Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

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Un des principaux objectifs de l'expérience ATLAS auprès du LHC est l'observations ou l'exclusion de nouvelle physique au-delà du Modèle Standard, en passant par les mesures de sections efficaces de production de processus du Modèle Standard. Sachant que le taux de production d'une particule dépends de sa section efficace de production ainsi que de la luminosité, il est necessaire de mesurer cette luminosité avec une grande précision. L'expérience ATLAS possède plusieurs détecteurs capable de mesurer la luminosité, dont les deux principaux: LUCID (Luminosity measurement Using Cerenkov Integrating Detector), et BCM (Beam Condition Monitor). Ces détecteurs sont calibrés absolument pendant des prises de données dédiées appelés van der Meer scans, qui ont permis d'obtenir une erreur systématique sur la détermination de la luminosité de 3.4% en 2010. Afin d'obtenir un maximum de différentes approches à la luminosité, plusieurs autres détecteurs contribuent aux différentes comparaisons. Ce document présente les calorimètres à argon liquide du détecteur ATLAS, et en particulier la mise en route et l'opération de leur système haute-tension. Il est montré qu'en mesurant les courant de ce système haute-tension pendant les prises de données de collisions de protons, il est possible d'obtenir des signaux proportionnels a la luminosité. En calibrant ces courants par rapport a un autre luminomètre, il est montré que cette calibration est stable au niveau de 0.5%. / The main goals of the ATLAS scientific programme are the observation or exclusion of physics beyond the Standard Model (SM), as well as the measurement of production cross-sections of SM processes. As the rate of events N of a given physics process is linked to the cross-section through the luminosity, it is important to measure the luminosity with great precision. The ATLAS experiment has two major luminosity monitors, LUCID (Luminosity measurement Using Cerenkov Integrating Detector), which consists of Cerenkov tubes located around the beam axis 17m away from the interaction point, and BCM (Beam Condition Monitor) which is a diamond-based detector and has both beam-abort and luminosity capabilities. As these detectors provide a relative luminosity measurement, they were absolutely calibrated in 2010 using the van der Meer procedure, achieving a total systematic uncertainty of 3.4%. The ultimate plan is to provide an absolute calibration using the ALFA detector during a run with special beam optics. In order to provide more cross-checks and a better control on the systematic uncertainties, other luminosity handles are always needed. In particular, an independent measurement using the liquid argon forward calorimeter (FCal), based on the readout current of its high-voltage system, has been developed. This document presents the commissioning and operations of the ATLAS liquid argon calorimeter high-voltage system, as well as its usage to perform a luminosity determination. Analysis of the high-voltage currents during LHC collisions and comparisons with other luminosity detectors have led to a calibration of these currents with a precision better than 0.5%.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 164-178). Also available on the World Wide Web.

Liquid argon is an attractive target for dark matter searches due to its low cost and exemplary event discrimination. However, atmospherically derived argon contains the beta-emitter 39Ar which confounds the growth of dual-phase time projection chamber (TPC) style detectors to the ton-scale. The DarkSide Collaboration seeks to bypass this limitation by extracting argon from deep underground, from a location known to contain significantly less 39Ar than atmospherically derived argon. This thesis will summarize the e orts taken to produce the first batch of underground argon, focusing on the first operation of the underground argon in a dual-phase TPC to validate the purity of the product, performed at Fermilab using the SCENE cryostat.

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Thesis (M.S.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains viii, 45 p. : ill. Includes abstract. Includes bibliographical references (p. 43-45).