The Compact Muon Solenoid (CMS) Experiment operates at the Large Hadron Collider (LHC) which is the highest energy particle accelerator in the world. CMS is a general purpose detector designed to investigate a wide range of physics, including the search for the Higgs boson. The measurement of photon production in the CMS experiment is crucial since it represents an irreducible background for many new physics searches, such as decay of Higgs to two photon, supersymmetry and extra-dimensions. The study of beam halo contamination is important for the correct measurement of photon production. This thesis presents a way to identify and remove this contamination by using the timing and the shower shape of the photons.

<p>For some cases of lattice layout in particle accelerators, the major part of the energy deposition coming from the collision is located in the midplane of the magnets. The heat produced might result in a quench in superconducting magnets. One solution for reducing the energy deposition in the coil is to introduce an opening in the midplane, which will lead away most of the particles to a safe zone instead of hitting the superconductors in the magnets.</p><p>The aim of this work is to optimize the field quality in dipoles based on the cosθ-design, where an opening in the midplane has been inserted. The equations for finding the solutions for the coil layout for different sizes of the opening are studied, and the solution giving the best field quality for each case is presented. Then, optimization procedures are applied to lay-outs with Rutherford cables. Finally, the resulting field strength from the solutions obtained is presented.</p>

<p>The construction of a high intensity neutrino source requires multi megawatt beams and challenges the targets in use. MERIT is a proof-of-principle test for a novel kind of neutrino factory target, employing a 24 GeV/c proton beam and a 1 cm in diameter free mercury jet as beam target. This thesis describes the design and implementation of a secondary particle flux production detection system. Employed detectors are polycrystalline diamond detectors and electron multipliers. Simulations of the secondary particle production have been made using FLUKA. The detection system is remotely controlled by a LabView interface and experimental observations from the initial analysis are presented.</p>

AEgIS is an experiment at CERN where the goal is to directly measure the gravitational force on antimatter by producing antihydrogen. The antihydrogen will be produced by a charge exchange reaction using laser excited positronium and cold antiprotons. Having a well-characterized positron plasma with at least 108 positrons and knowing how it can be controlled is essential for the positronium production. This thesis is based on the goals of AEgIS experiment and describes the positron plasma manipulations being used in AEgIS in order to achieve the required plasma properties for the experiment. The positron system is made up by a source, a Surko trap and a Penning-Malmberg trap. This system was first optimized to increase the number of positrons. The plasma was then moved to the main traps of the experiment where it was systematically characterized in terms of lifetime, cooling efficiency and compression. Positron plasma compression in time, trapping and cooling was tested for the first time in AEgIS using a buncher and Penning-Malmberg traps respectively. In this thesis, it is shown that a compression of more than 50 % in time of the positron cloud using a buncher can be achieved. It is also shown that trapping and cooling with an efficiency of nearly 100 % in the main traps using a “V” shaped potential trap was successful. On top of that, the lifetime inside this “V” shaped potential trap was observed to be longer than 30 minutes.

This thesis presents a measurement of the mass, natural width, and signal strength, defined as the yield normalized to the Standard Model prediction, of the Higgs boson in the \(H \rightarrow ZZ^{(*)} \rightarrow 4l\) decay channel using an approach which utilizes event-by-event detector response information. The measurement is performed on p-p collision data recorded by the ATLAS experiment at the CERN Large Hadron Collider. The data corresponds to an integrated luminosity of \(25 fb^{-1}\) with center-of-mass energies of 7 TeV and 8 TeV. The measured mass of the Higgs boson is \(m_H = 124.57_{-0.43}^{+0.48} GeV\). The signal strength was estimated at \(\mu = 1.76_{-0.37}^{+0.46}\). Finally, the natural width of the Higgs was determined to be < 2.6 GeV with 95% confidence. The event-by-event approach used in this analysis involves the parameterization of the behavior of single leptons in the ATLAS detector and the convolution of a mass response with the Higgs truth distribution to derive the reconstruction level signal model. / Physics

The Large Hadron Collider (LHC) is presently under construction at CERN. The LHC is a circular accelerator that stores proton beams and accelerates them to a 7 TeV beam energy for high energy physics research. The required bending and focusing/defocusing fields are achieved with superconducting magnets. Such a superconducting magnet-based accelerator can be controlled only when the field errors of production and installation of all magnetic elements are known to the required accuracy. The ideal way to compensate the field errors is to have direct diagnostics on the beam. For the LHC, however, a system solely based on beam feedback may be too demanding. The present baseline for the LHC control system hence requires an accurate forecast of the magnetic field and the multipole field errors to reduce the burden on the beam-based feedback. The field model is the core of this magnetic prediction system, also known as \emph{the Field Description for the LHC} (FIDEL). The model will provide the forecast of the magnetic field at a given time, magnet operating current, magnet ramp rate, magnet temperature, and magnet powering history. The model is based on the identification and physical decomposition of the effects that contribute to the total field in the magnet aperture of the LHC dipoles. This thesis presents the tool that was constructed to ease the detection, identification and finally correction of errors in the raw data from the series measurements of the main dipoles of the LHC. The results after cleaning all measurement data for the over 240 dipoles measured at cold, using this tool, is also presented. Another aspect of the Thesis is the presentation of a procedure devised to extract the model parameters for the main dipole magnets of the LHC by using the cleaned data. The procedure and the model are verified and validated by application to the magnets of the 7-8 sector of the LHC.

For some cases of lattice layout in particle accelerators, the major part of the energy deposition coming from the collision is located in the midplane of the magnets. The heat produced might result in a quench in superconducting magnets. One solution for reducing the energy deposition in the coil is to introduce an opening in the midplane, which will lead away most of the particles to a safe zone instead of hitting the superconductors in the magnets. The aim of this work is to optimize the field quality in dipoles based on the cosθ-design, where an opening in the midplane has been inserted. The equations for finding the solutions for the coil layout for different sizes of the opening are studied, and the solution giving the best field quality for each case is presented. Then, optimization procedures are applied to lay-outs with Rutherford cables. Finally, the resulting field strength from the solutions obtained is presented.

The LHCb experiment is dedicated to making precision measurements involving beauty and charm hadrons at the CERN Large Hadron Collider. The LHCb RICH detectors provide charged particle identification required to distinguish final states in many decays important to the LHCb physics programme. Time alignment of the RICH photon detectors is necessary in order to ensure a high photon collection efficiency. Using both a pulsed laser and proton-proton collision data the photon detectors are aligned to within 1 ns. The LHCb detector is uniquely positioned to measure production cross-sections at energies and rapidities inaccessible to other experiments. With 1.81 nb−1 of proton-proton collisions collected by the LHCb experiment in 2010 at center-of-mass energy √s = 7 TeV the production crosssection of D±s and D± mesons decaying to the φ{K+K−}π ± final state have been determined in bins of transverse momentum and rapidity. These measurements use a data-driven recursive optimisation technique to improve signal significance. The cross-section ratio is measured to be σ(D± ) σ(D± s ) = 2.32±0.27(stat)±0.26(syst), consistent with the ratio of charm-quark hadronisation fractions to D± and D±s mesons. Time-dependent interference between mixing of B0s -B0s mesons and decay to the final state J/ψφ gives rise to a CP violating phase φs. This phase is constrained to be small within the Standard Model, a significant deviation from which would be a signal of new physics. φs has been measured with 0.37 fb−1 of protonproton collision data recorded during 2011 by the LHCb experiment. Isolation of the signal distribution is achieved using the S-plot technique, and the analysis accounts for inclusive B0s →J/ψK+K− s-wave contributions. The measured value of φs = 0.16±0.18(stat)±0.06(syst) rad is the most precise measurement to date, and is consistent with Standard Model predictions.

Le compact linear collider (CLIC) est le projet de collisionneur de particules proposé par l'organisation européenne pour la recherche nucléaire (CERN) visant à succéder au large hadron collider (LHC). Du fait des dimensions nanométriques des faisceaux de leptons de ce projet, les accroissements admissibles de l'émittance sont extrêmement faibles. Cela a pour conséquence des tolérances d'alignement des composants du CLIC jamais atteintes. La dernière étape de l'alignement sera effectuée par rapport au faisceau de particules du CLIC. Elle est du ressort des physiciens du faisceau. Toutefois son implémentation nécessite un pré-alignement qui lui-même représente un défi métrologique et géodésique : atteindre 10 μm à 3σ le long d'une fenêtre coulissante de 200 m. Un tel niveau de précision requiert le développement d'une méthode compatible avec des systèmes de repositionnement qui seront constamment sollicités. Le pré-alignement du CLIC devra être actif. Cette thèse ne démontre pas la faisabilité du pré-alignement actif du CLIC mais montre le chemin des derniers développements à effectuer dans ce but. Il y est proposé une méthode, fondée sur la gestion des similitudes entre systèmes euclidiens de coordonnées, qui, de la géodésie aux mesures métrologiques, est susceptible d'apporter la solution. Des expériences sur de longues distances ont été construites dans le but d'éprouver, en parallèle de simulations de Monte-Carlo, les modèles mathématiques des systèmes de mesure et des références d'alignement ainsi créés. L'extrapolation de ces modèles, une fois validés expérimentalement, sur toute la longueur du CLIC, sera la dernière étape prouvant la faisabilité du pré-alignement

The position reconstruction performance of the Electromagnetic Endcap Calorimeter (EMEC) is assessed in terms of its response to electrons. The electromagnetic and hadronic endcap calorimeter modules of the ATLAS detector are exposed to beams of electrons, pions, and muons in the energy range 6 GeV ≤ E ≤ 200 GeV at several impact positions in the pseudo-rapidity 1.6 ≤ |η| ≤ 1.8 in a beam test at CERN. The EMEC is a lead-liquid argon sampling calorimeter with a unique accordion structure designed to provide complete hermiticity and excellent energy and position resolution, the attribute on which several physics measurements envisioned at the LHC will depend. Unlike the real ATLAS situation, the beam test setup used a non-pointing geometry in η due to the experimental constraints. Hence, the position resolution of the EMEC is evaluated in the φ direction only and found to be at least as good as σφ = (4.36 ± 0.10)/ √E (12.64 ± 0.82) / E (0.00 ± 0.10) in milliradians.