In free-electron laser injectors the so-called microbunching instability can severely degrade the beam quality of electron bunches and therefore negatively impact the performance of the free-electron laser. Precise understanding of the microbunching process is required to develop mitigation strategies that minimize the negative impact of the instability.In this work, two approaches of investigating the microbunching instability are presented – one analytical and one numerical. [...]

The de novo synthesis of vitamin B6 (pyridoxal 5-phosphate) is conserved in most organisms but mammals. The synthesis of pyridoxal 5-phosphate (PLP) is carried out by a complex of two enzymes: Pdx1 and Pdx2. [...]

The filamentous fungus Aspergillus niger is the foundation of modern biotechnology and is still of great economic importance, especially with regards to the production of organic acids and proteins. Its tube shaped and branched multicellular segments called hyphae are protected by a strong and flexible outer layer - the cell wall. [...]

This thesis is aimed at establishing modalities of time-resolved photoelectron spectroscopy (tr-PES) conducted at a free-electron laser (FEL) source and at a high harmonic generation (HHG) source for imaging the motion of atoms, charge and energy at photoexcited hybrid organic/inorganic interfaces. Transfer of charge and energy across interfaces lies at the heart of surface science and device physics and involves a complex interplay between the motion of electrons and atoms [...]

S-band RF-guns are highly developed for producing low emittance relativistic electron bunches, but require powerful klystrons for driving. Here, I present the design and first experimental tests of a compact S-band gun that is capable of accelerating electrons up to 180 keV powered by only 10 kW peak power using a compact rack-mountable solid-state amplifier. [...]

The particle physics community is currently discussing the next large-scale electron-positron collider experiment, with a major interest in the Higgs production threshold around 250 GeV. Multiple proposals have emerged for such a machine, differing in machine and detector designs, as well as energy stages and luminosities. [...]

The crystallographic data processing is investigated with the goal of extracting more structural information from serial crysallographic experiments. Systematic errors resulting from uncontrollable aspects in the experimental setup were reduced in several places, but most significantly by modelling the expected intensity of partially observed intensities using Gaussian basis functions to improve merging. [...]

Unter dem geografischen Südpol liegt das IceCube Neutrino Observatorium. Es nutzt einen Kubikkilometer Gletschereis, um Sekundärteilchen aus Neutrinointerkationen zu detektieren. [...]

Dark matter (DM) remains one of the unrevealed mysteries of the universe. Even though it constitutes ∼ 85% of the matter, considerably little is known about DM, despite its significant influence on the dynamics of galaxies and the expansion of the universe. [...]

Pathological iron accumulation in the brain is a hallmark of several neurodegenerative diseases like Parkinson’s, Alzheimer’s and Huntington’s disease. Magnetic resonance imaging offers a unique non-invasive method to measure brain iron because iron affects the spin relaxation parameters of water protons and magnetic susceptibility of the brain tissue [...]

The α↔γ transformation is very well known and important in steel metallurgy, present in many heat treatments with the purpose of improving steel. Treatments to increase resistance (quenching), grain refining, solubilization for homogenization, elimination of texture, increase of tenacity involve austenitization, formation of ferrite or martensite. [...]

The first goal of this thesis was to check whether the parameter variations of the 2HDM+a model,in the process of bbH$\to$Za$\to$ll$_{χχ}$, have an impact on multivariate methods. The second goalwas to check the feasibility of using a singular deep neural network trained on all given masspoints of the heavy Higgs and dark matter mediator.It was found that the variation of model parameters unrelated to mass of particles had no sig-nificant impact on the performance of multivariate methods. [...]

For the HL-LHC phase, the calorimeter end-cap of the CMS detector will be upgraded with a High Granularity Calorimeter (HGCAL) with increased transverse and longitudinal granularity to cope with the expected pileup and radiation. In regions where radiation levels allow, the hadronic calorimeter will use scintillator tiles coupled to silicon photomultipliers (SiPM-on-tiles) as active materials. [...]

Catalytic oxidation of carbon monoxide (CO) is one of the most studied reactions that still needs to be improved because of its practical use in the chemical industry including feedstock purification and applications such as emission control, in-door air cleaning, improvement of fuel cell efficiency, etc. Concerning CO emissions, the transportation sector is a large contributor. [...]

The particle physics community has expressed significant interest in a 10 TeV-class electron-positron collider to advance our understanding of matter. However, the costs associated with such a collider usingconventional radio-frequency technology seem to be prohibitive. [...]

Climate change, antibiotic resistances and environmental pollution are growing threats. Therefore, finding alternatives for fossil resources and discovery of new pharmaceuticals grows more important every day [...]

Phenomena such as dark matter can be connected to the standard model via additionalspin-0 mediators. This doctoral thesis describes a search for a long-lived spin-0 particleS in rare B-meson decays mediated by b → s quark transitions.A dataset corresponding to an integrated luminosity of 189 fb−1of e+e− collisionscollected at the Υ(4S) resonance energy by the Belle II experiment is analysed. [...]

Laser-wakefield acceleration (LWFA) is a promising, emerging technology for future accelerator-based X-ray light sources, which are essential tools in various fields of science, industry and medicine. In laser-wakefield acceleration, an intense laser pulse drives a plasma wave that supports high accelerating field gradients. [...]

The key feature of X-ray Free Electron Lasers (XFELs) is their capability to generate ultrashort and at least partially coherent X-ray pulses with extreme intensity. This capability holds the promise to revolutionize X-ray physics in a way similar to how lasers have revolutionized optics, as the non-linear and coherent interactions known from theoptical regime combined with the properties of X-ray radiation could enable techniques with unprecedented analyzing power. [...]

In dieser Arbeit nutzen wir Effektive Feldtheorien, genauer gesagt die SMEFT, um BSM-Effekte modellunabhängig zu parametrisieren. Wir demonstrieren die Relevanz von Präzisionsmessungen sowohl an aktuellen als auch an zukünftigen Hadronenbeschleunigern durch die Untersuchung von Vh-Dibosonen-Prozessen. [...]

Double parton scattering (DPS) describes a process in hadron-hadron scattering in which two partons are extracted from each initial hadron and then initiate hard scattering processes separated by a finite distance. After factorising the hadronic process, one obtains parton distributions functions that characterise the behaviour of partons inside the hadron at non-perturbative scales. [...]

The measurement of the CP properties of the Yukawa coupling of the Higgs boson to τleptons is presented. The data set used for the analysis is collected by the CMS experiment atthe LHC during the Run 2 data-taking period in proton-proton collisions at √s = 13 TeV andcorresponds to an integrated luminosity of 137 fb$^{−1}$. [...]

The interstellar space is filled with numerous molecules. The interaction of the interstellar radiation with these molecules play an active role in maintaining the charge balance of the interstellar medium and governs the photochemical and photophysical processes. [...]

This thesis presents the first measurement of the associated production of a Higgs boson and a top-quark-antiquark pair ($\text{t}\overline{\text{t}}\text{H}$) in final states with two leptons and where the Higgs boson decays into a bottom-quark-antiquark pair ($\text{H} \rightarrow \text{b} \overline{\text{b}}$). The measurement utilizes proton-proton collision data collected at the CERN LHC with the CMS experiment at a center-of-mass energy $\sqrt{s}$=13 TeV during 2016-2018 of Run 2, which corresponds to an integrated luminosity of 138 $\text{fb}^{-1}$. [...]

Precision measurements of Standard Model processes are a fundamental part of experimental particle physics. Diboson channels at the Large Hadron Collider (LHC) are interesting processes for precision measurements since the relatively high cross-sections and low background contamination allow for small uncertainties. [...]

Visual perception greatly influences human experience, emotion and evolution. The ability to observe and draw conclusions from the observed process is a key capacity for scientific advancement as well. [...]

Various astrophysical observations point towards an as-of-yet unexplained, mainly gravitationally interacting type of matter. If this matter, called Dark Matter, is an elementary particle, it could be produced in particle collisions at the Large Hadron Collider [...]

The success of the physical model of quantum electrodynamics relies on the use of a small perturbation above a quantum vacuum solution. In the physically possible case of a strong electric field, defined as being near or greater than the Schwinger limit, the assumption underlying this perturbation theory approach becomes unviable. [...]

Gold nanoparticles have gained significant attention in nanoscience for their plasmonic properties. The localized surface plasmon resonance of gold nanoparticles is a strong interaction between electrons and light, which results in high absorbance in the visible spectrum, highly localized enhancement of the electric field at the particle surface, as well as the generation of highly excited electrons [...]

The last building block of the standard model of particle physics was observed in 2012 with the discovery of the Higgs boson. Even with the standard model being one of the most successful theories in physics, there are several questions it can not answer. [...]

The thesis reports the cross-section measurements of the three-jets production and the production of jets associated with a Z-boson, Z+jets. The measurements are performed using proton-proton collision data with centre-of-mass energies of 7 and 8 TeV. [...]

The advent of highly brilliant synchrotron X-ray sources and the development of X-ray optics offer new capabilities to examine materials with high photon energy X-rays that can offer nano-scale resolution. This thesis aims to explore new ways to study nano-structured samples by employing state-of-the-art high numerical aperture multilayer Laue lenses (MLLs) fabricated in our group. [...]

Laser-plasma accelerators (LPA) utilize intense laser pulses to drive plasma waves, generating strong electric fields capable of accelerating electrons to relativistic energies. This technology promises accelerator facilities that are orders of magnitude smaller than their conventional counterparts. [...]

Detailed knowledge about particle beam properties is of great importance to understand and push the performance of existing and next generation particle accelerators.In this thesis, two novel contributions to the characterization of charged particle beams are presented.First, a new phase space tomography method is proposed and experimentally demonstrated.It provides the tomographic reconstruction of the full five-dimensional phase space of the particle beam, i.e., the charge density distribution in all spatial directions and the two transverse momenta. This is done by combining a quadrupole-based transverse phase-space tomography with the streaking of the beam at various angles using a PolariX transverse deflection structure.Detailed simulations show the ability of the method to reconstruct various complex phase-space distributions and its applicability to highly non-Gaussian beams. [...]

Inverse Compton Scattering (ICS) has gained much attention recently because of its promise for the development of compact X-ray light sources. Precise and fast simulation is an essential tool for predicting the radiation property of a given machine design and to optimize its parameters. [...]

MsbA is an essential, prokaryotic ATP binding cassette (ABC-)transporter which transportslipopolysaccharides, lipid A, and glycolipids from the inner to the outer leaflet of the bacterialinner membrane. Also, MsbA can function as a multidrug-resistance transporter and could betarget for new antibiotic developments and thus shows high biomedical relevance. [...]

AbstractThis master’s thesis explores the ageing effects, offset calibration, and cross-talk inthe pixel vertex detector (PXD) of the Belle II experiment. The PXD is the innermostdetector of the Belle II experiment, consisting of self-supporting ladders using DEP-FET technology. [...]

Novel all-optical terahertz (THz)-based accelerators promise to enable new science by providing ultrafast and bright electron bunches at a small footprint. While practical prototypes of THz-based devices have been demonstrated and have shown exceptional capabilities to accelerate and manipulate electron beams on sub-ps timescales, the development of practical THz-driven photoguns has lagged behind due to challenges associated with physical miniaturization and the high THz pulse energy required. [...]

Biodegradable magnesium-based implants are playing an increasingly important role in the area of orthopaedic implants as they eliminate the need for a second surgery to remove the implant, consequently reducing the chance of patients’ harm as well as the financial burden. There is a need for degradable magnesium-based implants to be fully characterized in terms of microstructure, corrosion performance in vitro and in vivo due to the implants’ performance differences in these different environments.Two magnesium gadolinium alloys (Mg-5 weight % Gd and Mg-10 weight % Gd) in the shape of M2 screws have been investigated with regards to their microstructure and their degradation performance over 1 - 56 days period in vitrovia both weight loss and volume loss measurements. [...]

In this work, the synthesis of star-shaped octapod iron oxide nanoparticles was analyzed. The synthesis is based on the thermal decomposition of iron(II) oleate, which in turn wassynthesized from iron(II) carbonate and oleic acid. [...]

Colloidal crystals are ordered arrays of colloidal particles forming a superlattice similar to that in conventional crystals. In recent decades, the research on colloidal crystals has blossomed due to their fascinating structure-related properties such as diffraction of light at optical wavelengths, high porosity, etc. [...]

This thesis explores wave dark matter and its intriguing phenomenological implications, namely the presence of wave-like signatures on astrophysical length scales.Specifically, we assume the dark matter is composed of light bosons with masses below 10 eV, allowing, due to the high phase space occupation number, for a classical wave description. We develop a formalism to describe the wave dark matter’s response to gravity, accounting for the statistical properties of the field.Our first subject of investigation is the behavior of the wave dark matter in the Solar system. [...]

We study the different extensions of the Two-Higgs-Doublets model (2HDM), including singlet extensions and CP-violating models. We analyse the complex singlet extension of the 2HDM with the NMSSM like $\mathbb{Z}_3$ symmetry (2HDMS), and derive the boundedness from below and perturbative unitarity bounds for the 2HDMS. [...]

Trotz der zahlreichen astrophysikalisch und kosmologisch überzeugenden Beweise für Dunkle Materie bleibt ihre wahre Natur unbekannt. Eine Motivation für die Suche nach Dunkler Materie am Large Hadron Collider (LHC) und insbesondere mit dem ATLAS-Experiment ist die besonders vielversprechende Möglichkeit, dass Wechselwirkungen zwischen gewöhnlicher Materie und Dunkler Materie durch neue Spin-0-Teilchen vermittelt werden. [...]

The goal of this thesis is the investigation of decay processes in innershell ionised xenon dimers and trimers. To this end, the small clusters were ionised using 100 eV photons from a Free-Electron Laser and the momenta of the created ion fragments and electrons were measured using the Reaction Microscope at FLASH2 [...]

A measurement of inclusive jet cross sections in high-$Q^2$ neutral current deep-inelastic scatteringis performed using data collected by the ZEUS detector at the HERA $e^±p$ collider. The datawere taken in the years 2004 to 2007 at a centre-of-mass energy of 318 $GeV$ and correspond toan integrated luminosity of 347 $pb^{−1}$. [...]

Before the successful detection of gravitational waves (GWs) with LIGO and VIRGO, superconductingradio frequency (SCRF) cavities were already considered as potential alternativesfor large laser interferometers. They are particularly suited to probe high frequencies above∼ 10 kHz by using a heterodyne approach where the GW has to be resonant with the frequencydifference of two cavity eigenmodes. [...]

Single-particle imaging (SPI) is a method that promises high-resolution structure determination of artificial or biological nanoparticles, including proteins. In a thin stream, these particles are guided into the brilliant flashes of free-electron lasers. [...]

Fiber lasers were proposed shortly after the invention of the first laser [1,2] and identified as potential candidates for numerous industrial and scientific applications [3,4]. There are a number of unique features that differ fiber lasers from other laser technologies and lead to superior overall performance, such as better thermal management due to the large surface-to-volume ratio, excellent beam quality, higher wall-plug efficiencies, lower cost, and a smaller footprint compared to solid state lasers. [...]

Complex particle tracking software used in High Energy Physics experiments already pushes the edges of computing resources with demanding requirements for speed and memory throughput, but the future experiments pose an even greater challenge. Although many supercomputers already reached petascale capacities using many-core architectures and accelerators, many scientific applications still need to efficiently make use of the new resources. [...]

Conformal field theories are universal descriptions of scale-invariant systems, ranging from critical phenomena all the way to theories of quantum gravity. In this context, the lightcone bootstrap program is an analytic approach to extracting physical data from the crossing symmetry equation of correlation functions. [...]

In this thesis, I present my contributions to the field of ultrafast molecular spectroscopy. Using the molecule 2-thiouracil as an example, I use ultrashort x-ray pulses from free- electron lasers to study the relaxation dynamics of gas-phase molecular samples. [...]

The BCM1F detector at the CMS experiment is responsible for the measurement of theluminosity, as well as the beam-induced background. It is assumed that the sensors will haveto be replaced during Run 3 of the LHC, which is why work is already underway to build areplacement system [...]

This PhD thesis presents improved theoretical predictions for fully-differential decay rates of inclusive $B\to X_s\gamma$ and $B\to X_ul\bar{\nu}$ decays.The improved predictions for the $B\to X_s\gamma$ photon energy spectrum include all the known singular contributionsat $\mathrm{N^3LO}$, with the exception of one yet-unknown 3-loop hard function coefficient.In the endpoint region of the spectrum all the singular contributions are resummed at the $\mathrm{N^3LL}$ accuracy.The remaining, nonsingular contributions are included at $\mathrm{NNLO}$.To combine the singular contributions at $\mathrm{N^3LO}$ with the nonsingular contributions at $\mathrm{NNLO}$,the yet-unknown 3-loop nonsingular contributions are parametrized in terms of nuisance parameters.The used parametrization avoids the artifactsthat arise due to the mismatch of perturbative order of singular and nonsingular contributions.The missing 3-loop hard function coefficient is also treated as a nuisance parameter.The uncertainty related to these missing corrections is estimated and compared to the perturbative truncation uncertainty.The impact of different definitions of the $b$-quark mass on the convergence of the perturbative series is studied.The $\mathrm{1S}$ mass scheme, which has been used for $B\to X_s\gamma$ in the past, is demonstrated to break down starting at $\mathrm{N^3LO}$.In contrast, the MSR mass scheme is shown to yield much more stable results.The convergence is further improved by an appropriate choice of short-distance definitions of the hadronic parameters $\lambda_1$ and $\rho_1$.In the context of these short-distance mass corrections, a novel kind of correction, which first appears at $\mathrm{N^3LO}$, is identified.This correction is formally subleading in the power counting of Soft-Collinear Effective Theory (SCET), but is nevertheless singular in the peak region of the spectrum.Therefore, it cannot be naively accounted for within the previously-used approach.A prescription for the resummation of such terms is developed.Additionally, the impact of a different treatment of higher-order cross-terms in the factorization theorem is studied.The improved $B\to X_ul\bar{\nu}$ predictions include all singular contributions at $\mathrm{NNLO}$,and the nonsingular corrections are included at $\mathrm{NLO}$.In the endpoint region the singular contributions are resummed at $\mathrm{N^3LL}$ accuracy.The resummed and fixed-order results are combined using a matching procedure that avoids artificial singularitiesand yields meaningful results in all regions of the phasespace, with the exception of the deep resonance region,where the inclusive approach is not applicable.The theoretical predictions are compared to the recently published measurements of differential $B\to X_ul\bar{\nu}$ spectra by the Belle collaboration.The agreement is adequate for the used inclusive model, and the differences are discussed..

Thin-film photovoltaic devices are used to harvest solar energy. To be economically competitive, three aspects are particularly challenging, which we addressed in this work: cost efficiency, defect passivation, and spatial homogeneity. [...]

The Large Hadron Collider (LHC) will undergo a major “High Luminosity” upgrade with the goal of delivering a peak instantaneous luminosity of 5 − 7.5 × 10^34 cm−2s−1 by 2029. In order for the CMS experiment to cope with the higher radiation levels and data rates, the current CMS Silicon Tracker will be replaced. [...]

This thesis presents the study of three quantum materials conducted by means of a novel photon source for Time- and Angle-Resolved Photoelectron Spectroscopy (TR-ARPES) developed at the T-ReX laboratory at FERMI (Elettra, Trieste). This source provides pulses at a photon energy of 10.8 eV up to the MHz repetition rate, while offering picosecond time resolution and few tens of meV energy resolution. [...]

In this thesis, measurements performed using proton-proton collision data at $\sqrt{s} = 13$TeV collected by the CMS experiment at the CERN LHC, in the years 2016, 2017, and 2018, are presented. The data correspond to an integrated luminosity of 138$~\mathrm{fb}^{-1}$.New results on top quark pair production in association with a photon ($\mathrm{t\bar{t}\gamma}$) are presented. [...]

With the advent of ultrafast optics and controllable waveforms consisting of only a few oscillations of the electric field, the idea of controlling electrons at the frequency of light was born. This established the potential of using a controlled optical waveform to switch electronic circuit elements at the frequency of an optical wave, typically on the order of 0.1 to 1 petahertz(1015 Hz). [...]

This thesis presents a search for a heavy scalar and a heavy pseudoscalar Higgs boson decaying into a top quark and a top antiquark. The used data was collected by the CMS experiment at the LHC at an energy of √s=13 TeV during 2016, 2017 and 2018 corresponding to an integrated luminosity of 138 fb⁻¹. [...]

Compressed mass spectra models with low transverse momentum displaced leptons signature have low sensitivity for direct detection at the CMS experiment due to hard trigger constraints. It has been shown in this work that the search significance is obtained over lepton displacements of O(0.1cm) to O(100cm) by lowering the trigger pT threshold on the leptons to 20 GeV. [...]

Major problems in quantum molecular physics, such as quantum modeling of chemical dynamics and studying atmospheres of hot exoplanets, pose prohibitive computational challenges that are at the forefront of research efforts in numerical analysis and scientific computing. In particular, it is often required in these applications to approximate a vast number of highly-oscillatory solutions of infinite-dimensional eigenvalue problems and evolution equations in very high dimensions. [...]

The motivation to control and temporarily isolate a single quantum mechanical event like an electronic transition has driven the quest for ever shorter light pulses. Controlling a highly intense electric field in the visible to infrared wavelength range on a sub-cycle time scale becomes feasible with the concept of the parametric waveform synthesizer. [...]

In this thesis, data collected by the CMS Experiment at the CERN LHC is analysed. The data was collected during LHC Run 2 in the years 2016-2018 and corresponds to an integrated luminosity of 138 $\textrm{fb}^{-1}$. [...]

Bei der Bestrahlung von Tumoren findet unter anderem Elektronenstrahlung Anwendung.Ein noch weitgehend unerforschter und vielversprechender Effekt ist der sogenannteFLASH-Effekt, bei welchem eine kurzzeitige und hochdosierte Bestrahlung zu wenigerSch¨aden am gesunden Gewebe f¨uhrt als eine l¨anger dauerende mit niedriger Dosis. Umden optimalen Parameterbereich f¨ur diese Bestrahlungsart zu ermitteln, entsteht am DeutschenElektronen-Synchrotron (DESY) in Zeuthen ein Forschungsbereich zur Dosimetrievon Elektronenstrahlung in biologischem Gewebe. [...]

Zinc-dependent hydrolases are a class of metalloenzymes that require zinc ions to catalysehydrolytic reactions. Structural studies of these enzymes shall provide detailed information aboutthe processing of their natural substrates, domain organization, and overall structural fold. [...]

In this thesis, two novel structures were presented, jointly illuminating dimerization and tRNA binding by human TGT. A first structure, obtained by X-ray crystallography, allowed to give a thorough account of the atomic details of the heterodimeric interface as well as active site recognition of the substrate RNA. [...]

European XFEL is a particle accelerator that generates X-ray laser pulses for scientific research. The currently discussed High Duty Cycle upgrade will drastically change the way the machine operates. [...]

This thesis introduces the application of the Carrier-Suppression Interferometer (CSI) method for precision phase-noise measurements at attosecond resolution in the field of particle accelerator control systems. Starting from the thorough investigation of crucial system components and their phase noise contribution, the CSI setup reported here outperforms conventional noise detection methods for accelerator controls by more than two orders of magnitude. [...]

While the Standard Model (SM) of particle physics has been incredibly successfulin describing fundamental particles and their interactions, there are a fewphenomena that remain without explanation in the current understanding ofthe building blocks of this world. These open questions are the source of new ideas andmotivation for searches for new physics with experiments at the Large Hadron Colliderat CERN. [...]

This doctoral thesis presents an inclusive analysis of the photon energy spectrum in radiative B meson decays (B → X$_{s}γ$) that involve strange hadrons and a photon. The data set consists of $Υ(4S)$ mesons that primarily decay into pairs of B mesons. [...]

The investigation of proteins is highly relevant due to their various functions in living organisms mand their importance in nutrition. A technique that can access the collective dynamics of proteins in solution is X-ray photon correlation spectroscopy ($XPCS$). [...]

This work discusses and demonstrates the imaging method ‘photon-photon correlation of X-ray fluorescence’, also called ‘Incoherent Diffraction Imaging (IDI)’. This method corresponds to the ‘intensity interferometry’, known from astronomy. [...]

The dissociation dynamics of diiodomethane molecules (CH2I2) have been investigated in a 97.6 eV XUV-pump XUV-probe measurement at the reaction microscope endstation at the free-electron laser FLASH2. Ionic fragments created by 4d inner-valence ionisation followed by Auger decay have been detected in coincidence, enabling a kinematically complete reconstruction of the dissociation pathways [...]

RNA is a single-stranded biopolymer that plays a myriad of roles in physiological and pathological processes and is the carrier of genetic information in many human pathogens. Hepatitis C virus (HCV) is one of the most impactful representatives of RNA viruses. [...]

Conformal Field Theories (CFTs) are ubiquitous in modern theoretical physics and play an important role in high-energy physics and condensed matter physics alike, describingthe universal behavior of second-order phase transitions. The notion of a CFT can be generalized by introducing extended objects, or defects. [...]

The production of four top quarks has been predicted by the Standard Model(SM) and has been considered as one of its important tests. The measurementsobtainable from this production, such as its cross section, can be comparedwith predictions provided by SM. [...]

In this thesis, a measurement of the top quark mass as defined in the on-shell renormalization scheme, also known as pole-mass $m_\text{t}^\text{pole}$, is presented.The analysis is performed using events where a top quark-antiquark pair ($\text{t}\overline{\text{t}}$) is produced in association with at least one additional jet ($\text{t}\overline{\text{t}}\text{+jet}$) in proton-proton collisions at the CERN LHC at a center-of-mass energy of 13 TeV. The data are recorded by the Compact Muon Solenoid experiment in 2016, corresponding to a total integrated luminosity of 36.3${\,\text{fb}^\text{-1}}$.Events with two opposite-sign leptons in the final state ($\text{e}^{+}\text{e}^{-}$, $\mathrm{\mu}^{+}\mathrm{\mu}^{-}$, $\text{e}^{\pm}\mathrm{\mu}^{\mp}$) are analyzed.The $\text{t}\overline{\text{t}}\text{+jet}$ production cross section is measured as a function of the inverse of the invariant mass of the $\text{t}\overline{\text{t}}\text{+jet}$ system, $\rho=340\,\text{GeV}/m_{\text{t}\overline{\text{t}}\text{+jet}}$.A novel analysis technique based on machine learning is developed for the reconstruction of the main observable and for the event classification.The measurement is unfolded to the parton level and is compared to the theoretical prediction at next-to-leading order, using the dynamic renormalization and factorization scales.The theoretical predictions are obtained by using two alternative sets of parton distribution functions (PDFs). [...]

The production of $𝑍$+jets events at high $𝑝\small_𝑇$ in proton-proton collisions serves as a significant test for Quantum Chromodynamics ($QCD$). This thesis explores the azimuthal correlation of $𝑍$+jet production from both a phenomenological and an experimental perspective. [...]

In einer Photogun wird mit einem Laserpuls ein Elektronenpaket aus einer Photokathode herausgelöst, und sofort in einer Kavität auf hohe Energie beschleunigt. Zur Strahlführung dient ein Solenoidmagnet. [...]