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Belwal, Swasti [Verfasser]. "An Investigation of Constraints on Dark Matter Models from Mono-jet Searches at LHC / Swasti Belwal". Bonn : Universitäts- und Landesbibliothek Bonn, 2018. http://d-nb.info/1173789510/34.
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Lundberg, Olof. "Searches for Dark Matter and Large Extra Dimensions in Monojet Final States with the ATLAS Experiment". Doctoral thesis, Stockholms universitet, Fysikum, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-129384.
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This thesis presents searches for evidence for Weakly Interacting Massive Particles (WIMPs) and Extra Dimensions in proton-proton collisions recorded by the ATLAS experiment at the CERN Large Hadron Collider (LHC). The WIMP is one of the main candidates to constitute the particle content of Dark Matter. Extra Dimensions are introduced in several theories in order to explain the apparent weakness of gravity when compared to the other interactions in Nature. Theories with WIMPs as well as Extra Dimensions can manifest themselves at the LHC, with experimental signatures characterized by an energetic hadronic jet associated with large missing momentum. These signatures are known as monojet signatures, and are investigated in this thesis. The first analysis is performed using L = 20.3 fb-1 of proton-proton collisions at √s = 8 TeV recorded in the ATLAS Run 1. The second analysis is performed using L = 3.2 fb-1 of proton-proton collisions at √s = 13 TeV recorded in the ATLAS Run 2. No significant excess over the expected background is found in either of the analyses. New exclusion limits are set at 95% confidence level on Dark Matter particle production. New limits are also set on graviton production in the so-called ADD scenario with Extra Dimensions.
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Sunneborn, Gudnadottir Olga. "Exploring selections across channels in Dark Matter searches with top quarks at the ATLAS experiment of the LHC". Thesis, Uppsala universitet, Högenergifysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-393949.
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Current estimates put Dark Matter to 26% of the energy-matter content of the universe, but very little is known about it other than its gravitational interactions. Eorts to learn more about Dark Matter include searching for it at high energy particle colliders. The lack of information about the nature of Dark Matter makes this a complicated task, and many searches are performed in dierent channels, and considering dierent theoretical models. In this thesis, I explore two such analyses, performed in the ATLAS collaboration using data from the ATLAS detector at the Large Hadron Collider at CERN: the tW+MET (missing transverse energy) nal state and the tt+MET nal state. I have made a generation-level study of the overlap between the signal regions used, and come to the conclusion that there is some. I have also compared the models used in these analyses, the 2HDM+a and the simplied spin-0 pseudoscalar model. Given the simplications made in my study, however, more sophisticated approaches should be used before anything conclusive can be said.
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Hallsjö, Sven-Patrik. "Search for Dark Matter in the Upgraded High Luminosity LHC at CERN : Sensitivity of ATLAS phase II upgrade to dark matter production". Thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-107583.
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The LHC at CERN is now undergoing a set of upgrades to increase the center of mass energy for the colliding particles to be able to explore new physical processes. The focus of this thesis lies on the so called phase II upgrade which will preliminarily be completed in 2023. After the upgrade the LHC will be able to accelerate proton beams to such a velocity thateach proton has a center of mass energy of 14 TeV. One disadvantage of the upgrade is that it will be harder for the atlas detector to isolate unique particle collisions since more and more collisions will occur simultaneously, so called pile-up. For 14 TeV there does not exist a full simulation of the atlas detector. This thesis instead uses data from Monte Carlo simulations for the particle collisions and then uses so called smearing functions to emulate the detector responses. This thesis focuses on how a mono-jet analysis looking for different wimp models of dark matter will be affected by this increase in pile-up rate. The signal models which are in focus are those which try to explain dark matter without adding new theories to the standard model or QFT, such as the effective theory D5 operator and light vector mediator models. The exclusion limits set for the D5 operators mass suppression scale at 14 TeV and 1000 fb-1are 2-3 times better than previous results at 8 TeV and 10 fb-1. For the first time limits have been set on which vector mediator mass models can be excluded at 14 TeV.
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ROVELLI, GIULIA. "Searches for Dark Matter production in events with top quarks in the final state with the ATLAS detector at the LHC". Doctoral thesis, Università degli studi di Pavia, 2021. http://hdl.handle.net/11571/1429276.
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Many cosmological observations give convincing evidence for the existence of dark matter (DM), estimated to constitute around 26% of the Universe by measurements of the cosmic microwave background. While the existence of DM thus seems well established, very little is known about its nature. Numerous models of DM have been proposed, and a possible strategy to test them is to use particle accelerators.
This thesis focuses in particular on the detection of DM produced in the ATLAS experiment at the Large Hadron Collider, studying signatures with top quarks in the final state in the framework of a two-Higgs-doublet model with an additional pseudoscalar mediator, called 2HDMa.
The first part of the work consisted in the study of the production of DM in association with a pair of top quarks, trying to assess the sensitivity in the parameters space of 2HDMa of already existing ATLAS analyses. These analyses were performed in the framework of a different model, similar to the 2HDMa model since it included a pseudoscalar mediator. The production of DM in association with a pair of top quarks was chosen because it is directly sensitive to the nature of the mediator through the polarization of the two top quarks, which can be reconstructed from their decays products. The model employed in the existing analyses and the 2HDMa model were thus compared in detail, and after that a recasting strategy to translate the existing results in the parameter space of 2HDMa was developed and validated.
The second part of the present study focused instead on a new search channel for the 2HDMa model, never explored before, including the production of dark matter associated with a single top quark. This signature was identified as the only one sensitive to the production of charged Higgs bosons, and thus holds a key role in the ATLAS research program dedicated to the 2HDMa model. Being a new and challenging signature, dedicated strategies were developed to maximise the sensitivity of the analyses focusing on the different final states.Many cosmological observations give convincing evidence for the existence of dark matter (DM), estimated to constitute around 26% of the Universe by measurements of the cosmic microwave background. While the existence of DM thus seems well established, very little is known about its nature. Numerous models of DM have been proposed, and a possible strategy to test them is to use particle accelerators. This thesis focuses in particular on the detection of DM produced in the ATLAS experiment at the Large Hadron Collider, studying signatures with top quarks in the final state in the framework of a two-Higgs-doublet model with an additional pseudoscalar mediator, called 2HDMa. The first part of the work consisted in the study of the production of DM in association with a pair of top quarks, trying to assess the sensitivity in the parameters space of 2HDMa of already existing ATLAS analyses. These analyses were performed in the framework of a different model, similar to the 2HDMa model since it included a pseudoscalar mediator. The production of DM in association with a pair of top quarks was chosen because it is directly sensitive to the nature of the mediator through the polarization of the two top quarks, which can be reconstructed from their decays products. The model employed in the existing analyses and the 2HDMa model were thus compared in detail, and after that a recasting strategy to translate the existing results in the parameter space of 2HDMa was developed and validated. The second part of the present study focused instead on a new search channel for the 2HDMa model, never explored before, including the production of dark matter associated with a single top quark. This signature was identified as the only one sensitive to the production of charged Higgs bosons, and thus holds a key role in the ATLAS research program dedicated to the 2HDMa model. Being a new and challenging signature, dedicated strategies were developed to maximise the sensitivity of the analyses focusing on the different final states.
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Busoni, Giorgio. "Dark Matter Indirect Detection and Collider Search: the Good and the Bad". Doctoral thesis, SISSA, 2015. http://hdl.handle.net/20.500.11767/3909.
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In this work I aim to point out some theoretical issues and caveats in DM search. In the first chapters I review the evidence for DM existence, the DM candidates and the different kinds of DM experimental search. The bulk of the work investigates three different topics. In the first topic, concerning neutrino from the Sun, I show the fact that evaporation does not allow to probe part of the parameter space, in the low mass range. In the second one, I show that, like in the case of the detected positron excess, that could be explained both by DM or by astrophysical source, even a possible excess of antiprotons could suffer from the same kind of degeneracy. In the third part, I consider DM search at collider. I point out some problems about using the EFT low-energy approximation at LHC, arising from the fact that the experimental bounds and the average energy of collisions at LHC are of the same order of magnitude. Afterward, to take this fact into account, I propose a method to rescale experimental bounds, and I review an alternative way of analyzing experimental results, that is using Simplified Models. Finally, I also show which is the part of the parameter space for both Simplified Models and EFT giving the DM the right relic abundance, in the case of thermal freeze-out.
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Hessler, André [Verfasser], Alejandro [Akademischer Betreuer] [Gutachter] Ibarra i Wolfgang [Gutachter] Hollik. "Exotic Particles at the LHC: Production via the Higgs Portal and FIMP Dark Matter Searches / André Hessler ; Gutachter: Alejandro Ibarra, Wolfgang Hollik ; Betreuer: Alejandro Ibarra". München : Universitätsbibliothek der TU München, 2016. http://d-nb.info/1117135128/34.
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Shcherbakova, Anna. "Calibration of b-tagging and search for Dark Matter : Calibration of b-tagging efficiency and search for Dark Matter production in association with heavy flavour quarks with the ATLAS experiment". Doctoral thesis, Stockholms universitet, Fysikum, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-146034.
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The Large Hadron Collider (LHC) is the most powerful and complex particle accelerator ever built. The ATLAS and the CMS are the two multipurpose particle detectors at the LHC, designed to cover a wide range of physics measurements. Three physics studies performed using data of proton-proton collisions collected with the ATLAS detector are presented. The identification of jets originating from b quarks, also known as b-tagging, is a crucial tool for many physics analyses at the LHC. This thesis presents a calibration of the b-tagging efficiency for high transverse momentum jets using a new calibration technique. This analysis is based on template fits and uses multi-jet events, which allows to perform the calibration for jets with transverse momenta up to 1200 GeV. This thesis also describes a completed and connected technical project on the development of the b-tagging ATLAS software. Dark Matter (DM) is a new phenomenon introduced to explain astrophysical observations. The nature of DM is one of the most important subjects of investigations in the modern physics, and many of these investigations are carried out at the LHC. A search for DM production in association with a pair of heavy flavour quarks has been recently performed in ATLAS at a centre-of-mass energy √s = 8 TeV under the Effective Field Theory approach. A re-interpretation of the results of this search under assumption of the simplified models is presented. A set of simplified models is considered with various DM masses, masses of the spin-0 exchange particle, that mediates the interaction between DM and the regular matter, and various values of couplings. Benchmark models are chosen to be used in the DM searches at √s = 13 TeV. The last part of the thesis presents a search for DM production in association with a pair of top quarks performed under assumption of the simplified models with spin-0 mediator, using the data collected at a centre-of-mass energy √s = 13 TeV. The observed data are shown to be in good agreement with the Standard Model predictions, and upper limits are set on a ratio between the observed DM production cross section and the value expected by the simplified model.
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Anders, J. "Searches for direct pair production of third generation squarks, and dark matter, in final states containing b−jets and ETmiss using the ATLAS detector at the LHC". Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3009386/.
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Beresford, Lydia Audrey. "Searches for dijet resonances using √s = 13 TeV proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider". Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:c516b04b-2763-487a-a633-6c506cec93ad.
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This thesis presents three searches for new resonances in dijet invariant mass spectra. The spectra are produced using √s = 13 TeV proton-proton collision data recorded by the ATLAS detector. New dijet resonances are searched for in the mass range 200 GeV to 6.9 TeV in mass. Heavy new resonances, with masses above 1.1 TeV, are targeted by a high mass dijet search. Light new resonances, with masses down to 200 GeV, are searched for in dijet events with an associated high momentum object (a photon or a jet) arising from initial state radiation. The associated object is used to efficiently trigger the recording of low mass dijet events. All of the analyses presented in this thesis search for an excess of events, localised in mass, above a data-derived estimate of the smoothly falling QCD background. In each search no evidence for new resonances is observed, and the data are used to set 95% C.L. limits on the production cross-section times acceptance times branching ratio for model-independent Gaussian resonance shapes, as well as benchmark signals. One particular benchmark signal which is considered in all of the searches is an axial-vector Z' dark matter mediator model whose parameter space is reduced due to the results presented in this thesis.
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Fischer, Cora. "Search for new phenomena in events with a high-energetic jet and missing transverse momentum with the ATLAS detectora". Doctoral thesis, Universitat Autònoma de Barcelona, 2017. http://hdl.handle.net/10803/457899.
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En esta tesis se presenta una búsqueda de nuevos fenómenos en sucesos de colisiones entre protones con un chorro de hadrones (jet) energético y un gran momento transverso faltante en el estado final. El análisis se realiza con un conjunto de datos recogido en 2015 y 2016 por el detector ATLAS con una energía de centro de masa de 13 TeV, correspondiente a una luminosidad integrada de 36,1 fb⁻¹.
Muchas teorías más allá del Modelo Estándar predicen una abundancia de eventos con un momento transverso faltante muy alto sobre los eventos esperados de los procesos de fondo del Modelo Estándar. La selección de eventos requiere como máximo cuatro jets, un jet principal con pT > 250 GeV, ETmiss > 250 GeV y sin leptones reconstruidos en el estado final.
Requisitos adicionales aseguran que los datos se correspondan con un detector completamente operativo y suprimen las contribuciones de fondo de los eventos multijet y eventos inducidos por los haces y muones cósmicos.
Se definen cuatro regiones de control ortogonales a la región de señal que requieren electrones o muones en el estado final. Estas regiones de control se utilizan para estimar los fondos principales en la región de señal que provienen de la producción de W/Z + jets, y para restringir las incertidumbres relacionadas con W/Z+jets y la producción de top-quarks.
La producción de los sucesos Z (-> νν)+jets y W (-> τν)+jets constituyen los fondos dominantes. Se estiman en un ajuste de probabilidad simultánea a las distribuciones en las regiones de control. Por lo tanto, la predicción de Monte Carlo de todos los procesos V+jets se vuelve a ponderar de acuerdo con los órdenes más altos en el cálculo perturbativo: NNLO QCD y nNLO EW.
Con el conocimiento de las correlaciones entre los diferentes procesos y la propagación de errores en diferentes regiones del pT del bosón, todos los procesos de V + jets pueden combinarse con un solo factor de escala que se obtiene por el ajuste simultáneo a los datos en las regiones de control. Un segundo factor de escala asignado a la normalización controlada por datos del fondo del quark top es un parámetro libre en el ajuste. Estos factores de escala obtenidos se aplican a los respectivos fondos en el SR para obtener la estimación de fondo final. Dado que los datos están de acuerdo con la predicción de fondo del Modelo Estándar y no hay exceso significativo, los resultados se interpretan en términos de límites de exclusión en varios modelos: el modelo ADD de dimensiones extra espaciales, los procesos de supersimetría que involucran escenarios comprimidos y producción de materia oscura en modelos simplificados.
Los límites existentes de los análisis ATLAS anteriores se han mejorado en un 15-30%. Los límites de los modelos ADD de dimensiones adicionales se establecen en el espacio de parámetros de n (número de dimensiones adicionales) y MD(reducción de la masa de Planck en n dimensiones adicionales). Los límites alcanzan hasta MD= 7.74 TeV para n = 2 y MD=4.77 TeV para n = 6. Límites en la producción supersimétrica de squarks ligeros con una diferencia de masa de 5 GeV entre el squark y el neutralino alcanzan hasta 710 GeV en la masa del squark.
Se excluye la producción de pares de stop (decaimiento a quark charm + neutralino) y de bbstom (decaimiento a b-quark + neutralino) hasta masas de squark de 430 GeV, en el escenario comprimido de masas de squarks y neutralino. La producción de pares de stop con un posterior decaimiento de cuatro cuerpos se excluye hasta 390 GeV para diferencias entre masas de stop y neutralino de hasta 7 GeV. En el caso de la producción de WIMPs, los límites se derivan en el plano de masa de materia oscura frente a masa del mediador. La masa máxima de mediador excluida es 1,55 TeV (masa de materia oscura baja), la masa máxima de materia oscura excluida es de 440 GeV con una masa de mediador de 1.2 TeV para un modelo de mediador vector-axial con producción en el canal s.A search for new phenomena in pp-collision events with a high-energetic jet and large missing transverse momentum is presented in this thesis. The analysis is carried out with a dataset collected in 2015 and 2016 by the ATLAS detector at a centre-of-mass energy of =13 TeV corresponding to an integrated luminosity of 36.1 fb⁻¹. Many theories beyond the Standard Model predict an abundance of events with very high missing transverse momentum over the events expected from Standard Model background processes. The event selection requires at most four jets, a leading jet with pT >250 GeV, missing transverse momentum with formula ETmiss >250 GeV and no reconstructed leptons. Additional requirements ensure that the data corresponds to a fully operational detector and suppress background contributions from multijet events (mismeasured jet momenta) and non-collision events (beam induced, comsic muons). Four control regions are defined orthogonal to the signal region requiring either electrons or muons in the final state. These control regions are utilised to estimate the major backgrounds in the signal region stemming from vector-boson+jets production and to constrain the uncertainties related to the former and to top-quark production. The production of Z(->νν)+jets and W(->τν)+jets constitute the dominant backgrounds. They are estimated in a simultaneous likelihood fit to the formula distributions in the control regions. Therefore, the Monte Carlo prediction of all W/Z+jets processes is reweighted according to the predictions from higher-orders perturbative calculations: next-to-leading order in QCD and next-to-next-to-leading order in EW precision. With the knowledge of the correlations among different processes and the error propagation in different regions of boson-pT, all W/Z+jets processes can be combined with one single scale factor that is obtained by the simultaneous fit to the data in the control regions. A second scale factor assigned to the data-driven normalisation of the top-quark background is a free parameter in the likelihood fit. These obtained scale factors are applied to the respective backgrounds in the SR to obtain the final background estimate. Since the data is in agreement with the Standard Model background prediction and no significant excess is present, the results are interpreted in terms of exclusion limits on various models: the model of ADD large extra spatial dimensions, Supersymmetry processes involving compressed scenarios and WIMP dark matter production in simplified models. Existing limits from previous ATLAS analyses have been improved by 15%-30%. Limits on ADD extra dimensions models are set in the parameter space of n (number of additonal dimensions) and (reduced Planck-mass MD in n extra dimensions). The limits reach up to MD = 7.74 TeV for n=2 and MD = 4.77 TeV for n=6. Limits in Supersymmetric production of light squarks with a mass splitting of 5 GeV between squark and neutralino mass reach up to 710 GeV in squark mass. The production of stop (decay to charm-quark+neutralino) and sbottom-pairs (decay to bottom-quark+neutralino) and same mass splittings is excluded up to squark masses of 430 GeV. The pair production of stop-quarks with a subsequent four-body decay is excluded up to 390 GeV for mass splittings of 7 GeV. In the case of WIMP DM production, limits are derived in the plane of dark matter mass vs. mediator mass. The maximum mediator mass excluded is 1.55 TeV (low dark matter mass), the maximum dark matter mass excluded is 440 GeV at mediator mass of 1.2 TeV for an s-channel axial-vector mediator model.
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Lou, Xuanhong [Verfasser]. "Search for Dark Matter Produced in Association with Heavy Standard Model Particles at √s = 13TeV with the ATLAS Detector at the LHC / Xuanhong Lou". Hamburg : Staats- und Universitätsbibliothek Hamburg Carl von Ossietzky, 2020. http://d-nb.info/1230555129/34.
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Perego, Marta Maria. "Search for new physics produced via Vector Boson Fusion in final states with large missing transverse momentum with the ATLAS detector". Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS088/document.
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Cette thèse présente des recherches sur la nouvelle physique produite par le processus de Fusion de Bosons Vecteur (VBF) dans les états finaux avec une grand impulsion transverse manquante (Etmiss) en utilisant 36.1 fb⁻¹ de données de collisions proton-proton avec une énergie dans le centre de masse de 13 TeV, recueillies par l'expérience ATLAS au Large Hadron Collider (LHC) au CERN en 2015 et 2016. En particulier, elle se concentre sur la recherche de la désintégration invisible du boson de Higgs produit via le mode VBF. Comme le modèle standard de la physique des particules (MS) prédit une désintégration invisible de Higgs uniquement à travers le mode H->ZZ*->4v avec un rapport d’embranchement BR ~ 0,1%, si une désintégration en particules invisibles du boson de Higgs était observée avec un BR supérieur, ce serait un signe de nouvelle physique. Plusieurs modèles au-delà du modèle standard (BSM) prédisent des désintégrations du boson de Higgs en particules de matière noire (DM, non détectées) ou en particules massives neutres à vie longue. Parmi les recherches H->particules invisibles, la plus sensible est celle où le Higgs est produit via le mode VBF. Son état final est caractérisé par deux jets énergétiques, avec les caractéristiques typiques du mode VBF (c'est-à-dire une grande séparation angulaire et une grande masse invariante des deux jets) et une grande impulsion transverse manquante (Etmiss>180 GeV). Pour sélectionner un échantillon d'événements candidats de signal, une région de signal (SR) est définie pour maximiser la fraction d'événements de signal attendus par rapport à la prédiction du MS (bruit de fond). Les processus MS qui peuvent peupler la SR proviennent principalement des processus Z->vv+jets et W->lv+jets, où le lepton est perdu ou non reconstruit. Leur contribution est estimée avec une approche semi-data driven : des régions dédiées enrichies en événements W->lv/Z->ll sont utilisées pour normaliser les données des estimations de Monte Carlo (MC) en utilisant une technique de fit simultané (méthode du facteur de transfert) et pour les extrapoler à la SR. L'estimation de fond prédit est comparée aux données SR observées. Comme aucun excès n'est trouvé, une limite supérieure sur le BR (H-> invisible) est calculée. L'analyse est ensuite réinterprétée dans le cadre de modèles inspirés du modèle Minimal Dark Matter. Le cas d'un nouveau triplet fermionique électrofaible, avec une hypercharge nulle et avec interactions respectant le nombre B-L, ajouté au MS fournit un bon candidat Dark Matter (WIMP pure). Si on considère l'abondance thermique, la masse du composant neutre est d’environ 3 TeV. Cependant des masses plus faibles sont également envisageables dans le cas de mécanismes de production non thermiques ou lorsque le triplet ne constitue qu'une fraction de l'abondance de DM. Il peut être produit à des collisionneurs proton-proton tels que le LHC et il peut être sondé de différentes manières. Une fois produites, les composantes chargées du triplet se désintègrent dans le composant neutre le plus léger, χ0 , avec en plus des pions très mous, en raison de la petite différence de masse entre les composants neutres et chargés. Ces pions de très faible impulsion ne peuvent pas être reconstruits et sont donc perdus. Le χ0 est reconstruit comme de l’Etmiss dans le détecteur. Par conséquent, lorsqu'il est produit via VBF, il donne lieu à une signature avec deux jets VBF et de l’Etmiss, le même état final que celui qui a été étudié pour l'analyse de VBF H->invisible. Des points de masse différentes (de 90 GeV à 200 GeV) ont été engendrés avec les programmes Monte Carlo Madgraph+Pythia, dans le cadre du logiciel officiel ATLAS, et les limites supérieures sont définies sur la section efficace fiducielle de production. Des extrapolations à des luminosités plus élevées (Run3 et HL-LHC) en utilisant une approche simplifiée sont également présentéesThis thesis presents searches for new physics produced via Vector Boson Fusion (VBF) in final states with large Missing Transverse Momentum (Etmiss) using 36.1 fb⁻¹ of data from proton-proton collisions at center-of-mass-energy of 13 TeV, collected by the ATLAS experiment at the Large Hadron Collider at CERN during 2015 and 2016. In particular, it focuses on the search for the invisible decay of the Higgs boson produced via the vector boson fusion (VBF) process. As the SM predicts an Higgs invisible decay only through H->ZZ*->4v with Branching Ratio BR~0.1%, if an invisibly decaying Higgs boson would be observed with a higher BR, this would be a sign of new physics. Several Beyond the Standard Model (BSM) models predict invisibly decaying Higgs boson where the Higgs can decay into dark matter particles or neutral long-lived massive particles. Among the H->invisible searches the most sensitive one is the one where the Higgs is produced via the VBF process. Its final state is characterized by two energetic jets, with the typical features of the VBF mode (i.e. large angular separation and large invariant mass) and large missing transverse momentum (Etmiss>180 GeV). To select a sample of signal candidate events, a Signal Region (SR) is designed to maximize the fraction of expected signal events with respect to the SM prediction (backgrounds). The SM processes which can populate the SR comes mainly from Z->vv+jets and W->lv+jets processes, where the lepton is lost or not reconstructed. Their contribution is estimated with a semi data driven approach: dedicated regions enriched in W->lv/Z->ll events are used to normalize to data the Monte Carlo (MC) estimates using a simultaneous fitting technique (transfer factor) and to extrapolate them to the SR. The predicted background estimate is compared to the observed SR data. Since no excess is found, an upper limit on the BR(H->inv) is set. The analysis is then reinterpreted in the context of models inspired by the Minimal Dark Matter model. The case of a new electroweak fermionic triplet, with null hypercharge and with interactions respecting the B-L number, added on top of the SM provides a good Dark Matter candidate. As such, it is an example of pure Weakly Interacting Massive Particle (WIMP), meaning that it is a DM particle with SU(2)_L SM interactions which is not mixing with other states (pure).If the thermal abundance is assumed, the mass of the neutral component is around 3 TeV, however smaller masses are also allowed in case of non-thermal production mechanisms or if the triplet constitutes only a fraction of the DM abundance. It can be produced at proton-proton colliders such as the LHC and it can be probed in different ways. Once produced, the charged components of the triplet decays into the lightest neutral component chi0 plus very soft charged pions. chi0 is reconstructed as Etmiss in the detector while the pions, because of the small mass splitting between the neutral and charged components, are so soft that are lost and are not reconstructed. Therefore, when produced via VBF, it gives rise to a signature with two VBF jets and Etmiss, the same final state that has been investigated for the VBF Higgs invisible analysis. Different mass point (from 90 GeV to 200 GeV) have been generated with the Madgraph+Pythia, Monte Carlo programs within the official ATLAS software, and upper limits are set on the fiducial cross section. Extrapolations to higher luminosities using a simplified approach are also presented
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Röhrig, Rainer-Christian [Verfasser], Hubert [Akademischer Betreuer] Kroha, Hubert [Gutachter] Kroha i Stefan [Gutachter] Schönert. "Search for Dark Matter Production in Association with a Higgs Boson with the ATLAS Detector at the LHC / Rainer-Christian Röhrig ; Gutachter: Hubert Kroha, Stefan Schönert ; Betreuer: Hubert Kroha". München : Universitätsbibliothek der TU München, 2019. http://d-nb.info/1185638083/34.
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Gadow, Paul Philipp [Verfasser], Oliver [Akademischer Betreuer] Kortner, Peter [Gutachter] Fierlinger i Oliver [Gutachter] Kortner. "Search for Dark Matter Produced in Association with Hadronically Decaying Bosons at √s = 13 TeV with the ATLAS Detector at the LHC / Paul Philipp Gadow ; Gutachter: Peter Fierlinger, Oliver Kortner ; Betreuer: Oliver Kortner". München : Universitätsbibliothek der TU München, 2020. http://d-nb.info/1221719521/34.
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Kahlhoefer, Felix Karl David. "Complementarity of searches for dark matter". Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:ec5b1afe-b75c-44d9-9dad-e0d342e46fa1.
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The striking evidence for the existence of dark matter in the Universe implies that there is new physics to be discovered beyond the Standard Model. To identify the nature of this dark matter is a key task for modern astroparticle physics, and a large number of experiments pursuing a range of different search strategies have been developed to solve it. The topic of this thesis is the complementarity of these different experiments and the issue of how to combine the information from different searches independently of experimental and theoretical uncertainties. The first part focuses on the direct detection of dark matter scattering in nuclear recoil detectors, with a special emphasis on the impact of the assumed velocity distribution of Galactic dark matter particles. By converting experimental data to variables that make the astrophysical unknowns explicit, different experiments can be compared without implicit assumptions concerning the dark matter halo. We extend this framework to include annual modulation signals and apply it to recent experimental hints for dark matter, showing that the tension between these results and constraints from other experiments is independent of astrophysical uncertainties. We explore possible ways of ameliorating this tension by changing our assumptions on the properties of dark matter interactions. In this context, we propose a new approach for inferring the properties of the dark matter particle, which does not require any assumptions about the structure of the dark matter halo. A particularly interesting option is to study dark matter particles that couple differently to protons and neutrons (so-called isospin-violating dark matter). Such isospin-violation arises naturally in models where the vector mediator is the gauge boson of a new U(1) that mixes with the Standard Model gauge bosons. In the second part, we first discuss the case where both the Z' and the dark matter particle have a mass of a few GeV and then turn to the case where the Z' is significantly heavier. While the former case is most strongly constrained by precision measurements from LEP and B-factories, the latter scenario can be probed with great sensitivity at the LHC using monojet and monophoton searches, as well as searches for resonances in dijet, dilepton and diboson final states. Finally, we study models of dark matter where loop contributions are important for a comparison of LHC searches and direct detection experiments. This is the case for dark matter interactions with Yukawa-like couplings to quarks and for interactions that lead to spin-dependent or momentum suppressed scattering cross sections at tree level. We find that including the contribution from heavy-quark loops can significantly alter the conclusions obtained from a tree-level analysis.
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Mishra-Sharma, Siddharth. "Extragalactic Searches for Dark Matter Annihilation". Thesis, Princeton University, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10928813.
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We are at the dawn of a data-driven era in astrophysics and cosmology. A large number of ongoing and forthcoming experiments combined with an increasingly open approach to data availability offer great potential in unlocking some of the deepest mysteries of the Universe. Among these is understanding the nature of dark matter (DM)—one of the major unsolved problems in particle physics. Characterizing DM through its astrophysical signatures will require a robust understanding of its distribution in the sky and the use of novel statistical methods.
The first part of this thesis describes the implementation of a novel statistical technique which leverages the “clumpiness” of photons originating from point sources (PSs) to derive the properties of PS populations hidden in astrophysical datasets. This is applied to data from the Fermi satellite at high latitudes (|b| ≥ 30°) to characterize the contribution of PSs of extragalactic origin. We find that the majority of extragalactic gamma-ray emission can be ascribed to unresolved PSs having properties consistent with known sources such as active galactic nuclei. This leaves considerably less room for significant dark matter contribution.
The second part of this thesis poses the question: “what is the best way to look for annihilating dark matter in extragalactic sources?” and attempts to answer it by constructing a pipeline to robustly map out the distribution of dark matter outside the Milky Way using galaxy group catalogs. This framework is then applied to Fermi data and existing group catalogs to search for annihilating dark matter in extragalactic galaxies and clusters.
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Palacio, Navarro Joaquim. "Indirect dark matter searches: MAGIC & CTA". Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/462764.
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Després de dècades d'observacions, és evident que les partíicules del model estàndard són insuficients per explicar el fort desequilibri gravitacional observat a diverses regions astronòmiques,
de diferents escales cosmològiques, des de satèl·lits de la Via Làctia fins a cúmuls de galàxies.
Si bé és veritat que algunes teories suggereixen a una modificació de les lleis gravitacionals actuals, l'existència d'una partícula (o un grup de partícules) nova, interaccionant de forma feble amb les partícules del model estàndard està considerada com l'opció més viable. Estimacions recents prediuen que aquest tipus de matèria fosca és 4 vegades més present que la matèria del model estàndard, modelant així la formació de les grans estructures de l'univers al llarg de la vida d'aquest.
Un escenari general de la matèria fosca és el dels WIMPs, partícules genèriques massives, amb masses entre pocs GeVs i alguns TeV, interaccions de l'ordre de les interaccions dèbils del model estàndard, i o bé estables o amb temps de vida mitjana prou llargs. L'escenari WIMP ha estat llargament debatut, i té l'avantatja d'estar a l'abast dels instruments més potents construïts a la terra, proporcionant així possibles deteccions independents que podria validar el descobriment.
En particular em centro en cerques indirectes de matèria fosca, on s'espera que WIMPs anihilats o decaient emetin rajos gamma amb energies detectables per telescopis IACT, com per exemple els telescopis MAGIC, actualment operant des de La Palma o la futura xarxa de telescopis CTA.
El senyal esperat de rajos gamma d'aquesta matèria fosca pot ser moderadament extensa, comparada amb el camp de visió dels IACTs, cosa que afegeix certa complexitat a les cerques de matèria fosca realitzades per a aquests telescopis.
En aquesta tesi, he contribuït a l'esforç realitzat per MAGIC en cerques indirectes de matèria fosca a diferents nivells d'analisis. He desenvolupat una eina per gestionar volums massius de dades que són típicament generats per MAGIC, però també per tota la comunitat experimental de física d'altes energies. També he desenvolupat un MonteCarlo per a fonts extenses que s'ajusta a l'emissió esperada de la font, obtenint així les funcions correctes de resposta de l'instrument. Finalment, un mètode per a optimitzar la configuració d'apuntat durant les observacions de fonts moderadament extenses amb IACTs ha estat proposat. El mètode té en compte la resposta finita dels IACTs al llarg de tot el camp de visió per a proporcionar la distància òptima a la qual el telescopi ha d'apuntar a la font, així com, quina seria la regió d'integració més adient. Apliquem aquest mètode per primera vegada a cerques de matèria fosca en galàxies satèl·lits de la Via Làctia. També exposo la meva contribució al telescopi més gran que operarà a CTA, el LST, que dominarà la sensibilitat de cerques de WIMPs estàndard.
Límits a la secció eficaç i/o temps de vida mitjana són imposats mitjançant 60 hores d'observació de la galàxia Triangulum-II i 202 hores del cúmul de galàxies de Perseus. En ambdues cerques, fem ús del mètode de màxima versemblança, optimitzat per a la morfologia espacial i energètica del senyal esperat de rajos gamma. Obtenim sensibilitats a la secció eficaç de 3·10^{-26}~\cm^{3}\s^{-1} i
temps de vida mitjana de 0.3·10^{25}~\s, essent aquests els resultats més restrictius obtinguts amb MAGIC en cerques de WIMPs.Decades of observational evidences have been accumulated to show that Standard Model (SM) particles cannot totally explain the strong gravitational unbalance observed in several astronomical regions, at all cosmological scales, from that of Milky Way (MW) satellite galaxies, to that of Cluster of Galaxies (CGs). Although some theories argue for the modification of the gravitational laws, the existence of a new massive particle (or a set of them), interacting only weakly with SM particles, provides a preferred explanation. It is estimated that this form of Dark Matter (DM) roughly accounts for 4 times the amount of SM matter, therefore shaping the evolution of cosmic structures along the history of the Universe. A well-motivated general framework for DM is that of a Weakly Interacting Massive Particle (WIMP), generic massive particles with a mass range expected between few GeVs and few hundreds TeV, interaction strengths at the weak scale, and either stable or very long lived. The WIMP paradigm has been long debated, and has the advantage of being at reach by different of the top-class instruments of the current times, so that a putative discovery could be validated independently. We focus on the indirect search of DM, where annihilating or decaying WIMPs are expected to emit gamma rays at energies detectable by Imaginc Atmospheric Cherenkov Telescopes (IACTs), as the currently operating MAGIC telescopes or the future Cherenkov Telescope Array (CTA). The expected DM signal can be moderate extended when compared to IACTs Field of View (FoV), what challenges the performance of the \acrshort{dm} search of these instruments. In this thesis, I contribute to the MAGIC ongoing efforts on indirect DM searches at different analysis levels. A tool for handling the massive data products generated by current high energy experiments is developed. More over, a tailored Monte Carlo (MC) for moderate extended sources is proposed as an upgrade of the current general MC for extended sources. Finally, a method to optimize the pointing strategy of IACTs while observing moderate extended sources taking into account the off-axis performance of the instrument has also been developed and, implemented for the first time to indirect DM searches on highly DM dominated nearby dwarf Sphereoidal galaxies (dSphs). I also show my contribution to the largest telescope to be part of CTA, the Large Size Telescopes, that will dominate the CTA sensitivity for standard WIMP searches. Constraints on the WIMP thermally averaged cross-section and/or decay life-time are put with 60~hours of data in the recently discovered dSph Triangulum-II and 202~hours on the Perseus CG. On both searches, we apply a binned likelihood analysis optimized for the spectral and morphological features of gamma-ray signals of DM from annihilating or decaying WIMPs. We reach sensitivities to the thermally averaged cross-section of 3·10^{-26}~\cm^{3}\s^{-1} and decay life-times of 0.3·\times10^{25}~\s, being this the most constraining MAGIC results on WIMP searches.
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Ingleby, Stuart. "Cryodetector readout for direct dark matter searches". Thesis, University of Oxford, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.558393.
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The next generation of cryodetector arrays for direct WIMP searches will aim to achieve large increases in WIMP-nucleon scattering target mass, an order of magnitude or more greater than existing detector arrays. The implementation of high-resolution measurements and background suppression by event discrimination will remain of paramount importance. Hardware development must be undertaken to increase the availability and density of read out channels while maintaining low-noise, low-heatload, high-radiopurity cryodetector performance. This thesis describes the development of scalable cryogenic cabling using etched metal foil fabrication techniques and the development of low-temperature high-voltage power supply for scintillation light readout using photomultiplier tubes. Etched metal foil cables were developed for cryodetector read out. Fabrication techniques for low-heatload, low-cost cabling were developed and commissioning tests were carried out to verify low-noise performance in both low-impedance and high-impedance cryodetector read out schemes. SQUID readout cabling with a heatload cost 24 times lower than existing cabling was installed and mean SQUID noise of 5.5 pAHz-l/2 was measured with low- impedance input. Photomultiplier tubes can be used for cryogenic scintillation light measurement, a key technique in cryodetector event discrimination. A low-heatload, low-noise photomultiplier tube power supply circuit was developed. Measurements of cryogenic scintillation light from a CaW04 crystal were carried out using a CWG/PMT module cooled to 0.95 mK.
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Mantani, Luca. "Simplified t-channel models for dark matter searches". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/13444/.
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Una enorme quantità di evidenze sperimentali sulla esistenza di una forma di materia non luminosa nell'Universo, si sono accumulate nel corso di circa un secolo. Chiarire la sua natura è diventata una delle sfide più eccitanti ed urgenti negli sforzi per capire il nostro Universo.
In questo lavoro presento uno studio su un approccio per scoprire la Materia Oscura interpretata come particella elementare e sulla possibilità di produrla e rilevarla negli acceleratori.
Nella parte introduttiva presento una breve storia delle evidenze astrofisiche e astronomiche che hanno portato alla ipotesi della esistenza di Materia Oscura. Assumendo che la Materia Oscura sia costituita da una particella elementare ulteriore a quelle predette dal Modello Standard, delineo poi i tre principali metodi di rilevazione utilizzati attualmente per identificarla.
Nella seconda parte discuto come si possono costruire teorie nelle quali sia possibile interpretare le ricerche attuali ed i risultati corrispondenti. Eseguo un confronto tra approcci diversi, partendo da modelli completi fino a quelli che utilizzano teorie di campo effettive. In particolare, discuto i loro lati positivi e negativi, motivando l'utilizzo di uno schema intermedio, il cosiddetto approccio con modelli semplificati, caratterizzati da un numero limitato di nuovi stati e parametri e che supera le limitazioni intrinseche delle teorie effettive nel contesto delle ricerche negli acceleratori.
Nell'ultima parte fornisco una esaustiva classificazione dei modelli semplificati nel canale t, che non sono ancora stati analizzati sistematicamente nella letteratura. Per ciascuno di essi presento un possibile completamento UV e i segnali più promettenti ad LHC. Per questa ragione tutti i modelli considerati sono stati implementati in strumenti Monte Carlo, validati nel confronto con risultati analitici, studiati in dettaglio e resi pronti per un rilascio pubblico per la comunità fenomenologica e sperimentale di LHC.
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Figueiredo, Vaz Pato Miguel. "A multi-disciplinary approach to Dark Matter Searches". Paris 7, 2011. http://www.theses.fr/2011PA077205.
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Une grande partie de notre Univers consiste en un type de matière non-lumineuse intrinsèquement différente de tous les types de matière connus. Les preuves expérimentales suggèrent fortement que cette "Matière Noire" contribue à environ 80-85% de la matière de l'Univers. Ces dernières années, de nombreux résultats expérimentaux concernant la Matière Noire ont été publiés, faisant de ce domaine de recherche un des plus excitants. Beaucoup de données sont également attendues dans un avenir proche. Le but de cette thèse est d'établir le lien entre certains modèles de Matière Noire et leurs signatures expérimentales visibles dans les détecteurs actuels ou futurs. En ce qui concerne la détection indirecte de Matière Noire, une attention particulière est accordée à l'excès de électrons/positrons, qui peut en principe être expliqué par annihilations de Matière Noire dans notre Galaxie. Afin de tester cette possibilité nous effectuons une analyse "multi-messenger" combinant les contraintes de différents canaux astrophysiques tels que antiprotons, rayons gamma et signaux radio. Les incertitudes entrant dans le calcul des signatures de Matière Noire sont très importants et limitent notre capacité à extraire les respectives propriétés en cas de découverte. Par conséquent, évaluer et prévoir toutes les incertitudes pertinentes est essentielle, et une grande partie de cette thèse est consacrée à ce sujet. En particulier, nous étudions les perspectives pour la détermination de la propagation des rayons cosmiques avec AMS-02, les incertitudes systématiques sur la densité locale de Matière Noire et l'effet des incertitudes astrophysiques sur les expériences de détection directeA large portion of the present Universe is composed of a non-luminous kind of matter, which is intrinsically distinct from ail mass constituents known to exist. The evidence for this so-called Dark Matter spans sub-galactic to cosmological scales, and strongly suggests that it contributes around 80-85% of the matter content in our Universe. Over the past years, numerous experimental results relevant for Dark Matter searches have been released, triggering a great deal of excitement in the field. Moreover, plenty of data are expected in the near future. This thesis aims at linking Dark Matter models and their experimental signatures in current and upcoming detectors. As far as indirect Dark Matter detection is concerned, special attention is paid to the recently reported electron/positron excess in cosmic rays, which can in principle be explained by Dark Matter annihilations in our Galaxy. In order to test this possibility we perform a multi-messenger analysis combining the constraints from different astrophysical channels such as antiprotons, gamma-rays and radio signals. The uncertainties entering the computation of Dark Matter signatures are very significant and ultimately limit our ability to extract the properties of Dark Matter in case of discovery. Therefore, to assess and forecast ail relevant uncertainties is crucial, and a large portion o this thesis is devoted to that topic. In particular, we study the prospects for pinpointing cosmic-ray propagation with AMS-02, the systematic uncertainties regarding the local Dark Matter density and the effect of astrophysical unknowns on direct detection experiments
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Scott, Pat. "Searches for Particle Dark Matter Dark stars, dark galaxies, dark halos and global supersymmetric fits /". Doctoral thesis, Stockholm : Department of Physics, Stockholm University, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-38221.
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Diss. (sammanfattning) Stockholm : Stockholms universitet, 2010.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Accepted. Paper 6: Submitted. Härtill 6 uppsatser.
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Currie, Alastair Edward. "Direct searches for WIMP dark matter with ZEPLIN-III". Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9980.
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Work contributing to experimental limits on WIMP dark matter scattering in a liquid xenon target is presented. The ZEPLIN-III detector at Boulby completed 83 days’ continuous operation in 2008 and, following a hardware upgrade, a further 319 days in 2010–11. Inelastic dark matter hypotheses to explain the DAMA/LIBRA modulation as scattering from iodine are excluded with ≥ 87% confidence using 2008 data. Upper limits on the elastic WIMP-nucleon cross section are set from the combined exposure, with a minimum of 3.9 × 10⁻⁸ pb for 50 GeVc⁻² WIMP mass at 90% CL, in addition to competitive limits on the WIMP-neutron spin-dependent cross section. The detector responses to scintillation and ionisation—throughout the fiducial volume and over the duration of the run — are characterised via calibration with ⁵⁷Co and ¹³⁷Cs sources, as well as sidebands in search data. Signal spectra are modeled using these responses and an in situ measurement of the energy-dependent light and charge yields of nuclear recoils. Analysis software, event selection and background estimation are all described. Confidence intervals based on sparse regions of parameter space (Yellin limits) and the likelihood ratios are implemented for ZEPLIN-III and discussed in the context of rare-event searches with significant background uncertainty.
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Danninger, Matthias. "Searches for Dark Matter with IceCube and DeepCore : New constraints on theories predicting dark matter particles". Doctoral thesis, Stockholms universitet, Fysikum, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-89820.
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The cubic-kilometer sized IceCube neutrino observatory, constructed in the glacial ice at the South Pole, searches indirectly for dark matter via neutrinos from dark matter self-annihilations. It has a high discovery potential through striking signatures. This thesis presents searches for dark matter annihilations in the center of the Sun using experimental data collected with IceCube. The main physics analysis described here was performed for dark matter in the form of weakly interacting massive particles (WIMPs) with the 79-string configuration of the IceCube neutrino telescope. For the first time, the DeepCore sub-array was included in the analysis, lowering the energy threshold and extending the search to the austral summer. Data from 317 days live-time are consistent with the expected background from atmospheric muons and neutrinos. Upper limits were set on the dark matter annihilation rate, with conversions to limits on the WIMP-proton scattering cross section, which initiates the WIMP capture process in the Sun.These are the most stringent spin-dependent WIMP-proton cross-sections limits to date above 35 GeV for most WIMP models. In addition, a formalism for quickly and directly comparing event-level IceCube data with arbitrary annihilation spectra in detailed model scans, considering not only total event counts but also event directions and energy estimators, is presented. Two analyses were made that show an application of this formalism to both model exclusion and parameter estimation in models of supersymmetry. An analysis was also conducted that extended for the first time indirect dark matter searches with neutrinos using IceCube data, to an alternative dark matter candidate, Kaluza-Klein particles, arising from theories with extra space-time dimensions. The methods developed for the solar dark matter search were applied to look for neutrino emission during a flare of the Crab Nebula in 2010.
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Raj, Nirmal. "Dark Matter and Supersymmetry in the LHC Era". Thesis, University of Oregon, 2015. http://hdl.handle.net/1794/19253.
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We report investigations of physical possibilities beyond the Standard Model, performed in the years between Runs I and II of the Large Hadron Collider (LHC).
First, we explore the feasibility of using a hadron collider to unmask hidden sectors by means of a novel signal, the ``monocline". Dilepton production provides the cleanest channel to anticipate a monocline. A compelling sector to seek is dark matter with scalar messengers coupling it to standard fermions. We present current bounds from dilepton spectrum measurements at the LHC and make predictions for sensitivities at Run II of the LHC as well as at a future 100 TeV collider. Second, we corner the space of parameters of supersymmetric frameworks with an appreciable Yukawa coupling between the Higgs fields and a gauge singlet, the so-called Fat Higgs and $\lambda$-SUSY models, in the context of the discovery of the 125 GeV Higgs particle. These models are motivated by their alleviation of the electroweak fine-tuning that supersymmetry breaking entails, via raising the tree-level quartic coupling Higgs boson. Heavy Higgs scalars that couple strongly to the standard Higgs boson induce large radiative corrections to the Higgs quartic coupling, which is crucial to phenomenology; in particular, a very large ratio of the Higgs VEVs ($\tan \beta$), that was previously presumed unfavorable in these models, becomes viable and can be probed by future experiments. In such regions, the most stringent limits come from dark matter constraints on the lightest neutralino.
Finally, we place limits on colored scalar production at the LHC in supersymmetric models where gauginos acquire both Dirac and Majorana masses, that we call ``mixed gauginos". While it was known that purely Dirac gluinos were less constrained by LHC searches than their purely Majorana counterparts, we find that the constraints further weaken or strengthen depending on which of the ``mixed" colored fermions acquires a Majorana mass. Also explored are the effects on squark production of turning on Majorana masses for electroweak gauginos.
This dissertation consists of previously published and unpublished co-authored material.
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Costa, Miguel António Felizardo da. "Advanced instrumentation for superheated liquid detectors in dark matter searches". Doctoral thesis, Faculdade de Ciências e Tecnologia, 2013. http://hdl.handle.net/10362/8863.
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Dissertação para obtenção do Grau de Doutor em
Engenharia FísicaThe initial goal of the thesis work was to improve the performance of the instrumentation used in the SIMPLE dark matter search. Consequently, the ultimate objective is to find a possible candidate for Dark Matter or improve the knowledge of its nature. Upon a brief description of Dark Matter and the status of its search, the fundamentals of Superheated Liquid Detectors are presented. This thesis presents a robust acoustic instrumentation together with a new method for the identification of bubble nucleations in Superheated Droplet Detectors. This is accomplished through straightforward signal processing techniques applied to the acoustical recording of the nucleation events, which consists of pulse shape identification procedures. A set of tests are presented to evaluate the performance of the proposed algorithms, as well as the new and more reliable instrumentation. An effort to locate a bubble nucleation in the SDDs is accomplished through some elaborated signal processing techniques applied to the acoustical recording of the nucleation events. These include the application of wavelets, the chirp-z transform and pulse shape identification procedures to locate temporally and validate the nucleation for its spatial localization. Acoustic and SDD associated backgrounds are completely discriminated with the developed signal processing techniques. Results from systematic studies are presented for the instrumentation and SDD response,which are used in the SIMPLE dark matter search experiment and possibly in neutron dosimetry. A new bubble nucleation efficiency is drawn out, together with particle discrimination confirmation determined throughout a-n calibrations. SIMPLE's Phase-II Dark Matter results are presented with the implementation of the complete instrumentation in operation for SDDs. These results are simultaneously presented with the full characterization of the local background scenario and gained knowledge of SDD characteristics and dynamics. Interpretations of these results are laid out. The direct future is given through the R&D of a rejuvenation superheated liquid detector, the Big Droplet Chamber. A prototype of this new Bubble Chamber is shown together with its first results of a more prevailing ultrasound acoustic system. Which can possibly reveal in the near future, unseen aspects such as the bubble formation stage in superheated liquids up to now.
Fundação para a Ciência e Tecnologia - (SFRH/BD/46545/2008)
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Genolini, Yoann. "Refined predictions for cosmic rays and indirect dark matter searches". Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY049/document.
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Il y a tout juste cent ans que les premières mesures du taux d'ionisation de l'air ont dévoilé que la terre est sans cesse bombardée par une pluie de particules énergétiques provenant du Cosmos. D'un point de vue astrophysique, l'origine de ces particules hautement relativistes, appelés rayons cosmiques (CRs), ainsi que leur mécanisme d'accélération restent très peu connus. Le paradigme actuel suppose une injection sporadique des CRs accélérés par la propagation d'ondes de choc au cours de la mort de certaines étoiles (SNRs).Les mesures récentes des flux de CRs (par les expériences PAMELA et AMS-02 par exemple) inaugurent une nouvelle ère de précision dans la mesure où les incertitudes statistiques sont désormais considérablement réduites. Dans ce mémoire de thèse, nous proposons et approfondissons de nouvelles pistes théoriques de manière à maximiser l'information extraite de ces nouvelles données.Après une introduction générale sur la physique des CRs, nous nous concentrons sur les espèces dites primaires, qui sont produites directement par les SNRs. De la nature discrète des SNRs et de la méconnaissance quasi-complète de leurs positions et de leurs ages résulte une incertitude théorique qui nécessite d'être estimée pour la prédiction des flux observés sur Terre. Jusqu'alors ces prédictions se contentent de calculer la moyenne d'ensemble de ce flux. Dans cette partie nous exposons la théorie statistique que nous avons élaborée, permettant de calculer la probabilité d'une déviation du flux mesuré par rapport à la moyenne d'ensemble. Nous sommes amenés à utiliser une version généralisée du théorème de la limite centrale, avec lequel nous montrons que la loi de probabilité est intimement reliée à la distribution des sources et qu'elle converge vers une loi stable. Cette dernière diffère de la loi gaussienne par sa queue lourde en loi de puissance. Le cadre théorique développé ici peut non seulement être étendu à d'autres observables du rayonnement cosmique, mais aussi enrichi en incluant une description plus complète des corrélations entre les sources. De plus, la méthode que nous avons développée peut être appliquée à d'autres problèmes de physique/astrophysique impliquant des distributions à queue lourde.Deuxièmement nous nous penchons sur les CRs dits secondaires (comme le bore), qui sont produits par les collisions des espèces primaires avec le milieu interstellaire. Plus précisément nous nous concentrons sur le rapport du flux du bore sur celui du carbone qui est traditionnellement utilisé pour comprendre la propagation des CRs. Ainsi, tout porte à croire que les mesures extrêmement précises de ce rapport nous donneraient de fortes contraintes sur les scénarios de propagation. Malheureusement il n'en est rien et nous montrons que le calcul théorique dépend fortement de certaines hypothèses telles que le lieu de production des secondaires et le choix du jeux de sections efficaces d’interaction. Nous estimons à au moins 20 % les incertitudes sur les paramètres de propagation dérivés jusqu'à maintenant. Grâce aux nouvelles données de l'expérience AMS-02, nous présentons les points de départ de notre nouvelle analyse pour laquelle nous utilisons le code semi-analytique USINE.Finalement, dans une troisième partie, nous utilisons ces données de précision pour réactualiser les analyses portant sur la recherche indirecte de matière noire. En effet, les CRs d'antimatière seraient -au même titre que le bore- des particules secondaires. La prédiction de leur fond astrophysique repose sur une connaissance précise de la propagation des CRs et de leurs interactions dans la Galaxy. Nous les traitons ici sous les hypothèses habituelles et réévaluons les flux de positrons et d'antiprotons à la lumière des nouvelles données d'AMS-02. Nous discutons ensuite les conséquences pour la matière noire et les possibles explications astrophysiques d'éventuels excès observésA hundred years ago, pioneering observations of air ionization revealed that the Earth is showered with particles coming from the Galaxy and beyond. Because of their high energies, these particles coined cosmic-rays are still a crucial tool in the field of particle physics, complementary to man-made accelerators. From an astrophysical point of view, the origin of cosmic-rays and the mechanisms which accelerate them are still very poorly known. The present paradigm involves sporadic production associated with the expanding shock waves from dying stars (SNRs).Recent experiments (notably PAMELA and, more recently, AMS-02) are ushering us into a new era of measurements of cosmic-ray fluxes with greatly reduced statistical uncertainties. In this dissertation, we propose and investigate new theoretical refinements of our predictions to fully benefit from these advances.After a general introduction on cosmic-ray physics, we first focus on the so-called primary species which are directly produced by SNRs. In this context of precision measurements, the discreteness of the sources in space and time, together with a substantial ignorance of their precise epochs and locations (with the possible exception of the most recent and close ones) may lead to significant uncertainties in the predictions of the fluxes at the Earth. So far, the conventional approach just relied on average trends. Here, we elaborate a statistical theory in order to compute the probability for the actual flux to depart from its ensemble average. Using the generalized version of the central limit theorem, we demonstrate that the probability distribution function of the flux is intimately related to the source distribution and follows a stable law with a heavier tail than the Gaussian distribution. Our theoretical framework can not only be extended to other cosmic-ray observables, such as the lepton flux, but also can be enriched to include a more comprehensive description of the correlations between the sources. Moreover the method which we have developed may be applied to a variety of problems in physics/astrophysics involving heavy tail distributions.Secondly, we concentrate on secondary CRs, like the boron nuclei, which are thought to be produced only by the collisions of cosmic-rays on the interstellar medium. More precisely, the ratio of the boron to carbon fluxes is a traditional tool used to understand and gauge the propagation of cosmic-rays in the Galaxy. Hence a very precise measurement of this ratio should imply stringent constraints on the propagation scenario. However we show that its theoretical derivation strongly depends on where these secondary species are produced as well as on the chosen set of nuclear cross-sections. Hence we assess at the 20% level the theoretical uncertainties on the so far derived propagation parameters. As new data from AMS-02 were freshly released, we present the starting points of a comprehensive new analysis for which we use the semi-analytical code USINE.Finally these high precision measurements offer new opportunities for a number of astroparticle problems, such as indirect dark matter searches which is the main thrust of the third part of the thesis. Antimatter cosmic rays are thought to be secondary species and their relatively low fluxes make them a channel of choice to look for rare processes such as dark matter annihilation. Nonetheless, the predictions of the expected backgrounds rely on a precise modeling of cosmic-ray propagation and interactions in the Galaxy. We treat them under commonly used simplified assumptions and discuss two studies where we re-evaluate the anti-proton and the positron fluxes in the light of the new AMS-02 data. Then we discuss the implications for dark matter and astrophysical explanations
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Wolf, Martin. "Indirect Searches for Galactic Dark Matter with IceCube-DeepCore and PINGU". Licentiate thesis, Stockholms universitet, Fysikum, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-104786.
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The cubic-kilometer sized IceCube neutrino observatory is burieddeep in the glacial ice at the Earth’s South Pole. Its low-energyextension array DeepCore enables physicists to search indirectlyfor light Dark Matter (DM) particles with masses as low as tensof GeV/c2 situated within our home galaxy, the Milky Way. GeVneutrinos could be produced through DM particle annihilations,propagating to the Earth where they could be detected by IceCube. This licentiate thesis presents a search for Weakly Interacting Mas-sive Particles (WIMPs) with masses as low as 30 GeV/c2 in theGalactic center (GC) using the 79-string configuration of the IceCubeneutrino detector. Data from 319.7 live-days have been analyzedusing a cut-and-count analysis approach, and found to be consistentwith the background-only hypothesis with expected backgroundfrom atmospheric muons and neutrinos. Thus, upper limits wereset on the velocity averaged DM annihilation cross-section. The Precision IceCube Next Generation Upgrade (PINGU) as apossible future neutrino detector within DeepCore would reducethe neutrino energy detection threshold to a few GeV. In additionto the data analysis with DeepCore, a sensitivity study has beenconducted to investigate the performance of PINGU for indirectDM searches in the GC and the Sun. In the Sun WIMPs could begravitationally captured through elastic scattering off nucleons. Inthis thesis, we derive PINGU sensitivities for the velocity averagedDM annihilation cross-section of WIMPs in the GC, and for theSpin-Dependent (SD) and Spin-Independent (SI) WIMP-protonscattering cross-sections, under the assumption of thermodynamicequilibrium between the WIMP capturing and annihilation rate inthe Sun.IceCube
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Gastler, Daniel E. "Design of single phase liquid argon detectors for dark matter searches". Thesis, Boston University, 2012. https://hdl.handle.net/2144/31557.
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Thesis (Ph.D.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
Within our current understanding of the makeup of the universe, dark matter makes up 25% of the total energy and over 80% of the matter in the universe. Little is known about the makeup of dark matter, but its existence has been indirectly measured using the rotation curves of galaxies, clusters of galaxies, and the Cosmic Microwave Background. To gain a greater understanding of this component of the universe, direct detection of dark matter is a major objective in particle astrophysics. One popular candidate for dark matter is the weakly interacting massive particle, or WIMP. The allowed rate of interaction between a WIMP and normal matter is extremely low, requiring new detection technologies with greater sensitivity to be explored. Though several experiments have already been conducted, no direct detection experiment has unambiguously identified a dark matter signal. This work explores the use of noble liquids, in a single liquid phase design, to detect single scatters of dark matter particles. The goal of current experiments is to investigate matter-dark-matter interaction cross-sections down to 10 -45 cm2 . With that in mind, the MiniCLEAN detector has been designed with a 500 kg liquid argon detector volume and will be viewed by a spherical 4π configuration of 92 photo-multiplier tubes. In order to determine the ability for single phase noble liquid to detect nuclear recoils from dark matter, several R&D experiments have been performed. These experiments undertook the measurement of how dark-matter-like nuclear recoils and background-like electronic recoils behave in liquid argon. In addition to reviewing the measurements of pulse shape discrimination and other noble liquid properties, my measurement of the scintillation efficiency is described. The scintillation efficiency characterizes the differing energy responses for nuclear and electron recoils. This was the first measurement of the scintillation efficiency in liquid argon for nuclear recoils over a wide energy range. Additionally, this work covers the design and testing of the front-end electronics and data acquisition software I developed for the MiniCLEAN experiment. This system has been designed to record and process thousands of physics events per second and has been tested using novel simulators, that I developed, that approximately represent the expected PMT signals of the MiniCLEAN detector.
2031-01-01
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Birsin, Emrah. "Searches for a Dark Matter annihilation signal with Imaging Atmospheric Telescopes". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2015. http://dx.doi.org/10.18452/17290.
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Erste Anzeichen für die Existenz von Dunkler Materie wurden 1933 entdeckt. Der Astrophysiker Fritz Zwicky beobachtete die Geschwindigkeitsverteilung im Coma Cluster und fand dabei heraus, dass 400 mal mehr Materie im Galaxie Haufen sein muss, damit dieser gravitativ gebunden sein kann oder der Galaxie Haufen würde sich aufösen. Trotz erheblicher Bemühungen über die letzten 80 Jahre ist nicht viel über Dunkle Materie bekannt. Das einzige was man weiÿ ist, dass Dunkle Materie gravitativ aber nicht elektromagnetisch wechselwirkt und Dunkle Materie stellt den gröÿten Bestandteil der Materie im Universum da. Doch derzeitige Experimente die nach Dunkler Materie suchen, sowohl direkte Suchen als auch indirekte, beginnen sensitiv genug zu werden um interessante Parameterbereiche von Dunkle Materie Kandidaten zu untersuchen wie das leichteste Super-symmetrische Teilchen, was bedeutet, dass die Entdeckung von Dunkler Materie in der nahen Zukunft sein könnte. In dieser Arbeit wird eine Signalsummierung von H.E.S.S. Zwerg Galaxien Daten durchgeführt und obere Ausschlussgrenzen berechnet. Weiterhin wird die Leistung einer Dunklen Materie Suche im galaktischen Zentrum durch CTA präsentiert für verschiedene mögliche Teleskop Anordnungen und verschiedene Annihilation Kanäle. Die Ergebnisse werden zeigen, dass CTA in der Lage sein wird geschwindigkeitsgemittelte Annihilations Wirkungsquerschnitte von 3 * 10^-26 cm^3s^1 und geringer, der geschwindigkeitsgemittelte Annihilations Wirkungsquerschnitt der für schwach wechselwirkende Dunkle Materie erwartet wird, in 100 h zu erreichen. Diese Beobachtungszeit kann innerhalb von ein bis zwei Jahren erreicht werden.First indications for the existence of Dark Matter appeared in 1933. The astrophysicist Fritz Zwicky observed the velocity dispersion of the Coma Cluster and found out that 400 times the visible mass must be contained in the galaxy cluster or the cluster could not be gravitationally bound and would disperse.Despite extensive efforts over the last 80 years not much is known about Dark Matter. The facts known are that Dark Matter interacts via gravitation, does not interact electromagneticly and is the main constituent of matter. But current experiment searching for Dark Matter directly and indirectly begin to reach sensitivities that can probe interesting parameter spaces for Dark Matter candidates like the lightest supersymmetric particle, meaning the first Dark Matter detections could happen in the near future.In this thesis a dwarf stacking analysis for Dark Matter signal search using H.E.S.S. data is performed and a upper limit is calculated. Furthermore the prospect for a Dark Matter search with CTA in the galactic center region of the Milky Way is presented for different candidate arrays and different annihilation channels. The results will show that CTA will be able to reach velocity annihilation below 3 *10^-26 cm^3s^-1, the velocity annihilation crosssection expected for a weakly interacting Dark Matter particle, within 100 h of observation which can reasonably be acquired within one to two years.
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Ingebretsen, Carlson Tom. "Characterization of the Spin of Dark Matter at the LHC". Thesis, Uppsala universitet, Högenergifysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-388421.
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The potential for characterizing the spin and mass of dark matter at the Large Hadron Collider (LHC) given a 5 sigma confidence level discovery has been studied. The search for dark matter is one of the big open question in particle physics as observations predict 84 percent of the matter in the universe to be dark matter, however no detection has been made. In this study two production channels at the LHC of weakly interacting massive particles with different spin have been studied in the framework of a simplified model. The processes if detected have the signature of a mono-jet and missing transverse energy. The assumption made is that the dark matter is a scalar or a Dirac fermion particle and interacts with the top quark and a Beyond the Standard Model color charged mediator via a loop process. The considered mediators are a scalar top partner and a fermionic top partner. The results from recasting conclude that in a narrow region in the mass-mass-plane for the dark matter and the mediator a search is adequate and given a discovery characterization of the spin and mass is possible.
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Bailey, Adam. "Dark matter searches and study of electrode design in LUX and LZ". Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/41878.
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There is substantial evidence that over 80% of matter in the universe is dark matter - which is non-baryonic in nature and is thought to be composed of a new, slow-moving, stable particle not found in the Standard Model of Particle Physics. Its presence is inferred from gravitational effects on luminous matter from several independent observations, from the galactic to the cosmological scale. Weakly Interacting Massive Particles (WIMPs) are the leading candidate, which can explain all of the observed effects. LUX and LZ are dual-phase xenon time projection chambers (TPC), aiming to observe scattering of WIMPs from xenon nuclei. LUX has an active mass of 250 kg of liquid xenon, and took data at the Sanford Underground Research Facility in Lead, South Dakota, between 2013 and 2016. The first WIMP search run of 85 live days in 2013 set world-leading exclusion limits on the spin-independent WIMP-nucleon cross section. This was improved by a reanalysis of those data, and subsequently by a new run yielding 332 live days, which set a minimum exclusion limit of 2.2 x 10⁻⁴⁶ cm² for a 50 GeV WIMP (90% CL). In addition, the most stringent limit to date on the spin-dependent WIMP-neutron scattering cross section comes from the reanalysis of the 2013 dataset, with a minimum exclusion of 9.4 x 10⁻⁴¹ cm² for a 33 GeV WIMP. LZ is a next generation experiment with a 7 tonne active mass to be deployed in the same location as LUX, expected to be 100 times more sensitive. Work presented in this thesis includes analysis of the 2013 LUX search data to produce the spin-dependent results, evaluating the detector response using a tritium β-source, and determining the 85Kr background from data. A study was carried out on spurious electron emission phenomena from thin cathodic wires under high electric fields, using LUX engineering data where the grid voltages were increased above nominal operating values; this led to new insights into the microscopic breakdown mechanisms which have affected these (and other) TPC detectors for decades. The detailed understanding of the electroluminescence response gained in LUX was applied to the design of the LZ electroluminescence region; detailed simulation work of electrode geometry was performed to assess the performance of several candidate designs.
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Wolf, Martin. "Indirect Searches for Dark Matter in the Milky Way with IceCube-DeepCore". Doctoral thesis, Stockholms universitet, Fysikum, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-128785.
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Many astronomical observations, including rotational curve measurements of stars and the analysis of the cosmic microwave background, suggest the existence of an invisible matter density content in the Universe, commonly called Dark Matter (DM). Possibly, DM could be of particle nature, where Weakly Interacting Massive Particles (WIMPs) could be a viable DM candidate. The cubic-kilometer sized IceCube neutrino observatory located at the Earth’s South Pole can search indirectly for the existence of DM by detecting neutrino signals from WIMP self-annihilation in the Galactic center (GC) and the Galactic halo (GH). Two main physics analyses were developed and conducted to search indirectly for WIMP self-annihilation in the Milky Way’s GC and GH. Signal hypotheses for different WIMP annihilation channels, WIMP masses and DM halo profiles were tested. The results of both analyses were compatible with the background-only hypothesis for all tested signal hypotheses. Thus, upper limits at the 90% confidence level (C.L.) on the thermally averaged DM self-annihilation cross-section, <σΑv>, were set. Dedicated atmospheric muon veto techniques have been developed for the GC search making such an IceCube analysis possible for the first time. The GC analysis utilized data from 319.7 days of live-time of the IceCube detector running in its 79-string configuration during 2010 and 2011, whereas the GH analysis utilized pre-existing data samples developed for point-like neutrino sources with a live-time of 1701.9 days between 2008 and 2013. The most stringent upper limits on <σΑv> were obtained for WIMP annihilation directly into a pair of neutrinos assuming a Navarro-Frenk-White (NFW) DM halo profile. Conducting the GC and GH analyses for this annihilation channel an upper limit on <σΑv> as low as 4.0 · 10-24 cm3 s-1 and 4.5 · 10-24 cm3 s-1 is set for a 65 GeV and 500 GeV massive WIMP, respectively. These galactic indirect neutrino searches for DM are complementary to the indirect gamma-ray DM searches usually performed on extra-galactic targets like spheroidal dwarf galaxies.At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript.
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Méndez, Isla Miguel Alfonso. "Dark matter searches with cosmic-ray detectors and the Square Kilometre Array". Doctoral thesis, Faculty of Science, 2020. http://hdl.handle.net/11427/32379.
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Beyond gravitational evidence for dark matter, a set of search techniques are employed in the present thesis within the particle dark matter paradigm. Under the possibility of dark matter annihilating into particles of the Standard Model of Particle Physics, we study the products of annihilation with cosmic-ray detectors, such as AMS, Fermi-LAT and PAMELA, and radio telescopes, such as the SKA. In this work, we focus on the positron fraction measured in the Solar System due to dark matter annihilating in the dark matter galactic halo, but also on radio signals from the Milky Way and dwarf spheroidal galaxies. Our main purpose is to constrain the dark matter parameter space under the light of the latest experimental data for cosmic-rays and the new sensitivities reached in radio astronomy. Furthermore, we discuss some of the most promising locations and synchrotron frequencies to search for dark matter with masses around the TeV scale. The analysis presented in this thesis lies in setting constraints on modelindependent dark matter. However, some specific dark matter candidates in the context of extra-dimensional theories are considered as well. Indeed, brane fluctuations, dubbed branons, are new degrees of freedom appearing in flexible brane-world models. These new fields behave as standard weakly interacting massive particles with a significant associated thermal relic density and would explain dark matter observational features.
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Hütten, Moritz. "Prospects for Galactic dark matter searches with the Cherenkov Telescope Array (CTA)". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2017. http://dx.doi.org/10.18452/17766.
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Die vorliegende Arbeit beschreibt einen semi-analytischen Ansatz zur Modellierung der Dichteverteilung von DM im Galaktischen Halo. Aus den verschiedenen Substrukturmodellen wird die γ-Strahlungsintensität, welche die Erde erreicht, berechnet. Eine Spannbreite plausibler γ-Strahlungsintensitäten aufgrund der Paarvernichtung Galaktischer DM wird vorgeschlagen, welche die Vorhersagen verschiedener früherer Studien umfasst, und es werden die durchschnittlichen Massen, Abstände und ausgedehnten Strahlungsprofile der γ-strahlungsintensivsten DM-Verdichtungen berechnet. Schließlich werden die DM-Modelle für eine umfassende Berechnung der Nachweismöglichkeit Galaktischer Substrukturen mit CTA verwendet. Die instrumentelle Sensitivität zum Nachweis der γ-strahlungsintensivsten DM-Substruktur wird für eine mit CTA geplanten großflächigen Himmelsdurchmusterung außerhalb der Galaktischen Ebene berechnet. Die Berechnung wird mit CTA Analyse- Software und einer Methode durchgeführt, welche auf einer Likelihood beruht. Eine alternative, ebenfalls Likelihood-basierte Analysemethode wird entwickelt, mit welcher DM-Substrukturen als äumliche Anisotropien im Multipolspektrum des Datensatzes einer Himmelsdurchmusterung nachgewiesen werden können. Die Analysen ergeben, dass eine Himmelsdurchmusterung mit CTA und eine anschließende Suche nach γ-Strahlung von DM-Substrukturen Wirkungsquerschnitte für eine Paarvernichtung in der Größenordnung von (σv) > 1 × 10−24 cm3 s−1 für eine DM-Teilchenmasse von mχ ∼ 500 GeV auf einem Vertrauensniveau von 95% ausschließen kann. Diese Sensitivität ist vergleichbar mit Langzeitbeobachtungen einzelner Zwerggalaxien mit CTA. Eine modellunabhängige Analyse ergibt, dass eine Himmelsdurchmusterung mit CTA Anisotropien im diffusen γ-Strahlungshintergrund oberhalb von 100 GeV für relative Schwankungen von CPF > 10−2 nachweisen kann.In the current understanding of structure formation in the Universe, the Milky Way is embedded in a clumpy halo of dark matter (DM). Regions of high DM density are expected to emit enhanced γ-radiation from the DM relic annihilation. This γ-radiation can possibly be detected by γ-ray observatories on Earth, like the forthcoming Cherenkov Telescope Array (CTA). This dissertation presents a semi-analytical density modeling of the subclustered Milky Way DM halo, and the γ-ray intensity at Earth from DM annihilation in Galactic subclumps is calculated for various substructure models. It is shown that the modeling approach is able to reproduce the γ-ray intensities obtained from extensive dynamical DM simulations, and that it is consistent with the DM properties derived from optical observations of dwarf spheroidal galaxies. A systematic confidence margin of plausible γ-ray intensities from Galactic DM annihilation is estimated, encompassing a variety of previous findings. The average distances, masses, and extended emission profiles of the γ-ray-brightest DM clumps are calculated. The DM substructure models are then used to draw reliable predictions for detecting Galactic DM density clumps with CTA, using the most recent benchmark calculations for the performance of the instrument. A Likelihood-based calculation with CTA analysis software is applied to find the instrumental sensitivity to detect the γ-ray-brightest DM clump in the projected CTA extragalactic survey. An alternative Likelihood-based analysis method is developed, to detect DM substructures as anisotropies in the angular power spectrum of the extragalactic survey data. The analyses predict that the CTA extragalactic survey will be able to probe annihilation cross sections of ⟨σv⟩ > 1 × 10−24 cm3 s−1 at the 95% confidence level for a DM particle mass of mχ ∼ 500 GeV from DM annihilation in substructures. This sensitivity is compatible with long-term observations of single dwarf spheroidal galaxies with CTA. Independent of a particular source model, it is found that the CTA extragalactic survey will be able to detect anisotropies in the diffuse γ-ray background above 100 GeV at a relative amplitude of CP_F > 10−2.
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Dumont, Béranger. "Higgs, supersymmetry and dark matter after Run I of the LHC". Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENY025/document.
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Deux problèmes majeurs requièrent une extension du Modèle Standard (MS) : le problème de hiérarchie dans le secteur de Higgs, et la matière noire de notre Univers. La découverte d'un boson de Higgs avec une masse d'environ 125 GeV est clairement l'événement majeur en provenance du Large Hadron Collider (LHC) du CERN. Cela représente le triomphe définitif du MS, mais cela met également en lumière le problème de hiérarchie et ouvre de nouvelles voies pour sonder la nouvelle physique. Les différentes mesures effectuées pendant le run I du LHC contraignent les couplages du Higgs aux particules du MS ainsi que les désintégrations invisibles et non-détectées. Dans cette thèse, l'impact des résultats sur le boson de Higgs au LHC est étudié dans le cadre de différents modèles de nouvelle physique, en prenant soigneusement en compte les incertitudes et leurs corrélations. Des modifications génériques à la force des couplages du Higgs (pouvant provenir de secteurs de Higgs étendus ou d'opérateurs de dimension supérieure) sont étudiées. De plus, des modèles de nouvelle physique spécifiques sont testés, notamment, mais pas seulement, le Modèle Standard Supersymétrique Minimal phénoménologique.Alors qu'un boson de Higgs a été trouvé, il n'y a toutefois nulle trace de physique au-delà du MS au run I du LHC en dépit du grand nombre de recherches effectuées par les collaborations ATLAS et CMS. Les conséquences des résultats négatifs obtenus lors de ces recherches constituent un autre volet important de cette thèse. Tout d'abord, des modèles supersymétriques avec un candidat à la matière noire sont étudiés à la lumière des résultats négatifs dans les recherches de supersymétrie au LHC, en utilisant une approche basée sur les "modèles simplifiés". Ensuite, des outils pour contraindre un modèle de nouvelle physique quelconque à partir des résultats du LHC et d'événements simulés sont présentés. De plus, au cours de cette thèse, les critères de sélection de plusieurs analyses au-delà du MS ont été réimplémentés dans le cadre de MadAnalysis 5 et ont été intégrés à une base de données publiqueTwo major problems call for an extension of the Standard Model (SM): the hierarchy problem in the Higgs sector and the dark matter in the Universe. The discovery of a Higgs boson with mass of about 125 GeV was clearly the most significant piece of news from CERN's Large Hadron Collider (LHC). In addition to representing the ultimate triumph of the SM, it shed new light on the hierarchy problem and opened up new ways of probing new physics. The various measurements performed at Run I of the LHC constrain the Higgs couplings to SM particles as well as invisible and undetected decays. In this thesis, the impact of the LHC Higgs results on various new physics scenarios is assessed, carefully taking into account uncertainties and correlations between them. Generic modifications of the Higgs coupling strengths, possibly arising from extended Higgs sectors or higher-dimensional operators, are considered. Furthermore, specific new physics models are tested. This includes, in particular, the phenomenological Minimal Supersymmetric Standard Model.While a Higgs boson has been found, no sign of beyond the SM physics was observed at Run I of the LHC in spite of the large number of searches performed by the ATLAS and CMS collaborations. The implications of the negative results obtained in these searches constitute another important part of this thesis. First, supersymmetric models with a dark matter candidate are investigated in light of the negative searches for supersymmetry at the LHC using a so-called "simplified model" approach. Second, tools using simulated events to constrain any new physics scenario from the LHC results are presented. Moreover, during this thesis the selection criteria of several beyond the SM analyses have been reimplemented in the MadAnalysis 5 framework and made available in a public database
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Garde, Lindholm Maja. "Dark Matter searches targeting Dwarf Spheroidal Galaxies with the Fermi Large Area Telescope". Doctoral thesis, Stockholms universitet, Fysikum, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-118905.
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In this thesis I present our recent work on gamma-ray searches for dark matter with the Fermi Large Area Telescope (Fermi-LAT). We have targeted dwarf spheroidal galaxies since they are very dark matter dominated systems, and we have developed a novel joint likelihood method to combine the observations of a set of targets. In the first iteration of the joint likelihood analysis, 10 dwarf spheroidal galaxies are targeted and 2 years of Fermi-LAT data is analyzed. The resulting upper limits on the dark matter annihilation cross-section range from about 10−26 cm3 s−1 for dark matter masses of 5 GeV to about 5 × 10−23 cm3 s−1 for dark matter masses of 1 TeV, depending on the annihilation channel. For the first time, dark matter models with a cross section above the canonical thermal relic cross section (∼ 3 × 10−26 cm3 s−1) are strongly disfavored by a gamma-ray experiment. In the second iteration we include 15 dwarf spheroidal galaxies in the combined analysis, employ 4 years of data and an improved calculation of the dark matter density. The obtained upper limits range from about 10−26 cm3 s−1 for dark matter masses of 2 GeV to about 10−21 cm3 s−1 for dark matter masses of 10 TeV, depending on the annihilation channel. I briefly describe some of the evidence for dark matter, the Fermi-LAT instrument and public data releases, dwarf spheroidal galaxies, likelihood analysis, and results from analyses of Fermi-LAT data. I also document some of the tests made to verify the method and to compare different analysis setups.
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Lundström, Erik. "Phenomenology of Inert Scalar and Supersymmetric Dark Matter". Doctoral thesis, Stockholms universitet, Fysikum, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-39278.
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While the dark matter has so far only revealed itself through the gravitational influence it exerts on its surroundings, there are good reasons to believe it is made up by WIMPs – a hypothetical class of heavy elementary particles not encompassed by the Standard Model of particle physics. The Inert Doublet Model constitutes a simple extension of the Standard Model Higgs sector. The model provides a new set of scalar particles, denoted inert scalars because of their lack of direct coupling to matter, of which the lightest is a WIMP dark matter candidate. Another popular Standard Model extension is that of supersymmetry. In the most minimal scenario the particle content is roughly doubled, and the lightest of the new supersymmetric particles, which typically is a neutralino, is a WIMP dark matter candidate. In this thesis the phenomenology of inert scalar and supersymmetric dark matter is studied. Relic density calculations are performed, and experimental signatures in indirect detection experiments and accelerator searches are derived. The Inert Doublet Model shows promising prospects for indirect detection of dark matter annihilations into monochromatic photons. It is also constrained by the old LEP II accelerator data. Some phenomenological differences between the Minimal Supersymmetric Standard Model and a slight extension, the Beyond the Minimal Supersymmetric Standard Model, can be found. Also, supersymmetric dark matter models can be detected already within the early LHC accelerator data.
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Chagani, Hassan. "Studies of the responses of liquid and solid targets for direct dark matter searches". Thesis, University of Sheffield, 2008. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.489361.
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The quenching factor for sodium recoils in a 2-inch Nal(Tl) scintillating crystal has been measured at room temperature. The crystal has been exposed to 2.45 MeV monoenergetic neutrons generated by a deuterium-deuterium fixed target accelerator in the energy range 10 to 100 keV nuclear recoil energy. A BC501A liquid scintillator detector has been used to tag neutrons that scatter off sodium nuclei in the crystal. Cuts on pulse shape discrimination in BC501A and neutron time of flight have been performed on pulses recorded by an Acqiris DC265 digitiser with a 2 ns sampling time. A quenching factor of 25.2 ± 6.4% has been determined for 10 keV sodium recoils. Measured quenching factors range from 19% to 26% in good agreement with other experiments. From pulse shape analysis, the mean time of pulses from electron and nuclear recoils have been compared down to 2 keV electron equivalent energy.
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Buchholz, Annika [Verfasser]. "Various Aspects of Astroparticle Physics and the Implications for Dark Matter Searches / Annika Buchholz". Bonn : Universitäts- und Landesbibliothek Bonn, 2020. http://d-nb.info/1218301287/34.
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Doro, Michele. "Novel Reflective Elements and Indirect Dark Matter Searches for MAGIC II and future IACTs". Doctoral thesis, Università degli studi di Padova, 2009. http://hdl.handle.net/11577/3425635.
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During the PhD I made my research following two principal research activities: a technological part relative to the development and the production of reflective units for the second MAGIC telescope and a second part more scientific, focused on strategy of indirect detection of dark matter with the MAGIC telescope.Durante la Scuola di Dottorato ho svolto la mia ricerca seguendo due attivita' principali: una parte tecnologica relativa allo sviluppo e la produzione di unita' riflettenti per il secondo telescopio MAGIC ed una parte maggiormente scientifica sulle strategie di rivelazione indiretta di Materia Oscura con il Telescopio MAGIC.
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Wahl, David. "Optimisation of light collection in inorganic scintillators for rare event searches". Thesis, University of Oxford, 2005. http://ora.ox.ac.uk/objects/uuid:c41d6500-c513-405f-926f-547a588aa1da.
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Inorganic scintillators are playing an ever increasing role in the search for rare events. Progress in the use of cryogenic phonon-scintillation detectors (CPSD) has allowed for a rapid increase in sensitivity and resolution of experiments using this technique. It is likely that CPSD will be used in future dark matter searches with multiple scintillator materials. Further improvements in the performance of CPSD can be expected if the amount of light collected is increased. In this thesis, two approaches are used to look at ways of maximising the amount of light collected in CPSD modules. The first approach is to obtain a detailed understanding of the spectroscopic properties in the crystal to identify ways of increasing their scintillation intensity. The second is to simulate the light collection properties using a Monte-Carlo simulation program. This requires a detailed understanding of the optical properties of inorganic scintillators and obtaining this information is the focus of the current work. Two new methods have been developed to evaluate the scintillation decay time and the intrinsic light yield of scintillators. These methods are tested on CRESST CaWO4 crystals so that all the input parameters necessary for the simulation of CRESST modules is available. These input parameters are used to successfully explain features of the light collection in CRESST CPSD modules and to suggest possible improvements to the design of the modules. In summary, the current work has contributed to the development of a standardised method to maximise the light yield that can be obtained from CPSD for application to rare event searches.
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El, Aisati Chaimae. "Gamma-ray and Neutrino Lines from Dark Matter: multi-messenger and dedicated smoking-gun searches". Doctoral thesis, Universite Libre de Bruxelles, 2018. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/266180.
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Identifying what makes up the Dark Matter is a long-standing problem to which the abundance of gravitational and cosmological evidence fails to answer. Indirect detection techniques have the aim to unveil the nature of Dark Matter by catching and identifying the products of potential decays and/or annihilations. The work exposed in this thesis is in line with this strategy and has for common thread the quest for line(-like) features in the extraterrestrial fluxes of gamma-rays and neutrinos. The motivation behind this specific interest is that, due to the absence of astrophysical counterparts beyond the GeV scale, these features constitute the ultimate probes (also called “smoking guns”) of the existence of Dark Matter.The thesis is organized in three Parts, the first of which is an introduction to the different facets of the Dark Matter conundrum and why it is not a trivial issue. The works involving gamma-ray line considerations are gathered in Part II, and those exclusively focusing on neutrino lines in Part III.Part II focuses on the effective field theory of Dark Matter decay, first in the context of millicharged particles decaying to gamma-ray lines, and then in the context of (neutral and millicharged) Dark Matter decays involving the simultaneous emission of gamma-ray and neutrino lines. In both cases, the simultaneous emission of cosmic rays is unavoidable and the decays are constrained in a multi-messenger fashion. The complementarity of the results obtained is used to derive model-independent constraints on the Dark Matter lifetime, and shows the possibility to exclude or distinguishsome specific scenarios on the basis of an explicit experimental conjecture.After an introduction to the neutrino detection principles and to the operation of the IceCube detector, Part III focuses on two careful searches for spectral features in the neutrino spectrum. The main goal behind these analyses, conducted in two different regions of the energy spectrum but using the same likelihood ratio procedure, is to popularize dedicated energy distribution studies by showing their ability to reach sensitivity levels comparable to—sometimes even going beyond—those obtained with angular distribution studies or even in the context of gamma-ray line searches.Option Physique du Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Wiebe, Klaus [Verfasser]. "All-flavor based searches for solar dark matter with the IceCube Neutrino Observatory / Klaus Wiebe". Mainz : Universitätsbibliothek Mainz, 2017. http://d-nb.info/1124030700/34.
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Ali, Cavasonza Leila [Verfasser], Michael [Akademischer Betreuer] Krämer i Stefan [Akademischer Betreuer] Schael. "Searches for leptophilic dark matter with astrophysical experiments / Leila Ali Cavasonza ; Michael Krämer, Stefan Schael". Aachen : Universitätsbibliothek der RWTH Aachen, 2016. http://d-nb.info/1130590267/34.
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BOSSA, MARIA. "Low-mass dark matter and neutrino-less double beta decay searches with tha darkside technology". Doctoral thesis, Gran Sasso Science Institute, 2019. http://hdl.handle.net/20.500.12571/9561.
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The DarkSide program has delivered the first results on searches for dark matter with a target of ultra-pure
low-radioactivity argon from underground sources (UAr) with the DarkSide-50 experiment, in operation at
LNGS since 2013. The key element provided by the use of UAr is the strong reduction in activity of 39Ar
relative to the atmospheric argon, which avoids the pile-up of events that would otherwise plague any argonbased events at the tonne scale and beyond. Thus the use of UAr enables the construction of very large
scale dark matter detectors, able to combine the advantages of the unsegmented design and very strong
rejection of electron recoils a↵orded by the pulse shape discrimination of liquid argon, thus able to probe
the entire discovery space at high masses (>100 GeV/c2) prior to and through the onset of background
from atmospheric neutrinos (the so called “neutrino floor”) in absence of any background from instrumental
sources.
The DarkSide Collaboration, which launched the DarkSide-50 program at LNGS, morphed to become the
“Global Argon Dark Matter Collaboration” (GADMC). The GADMC started a program for the complete
exploration of the discovery space of high-mass dark matter consisting of the DarkSide-20k experiment, at
the scale of a few tens of tonnes, that is going to be constructed at LNGS and expected in operation by 2023,
and Argo, at the scale of a few hundred tonnes, and proposed for installation at SNOLAB.
The full exploitation of the UAr target for high-mass dark matter searches required the development of very
special technologies. The GADMC developed special photodetector modules (PDMs) made of assemblies
of silicon photomultipliers (SiPMs) and characterized by very high photon detection eciency, background
much lower than traditional photomultiplier tubes (PMTs), and dark noise lower than that of PMTs when
operated near a temperature of 87 K. The GADMC also developed a special plan for the high-throughput
extraction of UAr at special gas wells in Colorado, USA, with the Urania plant and for its purification in the
novel cryogenic distillation column Aria, characterized by the presence of thousands of equilibrium stages
and currently under installation in a mine shaft in Sardinia, Italy. The Aria column with its unprecedented
height may be able to provide further isotopic depletion in 39Ar of the UAr target.
Exploration of high-mass dark matter is one of the main thrusts for the discovery of new physics beyond
the standard model. In this dissertation, I will focus on the possible use of the DarkSide technology to tackle
two di↵erent but equally crucial problems, which may also lead to new discoveries: the search for low-mass
(<10 GeV/c2) dark matter and the search for the neutrinoless double beta decay
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Arcadi, Giorgio. "Interplay between Generation Mechanisms and Detection of Supersymmetric Dark Matter in the LHC Era". Doctoral thesis, SISSA, 2012. http://hdl.handle.net/20.500.11767/3866.
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The object of this thesis is the study of several, possibly complementary, aspects of generation mechanism and detection of the two dark matter (DM) candidates provided by the Minimal Supersymmetric extension of the Standard Model (MSSM), i.e. the gravitino and the neutralino. We have first of all focused on the generation mechanism of neutralino dark matter, examining the possible consequences of relaxing some of the hypothesis on which the typically adopted thermal WIMP paradigm relies. We have, indeed, considered non-thermal dark matter production scenarios motivated, in the context of Supersymmetric theories, in supergravity and superstring frameworks. These classes of theories often feature the presence of long-lived states capable of dominating the energy budget of the Universe at early stages before possibly decaying into dark matter particles. Non thermal production have been studied in a systematic way by mean of a numerical code developed for this purpose. In particular the impact in selecting a preferred mass scale for the Dark matter and, consequently, the impact on the interpretation of new physics discovered or excluded at LHC have been discussed.
The second aspect of neutralino dark matter generation which has been investigated
is the assumption of kinetic equilibrium during the whole phase of dark matter
generation and the validity of the factorization usually implemented to rewrite the
system of coupled Boltzmann equation for each coannihilating species as a single
equation for the sum of all the number densities. To this purpose has been developed
and numerically implemented a formalism for the computation of the kinetic
decoupling temperature in the case of coannhilating particles. This formalism has
been applied to a definite scenario referred as G2-MSSM. The next topic discussed in this thesis, remaining in the context of neutralino DM, is the capability of current and next generation direct detection experiments of probing the MSSM parameter space. Focusing on some definite setups, satisfying the cosmological bounds on the DM relic density and the current particle physics constraints, the possibility for them of producing direct detection signals has been inspected through Montecarlo Simulations. The final purpose of this analysis is to show as indications about the DM properties, as provided by an experimental detection, can influence some features of the underlying Supersymmetric model which can be probed in the next future by LHC. We have finally moved the focus to the other dark matter candidate within the MSSM, i.e. the gravitino. Remarkably it is a viable dark matter candidate also in presence of R-parity violation. Gravitino dark matter have been studied in the context of a class of Supersymmetric models referred as Tree-Level Gauge Mediation (TGM). These models provide rather definite predictions for the mass of the dark matter being it related to the mechanism of mediation of SUSY breaking. In particular has been investigated a realization of TGM predicting a gravitino mass in the range 10-100 GeV. Cosmological bounds have been investigated both in presence and in absence of R-parity. The model results disfavored in case the R-parity holds, being in severe tension with Big Bang Nucleosynthesis; on the contrary is naturally feasible in presence of a small amount of R-parity violation.
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Marzioni, Maria Francesca. "Axion dark matter and two-neutrino double electron capture searches in the Large Underground Xenon experiment". Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31054.
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The hunt for Dark Matter plays a truly critical role in contemporary physics. At both the largest and smallest scales, deep questions are being raised about the fundamental nature of the universe - questions that confirmation and then characterisation of particle dark matter will provide many answers to. This thesis presents some of the world's most sensitive searches to date for certain types of axion dark matter, axion-like particles, and two-neutrino double electron capture. These have been conducted using the Large Underground Xenon (LUX) experiment. Evidence for dark matter and physics beyond the Standard Model of particle physics is described in Chapter 1, while Chapter 2 gives an overview of proposed candidates for particle dark matter. The various experimental approaches being used to detect particle dark matter are presented in Chapter 3. Direct detection with time projection chambers plays a major role in this thesis, with particular interest in the LUX detector, that is described in its components and operations. Chapter 4 presents LUX direct searches for weakly interacting massive particles. Although I have contributed to these analyses, they are included for completeness only, as they are not part of my central work. The LUX collaboration's searches for axion dark matter and axion-like particle have delivered world-leading results on the axion-electron coupling constant. These results, that I personally led and which have been published in Physics Review Letters, are presented in Chapter 5, along with sensitivity studies, also led by me, made for the future LUX-ZEPLIN experiment. Finally, a search for two-neutrino double electron capture of 124Xe, that I performed using LUX data to extract a limit on the half life of the process, is presented in Chapter 6. Although being allowed by the Standard Model, two-neutrino double electron capture shares the matrix element calculation framework with the neutrinoless channel of the same process, becoming of great interest in the scope of neutrino physics. Conclusions follow and close the thesis.
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Olzem, Jan. "Signatures of SUSY dark matter at the LHC and in the spectra of cosmic rays". [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=984327568.
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Dienes, Keith R., Shufang Su i Brooks Thomas. "Beyond the bump-hunt: A game plan for discovering dynamical dark matter at the LHC". AMER INST PHYSICS, 2016. http://hdl.handle.net/10150/621546.
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Dynamical Dark Matter (DDM) is an alternative framework for dark-matter physics in which an ensemble of individual constituent fields with a spectrum of masses, lifetimes, and cosmological abundances collectively constitute the dark-matter candidate, and in which the traditional notion of dark-matter stability is replaced by a balancing between lifetimes and abundances across the ensemble. In this talk, we discuss the prospects for distinguishing between DDM ensembles and traditional dark-matter candidates at hadron colliders - and in particular, at the upgraded LHC - via the analysis of event-shape distributions of kinematic variables. We also examine the correlations between these kinematic variables and other relevant collider variables in order to assess how imposing cuts on these additional variables may distort - for better or worse - their event-shape distributions.