Publications
479 results found
Akerib DS, Alsum S, Araujo HM, et al., 2020, Search for two neutrino double electron capture of(124)Xe and(126)Xe in the full exposure of the LUX detector, Journal of Physics G: Nuclear and Particle Physics, Vol: 47, Pages: 1-13, ISSN: 0954-3899
Two-neutrino double electron capture is a process allowed in the standard model of particle physics. This rare decay has been observed in 78Kr, 130Ba and more recently in 124Xe. In this publication we report on the search for this process in 124Xe and 126Xe using the full exposure of the large underground xenon (LUX) experiment, in a total of 27769.5 kg-days. No evidence of a signal was observed, allowing us to set 90% C.L. lower limits for the half-lives of these decays of 2.0 × 1021 years for 124Xe and 1.9 × 1021 years for 126Xe.
Akerib DS, Akerlof CW, Alqahtani A, et al., 2020, Projected sensitivity of the LUX-ZEPLIN experiment to the 0νββ decay of 136Xe, Physical Review C, Vol: 102, Pages: 014602 – 1-014602 – 13, ISSN: 2469-9985
The LUX-ZEPLIN (LZ) experiment will enable a neutrinoless double β decay search in parallel to the main science goal of discovering dark matter particle interactions. We report the expected LZ sensitivity to 136Xe neutrinoless double β decay, taking advantage of the significant (>600 kg) 136Xe mass contained within the active volume of LZ without isotopic enrichment. After 1000 live-days, the median exclusion sensitivity to the half-life of 136Xe is projected to be 1.06×1026 years (90% confidence level), similar to existing constraints. We also report the expected sensitivity of a possible subsequent dedicated exposure using 90% enrichment with 136Xe at 1.06×1027 years.
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.
Yang F, Bai Y, Hong W, et al., 2020, Investigation of charge management using UV LED device with a torsion pendulum for TianQin, CLASSICAL AND QUANTUM GRAVITY, Vol: 37, ISSN: 0264-9381
Armano M, Audley H, Baird J, et al., 2020, Spacecraft and interplanetary contributions to the magnetic environment on-board LISA Pathfinder, Monthly Notices of the Royal Astronomical Society, Vol: 494, Pages: 3014-3027, ISSN: 0035-8711
LISA Pathfinder (LPF) has been a space-based mission designed to test new technologies that will be required for a gravitational wave observatory in space. Magnetically driven forces play a key role in the instrument sensitivity in the low-frequency regime (mHz and below), the measurement band of interest for a space-based observatory. The magnetic field can couple to the magnetic susceptibility and remanent magnetic moment from the test masses and disturb them from their geodesic movement. LPF carried on-board a dedicated magnetic measurement subsystem with noise levels of 10 nT Hz−1/2 from 1 Hz down to 1 mHz. In this paper we report on the magnetic measurements throughout LPF operations. We characterize the magnetic environment within the spacecraft, study the time evolution of the magnetic field and its stability down to 20 μHz, where we measure values around 200 nT Hz−1/2, and identify two different frequency regimes, one related to the interplanetary magnetic field and the other to the magnetic field originating inside the spacecraft. Finally, we characterize the non-stationary component of the fluctuations of the magnetic field below the mHz and relate them to the dynamics of the solar wind.
Armano M, Audley H, Baird J, et al., 2020, Analysis of the accuracy of actuation electronics in the laser interferometer space antenna pathfinder, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 91, ISSN: 0034-6748
Akerib DS, Alsum S, Araújo HM, et al., 2020, An effective field theory analysis of the first LUX dark matter search, Publisher: arXiv
The Large Underground Xenon (LUX) dark matter search was a 250-kg active massdual-phase time projection chamber that operated by detecting light andionization signals from particles incident on a xenon target. In December 2015,LUX reported a minimum 90% upper C.L. of 6e-46 cm^2 on the spin-independentWIMP-nucleon elastic scattering cross section based on a 1.4e4 kg*day exposurein its first science run. Tension between experiments and the absence of adefinitive positive detection suggest it would be prudent to search for WIMPsoutside the standard spin-independent/spin-dependent paradigm. Recenttheoretical work has identified a complete basis of 14 independent effectivefield theory (EFT) operators to describe WIMP-nucleon interactions. In additionto spin-independent and spin-dependent nuclear responses, these operators canproduce novel responses such as angular-momentum-dependent and spin-orbitcouplings. Here we report on a search for all 14 of these EFT couplings withdata from LUX's first science run. Limits are placed on each coupling as afunction of WIMP mass.
El-Neaj YA, Alpigiani C, Amairi-Pyka S, et al., 2020, AEDGE: Atomic Experiment for Dark Matter and Gravity Exploration in Space, EPJ QUANTUM TECHNOLOGY, Vol: 7, ISSN: 2662-4400
Collaboration TLUX, Akerib DS, Alsum S, et al., 2020, Improved modeling of $β$ electronic recoils in liquid xenon using LUX calibration data, Journal of Instrumentation, ISSN: 1748-0221
We report here methods and techniques for creating and improving a model thatreproduces the scintillation and ionization response of a dual-phase liquid andgaseous xenon time-projection chamber. Starting with the recent release of theNoble Element Simulation Technique (NEST v2.0), electronic recoil data from the$\beta$ decays of ${}^3$H and ${}^{14}$C in the Large Underground Xenon (LUX)detector were used to tune the model, in addition to external data sets thatallow for extrapolation beyond the LUX data-taking conditions. This paper alsopresents techniques used for modeling complicated temporal and spatial detectorpathologies that can adversely affect data using a simplified model framework.The methods outlined in this report show an example of the robust applicationspossible with NEST v2.0, while also providing the final electronic recoil modeland detector parameters that will used in the new analysis package, the LUXLegacy Analysis Monte Carlo Application (LLAMA), for accurate reproduction ofthe LUX data. As accurate background reproduction is crucial for the success ofrare-event searches, such as dark matter direct detection experiments, thetechniques outlined here can be used in other single-phase and dual-phase xenondetectors to assist with accurate ER background reproduction.
Sumner TJ, Mueller G, Conklin JW, et al., 2020, Charge induced acceleration noise in the LISA gravitational reference sensor, CLASSICAL AND QUANTUM GRAVITY, Vol: 37, ISSN: 0264-9381
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.
Akerib DS, Alsum S, Araujo HM, et al., 2020, Extending light WIMP searches to single scintillation photons in LUX, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 101, Pages: 1-11, ISSN: 1550-2368
We present a novel analysis technique for liquid xenon time projection chambers that allows for a lower threshold by relying on events with a prompt scintillation signal consisting of single detected photons. The energy threshold of the LUX dark matter experiment is primarily determined by the smallest scintillation response detectable, which previously required a twofold coincidence signal in its photomultiplier arrays, enforced in data analysis. The technique presented here exploits the double photoelectron emission effect observed in some photomultiplier models at vacuum ultraviolet wavelengths. We demonstrate this analysis using an electron recoil calibration dataset and place new constraints on the spin-independent scattering cross section of weakly interacting massive particles (WIMPs) down to 2.5 GeV/c2 WIMP mass using the 2013 LUX dataset. This new technique is promising to enhance light WIMP and astrophysical neutrino searches in next-generation liquid xenon experiments.
Akerib DS, Alsum S, Araujo HM, et al., 2020, First direct detection constraint on mirror dark matter kinetic mixing using LUX 2013 data, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 101, Pages: 012003 – 1-012003 – 8, ISSN: 1550-2368
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.
Touboul P, Metris G, Rodrigues M, et al., 2019, Space test of the equivalence principle: first results of the MICROSCOPE mission, Classical and Quantum Gravity, Vol: 36, Pages: 1-34, ISSN: 0264-9381
The weak equivalence principle (WEP), stating that two bodies of different compositions and/or mass fall at the same rate in a gravitational field (universality of free fall), is at the very foundation of general relativity. The MICROSCOPE mission aims to test its validity to a precision of 10−15, two orders of magnitude better than current on-ground tests, by using two masses of different compositions (titanium and platinum alloys) on a quasi-circular trajectory around the Earth. This is realised by measuring the accelerations inferred from the forces required to maintain the two masses exactly in the same orbit. Any significant difference between the measured accelerations, occurring at a defined frequency, would correspond to the detection of a violation of the WEP, or to the discovery of a tiny new type of force added to gravity. MICROSCOPE's first results show no hint for such a difference, expressed in terms of Eötvös parameter (both 1 uncertainties) for a titanium and platinum pair of materials. This result was obtained on a session with 120 orbital revolutions representing 7% of the current available data acquired during the whole mission. The quadratic combination of 1 uncertainties leads to a current limit on of about .
Armano M, Audley H, Baird J, et al., 2019, Novel methods to measure the gravitational constant in space, PHYSICAL REVIEW D, Vol: 100, ISSN: 2470-0010
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Thorpe J, Slutsky J, Baker JG, et al., 2019, Micrometeoroid events in LISA pathfinder, The Astrophysical Journal: an international review of astronomy and astronomical physics, Vol: 883, Pages: 1-15, ISSN: 0004-637X
The zodiacal dust complex, a population of dust and small particles that pervades the solar system, provides important insight into the formation and dynamics of planets, comets, asteroids, and other bodies. We present a new set of data obtained from direct measurements of momentum transfer to a spacecraft from individual particle impacts. This technique is made possible by the extreme precision of the instruments flown on the LISA Pathfinder spacecraft, a technology demonstrator for a future space-based gravitational wave observatory. Pathfinder employed a technique known as drag-free control that achieved rejection of external disturbances, including particle impacts, using a micropropulsion system. Using a simple model of the impacts and knowledge of the control system, we show that it is possible to detect impacts and measure properties such as the transferred momentum, direction of travel, and location of impact on the spacecraft. In this paper, we present the results of a systematic search for impacts during 4348 hr of Pathfinder data. We report a total of 54 candidates with transferred momenta ranging from 0.2 to 230 μNs. We furthermore make a comparison of these candidates with models of micrometeoroid populations in the inner solar system, including those resulting from Jupiter-family comets (JFCs), Oort Cloud comets, Halley-type comets, and asteroids. We find that our measured population is consistent with a population dominated by JFCs, with some evidence for a smaller contribution from Halley-type comets, in agreement with consensus models of the zodiacal dust complex in the momentum range sampled by LISA Pathfinder.
Armano M, Audley H, Baird J, et al., 2019, LISA pathfinder performance confirmed in an open-loop configuration: results from the free-fall actuation mode, Physical Review Letters, Vol: 123, Pages: 111101-1-111101-7, ISSN: 0031-9007
We report on the results of the LISA Pathfinder (LPF) free-fall mode experiment, in which the control force needed to compensate the quasistatic differential force acting on two test masses is applied intermittently as a series of “impulse” forces lasting a few seconds and separated by roughly 350 s periods of true free fall. This represents an alternative to the normal LPF mode of operation in which this balancing force is applied continuously, with the advantage that the acceleration noise during free fall is measured in the absence of the actuation force, thus eliminating associated noise and force calibration errors. The differential acceleration noise measurement presented here with the free-fall mode agrees with noise measured with the continuous actuation scheme, representing an important and independent confirmation of the LPF result. An additional measurement with larger actuation forces also shows that the technique can be used to eliminate actuation noise when this is a dominant factor.
Akerib DS, Alsum S, Araujo HM, et al., 2019, Improved measurements of the beta-decay response of liquid xenon with the LUX detector, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 100, ISSN: 1550-2368
We report results from an extensive set of measurements of the β-decay response in liquid xenon. These measurements are derived from high-statistics calibration data from injected sources of both 3H and 14C in the LUX detector. The mean light-to-charge ratio is reported for 13 electric field values ranging from 43 to 491 V/cm, and for energies ranging from 1.5 to 145 keV.
Armano M, Audley H, Baird J, et al., 2019, Temperature stability in the sub-milliHertz band with LISA Pathfinder, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 486, Pages: 3368-3379, ISSN: 0035-8711
Armano M, Audley H, Baird J, et al., 2019, LISA Pathfinder micronewton cold gas thrusters: In-flight characterization, PHYSICAL REVIEW D, Vol: 99, ISSN: 2470-0010
Wass PJ, Hollington D, Sumner TJ, et al., 2019, Effective decrease of photoelectric emission threshold from gold plated surfaces, Review of Scientific Instruments, Vol: 90, ISSN: 0034-6748
Many applications require charge neutralization of isolated test bodies, and this has been successfully done using photoelectric emission from surfaces which are electrically benign (gold) or superconducting (niobium). Gold surfaces nominally have a high work function (∼5.1 eV) which should require deep UV photons for photoemission. In practice, it has been found that it can be achieved with somewhat lower energy photons with indicative work functions of (4.1–4.3 eV). A detailed working understanding of the process is lacking, and this work reports on a study of the photoelectric emission properties of 4.6 × 4.6 cm2 gold plated surfaces, representative of those used in typical satellite applications with a film thickness of 800 nm, and measured surface roughnesses between 7 and 340 nm. Various UV sources with photon energies from 4.8 to 6.2 eV and power outputs from 1 nW to 1000 nW illuminated ∼0.3 cm2 of the central surface region at angles of incidence from 0° to 60°. Final extrinsic quantum yields in the range 10 ppm–44 ppm were reliably obtained during 8 campaigns, covering a period of ∼3 years but with intermediate long-term variations lasting several weeks and, in some cases, bake-out procedures at up to 200 °C. Experimental results were obtained in a vacuum system with a baseline pressure of ∼10−7 mbar at room temperature. A working model, designed to allow accurate simulation of any experimental configuration, is proposed.
Armano M, Audley H, Baird J, et al., 2019, LISA Pathfinder platform stability and drag-free performance, Physical Review D - Particles, Fields, Gravitation and Cosmology, Vol: 99, ISSN: 1550-2368
The science operations of the LISA Pathfinder mission have demonstrated the feasibility of sub-femto-g free fall of macroscopic test masses necessary to build a gravitational wave observatory in space such as LISA. While the main focus of interest, i.e., the optical axis or the x-axis, has been extensively studied, it is also of great importance to evaluate the stability of the spacecraft with respect to all the other degrees of freedom (d.o.f.). The current paper is dedicated to such a study: the exhaustive and quantitative evaluation of the imperfections and dynamical effects that impact the stability with respect to its local geodesic. A model of the complete closed-loop system provides a comprehensive understanding of each component of the in-loop coordinates spectral density. As will be presented, this model gives very good agreement with LISA Pathfinder flight data. It allows one to identify the noise source at the origin and the physical phenomena underlying the couplings. From this, the stability performance of the spacecraft with respect to its geodesic is extracted as a function of frequency. Close to 1 mHz, the stability of the spacecraft on the XSC, YSC and ZSC d.o.f. is shown to be of the order of 5.0×10−15 m s−2 Hz−1/2 for X, 6.0×10−14 m s−2 Hz−1/2 for Y, and 4.0×10−14 m s−2 Hz−1/2 for Z. For the angular d.o.f., the values are of the order of 3×10−12 rad s−2 Hz−1/2 for ΘSC, 5×10−13 rad s−2 Hz−1/2 for HSC, and 3×10−13 rad s−2 Hz−1/2 for ΦSC. Below 1 mHz, however, the stability performances are worsened significantly by the effect of the star tracker noise on the closed-loop system. It is worth noting that LI
Akerib DS, Alsum S, Araujo HM, et al., 2019, Results of a search for sub-GeV Dark Matter using 2013 LUX data, Physical Review Letters, Vol: 122, ISSN: 0031-9007
The scattering of dark matter (DM) particles with sub-GeV masses off nuclei is difficult to detect using liquid xenon-based DM search instruments because the energy transfer during nuclear recoils is smaller than the typical detector threshold. However, the tree-level DM-nucleus scattering diagram can be accompanied by simultaneous emission of a bremsstrahlung photon or a so-called “Migdal” electron. These provide an electron recoil component to the experimental signature at higher energies than the corresponding nuclear recoil. The presence of this signature allows liquid xenon detectors to use both the scintillation and the ionization signals in the analysis where the nuclear recoil signal would not be otherwise visible. We report constraints on spin-independent DM-nucleon scattering for DM particles with masses of 0.4–5 GeV/c2 using 1.4×104 kg day of search exposure from the 2013 data from the Large Underground Xenon (LUX) experiment for four different classes of mediators. This analysis extends the reach of liquid xenon-based DM search instruments to lower DM masses than has been achieved previously.
Armano M, Audley H, Baird J, et al., 2019, Forbush Decreases and < 2 Day GCR Flux Non-recurrent Variations Studied with LISA Pathfinder, Astrophysical Journal, Vol: 874, ISSN: 0004-637X
Non-recurrent short-term variations of the galactic cosmic-ray (GCR) flux above 70 MeV n−1 were observed between 2016 February 18 and 2017 July 3 on board the European Space Agency LISA Pathfinder (LPF) mission orbiting around the Lagrange point L1 at 1.5 × 106 km from Earth. The energy dependence of three Forbush decreases is studied and reported here. A comparison of these observations with others carried out in space down to the energy of a few tens of MeV n−1 shows that the same GCR flux parameterization applies to events of different intensity during the main phase. FD observations in L1 with LPF and geomagnetic storm occurrence are also presented. Finally, the characteristics of GCR flux non-recurrent variations (peaks and depressions) of duration <2 days and their association with interplanetary structures are investigated. It is found that, most likely, plasma compression regions between subsequent corotating high-speed streams cause peaks, while heliospheric current sheet crossing causes the majority of the depressions.
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.
Anderson G, Anderson J, Anderson M, et al., 2018, Experimental results from the ST7 mission on LISA Pathfinder, Physical Review D, Vol: 98, ISSN: 2470-0010
The Space Technology 7 Disturbance Reduction System (ST7-DRS) is a NASA technology demonstration payload that operated from January 2016 through July 2017 on the European Space Agency’s (ESA) LISA Pathfinder spacecraft. The joint goal of the NASA and ESA missions was to validate key technologies for a future space-based gravitational wave observatory targeting the source-rich millihertz band. The two primary components of ST7-DRS are a micropropulsion system based on colloidal micro-Newton thrusters (CMNTs) and a control system that simultaneously controls the attitude and position of the spacecraft and the two free-flying test masses (TMs). This paper presents our main experimental results and summarizes the overall performance of the CMNTs and control laws. We find the CMNT performance to be consistent with preflight predictions, with a measured system thrust noise on the order of 100 nN/√Hz in the 1 mHz≤f≤30 mHz band. The control system maintained the TM-spacecraft separation with an RMS error of less than 2 nm and a noise spectral density of less than 3 nm/√Hz in the same band. Thruster calibration measurements yield thrust values consistent with the performance model and ground-based thrust-stand measurements, to within a few percent. We also report a differential acceleration noise between the two test masses with a spectral density of roughly 3 fm/s2/√Hz in the 1 mHz≤f≤30 mHz band, slightly less than twice as large as the best performance reported with the baseline LISA Pathfinder configuration and below the current requirements for the Laser Interferometer Space Antenna mission.
Akerib DS, Alsum S, Araujo HM, et al., 2018, LUX trigger efficiency, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol: 908, Pages: 401-410, ISSN: 0168-9002
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 0.2 keV and above for ER, and 1.3 keV and above for NR. The measured trigger efficiency varies between 99% and 100% over the fiducial volume of the detector.
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.
Akerib DS, Alsum S, Araujo HM, et al., 2018, Search for annual and diurnal rate modulations in the LUX experiment, Physical Review D - Particles, Fields, Gravitation and Cosmology, Vol: 98, ISSN: 1550-2368
Various dark matter models predict annual and diurnal modulations of dark matter interaction rates in Earth-based experiments as a result of the Earth’s motion in the halo. Observation of such features can provide generic evidence for detection of dark matter interactions. This paper reports a search for both annual and diurnal rate modulations in the LUX dark matter experiment using over 20 calendar months of data acquired between 2013 and 2016. This search focuses on electron recoil events at low energies, where leptophilic dark matter interactions are expected to occur and where the DAMA experiment has observed a strong rate modulation for over two decades. By using the innermost volume of the LUX detector and developing robust cuts and corrections, we obtained a stable event rate of 2.3±0.2 cpd/keVee/tonne, which is among the lowest in all dark matter experiments. No statistically significant annual modulation was observed in energy windows up to 26 keVee. Between 2 and 6 keVee, this analysis demonstrates the most sensitive annual modulation search up to date, with 9.2σ tension with the DAMA/LIBRA result. We also report no observation of diurnal modulations above 0.2 cpd/keVee/tonne amplitude between 2 and 6 keVee.
Armano M, Audley H, Baird J, et al., 2018, Precision charge control for isolated free-falling test masses: LISA pathfinder results, Physical Review D, Vol: 98, ISSN: 2470-0010
The LISA Pathfinder charge management device was responsible for neutralizing the cosmic-ray-induced electric charge that inevitably accumulated on the free-falling test masses at the heart of the experiment. We present measurements made on ground and in flight that quantify the performance of this contactless discharge system which was based on photoemission under UV illumination. In addition, a two-part simulation is described that was developed alongside the hardware. Modeling of the absorbed UV light within the Pathfinder sensor was carried out with the Geant4 software toolkit and a separate Matlab charge transfer model calculated the net photocurrent between the test masses and surrounding housing in the presence of AC and DC electric fields. We confront the results of these models with observations and draw conclusions for the design of discharge systems for future experiments like LISA that will also employ free-falling test masses.
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