Dual-phase xenon detectors, as currently used in direct detection dark matter experiments, have observed elevated rates of background electron events in the low energy region. While this background ...negatively impacts detector performance in various ways, its origins have only been partially studied. In this paper we report a systematic investigation of the electron pathologies observed in the LUX dark matter experiment. Here, we characterize different electron populations based on their emission intensities and their correlations with preceding energy depositions in the detector. By studying the background under different experimental conditions, we identified the leading emission mechanisms, including photoionization and the photoelectric effect induced by the xenon luminescence, delayed emission of electrons trapped under the liquid surface, capture and release of drifting electrons by impurities, and grid electron emission. We discuss how these backgrounds can be mitigated in LUX and future xenon-based dark matter experiments.
We report here methods and techniques for creating an improved model that reproduces the scintillation and ionization response of a dual-phase liquid and gaseous xenon time projection chamber. ...Starting with the recent release of the Noble Element Simulation Technique (NEST v2.0), electronic recoil data from the β decays of 3H and 14C in the Large Underground Xenon (LUX) detector were used to tune the model, in addition to external data sets that allow for extrapolation beyond the LUX data-taking conditions. This paper also presents techniques used for modeling complicated temporal and spatial detector pathologies that can adversely affect data using a simplified model framework. The methods outlined in this report show an example of the robust applications possible with NEST v2.0 framework and how it can be modified to produce a final, detector-specific, electronic recoil model. This example provides the final model for LUX and detector parameters that will used in the new analysis package, the LUX Legacy Analysis Monte Carlo Application (LLAMA), for accurate reproduction of the LUX data. As accurate background reproduction is crucial for the success of rare-event searches, such as dark matter direct detection experiments, the techniques outlined here can be used in other single-phase and dual-phase xenon detectors to assist with accurate ER background reproduction.
LUX trigger efficiency Akerib, D.S.; Alsum, S.; Araújo, H.M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2018, Letnik:
908, Številka:
C
Journal Article
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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.
We present limits on the WIMP–nucleon cross section for inelastic dark matter from a reanalysis of the 2008 run of ZEPLIN-III. Cuts, notably on scintillation pulse shape and ...scintillation-to-ionisation ratio, give a net exposure of 63kgday in the range 20–80keV nuclear recoil energy, in which 6 events are observed. Upper limits on signal rate are derived from the maximum empty patch in the data. Under standard halo assumptions a small region of parameter space consistent, at 99% CL, with causing the 1.17tonyr DAMA modulation signal is allowed at 90% CL: it is in the mass range 45–60GeVc−2 with a minimum CL of 87%, again derived from the maximum patch. This is the tightest constraint yet presented using xenon, a target nucleus whose similarity to iodine mitigiates systematic error from the assumed halo.
A search for diffuse neutrinos with energies in excess of 10 super(5) GeV is conducted with AMANDA-II data recorded between 2000 and 2002. Above 10 super(7) GeV, the Earth is essentially opaque to ...neutrinos. This fact, combined with the limited overburden of the AMANDA-II detector (roughly 1.5 km), concentrates these ultra-high-energy neutrinos at the horizon. The primary background for this analysis is bundles of downgoing, high-energy muons from the interaction of cosmic rays in the atmosphere. No statistically significant excess above the expected background is seen in the data, and an upper limit is set on the diffuse all-flavor neutrino flux of image GeV cm super(-2) s super(-1) sr super(-1) valid over the energy range of image to 10 super(9) GeV. A number of models that predict neutrino fluxes from active galactic nuclei are excluded at the 90% confidence level.
Many Antarctic lakes provide habitat for extensive microbial mats that respond on various timescales to environmental change. Lake Joyce contains calcifying microbialites and provides a natural ...laboratory to constrain how environmental changes influence microbialite development. In Lake Joyce, depth‐specific distributions of calcitic microbialites, organic carbon, photosynthetic pigments and photosynthetic potential cannot be explained by current growth conditions, but are a legacy of a 7‐m lake level rise between 1973 and 2009. In the well‐illuminated margins of the lake, photosynthetically active benthic communities colonised surfaces submerged for just a few years. However, observed increases in accumulated organic material with depth from 5 to 20 m (2–40 mg ash‐free dry weight cm−2) and the presence of decimetre‐scale calcite microbialites at 20–22 m depth, apparently related to in situ photosynthetic growth, are inconsistent with the current distributions of irradiance, photosynthetic pigments and mat photosynthetic potential (as revealed by pulse‐amplitude‐modulated fluorometry). The microbialites appeared photosynthetically active in 1986 and 1997, but were outside the depth zone where significant phototrophic growth was possible and were weakly photosynthetically competent in 2009. These complex microbial structures have persisted after growth has ceased, demonstrating how fluctuating environmental conditions and the hysteresis between environmental change, biological response and microbialite development can be important factors to consider when interpreting modern, and by inference ancient, microbially mediated structures.
Here, the LUX experiment has performed searches for dark matter particles scattering elastically on xenon nuclei, leading to stringent upper limits on the nuclear scattering cross sections for dark ...matter. Here, for results derived from ${1.4}\times 10^{4}\;\mathrm{kg\,days}$ of target exposure in 2013, details of the calibration, event-reconstruction, modeling, and statistical tests that underlie the results are presented. Detector performance is characterized, including measured efficiencies, stability of response, position resolution, and discrimination between electron- and nuclear-recoil populations. Models are developed for the drift field, optical properties, background populations, the electron- and nuclear-recoil responses, and the absolute rate of low-energy background events. Innovations in the analysis include in situ measurement of the photomultipliers' response to xenon scintillation photons, verification of fiducial mass with a low-energy internal calibration source, and new empirical models for low-energy signal yield based on large-sample, in situ calibrations.
We present the first measurements of the electroluminescence response to the emission of single electrons in a two-phase noble gas detector. Single ionization electrons generated in liquid xenon are ...detected in a thin gas layer during the 31-day background run of the ZEPLIN-II experiment, a two-phase xenon detector for WIMP dark matter searches. Both the pressure dependence and magnitude of the single electron response are in agreement with previous measurements of electroluminescence yield in xenon. We discuss different photoionization processes as possible cause for the sample of single electrons studied in this work. This observation may have implications for the design and operation of future large-scale two-phase systems.
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