Dissertations / Theses on the topic 'Standard search'

This thesis project is about the educational process of design by which one learns to see the human potential in the situation of the built environment. That I believe is the universal message of this work communicated through the language of architecture. In terms of the local conditions, the project seeks to achieve this through reintroducing the architectural heritage of the city of Salt Jordan to its local and foreign audiences, engendering new appreciation for its history.
Master of Architecture

Higgs bosons are present in many extensions of the Standard Model, yet we are still waiting for the experimental confirmation of their existence. This thesis discusses Minimal and Next-to Minimal Supersymmetric Models, and presents searches for leptonic Higgs boson decays in channels that may provide the first unambiguous evidence of Higgs physics beyond the Standard Model. The channels considered are1 : gg→a1, gg→h1→2a1, H+→τν, and H+→a1W+, where a1→µµ and τ→ℓνν . A full data analysis is presented for gg→a1→µµ channel, while sensitivity prospects are discussed for the other channels. For the data analysis, we consider a data set with an integrated luminosity of 39 pb−1 collected by the ATLAS Detector at the Large Hadron Collider in 2010, operating at the centre of mass energy of √s = 7 TeV. As we observe no evidence for a signal in the gg→a1 channel, we set a model independent 95% confidence level upper limit on Higgs production cross section and branching ratio: σgg→a1×B(a1→µµ). This result represents the first measurement of σgg→a1×B(a1→µµ) in the world, and improves on the current experimental constraints on the Higgs sector beyond the Standard Model.
Les bosons de Higgs sont présents dans de nombreuses extensions du Modèle Standard, mais nous sommes toujours en attente de la confirmation exprimentale de leur existence. Cette thèse traite des modèles communs supersymetriques, et presente les recherches de désintégrations leptoniques du boson de Higgs dans les processus qui peuvent fournir la premiere preuve, sans equivoque, du Higgs au-dela du Modèle Standard. Les processus considérés sont: gg→a1, gg→h1→2a1, H+→τν,et H+→a1W+, avec a1→µµ et τ→ℓνν. La sensibilité des perspectives sont discutées pour les trois derniers, alors qu'une analyse de données complète est présentée pour le premier processus. Nous considérons un ensemble de données avec une luminosité integrée de 39 pb−1 collectées par le detecteur ATLAS au Large Hadron Collider en 2010, operant au centre de masse de √s = 7 TeV. Comme on n'observe pas de signal, nous avons mis une limite superieure sur la section efficace de production de Higgs et du rapport de branchement: σgg→a1×B(a1→µµ). Ce résultat représente une toute première mesure de σgg→a1×B(a1→µµ) dans le monde, et s'améliore sur les contraintes expérimentales courantes sur le secteur de Higgs au delà du Modèle Standard.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 93-94).
The Higgs decay into a photon and a Z boson, with the Z boson decaying into an electron-positron pair (electron channel) or muon-antimuon pair (muon channel), allows for accurate reconstructions of the Higgs boson mass and measurement of the Higgs to Z-[gamma] coupling. We explore selection criteria for the photon and the two leptons and provide preliminary observed and expected limits for the Higgs boson production cross section in the mass range from 120 GeV to 150 GeV. The data used in this analysis was collected with the CMS detector and corresponds to 5 fb- 1 and 19 fb-1 at center-of-mass energies of 7 TeV and 8 TeV, respectively.
by Kevin Singh.
S.B.

Even though electroweak part of the Standard Model passed decades of testing and precision measurements, there is still a space for the presence of new physics. In particular, the neutrino sector in the last years has been reaching the level of precision oscillometry. However, the current data are not able to exclude many possible extended scenarios, in which new interactions comparable with the standard ones are still possible. This work is dedicated to beyond-Standard-Model interactions of neutrino and electron called Non-Standard Interactions or shortly NSI. Analogously to standard electroweak interactions, NSI could be charged current (CC) and neutral current (NC) type. Usually, in analyses of experiments, NC and CC NSI are considered separately, and I follow this strategy in the course of this work. The global search for NSI involves almost all experimental approaches of neutrino physics and goes far beyond the scope of this work. Here, instead, I look at the problem through the prism of the large-scale liquid scintillator experiments and confine the investigation to the search for NC NSI with solar neutrinos. In addition, I review CC NSI with reactor neutrinos at medium baseline. As a contribution into upcoming JUNO experiment, I investigate liquid scintillator energy response and radiopurity, which are essential for the successful realization of solar and reactor neutrino physics programs and, therefore, for NC and CC NSI search. I analyze in detail the non-linearity and energy resolution of liquid scintillator. I develop an experimental Compton coincidence technique with High Pure Germanium gamma spectrometer, provide a conservative measurement of the Birks’ ionization quenching constant kB and discuss problems related to its measurement. Throughout the study, I also formulate the optimal characteristics of the experimental apparatus for this improvement. The ultimate goal of this investigation is separating intrinsic energy resolution, which was never yet robustly measured for liquid organic scintillators. The intrinsic energy resolution may have an impact on the energy response of the new generation large liquid scintillator detectors such as JUNO and have to be carefully investigated. Applying single photon counting technique, I perform a calibration of the PMT charge scale and set apart statistical term from the total liquid scintillator energy resolution. Remaining term significantly differs from zero, indicating the presence of additional contribution associated with the intrinsic energy resolution. As an outlook, the precise estimation of the light collection should be conducted in order to ensure that its contribution is not significant to mimic the observed intrinsic resolution effect. The analysis of the radiopurity of the liquid scintillator showed that it is close to the one demanded for reactor neutrino program and CC-NSI search. Still, an improvement of purification procedure is necessary to fulfill solar neutrino program requirements for NC NSI search. Finally, I place the limits to NC NSI parameters for electron and tau neutrino with the Phase II data of Borexino experiment. The limits are quite stringent and compatible with other experiments. The best up-to-date limit to the left electron NSI-parameter is obtained. The allowed regions could be further significantly reduced by incorporating the current result in a global analysis. Besides, the same analysis approach is used to measure the squared sine of the Weinberg angle with a precision comparable with reactor neutrino experiments and place the most robust limit on the probability of ν−ν̄ conversion in the Sun for solar neutrinos with energies Eν < 1.8 MeV. I conclude with deliberation on the applicability of solar neutrino NC NSI approach for current JUNO detector configuration.

Several methods exists for performing similarity searches quickly using metric indexing. However, most of these methods are based on main memory indexing or require specialized disk access methods. We have described and implemented a method combining standard database access methods with the LAESA Linear Approximating Eliminating Search Algorithm to perform both range and K nearest neighbour (KNN) queries using standard database access methods and relational operators. We have studied and tested various existing implementations of R-trees, and implemented the R*-tree. We also found that some of the optimizations in R*-trees was damaging to the response time at very high dimensionality. This is mostly due to the increased CPU time removing any benefit from reducing the number of disk accesses. Further we have performed comprehensive experiments using different access methods, join operators, pivot counts and range limits for both range and nearest neighbour queries. We will also implement and experiment using a multi-threaded execution environment running on several processors.

Questa tesi descrive la ricerca di coppie di bosoni di Higgs nel canale di decadimento in cui uno dei due bosoni decade in una coppia quark-antiquark b e l'altro in una coppia leptone-antileptone tau. L'organizzazione della tesi segue fedelmente la struttura dell'analisi stessa e le strategie adottate per l'identificazione e la ricostruzione di eventi di segnale bbtautau. Sia l'ipotesi di produzione risonante che quella non risonante di una coppia HH sono sono prese in considerazione e analizzate utilizzando i dati raccolti dall'esperimento CMS nel 2016 e nel 2017 a un'energia nel centro di massa di 13 TeV. Dopo la scoperta, nel 2012, del bosone di Higgs, lo sforzo collettivo della comunità scientifica di fisica delle alte energie si è concentrato sulla caratterizzazione di questa particella. In questo contesto, le ricerche relative alla produzione di coppie di bosoni di Higgs giocano un ruolo fondamentale dal momento che permettono di osservare direttamente l'accoppiamento triplo dell'Higgs, misura altrimenti infattibile in altre analisi. Tale grandezza è, insieme alla massa del bosone stesso, l'unico parametro necessario a descrivere il potenziale del campo di Higgs e a permettere una profonda comprensione del meccanismo di rottura spontanea della simmetria all'origine della massa di tutte le particelle. Allo stesso tempo, dato il ridotto rate di produzione di coppie HH, qualunque deviazione dalla predizione teorica del Modello Standard implicherebbe notevoli cambiamenti nella cinematica e nel rate di produzione stesso, rendendo queste analisi estremamente sensibili a effetti di Nuova Fisica. Il canale di decadimento bbtautau rappresenta uno dei più interessanti stati finali nell'esplorazione di eventi con due bosoni di Higgs poichè caratterizzato da un branching fraction piuttosto elevato e relativamente poco affetto dalla contaminazione dei fondi. Allo stesso tempo però, questo canale presenta alcune problematiche di non triviale soluzione, come ad esempio la ricostruzione del decadimento dei leptoni tau che coinvolge l'emissione di neutrini. Questo rende necessario lo sviluppo di dedicate tecniche e algoritmi per l'identificazione e ricostruzione degli eventi di segnale. Nessun eccesso di eventi è osservato nell'analisi di 35.9/fb di dati raccolti nel 2016 e i risultati sono consistenti con l'ipotesi di solo fondo predetta dallo SM. Limiti superiori di esclusione al 95% di livello di confidenza sono dunque calcolati relativamente al prodotto della sezione d’urto e del branching ratio. Nel caso dell'analisi risonante tali limiti variano da 500 a 5 pb in funzione dell'ipotesi di massa della risonanza testata, mentre nel caso non risonante i limiti attesi ed osservati corrispondono a 25 e 30 volte, rispettivamente, la predizione del Modello Standard. Un'ulteriore interpretazione dei limiti non risonanti è data nel contesto di teorie effettive (EFT), al fine di esplorare modelli in cui gli accoppiamenti del bosone di Higgs sono differenti da quelli previsti nello Standard Model. Data la ridotta sezione d'urto di produzione di coppie di bosoni di Higgs, le analisi HH sono limitate dalla statistica disponibile, per questo, dopo il notevole risultato dell'analisi dei dati 2016, l'attenzione delle analisi HH a CMS è rivolta all'inclusione nelle ricerche della totalità dei dati raccolti durante il Run II e corrispondenti a circa 160/fb. L'aver lavorato a questa analisi sin dal suo inizio mi ha permesso di partecipare attivamente allo sviluppo di nuove strategie e di capire quali sono gli aspetti più critici dell'analisi stessa sui quali è necessario concentrare gli sforzi per massimizzare la sensitività. In ogni Sezione di questa tesi quindi, affiancherò alla descrizione delle tecniche utilizzate nel 2016, i cambiamenti e i miglioramenti apportati durante lo studio dei dati 2017 in vista dei risultati futuri, prima per il Run II e, in una prospettiva più ampia per la fase ad alta luminosità di LHC.
This thesis describes the search for Higgs boson pairs in the final state composed of two b quarks and two tau leptons. The structure of this dissertation closely follows the workflow of the analysis and the strategies adopted to identify and reconstruct the bbtautau signal candidates. Both the resonant and the non-resonant double double Higgs production mechanisms are explored with the data collected by the CMS experiment during 2016 and 2017 at a center of mass energy of 13 TeV. After the discovery of the Higgs boson in 2012 by the ATLAS and CMS collaborations, the collective efforts of the high energy physics community have been focused on a precise characterization of this particle. In this context, HH searches play a fundamental role as they represent the only way to measure the Higgs boson trilinear self coupling. This variable is, together with Higgs mass, the only parameter needed to fully describe the Higgs field potential, thus allowing a better understanding of the electroweak symmetry breaking mechanism, which is at the base of the masses of all particles. At the same time, given the low production rate of HH pairs, any deviation from the theoretical predictions of the Standard Model would lead to sizeable changes in both the event kinematics and in the production rate itself, thus making double Higgs searches extremely sensitive to New Physics effects. The bbtautau final state represents one of the most interesting channels to explore double Higgs processes, given the high branching ratio and the relatively small background contamination. At the same time however, this final state poses some non trivial experimental challenges such as the reconstruction of the tau lepton decay that involves the presence of hardly detectable neutrinos. This has prompted the development of specific algorithms and techniques to identify and reconstruct the signal events and to maximize the analysis sensitivity. No excess of events is observed in the analysis of 2016 data, corresponding to an integrated luminosity of 35.9/fb, and the results are found to be consistent with the Standard Model background predictions. Exclusion upper limits at 95% Confidence Level are thus set on the cross section times branching fractions. In the resonant search case, the limits vary from 500 to 5 pb depending on the mass of the signal resonance hypothesized, while in the non-resonant search, the observed and expected exclusion limits are set to about 30 and 25 times the theoretical Standard Model prediction, respectively. A further interpretation of the non resonant results is given in the context of effective field theories (EFT) in order to explore models that predict the modification of the Higgs couplings values. As double Higgs production rate is very small at the LHC, HH analyses are currently mainly limited by the available statistics and are expected to become more and more sensitive with the increase of the integrated luminosity collected. After the success of the 2016 results and in order to fully exploit the statistical power offered by the data, the bbtautau analysis strategy is now set on the combination of the full 2016-2018 statistics, that amounts to about 160/fb. Having collaborated to this analysis since the beginning or Run II, I was able to witness and actively participate in the changes and developments put in place during the 2016 data analysis, and to understand and learn the most critical aspects on which to focus our efforts in the future. Hence, each Section of this thesis is complemented with the changes introduced in the analysis workflow in 2017 and with ideas on how to further improve the performance and sensitivity on the road to the study of the full Run II statistics and, in a more wide perspective, of the High Luminosity phase of the LHC.

Radiative penguin decays of B mesons are favour-changing neutral current (FCNC) processes, studies of which provide fertile ground for precision tests of the Standard Model. Because such decays must proceed through 1-loop or higher order processes, they are rare and their amplitudes are particularly sensitive to interference from other FCNC interactions beyond the SM. This thesis presents the search for the rare radiative penguin process b -> d gamma, carried out at the BABAR experiment.

Diese Arbeit beschreibt die Suche nach dem Higgs Boson, welches in vielen theoretischen Modellen der Teilchenphysik vorhergesagt wird. Das Higgs Boson ist die Konsequenz der spontanen Symmetriebrechung, welche den Teilchen Masse verleiht. Zur Suche werden e+e- Annihilationen bei Schwerpunktenergien bis 209 GeV analysiert, welche vom Experiment L3 am Speicherring LEP in den Jahren 1998 bis 2000 registriert wurden. Die Suche erfolgte in allen relevanten Endzustaenden, wobei der Endzustand mit vier hadronischen Jets im Detail behandelt wird. Die Daten werden mit den Erwartungen eines Signals in verschiedenen Modellen bei Beruecksichtigung der bekannten Untergrundprozesse verglichen oder es wird modellunabhaengig nach der Erzeugung skalarer Teilchen gesucht. Die Produktion von Higgs Bosonen konnte nicht nachgewiesen werde. Die Daten wurden daher benutzt, um neue Grenzen fuer Parameter der Modelle oder der Kopplungen zu setzen. Als erstes wird die Suche nach dem Higgs Boson im Standard Modell der elektroschwachen Wechselwirkung beschrieben. Die Produktion des Higgs Bosons wird bei LEP Energien ueber die Higgs-Strahlung und der Zerfall des Higgs Bosons in ein Paar von b-Quarks vorhergesagt. Die Analysen beruhen daher wesentlich auf der Erkennung von B-Hadronen. Der HZ->qqqq Endzustand wird im Detail untersucht, und die Ergebnisse werden mit den anderen Kanaelen : HZ->qqvv, HZ->qql+l- und HZ->tau+tau- qq kombiniert. Die untere Massengrenze fuer das Higgs Boson wird zu mH > 112.0 GeV auf 95% Vertrauensniveau, bestimmt. Ausserdem werden Grenzen auf die HZZ Kopplung abgeleitet. Im minimalen supersymmetrischen Modell (MSSM) werden fuenf Higgs Bosonen vorhergesagt. Zur Higgs-Strahlung kommt die Paarproduktion von Higgs Bosonen, e+e- -> hA , hinzu. Die Ergebnisse der Suche im Standard Modell werden durch die Suche in den Endzustaenden bb tau+tau- (tau+tau- bb), bbbb und hZ->AAqq ergaenzt. Im Rahmen von drei Standard-Szenarien, benannt als "mh-max", "no mixing" und "large-mu" werden untere Grenzen auf die Higgs Boson Massen von mh > 84.5 GeV und mA > 86.3 GeV fuer tan(beta) > 0.7 abgeleitet. Weiterhin werden im "mh-max" Szenario 0.55 < tan(beta) < 2.2, im "no mixing" Szenario 0.4 < tan(beta) < 4.9, und im "large-mu" Szenario 0.7 < tan(beta) < 6.2 ausgeschlossen. Eine modellunabhaengige Suche nach dem Prozess e+e- -> hZ wird fuer den vier-Jet Endzustand durchgefuehrt. In Kombination mit den Ergebnissen von den anderen Kanaelen werden Grenzen fuer die hZZ Kopplung bestimmt. Wird die hZZ Kopplung auf den Wert im Standard Modell gesetzt und der Zerfall des Higgs Bosons zu 100% in Hadronen angenommen, ergibt sich als Grenze der Higgs Boson Masse, mh > 97 GeV. Modellunabhaengige obere Grenzen fuer die hAZ Kopplung werden aus der Suche nach der Paarerzeugung von Higgs Bosonen in den Kanaelen hA->qqqq und hA->qq tau+tau- in Abhaengigkeit von den Higgs Boson Massen abgeleitet. Die Resultate aus der Kombination aller LEP Experimente werden fuer die oben genannten Analysen vorgestellt. Die Perspektiven der Higgs Boson Suche an den TEVATRON und LHC Speicherringen werden diskutiert und die Higgs Boson Physik an kuenftigen e+e- Linearbeschleunigern behandelt. Ein Linearbeschleuniger wie TESLA waere ideal fuer Untersuchungen eines leichten Higgs Bosons. Fuer ein Higgs Boson mit einer Masse zwischen 120 und 180 GeV kann mH mit einer Praezision von 40 bis 70 MeV bestimmt werden. Im gleichen Massenbereich ist die Messung des Wirkungsquerschnitts, weitgehend modellunabhaengig, mit einem relativen Fehler von 2.6 bis 3.8% moeglich. In vier-Fermion und sechs-Fermion Endzustaenden werden topologische Wirkungsquerschnitte, definiert als Produkt des totalen Wirkungsquerschnitts fuer e+e- -> HZ mit dem Verzweigungsverhaeltnis eines Zerfallskanals, untersucht. Fuer den Messfehler werden 1.1% fuer HZ->bbqq und 13% fuer HZ->W+W-l+l- bei mH = 120 GeV abgeschaetzt. Die Gesamtheit dieser und weiterer Messungen erlaubt eine genaue Bestimmung des Higgs Boson Profils und gibt Aufschluss ueber die Struktur des Higgs Sektors in der Natur.
This thesis is devoted to the search for neutral Higgs bosons predicted by various theoretical models. The Higgs boson arises as a result of spontaneous breaking of SU(2) symmetry leading to the generation of masses of fermions and weak bosons. The search is done in all experimentally related channels using the data collected at center-of-mass energies up to 209 GeV in the years 1998-2000 with the L3 detector at the Large Electron Positron collider, LEP. Here the study of the final states characterised by four jets is described in detail. For other final states the analyses are briefly reviewed and the results are reported. The data are compared with the expectation from the Standard Model background processes and with various signal hypotheses. A model independent search for neutral Higgs bosons is also performed. No evidence for the production of Higgs bosons is found. New mass limits are determined superseding previous mass limits established by L3 and other experiments. First I describe the analysis searching for the Standard Model Higgs Boson. Its production at LEP is expected mainly via the Higgs-strahlung process. In the mass range accessible at LEP the Standard Model Higgs Boson is predicted to decay dominantly into a pair of b and anti-b quarks, hence the dedicated analyses are optimised for the H->bb decay mode. The four-jet signal topology is investigated and then combined with the other search channels leading to a lower mass limit of mH > 112.0 GeV at 95% C.L.. The results of the search are also interpreted in terms of limits on the HZZ coupling. In the Minimal Supersymmetric Standard Model (MSSM) the Higgs sector is extended to five physical states. The Higgs-strahlung process is complemented by the mechanism of the Higgs boson pair production e+e- -> hA. Therefore, for the interpretation of the results in the framework of the MSSM the Standard Model analyses are combined with the hA -> bb tau+tau-, hA -> bbbb and hZ->AAqq channels. Three benchmark MSSM scenarios denoted "mh-max", "no mixing" and "large-mu" are considered. Using L3 data the lower bounds on the Higgs boson masses mh > 84.5 GeV mA > 86.3 GeV are derived at 95% C.L. for tan(beta) > 0.7. For the "mh-max", "no mixing" and "large-mu" scenarios, ranges 0.55 < tan(beta) < 2.2, 0.4 < tan(beta) < 4.9 and 0.7 < tan(beta) < 6.2, respectively, are ruled out. A model independent search for the Higgs-strahlung process with subsequent decay of h into hadrons is carried out in the four-jet channel. The results of the analysis are then combined with the other channels. A limit on the hZZ coupling as a function of the Higgs boson mass is derived. The results of L3 combined search establish a 95% C.L. lower mass limit, mh > 97 GeV, for a hadronically decaying Higgs boson assuming the cross section of the Higgs-strahlung process to be equal to the value predicted by the Standard Model and the branching fraction of the Higgs boson into hadrons equal to 100%. Analyses are developed to search exclusively for the hA -> bbbb, hA -> qqqq, hA -> bb tau+tau- and hA -> qq tau+tau- final states. Results of these analyses are translated into a 95% C.L. upper limit on the hAZ coupling as a function of Higgs boson masses. Searches for neutral Higgs bosons carried out by the L3 collaboration are combined with searches performed in other LEP experiments. The results of this combination are reported. The perspectives of Higgs boson searches at TEVATRON and LHC are briefly reviewed. The prospects of Higgs physics at a future linear e+e- collider are discussed. The potential of the TESLA detector foreseen at the TESLA linear collider for the determination of Higgs boson properties is studied. The Higgs boson masses 120, 150 and 180 GeV are considered. It is shown that a precision of 40 - 70 MeV in the measurement of the Higgs boson mass can be achieved. A model independent method to measure the e+e- -> HZ cross section is proposed. The method is based on the study of the inclusive HZ -> X e+e- and X mu+mu- channels. The relative error in the determination of the cross section varies between 2.6% and 3.8% for Higgs boson mass ranging from 120 GeV to 180 GeV. For the four-fermion and six-fermion final states arising from the Higgs-strahlung process the accuracy of the measurement of a topological cross section, defined as the product of the Higgs-strahlung cross section and the branching fraction of the specific final state, is investigated. The relative uncertainty of this measurement varies from 1.1% and 13%, depending on final state and Higgs boson mass. These and other measurements will allow to determine the profile of the Higgs boson and give insight into the structure of the Higgs sector in nature.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 255-264).
In this thesis, we search for the production of the Standard Model Higgs boson at the Large Hadron Collider, through its decay mode to two W bosons, which each in turn decay into a charged lepton and a neutrino. The Higgs boson is the only elementary particle predicted by the Standard Model of particle physics which has not yet been experimentally observed. The question of its existence has been the subject of a wide body of experimental and theoretical work for the past half-century. Using 4.9 fb-1 of integrated luminosity, this search is expected, on average, to exclude the Standard Model predicted Higgs boson production cross section for masses between 126 GeV/c 2 and 260 GeV/c 2 under the background-only hypothesis. We observe no statistically significant excesses in the data, and we exclude the Standard Model Higgs boson production for masses between 129 GeV/c 2 and 260 GeV/c 2 . This result represents a significant reduction of the mass region in which the Standard Model Higgs boson is allowed to exist.
by Si Xie.
Ph.D.

Thesis (Ph. D.)--University of Oregon, 2005.
Typescript. Includes vita and abstract. Includes bibliographical references (leaves 219-223). Also available for download via the World Wide Web; free to University of Oregon users.

Le Modèle Standard (MS) qui décrit la physique des particules a été confirmé avec une grande précision par les mesures expérimentales. Cependant, certaines de ses caractéristiques semblent nécessiter une théorie plus complète, en effet, la hiérarchie entre l'échelle Electrofaible et celle de Planck, et l'instabilité de la masse du boson de Higgs aux corrections radiatives demeurent notamment non expliqué. Un nouveau scénario est à considérer avec les récentes mesures cosmologiques de précision indiquant que l'Univers est principalement constitué par de la Matière Noire et de l'Energie Noire qui n'existe pas dans le MS. Le Large Hadron Collider (LHC) est un collisionneur hadronique en construction au CERN de Genève : deux faisceaux de protons circuleront en sens et se croiseront en 4 points avec une énergie dans le centre de masse de 14 TeV. A cette énergie, il sera alors possible de tester le bien fondé de théories au-delà du Modèle Standard. Une des expérience construite près du collisionneur LHC est le détecteur CMS (Compact Muon Solenoid) dont un des principaux objectifs est la recherche de signaux de nouvelle physique. Les deux théories principales qui pourraient résoudre les problèmes posés par le Modèle Standard précédemment décrits sont le Modèle Super Symétrique Minimale (MSSM) et le Modèle ADD. Dans cette thèse, on a envisagé les possibles signatures expérimentales dans l'expérience CMS pour ce type de physique. La Super Symétrie, dans sa formulation minimale MSSM , prévoit pour chaque particule du MS l'existence d'un partenaire 'super-symétrique' avec une statistique opposée. Cette théorie décrit aussi le mécanisme qui stabiliserait, de façon radiative, la masse du boson de Higgs, dans le cas où la symétrie appelée R-parité est conservée. Elle prévoit ansi l'existence d'une particule neutre massive faiblement interactive avec la matière ordinaire: cette particule, appelée Lightest Supersymmetric Particle (LSP) est un candidat idéale pour la Matière Noire. Dans MSSM les combinaisons linéaires des partenaires super symétriques des bosons de gauge neutres et chargés, et des bosons de Higgs super symétriques sont appelés "neutralinos" et ont la caractéristique d' être états propres CP. La plupart des scénarios proposés par le MSSM prévoient le LSP comme étant le plus léger entre ces neutralinos. La connaissance des propriétés du neutralino (masse et composition) est fondamentale pour estimer son abondance résiduelle dans l'Univers et les collisionneurs hadroniques peuvent fournir d'importantes informations à son sujet. Dans cet étude de thèse on a considéré, pour un modèle "Not Universal Higgs Masses" (un des possibles scénario du MSSM), la production directe des deux plus légers neutralinos au collisionneur LHC. On a étudié la dépendance des sections efficaces et des amplitudes de plusieurs possibles désintégrations pour le neutralino plus léger à l'aide de simulations et développements de diagrammes de Feynman connus par précédents travaux. Dans ce milieu, on a crée une procédure pour la mesure expérimental à CMS de cette dépendance dans les sections efficaces considérées. Dans les canaux pris en compte dans ces études, la séparation de signal du bruit de fond dû au Modèle Standard est particulièrement compliqué à cause de la cinématique des événements. Le modèle ADD (Arkani-Hamed, Dvali et Dimopoulos) prévoit l'existence d'extra dimensions compactées en une seule échelle macroscopique (dans l'ordre du micromètre) appelée MD. Ce modèle résolut le problème de la hiérarchie à l'aide d'une relation géométrique qui introduit des extra dimensions compactées entre l'échelle Electrofaible et l'échelle de Planck. Seuls les gravitons, les particules qui joue le rôle de médiateur de la force gravitationnelle, peuvent se propager à travers les extra dimensions, alors que la matière ordinaire est confinée dans l'espace ordinaire quadridimensionnel. Ils existent plusieurs canaux physiques à travers lesquels il est possible de vérifier la véracité du modèle ADD, notamment l'émission d'un single photon et d'un graviton ou l'émission d'un single jet hadronique très énergétique et d'un graviton (qui n'interagit pas avec le détecteur et qui se manifeste comme énergie manquante). Dans ce travail de thèse on a étudié le potentiel de découverte de ce dernier canal dans l'expérience CMS. On a étudié les procédures pour obtenir, à partir des données expérimentales, la contribution des fonds dérivés par les canaux prévus par le MS, principalement dus à l'émission de bosons W, Z et jets hadroniques, à la production de couples de quark top et événements purement hadroniques. On a tenu en compte et étudié les effets systématiques sur le nombre prévu des événements dus au détecteur (par exemple la résolution énergétique du calorimètre) et les erreurs systématiques théoriques intervenus dans le calcul des sections efficaces dans le modèle ADD. Les simulations réalisées à l'aide de la description détaillée du détecteur montrent qu'avec le LHC, il sera possible d'exclure les modèles ADD avec MD < 4. 3 (3. 1) TeV pour n=2 (n=4) extra dimensions à partir d'une statistique de 100 pb-1. Avec la même statistique on prévoit une possibilité de mise en évidence à 5 sigma des modèles ADD avec MD<3. 1 (2. 2) TeV pour n=2 (n=4) extra dimensions. L'expérience CMS peut donc améliorer déjà à partir de 100 pb-1 de statistique les actuels limites du collisionneur hadronique Tevatron (Fermilab, Chicago) et du collisionneur électronique LEP (CERN, Genève), posés à MD<1. 6 (1. 0) TeV pour n=2 (n=4) extra dimensions
The Standard Model of Particle Physics is a well established physical theory whose parameters have been measured with precision by many experiments. Nevertheless, some of its features seem to be demanding for a more comprehensive theory: among them, the Hierarchy Problem between the Electroweak and the Planck scales and the radiative stability of the Higgs boson mass. Furthermore, according to the recent cosmological precision measurements the Universe is made by yet unknown components without a counterpart in the Standard Model, called Dark Energy and Dark Matter. The 14 TeV centre-of-mass energy proton-proton Large Hadron Collider (LHC) built at Cern which with its 14 TeV of energy in the center of mass represents a powerful tool the investigation of theories Beyond the Standard Model. The Compact Muon Solenoid (CMS) is one of the two multi- purpose experiment located at the LHC designed also for the search of signature of new physics. In this thesis the possibility to observe signals produced by two models proposed to solve some of the problems of the Standard Model has been studied: the Minimal Supersymmetric Model (MSSM) and the ADD model. Supersymmetry, in its minimal formulation called MSSM, predicts a Supersymmetric partner with opposite statistics for each SM particle. Besides providing a mechanism to radiatively stabilize the Higgs mass, if a new symmetry called R-parity is conserved, it predicts also a massive stable neutral particle which interacts very weakly: this particle, called Lightest SuperSymmetric Particle (LSP), is a good Dark Matter candidate. In many scenarios described by the MSSM, the LSP is the neutralino, defmed as a linear combination of the Supersymmetric partner of the neutral gauge bosons W, B and the Supersymmetric CP-even Higgs bosons. The knowledge of neutralino's properties (mass and composition) is fundamental to estimate its relic density in the Universe: in this framework the hadron colliders can give important information. In this work the direct production of the first two lightest neutralinos at the LHC has been considered in the scenario described by the Not Universal Higgs Masses model (one of the possibile realizations of the MSSM). Cross sections and branching ratios dependence on the lightest neutralino composition has been verified from the known Feynman rules for Supersymmetry and simulations. A procedure to measure this dependence at CMS has been investigated. The separation of signal events from the SM background in the chosen channels has proven to be difficult mainly due to the kinematic of the events. In the ADD model, developed by Arkani-Hamed, Dvali and Dimopoulos, the existence of extradimensions compactified on a macroscopic scale (order of the micrometer) called M_D is proposed. This model solves the Hierarchy problem with a geometrical relationship between the Electroweak and the Planck scales mediated by the delta compactified extradimensions. Only thé gravitons, spin-2 particles that mediate the gravitational force, can propagate in the extradimensions, while the ordinary matter is confined on a four dimensional space. The ADD model predicts several distinctive physical channels that can measured by the CMS experiment in order to validate or falsify it. Amongst them there are the emission of a single photon, or an hadronic jet plus a graviton, which would be recorded as missing energy in the calorimeter. The discovery potential of the latter at CMS has been the subject of this work. Data-driven methods have been proposed for extrapolating the main SM backgrounds, consisting in the emission of a W, Z boson plus jets, production of top pairs and QCD events. Systematic effects due to the detecter (e. G. The jet energy scale) and to theoretical uncertainties in thé computation of the ADD cross sections have been studied and quantified. The simulations performed with a detailed detector simulation show that it is possible to exclude ADD models with M_D < 4. 2, 3. 7, 3. 2 TeV for delta=2, 3, 4 respectively already with 100 pb-1 of integrated luminosity. With the same statistics the 5sigma discovery of ADD models with M_D < 3. 1, 2. 5 and 2. 2 TeV for delta=2, 3 and 4 respectively has been shown. These values are a significant improvement with respect to the current limits set by the Tevatron collider at FermiLab and by the LEP colliderat CERN, which are M D < 1. 6 (1. 0) TeV for delta=2 (delta=4)

Diese Dissertation beschäftigt sich mit der Suche nach dem skalaren Top Quark (stop) und dem skalaren Bottom Quark (sbottom) innerhalb des Minimal Supersymmetric Standard Model (MSSM) unter der Annahme der R-Paritätserhaltung. Suchen nach den folgenden Zerfallsmoden des Stop-Quark wurden durchgeführt: stop -> c neutralino_1, stop -> b l sneutrino (wobei l mit gleichen Wahrscheinlichkeiten entweder electron, muon oder tau-lepton ist) und stop -> b tau sneutrino (nur das Tau-Lepton wird berücksichtigt). Zusätzlich wurde der Dreikörperzerfall stop -> b W neutralino_1 im erlaubten Massenbereich M_stop > M_b + M_W + M_neutralino1 >= 86 GeV gesucht. Für das Sbottom-Quark wurde der Zerfall sbottom -> b neutralino_1 studiert. Jede dieser Zerfallsmoden wurde voneinander unabhängig unter der Annahme eines 100 %-igen Verzweigungsverhältnisses untersucht. Für diese Suche wurden Daten aus electron-positron-Kollisionen bei Schwerpunktsenergien im Bereich von 202-208 GeV benutzt. Die Daten wurden im Jahr 2000 von dem L3 Detektor am Large Electron Positron Collider (LEP) am CERN aufgenommen. Ferner wurden die Resultate der Datenanalyse aus dem Jahr 2000 mit Resultaten der Squark-Suche kombiniert, die die L3 Kollaboration in vorhergehenden Jahren bei Schwerpunktsenergien von 161 bis 202 GeV durchgeführt hat. Die untersuchten Squark Zerfallskanäle bestimmen die Topologie der für uns interessanten Ereignisse: 2 Jets (oder b-Jets) + fehlende Energie (+ 2 Leptonen für die Stop-Dreikörperzerfälle). Die stop -> b W neutralino_1 Zerfallstopologie hängt signifikant von den weiteren Zerfällen des W-Bosons ab und kann bis zu 6 Jets im Endzustand haben. Die Annahme der R-Paritätserhaltung impliziert die Stabilität des leichtesten supersymmetrischen Teilchens (des LSP), das das leichteste Neutralino ist. Das LSP wechselwirkt nur schwach und entweicht deswegen unentdeckt. Ein besonderes Merkmal der Signal-Ereignisse ist somit eine erhebliche Menge fehlender Energie. Die sichtbare Energie ist in etwa proportional zu der Massendifferenz zwischen dem Squark und dem LSP. Weil die Standardmodell-Untergrundzusammensetzung vom Anteil der sichtbaren Energie abhängt, hängt die Analyse auch vom Wert von der Massendifferenz ab. Abhängig von der Menge fehlender Energie kann der Standardmodell-Untergrund in drei Kategorien eingeteilt werden: - die zwei-Fermion-Prozesse sind e e -> e e, e e -> mu mu, e e -> tau tau und e e -> e e q q; - die vier-Fermion-Kategorie besteht aus e e -> W W, e e -> W e nu, e e -> Z Z und e e -> Z e e Prozessen; - die zwei-Photon-Untergrundprozesse sind e e -> e e e e, e e -> e e mu mu, e e -> e e tau tau und e e -> e e q q. Der letzte Prozess, e e -> e e q q, trägt den grössten Anteil zu den SM-Untergrundprozessen bei (wegen sehr hohem und stark schwankendem E_miss und dem grössten Wirkungsquerschnitt). Im ersten Schritt der Analyse wurden Events mit der gewünschten Topologie (2 Jets und hohes E_miss) vorselektiert. Die Selektion von Stop- und Sbottom-Ereignissen wurde durch die Minimierung der mit 95 % Confidence Level (C.L.) erwarteten oberen Grenze des Squark-Wirkungsquerschnitts - berechnet aus MC-Vorhersagen - optimiert, wobei der kleine theoretisch vorhergesagte Produktionswirkungsquerschnitt des Squarks berücksichtigt wurde. In allen für den jeweiligen Squark Zerfallskanal optimierten Selektionen stimmt die Anzahl von Daten Events mit der erwarteten Anzahl von Standardmodellprozessen überein: - für den stop -> c neutralino_1 Zerfall wurden 29 Daten-Events beobachtet, wobei 26.5 +- 2.7 Events von den SM-Prozessen erwartet wurden; - für den Dreikörperzerfall stop -> b l sneutrino, wurden 4 Daten-Events selektiert bei einer Standardmodell-Erwartung von 4.0 +- 1.0 Events; - für den Zerfall stop -> b tau sneutrino sind die Daten- und SM-Eventzahlen 5 bzw. 3.9 +- 1.0; - in der Selektion für stop -> b W neutralino_1, wurden 184 Daten Events beobachtet und 181.6 +- 3.0 Events wurden vom Standardmodell vorhergesagt; - für den Bottom Squark Zerfall sbottom -> b neutralino_1 entsprachen die beobachteten 6 Events der SM-Erwartung von 7.7 +- 1.3 Events. Es wurden keine MSSM-Skalar-Quarks in den Daten des Experiments beobachtet und das Resultat der Suche ist negativ. Die modellunabhängige 95 % C.L. obere Grenze für den Squark-Produktionswirkungsquerschnitt wurde aus der gemessenen Anzahl von Daten-Events und der aus dem Standardmodell erwarteten Eventanzahl berechnet. Für die Berechnung der oberen Grenzen der Produktionswirkungsquerschnitte wurden die Resultate der Squark-Suchen aus den L3-Daten bei Schwerpunktsenergien von c.m.s. Energie 202 - 208 GeV mit den Resultaten aus vorherigen Suchen der L3-Kollaboration bei 161 GeV - 202 GeV kombiniert. Eine neue Methode wurde entwickelt, um die kombinierten Grenzen zu berechnen. Die Methode berücksichtigt die statistische Unabhängigkeit jeder Messung und die Abhängigkeit des Squark-Produktionswirkungsquerschnittes von der Schwerpunktsenergie. In der Berechnung wurde den systematischen Unsicherheiten in der Standardmodell-Untergrundabschätzung und der Signal-Selektionseffizienz Rechnung getragen. Für die hier betrachteten Squark-Zerfälle werden typisch folgende oberen Grenzen mit 95 % C.L. für den Squark Produktionswirkungsquerschnitt erhalten: ~ 0.05-0.2 pb (für stop) und ~ 0.05-0.1 pb (für sbottom). Bei den Suchen nach dem Stop-Dreikörperzerfall stop -> b W neutralino_1 wurden die Produktionswirkungsquerschnitte über 0.7-1.0 pb mit 95 % C.L. ausgeschlossen. Innerhalb des Minimal Supersymmetrischen Standard Modells mit R-Paritätserhaltung wurden die unabhängigen Wirkungsquerschnittsgrenzen für den Ausschluss von MSSM Parametern benutzt, insbesondere für die Stop- und Sbottom-Massen. Die Squark-Massen wurden für jeden betrachteten Zerfallskanal in zwei möglichen Szenarien ausgeschlossen: für den maximalen und den (näherungsweise) minimalen theoretischen Wirkungsquerschnitt. Der erste Fall korrespondiert zur maximalen Mischung zwischen den links- und rechtshändigen Squark-Eigenzuständen, $\cos\theta_{LR}$ = 1; der zweite Fall ist definiert durch den Wert von $\cos\theta_{LR}$, bei dem die Squarks vom $Z^0$ Boson entkoppeln. Abhängig vom Wert $\Delta M$ wurden die Squark Massen mit 95 % C.L. bis zu den folgenden Werten ausgeschlossen: - für stop -> c neutralino_1: M_stop < 90-93 GeV (min. Wirkungsquerschnitt), M_stop < 95-96 GeV (max. Wirkungsquerschnitt), - für stop -> b l sneutrino: M_stop < 87-89 GeV (min. Wirkungsquerschnitt), M_stop < 90-91 GeV (max. Wirkungsquerschnitt), - für stop -> b tau sneutrino: M_stop < 83-88 GeV (min. Wirkungsquerschnitt), M_stop < 88-91 GeV (max. Wirkungsquerschnitt), - für sbottom -> b neutralino_1: M_stop < 76-83 GeV (min. Wirkungsquerschnitt), M_stop < 94-97 GeV (max. Wirkungsquerschnitt), In beiden Fällen werden die experimentell beobachteten 95 % C.L. Massen Ausschlussgrenzen mit den aus Monte Carlo Simulationen ohne SUSY Teilchen erwarteten verglichen. Die experimentallen Ausschlussgrenzen Sind verträglich mit den erwarteten. Die mit 95 % C.L. erhaltene obere Grenze für den Stop-Produktionquerschnitt ist im Zerfall stop -> b W neutralino_1 grösser als die zugehörige theoretische Vorhersage. Der Ausschluss mit 95 % C.L. auf Massen war mit dem zur Verfügung stehenden Datensatz aus diesen Grund nicht möglich. Unter der Annahme, dass die Zerfallstopologie der skalaren Quarks der ersten zwei Generationen ähnlich dem Zweikörperzerfall des Stop ist, wurden die Resultate der Suche nach dem Zerfall stop -> c neutralino_1 auch für die Berechnung der Massenausschlussgrenzen für die Squarks der ersten beiden Familien benutzt. Zwei Möglichkeiten wurden hier in Erwägung gezogen: die Massenentartung zwischen vier (scalar u, d, c, s) und fünf (sbottom zusätzlich) Squarks. Die Ausschlussgrenzen mit 95 % C.L. auf die massenentarteten skalaren Quarks in den Fällen der "nur-rechts" oder "links-und-rechts" Eigenzustände sind die folgenden: - für die Massenentartung zwischen vier Squarks: M_squark < 95-96 GeV ("nur-rechts"), M_squark < 99-100 GeV ("links-und-rechts"); - für die Massenentartung zwischen fünf Squarks: M_squark < 96-97 GeV ("nur-rechts"), M_squark < 99-101 GeV ("links-und-rechts"); Mit der Annahme der Gaugino-Vereinigung an der GUT-Skala im MSSM wurden die Grenzen für die vierfach massenentarteten Squarks erneut in der Squark-Gluino Ebene interpretiert. Ferner wurde das absolute Limit auf den MSSM-Parameter M_2, der für tan(beta) = 4 aus anderen L3-SUSY-Suchen (für Chargino, Neutralino und skalare Leptonen) ermittelt worden ist, in ein Gluino-Massenlimit übersetzt. Die mit 95 % C.L. erhaltenen Ausschlussgrenzen in der Squark-Gluino Massenebene sind - M_gluino > 267-314 GeV, - M_squark > 99-100 GeV.
This thesis is devoted to searches for the scalar top and the scalar bottom quarks within the framework of the Minimal Supersymmetric Standard Model (MSSM) with the assumption of R-parity conservation. Searches for the following decay modes of the stop quark have been performed: stop -> c neutralino_1, stop -> b l sneutrino, (where l is either electron, muon or tau-lepton with equal probabilities) and stop -> b tau sneutrino (where only the tau-lepton is considered). In addition, a three body decay stop -> b W neutralino_1 has been searched for in the allowed mass region of M_stop > M_b + M_W + M_neutralino1 >= 86 GeV. For the sbottom quark the decay sbottom -> b neutralino_1 was considered. Each of these decay modes was considered independently assuming a branching ratio of 100 %. For this search, the experimental data of electron-positron collisions at center-of-mass energies (c.m.s.) in the range of 202-208 GeV have been used. These data were collected in the year 2000 by the L3 detector at the Large Electron Positron Collider (LEP) at CERN. The results of the year 2000 data analysis were also combined with results of the squark searches performed by the L3 Collaboration in previous years at center-of-mass energies from 161 up to 202 GeV. The analyzed squark decay channels determine the topology of the events of our interest: 2 jets (or b-jets) + missing energy (+ 2 leptons for stop three body decays). The stop -> b W neutralino_1 decay topology depends significantly on the further decay of the W boson and can have up to 6 jets in the final state. The assumed conservation of R-parity implies stability of the lightest supersymmetric particle (the LSP), which is the lightest neutralino. The LSP interacts only weakly and thus escapes undetected. This leads to a large missing energy as a feature of the signal events. The visible energy is roughly proportional to the difference between the masses of the squark and the LSP, and since the Standard Model background composition depends on the visible energy fraction, the whole analysis depends also on the value of this mass difference. Depending on the magnitude of visible energy, the Standard Model background can be grouped into three categories: - the two-fermion processes are e e -> e e, e e -> mu mu, e e -> tau tau and e e -> q q; - the four-fermion category is composed of e e -> W W, e e -> W e nu, e e -> Z Z and e e -> Z e e processes; - the two-photon background processes are e e -> e e e e, e e -> e e mu mu, e e -> e e tau tau and e e -> e e q q. The last process, e e -> e e q q, constitutes the largest fraction of all SM background processes (due to very high and highly fluctuating missing energy and the highest cross section). At the very first step of the analysis, only the events of interesting topology (with 2 jets and high missing energy) were preselected. Then, taking into account the small value of the theoretically predicted production cross section of the scalar quarks, the selection of stop and sbottom events was optimized by minimization of the 95 % confidence level expected upper limit on the squark cross section using calculated Monte Carlo events. In all selections optimized for each particular squark decay channel, the number of selected data events statistically agrees with the number of events expected from the Standard Model processes: - for stop -> c neutralino_1 decay, 29 data evens were observed, while 26.5 +- 2.7 were expected from the SM processes; - for the three body decay stop -> b l sneutrino, 4 data events were selected and the expectation from the Standard Model is 4.0 +- 1.0 events; - for the decay stop -> b tau sneutrino, the data and SM event numbers are 5 and 3.9 +- 1.0, respectively; - in the selection for stop -> b W neutralino_1, 184 data events were observed and 181.6 +- 3.0 were expected from the Standard Model; - for the bottom squark decay sbottom -> b neutralino_1 the observed 6 events correspond to the SM expectation of 7.7 +- 1.3. Thus, the MSSM scalar quarks were not observed in the experimental data and the search results are negative. The model independent 95 % C.L. upper limits on the squark production cross section have been derived from the numbers of the observed data events and numbers of events expected from the Standard Model. For calculation of the upper cross section limits, the results of the squark searches performed in the L3 data of c.m.s. energy 202 - 208 GeV were combined with results of searches performed by the L3 Collaboration previously in the data of c.m.s. energy from 161 up to 202 GeV. A new method has been developed for calculating such combined limits. This method takes into account the statistical independence of each measurement and the dependency of the squark production cross section on the center-of-mass energy. In this calculation, the systematic uncertainties in the Standard Model background estimation and in the signal selection efficiency have been also accounted for. For the considered squark decays, the typical obtained 95 % C.L. upper limits on the squark production cross section are: ~ 0.05-0.2 pb (for stop) and ~ 0.05-0.1 pb (for sbottom). In the searches for the stop three body decay stop -> b W neutralino_1, the cross sections above 0.7-1.0 pb have been excluded at 95 % C.L. Within the framework of MSSM with conserved R-parity, the experimental model independent cross section limits have been used for exclusion of the MSSM model parameters, in particular, exclusion of the stop and the sbottom masses. For each considered decay channel, the squark masses have been excluded in two possible scenarios: for the maximal and for the (approximately) minimal theoretical cross section. The first case corresponds to the maximal mixing between the left and right squark eigenstates, cos(theta) = 1; the second case is defined by the cos(theta) value, where squarks decouple from the Z boson. Depending on the mass difference between squark and the LSP, the squark masses have been excluded at 95 % C.L. up to the following values: - for stop -> c neutralino_1: M_stop < 90-93 GeV for minimal cross section, M_stop < 95-96 GeV for maximal cross section; - for stop -> b l sneutrino: M_stop < 87-89 GeV for minimal cross section, M_stop < 90-91 GeV for maximal cross section; - for stop -> b tau sneutrino: M_stop < 83-88 GeV for minimal cross section, M_stop < 88-91 GeV for maximal cross section; - for sbottom -> b neutralino_1: M_stop < 76-83 GeV for minimal cross section, M_stop < 94-97 GeV for maximal cross section. For both cases, the experimentally observed 95 \% C.L. mass exclusions are compared to the expected ones, which have been obtained from the Monte-Carlo assuming no SUSY particles. The observed exclusions of the squark masses are at the same level as the expected ones. The obtained 95 % C.L. upper limits on the stop production cross section in the decay stop -> b W neutralino_1 are bigger than the corresponding theoretical predictions, so, the exclusion of masses at 95 % C.L. was not possible with the available data sample. Assuming the topology of decays of the scalar quarks of the first two generations to be similar to the two body decay of the stop, the results of the searches for the decay stop -> c neutralino_1 have been also used for calculation of the mass exclusion limits for the squarks of the first two families. Two possibilities were considered here: the mass degeneracy between four (scalar u, d, c, s) and five (scalar b in addition) squarks. The 95 % C.L. exclusion limits on the mass degenerate scalar quarks for the cases of the "right-only" or "left-and-right" eigenstates are the following: - for the mass degeneration between 4 squarks: M_squark < 95-96 GeV ("right-only"), M_squark < 99-100 GeV ("left-and-right"); - for the mass degeneration between 5 squarks: M_squark < 96-97 GeV ("right-only"), M_squark < 99-101 GeV ("left-and-right"). Using the MSSM assumption about gaugino unification at the GUT scale, the limits on the four mass degenerate squarks have been reinterpreted on the squark-gluino mass plane. Moreover, the absolute limit on the MSSM parameter M_2, obtained for tan(beta) = 4 from other L3 SUSY searches (for chargino, neutralino and scalar leptons), has been translated into a gluino mass limit. The obtained 95 % C.L. exclusions in the squark-gluino mass plane are - M_gluino > 267-314 GeV, - M_squark > 99-100 GeV.

La recherche indirecte des effets de la physique au-delà du Modèle Standard à travers les processus de la saveur est complémentaire aux efforts au LHC pour observer directement la nouvelle physique. Dans cette thèse nous discutons plusieurs scénarios au-delà du Modèle Standard (a) en utilisant une approche basée sur les théories de champs effective et (b) en considérant des extensions explicites du Modèle Standard, à savoir les modèles à deux doublets de Higgs et les scénarios postulant l'existence des bosons leptoquarks scalaires à basse énergie. En particulier, nous discutons le phénomène de la brisure de l'universalité des couplages leptoniques dans les désintégrations basées sur les transitions b → sℓℓ et b → cτν, et la possibilité de chercher les signatures de la violation de la saveur leptonique à travers les modes de désintégration similaires. Une proposition pour tester la présence d'un boson pseudoscalaire léger à travers les désintégrations des quarkonia est aussi présentée
Indirect searches of physics beyond the Standard Model through flavor physics processes at low energies are complementary to the ongoing efforts at the LHC to observe the New Physic phenomena directly. In this thesis we discuss several scenarios of physics beyond the Standard Model by (a) reusing the effective field theory approach and (b) by considering explicit extensions of the Standard Model, namely the two-Higgs doublet models and the scenarios involving the low energy scalar leptoquark states. Particular emphasis is devoted to the issue of the lepton flavor universality violation in the exclusive decays based on b → sℓℓ and b → cτν, and to the possibility of searching for signs of lepton flavor violation through similar decay modes. A proposal for testing the presence of the light CP-odd Higgs through quarkonia decays is also made

Cette thèse de doctorat présente une enquête approfondie sur la détection des signaux d'ondes gravitationnelles provenant de fusions binaires compactes, en mettant l'accent particulier sur l'analyse des données de la troisième campagne d'observation de la Collaboration LIGO-Virgo. Le manuscrit commence par fournir une introduction aux principes fondamentaux de la théorie de la relativité générale, y compris la prédiction de l'existence des ondes gravitationnelles et un aperçu des sources astrophysiques qui génèrent ces ondes. Il fournit également une description détaillée des interféromètres, les instruments utilisés dans les observatoires d'ondes gravitationnelles, ainsi que leur fonctionnement de base. Ensuite, le manuscrit se concentre sur les techniques avancées d'analyse des données développées pour extraire les signaux d'ondes gravitationnelles du bruit du détecteur. Une attention particulière est accordée au pipeline d'analyse MBTA (Multi-Band Template Analysis), auquel l'auteur contribue activement en tant que membre de l'équipe MBTA. Le fonctionnement et la méthodologie du pipeline MBTA sont décrits en détail, mettant en évidence son rôle dans la détection et l'analyse des signaux d'ondes gravitationnelles. Ensuite, le manuscrit présente les résultats obtenus à partir de l'analyse standard réalisée pour rechercher des signaux provenant de trous noirs binaires, d'étoiles à neutrons binaires et de binaires trou noir-étoile à neutrons dans les données recueillies lors de la troisième campagne d'observation. L'analyse comprend un examen approfondi des signaux observés, de leurs propriétés et des implications astrophysiques des fusions détectées. De plus, le manuscrit explore les dernières avancées dans la recherche des ondes gravitationnelles émises par des binaires de masse sub-solaire, qui impliquent des systèmes binaires comprenant au moins un objet ayant une masse inférieure à celle du Soleil, offrant une enquête approfondie sur la méthodologie et les résultats de la recherche de masse sub-solaire lors de la troisième campagne d'observation. Grâce à cette enquête approfondie, le manuscrit vise à contribuer à l'avancement de l'astronomie des ondes gravitationnelles, offrant une exploration complète de la recherche sur les ondes gravitationnelles, couvrant les principales réalisations de la troisième campagne d'observation dans les recherches standard et de masse sub-solaire
This PhD thesis presents a comprehensive investigation into the detection of gravitational wave signals from compact binary mergers, with a specific focus on the analysis of data from the third observing run of the LIGO-Virgo Collaboration. The manuscript begins by providing an introduction to the fundamental principles of the theory of General Relativity, including the prediction of the existence of gravitational waves and an overview of the astrophysical sources that generate these waves. It also provides a detailed description of interferometers, the instruments used in gravitational wave observatories, and their basic functioning. Subsequently, the manuscript focuses on advanced data analysis techniques developed to extract gravitational wave signals from the detector noise. Special attention is given to the Multi-Band Template Analysis (MBTA) pipeline, which the author actively contributes to as part of the MBTA team. The functioning and methodology of the MBTA pipeline are described in detail, highlighting its role in the detection and analysis of gravitational wave signals. The manuscript then proceeds to present the results obtained from the standard analysis conducted to search for signals originating from the coalescence of binary black holes, binary neutron stars, and black hole-neutron star binaries in the data collected during the third observing run. The analysis includes a comprehensive examination of the observed signals, their properties, and the astrophysical implications of the detected mergers. Additionally, the manuscript explores the latest advancements in the search for gravitational waves emitted by sub-solar mass binaries, which involve binary systems comprising at east one object with a mass below the threshold of the mass of the Sun, providing an in-depth investigation into the methodology and results of the sub-solar mass search during the third observing run. Through this comprehensive investigation, the manuscript aims at contributing to the advancement of gravitational wave astronomy, offering a comprehensive exploration of gravitational wave research, encompassing the main achievement of the third observing run in both standard and sub-solar mass searches

Cette thèse est le fruit d’un projet de recherche qui mêle la pratique et la théorie de la traduction. Divisée en deux volumes, elle étudie des questions liées à la traduction de l’argot tel qu’utilisé dans des oeuvres de fiction. Le premier comprend un commentaire critique composé de trois parties, et le second une traduction en anglais du roman Moi non (P. Goujon, Gallimard, 2003). L’intrigue du roman se déroulant en banlieue parisienne, le commentaire explore la façon dont les jeunes adultes marginalisés peuvent s’exprimer par l’emploi de l’argot, une variété linguistique non-standard. Cette variété est souvent représentative d’un lieu précis et d’une identité particulière, participant à un ensemble de formes d’expression qui sert à distinguer la jeunesse marginalisée de groupes dominants. Une telle utilisation de la langue soulève des questions concrètes et abstraites quand on décide de la transcrire et de la traduire dans une oeuvre de fiction. Souvent, le traducteur a recours à l’emploi d’une langue standard ou à l’utilisation d’un argot dit « équivalent ». La traduction proposée de Moi non s’inscrit dans une méthode alternative qui s’inspire d’un style informel ainsi que de procédés créatifs que l’on peut notamment employer dans le rap et dans l’élaboration de nouvelles expressions argotiques. Préférant éviter de situer la traduction dans une aire géographique spécifique, cette traduction invite à explorer les points communs de l’ensemble des parlers jeunes du monde anglophone. Ce projet représente ainsi une opportunité de vérifier la cohérence et la logique de cette démarche alternative de la traduction de l’argot d’un roman, et de la comparer avec l’approche empruntée par les traducteurs de textes similaires
This thesis is the fruit of a research project which marries translation practice and theory. Separated into two volumes, it explores questions related to the translation of slang in fictional texts. The first volume is a critical commentary composed of three parts, and the second a translation from French into English of the novel Moi non by Patrick Goujon (Gallimard, 2003). Since the plot unfolds in the banlieue of Paris, the critical component investigates the way in which marginalised youth can express themselves through slang, a variety of non-standard language. Often representative of a specific place and identity, slang constitutes one of many forms of expression that contribute to setting marginalised youth apart from dominant groups. Such use of language raises a number of questions, both concrete and abstract in nature, when one decides to transcribe and translate it in a work of fiction. Translators often employ standard language to render this voice in the translated text or otherwise make use of an “equivalent” slang. The proposed translation of Moi non embodies an alternative method inspired by an overall informal style of writing, as well as by the creative devices employed in rap lyrics and in the creation of slang words and expressions. In an effort to avoid suggesting a specific setting outside of the banlieue, this translation seeks to identify and harness features of English shared by young people throughout the Anglosphere. This thesis thus represents an opportunity to ensure the coherence and the logic of this alternative approach to translating slang in an entire novel, and to compare this approach with that adopted by the translators of similar texts

Die Suche nach dem Higgs-Boson des Standardmodells der Teilchenphysik stellte einen der Hauptgründe für den Bau des Large Hadron Colliders (LHC) dar, dem derzeit größten Teilchenphysik-Experiment der Welt. Die vorliegende Arbeit ist gleichfalls von dieser Suche getrieben. Der direkte Zerfall des Higgs-Bosons in Myonen wird untersucht. Dieser Kanal hat mehrere Vorteile. Zum einen ist der Endzustand, bestehend aus zwei Myonen unterschiedlicher Ladung, leicht nachzuweisen und besitzt eine klare Signatur. Weiterhin ist die Massenauflösung hervorragend, sodass eine gegebenenfalls vorhandene Resonanz gleich in ihrer grundlegenden Eigenschaft - ihrer Masse - bestimmt werden kann. Leider ist der Zerfall des Higgs-Bosons in ein Paar von Myonen sehr selten. Lediglich etwa 2 von 10000 erzeugten Higgs-Bosonen zeigen diesen Endzustand . Außerdem existiert mit dem Standardmodellprozess Z/γ∗ → μμ ein Zerfall mit einer sehr ähnlichen Signatur, jedoch um Größenordnungen höherer Eintrittswahrscheinlichkeit. Auf ein entstandenes Higgs-Boson kommen so etwa 1,5 Millionen Z-Bosonen, welche am LHC bei einer Schwerpunktsenergie von 8 TeV produziert werden. In dieser Arbeit werden zwei eng miteinander verwandte Analysen präsentiert. Zum einen handelt es sich hierbei um die Untersuchung des Datensatzes von Proton-Proton-Kollisionen bei einer Schwerpunktsenergie von 8 TeV, aufgezeichnet vom ATLAS-Detektor im Jahre 2012, auch als alleinstehende Analyse bezeichnet. Zum anderen erfolgt die Präsentation der kombinierten Analyse des kompletten Run-I Datensatzes, welcher aus Aufzeichnungen von Proton-Proton-Kollisionen der Jahre 2011 und 2012 bei Schwerpunktsenergien von 7 TeV bzw. 8 TeV besteht. In beiden Fällen wird die Verteilung der invarianten Myon-Myon-Masse nach einer schmalen Resonanzsignatur auf der kontinuierlichen Untergrundverteilung hin untersucht. Dabei dient die theoretisch erwartete Massenverteilung sowie die Massenauflösung des ATLAS-Detektors als Grundlage, um analytische Parametrisierungen der Signal- und Untergrundverteilungen zu entwickeln. Auf diese Art wird der Einfluss systematischer Unsicherheiten auf Grund von ungenauer Beschreibung der Spektren in Monte-Carlo Simulationen verringert. Verbleibende systematische Unsicherheiten auf die Signalakzeptanz werden auf eine neuartige Weise bestimmt. Zusätzlich wird ein bisher einzigartiger Ansatz verfolgt, um die systematische Unsicherheit resultierend aus der Wahl der Untergrundparametrisierung in der kombinierten Analyse verfolgt. Zum ersten Mal wird dabei die Methode des scheinbaren Signals auf einem simulierten Untergrunddatensatz auf Generator-Niveau angewendet, was eine Bestimmung des Einflusses des Untergrundmodells auf die Anzahl der ermittelten Signalereignisse mit nie dagewesener Präzision ermöglicht. In keiner der durchgeführten Analysen konnte ein signifikanter Überschuss im invarianten Massenspektrum des Myon-Myon-Systems nachgewiesen werden, sodass obere Ausschlussgrenzen auf die Signalstärke μ = σ/σ(SM) in Abhängigkeit von der Higgs-Boson-Masse gesetzt werden. Dabei sind Stärken von μ ≥ 10,13 bzw. μ ≥ 7,05 mit einem Konfidenzniveau von 95% durch die alleinstehende bzw. kombinierte Analyse ausgeschlossen, jeweils für eine Higgs-Boson-Masse von 125,5 GeV. Die erzielten Ergebnisse werden ebenfalls im Hinblick auf die kürzlich erfolgte Entdeckung des neuen Teilchens interpretiert, dessen Eigenschaften mit den Vorhersagen eines Standardmodell-Higgs-Bosons mit einer Masse von etwa 125,5 GeV kompatibel sind. Dabei werden obere Grenzen auf das Verzweigungsverhältnis von BR(H → μμ) ≤ 1,3 × 10^−3 und auf die Yukawa-Kopplung des Myons von λμ ≤ 1,6 × 10^−3 gesetzt, jeweils mit einem Konfidenzniveau von 95%
The search for the Standard Model Higgs boson was one of the key motivations to build the world’s largest particle physics experiment to date, the Large Hadron Collider (LHC). This thesis is equally driven by this search, and it investigates the direct muonic decay of the Higgs boson. The decay into muons has several advantages: it provides a very clear final state with two muons of opposite charge, which can easily be detected. In addition, the muonic final state has an excellent mass resolution, such that an observed resonance can be pinned down in one of its key properties: its mass. Unfortunately, the decay of a Standard Model Higgs boson into a pair of muons is very rare, only two out of 10000 Higgs bosons are predicted to exhibit this decay. On top of that, the non-resonant Standard Model background arising from the Z/γ∗ → μμ process has a very similar signature, while possessing a much higher cross-section. For one produced Higgs boson, there are approximately 1.5 million Z bosons produced at the LHC for a centre-of-mass energy of 8 TeV. Two related analyses are presented in this thesis: the investigation of 20.7 fb^−1 of the proton-proton collision dataset recorded by the ATLAS detector in 2012, referred to as standalone analysis, and the combined analysis as the search in the full run-I dataset consisting of proton-proton collision data recorded in 2011 and 2012, which corresponds to an integrated luminosity of L = 24.8 fb^−1 . In each case, the dimuon invariant mass spectrum is examined for a narrow resonance on top of the continuous background distribution. The dimuon phenomenology and ATLAS detector performance serve as the foundations to develop analytical models describing the spectra. Using these analytical parametrisations for the signal and background mass distributions, the sensitivity of the analyses to systematic uncertainties due to Monte-Carlo simulation mismodeling are minimised. These residual systematic uncertainties are addressed in a unique way as signal acceptance uncertainties. In addition, a new approach to assess the systematic uncertainty associated with the choice of the background model is designed for the combined analysis. For the first time, the spurious signal technique is performed on generator-level simulated background samples, which allows for a precise determination of the background fit bias. No statistically significant excess in the dimuon invariant mass spectrum is observed in either analysis, and upper limits are set on the signal strength μ = σ/σ(SM) as a function of the Higgs boson mass. Signal strengths of μ ≥ 10.13 and μ ≥ 7.05 are excluded for a Higgs boson mass of 125.5 GeV with a confidence level of 95% by the standalone and combined analysis, respectively. In the light of the discovery of a particle consistent with the predictions for a Standard Model Higgs boson with a mass of m H = 125.5 GeV, the search results are reinterpreted for this special case, setting upper limits on the Higgs boson branching ratio of BR(H →μμ) ≤ 1.3 × 10^−3, and on the muon Yukawa coupling of λμ ≤ 1.6 × 10^−3 , both with a confidence level of 95 %

Thesis (Ph. D.)--University of California, San Diego, 2009.
Title from first page of PDF file (viewed July 2, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 149-150).

A search for heavy exotic diboson resonances decaying to llqq final states is presented using pp collision data collected with the ATLAS detector at the Large Hadron Collider. The analysis uses a data sample corresponding to an integrated luminosity of 20.3 fb^-1 at sqrt(s) = 8 TeV collected between April and December 2012. No significant excess of data events over the predicted Standard Model background is observed and 95% confidence level upper limits are set on the product of the production cross-section and the branching ratio for spin-2 Kaluza-Klein gravitons predicted by the bulk Randall-Sundrum model and for Extended Gauge Model W’ bosons. These results are subsequently combined with limits obtained from searches using the lvll, lvqq, and qqqq final states, and new mass limits are set on both signal models.

Since its discovery a large effort has been made to improve analyses and make precision measurments of the properties of the Higgs Boson. At a mass of 125 GeV Higgs to bb is the dominant decay mode. However, large QCD backgrounds mean that the gluon-gluon fusion production mode is not directly accessible at the LHC. Instead an analysis of Higgs to bb can considered where the Higgs is produced in association with a Vector Boson (W/Z). This document outlines such an analysis perfomed on the ATLAS Run I 8 TeV data with focus on one particular channel where the Higgs is produces in association with a Z Boson which subsequently decays to a pair of neutrinos.

Searches for the supersymmetric partner of the top quark (stop) are motivated by natural supersymmetry, where the stop has to be light to cancel the large radiative corrections to the Higgs boson mass. This thesis presents three different searches for the stop at √s = 8 TeV and √s = 13 TeV using data from the ATLAS experiment at CERN’s Large Hadron Collider. The thesis also includes a study of the primary vertex reconstruction performance in data and simulation at √s = 7 TeV using tt and Z events. All stop searches presented are carried out in final states with a single lepton, four or more jets and large missing transverse energy. A search for direct stop pair production is conducted with 20.3 fb−1 of data at a center-of-mass energy of √s = 8 TeV. Several stop decay scenarios are considered, including those to a top quark and the lightest neutralino and to a bottom quark and the lightest chargino. The sensitivity of the analysis is also studied in the context of various phenomenological MSSM models in which more complex decay scenarios can be present. Two different analyses are carried out at √s = 13 TeV. The first one is a search for both gluino-mediated and direct stop pair production with 3.2 fb−1 of data while the second one is a search for direct stop pair production with 13.2 fb−1 of data in the decay scenario to a bottom quark and the lightest chargino. The results of the analyses show no significant excess over the Standard Model predictions in the observed data. Consequently, exclusion limits are set at 95% CL on the masses of the stop and the lightest neutralino.

The Standard Model of particle physics is the framework that describes all known phenomenaand interactions between elementary particles. It has proven to give outstanding results overthe years and was succesfully completed with the discovery of the Brout-Englert-Higgs boson in2012 by the ATLAS and CMS collaborations at CERN. However, several observations escape itsreach: the matter-antimatter asymmetry, the nature of Dark Matter or the quantization of theelectric charge. These are all examples of measured facts not explained by the Standard Modelformalism and that call for an extension to a Beyond the Standard Model (BSM) theory. In thisthesis, we have looked for evidence of new physics using proton-proton collision data producedby CERN’s Large Hadron Collider (LHC) at a center-of-mass energy of 13 TeV. Collected from2016 to 2018 by the CMS detector, it corresponds to an integrated luminosity of 136/fb .Afteran introduction to the theoretical context and the experimental tools, two analyses are presented.The first one is a search for Dark Matter particles recoiling against a jet and leaving the detectorunnoticed. With this ”monojet” analysis, we are able to exclude mediator masses up to 1.8TeV, and masses of Dark Matter particles up to 700 GeV. The second analysis is a search forfractionally charged particles. Using the fact that their stopping power is lower than StandardModel particles, we are able to exclude their existence up to masses of 765 GeV for a charge of2/3 e.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Cette thèse présente une recherche de la production de paires de bosons de Higgs en utilisant les données des collision proton-proton à sqrt(s) = 13 TeV enregistrées avec les détecteur CMS auprès du LHC du CERN. Les évènements avec les deux boson de Higgs se désintégrant en une paire de quark b et de leptons tau (HH -> bb tau+tau-) sont utilisés pour l’exploration des mécanismes de production résonante et non-résonante.La mesure de la production de HH est expérimentalement difficile à cause de la petite section efficace prévue par le modèle standard de la physique des particules. Sa recherche est néanmoins motivée par les informations qu’elle peut révéler sur la nature de la brisure de la symétrie électrofaible. La production de HH donne accès à l’auto-couplage trilineaire du boson de Higgs et, par conséquent, à la forme du potentiel scalaire. En plus, elle est sensible à la présence de physique au-délà du modèle standard. La présence de nouvelles résonances se désintégrant en HH et de couplages anormales du boson de Higgs sont étudiées dans ce travail.Les leptons tau ont un rôle de premier plan dans cette recherche et un effort important a été consacré à l’amélioration de leur efficacité de sélection par le système de déclenchement de l’expérience CMS. En particulier, le déclenchement de premier niveau (L1) a été amélioré pour faire face aux nouvelles conditions des collisions du Run II du LHC, marqué par une augmentation de l’énergie dans le centre de masse et de la luminosité instantanée. Ce nouveau système de déclenchement permet de développer un algorithme spécifique pour la reconstruction des leptons tau se désintégrant en hadrons (tauh) et un neutrino.Cet algorithme se fonde une technique avancée de regroupement dynamique de l’énergie et utilise des critères dédiés pour la réjection du bruit de fond. Le développement, l’implementation, et la vérification de son fonctionnement pour le redémarrage du LHC sont présentés ici. La performance de l’algorithme est initialement évaluée grâce à une simulation et puis mesurée avec les données de l’expérience CMS. Son excellente performance est un element essentiel dans la recherche de la production de HH.L’investigation du processus HH -> bb tau+tau- utilise les trois canaux de désintégration du système tau+tau- avec au moins un tauh dans l’état final. La sélections et categorisation des évènements sont conçues pour optimiser la sensibilité de la recherche, et des techniques d’analyse multivariés sont mises en place pour distinguer le signal du bruit de fond.Les résultats sont présentés en utilisant une luminosité intégrée de 35.9 fb-1. Ils sont compatibles, dans les incertitudes expérimentales, avec les prédictions du modèle standard pour les bruits de fond. Des limites supérieures à la production résonante de HH sont évaluées et interprétées dans le contexte du modèle standard supersymmétrique minimal. Les limites supérieures à la production non-résonante permettent de contraindre l’espace des paramètres des couplages anormales du boson de Higgs. Les limites supérieures observées et attendues correspondent respectivement à environ 30 et 25 fois la prédiction du modèle standard. Ils représentent l’un des résultats les plus sensibles à la production de HH atteint jusqu'à présent au LHC.Les perspectives pour l‘observation de la production de HH au LHC sont enfin discutées. Les résultats précédemment obtenus sont extrapolés à une luminosité intégrée de 3000 fb-1 sous des différentes assomptions pour la performance du détecteur et de l’analyse
This thesis describes a search for Higgs boson pair (HH) production using proton-proton collision data collected at sqrt(s) = 13 TeV with the CMS experiment at the CERN LHC. Events with one Higgs boson decaying into two bottom quarks and the other decaying into two tau leptons (HH -> bb tau+tau-) are explored to investigate both resonant and nonresonant production mechanisms. The measurement of HH production is experimentally challenging because of the tiny cross section predicted by the standard model of particle physics (SM). However, this process can reveal invaluable information on the nature of electroweak symmetry breaking by giving access to the Higgs boson trilinear self-coupling and, consequently, to the shape of the scalar potential itself. Moreover, HH production is sensitive to the presence of physics beyond the SM. Both the presence of new states decaying to HH and of anomalous Higgs boson couplings are investigated in this work.Tau leptons have a key role in this search and considerable effort has been devoted to ensure a high efficiency in their selection by the trigger system of the CMS experiment. In particular, the CMS Level-1 (L1) trigger was upgraded to face the increase in the centre-of-mass energy and instantaneous luminosity conditions expected for the LHC Run II operations. The upgrade opened up the possibility to develop an efficient and dedicated algorithm to reconstruct tau leptons decaying to hadrons (tauh) and a neutrino.The tau algorithm implements a sophisticated dynamic energy clustering technique and dedicated background rejection criteria. Its development, optimisation, implementation, and commissioning for the LHC restart are presented. The algorithm performance is initially demonstrated using a simulation and subsequently measured with the data collected with the CMS experiment. The excellent performance achieved is an essential element of the search for HH production.The investigation of the HH -> bb tau+tau- process explores the three decay modes of the tau+tau- system with at least one tauh object in the final state. A dedicated event selection and categorisation is developed and optimised to enhance the sensitivity, and multivariate techniques are applied for the first time to these final states to separate the signal from the background.Results are derived using an integrated luminosity of 35.9 fb-1. They are found to be consistent, within uncertainties, with the SM background predictions. Upper limits on resonant production are set and interpreted in the context of the minimal supersymmetric standard model. Upper limits on nonresonant production constrain the parameter space for anomalous Higgs boson couplings. The observed and expected upper limit are about 30 and 25 times the SM prediction, respectively, corresponding to one of the most stringent limits set so far at the LHC.Finally, prospects for future measurements of HH production at the LHC are evaluated by extrapolating the current results to an integrated luminosity of 3000 fb-1 under different detector and analysis performance scenarios

Since the late 1960s the safety of inhaled B2-agonists has been questioned and the longtenn regular use of these drugs has been linked to increasing morbidity and mortality. National and international guidelines recommend that short acting inhaled B2-agonists should only be used on an "as needed" basis and yet the evidence for these recommendations is still unclear, one reason being the lack of common definition for an outcome. The Regular Use of Salbutamol Trial (TRUST) was designed to assess the risks and benefits of regular versus as needed salbutamol in mild to moderate asthma. In order to establish whether a common primary outcome measure could improve the comparability and interpretation of different trials, a systematic rcyiew of randomised controlled trials of long and short acting inhaled B2-agonists in asthmatic subjects was undertaken to identify well designed trials in this field and primary outcome measures used. The systematic review identified five different primary outcome measures from 26 trials of long and short acting inhaled B2-agonists. The TRUST definition of exacerbation was compared with the five primary outcome measures identified using the TRUST diary card data. In addition, the diary card variables (changes in PEF, symptom scores and medication use) were examined to determine the extent to which they predicted exacerbations according to the different definitions. The use of additional corticosteroids and an increase in daytime symptoms of two or more above baseline were the strongest predictors of all four definitions of exacerbation. A fall in morning PEF of 100 lImin was strongly associated with all definitions of exacerbation but was not a sensitive measure. In conclusion, exacerbations of asthma could be identified by use of additional corticosteroids and an increase in two or more of daytime symptoms. The specificity could be improved by including morning PEF but this may reduce patient compliance with study protocol in asthma trials.

The discovery of the Standard Model (SM) Higgs boson is one of the primary physics objectives of the Large Hadron Collider at CERN. This thesis describes a search carried out for the SM Higgs boson on data collected during the 2011 and 2012 proton-proton (pp) collision runs with the CMS detector corresponding to integrated luminosities of 5:1fb-1 and 5:3fb-1 respectively. A detailed description of the search for the SM Higgs boson decaying to two photons from the full dataset collected at CMS during the 2011 pp collision run is provided. In particular, the development of signal and background modelling techniques used for statistical interpretations of the data are highlighted. Results of the search using these techniques from the 2011 dataset are presented. In addition, an update to the analysis including data taken during 2012 is described and the results from the combined 2011 and 2012 analyses given. Results from the combination of several Higgs decay channels at CMS are reported, including those presented in the International Conference on High Energy Physics in July 2012 at which the announcement of discovery was made. Ongoing studies to ascertain the properties of the new particle are discussed and preliminary results from the combined 7 and 8 TeV datasets (corresponding to 5:1fb-1 and 12:2fb-1 respectively) are presented.

Experiments with polarized "ultracold neutrons" (UCN) offer a new way to measure the decay correlations of neutron beta decay; these correlations can be used to test the completeness of the Standard Model and predict physics beyond it. Ultracold neutrons are very low energy neutrons that can be trapped inside of material and magnetic bottles. The decay correlations in combination with the neutron and muon lifetimes experimentally find the first element (Vud) of the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix. The CKM matrix is a unitary transform between the mass and weak eigenstates of the d, s and b quarks; if the matrix is not unitary this would imply that the Standard Model is not complete. Currently the first row of the CKM matrix is over 2 sigma from unitarity and Vud is the largest component of the row. The UCNA experiment looks at the correlation between the polarization of the neutron and the momentum of the electron resulting from the beta decay of the neutron (the A-correlation). The keys to making a high precision measurement of A-correlation are a near 100% polarization of the neutrons that decay, low"backscatter electron detectors, and small, well characterized backgrounds. UCN can be 100% polarized by passing them through a seven Telsa magnetic field. The key to the UCNA experiment is keeping them polarized until they decay or are lost. This dissertation covers the development of guides that are minimally depolarizing and efficient transporters of UCN and their use in the UCNA experiment. The entire guide development process is covered from conception to manufacturing and testing. This process includes development of a pulsed laser deposition, diamond-like carbon coating system and materials studies of the resulting coatings. After the initial studies of the guide coating, meter"long sections of guide are tested with UCN to determine their depolarization and transport properties. The guide technology developed in this dissertation has been used in the entire UCNA experiment. Also, this technology is currently the state of the art for polarized and non-polarized UCN guide systems and it is being implemented in several new UCN experiments.
Ph. D.

The impressive progress that elementary particle physics made in the second half of the last century led to the formulation of a comprehensive theory, known as the Standard Model (SM), which correctly describes all fundamental interactions in nature, except for the gravitational one. Indirect discoveries have always played an important role in high energy physics scenario and indirect research can be considered to all intents and purposes complementary to the direct one, since allows to test much higher energy scales than those the current colliders are able to reach. This is very important now that electroweak precision tests and measurements on Flavour Changing Neutral Currents (FCNC) processes put very stringent constraints on physics beyond the SM, requiring it to appear at scales O(10 TeV). On the other hand, New Physics (NP) is expected already at scales O(1 TeV) in order to offer a natural explanation to the smallness of the Higgs mass. This scale is also confirmed by recent constraints on thermal dark matter [1] which show how new physics should manifest not far above the electroweak scale. Rare B decays have always played a crucial role in shaping the flavour structure of the SM and particle physics in general. Since the first measurement of rare radiative B æ Kú“ decays by the CLEO Collaboration [2] this area of particle physics has received much experimental and theoretical attention. In particular, FCNC B decays, involving the b-quark transition b æ (s, d) + “ and b æ (s, d) + ¸+¸≠(¸ = e, μ, ·, ‹), provided crucial tests for the SM at the quantum level since they proceed through loop or box diagrams, and they are highly suppressed in the SM (also by helicity). Hence, these rare B decays are characterised by their high sensitivity to NP. The B0 s æ μ+μ≠ channel is the most direct example of the b æ s ¸¸ transitions. The SM predicted branching ratio [3] can be enhanced by coupling to non-SM heavy particles, such as those predicted by the Minimal Supersymmetric Standard Model (MSSM) and other extensions. Updated measurements on the B0 s æ μ+μ≠ branching ratio have been presented by ATLAS [4], LHCb [5] and CMS [6] collaborations. In this thesis I will report all the studies I performed within the rare B decays ATLAS group, measuring the branching ratio of the B0 s æ μ+μ≠ channel on data collected during LHC Run 1. The first chapter provides a general introduction to the SM, focusing in particular on the flavour sector and the possible new physics scenarios. Chapter 2 briefly introduces the LHC collider and the ATLAS detector, detailing the muon and trigger systems, fundamental for the rare B decays measurements. In chapters 3 and 4, I will summarise the work done, during my presence at CERN, on the ATLAS semiconductor strip detector, monitoring the Lorentz angle during Run 1 and measuring the backplane resistance of the silicon modules installed in the ATLAS cavern. In chapter 5, I will review the strategy adopted to measure the B0 s æ μ+μ≠ branching ratio, reporting all the studies I performed on the combinatorial background, and the results obtained on 4.9 fb≠1 of data collected in 2011. Chapters 6 and 7 detail respectively the additional studies I performed on the 2011 datasets and all the tests I made in preparation for the analysis on 20 fb≠1 of data collected in 2012. I will show the studies on the discriminating variables for the rejection of the background, the tests on the multivariate analysis and on the possible strategies for the invariant mass fit for the extraction of the signal yield. All these studies proved to be fundamental for the 2012 measurement detailed in chapter 8.

The Large Hadron Collider is the most powerful particle accelerator built to date. It is a proton-proton and heavy ion collider which in 2015 and 2016 operated at an unprecedented center of mass energy of √s = 13 TeV. The Tile Calorimeter is the ATLAS hadronic calorimeter covering the central region of the detector. It is designed to measure hadrons, jets, tau particles and missing energy. In order to accurately be able to properly reconstruct these physical objects a careful description of the electronic noise is required. This thesis presents the work done in updating, monitoring and studying the noise calibration constants used in the processing and identication of hadronic jet in the 2011 data. Moreover the results of the searches for compressed supersymmetric squark-neutralino and large extra dimensions models are also presented in this thesis. The present work uses an experimental signature with a high energy hadronic jet and large missing transverse energy later often referred to as monojet signature. The search for supersymmetry is carried out using an integrated luminosity of 3.2 fb-1 recorded by the ATLAS experiment in 2015. The search for large extra dimensions presented in this work uses the full 2015 + 2016 dataset of 36.1 fb-1. No signicant excess compared to the Standard Model prediction has been observed on the production of squark pairs with the subsequent decay of the squark in a quark and a neutrino. Exclusion limits are set on squark production as a function of the neutralino mass. Squark masses up to 608 GeV are excluded for a mass difference between the squark and the neutralino of 5 GeV. In the second search for the presence of large extra spatial dimensions in the Arkani-Hamed, Dimopoulos and Dvali model scenario a good agreement between data and Standard Model prediction is observed and exclusion limits are set on the effective Planck scale MD of 7.7 and 4.8 TeV for two and six hypothesized large extra dimensions respectively signicantly improving earlier results.

Nel modello standard (SM), le masse dei fermioni sono generate attraverso gli accoppiamenti di Yukawa tra i campi di Higgs e fermionico. La misura di questi accoppiamenti e' fondamentale per corroborare la natura del bosone con massa intorno a 125 GeV scoperto dalle Collaborazioni ATLAS e CMS nel 2012. Il canale tautau e' particolarmente promettente, grazie al branching ratio relativamente alto e alla contenuta contaminazione da parte dei processi di fondo. In questa tesi vengono riportati i risultati della ricerca di un bosone di Higgs SM nello stato finale comprendente due leptoni tau. Sono stati analizzati gli interi dataset di collisioni p-p raccolti da CMS nel 2011 e nel 2012, corrispondenti alla luminosita' di 4.9 fb-1 a sqrt(s)=7 TeV e 19.7 fb-1 a sqrt(s)=8 TeV. Sono stati studiati tutti i sei possibili stati finali di-tau: mutau, etau, tautau, emu, mumu e ee. Questa tesi, in particolare, descrive l'analisi condotta nello stato finale doppio adronico tautau. Nei dati e' stato osservato un eccesso di eventi rispetto alla predizione per i soli fondi. La significanza locale eccede le 3 deviazioni standard per valori di mH compresi tra 115 e 130 GeV. Il prodotto della sezione d'urto per branching ratio, misurato per il segnale a mH=125 GeV, corrisponde a 0.78+/-0.27 volte il valore predetto dallo SM. Questo costituisce l'evidenza dei decadimenti in coppie di leptoni tau del bosone di Higgs a 125 GeV. Nello SM, la massa del bosone di Higgs non è protetta da divergenze date dalle correzioni a loop e la cancellazione di queste divergenze avviene tramite il cosiddetto fine tuning. In modelli oltre lo SM, ad esempio il Minimal Supersymmetric Standard Model (MSSM), la cancellazione avviene in maniera naturale grazie all'introduzione di un bosone (fermione) per ogni fermione (bosone) presente nello SM. In questa tesi viene anche descritta la ricerca di un bosone di Higgs neutro MSSM nel canale tautau. Questo canale e' particolarmente interessante poiche' i decadimenti in tau sono favoriti in buona parte dello spazio dei parametri. Non viene osservato nessun eccesso e si procede quindi a fissare limiti di esclusione nello spazio dei parametri di diversi benchmark scenarios. Vengono inoltre forniti limiti sul prodotto di sezione d'urto per branching ratio per i due piu' rilevanti modi di produzione, gluon-gluon fusion e produzione associata con b-quark.

An important question at present in particle physics is whether the recently discovered boson with a mass of about 125 GeV is the Standard Model Higgs boson. A Standard Model Higgs boson with a mass of 125 GeV will predominantly decay to b-quark pairs. This work presents the author's contribution to the search with the ATLAS detector for a Standard Model Higgs boson produced in association with a W or Z boson and decaying to b-quark pairs. In order to search for the decay modes ZH → vvb¯b, WH → lvb¯b and ZH → l¯lb¯b, where l is either an electron or muon, events with zero, one or two electrons or muons are considered in 20:3 fb¯1 of 8 TeV LHC data. A Standard Model Higgs boson is not observed decaying to b-quark pairs, although neither is this decay mode ruled out. A Standard Model Higgs boson with a mass of between 110 GeV and 115 GeV is excluded. For mH = 125 GeV the observed (expected) upper limit on the cross- section times the branching ratio is found to be 2.16 (1.07) times the Standard Model prediction. For a Standard Model Higgs boson with a mass of 125 GeV, the best fit signal strength is μ = 1:09 +0:43-0:42 (stat) +0:44-0:37 (syst) = 1:09 +0:61-0:56. The combined results are consistent with a Standard Model Higgs boson with a mass of 125 GeV. The author's own work is presented, including estimation of systematic uncertainties on WH → lvb¯b modelling, and future ATLAS data selection methods for WH → lvb¯b searches. Overviews of underlying theoretical matters and the experimental facilities used are given.

Cette thèse présente une recherche du boson de Higgs du Modèle Standard (MS) et de son extension supersymétrique minimale (MSSM) dans la voie de désintégration en paires de leptons tau avec l'expérience CMS pendant les premières années d'exploitation du LHC. Après une introduction du contexte théorique pertinent pour la recherche du boson de Higgs du MS et du MSSM, les aspects phénoménologiques sont exposés. La découverte en 2012 d'un boson scalaire par les collaborations ATLAS et CMS est ensuite présentée. La description du détecteur CMS est abordée et la reconstruction des objets nécessaires a l'analyse est décrite. Une attention particulière est portée à la reconstruction des leptons tau avec notamment un algorithme d'isolation original incluant des informations sur le temps de vie. Nous avons optimisé cet outil en termes d'efficacité d'identification et de réjection de bruit de fond. Une nouvelle technique visant à supprimer des électrons reconstruits a tord comme des taus est également présentée: le développement d'un discriminateur anti-électron, basé sur une analyse multivariée réduit considérablement cette contamination tout en préservant l'efficacité d'identification. La recherche du boson de Higgs du MS et MSSM dans ses désintégrations en paires de taus est exposée. Les données utilisées correspondent à une luminosité intégrée de 4. 9 fb-1 avec une énergie dans le centre de masse sqrt{s}=7 TeV et 19. 7 fb-1 avec sqrt{s}=8 TeV collectées par CMS en 2011 et 2012 respectivement. Une attention particulière est portée aux canaux de désintégration semi-leptoniques: $$H\to\tau\tau\to l\tau_{h}$$ où $$l$$ représente un électron ou un muon et $$\tau_{h}$$ une désintégration hadronique de tau. La combinaison de tous les canaux de désintégration du Higgs du MS en paire de taus avec en particulier l'utilisation du nouveau discriminateur anti-électron conduit à un excès d'événements par rapport aux bruits de fond attendus. L'interprétation statistique correspond à 3. 2 déviations standard pour une masse de 125 GeV et la force du signal est compatible avec le boson de Higgs du Modèle Standard. Ce résultat constitue une indication directe du couplage du boson de Higgs aux leptons. Finalement, une stratégie originale de recherche de bosons de Higgs du MSSM est présentée. Elle combine d'une part la nouvelle technique d'isolation de tau et d'autre part une définition optimisée des catégories d'analyse fondées sur l'impulsion transverse des taus. La sensibilité de l'analyse est ainsi augmentée de plus de 30 % par rapport au dernier résultat public de CMS (2013) ce qui est équivalent à un accroissement de 3 à 4 fois la luminosité totale intégrée. Aucun excès d'événements n'est observé par rapport aux bruits de fonds prédits par le MS suite à l'interprétation modèle indépendante des limites supérieures sur la section efficace fois le rapport d'embranchement pour chacun des modes de production
This thesis presents a search for Higgs bosons decaying into tau pairs in the context of the Standard Model (SM) and its minimal supersymmetric extension (MSSM) with the Compact Muon Solenoid (CMS) experiment, using the data collected during the first years of operation at the LHC. After introducing the theoretical context relevant for the SM and MSSM Higgs bosons searches, the corresponding phenomenological aspects are discussed. The discovery of a scalar boson by the ATLAS and CMS Collaborations in 2012 is then presented. The design and performance of the CMS experiment are described as well as the identification and measurements of physical objects needed for the analysis. The accent is put on the tau lepton reconstruction including in particular a novel tau isolation that uses the lifetime information. We optimized this tool in terms of tau identification efficiency and fake tau rejection, particularly suited for boosted taus. A new technique for rejecting the electrons faking taus is also presented: a discriminator based on a multivariate analysis which considerably reduces the contamination from electrons faking taus while preserving the efficiency of identification is exposed. The SM and MSSM Higgs boson searches in the di-tau final state are presented. The dataset corresponds to an integrated luminosity of 4. 9 fb-1 at sqrt{s}=7 TeV and 19. 7 fb-1 at sqrt{s}=8 TeV recorded by CMS respectively in 2011 and 2012. The focus is put on the most sensitive semi-leptonic decay channels: $$H\to\tau\tau\to l\tau_{h}$$ where $$l$$ is either an electron or muon and $$\tau_{h}$$ stands for hadronic tau decays. After combining all the decay channels in SM Higgs boson to di-tau search and in particular using the new anti-electron discriminator, an excess of observed events with respect to the background-only hypothesis is found. The statistical significance of this excess corresponds to 3. 2 standard deviations at a mass of 125 GeV. The measured signal strength is compatible with the SM Higgs signal expectation. This result constitutes an evidence for a coupling between the scalar boson and leptons. Finally, a new strategy in the search for the MSSM Higgs bosons is presented in this thesis. It combines both the novel tau isolation technique and a new refined categorization based on the $$\tau_{h}$$ transverse momentum. With respect to the previous CMS public result (2013), the sensitivity of the analysis presented in this document is improved by more than 30%. This is equivalent to an increase of the total integrated luminosity by a factor 3 to 4. The interpretation of the model independent upper limits on the cross-section times branching ratio of the production process shows no significant excess over the Standard Model backgrounds