1,720,972 research outputs found
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
The ϕ(1020)-meson production cross section measured with the ATLAS detector at √s=7 TeV
Get PDFA 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
Get PDFThis 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
Search for scalar top quarks decaying into scalar tau leptons with ATLAS at √s = 8 TeV
Get PDFThis thesis presents a search for Supersymmetry carried out in a particular scenario arising from the Gauge Mediated Supersymmetry breaking mechanism that assumes a massless gravitino as lightest supersymmetric particle, a scalar tau lepton as next-to-lightest supersymmetric particle and the top squark as the lightest among the quark superpartners. The analysis is performed using the data collected by ATLAS at a centre-of-mass energy √s = 8 TeV during 2012 data taking, for a total of 20.3 fb−1 of integrated luminosity of proton-proton collisions. Scalar top quark candidates are searched for in events with either two light leptons, one hadronically decaying tau and one light lepton or two hadronically decaying taus in the final state. No significant excess over the Standard Model expectation is found and the results are interpreted as 95% confidence lower limits not top squark and scalar tau masses. Depending on the scalar tau mass, lower limits between 490 and 650 GeV are placed on the top squark mass within the model considered. This thesis presents also the results of the track-based alignment of the ATLAS Inner Detector during 2015 data taking campaign and the characterisation of the mechanical deformation of the Insertable B-Layer as function of the operating temperature
A spark in the dark: Scintillation time dependence and neutron-induced signals in dual-phase xenon TPCs
Get PDFDual-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
To the bottom of the stop: Calibration of bottom-quark jets identification algorithms and search for scalar top-quarks and dark matter with the Run I ATLAS data
Get PDFIn the first part of this thesis, the results of a calibration of bottom quark jets identification algorithms are reported. The analysis is performed with 5 fb of proton-proton collisions at 7 TeV centre-of-mass energy recorded by the ATLAS detector at the LHC. A b-jet enriched sample from fully reconstructed was used to validate the Monte Carlo simulation of b-jets properties and identification algorithms to the experimental data. In the second part of the thesis, the results of a search for top squark pair production in final states with one isolated lepton, jets, and missing transverse momentum are reported. The search is based on 20 fb of pp collisions at 8 TeV centre-of-mass energy recorded by the ATLAS detector. No significant excess over the Standard Model prediction is observed. The results were interpreted in terms of exclusion limits on a wide range of scenarios with different decay modes of the top squark and mass assumptions for the top squark and the other particles considered in the decay chain. Finally, the search was interpreted in terms of dark matter plus top pairs associate production. Limits were derived on dark matter nucleon scattering cross section for two contact operators (D1 and C1) in the context of dark matter effective field theory
Low-mass Dark Matter search with the XENON100 experiment
Get PDFIt 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
Measurement of the charged particle density with the ATLAS detector: First data at vs = 0.9, 2.36 and 7 TeV
Get PDFVolgens de planning zullen in de Large Hadron Collider (LHC), de krachtigste deeltjesversneller van de wereld, de komende twintig jaar protonen op elkaar botsen in het ATLAS-experiment. Hierdoor is het mogelijk elementaire deeltjes gedetailleerd te bestuderen. Manuel Kayl analyseerde de gegevens van kosmische straling, voor het eerst gemeten met een volledig geassembleerde detector. Hij richtte zich daarbij vooral op de meting van de dichtheid van geladen deeltjes waarmee wij ons begrip van de fundamentele deeltjes en hun eigenschappen kunnen testen. Voor deze metingen zijn de eerste proton-protonbotsingen bij de LHC gebruikt. De gemeten dichtheden van de geladen deeltjes zette Kayl in voor de aanpassing van theoretische modellen die tot een betere beschrijving van de onderzochte processen kunnen leiden. Deze verbeterde modellen worden gebruikt als fundering bij het zoeken naar nieuwe natuurkundige fenomenen bij de LHC
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