The HERA accelerator, an electron-proton collider facility based at the DESY laboratory in Hamburg, started delivering luminosity to the ZEUS experiment in May 1992. The short time of 96ns between bunch crossings and the fact that the primary source of detector activity in ZEUS does not come from the e-p interactions of interest but rather from other sources makes a high performance three level trigger system essential to data-taking. We present one part of the ZEUS trigger system, the Central Tracking Detector First Level Trigger (CTD-FLT). The principle of operation and the hardware implementation are discussed at length. A prototype system which was used during the early stages of ZEUS data-taking is described. We detail the principles of the CTD-FLT hardware testing and discuss aspects of the First Level Trigger data from the 1993 running period. During this time the CTD trigger has proved to be an invaluable part of the overall system. The high energies accessible at HERA make it possible to probe a variety of new physics models. The second part of this thesis focuses on one such model - Supersymmetry (SUSY). After an introduction to the model, a search for R-parity violating SUSY in the ZEUS data from the 1992 running period is described. No evidence for such signals has been found and hence we set upper limits on the mass scale of the theory. Finally we present a Monte Carlo study of the potential discovery reach of HERA for R-parity violating SUSY models, and come to the conclusion that HERA is an ideal place to look for such phenomena.

Thesis (Ph. D.)--Michigan State University. Dept. of Physics and Astronomy, 2008. / Title from PDF t.p. (viewed on Mar. 30, 2009). Includes bibliographical references (p. 137-146). Also issued in print.

Thesis (M.S.)--Rutgers University, 2008. / "Graduate Program in Physics and Astronomy." Includes bibliographical references (p. 117-121).

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 163-169).

The FONT beam-based, intra-train feedback system has been designed to provide beam position stabilisation in single-pass accelerators. A FONT feedback system utilising position information from three high-resolution cavity beam position monitors (BPMs) has been commissioned at the interaction point (IP) of the Accelerator Test Facility 2 (ATF2) at KEK, Japan. The ultimate goal of the feedback in the IP region is to stabilise the low-emittance electron beam to the nanometre level. The operation, optimisation and resolution performance of this IP system forms the subject of this thesis. The IP feedback system makes use of beam position measurements from the BPMs to drive an upstream kicker and provide a local correction. The BPMs have a fast decay time of ~25 ns to allow bunches within the beam train to be resolved. The operation of the IP BPMs, the noise floor, and position sensitivity to phase are discussed in detail. Attempts are made to diagnose an unwanted ~60 MHz oscillation in the cavity signals, which is bunch charge-dependent and thus likely beam generated. The BPM resolution estimate was notably improved from 50 nm to 20 nm using waveform integration in analysis of the BPM signals. A multi-parameter fit was used to address inaccurate calibrations and charge-dependencies to achieve more consistent resolution performance and produce a best-ever resolution estimate for the BPMs of 17.5 ± 0.4 nm. A novel mode of IP beam position stabilisation using two BPMs as input to the feedback has been successfully demonstrated. The beam position was stabilised to 57 ± 4 nm, as measured at an independent BPM. Feedback performance was improved to this level by sampling the waveform to optimise bunch-to-bunch correlation. Analysis suggests correction capability could be enhanced by firmware waveform integration to achieve a measurable beam stabilisation of ~40 nm in the future.

The FONT beam-based, intra-train feedback system has been designed to provide beam stability at single-pass accelerators, such as at the interaction point (IP) of the International Linear Collider. Two FONT feedback systems have been commissioned at the Accelerator Test Facility (ATF) at KEK, Japan, and the operation, optimisation and performance of these systems is the subject of this thesis. For each system, the accelerator is operated with two-bunch trains with a bunch separation of around 200 ns, allowing the first bunch to be measured and the second bunch to be subsequently corrected. The first system consists of a coupled-loop system in which two stripline beam position monitors (BPMs) are used to characterise the incoming beam position and angle, and two kickers are used to stabilise the beam. A BPM resolution of about 300 nm has been measured. On operating the feedback system, a factor ~ 3 reduction in position jitter has been demonstrated at the feedback BPMs and the successful propagation of this correction to a witness BPM located 30 m downstream has been confirmed. The second system makes use of a beam position measurement at the ATF IP that is used to drive a kicker to provide a local correction. The measurement is performed using a high-resolution cavity BPM with a fast decay time of around 20 ns designed to allow multiple bunches to be resolved. The linearity of the cavity BPM system and the noise floor of the electronics are discussed in detail. The performance of the BPM system under standard ATF operation and with the beam waist at the BPM is described. A BPM resolution of about 50 nm has been measured. This IP feedback system has been used to stabilise the beam position to the 75 nm level.

Malgré le succès incontestable du Modèle Standard de la physique des particules, il est vraisemblable qu'il ne soit qu'une partie de la théorie complète de physique des particules -- comme c'est le cas des hypothèses de théories unifiées -- et ainsi de nombreux efforts ont été dédiés au développement de théorie de Nouvelle Physique. La Supersymmétrie est l'une des extensions les plus populaires puisque qu'elle permet non seulement de résoudre le problème de Naturalité mais présente aussi une candidat viable de matière sombre. Ce dernier point a été particulièrement mis en avant avec les récentes mesures expérimentales qui ont permis d'affiner significativement notre connaissance des propriétés de cette matière sombre. En particulier, la détermination de la densité relique de matière sombre dans l'univers est à présent réalisée avec une précision de l'ordre du pourcent. Dans le cadre du Modèle Standard Supersymmétrique Minimal (le MSSM), cette contrainte permet ainsi de tester la structure à une boucle de la théorie. Cependant c'est aussi un modèle présentant un très grand nombre de paramètres, comparé au Modèle Standard, et le calcul complet des observables à une boucle reste trop long pour être effectué sur l'ensemble de l'espace des paramètres. Dans cette thèse, je me suis ainsi intéressé à la possibilité de reproduire ces corrections à la boucle par un ensemble de couplages effectifs. L'approche effective présentant l'avantage de garder la simplicité d'un calcul effectué à l'arbre tout en conservant une trace des effets caractéristiques de boucles comme le non-découplage de certaines particules lourdes. Le LHC (Large Hadron Collider), dont les opérations ont démarrées juste après le début de ma thèse, soit à l'automne 2009, a fourni des données complémentaires aux observables de matière sombre. En effet le secteur du Higgs du MSSM est très peu flexible, ce qui a pour effet d'introduire ce que l'on appelle le problème du ``fine-tuning'', c'est à dire la nécessité d'avoir des valeurs très précises pour les paramètres. Afin d'y remédier, de nombreux modèles ont été créés au delà du MSSM, comme le NMSSM (en anglais Next-to-MSSM). Dans le but de suivre une approche plus générale, j'ai décidé au cours de cette thèse d'utiliser à nouveau l'approche effective, mais dans un but différent : alors que les couplages effectifs utilisés dans le cas de la matière sombre sont choisi pour reproduire le plus fidèlement possible les corrections à la boucle des particules du MSSM, les opérateurs effectifs que nous ajoutons au secteur du Higgs sont les effets à basse énergie (c'est à dire l'énergie de production du Higgs) d'une nouvelle physique à haute énergie. Bien que dédiées à deux buts différents, ces deux implémentations d'une même technique montrent bien ses différents atouts. Dans un des cas (celui du Higgs) les opérateurs effectifs permettent de paramétrer l'effet d'une physique ultraviolette inconnue, alors que dans l'autre cas cette physique ultraviolette se réduit au simple MSSM. / Despite the numerous successes of the Standard Model of particle physics, it is believed that the complete picture of particle physics could be larger, as a unified theory for instance, and thus many efforts have been devoted to the development of theories of new physics. Supersymmetry is one of the most popular extensions since in addition to a solution of the naturalness issue, it provides a viable dark matter candidate. This last sector being all the more important now that recent experimental measurements have significantly increased our knowledge about dark matter properties, in particular the experimental determination of the relic density has reached the accuracy of a few percent. When applied to the Minimal Supersymmetric Standard Model (the MSSM, which is the simplest supersymmetric extension of the Standard Model), this constraint will thus shed light on the one-loop structure of the model. The MSSM is however much more liberal with unconstrained parameters than the Standard Model is, and the full one-loop computation of the relic density tends to be too long to be carried out throughout this large parameter space. In this thesis I have thus explored the opportunity of accounting for those loop corrections through a set of effective couplings. This effective approach has the advantage of keeping the simplicity of a tree-level computation but encoding at the same time genuine loop features such as the non-decoupling of heavy particles. Complementary to those constraints are the observables related to the LHC, which started taking data shortly after the beginning of my PhD in fall 2009. The Higgs sector of the MSSM is tightly constrained and this results in a certain fine-tuning of the model, which led to the creation of many models beyond the MSSM (such as the Next-to-Minimal Supersymmetric Standard Model). Arguing for a more general approach, I have decided in this thesis to use again the effective approach but with a different aim : while the effective couplings in the case of dark matter are determined to account for the MSSM loop corrections, the effective operators we add to the Higgs sector of the MSSM are the remnants of the integration of a heavy extra spectrum. This effective approach, called the BMSSM (for Beyond the MSSM) is known to account for many different realisations of non-minimal supersymmetry, and we have used it as a framework to recast the results of the Higgs analyses carried out by ATLAS and CMS collaborations. This study has led to the caracterisation of the rich phenomenology of the Higgs sector in the BMSSM, with in particular the possibility for a signal quite different from Standard Model or MSSM expectations. Though based on distinct aims, the two implementations of the effective approach show the different advantages of an effective field theory. In the first case the effective operators are parametrising the effect of an unknown UV completion, whereas in the second we assume this UV completion to be the MSSM.

Apresentamos um estudo fenomenológico de algumas extensões do modelo padrão da física de partículas no LEP e no LHC. Concentramos nossa atenção, em particular1 na busca por evidências de supersimetria com violação de paridade--R no LEP I, LEP II e LHC. Estudamos um modelo supersirnétrico com violação espontânea de paridade-R bem como um modelo efetivo onde a violação ocorre explicitamente. Realizamos, também, um estudo independente de modelo para leptoquarks no LHC a partir de colisões eq baseado em uma lagrangiana efetiva. Mostramos que os efeitos destas duas extensões do modelo padrão poderão ser visíveis no intervalo de energia dos aceleradores considerados. / We present a phenomenologic study of some extensions of standard model of elementary particles at LEP and LHC. We concentrate our attention, for instance, on the search of R-parity violating supersymmetry evidences at LEP I, LEP II and LHC. We study a spontaneous R-parity violating model as well an effective one where the violation occurs explicitly. We also perform an independent model study on leptoquarks at LHC coming from e q collisions, in the frame of an effective lagrangian. We show that the effects of these two standard model extensions can be visible in the range of energy of the chosen colliders.

Double hard parton-parton interactions are expected to occur frequently in proton-proton (p-p) collisions at the LHC. They can give rise to significant backgrounds to certain rare single scattering (SPS) signals, and are an interesting signal process in their own right. In this thesis, we discuss the theoretical description of the double parton scattering (DPS) cross section in the context of Quantum ChromoDynamics (QCD). After an overview of QCD and an introduction to DPS in Chapter 1, we describe in Chapter 2 a framework for calculating the p-p DPS cross section introduced by Snigirev et al., in which this cross section is expressed in terms of double PDFs D_p {ij}(x_1,x_2,Q_A 2,Q_B 2) (dPDFs). We show that the equal-scale dPDFs are subject to momentum and number sum rule constraints, and use these in the construction of an explicit set of leading order (LO) equal-scale dPDFs (the 'GS09' dPDFs). The leptonic same-sign WW DPS signal obtained using GS09 dPDFs is compared with that obtained using simple factorised forms, and the prospects of observing this signal taking into account SPS backgrounds are analysed. We discuss two ways in which the dPDF framework for describing p-p DPS is deficient in Chapter 3. We discuss interference and correlated parton effects in flavour, spin, colour, and parton type, which are ignored by the dPDF framework. We then study DPS-type graphs in which the parton pairs from both protons have arisen from a perturbative 1->2 branching, derive an expression for the part of such graphs associated with the particles arising from the 1->2 branchings being almost on-shell, and use this to demonstrate that the treatment of these graphs by the the dPDF framework is unsatisfactory. In Chapter 4, we study DPS-type graphs in which the parton pair from only one proton has arisen from a perturbative 1->2 branching. We discover that such graphs contribute to the LO p-p DPS cross section, and that crosstalk between partons in the 'nonperturbatively generated' pair is allowed provided that it occurs at a lower scale than that of the perturbative 1->2 branching in the other proton. The result of this analysis is combined with that of the previous chapter to propose a formula for the LO total DPS cross section, and our proposal is compared with those from other authors. We finish in Chapter 5 with some conclusions and suggestions for further work.

Die am LHC gewonnen Ergebnisse stimmen überwiegend mit den Vorhersagen des Standardmodells der Teilchenphysik (SM) überein, doch die Notwendigkeit von Physik jenseits des Standardmodells (BSM) bleibt. Allerdings führt kein klarer Weg zu einem Nachfolger des Standardmodells. In dieser Arbeit wird daher ein allgemeines theoretisches Werkzeug für die Erforschung der Grenzen des SM verwendet: die Effektiven Feldtheorien (EFTs). In dieser Arbeit wird die Standard Model Effective Field Theory (SMEFT) benutzt, um das Potential des zukünftigen Hadronenbeschleunigers FCC-hh zu beurteilen. Hierfür wird der Vh-Produktionsprozess untersucht. Die Sensitivität dieser Kanäle wird durch die Messung von doppelt differenziellen Wirkungsquerschnitten möglich. Die Abwesenheit von Eich-Anomalien ist nötig, um die Konsistenz einer Quantenfeldtheorie zu bewahren. Es wird gezeigt, dass die SMEFT bis zur Massendimension 6 für beliebige Werte seiner WCs frei von aus Dreiecks-Anomalien stammenden Eich-Anomalien ist. Die bosonischen EFT-Techniken werden auch benutzt, um die Beziehung zwischen gemischten globalen Eich-Anomalien und Axion-Kopplungen zu Vektorbosonen in Axion-EFTs zu analysieren. Es ergibt sich, dass diese in keiner Beziehung zueinander stehen, wenn schwere chirale Fermionen ausintegriert werden. Dieser Fakt verknüpft Axion-EFTs mit chiralen Erweiterungen des Standardmodells. Für nichtabelsche Eichbosonen werden IR-Summenregeln gefunden, deren Verletzung die Anwesenheit chiraler Felder im UV-Bereich anzeigen. Es wird eine minimale Erweiterung des Standardmodells als Beispiel studiert. Letztlich wird gezeigt, wie alte Formalismen zu neuen Einsichten führen können. Helizitäts-Spinoren und Streuamplituden werden eingeführt und es wird diskutiert, wie sie die Berechnung der Amplituden erleichtern und inwiefern sie eine Alternative zu EFTs darstellen. Die VVh- und VVhh-Amplituden werden studiert und ihre Hoch-Energie-Grenzwerte einschließlich verschiedener BSM-Beiträge berechnet. / The results obtained at the LHC agree well with the predictions of the Standard Model of particle physics (SM). However, the need for Beyond the Standard Model (BSM) physics remains. But there is no clear path towards a successor for the SM. Hence, we must prepare the tools needed to explore the frontiers of physics thoroughly. In this work, we study one of the main theoretical tools that can be used for such an exploration, Effective Field Theories (EFTs). We use the Standard Model Effective Field Theory (SMEFT) to study the Vh production process at FCC-hh, assessing the discovery potential of that future collider. The sensitivity to BSM effects is improved via the measurement of doubly-differential cross-sections. We also study the relation between EFTs and anomalies. The absence of gauge anomalies is required to preserve the consistency of a Quantum Field Theory. We prove that SMEFT at dimension 6 is free from gauge anomalies coming from triangle diagrams for any value of its WCs. Then, we analyse the relationship in axion EFTs between mixed global-gauge anomalies and axion couplings to vector bosons. They turn out to be unrelated when heavy chiral fermions are integrated out, linking axion EFTs to chiral extensions of the SM. We find IR sum rules whose violation indicate the presence of chiral fields in the UV. We show and study a minimal phenomenologically relevant model as an example. Finally, we explore how revisiting old formalisms can lead to new insights. We introduce the helicity spinor and scattering amplitudes formalisms and show how they facilitate the computation of cross sections and discuss how they constitute an alternative to EFTs as a parametrisation of BSM effects. We study the VVh and VVhh amplitudes, of which we compute the high-energy limit including different BSM contributions.