Browsing by Supervisor "Albert, Justin E."
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Item ALTAIR project for ultra-precise astronomical photometric calibration: Design, production and testing(2025) Reyes Olguin, Diego Gabriel; Albert, Justin E.In quantitative fields, such as astronomy, uncertainties play a huge role. This is particularly true for measurements of dark energy using Type Ia supernovae, where systematics from photometric calibration are the largest source of uncertainty. The ALTAIR (Airborne Laser for Telescopic Atmospheric Interference Reduction) project will tackle this problem using in-situ calibrated light sources at altitudes of ∼ 20 km to provide precise and accurate knowledge of optical throughput at a variety of wavelengths, making photometric uncertainty no longer dominant. This thesis details the design, production, and laboratory testing of ALTAIR payload electronics, with a focus on the custom photodiode readout electronics responsible for monitoring the light source’s stability over a wide dynamic range, ranging from picoamperes (10^−12A) to microamperes (10^−6A) of photocurrent. The results from linearity testing demonstrate an exceptionally linear response across all operational modes. The transimpedance amplifier shows measured deviations from linearity of less than 0.011% over its operational dynamic range, while the switched-integrator circuits, critical for low-current measurements, exhibit non-linearities of less than 0.0613% of their full-scale range. These results validate a critical subsystem of the ALTAIR payload and confirm that the custom electronics meet the requirements for sub-percent precision photometry.Item Derivation of electron charge misidentification scale factors with Run 2 and Run 3 data at the ATLAS experiment(2025) Kaur, Damandeep; Albert, Justin E.Electron charge misidentification constitutes a significant background in analyses involving same-sign electron pairs, such as searches for electroweak production of same sign W±W± bosons. An estimation of this background is essential for improving signal sensitivity in such processes. This thesis presents the derivation of charge misidentification scale factors using a Deep Neural Network (DNN) based electron identification (ID) in the ATLAS experiment, utilizing proton–proton collision data produced at √s = 13 TeV and √s = 13.6 TeV. A data-driven method based on the Z → e+e− process is employed to estimate charge flip probabilities in data and Monte Carlo simulation, across different kinematic bins of transverse momentum and pseudorapidity. The DNN-based ID algorithm offers improved discrimination power compared to traditional likelihood-based methods, particularly in complex detector regions. The derived scale factors correct for mismodelling of charge flip rates in Monte Carlo simulations and are parametrized in both one-dimensional and two-dimensional schemes. Closure tests are performed to validate the robustness of the scale factors and their applicability across various physics analyses.Item Design, construction and analysis of a solid state nearly-isotropic light source(2016-12-09) Kovacs, Paul; Albert, Justin E.Isotropic radiators are known to be a useful tool across a wide range of applications, from applications in light dosimetry in human/animal tissue to calibration of sensitive laboratory equipment. While the bene ts are known, constructing such a tool has proven to be di cult. Currently, there are no commercially available isotropic or nearly isotropic radiators. Previous attempts at constructing an isotropic radiator have been limited to a 10% isotropy level. This thesis covers the design, construction, and analysis of a nearly isotropic optical light source. The constructed source has extrema anisotropies, over a solid angle of approximately 3 steradians, of +\-3% (with 95% of that solid angle being within +\- 2.5% anisotropy).Item Prospects for the measurement of the Higgs CP structure at ATLAS in Higgs to four lepton decays(2011-04-29) Jarrett, Michael; Albert, Justin E.A Monte Carlo simulation is performed of Higgs decays in the H → ZZ → 4l channel at ATLAS. Decay parameters are varied in order to model Higgs decays of differing CP states. A full analysis is performed, including trigger and background studies. Using various angular distributions as observables it is found that ATLAS should be able to exclude an anomalous CP odd coupling at 50 fb−1 and an anomalous CP even coupling at 100 fb−1. The CP violating case studied could not be excluded.Item Search for dark Higgs boson production in pp events at √s = 13 TeV with the ATLAS detector at the LHC(2021-11-18) Wright, Benjamin; Albert, Justin E.This thesis presents the design of a signal region, as well as two control regions to constrain the tt ̄ background, in the search for the theorized dark sector process qq ̄ → Z′∗ → Z′s with s → W W → qq ̄lν and Z′ → χχ(invisible). In this process, dark matter is produced as a new heavy vector boson, Z′, together with a scalar “dark Higgs” boson, s, that decays to a pair of W bosons with a semileptonic final state. In this model, a new Higgs mechanism associated with s generates the masses of the dark sector particles, and the mixing of s with the Standard Model Higgs boson allows it to decay to Standard Model particles and be observable over a large range of model parameter space at the Large Hadron Collider. This search uses 139 fb−1 of proton-proton collision data collected by the ATLAS experiment at a center-of-mass energy of 13 TeV. Using the designed signal and control regions, in this search we will be able to exclude Z′ masses up to a range between approximately 1200 to 2200 GeV, and s masses from approximately 150 GeV up to a range between approximately 290 to 360 GeV.Item Search for supersymmetry in final states with multiple bottom quarks with the ATLAS detector(2021-07-09) Ghasemi Bostanabad, Meisam; Albert, Justin E.The theoretical development of the Standard Model in the 1960s and 1970s has led to the discovery of its missing piece, the Higgs boson, at the ATLAS experiment (together with its sister experiment, CMS) at the Large Hadron Collider at CERN in 2012. In order to solve the problem of large quantum corrections to the leading expansion of the Higgs boson mass, additional symmetries need to be added to the Standard Model. A possible solution to this problem of Higgs mass quantum corrections is the theory of Supersymmetry, which includes partners to each Standard Model particle, such as gluinos, squarks, and the lightest supersymmetric particle. This dissertation describes a search for pair-produced gluinos, where each gluino decays via a top squark or a bottom squark to the lightest supersymmetric particle (a neutralino). Events which contain a large jet multiplicity in the final state (i.e. at least four jets of which at least three must be b-jets), and large amounts of missing transverse energy, are obtained for further studies. The dataset used for this search includes 139 fb^−1 of integrated luminosity recorded by the ATLAS experiment between 2015 and 2018 at a center-of-mass energy √s = 13 TeV. No significant excess is observed in data above the Standard Model backgrounds, and gluino masses up to 2.3 TeV for both the Gtt and the Gbb models are excluded at a 95% confidence level. This dissertation also contains an overview of, and the author’s work on, the data quality monitoring of the ATLAS liquid argon calorimeter during 2017 data taking.Item Search for the Higgs Boson in the Vector Boson Fusion Channel at the ATLAS Detector(2014-01-16) Ouellette, Eric Alexandre; Albert, Justin E.The search for the Higgs boson has been a cornerstone of the physics program at the Large Hadron Collider in Geneva Switzerland. The ATLAS experiment successfully discovered the Higgs using the so-called ‘Golden Channels’ of H0 -> gamma gamma and H0 -> ZZ(∗) using data samples collected during the 2011 and 2012 run periods. In order to check if the discovered Higgs is consistent with purely Standard Model behaviour, it is necessary to further confirm the existence of the Higgs in each production mode and decay channel predicted by the Standard Model. For this dissertation, a search for the Higgs was conducted using the H0 -> b bbar decay channel, where the Higgs is produced by the inverse pair decay of two weak bosons exchanged by a scattered quark pair, also known as Vector Boson Fusion (VBF). This analysis uses data samples collected during the 2011 run period by the ATLAS detector totalling 4.2 /fb of proton-proton collisions at sqrt(s) = 7 TeV. No excess of events above background expectation is observed and 95% confidence level upper limits on the Standard Model Higgs cross section times branching ratio, sigma(VBF) x BR(H0 -> b bbar), are derived for Higgs masses in the range 115 < mH < 130 GeV. An observed 95% confidence level upper limit of 18.7 times the Standard Model cross section is obtained for a Higgs boson mass of 125 GeV.