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Low-mass Dark Matter search with the XENON100 experiment
Full text linkIt is hypothesized that 26% of the mass and energy content of the universe consists of Dark Matter. The most promising Dark Matter candidates are Weakly Interacting Massive Particles (WIMP). If WIMPs are the Dark Matter particles, then they could be directly de-tected via their scattering off nuclei. The XENON100 experiment aims to detect the scattering of a WIMP with a xenon nucleus. This experiment is a xenon-based dual-phase (liquid-gas) Time Projection Chamber (TPC). The interaction of a particle in the TPC produces both scintillation photons and ionization electrons, which are both detected as light signals by photomultipliers. So far, the XENON100 experiment has not observed WIMPs, and exclusion limits have been produced. The data analysis relies on an accurate description of the backgrounds. In this thesis I present an analysis that assumes potentially unknown backgrounds to be present in the data. In this way, a WIMP exclusion limit without background subtraction is calculated with a minimum WIMP-nucleon cross section of 2.05 × 10-45 cm2 at a WIMP mass of 50 GeV. Furthermore, I developed a new method to enhance the sensitivity of the XENON100 experiment towards low-mass WIMPs using solely the ionization signal to calculate the recoil energy. Using this method, the sensitivity of the XENON100 experiment is improved by several orders of magnitude for WIMP masses below 7 GeV, excluding a WIMP-nucleon cross section of 1.4 × 10-41 cm2 at a WIMP mass of 6 GeV
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
First WIMP results of XENONnT and its signal reconstruction
No full textAs physicists, we are trying to solve the puzzle that is our Universe. Yet, ordinary, baryonic matter, only accounts for 16% of the total mass of the Universe. The remaining 84% should be some form of matter that has never been observed. This mysterious matter component is called Dark Matter. XENONnT is one of the experiments at the forefront of the search for Dark Matter, and located at a deep underground lab in Italy. It searches, primarily, for a Dark Matter candidate called the weakly interacting massive particle (WIMP) by monitoring a volume of liquid xenon. Other experiments like the Super Cryogenic Dark Matter Search (SuperCDMS) at SNOLAB in Canada, use semiconductors (germanium and silicon) as target materials and may also detect WIMPs, especially if they are relatively light. In this thesis we describe how XENONnT aims to detect WIMPs if they interact with liquid xenon, and how well XENONnT or SuperCDMS may be able to reconstruct the properties of Dark Matter if we find it. In this case, and by combining the results of XENONnT and SuperCDMS, the properties of Dark Matter will be more precisely reconstructed. We further describe the data acquisition and the signal reconstruction of XENONnT. The final chapter of this thesis discusses the latest Dark Matter search result of XENONnT, which sets new stringent limits to the cross-section of the WIMP scattering off ordinary matter
First WIMP results of XENONnT and its signal reconstruction
No full textAs physicists, we are trying to solve the puzzle that is our Universe. Yet, ordinary, baryonic matter, only accounts for 16% of the total mass of the Universe. The remaining 84% should be some form of matter that has never been observed. This mysterious matter component is called Dark Matter. XENONnT is one of the experiments at the forefront of the search for Dark Matter, and located at a deep underground lab in Italy. It searches, primarily, for a Dark Matter candidate called the weakly interacting massive particle (WIMP) by monitoring a volume of liquid xenon. Other experiments like the Super Cryogenic Dark Matter Search (SuperCDMS) at SNOLAB in Canada, use semiconductors (germanium and silicon) as target materials and may also detect WIMPs, especially if they are relatively light. In this thesis we describe how XENONnT aims to detect WIMPs if they interact with liquid xenon, and how well XENONnT or SuperCDMS may be able to reconstruct the properties of Dark Matter if we find it. In this case, and by combining the results of XENONnT and SuperCDMS, the properties of Dark Matter will be more precisely reconstructed. We further describe the data acquisition and the signal reconstruction of XENONnT. The final chapter of this thesis discusses the latest Dark Matter search result of XENONnT, which sets new stringent limits to the cross-section of the WIMP scattering off ordinary matter
A spark in the dark: Scintillation time dependence and neutron-induced signals in dual-phase xenon TPCs
Full text linkDual-phase (liquid and gas) xenon time projection chambers (TPCs) are currently the world's leading detector technology in the search for dark matter by direct detection. The XENON1T experiment, which contains an instrumented mass of 2 tons of liquid xenon, measured for a year and found no indication for any dark matter interaction, thus further constraining dark matter models. TPCs require excellent background rejection, part of which is achieved by making a distinction between a nuclear and an electronic interaction. This in turn requires a calibration with a neutron source, which in the case of XENON1T is a plasma fusion neutron generator. In this manuscript, a complete characterization of the neutron generator is presented. The calibration using the neutron generator is also shown. In addition to large xenon TPCs looking for dark matter, there are several smaller R&D setups worldwide. One of such setups is the XAMS experiment in Amsterdam. This manuscript elaborates on details on the setup and its data taking. There have been extensive measurements with various radiation sources and at several electric fields. Based on this data, the conclusion can be drawn that pulse shape discrimination, once believed to aid background rejection, does not meaningfully contribute to this. The data at various fields shows that the parameters of interest to TPC operation change significantly at low fields, which could present challenges to future large-scale TPCs looking for dark matter
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
The ϕ(1020)-meson production cross section measured with the ATLAS detector at √s=7 TeV
Full text linkA measurement of the differential production cross section of the ϕ(1020)-meson at √s=7 TeV using pp collision data collected with the ATLAS at the LHC experiment is presented in this thesis. The ϕ(1020)-meson selection is based on the identification of kaons by their energy loss in the pixel detector. The differential cross section is measured as a function of the transverse momentum and rapidity. The measurement is compared to the prediction of various Monte Carlo simulations
Track and vertex reconstruction in the ATLAS inner detector
Full text linkThis thesis describes the construction and commissioning of ATLAS SCT endcap A. The performance of the detector modules and the optical readout system was measured during various construction stages and the results are presented in this document. This thesis also describes a tool for vertex fitting with kinematic constraints in ATLAS. A study was made for solving systematic misalignments using a mass constraint in events of J/psi decaying to two muons
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