LUXSim: A component-centric approach to low-background simulations Akerib, D.S.; Bai, X.; Bedikian, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2012, Letnik:
675, Številka:
C
Journal Article
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Geant4 has been used throughout the nuclear and high-energy physics community to simulate energy depositions in various detectors and materials. These simulations have mostly been run with a source ...beam outside the detector. In the case of low-background physics, however, a primary concern is the effect on the detector from radioactivity inherent in the detector parts themselves. From this standpoint, there is no single source or beam, but rather a collection of sources with potentially complicated spatial extent. LUXSim is a simulation framework used by the LUX collaboration that takes a component-centric approach to event generation and recording. A new set of classes allows for multiple radioactive sources to be set within any number of components at run time, with the entire collection of sources handled within a single simulation run. Various levels of information can also be recorded from the individual components, with these record levels also being set at run time. This flexibility in both source generation and information recording is possible without the need to recompile, reducing the complexity of code management and the proliferation of versions. Within the code itself, casting geometry objects within this new set of classes rather than as the default Geant4 classes automatically extends this flexibility to every individual component. No additional work is required on the part of the developer, reducing development time and increasing confidence in the results. We describe the guiding principles behind LUXSim, detail some of its unique classes and methods, and give examples of usage.
Weakly interacting massive particles (WIMPs) are a leading candidate for dark matter and are expected to produce nuclear recoil (NR) events within liquid xenon time-projection chambers. We present a ...measurement of the scintillation timing characteristics of liquid xenon in the LUX dark matter detector and develop a pulse shape discriminant to be used for particle identification. To accurately measure the timing characteristics, we develop a template-fitting method to reconstruct the detection times of photons. Analyzing calibration data collected during the 2013–2016 LUX WIMP search, we provide a new measurement of the singlet-to-triplet scintillation ratio for electron recoils (ER) below 46 keV, and we make, to our knowledge, a first-ever measurement of the NR singlet-to-triplet ratio at recoil energies below 74 keV. We exploit the difference of the photon time spectra for NR and ER events by using a prompt fraction discrimination parameter, which is optimized using calibration data to have the least number of ER events that occur in a 50% NR acceptance region. We then demonstrate how this discriminant can be used in conjunction with the charge-to-light discrimination to possibly improve the signal-to-noise ratio for nuclear recoils.
Liposome mediated gene transfer Mannino, R J; Gould-Fogerite, S
BioTechniques,
07/1988, Letnik:
6, Številka:
7
Journal Article
Recenzirano
Liposomes, artificial membrane vesicles, are being intensively studied for their usefulness as delivery vehicles in vitro and in vivo. Substantial progress has been made in the development of ...procedures for liposome preparation, targeting and delivery of contents. The broad flexibility now available in the design of the structure and composition of liposomes, coupled to recent reports of liposome mediated gene transfer in animals, suggest that liposome technology is now poised to be utilized in the creation of custom-designed cell-type-specific gene transfer vehicles.
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.
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. Here, 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 1.3 keV and above, for both ER and NR. In conclusion, the measured trigger efficiency varies between 99% and 100% over the fiducial volume of the detector.
We report an absolute calibration of the ionization yields (Qy) and fluctuations for electronic recoil events in liquid xenon at discrete energies between 186 eV and 33.2 keV. The average electric ...field applied across the liquid xenon target is 180 V/cm. The data are obtained using low energy Xe127 electron capture decay events from the 95.0-day first run from LUX (WS2013) in search of weakly interacting massive particles. The sequence of gamma-ray and x-ray cascades associated with I127 deexcitations produces clearly identified two-vertex events in the LUX detector. We observe the K-(binding energy, 33.2 keV), L-(5.2 keV), M-(1.1 keV), and N-(186 eV) shell cascade events and verify that the relative ratio of observed events for each shell agrees with calculations. The N-shell cascade analysis includes single extracted electron (SE) events and represents the lowest-energy electronic recoil in situ measurements that have been explored in liquid xenon.
LUX was the first dark matter experiment to use a Kr83m calibration source. In this paper, we describe the source preparation and injection. We also present several Kr83m calibration applications in ...the context of the 2013 LUX exposure, including the measurement of temporal and spatial variation in scintillation and charge signal amplitudes, and several methods to understand the electric field within the time projection chamber.
The dual-phase xenon time projection chamber (TPC) is a powerful tool for direct-detection experiments searching for WIMP dark matter, other dark matter models, and neutrinoless double-beta decay. ...Successful operation of such a TPC is critically dependent on the ability to hold high electric fields in the bulk liquid, across the liquid surface, and in the gas. Careful design and construction of the electrodes used to establish these fields is therefore required. We present the design and production of the LUX-ZEPLIN (LZ) experiment's high-voltage electrodes, a set of four woven mesh wire grids. Grid design drivers are discussed, with emphasis placed on design of the electron extraction region. We follow this with a description of the grid production process and a discussion of steps taken to validate the LZ grids prior to integration into the TPC.
Although gene therapy holds great promise for the treatment of both acquired and genetic diseases, its development has been
limited by practical considerations. Nonviral efficacy of delivery remains ...quite poor. We are investigating the feasibility
of a novel lipid-based delivery system, cochleates, to deliver transgenes to mammalian cells. Rhodamine-labelled empty cochleates
were incubated with two cell-lines (4T1 adenocarcinoma and H36.12 macrophage hybridoma) and primary macrophages in vitro and
in vivo. Cochleates containing green fluorescent protein(GFP) expression plasmid were incubated with 4T1 adenocarcinoma cells.
Cellular uptake of labelled cochleates or transgene GFP expression were visualised with fluorescence microscopy. 4T1 and H36.12
lines showed 39% and 23.1% uptake of rhodamine-cochleates, respectively. Human monocyte-derived macrophages and mouse peritoneal
macrophages had 48±5.38% and 51.46±15.6% uptake of rhodamine-cochleates in vitro. In vivo 25.69±0.127% of peritoneal macrophages
were rhodaminepositive after intra-peritoneal injection of rhodamine-cochleates. 19.49±10.12% of 4T1 cells expressed GFP.
Cochleates may therefore be an effective, non-toxic and non-immunogenic method to introduce transgenes in vitro and in vivo.
An effective vaccine against the human immunodeficiency virus should be capable of eliciting both an antibody and a cytotoxic T lymphocyte (CTL) response. However, when viral proteins and peptides ...are formulated with traditional immunological adjuvants and inoculated via a route acceptable for use in humans, they have not been successful at eliciting virus-specific, major histocompatibility complex (MHC) class I-restricted CTL. We have designed a novel viral subunit vaccine by encapsulating a previously defined synthetic peptide CTL epitope of the simian immunodeficiency virus (SIV) gag protein within a proteoliposome capable of attaching to and fusing with plasma membranes. Upon fusing, the encapsulated contents of this proteoliposome can enter the MHC class I processing pathway through the cytoplasm. In this report, we show that after a single intramuscular vaccination, rhesus monkeys develop a CD8+ cell-mediated, MHC class I-restricted CTL response that recognizes the synthetic peptide immunogen. The induced CTL also demonstrate antiviral immunity by recognizing SIV gag protein endogenously processed by target cells infected with SIV/vaccinia recombinant virus. These results demonstrate that virus-specific, MHC class I-restricted, CD8+ CTL can be elicited by a safe, nonreplicating viral subunit vaccine in a primate model for acquired immune deficiency syndrome. Moreover, the proteoliposome vaccine formation described can include multiple synthetic peptide epitopes, and, thus, offers a simple means of generating antiviral cell-mediated immunity in a genetically heterogeneous population.
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