Synthesis and capture of antihydrogen in controlled laboratory conditions will enable precise studies of neutral antimatter. The work presented deals with some of the physics pertinent to manipulating charged antiparticles in order to create neutral antimatter, and may be applicable to other scenarios of plasma confinement and charged particle interaction. The topics covered include the electrostatic confinement of a reflecting ion beam and the transverse confinement of an ion beam in a purely electrostatic configuration; the charge sign effect on the Coulomb logarithm for a two component (e.g., antihydrogen) plasma in a Penning trap as well as the collisional scattering for binary Coulomb interactions that are cut off at a distance different than the Debye length; and the formation of magnetobound positronium and protonium.

The performance of the ATLAS missing transverse momentum (ETmiss) high-level trigger during 2015 operation is presented. In 2015, the Large Hadron Collider operated at a higher centre-of-mass energy and shorter bunch spacing (sqrt(s) = 13 TeV and 25 ns, respectively) than in previous operation. In future operation, the Large Hadron Collider will operate at even higher instantaneous luminosity (O(10^34 cm^−2 s^−1)) and produce a higher average number of interactions per bunch crossing, <mu>. These operating conditions will pose significant challenges to the ETmiss trigger efficiency and rate. An overview of the new algorithms implemented to address these challenges, and of the existing algorithms is given. An integrated luminosity of 1.4 fb^−1 with <mu> = 14 was collected from pp collisions of the Large Hadron Collider by the ATLAS detector during October and November 2015 and was used to study the efficiency, correlation with offline reconstruction, and rates of the trigger algorithms. The performance was found to be satisfactory. From these studies, recommendations for future operating specifications of the trigger were made. / Graduate / 0798, / jchiu@uvic.ca

An angular analysis of the rare decay B0 → K∗ (K+ π− )µ+ µ− is presented. The study is based on a data sample from pp collisions at centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the Large Hadron Collider which corresponds to an integrated luminosity of 20.3 fb−1 . An extended unbinned maximum-likelihood fit of the decay angular distribution is used to measure the CP-averaged angular observables FL, S3, S4, S5, S7 and S8 and the cor- responding form-factor independent observables P1, P4, P5, P6 and P8. The measurements are performed in the region 0.04 GeV2 < q2 < 6 GeV2 , where q is the dimuon invariant mass. The results are in agreement with the Standard Model predictions and com- patible with measurements published by other experiments. The most signifi- cant deviations are observed for parameters P4, P5 at the level of 2.7 standard deviations and for P8 which is 1.9 standard deviations away from one of the predictions. The P5 deviation in bin 4 GeV2 < q2 < 6 GeV2 is consistent with the one reported by the LHCb collaboration. The second part of this work shortly summarises the operation of the ATLAS Semiconductor Tracker, testing of the prototype module for the Inner Tracker strip upgrade, and the monitoring of non-collision background which was devel- oped as a part of this thesis.

This thesis presents studies on a novel ‘meta-material’ as a potential candidate to replace the traditional Electro-Optic crystals (GaP, ZnTe) used in ultrashort bunch monitors for electron/positron accelerators. This study is aimed at showing the linear and non-linear optical properties of such materials, and creating a toolbox for both optical characterisation and manipulation of their properties using an ultra-short pulsed laser. The material studied throughout this thesis is a composite of silver nanoparticles (a “nanocomposite”) embedded within soda-lime glass. The Surface Plasmon Resonance (SPR) is a feature of these particles that is responsible for its unique optical properties. It is shown in this work how SPR is utilised for shape modification of silver nanoparticles with the use of a ps- pulsed laser with various laser beam polarisations. The impact of linear polarisation irradiation is investigated. It is found that multipulse irradiation has the effect of elongating nanoparticles to form prolate spheroids, which results in a dichroic effect on the composite as a whole, caused by the anisotropic SPR band shift. It is also shown that changing the laser polarisation from linear to radial and/or azimuthal changes the character of the reshaped nanoparticles. It was observed that a localised change of ellipsoid orientation is achieved, resulting in a non-directionally-dependent SPR band shift. Second Harmonic Generation (SHG) has been observed from reshaped nanoparticles embedded in soda-lime glass. A comparison of the effect was made between ps-pulsed reshaped, fs-pulsed reshaped and mechanically stretched samples containing silver nanoparticles. Multiphoton Absorption Induced Luminescence (MAIL) was observed along with the SHG and characterised for the various laser polarisation components. The dependence of the aforementioned effects on the elongated nanoparticle aspect ratio was shown to have a great impact. A novel method for reshaped nanoparticles characterisation is presented. It is based on the laser-induced SHG and MAIL signal and is proved to give a precise measurement of the nanoparticle shape and orientation. Frequency Resolved Optical Gating (FROG) measurement of a fs-pulse is measured with great accuracy, in the case where the BBO nonlinear crystal is replaced by the reshaped nanoparticle composite. This was demonstrated to be caused by the anisotropic SHG of the ellipsoidal nanoparticles. Preliminary THz based measurements were performed as a part of a feasibility study of the application of these composites in the EO-based detection of ultrashort electron bunches. Future work is suggested in order to achieve more efficient EO detection.

In this thesis, the search for the production of the Higgs boson in associationwith two top quarks is presented. The main focus of this work is on the analysis optimised for the decay of the Higgs boson to a b-quark pair. The analysis is performed using 36.1 fb−1 of ppcollision data at a centre of mass energy sqrt(s)=13 TeV collected by the ATLAS detector at the Large Hadron Collider during 2015 and 2016. The signal strength of ttH in relation to the Standard Model prediction for a Higgs boson with a mass of 125 GeV is measured to be mu(ttH) = 0.87 +0.64−0.61, with signal strengths greater than 2.0 excluded at the 95% confidence level. The combination of this analysis with searches targeting additional Higgs boson decay modes is subsequently presented. The measured signal strength in relation to the Standard Model prediction is mu(ttH) = 1.2 +/-0.3. This correspondsto an observed (expected) significance for ttH of 4.2sigma (3.8sigma), constituting evidence for the ttH production mode. Finally, a study into the ability to observe and model the colour connection of b-quarks in ttH(bb) and ttbar+jets events is presented. The jet pull angle observable is used to investigate the effect of colour connection on jet substructure. Such an observable is found to be sensitive to the underlying colour structure in events, showing differences between b-quarks which decay from a colour singlet in comparison to a colour octet. However, the effect is found to be small and a larger dataset is required to measure the effect in ttH events.

This thesis presents two measurements made using data collected by the LHCb detector, operating at the Large Hadron Collider accelerator at the CERN particle physics laboratory. The first is a measurement of the production rates of promptly produced D0, D+, Ds+, and D*+ open charm mesons, using data collected in 2015 at a proton-proton centre-of-mass energy of √s = 13 TeV. The second is a search for direct CP violation in two three-body decays of the Lambda_c charm baryon, pKK and ppipi, using data collected in 2011 at √s = 7 TeV and in 2012 at √s = 8 TeV. For each measurement, motivation and context are given from the standpoint of improving the theoretical understanding of the Standard Model and searching for signs of physics that cannot be explained by it, and then the various statistical analysis techniques used to extract physical quantities from the data are explained. The systematic limitations of the method are explored and quantified, and then the results are presented.

No description available.

La recherche des bosons de Higgs est une des priorites du programme LEP200 developpe au CERN. En effet, le mecanisme de Higgs, qui predit l'existence de bosons scalaires de masse inconnue, permet de donner des masses aux particules elementaires du modele standard et de ses extensions supersymetriques. Nous avons effectue une recherche des bosons de Higgs neutres dans les deux canaux de production $\mathrm(e^+e^-\rightarrow\PZz^*\rightarrow \Phz\PZz)$\, et $\mathrm(e^+e^-\rightarrow\PZz^*\rightarrow \Phz\PAz)$\, prevus dans les modeles supersymetriques en se limitant aux seuls etats finals a quatre jets qui representent, respectivement 65% et 84% des modes possibles. Un effort particulier a ete porte sur la reconstruction de la masse du boson de Higgs standard (canal hZ) et sur l'amelioration des procedures de selection des evenements. Les etudes faites sur les donnees enregistrees par DELPHI de 1995 a 1997 (ecm=161, 172 et 183 GeV) ont permis d'exclure a 95% de niveau de confiance un boson de Higgs standard plus leger que: \mathrm(m_\Phz \ge 84.4~ GeV)/c^2~~~~~ \mathrm(\grave(a) ~95\%~ C.L. ~~(limite~ observ\acute(e)e))\nonumber\\ \mathrm(m_\Phz \ge 86.4~ GeV)/c^2~~~~~ \mathrm(\grave(a) ~95\%~ C.L. ~~(limite~ attendue))\nonumber en incluant l'ensemble des modes de desintegration du Z. Une analyse originale, developpee dans cette these, a permis d'obtenir une limite attendue egale a 86.5 GeV/c2, en utilisant uniquement l'etat final a 4 jets ce qui constitue un gain de ~ 3 GeV/c2, par rapport a la limite evaluee jusqu'ici dans DELPHI. L'interpretation dans le cadre du modele supersymetrique minimal (MSSM) des resulats obtenus dans les canaux hZ, et hA, a permis d'établir les limites suivantes sur les deux bosons de Higgs neutres h, et A: \mathrm(m_\Phz \ge 74.4~ GeV)/c^2~~~~~ \mathrm(\grave(a) ~95\%~ C.L. ~~~~\forall~ tan\beta) \nonumber\\ \mathrm(m_\PAz \ge 75.2~ GeV)/c^2~~~~~ \mathrm(\grave(a) ~95\%~ C.L. ~~~~\forall~ tan\beta) \nonumber

Ce travail de thèse s'attache à simuler le potentiel de découverte de la supersymétrie (SUSY) au collisionneur LHC du CERN avec le détecteur ATLAS dans le canal pp->w1+z2->3l+X. Les résultats sont fournis pour les phases de basse et de haute luminosité du LHC. Dans un premier temps, nous montrons que la SUSY induit un excès à 5 écart-standards par rapport aux pédictions du Modèle Standard (MS) dans la topologie inclusive trilepton dans un grand domaine de l'espace des paramètres SUSY. Nous indiquons que les contributions des processus SUSY autres que pp->w1+z2 (fond supersymétrique) sont non négligeables. Ensuite, nous affinons l'analyse pour augmenter la pureté du signal pp->w1+z2->3l+X. Ceci nous permet d'étudier les propriétés spécifiques de ce processus. En particulier nous reconstruisons la différence de masse m(z2)-m(z1). Nous proposons une méthode originale pour reconstruire tout le secteur des gauginos à partir de cette observable expérimentale (cette méthode suppose l'unification de la masse des gauginos). Un chapitre est également consacré à l'étude de l'uniformité spatial e de la réponse des photomultiplcateurs Hamamatsu R5900 utilisés pour la lecture du calorimètre hadronique (Tilecal) d'ATLAS.

Cette thèse présente le travail de trois ans effectué dans l'expérience CMS, dans le contexte des premières collisions du LHC. L'étude porte en particulier sur les électrons, objets essentiels pour les analyses de recherche en canaux multi-leptons, notamment l'analyse H → ZZ(∗) → 4ℓ. Durant les premiers mois de collisions, nous avons pris part à la validation des données enregistrées par le calorimètre électromagnétique. Nous avons mesuré l'efficacité du système de déclenchement de niveau 1 en électrons et photons tout au long de l'année 2010. L'efficacité sur le plateau est de 99.6 % (resp. 98.5 %) pour des électrons dans le tonneau (resp. dans les bouchons) du calorimètre. En vue d'optimiser le potentiel de découverte, nous avons mis au point un nouvel algorithme de mesure de la charge des électrons. Dans CMS, celle-ci est affectée par la grande quantité de matière présente dans le trajectographe. Les performances de cet algorithme ont été mesurées sur les données enregistrées en 2010, sur des électrons issus de désintégrations de bosons Z, passant une sélection standard. La probabilité d'erreur est de 1.06 % (0.19 % après une sélection spécifique), en accord avec la simulation. L'analyse de physique effectuée dans cette thèse porte sur la recherche de bosons de Higgs doublement chargés, dans leurs désintégrations en paires de leptons. Avec les données enregistrées en 2010, un événement de bruit de fond est attendu à la fin de la sélection, pour un nombre d'événements de signal qui dépend de l'hypothèse de masse et du modèle considéré. Un événement est observé dans les données, en accord avec le bruit de fond attendu, ce qui permet d'exclure ce signal sur des domaines de masse plus larges que précédemment : la limite varie de 122 GeV à 176 GeV en fonction du modèle.