| 1. |
- Andrean, Stefio Yosse, 1991-
(författare)
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Search for Stop Using the ATLAS Detector and Performance Analysis of the Tile Calorimeter with Muons from W Decays
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents a search for the supersymmetric partner of the top quark in the final state with one lepton. The search focuses especially in the region of the parameter space where the 2-body decay dominates. The analysis is performed using LHC full Run 2 data at √s = 13 TeV as recorded by the ATLAS detector. No significant excess above the backgrounds is observed, and 95% confidence level exclusion limits are calculated in the stop-neutralino mass plane. Stops are excluded up to 1200 GeV in the low neutralino mass scenario of below 400 GeV.The Tile Calorimeter is part of the ATLAS calorimeter system whose main task is to measure the energy of hadrons. A performance study is conducted on the Tile Calorimeter using muons from W boson decay originating from proton-proton collisions. Each calorimeter cell response is measure in data and compared with detector simulation. The azimuthal cell response uniformity is also investigated using a likelihood method. Overall, a good data to detector simulation agreement and azimuthal uniformity is observed which shows well-calibrated cells and uniform responses among the calorimeter modules.
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| 2. |
- Bolander Laksov, Klara, 1973-, et al.
(författare)
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Managing Change in Higher Education in Times of Pressure : a Case Study of Stanford and Stockholm University
- 2021
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Ingår i: Renewing Higher Education. - Lund : Media-Tryck, Lund. - 9789178957927 ; , s. 235-266
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The aim with this study was to explore how, when and why change happens and what opportunities for managing change can be found in higher education institutions. As the coronavirus pandemic hit the world an opportunity for a case study comparing how our two universities, Stockholm university in Sweden and Stanford university in the US, dealt with the change from traditional campus-based education to online education during spring 2020. Based on a literature review regarding change in higher education, we explored how the educational systems and culture interact with change strategies. Our analysis provide understanding of how university management can contribute to sustainable change through several points for practice.
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| 3. |
- Jacobsen, Sunniva, 1994-
(författare)
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Probes of New Physics : Signatures of new particles in extreme objects and ground-based experiments
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Standard Model (SM) of particle physics is one of the greatest successes of the 20th century. It offers a beautiful description of the elementary par- ticles and their interactions based on symmetries and the breaking of them. Despite its success, the SM is regarded as incomplete both because it does not explain certain observed phenomena and because it exhibits fine-tuning prob- lems. This thesis explores how particles beyond the SM (BSM) interact with SM particles, and the signals we should expect from them. In particular, the classes of hypothetical, new particles denoted as "Weakly Interacting Massive Particles" (WIMPs) and "Axion-like Particles" (ALPs) are studied.This thesis consists of three papers, which all contribute to the search for new particles beyond the SM in different ways. The first paper focuses on a class of WIMPs called "inelastic DM" in which the DM particle must transfer onto a higher-mass state when it scatters off SM particles. In this paper, we have studied whether such a model can explain the discrepancy between the claimed DM signal in DAMA and the lack of one in other direct detection experiments. The second paper of this thesis focuses on ALPs and their signals in the γ-ray spectra of distant sources. ALPs and photons can oscillate in the presence of external magnetic fields, such as the ones that are expected to be present in the jets of blazars (active galactic nuclei). These oscillations should lead to an increased flux in the TeV spectra of these sources. In this paper we used data from the HAWC observatory to study whether the observed γ-ray spectra of these sources were in conflict with the expected spectra for different ALP models.The last paper in this thesis does not involve any new particles beyond the SM, but investigates whether current models of the isotropic gamma-ray back- ground (IGRB) is consistent with observations. Since searches for new par- ticles depend heavily on our understanding of astrophysical phenomena and the SM processes that take place, studies of these are important. The IGRB consists of all the diffuse γ-ray emission that cannot be assigned to individ- ual point sources. In this paper, we calculated the expected contribution to the IGRB from resolved blazars and found that this introduces an emerging tension between blazar models and observations.
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| 4. |
- Renk, Janina J., 1990-
(författare)
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Delving in the Dark : Searching for Signatures of Non-Standard Physics in Cosmological and Astrophysical Observables
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The dark sectors of our Universe, dark matter and dark energy, together constitute about 96 % of the total energy content of the Universe. To date, we only have observational evidence for their existence. What is still lacking is a complete theoretical framework consistent with all observational data to embed a dark matter particle or component into the standard models of particle physics and cosmology, as well as an explanation for the nature or origin of dark energy.Since the discovery of these dark components decades ago, a variety of different theories have been proposed to overcome the shortcomings of our current standard models. To assess the viability of these non-standard theories, they ideally should be tested against all relevant available datasets. In this thesis, I show two examples of how cosmological and astrophysical observables are used to constrain or even rule out non-standard cosmological models. Further, I present the first software tool that provides a general framework to test non-standard physics with global fits to data from particle physics and cosmology simultaneously.The first example is minimally coupled covariant Galileons, a modification of General Relativity to explain dark energy without the need for a fine-tuned cosmological constant. I demonstrate how the combination of constraints arising from the integrated Sachs-Wolf effect and the propagation speed of gravitational waves can rule out all three branches of the theory.The second example shows how the existence and parameter space of cosmic superstrings can be constrained. These are the hypothesised fundamental building blocks of Type IIb Superstring theory, stretched out to cosmological scales during the phase of inflation. The theory can be tested through the unique microlensing signature of cosmic superstrings when crossing the line of sight of an observer monitoring a point-like source. I show how, based on simulations, we can estimate the expected detection rates from observations of distant Type Ia Supernovae and stars in Andromeda; from these estimates I assess the implications for the theory.Finally, I present CosmoBit, a new module for the Global and Modular Beyond-Standard Model Inference Tool (GAMBIT). \gambit allows the user to test a variety of extensions to the Standard Model of particle physics against data from, e.g. collider searches, dark matter direct and indirect detection experiments, as well as laboratory measurements of neutrino properties. CosmoBit augments this with the inclusion of cosmological likelihoods. This addition opens up the possibility to test a given model against data from, e.g. the Big Bang Nucleosynthesis proceeding minutes after the Big Bang, probes of the Cosmic Microwave Background ~ 380,000 years later, and (laboratory) measurements from the present day, 13.8 billion years after the Big Bang. Including measurements that span several different epochs and orders of magnitude in energy, the combination of CosmoBit with other GAMBIT modules provides a promising tool for shedding light on the dark sectors of the Universe.
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