Search

Cosmological evidence indicates that nonbaryonic dark matter makes up a quarter of the energy density of the universe. One hypothesis for the particle nature of dark matter is the weakly-interacting massive particle (WIMP). The Large Underground Xenon (LUX) experiment is a dual-phase xenon WIMP search experiment with a 250kg active volume. Computational tools developed to support LUX analyses include data mirroring and a data visualization web portal.Within the LUX detector, particle interactions produce pulses of scintillation light. A pulse shape discrimination (PSD) technique is shown to help classify interaction events into nuclear recoils and electron recoils based on the time-structure of the pulses. This approach is evaluated in the context of setting limits on inelastic effective field theory (IEFT) dark matter models. Although PSD is not found to provide significant improvement in the limits, LUX is nevertheless able to set world-leading limits on some IEFT models, while limits for other IEFT models are reported here for the first time.

We present a comprehensive analysis of electronic recoil vs. nuclear recoil discrimination in liquid/gas xenon time projection chambers, using calibration data from the 2013 and 2014-16 runs of the Large Underground Xenon (LUX) experiment. We observe strong charge-to-light discrimination enhancement with increased event energy. For events with S1 = 120 detected photons, i.e. equivalent to a nuclear recoil energy of $\sim$100 keV, we observe an electronic recoil background acceptance of $, 29 pages, 33 figures; minor typos corrected, references updated

Author(s): Akerib, DS; Alsum, S; Araujo, HM; Bai, X; Balajthy, J; Baxter, A; Bernard, EP; Bernstein, A; Biesiadzinski, TP; Boulton, EM; Boxer, B; Bras, P; Burdin, S; Byram, D; Carmona-Benitez, MC; Chan, C; Cutter, JE; De Viveiros, L; Druszkiewicz, E; Fan, A; Fiorucci, S; Gaitskell, RJ; Ghag, C; Gilchriese, MGD; Gwilliam, C; Hall, CR; Haselschwardt, SJ; Hertel, SA; Hogan, DP; Horn, M; Huang, DQ; Ignarra, CM; Jacobsen, RG; Jahangir, O; Ji, W; Kamdin, K; Kazkaz, K; Khaitan, D; Korolkova, EV; Kravitz, S; Kudryavtsev, VA; Leason, E; Lenardo, BG; Lesko, KT; Liao, J; Lin, J; Lindote, A; Lopes, MI; Manalaysay, A; Mannino, RL; Marangou, N; Marzioni, MF; McKinsey, DN; Mei, DM; Moongweluwan, M; Morad, JA; Murphy, ASJ; Naylor, A; Nehrkorn, C; Nelson, HN; Neves, F; Nilima, A; Oliver-Mallory, KC; Palladino, KJ; Pease, EK; Riffard, Q; Rischbieter, GRC; Rhyne, C; Rossiter, P; Shaw, S; Shutt, TA; Silva, C; Solmaz, M; Solovov, VN; Sorensen, P; Sumner, TJ; Szydagis, M; Taylor, DJ; Taylor, R; Taylor, WC; Tennyson, BP; Terman, PA; Tiedt, DR; To, WH; Tripathi, M | Abstract: We present the results of a direct detection search for mirror dark matter interactions, using data collected from the Large Underground Xenon experiment during 2013, with an exposure of 95 live-days×118 kg. Here, the calculations of the mirror electron scattering rate in liquid xenon take into account the shielding effects from mirror dark matter captured within the Earth. Annual and diurnal modulation of the dark matter flux and atomic shell effects in xenon are also accounted for. Having found no evidence for an electron recoil signal induced by mirror dark matter interactions we place an upper limit on the kinetic mixing parameter over a range of local mirror electron temperatures between 0.1 and 0.9 keV. This limit shows significant improvement over the previous experimental constraint from orthopositronium decays and significantly reduces the allowed parameter space for the model. We exclude mirror electron temperatures above 0.3 keV at a 90% confidence level, for this model, and constrain the kinetic mixing below this temperature.

The purpose of current XMASS project is dark matter detection. With 835 kg liquid xenon, we searched for various kinds of dark matter candidate using commissioning data. In order to reduce the background contribution from the PMT surface material, we have refurbished the detector and restarted to take data in November, 2013. Future project of XMASS is also shown.

The XENON Collaboration is searching for Dark Matter interactions in a liquid xenon target. The XENON100 detector, a dual phase xenon Time Projection Chamber employing 161 kg of liquid xenon, started the first science run at the Laboratori Nazionali del Gran Sasso in Italy in 2009. It provided limits on the spin-independent and spin-dependent interaction cross sections of Weakly Interacting Massive Particles (WIMPs), and the couplings of solar axions and galactic axion-like particles. We present these results and the status of the successor experiment, XENON1T. The new detector, currently under construction and starting data taking in 2015, will employ 3.3 tons of liquid xenon, reaching a sensitivity to spin-independent WIMP-nucleon cross section of the order of 10 − 47 cm 2 .

The Large Underground Xenon experiment (LUX) searches for dark matter using a dual-phase xenon detector. LUX uses a custom-developed trigger system for event selection. In this paper, the trigger efficiency, which is defined as the probability that an event of interest is selected for offline analysis, is studied using raw data obtained from both electron recoil (ER) and nuclear recoil (NR) calibrations. The measured efficiency exceeds 98\% at a pulse area of 90 detected photons, which is well below the WIMP analysis threshold on the S2 pulse area. The efficiency also exceeds 98\% at recoil energies of \mbox{0.2 keV} and above for ER, and \mbox{1.3 keV} and above for NR. The measured trigger efficiency varies between 99\% and 100\% over the fiducial volume of the detector., Comment: 31 pages, 14 figures

We revisit the status of a Majorana fermion as a dark matter candidate when a sequential Z' gauge boson dictates the dark matter phenomenology. Direct dark matter detection signatures rise from dark matter-nucleus scatterings at bubble chamber and liquid xenon detectors, and from the flux of neutrinos from the Sun measured by the IceCube experiment, which is governed by the spin-dependent dark matter-nucleus scattering. On the collider side, LHC searches for dilepton and mono-jet + missing energy signals play an important role. The relic density and perturbativity requirements are also addressed. By exploiting the dark matter complementarity we outline the region of parameter space where one can successfully have a Majorana dark matter particle in light of current and planned experimental sensitivities., Comment: 22 pages, 6 figures

The goal of the XMASS experiment is direct detection of dark matter using single-phase liquid xenon. The current-phase detector XMASS-I has the largest target mass (835 kg in total) and achieves the lowest energy threshold (300-eV-electron equivalent). The next phase detector XMASS-1.5 will have a total five tons of liquid xenon and is planned to start in 2015. This paper reports results of searches conducted with XMASS-I [low-mass weakly interacting massive particles (WIMPs), solar axions, annual modulation of event rate at low energy, and inelastic scattering of 129 Xe nuclei by WIMPs] the current status of hardware modification of XMASS-I to reduce background, and progress in designing XMASS-1.5.

We present results of searches for vector and pseudo-scalar bosonic super-WIMPs, which are dark matter candidates with masses at the keV-scale, with the XENON100 experiment. XENON100 is a dual-phase xenon time projection chamber operated at the Laboratori Nazionali del Gran Sasso. A profile likelihood analysis of data with an exposure of 224.6 live days $\times$ 34\,kg showed no evidence for a signal above the expected background. We thus obtain new and stringent upper limits in the $(8-125)$\,keV/c$^2$ mass range, excluding couplings to electrons with coupling constants of $g_{ae} > 3\times10^{-13}$ for pseudo-scalar and $\alpha'/\alpha > 2\times10^{-28}$ for vector super-WIMPs, respectively. These limits are derived under the assumption that super-WIMPs constitute all of the dark matter in our galaxy., Comment: 6 pages, 6 figures

The first searches for axions and axionlike particles with the Large Underground Xenon experiment are presented. Under the assumption of an axioelectric interaction in xenon, the coupling constant between axions and electrons g_{Ae} is tested using data collected in 2013 with an exposure totaling 95 live days ×118 kg. A double-sided, profile likelihood ratio statistic test excludes g_{Ae} larger than 3.5×10^{-12} (90% C.L.) for solar axions. Assuming the Dine-Fischler-Srednicki-Zhitnitsky theoretical description, the upper limit in coupling corresponds to an upper limit on axion mass of 0.12 eV/c^{2}, while for the Kim-Shifman-Vainshtein-Zhakharov description masses above 36.6 eV/c^{2} are excluded. For galactic axionlike particles, values of g_{Ae} larger than 4.2×10^{-13} are excluded for particle masses in the range 1-16 keV/c^{2}. These are the most stringent constraints to date for these interactions.

The standard model of cosmology indicates that approximately 27% of the energy density of the Universe is in the form of dark matter. The nature of dark matter is an open question in modern physics. Indirect dark matter searches with imaging atmospheric Cherenkov telescopes are playing a crucial role in constraining the nature of the dark matter particle through the study of their potential annihilation that could produce very high energy gamma rays from different astrophysical structures. The Cherenkov Telescope Array will provide an unprecedented sensitivity over a range of dark matter mass from ~100 GeV to ~30 TeV. In this contribution we review the status of indirect dark matter searches at dwarf spheroidal galaxies.

We present experimental constraints on the spin-dependent WIMP-nucleon elastic cross sections from the total 129.5 kg-year exposure acquired by the Large Underground Xenon experiment (LUX), operating at the Sanford Underground Research Facility in Lead, South Dakota (USA). A profile likelihood ratio analysis allows 90% CL upper limits to be set on the WIMP-neutron (WIMP-proton) cross section of $\sigma_n$ = 1.6$\times 10^{-41}$ cm$^{2}$ ($\sigma_p$ = 5$\times 10^{-40}$ cm$^{2}$) at 35 GeV$c^{-2}$, almost a sixfold improvement over the previous LUX spin-dependent results. The spin-dependent WIMP-neutron limit is the most sensitive constraint to date., Comment: 7 pages, 3 figures, version accepted by PRL

Dark matter, the most abundant form of matter in the universe, is invisible and intangible. But that doesn't keep Leslie Rosenberg from seeing it nearly everywhere he looks. Like most physicists, he finds ample evidence of it written on the sky. It's there in the swirling of galaxies, the aftermath of cosmic collisions, and the vast, weblike scaffolding that the universe's luminous matter seems to hang upon. /spl moddot/ It's also, he hopes, near at hand. Dark matter almost certainly sweeps through Earth like water through cheesecloth. But Rosenberg, a professor at the University of Washington, in Seattle, thinks he might have just the thing to coax it out of hiding. Tucked into the concrete floor of a large warehouselike laboratory at the edge of campus, the Axion Dark Matter eXperiment (ADMX) contains the world's most sensitive radio receiver in its frequency range. Its builders are fond of boasting that if the detector were placed on Mars, it could pick up a cellphone signal sent from Earth, assuming there were no interference.

A wide range of astrophysical measurements evidence that the stars and gas in all galaxies are immersed in a much larger cloud of non-luminous and non-baryonic dark matter. The nature of the dark matter is still totally unknown, and the resolution of the dark matter puzzle is of fundamental importance to cosmology, astrophysics, and elementary particle physics. One of the major lines of researches directing their efforts at detection of dark matter is direct searches of Weakly Interacting Massive Particles (WIMPs) with detectors operated in deep underground laboratories. The new generation of direct searches of WIMPs promises to probe the most interesting region of parameters for the dark matter candidates. I will review and describe the DarkSide-50 underground Argon detector at Laboratori Nazionali del Gran Sasso.

The XENON100 experiment, situated in the Laboratori Nazionali del Gran Sasso, aims at the direct detection of dark matter in the form of weakly interacting massive particles (WIMPs), based on their interactions with xenon nuclei in an ultra low background dual-phase time projection chamber. This paper describes the general methods developed for the analysis of the XENON100 data. These methods have been used in the 100.9 and 224.6 live days science runs from which results on spin-independent elastic, spin-dependent elastic and inelastic WIMP-nucleon cross-sections have already been reported., Comment: 18 pages, 17 figures, information for the 224.6 live days run included

Germanium detectors with sub-keV sensitivities open a window to search for low-mass WIMP dark matter. The latest limit on spin-independent couplings from the TEXONO experiment at the Kuo-Sheng Reactor Neutrino Laboratory is reported. Highlights of our R&D program, as well as the status and plans are discussed.

The dynamics of the Milky Way provides evidence for a non-luminous mass component. The dark matter could be made of new, color and charge neutral particles, which were non-relativistic when they decoupled from ordinary matter in the early Universe. Dark matter particles are predicted to have a non-zero coupling to baryons and could be detected via their collisions with atomic nuclei in ultra-low background, deep underground detectors. Predicted nuclear recoil energies are smaller than ∼50 keV and expected scattering rates are well below 1 event per year and kg of target material. After an introduction to the methodology, I will briefly discuss the main experimental techniques used in direct dark matter searches, with emphasis on current results and on the status of future projects.

In scenarios where the dark matter interacts differently with protons and neutrons (isospin-violating dark matter), the interpretation of the experimental limits on the dark matter spin-independent cross section may be significantly modified. On the one hand, the direct detection constraints are shifted depending on the target nucleus, possibly changing the hierarchy among different experiments. On the other hand, the relative strength between the bounds from neutrino detectors and those from direct detection experiments is altered, allowing the former to be more competitive. In this paper, the status of isospin-violating dark matter is assessed in the light of recent data, and the prospects for its detection in the near future are analyzed. We find, for example, that there are regions in the parameter space where IceCube currently provides the most stringent limits on the spin-independent cross section, or others where the expected sensitivity of DEAP-3600 is well above the LUX exclusion limit. Our results highlight the complementarity among different targets in direct detection experiments, and between direct detection and neutrino searches in the quest for a dark matter signal., 20 pages, 9 figures

Understanding the nature of dark matter is one of the major challenges in modern physics. Many effects caused by this mysterious matter have been seen, but until today, there is no clear idea on what this dark matter is made of. The current best model to describe our Universe, the Lambda Cold Dark Matter model, incorporates a dark matter component, which makes up about 27% of all the energy in the Universe and roughly 80% of all the matter. In the most popular models, the dark matter consists of particles which are stable, slowly moving (cold), heavy and only interact weakly and gravitationally with ordinary baryonic matter. These particles are therefore called Weakly Interacting Massive Particles (WIMPs). An excellent candidate for the WIMP is the hypothetical neutralino, the Lightest Supersymmetric Particle (LSP), arising in supersymmetric theories beyond the Standard Model of particle physics. Heavy celestial bodies, such as the Earth, could capture these WIMPs and accumulate them. Over time the WIMPs will self-annihilate and may produce standard model particles, including neutrinos. The dark matter annihilation rate in the center of the Earth, and thus the resulting neutrino flux depend on the local Dark Matter density and the mass of the Dark Matter particle. The neutrino flux could be within reach of a large scale neutrino telescope like the cubic kilometer IceCube Neutrino Observatory located at the South Pole. IceCube would indirectly observe the presence of Earth WIMPs as an excess of neutrinos from the center of the Earth. In this thesis, the first search for Earth WIMPs with the IceCube detector is presented. No significant excess from the direction of the center of the Earth has been found in one year of IceCube data. As a result, upper-limits have been set on the annihilation rate of the WIMPs, the muon flux caused by Earth WIMP-induced neutrinos and the spin-independent component of the WIMP-nucleon cross-section. The obtained upperlimits are the current best limits on the annihilation rate of Earth WIMPs and on the muon flux caused by Earth WIMP-induced neutrinos.

"Searching for Dark Matter with Cosmic Gamma Rays" summarizes the evidence for dark matter and what we can learn about its particle nature using cosmic gamma rays. It has almost been 100 years since Fritz Zwicky first detected hints that most of the matter in the Universe that doesn't directly emit or reflect light. Since then, the observational evidence for dark matter has continued to grow. Dark matter may be a new kind of particle that is governed by physics beyond our Standard Model of particle physics. In many models, dark matter annihilation or decay produces gamma rays. There are a variety of instruments observing the gamma-ray sky from tens of MeV to hundreds of TeV. Some make deep, focused observations of small regions, while others provide coverage of the entire sky. Each experiment offers complementary sensitivity to dark matter searches in a variety of target sizes, locations, and dark matter mass scales. We review results from recent gamma-ray experiments including anomalies some have attributed to dark matter. We also discuss how our gamma-ray observations complement other dark matter searches and the prospects for future experiments.

We report the weakly interacting massive particle (WIMP) dark matter search results using the first physics-run data of the PandaX-II 500 kg liquid xenon dual-phase time-projection chamber, operating at the China JinPing underground laboratory. No dark matter candidate is identified above background. In combination with the data set during the commissioning run, with a total exposure of 3.3×10^{4} kg day, the most stringent limit to the spin-independent interaction between the ordinary and WIMP dark matter is set for a range of dark matter mass between 5 and 1000 GeV/c^{2}. The best upper limit on the scattering cross section is found 2.5×10^{-46} cm^{2} for the WIMP mass 40 GeV/c^{2} at 90% confidence level.

Future dark matter detectors plan to have sensitivities such that solar neutrinos will start to become a problematic background. In this work we show that a polarised helium-3 detector would in principle be able to eliminate 98% of these events when the orientation of the polarisation axis is antiparallel to the direction of the Sun. We comment on the possible improvement in sensitivity of dark matter direct detection experiments due to this effect and the feasibility of building such a detector.

Matter, as we know it, makes up less than 5% of the Universe. Various astrophysical observations have confirmed that one quarter of the Universe and most of the matter content in the Universe is made up of dark matter. The nature of dark matter is yet to be discovered and is one of the biggest questions in physics. Particle physics combined with astrophysical measurements of the abundance gives rise to a dark matter candidate called weakly interacting massive particle (WIMP). The low density of WIMPs in the galaxies and the extremely weak nature of the interaction with ordinary matter make detection of the WIMP an extraordinarily challenging task, with abundant fakes from various radioactive and cosmogenic backgrounds with much stronger electromagnetic interaction. The extremely weak nature of the WIMP interaction dictates detectors that have extremely low naturally occurring radioactive background, a large active volume (mass) of sensitive detector material to maximize statistics, a highly efficient detector-based rejection mechanism for the dominant electromagnetic background and sophisticated analysis techniques to reject any residual background. This paper reviews currently available major technologies being pursued by various collaborations, with special emphasis on the cryogenic Ge detector technology used by the Cryogenic Dark Matter Search Collaboration (CDMS).

The TEXONO-CDEX Collaboration (Taiwan experiment on neutrino–China dark matter experiment) explores high-purity germanium (HPGe) detection technology to develop a sub-keV threshold detector for pursuing studies on low mass weakly interacting massive particles (WIMPs), properties of neutrino and the possibilities of neutrino-nucleus coherent scattering observation. This article will introduce the facilities of newly established China Jing-Ping Underground Laboratory (CJPL), preliminary result of cosmic ray background studies at CJPL, the dark matter studies pursued at Kuo-Sheng Neutrino Laboratory (KSNL) and research efforts to accomplish our physics goals.

The theme of the TEXONO-CDEX research program is on the studies of low energy neutrino and dark matter physics at Kuo-Sheng Reactor Neutrino Laboratory and China Jin-Ping Underground Laboratory. The current goal is to open the "sub-keV" detector window with germanium detectors. The three main scientific subjects are neutrino magnetic moments, neutrino-nucleus coherent scattering, and dark matter searches. We highlight the status, results and plans in this article.

The theme of the TEXONO research program is on the studies of low energy neutrino and dark matter physics. The current goals are on the development of germanium detectors with sub-keV sensitivities to realize experiments on neutrino magnetic moments, neutrino-nucleus coherent scattering, as well as WIMP dark matter searches. A threshold of 100–200 eV was achieved with prototype detectors at the Kuo-Sheng Neutrino Laboratory. New limits were placed for low-mass WIMPs. The dark matter program will move to a new underground laboratory currently under construction in Sichuan, China.

The ZEPLIN-III experiment has just completed its first stage at the Boulby Underground Laboratory in search of dark matter WIMPs. We report on the successful operation of the instrument over the continuous 5-month run devoted to collection of WIMP search data and extensive calibration, and present preliminary performance results. Low threshold in the light and ionisation channels and excellent discrimination of γ-ray backgrounds have been achieved.

In this review article the current status of particle dark matter is addressed. We discuss the main theoretical extensions of the standard model which allow to explain dark matter in terms of a (yet undiscovered) elementary particle. We then discuss the theoretical predictions for the searches of particle dark matter: direct detection in low background underground experiments and indirect detection of neutrinos, gamma-rays and antimatter with terrestrial and space-borne detectors. Attention will be placed also on the discussion of the uncertainties, mainly of astrophysical origin, which affect the theoretical predictions. The constraints placed by these searches on the extensions of the standard models will be briefly addressed., 18 pages, 20 figures. Invited talk at the 36th COSPAR Scientific Assembly, Beijing, China, 16-23 July 2006

The Cryogenic Dark Matter Search (CDMS) and XENON experiments aim to directly detect dark matter in the form of weakly interacting massive particles (WIMPs) via their elastic scattering on the target nuclei. The experiments use different techniques to suppress background event rates to the minimum, and at the same time, to achieve a high WIMP detection rate. The operation of cryogenic Ge and Si crystals of the CDMS-II experiment in the Soudan mine has yielded the most stringent spin-independent WIMP-nucleon crosssection (~ 10-43 cm2) at a WIMP mass of 60 GeV/c2. The two-phase xenon detector of the XENON10 experiment is currently taking data in the Gran Sasso underground lab and promising preliminary results were recently reported. Both experiments are expected to increase their WIMP sensitivity by a one order of magnitude in the scheduled science runs for 2007.

We present the status and prospects of the LUX experiment, which employs approximately 300 kg of two-phase xenon to search for WIMP dark matter interactions. The LUX detector was commissioned at the surface laboratory of the Sanford Underground Research Facility in Lead, SD, between December 2011 and February 2012 and the detector has been operating underground since January, 2013. These proceedings review the results of the commissioning run as well as the status of underground data-taking through the summer of 2013.

We report the results of a weakly-interacting massive particle (WIMP) dark matter search using the full 80.1\;live-day exposure of the first stage of the PandaX experiment (PandaX-I) located in the China Jin-Ping Underground Laboratory. The PandaX-I detector has been optimized for detecting low-mass WIMPs, achieving a photon detection efficiency of 9.6\%. With a fiducial liquid xenon target mass of 54.0\,kg, no significant excess event were found above the expected background. A profile likelihood analysis confirms our earlier finding that the PandaX-I data disfavor all positive low-mass WIMP signals reported in the literature under standard assumptions. A stringent bound on the low mass WIMP is set at WIMP mass below 10\,GeV/c$^2$, demonstrating that liquid xenon detectors can be competitive for low-mass WIMP searches., Comment: v3 as accepted by PRD. Minor update in the text in response to referee comments. Separating Fig. 11(a) and (b) into Fig. 11 and Fig. 12. Legend tweak in Fig. 9(b) and 9(c) as suggested by referee, as well as a missing legend for CRESST-II legend in Fig. 12 (now Fig. 13). Same version as submitted to PRD

We demonstrate that current and planned underground neutrino experiments could offer a powerful probe of few-MeV dark matter when combined with a nearby high-intensity low-to-medium energy electron accelerator. This experimental setup, an underground beam-dump experiment, is capable of decisively testing the thermal freeze-out mechanism for several natural dark matter scenarios in this mass range. We present the sensitivity reach in terms of the mass-coupling parameter space of existing and planned detectors, such as Super-K, SNO+, and JUNO, in conjunction with a hypothetical 100 MeV energy accelerator. This setup can also greatly extend the sensitivity of direct searches for new light weakly-coupled force-carriers independently of their connection to dark matter., Comment: 9 pages, 4 figures

The XMASS project utilizes ultrapure liquid xenon and aims to detect pp and 7Be solar neutrinos by means of ν e e scattering. It requires low background and a low threshold, which will also enable us to search for dark matter in the Galactic halo. By using a prototype detector, we have confirmed its feasibility to realize low background and low threshold. We have estimated the sensitivity of an 800-kg liquid-xenon detector for a dark matter search experiment based on the experimental results.

The mass density of the universe seems to be dominated by particles whose nature is unknown. As the existence of new particles is postulated not only by cosmology but also by particle physics, there is a big effort to detect them and to determine their physical properties. However, as the interaction rate between Dark Matter particles and ordinary matter is extremely low, detectors have to be extremely sensitive. Low temperature detectors have been developed for more than one decade now and in the mean time have reached the highest sensitivity for direct Dark Matter detection.

The search for Dark Matter (DM) with heat-and-ionization detectors is one of the most sensitive direct approaches to detect a recoil signal of DM particles such as neutralinos, or weakly interacting massive particles (WIMPs), from scattering off nuclei within the detector material. We present the experimental technique and its results using germanium (Ge) and silicon (Si) bolometric detectors in the EDELWEISS (Experience pour detecter les WIMPs en site souterrain) and CDMS (Cryogenic Dark Matter Search) experiments. The experimental configuration for the second phase of EDELWEISS is described.

The XENON experiment searches for dark matter particles called WIMPs using liquid xenon (LXe) as the active target. The detector is a 3D position sensitive Time Projection Chamber optimized to simultaneously measure the ionization and scintillation produced by a recoil event of energy as low as 16 keV. The distinct ratio of the two signals for nuclear recoils arising from WIMPs and neutrons and for electron recoils from the dominant gamma-ray background determines its event-by-event discrimination. With 1 ton of LXe distributed in ten identical modules, the proposed XENON1T experiment will achieve a sensitivity more than a factor of thousand beyond current limits. A phased program will test a 10 kg detector (XENON10) followed by a 100 kg (XENON100) one as unit module for the XENON1T scale experiment. We review the progress of the XENON R & D phase before presenting the status of XENON10. The experiment will be based at the Gran Sasso Underground Laboratory and is expected to start data taking in early 2006.

The PICASSO experiment investigates the presence and nature of dark matter in the Universe. The experiment is based on the detection of acoustic signals generated in explosive phase transitions induced by dark matter particles. This technique is an alternative more traditional detection technique like scintillation and ionisation, which are largely employed for dark matter search. One of the main advantages of this technique, besides its sensitivity to very low nuclear recoil energies (few keV), is its excellent background suppression features. A pilot experiment consisting of six superheated droplet detectors (40 g of active mass) is presently taking data at the Sudbury Neutrino Observatory (SNO) at a depth of 2000 m. We discuss the operation, calibration and data acquisition of the experiment and also the ongoing work to increase the sensitivity and the active mass of the detectors.

We present a possible design of future large-scale dark matter detector using liquid xenon. A low energy threshold is achieved by using a large CsI-coated internal photocathode for primary light collection. A focusing field, in the active volume and an electron focusing structure at the liquid surface, are used to transport free-electrons to the luminescence field. A 3D reconstruction of the events can be achieved by timing and location of the luminescent signal. A liquid xenon Compton veto and self-shield are integrated in the compact design. This detector could be used to probe most of the SUSY predicted dark matter. ZEPLIN IV can be initially tested at Boulby and then be moved to the USA to operate at a US deep underground science and engineering laboratory.

The ZEPLIN I detector is a zero field liquid xenon detector used in the direct search for Galactic WIMP dark matter and has been operated at 2800 mwe depth in the Boulby mine underground facility in the UK. Discrimination between the types of interaction within the liquid xenon volume is performed through measurement of the time constant of the scintillation light, nuclear recoils being characterized by a faster time constant than the predominant background from gamma and beta events. The detector design is outlined, with a discussion of the detection efficiencies and analysis procedure, leading to a 90% c.l. spin independent cross-section upper limit of 1.1 × 10−6 pb at 60 GeV WIMP mass.

ZEPLIN III is an advanced two-phase xenon detector designed to search for weakly interacting massive particles (WIMPs), such as the neutralino, which make up the dark matter halo of the Galaxy. It has an active target mass of ∼6 kg and uses two signal channels to discriminate between different particle species interacting in the detector. This allows nuclear recoil signatures of WIMPs to be separated from the more numerous background of events generated by photons. By pushing the performance of this type of detector to its limits and incorporating a neutron veto, it will be shown that ZEPLIN III should reach a limiting sensitivity to a coherent elastic WIMP-nucleon scattering cross-section of 10 −8 pb.

We report on progress of the XENON collaboration, which is developing a liquid xenon time projection chamber technology for use in a very-large-mass dark matter experiment. The collaboration is working towards demonstration of simultaneous ionization and scintillation measurement to provide strong background rejection. A 100 kg module will powerfully probe WIMP rates predicted by supersymmetry.

The current status of direct dark matter searches by the Boulby Dark Matter Collaboration is presented with the latest result from the ZePLiN I liquid xenon detector. An upper limit in the interaction cross section per nucleon of ∼1×10−6 pb for a WIMP mass of 100 GeV is found. Details of ZePLiN’s II and III—two future liquid xenon dark matter are presented. Extensive two-phase liquid-gas xenon prototype work has been undertaken and results of characterization studies are presented. The detector response to internal alpha and external gamma and neutron sources is shown. The potential discrimination power of the two-phase technique is displayed. Finally, prospects for the future dark matter search program are discussed.

The recent result [1] from the Heidelberg-Moscow double beta experiment allows neutrinos still to play an important role as hot dark matter in the Universe. HDMS has started in 2001 its search for cold dark matter (WIMPS), with a HPGe crystal of enriched 73 Ge [2]. Concerning hot dark matter, GENIUS will improve the present accuracy for the (effective) neutrino mass. At the same time GENIUS will extend the range of sensitivity in an unprecedented way to cover a wide range of the parameter space of SUSY parameters for neutralinos as cold dark matter. A GENIUS Test Facility in the Gran Sasso has been approved in 2001 and will come into operation by end of 2002. Finally some comments are given to some criticism of the result presented in [1,6].

We report on the results of the first underground dark matter search with light versus heat discrimination. It has been performed at the Canfranc Underground Laboratory in the frame of the Rare Objects SEarch with Bolometers UndergrounD (ROSEBUD) Collaboration with a double bolometer consisting of a 54 g scintillating CaWO 4 and a thin Ge (0.26 g) for light detection. Its capability to distinguish nuclear against electron recoils has been proved and applied to derive limits for weakly interacting massive particle (WIMP) dark matter candidates.

The question of the nature of dark matter in the universe is perhaps the greatest problem facing cosmology and particle physics at present. New observations of the cosmic microwave background radiation and distant supernovae show that more that 90% of the mass in the universe is in the form of some unknown matter. Many lines of evidence from cosmology and particle physics suggest that the best candidate for this dark matter is a weakly interacting massive particle, or WIMP. Such particles are predicted by supersymmetry, a theory extending the Standard Model of particle physics, and many experiments around the world are now trying to directly detect these WIMPs. This article reviews the reasons for believing WIMPs to be the dark matter, and considers the challenges involved in detecting their rare low-energy interactions with normal matter. Current experimental searches are reviewed with regard to the claimed detection of WIMPs by the DAMA group. These experiments are just beginning to reach the sensitivit...

International audience; DarkSide-50 (DS-50) at Gran Sasso underground laboratory (LNGS), Italy, is a direct dark matter search experiment based on a TPC with liquid argon. DS-50 has completed its first dark matter run using atmospheric argon as target. The DS-50 detector performances and the results of the first physics run are reviewed in this proceeding.

© 2014 Elsevier B.V. All rights reserved. The LUX (Large Underground Xenon) experiment aims at the direct detection of dark matter particles via their collisions with xenon nuclei. The 370 kg two-phase liquid xenon time projection chamber measures simultaneously the scintillation and ionization from interactions in the target. The ratio of these two signals provides very good discrimination between potential nuclear recoil and electronic recoil signals to search for WIMP-nucleon scattering. The LUX detector operates at the Sanford Underground Research Facility (Lead, South Dakota, USA) since February 2013. First results were presented in late 2013 setting the world's most stringent limits on WIMP-nucleon scattering cross-sections over a wide range of WIMP masses. A 300 day run beginning in 2014 will further improve the sensitivity and new calibration techniques will reduce systematics for the WIMP signal search.

The landscape of dark matter direct detection has been profoundly altered by the slew of recent experiments. While some have claimed signals consistent with dark matter, others have seen few, if any, events consistent with dark matter. The results of the putative detections are often incompatible with each other in the context of naive spin-independent scattering, as well as with the null results. In particular, in light of the conflicts between the DM interpretation of the three events recently reported by the CDMS-Si experiment and the first results of the LUX experiment, there is a strong need to revisit the assumptions that go into the DM interpretations of both signals and limits. We attempt to reexamine a number of particle physics, astrophysics and experimental uncertainties. Specifically, we examine exothermic scattering, isospin-dependent couplings, modified halo models through astrophysics independent techniques, and variations in the assumptions about the scintillation light in liquid Xenon. We find that only a highly tuned isospin-dependent scenario remains as a viable explanation of the claimed detections, unless the scintillation properties of LXe are dramatically different from the assumptions used by the LUX experiment.

The existence of dark matter is inferred from gravitational effects, but its nature remains a deep mystery. One possibility, motivated by considerations in elementary particle physics, is that dark matter consists of elementary particles, such as the hypothesized Weakly Interacting Massive Particles (WIMPs), with mass ~ 100 GeV and cross-section ~ 10−47 cm2, that can be gravitationally trapped inside our galaxy and revealed by their scattering on nuclei. It should be possible to detect WIMPs directly, as the orbital motion of the WIMPs composing the dark matter halo pervading the galaxy should result in WIMP-nucleus collisions of sufficient energy to be observable in the laboratory. The DarkSide-50 experiment is a direct WIMP search using a Liquid Argon Time Projection Chamber (LAr-TPC) with an active mass of 50 kg with a high sensitivity and an ultra-low background detector.