Mit der Entdeckung des Higgs-Bosons hat ein Messprogramm begonnen, bei dem die Eigenschaften dieses neuen Teilchens mit der höchstmöglichen Präzision untersucht werden soll um die Gültigkeit des Standardmodells der Teilchenphysik zu prüfen und nach neuer Physik jenseits des Standardmodells zu suchen. Für dieses Ziel wird der Large Hadron Collider (LHC) und sein Upgrade, der High Luminosity-LHC bis etwa zum Jahr 2035 laufen und Daten produzieren. Um an der Spitze der Teilchenphysik zu bleiben, hat die “European Strategy Group for Particle Physics” empfohlen, ambitionierte Nachfolgeprojekte für die Zeit nach dem LHC zu entwickeln. Entsprechend dieser Empfehlung hat das CERN die “Future Circular Collider” (FCC) -Studie gestartet, die die Machbarkeit neuer Speicherringe für Teilchenkollisionen (Collider) untersucht. In dieser Arbeit wird die Entwicklung der Wechselwirkungszonen für FCC-hh, einem Proton-Proton-Speicherring mit einer Schwerpunktsenergie von 100 TeV und einem Umfang von 100 km, beschrieben. Die Wechselwirkungszone ist das Herzstück eines Colliders, da sie die erreichbare Luminosität bestimmt. Es ist daher entscheidend, schon früh im Entwicklungsprozess eine möglichst hohe Kollisionsrate anzustreben. Ausgehend von der optische Struktur der Wechselwirkungszonen des LHC und dem geplanten High Luminosity-LHC (HL-LHC) werden Strategien zur Skalierung hergeleitet um der höheren Strahlenergie gerecht zu werden. Bereits früh im Entwicklungsprozess wird die Strahlungsbelastung durch Teilchentrümmer vom Wechselwirkungspunkt als entscheidender Faktor für das Layout der Wechselwirkungszone identifiziert und eine allgemeine Design-Strategie, die den Schutz der supraleitenden Endfokussierungsmagnete mit einer hohen Luminosität verbindet, wird formuliert und implementiert. Aufgrund des deutlichen Spielraums in Bezug auf beta* wurde die resultierende Magnetstruktur zum Referenzdesign für das FCC-hh-Projekt. / The discovery of the Higgs boson is the start of a measurement program that aims to study the properties of this new particle with the highest possible precision in order to test the validity or the Standard Model of particle physics and to search for new physics beyond the Standard Model. For that purpose, the Large Hadron Collider (LHC) and its upgrade, the High Luminosity-LHC, will operate and produce data until 2035. Following the recommendations of the European Strategy Group for Particle Physics, CERN launched the Future Circular Collider (FCC) study to design large scale particle colliders for high energy physics research in the post-LHC era. This thesis presents the development of the interaction region for FCC-hh, a proton-proton collider operating at 100 TeV center-of-mass energy. The interaction region is the centerpiece of a collider as it determines the achievable luminosity. It is therefore crucial to aim for maximum production rates from the beginning of the design process. Starting from the lattices of LHC and its proposed upgrade, the High Luminosity LHC (HL-LHC), scaling strategies are derived to account for the increased beam rigidity. After identifying energy deposition from debris of the collision events as a driving factor for the layout, a general design strategy is drafted and implemented, unifying protection of the superconducting final focus magnets from radiation with a high luminosity performance. The resulting FCC-hh lattice has significant margins to the performance goals in terms of beta*. Protecting the final focus magnets from radiation with thick shielding limits the minimum beta* and therefore the luminosity. An alternative strategy to increase the magnet lifetime by distributing the radiation load more evenly is developed. A proof of principle of this method, the so-called Q1 split, is provided. In order to demonstrate the feasibility of the derived interaction region lattices, first dynamic aperture studies are conducted.

Supersymmetry is a promising candidate theory that could solve the hierarchy problem and explain the dark matter density in the Universe. The ATLAS experiment at the Large Hadron Collider is sensitive to a variety of such supersymmetric models. This thesis reports on a search for pair production of the supersymmetric scalar partners of bottom and top quarks in 20.1 fb⁻¹ of pp collisions at a centre-of-mass energy of 8 TeV using the ATLAS experiment. The study focuses on final states with large missing transverse momentum, no electrons or muons and two jets identified as originating from a b-quark. This final state can be produced in a R-parity conserving minimal supersymmetric scenario, assuming that the scalar bottom decays exclusively to a bottom quark and a neutralino and the scalar top decays to a bottom quark and a chargino, with a small mass difference with the neutralino. As no signal is observed above the Standard Model expectation, competitive exclusion limits are set on scalar bottom and top production, surpassing previously existing limits. Sbottom masses up to 640 GeV are excluded at 95% CLs for neutralino masses of up to 150 GeV. Differences in mass between ^~<sub style='position: relative; left: -.7em;'>b</sub>₁ and ^~<sub style='position: relative; left: -.7em;'>X</sub>⁰<sub style='position: relative; left: -.5em;'>1</sub> larger than 50 GeV are excluded up to sbottom masses of 300 GeV. In the case of stop pair production and decay ^~<sub style='position: relative; left: -.7em;'>t</sub>₁ → b + ^~<sub style='position: relative; left: -.7em;'>X</sub>^±<sub style='position: relative; left: -.5em;'>1</sub> and ^~<sub style='position: relative; left: -.7em;'>X</sub>^±<sub style='position: relative; left: -.5em;'>1</sub> → ^~<sub style='position: relative; left: -.7em;'>X</sub>⁰<sub style='position: relative; left: -.5em;'>1</sub> + W* with mass differences &triangle;m = m_{^~<sub style='position: relative; left: -.7em;'>X}^±<sub style='position: relative; left: -.5em;'>1</sub></sub> − m_{^~<sub style='position: relative; left: -.7em;'>X}⁰<sub style='position: relative; left: -.5em;'>1</sub></sub> = 5 GeV (20 GeV), stop masses up to 580 GeV (440 GeV) are excluded for m_{^~<sub style='position: relative; left: -.7em;'>X}⁰<sub style='position: relative; left: -.5em;'>1</sub></sub> = 100 GeV. Neutralino masses up to 280 GeV (230 GeV) are excluded for m_{^~<sub style='position: relative; left: -.7em;'>t}₁</sub> = 420 GeV for &triangle;m = 5 GeV (20 GeV). In an extension of this analysis, sbottom quarks cascade-decaying to at least a Higgs boson are searched for in final states with large missing transverse momentum, at least 3 b-tagged jets and no electrons or muons, using neural network discriminants.

The LHCb experiment is an experiment based at the LHC in Geneva and is dedicated to the study of mesons containing bottom and charm quarks. One of the primary goals of the physics at LHCb is to measure CP-violating effects which lead to a dominance of matter over anti-matter in the universe. This thesis presents the measurement of the CP-violating phase Ø s which is one of the golden channels at LHCb. This phase is observed as the interference between mixing of B0s ↔ B-0s and decay of B0s → J/ψ K+K−. The results, based upon the 1.0 fb−1 dataset collected by LHCb during 2011, are: Ø s = 0.07±0.09±0.01 rad , ∆Γs = 0.100±0.016±0.002 ps−1 , Γs = 0.663±0.005±0.006 ps−1 . This analysis is also able to measure the mixing parameter ms = 17.71±0.10±0.01 ps−1. To improve upon this measurement the B0s → J/ψ K+K− analysis is combined with the B0s → J/ψ π+ π − decay channel to make the most accurate measurements to date of, Ø s = 0.01±0.07±0.01 rad, ∆Γs = 0.106±0.011±0.007 ps−1 and Γs = 0.661±0.004±0.006 ps−1. As an integral part of this work a comprehensive software suite known as RapidFit was developed, which is used by many other physicists and this is described.

At the dawn of the Large Hadron Collider era, the Brout-Englert-Higgs mechanism remains the most appealing theoretical explanation of the electroweak symmetry breaking, despite the fact that the associated fundamental scalar boson has escaped any direct detection attempt. In this thesis, we consider a particular extension of the minimal Brout-Englert-Higgs scalar sector implemented in the Standard Model of strong and electroweak interactions. This extension, which is a specific, "twisted", realisation of the generic two-Higgs-doublet model, is motivated by a relative phase in the definition of the phenomenologically successful CP and custodial symmetries. Considering extensively various theoretical, indirect and direct constraints, this model appears as a viable alternative to more conventional scenarios like supersymmetric models, and gives grounds to largely unexplored possibilities of exotic scalar signatures at present and future collider experiments.

A modified plate load (MPL) test was developed to measure the in situ cohesion of a carbonate or caliche cemented soil. The MPL test was performed on the crest of a vertical cut in alluvial soil with a steel plate loaded until the soil failed. A three-dimensional slope stability analysis was then used to back calculate soil cohesion. In situ test results were used in conjunction with laboratory testing of deaggregated soils samples to completely define the Mohr-Coulomb strength parameters of the in situ soil. In order to check the result of the in situ test procedure, the field test conditions were modeled for use in a two-dimensional slope stability analysis using the computer program CSLIP1. A comparison of the results shows reasonable values of soil cohesion were obtained using the MPL test method.

In the current LHC era, a vast number of models for BSM physics are being tested. For predictions accurate enough to match experimental errors, theoretical calculations have to go beyond LO estimates. However, calculating one-loop corrections in BSM models involves many new particles with specific model dependent properties. Therefore, they are done largely by hand, or in partially–automated ways. I present a fully automated tool for the calculation of generic massive one-loop Feynman diagrams with four external particles, implemented as a module within the fully automated MadGolem framework. With this one can compute the NLO–QCD corrections to generic BSM heavy resonance production processes, for example in the context of supersymmetric theories.

Despite its indisputable successes, the Standard Model of particle physics (SM) is widely considered to be an effective low-energy approximation to an underlying theory that describes physics at higher energy scales. While there are many candidates for such a theory, nearly all of them predict the existence of additional particles beyond those of the Standard Model. In this work, we present three analyses aimed at discovering new particles at current and future particle colliders. The first two analyses are designed to probe extended scalar sectors, which often arise in theories beyond the Standard Model (BSM). The structure of these extended scalar sectors can be described by a physically well-motivated class of models, known collectively as Two- Higgs Doublet Models (2HDMs). The scalar mass spectrum of 2HDMs is comprised of two CP-even states h and H, a CP-odd state A, and a pair of charged states H± . Traditional searches for these states at particle colliders focus on finding them via their decays to SM particles. However, there are compelling scenarios in which these heavy scalars decay through exotic modes to non-SM final states. In certain regions of parameter space, these exotic modes can even dominate the conven- tional decay modes to SM final states, and thus provide a complementary avenue for discovering new Higgs bosons. The first analysis presented aims to discover charged Higgs bosons H± via top decay at the LHC. We find that the exotic decay modes outperform the conventional decay modes for regions of parameter space with low values of the 2HDM parameter tan β. The second analysis aims to systematically cover all the exotic decay scenarios that are consistent with theoretical and experimental con- straints, at both the 14 TeV LHC and a future 100 TeV hadron collider. We find that the preliminary results are promising - we are able to ex- clude a large swathe of 2HDM parameter space, up to scalar masses of 3.5 TeV, for a wide range of values of tan β, at a 100 TeV collider. In addition to these two analyses, we also present a third, aimed at discovering pair produced higgsinos that decay to binos at a 100 TeV collider. Higgsinos and binos are new fermion states that arise in the Minimal Supersymmetric Standard Model (MSSM). This heavily- studied model is the minimal phenomenologically viable incorporation of supersymmetry - a symmetry that connects fermions and bosons - into the Standard Model. In the scenario we consider, the bino is the lightest supersymmetric partner, which makes it a good candidate for dark matter. Using razor variables and boosted decision trees, we are able to exclude Higgsinos up to 1.8 TeV for binos up to 1.3 TeV.

Dissertation presented in ful lment of the requirements for the degree of: Master of Science in Physics 2016 / The Phase-II upgrade of the Large Hadron Collider at CERN in the early 2020s will enable an order of magnitude increase in the data produced, unlocking the potential for new physics discoveries. In the ATLAS detector, the upgraded Hadronic Tile Calorimeter (TileCal) Phase-II front end read out system is currently being prototyped to handle a total data throughput of 5.1 TB/s, from the current 20.4 GB/s. The FPGA based Super Read Out Driver (sROD) prototype must perform an energy reconstruction algorithm on 2.88 GB/s raw data, or 275 million events per second. Due to the very high level of pro ciency required and time consuming nature of FPGA rmware development, it may be more e ective to implement certain complex energy reconstruction and monitoring algorithms on a general purpose, CPU based sROD co-processor. Hence, the feasibility of a general purpose ARM System on Chip based co-processing unit (PU) for the sROD is determined in this work. A PCI-Express test platform was designed and constructed to link two ARM Cortex-A9 SoCs via their PCI-Express Gen-2 x1 interfaces. Test results indicate that the latency of the PCI-Express interface is su ciently low and the data throughput is superior to that of alternative interfaces such as Ethernet, for use as an interconnect for the SoCs to the sROD. CPU performance benchmarks were performed on ve ARM development platforms to determine the CPU integer, oating point and memory system performance as well as energy e ciency. To complement the benchmarks, Fast Fourier Transform and Optimal Filtering (OF) applications were also tested. Based on the test results, in order for the PU to process 275 million events per second with OF, within the 6 s timing budget of the ATLAS triggering system, a cluster of three Tegra-K1, Cortex-A15 SoCs connected to the sROD via a Gen-2 x8 PCI-Express interface would be suitable. A high level design for the PU is proposed which surpasses the requirements for the sROD co-processor and can also be used in a general purpose, high data throughput system, with 80 Gb/s Ethernet and 15 GB/s PCI-Express throughput, using four X-Gene SoCs.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy, School of Physics. Johannesburg. February, 2017 / The discovery of the Higgs boson at the Large Hadron Collider in Switzerland marks the beginning of a new era: Physics beyond the Standard Model (SM). A model is proposed to describe numerous Run I features observed with both the ATLAS and CMS experiments. The model introduces a heavy scalar estimated to be around 270 GeV and an intermediate scalar which can decay into both dark matter and SM particles. Three different final state searches, linked by the new hypothesis, are presented. These are the hh → γγb¯ b, γγ + Emiss T and high mass diphoton channels. No significant excesses were observed in any channel using the available datasets and limits were set on the relevant cross sections times branching ratios. The lack of statistics in the γγb¯ b analysis prevents any conclusive statement in regard to the excess observed with Run I data. Observing no excess in the γγ + Emiss T channel with the current amount of data is also consistent with the intermediate scalar decaying to SM particles. This could explain the excess of Higgs bosons produced in associations with top quarks in the multilepton final states observed in ATLAS and CMS in Run I and Run II. The work presented provides a deeper understanding on the underlying phenomenology of the hypothesis and provides a foundation for future work. The ATLAS detector underwent a stringent consolidation and validation effort before data taking could commence in 2015. A high voltage board was designed and implemented into a portable test-bench used in the certification and validation process. In addition to these efforts, the electronics on the ATLAS detector are being improved for the Phase-II upgrade program in 2024. A software tool has been designed which integrates the envisioned Phase-II backend infrastructure into the existing ATLAS detector control system. This software is now an ATLAS wide common tool used by multiple sub-detectors in the community. / XL2017

A Dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2016. / Plastic scintillators play a key role in reconstructing the energy and tracks of hadronic particles that impinge the Tile Calorimeter of the ATLAS detector as a result of high energy particle collisions generated by the Large Hadron Collider of CERN. In the detector, plastic scintillators are exposed to harsh radiation environments and are therefore susceptible to radiation damage. The radiation damage effects to the optical properties and structural damage were studied for PVT based commercial scintillators EJ200, EJ208, EJ260 and BC408, as well as PS based UPS923A and scintillators manufactured for the Tile Calorimeter. Samples of dimensions 5x5x0.3 mm were subjected to irradiation using 6 MeV protons to doses of approximately 0.8 MGy, 8 MGy, 25 MGy and 25 MGy using the 6 MV tandem accelerator of iThemba LABS. Results show that damage leads to a reduced light output and loss in transmission character. Structural damage to the polymer base and the formation of free radicals occur for doses ≥ 8 MGy leading to reduced scintillation in the base and re-absorption of scintillation light respectively. Scintillators containing a larger Stokes shift, i.e. EJ260 and EJ208 exhibit the most radiation hardness. EJ208 is recommended as a candidate to be considered for the replacement of Gap scintillators in the TileCal for the 2018 upgrade. / LG2017