Probing the standard model with rare charm decays See

This thesis comprises a study of rare charm decays in the standard model (SM) and beyond. Within an effective theory framework, we calculate the SM Wilson coefficients to (partly) next-to-next-to leading logarithmic order in quantumchromodynamics. The calculation includes matching conditions and the running of the Wilson coefficients in the renormalization group-improved perturbation theory, thereby correcting expressions used in the literature. Furthermore, a calculation of phenomenologic...

Dynamics and interaction of magnons in the two dimensional Heisenberg antiferromagnet See

In this thesis the elementary excitations of the spin-1=2 Heisenberg antiferromagnet on the square lattice are studied. This fundamental model is a paradigmatic example for long range ordered quantum phases and the spontaneous breaking of a continuous symmetry in condensed matter. The elementary excitations at long wavelengths are well understood by quantized spin waves, i.e., magnons, which are the gapless Goldstone bosons of the broken SU(2) symmetry. However, recent findings reveal a...

Structural investigation of the impact of magnetostriction on GaMnAs thin film lattices and the thermal expansion of (In,Ga)As/GaAs quantum dots See

The combination of semiconductor based materials with magnetic properties in so called diluted magnetic semiconductors could revolutionize the field of spintronics. Here, the charge and spin properties of such devices can be utilized for the processing and storage of data. The magnetic properties of gallium manganese arsenide (GaMnAs), which is a promising candidate for ferromagnetic ordering at room temperature, have been extensively studied over the years. Especially, the Curie temperature ...

Electron and nuclear spin dynamics in fluorine-doped ZnSe epilayers See

Electron spins in semiconductors are considered as candidates for quantum bits. This thesis presents a study of the spin dynamics of the strongly localized donor-bound electrons in fluorine-doped ZnSe epilayers via pump-probe Kerr rotation technique. A method exploiting the spin inertia is developed and used to measure the longitudinal spin relaxation time (T1). The excitation of the same samples with helicity-modulated laser pulses results in a transverse nuclear spin polarization, which was...

Measuring the b-tagging efficiency in ATLAS data at √s = 8TeV and √s = 13 TeV using the ρTrel-method See

In dieser Dissertation wird die erste Messung der b-tagging Effizienz eff(b) mit der pTrel-Methode am ATLAS Experiment unter Run 2 Bedingungen präsentiert. Die Messung wurde durchgeführt mit semileptonisch zerfallenden b-Hadronen mit einem Myon im Endzustand. Dies wurde erreicht durch Selektion von Myonen in einem Jet Kegel. Die pTrel-Variable is dabei sensitiv auf die Masse des schwach zerfallenden Teilchens und damit auf den Flavor des Jets. Dieser Zusammenhang lässt sich mit einem log-like...

Commissioning of the ATLAS Insertable B-Layer and first operation experience See

Todays research in particle physics offers a wide field of opportunities for scientists from a variety of different subjects. Discoveries can only be made, with hundreds up to thousands of people working together in collaborations. Designing high precision detectors that can be up to several stories tall, followed by production, construction, commissioning and successful operation is only achievable with the combined effort of skilled and experienced detector physicists and engineers, while t...

Röntgenreflektometrie an der hydrophoben Festkörper-Flüssigkeits-Grenzfläche See

Grenzflächen spielen eine wichtige Rolle bei vielen Prozessen in Natur und Technik. In der vorliegenden Arbeit wurde die hydrophobe fest-flüssig-Grenzfläche an verschiedenen Synchrotronstrahlungsquellen mittels Röntgenreflektometrie untersucht. Hierzu wurden die Oberflächen von Siliziumwafern mit einer Monolage Oktadecyltrichlorsilane (OTS) beschichtet. Zwischen dieser hydrophoben Oberfläche und Wasser existiert ein Bereich verringerter Dichte. Der erste Abschnitt dieser Arbeit untersucht die...

Ab-initio Gutzwiller-DFT studies of diluted magnetic semiconductors See

We use a combination of Density Functional Theory (DFT) in the Generalized Gradient Approximation (GGA) and the multiband Gutzwiller variational method to investigate the magnetic properties of manganese-based II-VI and III-V Diluted Magnetic Semiconductors (DMS) from first principles. In order to model the dilute and random nature of the magnetic impurities in the semiconductor material, we employ a supercell approach with several hundred atoms in the unit cell. AWannier-basis obtained ...

Biological systems: semiflexible polymer networks and active rods See

In dieser Arbeit werden zwei verschiedene biologische Systeme numerisch und analytisch untersucht. Der erste Teil behandelt Faltenbildung in semiflexiblen Polymernetzwerken aufgrund von Scherdeformation. Als wesentlicher Bestandteil in vielen biologischen Systemen und durch ihre einzigartigen mechanischen Eigenschaften sind diese Netzwerke ein interessanter Forschungsgegenstand in der Biologie und den Materialwissenschaften. Mithilfe linearer Elastizitätstheorie wurden grundlegende Eigenscha...

When do structural anomalies of ionic crystals begin? See

The present work contributes to the search of anomalous effects in ionic crystals, and possible explications of those effects observed in pure NaCl and CuCl:NaCl system. Single nanocrystals can only be used if their positions arefixed in space which needs forces between a nanocrystals and its enviroment. Therfore, the research of nano-crystals structures requres also the study of these forces. Structural and optical anomalies are determinated by measurements in single crystals of NaCl which c...

A model-building approach to the origin of flavor See

In this thesis we link the recent anomalies reported in B meson and Higgs boson decays to the smallness of neutrino masses and aspects of the flavor puzzle, including the hierarchy of the Yukawa couplings and the disparate fermion mixings. By formulating various new models we attempt to shed light on the potential common origin of the distinct measurements in the flavor sector. To this end, discrete symmetries are utilized in this work as the governing principle behind all fermion interaction...

Development and application of a universal distributed data acquisition system for orbit feedback applications on electron and hadron synchrotrons See

To improve beam quality, the DELTA storage ring (TU Dortmund) conducted a number of orbit-feedback developments in the past, including a successful fast local orbit feedback project. To enable hadron accelerators to benefit from this knowledge, a collaboration was formed between DELTA, the storage ring COSY (Forschungszentrum Jülich) and the SIS18 accelerator (GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt). The goals were the development of a global fast orbit feedback system ...

Supramolecular structure of monohydroxy alcohols See

Hydrogen bonds are essential for the structure and dynamics of alcohols, aqueous solutions, and water. Because of their low tendency of crystallization and large variability in molecular configuration, monohydroxy alcohols have often been studied as model systems for hydrogen-bonded fluids in general. This thesis contains investigations of the structuring in monohydroxy alcohols on molecular level employing x-ray scattering methods such as x-ray diffraction and x-ray Raman scattering. The x...

Dynamic correlations in one-dimensional quantum magnets at finite temperature See

In this thesis we investigate dynamical correlations of spin systems at finite temperature. Especially we focus on the anomalous decoherence effects found previously in experiments of several quantum magnets. We develop and apply a diagrammatic perturbative approach, which incorporates the hard-core bosonic nature of spin excitations. This allows for a computation of the leading low-temperature contributions to the spectral function. The Jordan-Wigner transformation is used to benchmark the a...

On the hunt for photons: analysis of Crab Nebula data obtained by the first G-APD Cherenkov telescope See

In this thesis the analysis of data of the Crab Nebula obtained by the First G-APD Cherenkov Telescope (FACT) is presented. An analysis chain using modern machine learning methods for energy estimation and background suppression is developed. The generation and application of the machine learning models are validated using Monte Carlo simulated events. The Crab Nebula can be detected as a source of very high energy gamma rays with a significance of 39.89 σ. Its energy spectrum can be reconstr...

Measurements of sin 2β using charmonium and open charm decays at LHCb See

Aspects of charge carrier dynamics in Germanium and cadmium zinc telluride See

This thesis addresses two markedly different aspects of ultrafast carrier dynamics in semiconductors in all-optical studies based on pump-probe measurements with femtosecond laser pulses. Both parts of the presented study aim to contribute to the fundamental understanding of the respective physical processes and to foster the applicability of the corresponding semiconductor systems in the context of spintronics, quantum computing, or all-optical switching. The first part of the prese...

Atomic insights into muscle contraction by transmission electron cryomicroscopy See

Jede Kontraktion eines Muskels basiert auf dem Zusammenspiel von Millionen Myosinmolekülen mit Aktinfilamenten (F-Aktin). Dabei unterscheidet sich interessanterweise der fundamentale Mechanismus der Interaktion nicht von dem, der bei Transportprozessen in der Zelle stattfindet, wenn nur ein Myosindimer eine Fracht entlang des Aktinzytoskeletts bewegt. Sowohl die Muskelkontraktion als auch die Transportprozesse werden dabei von aktinbindenden Proteinen wie zum Beispiel Tropomyosin reguliert. D...

GaN- and VO 2-based nanostructures: physics and photonic applications See

This thesis presents fundamental research on potential materials and concepts for active photonic elements operating in the telecom wavelength regime. It is analyzed how the characteristics of the investigated nanostructures and the implementation of the proposed concepts could be applied in photonic research or devices. The first part of the thesis is devoted to the investigation of semiconductor heterostructures. The inter-miniband (IMB) transition in superlattices made of GaN and AlN in ...