Results from the First Use of Low Radioactivity Argon in a Dark Matter Search PDF Download

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Liquid argon is a bright scintillator with potent particle identification properties, making it an attractive target for direct-detection dark matter searches. The DarkSide-50 dark matter search here reports the first WIMP search results obtained using a target of low-radioactivity argon. DarkSide-50 is a dark matter detector, using a two-phase liquid argon time projection chamber, located at the Laboratori Nazionali del Gran Sasso. The underground argon is shown to contain Ar39 at a level reduced by a factor (1.4 ± 0.2) × 103 relative to atmospheric argon. Here, we report a background-free null result from (2616 ± 43) kg d of data, accumulated over 70.9 live days. When combined with our previous search using an atmospheric argon, the 90% C.L. upper limit on the WIMP-nucleon spin-independent cross section, based on zero events found in the WIMP search regions, is 2.0 × 10-44 cm2 (8.6 × 10-44 cm2, 8.0 × 10-43 cm2) for a WIMP mass of 100 GeV/c2 (1 TeV/c2, 10 TeV/c2).

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Languages : en
Pages : 7

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Our DarkSide-50 dark matter search reports the first results obtained using a target of lowradioactivity argon extracted from underground sources. The experiment is located at the Laboratori Nazionali del Gran Sasso and uses a two-phase time projection chamber as a detector. A total of 155 kg of low radioactivity argon has been obtained, and we have determined that underground argon is depleted in 39Ar by a factor (1.4 ±0.2) x 103 relative to atmospheric argon. The underground argon was also found to contain (2.05 ± 0.13)mBq=kg of 85Kr. We also found no evidence for dark matter in the form of WIMPs in 70.9 live-days of data with a fiducial mass of (36.9 ± 0.6) kg. When combined with our preceding search with an atmospheric argon target, we set a 90% C.L. upper limit on the WIMP-nucleon spin-independent cross section of 2.0 x 10-44 cm2 (8.6 x 10-44 cm2, 8.0 x 10-43 cm2) for a WIMP mass of 100 GeV=c2 (1TeV=c2, 10TeV=c2).

Author: Elena Aprile
Publisher: John Wiley & Sons
ISBN: 3527609636
Category : Science
Languages : en
Pages : 362

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This book discusses the physical properties of noble fluids, operational principles of detectors based on these media, and the best technical solutions to the design of these detectors. Essential attention is given to detector technology: purification methods and monitoring of purity, information readout methods, electronics, detection of hard ultra-violet light emission, selection of materials, cryogenics etc. The book is mostly addressed to physicists and graduate students involved in the preparation of fundamental next generation experiments, nuclear engineers developing instrumentation for national nuclear security and for monitoring nuclear materials.

Author: Dmitry Yu Akimov
Publisher: World Scientific
ISBN: 9811231109
Category : Science
Languages : en
Pages : 353

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One of the rapidly developing areas of modern experimental nuclear physics is non-accelerator experiments using low-background detectors. Such experiments, as a rule, are aimed at solving problems that are of fundamental importance for understanding the structure of the Universe, checking the Standard Model of elementary particles, and looking for new physics behind the observable world. The most interesting tasks include the search for dark matter in the form of new weakly interacting particles, the search for neutrinoless double beta decay, the determination of the magnetic moment of the neutrino, the study of neutrino oscillation and new types of interaction of elementary particles, such as coherent neutrino scattering off heavy nuclei.All these processes, occurring with extremely low cross sections, require the development of efficient large-mass detectors capable of detecting small energy releases down to individual ionization electrons. An effective method to do this is the emission method of detecting ionizing particles in two-phase media, which has been proposed at Moscow Engineering Physics Institute (MEPhI) 50 years ago. The origin of this technique can be traced to the research headed by Prof. Boris A Dolgoshein, whose study focus on the properties of condensed noble gases as a means to develop a tracking streamer chamber with a high-density working medium.This monograph, devoted exclusively to two-phase emission detectors, considers the technology's basic features while taking into account new developments introduced into experimental practice in the last ten years since the publication of its predecessor, Emission Detectors (Bolozdynya, 2010).

Author: Anyssa Navrer-Agasson
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Languages : en
Pages : 0

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The existence of dark matter is known because of its gravitational effects, and although its nature remains undisclosed, one of the leading candidate is the weakly interacting massive particle (WIMP) with mass of the order of 100 GeV/c2 and coupling with ordinary matter at or below the weak scale. In this context, DarkSide-50 aims to direct observe WIMP-nucleon collisions in a liquid argon dual phase time-projection chamber located deep underground at Gran Sasso National Laboratory, in Italy. This work first details the argon calibration realised by the ARIS experiment. ARIS characterised the argon response to low energy nuclear and electronic recoils, down to unprecedented energies. The nuclear quenching was measured with the best precision to this date, and the recombination probability extracted was compared to different models describing the behaviour of argon in presence of an electric field. A search for low mass WIMPs performed with DarkSide-50 data is also presented. This search focuses on the ionisation signal from the TPC, leading much to much lower detection threshold. The achieved exclusion limits are amongst the leading ones, and the most stringent for a liquid argon target. Finally a preliminary search for axions is presented. Axions are an alternative candidate to dark matter, proposed as a solution to the strong CP problem. They are detectable in DarkSide via their coupling to electrons. This search required the improvement of the modelling of the background sources, by taking into account atomic effects in beta emission spectra, as well as a redefinition of the energy scale converting the energy deposited into a number of extracted electrons. The results presented show an encouraging sensitivity to both solar and galactic axions.

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Languages : en
Pages : 11

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We report the first results of DarkSide-50, a direct search for dark matter operating in the underground Laboratori Nazionali del Gran Sasso (LNGS) and searching for the rare nuclear recoils possibly induced by weakly interacting massive particles (WIMPs). The dark matter detector is a Liquid Argon Time Projection Chamber with a (46.4 ± 0.7) kg active mass, operated inside a 30 t organic liquid scintillator neutron veto, which is in turn installed at the center of a 1 kt water Cherenkov veto for the residual flux of cosmic rays. We report here the null results of a dark matter search for a (1422 ± 67) kg d exposure with an atmospheric argon fill. As a result, this is the most sensitive dark matter search performed with an argon target, corresponding to a 90% CL upper limit on the WIMP-nucleon spin-independent cross section of 6.1×10-44 cm2 for a WIMP mass of 100 Gev/c2.

Author: Benjamin R. Schlitzer
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Languages : en
Pages : 0

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The nature of dark matter remains one of the most significant open questions in modern physics, despite the large body of astrophysical and cosmological evidence supporting its existence. The Weakly Interacting Massive Particle (WIMP) is a well-motivated candidate particle with mass in the range 1 GeV/c2 - 100 TeV/c2 and coupling to Standard Model matter at or below the weak scale. If WIMPs do exist, they should occasionally interact with baryonic particles and leave behind a small amount of energy. DarkSide is a phased experimental program which aims to detect the interaction of a WIMP with a liquid argon target in a dual-phase time projection chamber (TPC). In order to make a WIMP discovery, an accurate understanding of the signal region is required. To this end, small-scale experiments which measure the detector response to a recoiling argon nucleus (NR) or scattering with atomic electrons (ER) are critical in establishing results of the large-scale direct detection experiments. The Argon Response to Ionization and Scintillation (ARIS) experiment was designed to characterize liquid argon's response to both NR and ER events at low recoil energies using a small dual-phase TPC. This work presents a complete chronology of the ARIS experiment and analysis of the collected data. A detailed description of the design of the ARIS TPC and related subsystems is given, as well as an account of the commissioning and calibration performed at the University of California, Los Angeles. The inverse-kinematics neutron source LICORNE was used at the Institute De Physique Nucléaire Orsay to bombard the ARIS TPC with collimated low energy neutrons. Neutron detectors surrounding the TPC were used to tag events which scattered in the TPC at selected angles, and the resulting data were used to characterize both NR and ER events at tightly constrained recoil energies. A description of the low-level reconstruction and data selection cuts is given, as well as corrections made due to trigger efficiency and vertical position in the TPC. ER data were analyzed to provide an improved measurement of the linearity of LAr light yield for incident [gamma]/[beta] particles with energies below 511 keV. ARIS measured a constant light yield to within 1.6% in the [41.5, 511] keV recoil energy range. The linearity of the ER scintillation response measured by ARIS has also been used to derive the spectral shape of forbidden 39Ar [beta] decay, which is a background intrinsic to liquid argon. The NR data were analyzed to measure the relative scintillation efficiency for recoils between [7.1, 117.8] keV, and were in good agreement with the previous SCENE results at low recoil energy. The DarkSide collaboration has used ARIS results to precisely model the response of nuclear recoils in liquid argon in both field-on and field-off configurations. In addition to the characterization of argon response, this work presents an optimization of the electric fields used to drift ionization electrons in DarkSide TPCs. The relevant electrostatics models used by COMSOL simulation software to approximate electric field behavior are described, as well as a technique developed to quantify field uniformity in the TPC. Then, the uniformity of the electric field is optimized for several possible TPC design changes, including the fiducial radius, the first shaping ring voltage, and the cross-sectional geometry of shaping rings. This work was supervised by Dr. Emilija Pantic, and was completed in collaboration with both members of the DarkSide collaboration as well as scientists at the University of California, Davis.

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Languages : en
Pages : 1

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The DarkSide staged program utilizes a two-phase time projection chamber (TPC) with liquid argon as the target material for the scattering of dark matter particles. Efficient background reduction is achieved using low radioactivity underground argon as well as several experimental handles such as pulse shape, ratio of ionization over scintillation signal, 3D event reconstruction, and active neutron and muon vetos. The DarkSide-10 prototype detector has proven high scintillation light yield, which is a particularly important parameter as it sets the energy threshold for the pulse shape discrimination technique. The DarkSide-50 detector system, currently in commissioning phase at the Gran Sasso Underground Laboratory, will reach a sensitivity to dark matter spin-independent scattering cross section of 10-45 cm2 within 3 years of operation.

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Here, the DarkSide experiment is designed for the direct detection of Dark Matter with a double phase liquid Argon TPC operating underground at Laboratori Nazionali del Gran Sasso. The TPC is placed inside a 30 tons liquid organic scintillator sphere, acting as a neutron veto, which is in turn installed inside a 1 kt water Cherenkov detector. The current detector is running since November 2013 with a 50 kg atmospheric Argon fill and we report here the first null results of a Dark Matter search for a (1422 ± 67) kg.d exposure. This result correspond to a 90% CL upper limit on the WIMP-nucleon cross section of 6.1 × 10-44 cm2 (for a WIMP mass of 100 GeV/c2) and it's currently the most sensitive limit obtained with an Argon target.

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Languages : en
Pages : 7

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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. Here, the DS-50 detector performances and the results of the first physics run are reviewed in this proceeding.