The EDELWEISS experiment is one of the dark matter direct detection experiments. It aims to detect WIMP interactions using an array of cryogenic germanium detectors. In the previous EDELWEISS-II phase, the cables and connectors used have been identified as a major source of neutron background in the experiment, which means that further effort aimed at better WIMP-nucleon interaction detection sensitivity requires a new, different cold cabling solution connecting the detectors to the front-end electronics. Motivated by this, a new two-section cold cabling system based on semi-flexible laminated copper and stainless steel cables has been developed for the EDELWEISS- III phase at Oxford. Batches of prototypes have been tested first in a cryostat at Oxford as part of a phonon-scintillation detector module, and then at the LSM underground laboratory in several EDELWEISS-III commissioning runs. Following that, a final set of cabling has been produced and installed in the EDELWEISS-III setup, which is currently conducting a science run aiming to improve its sensitivity reach compared to the previous results. This new cold cabling system has shown similar electrical performance as the previous coaxial cabling when comparing different cold cabling configurations in a commissioning run at LSM. Also, its background contribution is within the EDELWEISS-III requirements, according to radioactivity level tests and Monte Carlo simulations. In addition, the assembled connectors have allowed hundreds of signal tracks to be installed within a few days and the low material and space budget has made the cables compatible with the compact cryostat design. Besides reading out detectors for dark matter detection, prototypes of this cabling solution for a wider application range have also been produced at Oxford. The next generation dark matter direct detection experiments aim to achieve detection sensitivity better by a few orders of magnitude. This requires a target mass at tonne-scale, which converts to thousands of cryogenic detectors. Cryogenic phonon-scintillation detectors used in current dark matter searches can provide excellent performance but they usually require individual tuning and attention, making operation in large-scale experiments difficult. It is also technically challenging to stably produce such detectors in large quantity. Therefore, a scalable, robust novel detector concept for cryogenic phonon- scintillation detectors to be used in future rare event search experiments has been developed in this work. This detector module consists of a phonon detector based on a CaMoO4 scintillating crystal as the target with an attached NTD-Ge sensor as the thermometer, and a light detector based on a low-temperature PMT. To provide the high voltage necessary for PMT operation while ensuring the detector module can be cooled down and that the performance of the phonon detector is unaffected, a high voltage supply system based on a Cockcroft-Walton generator (CWG), a transformer and a small AC input has been designed and tested in the cryostat. The laminated cabling system is chosen for reading out the phonon channel and connecting the CWG and the PMT. A test run has demonstrated that, the high voltage can be provided to the PMT without causing a problem to the detector operation, and it is feasible to operate the low-temperature PMT at a temperature as low as 17 mK. Testing with a cobalt-57 gamma source, the phonon detector and the light detector have achieved resolutions of 1.07 keV and 34.2 keV for the 122.06 keV peak respectively. This is close to the performance of detectors used in the current dark matter direct searches, proving this detector concept can be applied to future large-scale dark matter direct detection experiments and other rare event searches. Using the light channel in this detector setup, the scintillation properties of CaMoO4 has been studied. In this work, the experimental data of its scintillation decay time constant has been extended from the previous 7 K to milli-Kelvin temperatures. The data are interpreted using a three-level model, confirming the existence of a metastable emission level in CaMoO4, and giving various parameters of its emission centre. This suggests that the work related to producing a high voltage supply and demonstrating the excellent performance of a low-temperature PMT could also be attractive to scintillator studies at cryogenic temperatures.

Philosophiae Doctor - PhD / Numerical simulations play a crucial role in testing current cosmological models of the formation and evolution of the cosmic structure observed in the modern Universe. Simulations of the collapse of both baryonic and non-baryonic matter under the influence of gravity have yielded important results in our understanding of the large scale structure of the Universe. In addition to the underlying large scale structure, simulations which include gas dynamics can give us valuable insight into, and allow us to make testable predictions on, the nature and distribution of baryonic matter on a wide range of scales. In this work we give an overview of cosmological simulations and the methods employed in the solution of many body problems. We then present three projects focusing on scales ranging from individual galaxies to the cosmic web connecting clusters of galaxies thereby demonstrating the potential and diversity of numerical simulations in the fields of cosmology and astrophysics. We firstly investigate the environmental dependance of neutral hydrogen in the intergalactic medium by utilising high resolution cosmological hydrodynamic simulations in Chapter 3. We find that the extent of the neutral hydrogen radial profile is dependant on both the environment of the galaxy and its classification within the group ie. whether it is a central or satellite galaxy. We investigate whether this effect could arise from ram pressure forces exerted on the galaxies and find good agreement between galaxies experiencing high ram pressure forces and those with a low neutral hydrogen content. In Chapter 4 we investigate the velocity–shape alignment of clusters in a dark matter only simulation and the effect of such an alignment on measurements of the kinetic Sunyaev–Zeldovich (kSZ) effect. We find an alignment not only exists but can lead to an enhancement in the kSZ signal of up to 60% when the cluster is orientated along the line-of-sight. Finally we attempt to identify shocked gas in clusters and filaments using intermediate resolution cosmological hydrodynamic simulations in Chapter 5 with a view to predicting the synchrotron emission from these areas, something that may be detectable with the Square Kilometer Array.

We present a detailed strong lensing (SL) mass reconstruction of the core of the galaxy cluster MACS J2129.4-0741 (z(cl) = 0.589) obtained by combining high-resolution Hubble Space Telescope photometry from the CLASH (Cluster Lensing And Supernovae survey with Hubble) survey with new spectroscopic observations from the CLASH-VLT (Very Large Telescope) survey. A background bright red passive galaxy at z(sp) = 1.36, sextuply lensed in the cluster core, has four radial lensed images located over the three central cluster members. Further 19 background lensed galaxies are spectroscopically confirmed by our VLT survey, including 3 additional multiple systems. A total of 31 multiple images are used in the lensing analysis. This allows us to trace with high precision the total mass profile of the cluster in its very inner region (R < 100 kpc). Our final lensing mass model reproduces the multiple images systems identified in the cluster core with high accuracy of 0.4 arcsec. This translates to a high-precision mass reconstruction of MACS 2129, which is constrained at a level of 2 per cent. The cluster has Einstein parameter Theta(E) = (29 +/- 4) arcsec and a projected total mass of M-tot (< Theta(E)) = (1.35 +/- 0.03) x 10(14) M-circle dot within such radius. Together with the cluster mass profile, we provide here also the complete spectroscopic data set for the cluster members and lensed images measured with VLT/Visible Multi-Object Spectrograph within the CLASH-VLT survey.

Orientador: Pedro Cunha de Holanda / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-24T10:31:04Z (GMT). No. of bitstreams: 1 Miguez_BrunoSilvaRodriguez_D.pdf: 3341752 bytes, checksum: 929d02bdf7d42cd3826d597a0b6ceca8 (MD5) Previous issue date: 2014 / Resumo: Uma das grandes fronteiras da física atual é a identificação da Matéria Escura, que seria responsável por cerca de 25% da densidade do universo. Diversos candidatos a Matéria Escura foram propostos, entre eles os WIMPs (Weakly Interacting Massive Particle). A Colaboração Xenon tem como objetivo a detecção direta de matéria escura através de colisões elásticas com núcleos de xenônio, monitorados em uma câmara de projeção temporal. Os primeiros detectores da colaboração Xenon (Xenon10 e Xenon100) obtiveram grande sucesso impondo os limites mais restritivos para seção de choque WIMP-nucleon quando foram publicados seus resultados. Atualmente o terceiro detector da colaboração, o Xenon1T, está em construção e é esperado que ele verifique seções de choque até duas ordens de grandeza abaixo dos limites atuais. O Xenon1T possuirá um sistema de veto ativo, o Water Tank. A câmara de projeção temporal do Xenon1T será localizada dentro de um detector que busca, através da detecção de outros produtos, identificar nêutrons rápidos produzidos através da interação de múons com as rochas ou estrutura ao redor do detector. As paredes internas do Water Tank são cobertas com uma folha refletora DF2000MA para aumentar a captação de luz. Nesta tese foi estudada a taxa de eventos gerada pela resposta da folha DF2000MA à radioatividade do aço que compõe a estrutura do Water Tank e seu impacto no funcionamento do sistema de veto. A taxa destes eventos que gerariam um sinal no Water Tank seria da ordem de 10-4 Hz, muito abaixo da taxa de operação planejada para o Water Tank (? Hz), não sendo portanto um problema. Outro estudo realizado foi sobre o sinal gerado por neutrinos de supernovas através de espalhamento coerente com os núcleos. Supernovas próximas seriam responsável por menos de 10 eventos concentrados em poucos segundos, muito distintos do fundo esperado de recuos nucleares no Xenon1T, da ordem de 0.1 por ano. Sendo o sinal de uma supernova facilmente reconhecido durante a análise / Abstract: Actually an important frontier on physics is the Dark Matter identification. The Dark Matter is responsible for 80% Universe matter density on Universe. Different Dark Matter candidates have been proposed, among them the WIMPs (Weakly Interacting Massive Particle). The Xenon Collaboration have as goal the direct detection of Dark Matter by observation of elastic scattering on xenon nuclei. The first two Xenon phases achieved great sucess with the most constraining limits on WIMP-nuclei cross section at publishing time. Today the third detector (Xenon1T) is under construction and it expect to probe cross section two orders below the actual limits. One big difficult to increase the detector mass is the signal to noise ratio. The Xenon detectors keep record of excitation and ionization energy ratio to discriminate between electronic recoils and nuclear recoils. WIMPs should cause nuclear recoil by coherent elastic scattering on atomic nuclei. The nuclear recoil selection allows a huge increase on sensibility, once the background rate due to nuclear recoil on Xenon1T is five orders lower than the eletronic recoil one. Neutrinos and neutrons can produce nuclear recoils mimicating the WIMP signal. The Xenon1T will have an active veto system, the Water Tank. The Xenon1T time projection chamber will be placed inside a water tank monitored by photomultipliers. It will detect subproducts of muon interactions on rocks around the detector and tag the nuclear recoil due to fast neutrons produced by muons. To increase the light capture in the internal walls of Water Tank will be covered by a reflective foil, the DF2000MA. We studied the event rate due to the DF2000MA response to the alpha radioactivity of structural steel and its impact on veto system. The rate of these events that would generate a signal in veto system obtained by us was around 10-4 Hz, much lower than the operational planned rate (? Hz). Then this response will not be a problem to veto system. Another study was about the supernova neutrinos signal on Xenon1T. Neutrinos can produce nuclear recoils by coherent elastic scattering, mimicating the WIMP signal. We obtained ? 10 events due to a supernova at 8.5 kpc. Furthermore these events would be concentrated in seconds, much different from the Xenon1T nuclear recoil background (? 0.1/year). Then the supernova neutrino signal would be easilly recognized on analysis level / Doutorado / Física / Doutor em Ciências

In this dissertation, a low energy theory approach is applied to the studies of Dark Matter direct detection experiments and two-dimensional Quantum Chromodynamics (QCD) spectra. We build a general framework of non-relativistic effective field theory of Dark Matter direct detection using non-relativistic operators. Any Dark Matter particle theory can be translated into the coefficients of an effective operator and any effective operator can be related to a most general description of the nuclear response. Response functions are evaluated for common Dark Matter targets. Based on the effective field theory we perform an analysis of the experimental constraints on the full parameter space of elastically scattering Dark Matter. We also formulate an analytic approach to solving two-dimensional gauge theories. We find that in theories with confinement, in a conformal operator basis, the decoupling of high scaling-dimension operators from the low-energy spectrum occurs exponentially fast in their scaling-dimension. Consequently the low-energy spectrum of a strongly coupled system like QCD can be calculated using a truncated conformal basis, to an accuracy parametrized exponentially by the cutoff dimension. We apply the conformal basis approach in two models, a two-dimensional QCD with an adjoint fermion at large N, and a two-dimensional QCD with a fundamental fermion at finite N. It is shown that the low energy spectrum converges efficiently in both cases.

Uncovering the nature of dark matter is one of the most pressing problems in 21st century cosmology. Despite overwhelming evidence that dark matter exists and vigorous experimental efforts to detect it, dark matter has evaded detection and its fundamental nature remains shrouded in mystery. Indirect dark matter detection experiments search for Standard Model byproducts of dark matter annihilation or decay. At low energies, cosmic antideuterons provide an especially clean dark matter signature, since the production of low-energy antideuterons from conventional astrophysical processes is highly suppressed. The General Antiparticle Spectrometer (GAPS) is an Antarctic balloon experiment designed to search for low-energy cosmic antinuclei as signatures of dark matter. GAPS is optimized to detect low-energy antideuterons, as well as to provide unprecedented sensitivity to low-energy antiprotons and antihelium nuclei. GAPS uses a novel approach to detect antinuclei, based on the formation, decay, and annihilation of exotic atoms. At least three GAPS long-duration balloon (LDB) flights are planned, with the first launch date anticipated for December 2022. The core of the GAPS instrument is a particle tracker, comprised of >1000 lithium-drifted silicon (Si(Li)) detectors, that provides particle tracking and X-ray spectroscopy capabilities. In order to preserve the long-term performance of the tracker, the Si(Li) detectors require a surface passivation coating to protect against environmental contamination. In this thesis, I cover four main areas of my research: prototype Si(Li) detector fabrication and performance evaluation; development of a surface passivation technique to ensure the long-term stability of GAPS flight detectors; calculation of the GAPS antihelium sensitivity using particle tracking; and prediction of the antihelium exotic atom X-ray energies and yields for future identification studies. I discuss the prototype fabrication work that was carried out at Columbia, which led to the successful mass-production of large-area Si(Li) detectors for the GAPS LDB flights. I report the research and development of a surface passivation method to protect the GAPS flight detectors from environmental contamination. I then describe the calibration scheme for the GAPS Si(Li) detectors, and a simulation study that I conducted to disentangle the contribution of Compton scattering and intrinsic detector performance on the observed spectra. I then move on to discuss the simulation studies used to determine the performance capabilities of GAPS. I describe the benchmarking of the hadronic annihilation products in antinucleus-nucleus annihilations in Geant4. I review the exotic atom cascade model used to determine the X-rays produced by antiprotonic and antideuteronic exotic atoms, and discuss my work extending this model to describe the de-excitation of antihelium exotic atoms. Finally, I present the first GAPS antihelium nuclei sensitivity study, based on full instrument simulation, event reconstruction, and realistic atmospheric influence simulations.

Data collected at the LHC are analyzed by the ATLAS collaboration for evidence of dark matter. In this thesis, a fast simulation of the ATLAS detector response using the Delphes software is assessed for dark matter models with a leptonically decaying Z boson and a pair of dark matter particles in the final state. Limits for the Two Higgs Doublet plus pseudoscalar dark matter model are obtained using simplified systematics, and found to be nearly indistinguishable to limits obtained using the more complex standard ATLAS analysis. / Graduate

Cela fait plus de 80 ans que nous avons des preuves qu'environ 26% de la densité d'énergie de l'univers actuel se présente sous la forme de matière noire, qui interagit avec la matière ordinaire strictement par gravitation. Avec les neutrinos massifs, l’existence de particules de matière noire (DM) indique qu’il faut étendre le modèle standard de la physique des particules (SM) pour en tenir compte. Dans cette thèse, nous explorons la relation étroite entre la nature des couplages reliant la DM aux particules du SM et la production de l'abondance de la DM dans l'univers primordial. Nous commençons par examiner la classe la plus prédictive de candidats DM, les particules massives à interaction faible (WIMP). Leurs masses et couplages sont comparables à ceux du SM, et donc les deux secteurs ont déjà été en équilibre thermique, et l'abondance de DM respecte automatiquement les limites cosmologiques -- le "miracle WIMP". Les limites expérimentales actuelles repoussent l'espace paramétrique viable des modèles WIMP vers des limites complexes, rendant nécessaire l'ajout de particules supplémentaires dans le secteur sombre et la vérification plus précise de la condition de découplage. Après avoir considéré le statut phénoménologique d'une gamme significative de modèles pour les WIMP avec des masses dans l'intervalle 10-10⁴ GeV, nous examinons la phénoménologie d'une DM sur l'échelle MeV dans un modèle de portail Z'. En plus de chercher à améliorer la recherche de WIMPs, il convient de considérer le cas dans lequel DM et SM interagissent si faiblement qu’ils n’ont jamais atteint l’équilibre. Les particules massives à interaction faible (FIMP) sont des candidats DM produits à partir du SM dans des processus hors d'équilibre, un mécanisme appelé freeze-in. Nous montrons que si des champs lourds (10¹⁰-10¹⁶ GeV) interviennent dans les interactions DM-SM, le freeze-in est une possibilité naturelle qui fournit la bonne abondance de DM sans qu'il soit nécessaire d'imposer couplages extrêmement petits. Ces champs lourds sont en fait nécessaires dans des scénarios à hautes énergies théoriquement bien motivés tels que le GUT, le see-saw, la leptogénèse et l’inflation -- nous appelons cette coïncidence intéressante la "merveille FIMP". Nous explorons différentes réalisations de cette possibilité, avec des modèles impliquant des moduli, fermions, bosons de jauge et champs de spin-2 comme les médiateurs lourds. Nous montrons enfin dans quels cas la production de DM pendant le reheating après inflation a un impact sur l’espace paramétrique de tels modèles. / For more than eighty years, we face evidence that about 26% of the energy budget of the universe today is in the form of dark matter, whose interaction with ordinary matter is felt only gravitationally. Along with massive neutrinos, the existence of dark matter particles (DM) indicate that we must extend the standard model of particle physics (SM) in order to account for them. In this thesis, we explore the close relationship between the nature of couplings connecting DM to the SM sector and the production of the DM relic density in the Early Universe. We start by considering the most predictive class of DM candidates, the weakly interacting massive particles (WIMPs). Their masses and couplings are comparable to the SM ones, which ensure that both sectors were once in thermal equilibrium and automatically render the DM relic density within the inferred range -- the so-called "WIMP miracle". The current experimental bounds push the viable parameter space of WIMP models to complex corners, making necessary to add extra particles in the dark sector and to check the decoupling condition more carefully. After reviewing the phenomenological status of a comprehensive spectrum of models for WIMPs with masses in the range 10-10⁴ GeV, we consider the challenging phenomenology of an MeV DM in a Z' portal model. Besides seeking to improve the search for WIMPs, it is worth considering the case in which DM and SM interact so feebly that they had never reached equilibrium. Feebly interacting massive particles (FIMPs) are DM candidates produced from the SM thermal bath in out-of-equilibrium processes, a mechanism called freeze-in. We show that if heavy fields (10¹⁰-10¹⁶ GeV) mediate the DM-SM interactions, the freeze-in is a natural possibility that provide the right amount of DM in the universe without the need of extremely small gauge, yukawa or quartic couplings. Such heavy fields are actually needed in theoretically well motivated high-energy scenarios like for instance GUT, seesaw, leptogenesis and inflation -- we call this interesting coincidence the "FIMP wonder". We explore different realizations of such possibility, with models involving moduli, fermions, gauge bosons and spin-2 fields as heavy mediators. We finally show in which cases the DM production during reheating have impact on the parameter space of such models.

Dark Matter (DM) is believed to consist ofWeakly Interactive Massive Particles (WIMPs) which interact only through gravity and the weak nuclear force. These particles can become trapped in gravitational wells such as the Sun and a theoretical value of the capture rate can be calculated. At high particle density the WIMPs annihilating spontaneously into Standard Model (SM) particles. Due to particle equilibrium the total annihilation rate can be related to the capture rate by a simple expression. This report will focus on calculating the capture rate and the related annihilation rate as well as calculating the neutrino 　ux of the Sun. At rst we will give a brief introduction to cosmology and a theoretical argument for the WIMPs as the prime DM candidate. Then we will look at the theoretical background and the mechanism through which WIMPs become trapped and evaporate or annihilate. Finally we will perform a numerical analysis of the WIMP cycle within the Sun and calculate the capture rate for a variety of theoretical WIMP masses. We will look at the capture rate due to scattering both by hydrogen nucleii and by more massive elements. The Scattering by hydrogen will be the prime contributor to the total capture rate and is the only spin dependent contribution.

There is by now compelling evidence that most of the matter in the universe is in the form of dark matter, a form of matter quite different from the matter we experience in every day life. The gravitational effects of this dark matter have been observed in many different ways but its true nature is still unknown. In most models dark matter particles can annihilate with each other into standard model particles. The direct or indirect observation of such annihilation products could give important clues for the dark matter puzzle. For signals from dark matter annihilations to be detectable, typically high dark matter densities are required. Massive objects, such as stars, can increase the local dark matter density both via scattering off nucleons and by pulling in dark matter gravitationally as the star forms. Dark matter annihilations outside the star would give rise to gamma rays and this is discussed in the first paper. Furthermore dark matter annihilations inside the star would deposit energy inside the star which, if abundant enough, could alter the stellar evolution. Aspects of this are investigated in the second paper. Finally, local dark matter overdensities formed in the early universe could still be around today; prospects of detecting gamma rays from such clumps are discussed in the third paper. / Introduktionsdelen till en sammanläggningsavhandling