Publications
78 results found
Akerib DS, Akerlof CW, Akimov DY, et al., 2020, The LUX-ZEPLIN (LZ) radioactivity and cleanliness control programs, European Physical Journal C: Particles and Fields, Vol: 80, Pages: 1-52, ISSN: 1124-1861
LUX-ZEPLIN (LZ) is a second-generation direct dark matter experiment with spin-independent WIMP-nucleon scattering sensitivity above 1.4×10−48cm2 for a WIMP mass of 40GeV/c2 and a 1000days exposure. LZ achieves this sensitivity through a combination of a large 5.6t fiducial volume, active inner and outer veto systems, and radio-pure construction using materials with inherently low radioactivity content. The LZ collaboration performed an extensive radioassay campaign over a period of six years to inform material selection for construction and provide an input to the experimental background model against which any possible signal excess may be evaluated. The campaign and its results are described in this paper. We present assays of dust and radon daughters depositing on the surface of components as well as cleanliness controls necessary to maintain background expectations through detector construction and assembly. Finally, examples from the campaign to highlight fixed contaminant radioassays for the LZ photomultiplier tubes, quality control and quality assurance procedures through fabrication, radon emanation measurements of major sub-systems, and bespoke detector systems to assay scintillator are presented.
Collaboration TLUX-ZEPLIN, Akerib DS, Akerlof CW, et al., 2020, Simulations of Events for the LUX-ZEPLIN (LZ) Dark Matter Experiment, Astroparticle Physics, ISSN: 0927-6505
The LUX-ZEPLIN dark matter search aims to achieve a sensitivity to theWIMP-nucleon spin-independent cross-section down to (1-2) $\times$ $10^{-12}$pb at a WIMP mass of 40 GeV/$c^2$. This paper describes the simulationsframework that, along with radioactivity measurements, was used to support thisprojection, and also to provide mock data for validating reconstruction andanalysis software. Of particular note are the event generators, which allow usto model the background radiation, and the detector response physics used inthe production of raw signals, which can be converted into digitized waveformssimilar to data from the operational detector. Inclusion of the detectorresponse allows us to process simulated data using the same analysis routinesas developed to process the experimental data.
Akerib DS, Akerlof CW, Alsum SK, et al., 2020, Projected WIMP sensitivity of the LUX-ZEPLIN dark matter experiment, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 101, Pages: 1-17, ISSN: 1550-2368
LUX-ZEPLIN (LZ) is a next-generation dark matter direct detection experiment that will operate 4850 feet underground at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, USA. Using a two-phase xenon detector with an active mass of 7 tonnes, LZ will search primarily for low-energy interactions with weakly interacting massive particles (WIMPs), which are hypothesized to make up the dark matter in our galactic halo. In this paper, the projected WIMP sensitivity of LZ is presented based on the latest background estimates and simulations of the detector. For a 1000 live day run using a 5.6-tonne fiducial mass, LZ is projected to exclude at 90% confidence level spin-independent WIMP-nucleon cross sections above 1.4×10−48 cm2 for a 40 GeV/c2 mass WIMP. Additionally, a 5σ discovery potential is projected, reaching cross sections below the exclusion limits of recent experiments. For spin-dependent WIMP-neutron(-proton) scattering, a sensitivity of 2.3×10−43 cm2 (7.1×10−42 cm2) for a 40 GeV/c2 mass WIMP is expected. With underground installation well underway, LZ is on track for commissioning at SURF in 2020.
Akerib DS, Akerlof CW, Alsum SK, et al., 2020, Measurement of the gamma ray background in the Davis cavern at the Sanford Underground Research Facility, Astroparticle Physics, Vol: 116, Pages: 1-10, ISSN: 0927-6505
Deep underground environments are ideal for low background searches due to the attenuation of cosmic rays by passage through the earth. However, they are affected by backgrounds from γ-rays emitted by 40K and the 238U and 232Th decay chains in the surrounding rock. The LUX-ZEPLIN (LZ) experiment will search for dark matter particle interactions with a liquid xenon TPC located within the Davis campus at the Sanford Underground Research Facility, Lead, South Dakota, at the 4850-foot level. In order to characterise the cavern background, in-situ γ-ray measurements were taken with a sodium iodide detector in various locations and with lead shielding. The integral count rates (0–3300 keV) varied from 596 Hz to 1355 Hz for unshielded measurements, corresponding to a total flux from the cavern walls of 1.9 ± 0.4 γ cms. The resulting activity in the walls of the cavern can be characterised as 220 ± 60 Bq/kg of 40K, 29 ± 15 Bq/kg of 238U, and 13 ± 3 Bq/kg of 232Th.
Akerib DS, Akerlof CW, Akimov DY, et al., 2020, The LUX-ZEPLIN (LZ) experiment, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment, Vol: 953, Pages: 1-22, ISSN: 0168-9002
We describe the design and assembly of the LUX-ZEPLIN experiment, a direct detection search for cosmic WIMP dark matter particles. The centerpiece of the experiment is a large liquid xenon time projection chamber sensitive to low energy nuclear recoils. Rejection of backgrounds is enhanced by a Xe skin veto detector and by a liquid scintillator Outer Detector loaded with gadolinium for efficient neutron capture and tagging. LZ is located in the Davis Cavern at the 4850’ level of the Sanford Underground Research Facility in Lead, South Dakota, USA. We describe the major subsystems of the experiment and its key design features and requirements.
Tomás A, Araújo HM, Bailey AJ, et al., 2018, Study and mitigation of spurious electron emission from cathodic wires in noble liquid time projection chambers, Astroparticle Physics, Vol: 103, Pages: 49-61, ISSN: 0927-6505
Noble liquid radiation detectors have long been afflicted by spurious electron emission from their cathodic electrodes. This phenomenon must be understood and mitigated in the next generation of liquid xenon (LXe) experiments searching for WIMP dark matter or neutrinoless double beta decay, and in the large liquid argon (LAr) detectors for the long-baseline neutrino programmes. We present a systematic study of this spurious emission involving a series of slow voltage-ramping tests on fine metal wires immersed in a two-phase xenon time projection chamber with single electron sensitivity. Emission currents as low as 10−18A can thus be detected by electron counting, a vast improvement over previous dedicated measurements. Emission episodes were recorded at surface fields as low as ∼ 10 kV/cm in some wires and observed to have complex emission patterns, with average rates of 10–200 counts per second (c/s) and outbreaks as high as ∼ 106c/s. A fainter, less variable type of emission was also present in all untreated samples. There is evidence of a partial conditioning effect, with subsequent tests yielding on average fewer emitters occurring at different fields for the same wire. We find no evidence for an intrinsic threshold particular to the metal-LXe interface which might have limited previous experiments up to fields of at least 160 kV/cm. The general phenomenology is not consistent with enhanced field emission from microscopic filaments, but it appears instead to be related to the quality of the wire surface in terms of corrosion and the nature of its oxide layer. This study concludes that some surface treatments, in particular nitric acid cleaning applied to stainless steel wires, can bring about at least order-of-magnitude improvements in overall electron emission rates, and this should help the next generation of detectors achieve the required electrostatic performance.
Paredes BL, Araujo HM, Froborg E, et al., 2018, Response of photomultiplier tubes to xenon scintillation light, Astroparticle Physics, Vol: 102, Pages: 56-66, ISSN: 0927-6505
We present the precision calibration of 35 Hamamatsu R11410-22 photomultiplier tubes (PMTs) with xenon scintillation light centred near 175 nm. This particular PMT variant was developed specifically for the LUX-ZEPLIN (LZ) dark matter experiment. A room-temperature xenon scintillation cell coupled to a vacuum cryostat was used to study the full-face PMT response at both room and low temperature ( ∼ −100 °C), in particular to determine the quantum efficiency (QE) and double photoelectron emission (DPE) probability in LZ operating conditions. For our sample with an average QE of (32.4 ± 2.9)% at room temperature, we find a relative improvement of (17.9 ± 5.2)% upon cooling (where uncertainty values refer to the sample standard deviation). The mean DPE probability in response to single vacuum ultraviolet (VUV) photons is (22.6 ± 2.0)% at low temperature; the DPE increase relative to room temperature, measured here for the first time, was (12.2 ± 3.9)%. Evidence of a small triple photoelectron emission probability ( ∼ 0.6%) has also been observed. Useful correlations are established between these parameters and the QE as measured by the manufacturer. The single VUV photon response is also measured for one ETEL D730/9829QB, a PMT with a more standard bialkali photocathode used in the ZEPLIN-III experiment, for which we obtained a cold DPE fraction of (9.1 ± 0.1)%. Hence, we confirm that this effect is not restricted to the low-temperature bialkali photocathode technology employed by Hamamatsu. This highlights the importance of considering this phenomenon in the interpretation of data from liquid xenon scintillation and electroluminescence detectors, and from many other optical measurements in this wavelength region.
Scovell PR, Meehan E, Araújo HM, et al., 2017, Low-background gamma spectroscopy at the Boulby Underground Laboratory, Astroparticle Physics, Vol: 97, Pages: 160-173, ISSN: 0927-6505
The Boulby Underground Germanium Suite (BUGS) comprises three low-background, high-purity germanium detectors operating in the Boulby Underground Laboratory, located 1.1 km underground in the north-east of England, UK. BUGS utilises three types of detector to facilitate a high-sensitivity, high-throughput radio-assay programme to support the development of rare-event search experiments. A Broad Energy Germanium (BEGe) detector delivers sensitivity to low-energy gamma-rays such as those emitted by 210 Pb and 234 Th. A Small Anode Germanium (SAGe) well-type detector is employed for efficient screening of small samples. Finally, a standard p-type coaxial detector provides fast screening of standard samples. This paper presents the steps used to characterise the performance of these detectors for a variety of sample geometries, including the corrections applied to account for cascade summing effects. For low-density materials, BUGS is able to radio-assay to specific activities down to 3.6mBqkg −1 for 234 Th and 6.6mBqkg −1 for 210 Pb both of which have uncovered some significant equilibrium breaks in the 238 U chain. In denser materials, where gamma-ray self-absorption increases, sensitivity is demonstrated to specific activities of 0.9mBqkg −1 for 226 Ra, 1.1mBqkg −1 for 228 Ra, 0.3mBqkg −1 for 224 Ra, and 8.6mBqkg −1 for 40 K with all upper limits at a 90% confidence level. These meet the requirements of most screening campaigns presently under way for rare-event search experiments, such as the LUX-ZEPLIN (LZ) dark matter experiment. We also highlight the ability of the BEGe detector to probe the X-ray fluorescence region which can be important to identify the presence of radioisotopes associated with neutron production; this is of particular relevance in experiments sensitive to nuclear recoils.
Akerib DS, Akerlof CW, Akimov DY, et al., 2017, Identification of radiopure titanium for the LZ dark matter experiment and future rare event searches, Astroparticle Physics, Vol: 96, Pages: 1-10, ISSN: 0927-6505
The LUX-ZEPLIN (LZ) experiment will search for dark matter particle interactions with a detector containing a total of 10 tonnes of liquid xenon within a double-vessel cryostat. The large mass and proximity of the cryostat to the active detector volume demand the use of material with extremely low intrinsic radioactivity. We report on the radioassay campaign conducted to identify suitable metals, the determination of factors limiting radiopure production, and the selection of titanium for construction of the LZ cryostat and other detector components. This titanium has been measured with activities of 238Ue < 1.6 mBq/kg, 238Ul < 0.09 mBq/kg, 232The=0.28±0.03 mBq/kg, 232Thl=0.25±0.02 mBq/kg, 40K < 0.54 mBq/kg, and 60Co < 0.02 mBq/kg (68% CL). Such low intrinsic activities, which are some of the lowest ever reported for titanium, enable its use for future dark matter and other rare event searches. Monte Carlo simulations have been performed to assess the expected background contribution from the LZ cryostat with this radioactivity. In 1,000 days of WIMP search exposure of a 5.6-tonne fiducial mass, the cryostat will contribute only a mean background of 0.160 ± 0.001(stat) ± 0.030(sys) counts.
Irastorza IG, Aznar F, Castel J, et al., 2016, Gaseous time projection chambers for rare event detection: results from the T-REX project. II. Dark matter (vol 1, 034, 2016), JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, ISSN: 1475-7516
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- Citations: 1
Dafni T, Arik M, Armengaud E, et al., 2016, An update on the Axion Helioscopes front: current activities at CAST and the IAXO project., 37th International Conference on High Energy Physics (ICHEP), Publisher: ELSEVIER SCIENCE BV, Pages: 244-249, ISSN: 2405-6014
Irastorza IG, Aznar F, Castel J, et al., 2016, Gaseous time projection chambers for rare event detection: results from the T-REX project. I. Double beta decay, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, ISSN: 1475-7516
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- Citations: 14
Irastorza IG, Aznar F, Castel J, et al., 2016, Gaseous time projection chambers for rare event detection: results from the T-REX project. II. Dark matter, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, ISSN: 1475-7516
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- Citations: 13
Gonzalez-Diaz D, Alvarez V, Borges FIG, et al., 2015, Accurate gamma and MeV-electron track reconstruction with an ultra-low diffusion Xenon/TMA TPC at 10 atm, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, Vol: 804, Pages: 8-24, ISSN: 0168-9002
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- Citations: 27
Galan J, Dafni T, Ferrer-Ribas E, et al., 2015, Exploring 0.1-10 eV axions with a new helioscope concept, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, ISSN: 1475-7516
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- Citations: 6
Collaboration TLZ, Akerib DS, Akerlof CW, et al., 2015, LUX-ZEPLIN (LZ) Conceptual Design Report
The design and performance of the LUX-ZEPLIN (LZ) detector is described as ofMarch 2015 in this Conceptual Design Report. LZ is a second-generationdark-matter detector with the potential for unprecedented sensitivity to weaklyinteracting massive particles (WIMPs) of masses from a few GeV/c2 to hundredsof TeV/c2. With total liquid xenon mass of about 10 tonnes, LZ will be the mostsensitive experiment for WIMPs in this mass region by the end of the decade.This report describes in detail the design of the LZ technical systems.Expected backgrounds are quantified and the performance of the experiment ispresented. The LZ detector will be located at the Sanford Underground ResearchFacility in South Dakota. The organization of the LZ Project and a summary ofthe expected cost and current schedule are given.
Renner J, Gehman VM, Goldschmidt A, et al., 2015, Ionization and scintillation of nuclear recoils in gaseous xenon, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, Vol: 793, Pages: 62-74, ISSN: 0168-9002
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- Citations: 13
Arik M, Aune S, Barth K, et al., 2015, New solar axion search using the CERN Axion Solar Telescope with He-4 filling, PHYSICAL REVIEW D, Vol: 92, ISSN: 1550-7998
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- Citations: 36
Cebrian S, Dafni T, Ferrer-Ribas E, et al., 2015, Micromegas-TPC operation at high pressure in xenon-trimethylamine mixtures (vol 8, P01012, 2013), JOURNAL OF INSTRUMENTATION, Vol: 10, ISSN: 1748-0221
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- Citations: 4
Vogel JK, Armengaud E, Avignone FT, et al., 2015, The next generation of axion helioscopes: The International Axion Observatory (IAXO), 13th International Conference on Topics in Astroparticle and Underground Physics (TAUP), Publisher: ELSEVIER SCIENCE BV, Pages: 193-200, ISSN: 1875-3892
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- Citations: 9
Garza JG, Aune S, Aznar F, et al., 2015, Low Background Micromegas in CAST, 7TH INTERNATIONAL SYMPOSIUM ON LARGE TPCS FOR LOW-ENERGY RARE EVENT DETECTION, Vol: 650, ISSN: 1742-6588
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- Citations: 1
Rebel B, Hall C, Bernard E, et al., 2014, High voltage in noble liquids for high energy physics, JOURNAL OF INSTRUMENTATION, Vol: 9, ISSN: 1748-0221
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- Citations: 12
Armengaud E, Avignone FT, Betz M, et al., 2014, Conceptual design of the International Axion Observatory (IAXO), JOURNAL OF INSTRUMENTATION, Vol: 9, ISSN: 1748-0221
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- Citations: 159
Alvarez V, Borges FIGM, Carcel S, et al., 2014, Characterization of a medium size Xe/TMA TPC instrumented with microbulk Micromegas, using low-energy gamma-rays, JOURNAL OF INSTRUMENTATION, Vol: 9, ISSN: 1748-0221
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- Citations: 17
Arik M, Aune S, Barth K, et al., 2014, Search for Solar Axions by the CERN Axion Solar Telescope with He-3 Buffer Gas: Closing the Hot Dark Matter Gap, PHYSICAL REVIEW LETTERS, Vol: 112, ISSN: 0031-9007
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- Citations: 74
Alvarez V, Aznar F, Borges FIGM, et al., 2014, Description and commissioning of NEXT-MM prototype: first results from operation in a Xenon-Trimethylamine gas mixture, JOURNAL OF INSTRUMENTATION, Vol: 9, ISSN: 1748-0221
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- Citations: 11
Aune S, Castel JF, Dafni T, et al., 2014, Low background x-ray detection with Micromegas for axion research, JOURNAL OF INSTRUMENTATION, Vol: 9, ISSN: 1748-0221
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- Citations: 24
Cebrian S, Dafni T, Gomez H, et al., 2013, Pattern recognition of Xe-136 double beta decay events and background discrimination in a high pressure xenon TPC, JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS, Vol: 40, ISSN: 0954-3899
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- Citations: 12
Aune S, Aznar F, Calvet D, et al., 2013, X-ray detection with Micromegas with background levels below 10(-6) keV(-1)cm(-2)s(-1), JOURNAL OF INSTRUMENTATION, Vol: 8, ISSN: 1748-0221
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- Citations: 13
Aznar F, Castel J, Cebrian S, et al., 2013, Assessment of material radiopurity for Rare Event experiments using Micromegas, 3rd International Conference on Micro Pattern Gaseous Detectors, Publisher: IOP PUBLISHING LTD, ISSN: 1748-0221
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- Citations: 16
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