Eldorado - Repository of the TU Dortmund
Resources for and from Research, Teaching and Studying
This is the institutional repository of the TU Dortmund. Ressources for Research, Study and Teaching are archived and made publicly available.
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Recent Submissions
Cross-Border Investigative Journalism
(2025-07) Cosic, Jelena; Welz, Julian
Exploring the interplay between flavor and high-pT observables in the SMEFT framework
(2025) Nollen, Lara; Hiller, Gudrun; Stamou, Emmanuel
Diese Arbeit präsentiert eine globale Analyse zur Suche nach Physik jenseits des Standardmodells im Rahmen der Standardmodell-Effektiven Feldtheorie (SMEFT). Hierzu werden Hochenergie-Daten von Teilchenbeschleunigern mit Präzisionsmessungen aus dem Flavor-Sektor kombiniert, um weitgehend modellunabhängige Schranken auf mögliche neue Wechselwirkungen zu setzen, welche durch Wilson-Koeffizienten parametrisiert sind. Trotz der Erfolge des Standardmodells bei der Beschreibung fundamentaler Wechselwirkungen bleiben zentrale Fragen, wie etwa die Entstehung von Neutrinomassen, die Natur dunkler Materie und die beobachtete Baryonenasymmetrie, unbeantwortet und deuten somit auf die Existenz neuer Physik hin. Angesichts der Herausforderungen direkter Suche nach neuen Teilchen bieten effektive Feldtheorien einen komplementären Ansatz, um diese Phänomene indirekt zu untersuchen. Im Mittelpunkt unserer Analyse stehen die Synergien verschiedener Observablen, die uns erlauben unter Anwendung bayesischer Statistik gleichzeitig Schranken für zahlreiche Wilson-Koeffizienten zu setzen und unbeschränkte Richtungen im Parameterraum aufzulösen. Ein besonderer Schwerpunkt liegt zudem auf der Untersuchung von Flavor-Strukturen. Dazu verwenden wir den Ansatz der Minimalen Flavorverletzung im Quarksektor
sowie lepton-flavorspezifische Szenarien. Unsere Ergebnisse testen Skalen bis zu 1000 TeV, bieten indirekte Informationen über mögliche Flavorstrukturen und eröffnen Perspektiven für zukünftige Forschung.
Constraining light dark vectors and scalar leptoquarks with flavour observables
(2025) Folch Eguren, Jordi; Stamou, Emmanuel; Hiller, Gudrun
In this thesis we explore two complementary extensions of the Standard Model, corresponding to a light new physics scenario featuring a (dark) vector boson, and a heavy new physics scenario involving a scalar leptoquark. Focusing on their flavour-changing interactions and observables, which provide highly sensitive probes of physics beyond the Standard Model, we employ the framework of effective field theory to systematically analyse both setups. In the first part of this thesis, we provide an overview of the Standard Model, flavour and effective field theories. In the second part, we study the light dark vector boson model. We focus on flavour violating interactions between the new vector and the Standard Model fermions, and analyse how such interactions can arise from the Yukawa diagonalisation and the renormalisation group equations at 1-loop. Then, we use experimental data and our theory calculation from two-body decays to set constraints on the model parameters. Furthermore, we also use the tool of perturbative unitarity to set bounds on the model. In the third part, we consider scalar leptoquarks, corresponding to a heavy new physics model. Here, we compute the Wilson coefficients to order $\mathcal{O}(\alpha_s)$ for $\Delta F=2$ processes from matching the effective and full theories, which involves the calculation of 1-loop amplitudes in the effective theory and 2-loop in the full theory. Finally, we analyse the 1-loop corrections to the effective theory for $\Delta F=1$ processes. We focus on a particular computational procedure involving Dirac traces, which requires a careful examination of the Dirac algebra in different $\gamma_5$ schemes, and extract results in a general gauge and for different IR regulators.
Analysis of high-dimensional data in the context of intrinsic dimensionality
(2025) Thordsen, Erik; Schubert, Erich; Aumüller, Martin
Many modern machine learning applications and data analysis make use of or produce large amounts of high-dimensional data. While it is commonly known, that the performance of many algorithms degrades with increasing dimensionality both in terms of speed and quality, the performance on real-world datasets is often times much better than expected. In fact, real-world datasets tend to occupy only a lower-dimensional manifold in the available observed space, either due to the underlying generative process or the sparsity of the data. To describe that phenomenon, the concept of Intrinsic Dimensionality (ID) was introduced, which describes the minimum number of latent variables to produce the observed manifold. In a pursuit to estimate the ID of non-linear manifolds, small localities of the data are often considered, giving rise to the concept of Local Intrinsic Dimensionality (LID) which aside from estimating a global ID also allows for a spatially resolved analysis of the data. Since the LID eludes direct observation beyond two or three dimensions, it has to be estimated from the data. In this thesis, we explore multiple new approaches to estimate the LID of data in Euclidean spaces, investigate their analytical and empirical properties, and compare them to existing approaches both qualitatively and quantitatively. One of these approaches, the Angle-Based Intrinsic Dimensionality (ABID) estimator, has very useful theoretical properties. We therefore provide an exemplary derivation of ABID to vector fields as a potential control mechanism in algorithms such as Gradient Descent as a showcase of how LID estimation can be useful beyond point clouds. We also investigate if and how LID estimation approaches can be applied to non-Euclidean spaces. While the theory of LID estimation in non-Euclidean spaces remains largely unresolved, we provide a visionary prospect on the future of the field and provide anecdotical evidence for possible future applications of LID.
Measurement of top-quark involved CKM matrix elements in single-top-quark events using the full Run 2 dataset with the ATLAS experiment
(2025) Gocke, Benedikt; Kröninger, Kevin; Albrecht, Johannes
In this thesis, an interpretation of an ATLAS single top-quark t-channel cross section measurement to constrain the top-quark involved CKM matrix elements, |Vtb|, |Vtd| and |Vts|, as well as feasibility studies for a dedicated measurement are presented. The data used in this thesis corresponds to the full Run 2 dataset from proton-proton collisions at the LHC at a cebtre-of-mass energy of 13 TeV recorded by the ATLAS experiment. For the interpretation, all three different top-quark production modes and decay modes are considered. For the first time in ATLAS, single top-quark t-channel events with top-quark decays to light quarks are simulated. 2D profile likelihood scans are performed to constrain the CKM matrix elements at 95% CL: fLV·|Vtb| < 1.048, fLV·|Vtd| < 0.133, and fLV·|Vts| < 0.306, with fLV being the left-handed form factor. A two-step neural network approach is applied in feasibility studies to improve sensitivity to the relevant CKM matrix elements: the first network separates signal events from background events, while the second distinguishes between different signal processes.
Furthermore, a calibration of the charm mis-tag rate of the flavor tagging algorithm in Run 2 using W+c-jets is presented, exploiting semileptonic c-hadron decays by identifying jets with a muon inside. Likelihood fits are used to derive data-to-MC scale factors for jets with 20 < pT < 140 GeV. The derived scale factors are found to be mostly within unity and reduced uncertainties for jets with lower pT are observed compared to the standard calibration in ATLAS. An extrapolation was done to generalize the results to all c-jets.