which uses the same NaI(Tl) target/detector material. Moreover, the recently released DAMA/LIBRA-phase2 results are inconsistent with an interpretation as WIMP-nuclide scattering via the canonical SI interaction and prefer, instead, isospin-violating or spin-dependent interactions. Dark matter interpretations of the DAMA/LIBRA signal are sensitive to the NaI(Tl) scintillation efficiency for nuclear recoils, which is characterized by so-called quenching factors (QF), and the QF values used in previous studies differ significantly from recently reported measurements, which may have led to incorrect interpretations of the DAMA/LIBRA signal. In this article, the compatibility of the DAMA/LIBRA and COSINE-100 results, in light of the new QF measurements is examined for different possible types of WIMP-nucleon interactions. The resulting allowed parameter space regions associated with the DAMA/LIBRA signal are explicitly compared with 90% confidence level upper limits from the initial 59.5 day COSINE-100 exposure. With the newly measured QF values, the allowed 3σ regions from the DAMA/LIBRA data are still generally excluded by the COSINE-100 data.

Constraining FIMP from the structure formation of the Universe: analytic mapping from mWDM

A feebly interacting massive particle (FIMP), contrasting with a weakly interacting massive particle (WIMP), is an intriguing dark matter (DM) candidate. Light (keV-scale) FIMP DM is of particular interest: its radiative decay leaves a line signal in x-ray spectra; and it is warm dark matter (WDM) and alters the galactic-scale structure formation of the Universe from that with WIMP DM . Once a possible x-ray line is reported (e.g., 3.5 keV line infers 7 keV FIMP DM), one has to check whether or not this FIMP DM is compatible with the structure formation. Here is an issue: the structure formation constraint on WDM is often reported in terms of the so-called thermal WDM mass mWDM, which cannot be directly applied to FIMP parameters. In this paper, we introduce a benchmark FIMP model that represents well a broad class of FIMP models. A big advantage of this benchmark is that we can derive the analytic formula of the non-thermal phase space distribution of FIMPs produced from freeze-in processes. By further deriving a certain “warmness” quantity, we can analytically map mWDM to FIMP parameters. Our analytic map indicates that 7 keV FIMP DM, without entropy production or a degenerate spectrum, is in tension with the latest Lyman-α forest data. Our analytic map will be very useful for future updates of observational constraints and reports of x-ray lines. It is also very easy to incorporate our analytic formula into a Boltzmann solver so that a linear matter power spectrum is readily accessible. Our benchmark model will facilitate FIMP searches and particle physics model-building.