A test-bench is created that injects digital pulses that emulate ATLAS LAr Front End Board electronic signal pulses in order to test prototypes. The prototypes are for new electronics for an upgrade to the CERN Large Hadron Collider that increases the rate of proton-proton collisions by an order of magnitude. This High-Luminosity Large Hadron Collider requires a completely new Trigger and Data Acquisition system to deal with information from detectors. One such system that is currently being developed is the Liquid Argon Signal Processor (LASP) whose architecture is based on Field Programmable Gate Arrays (FPGA). Validation of individual modules of the LASP are of key importance in the development cycle. Additionally, verification of module behaviour with real ATLAS pulses will not be available until much later in the project timeline. The injector project is implemented on an Intel Stratix 10 FPGA, using a soft-core NIOS II processor for TCP/IP communication with a workstation in order to transfer Monte Carlo simulation pulses to the FPGA, where it is then stored in a 2 GB DDR3 external memory. The pulses are then retrieved into internal memory buffers and are transmitted to the LASP at 40 MHz. The user is in complete control of the data pulses injected which is a vital property that would test LASP behaviour for different cases and possible failure modes. / Graduate

Le thème des analyses présentées dans ce document est la mesure des propriétés du boson de Higgs se désintégrant dans le mode H→ZZ→4l dans l'expérience ATLAS au CERN. Le document commence par un résumé détaillé concernant la procédure d'étalonnage des électrons: l'algorithme de combinaison trace-cluster améliore la résolution en énergie (surtout pour les électrons ayant une faible énergie transverse) en exploitant les informations du cluster et de la trace dans un ajustement par maximum de vraisemblance. L'amélioration en résolution est approximativement de 18-20% pour les désintégrations du J/Ψ en di-électrons, et 3% pour Z→ee. Par la suite, la combinaison E-p est appliquée au canal H→ZZ→4l avec électrons dans l'état final permettant d’obtenir un gain modéré sur la distribution de la masse invariante (4-5%). En deuxième lieu, la masse du boson de Higgs et sa largeur sont estimées, en particulier afin de comprendre les effets apportés par l'utilisation de l'algorithme de combinaison trace-cluster. La masse a été calculée en se servant d'un ajustement à deux dimensions appliqué sur la masse invariante m4l et un score de discrimination du signal contre le bruit de fond ZZ*. Cette discrimination est obtenue en exploitant les corrélations angulaires dont les distributions sont sensibles au spin et à la parité du boson de Higgs. L’étude sur la largeur du boson est ensuite détaillée : les résultats sont basés sur une approche qui vise à contraindre cette largeur en analysant la région de haute masse m4l où le boson de Higgs se comporte comme un propagateur. La section efficace au pic de la résonance (« on-shell ») dépend de la largeur totale du boson de Higgs, ce qui n’est pas le cas pour la production dans la région de haute masse (« off-shell »). Par conséquent, des limites indirectes sur la largeur peuvent être déterminées en combinant les régions « on-shell » et « off-shell ». Une limite à 6.7 fois la largeur Higgs ΓSMH est obtenue via le canal 4l. En combinant la mesure « on-shell » avec tous les canaux de désintégration étudiés (notamment ZZ→4l, ZZ→2l2ν and WW→lνlν), les résultats aboutissent à une limite observée (attendue) sur la largeur totale de 22.7 (33.0) MeV. La dernière partie de ce travail de thèse est consacrée à l'analyse sur la largeur du boson de Higgs en quatre leptons à haute (High-Luminosity LHC) luminosité intégrée (respectivement 300 fb⁻¹ et 3000 fb⁻¹) : il s’agit d’une étude extrapolant à √s =14 TeV les techniques utilisées pour l’analyse à 8 TeV (Run 1). / The theme of the analyses presented in this Thesis is the measurement of the Higgs boson properties in the H→ZZ→4l decay channel with the ATLAS experiment at the LHC. A detailed overview on the electron calibration process is first presented. In this regard, the track-cluster combination algorithm is found to improve the energy resolution of low ET electrons by exploiting both track and cluster information into a maximum likelihood fit. The improvement in resolution is approximately 18-20% for J/Ψ dielectron decays, and of the order of 3% for Z→ee events. In addition, the E-p combination algorithm has also been applied to the H→ZZ→4l channel with electrons in the final state resulting in a non-negligible gain on the invariant mass distribution (4-5%). Secondly, the Higgs mass and its total width are evaluated in the H→ZZ→4l channel. The Higgs mass is measured in the 4l decay channel with particular interest on the beneficial effects brought by the improved electron calibration and the track-cluster combination. The mass on the full 2011 and 2012 datasets is worked out with a 2-dimensional fit on the invariant mass of the 4 lepton final state, m4l, and on a boosted decision tree (BDT)-based output conceived against the main ZZ irreducible background and constructed on variables that are sensitive to the Higgs boson spin-parity state. Regarding the Higgs width, results are based on a relatively recent approach aimed at indirectly constraining the Higgs boson width by exploiting the m4l high-mass region where the Higgs boson acts as a propagator. The Higgs production cross section in the on-shell m4l region, where the Higgs boson is a resonance, depends on the total Higgs width, whereas this is not the case for the high mass m4l (off-shell). Limits on the Higgs width can be therefore set when merging the off-shell results with the on-shell ones. A limit of ∼ 6.7 times ΓSMH is obtained in the four lepton channel. Secondly, by combining with the on-shell measurement and using all the decay channels in the analysis, i.e. ZZ→4l, ZZ→2l2ν and WW→lνlν, the results lead to an observed (expected) 95% C.L. upper limit on the Higgs boson total width of 22.7 (33.0) MeV (4.2 MeV is the Standard Model predicted Higgs width at mH=125 GeV).The last section of the thesis is devoted to the evaluation of the Higgs width at √s=14 TeV in the high luminosity scenario (High Luminosity LHC), 300 fb⁻¹ and 3000 fb⁻¹, by employing the same techniques exploited in the previous Run 1 analysis at √s=8 TeV.

Injection in the LHC is a delicate moment, since the LHC collimation system cannot offer adequate protection during beam transfer. For this reason, a complex chain of injection protection devices has been put in place. Among them, the SPS scrapers are the multi-turn cleaning system installed in the SPS aimed at halo removal immediately before injection in the LHC. The upgrade in luminosity of the LHC foresees beams brighter than those currently available in machine, posing serious problems to the performance of the existing injection protection systems. In particular, the integrity of beam-intercepting devices is challenged by unprecedented beam parameters, leading to interactions potentially destructive. In this context, a new design of scrapers has been proposed, aimed at improved robustness and performance. This thesis compares the two scraping systems, i.e. the existing one and the one proposed for upgrade. Unlike any other collimation system for regular halo cleaning, both are "fast" systems, characterised by the variation of the relative distance between the beam and the absorbing medium during cleaning, which enhances the challenge on energy deposition values. Assets/liabilities of the two systems are highlighted by means of numerical simulations and discussed, with particular emphasis on energy deposition in the absorbing medium, time evolution of the beam current during scraping and losses in the machine. Advantages of the system proposed for upgrade over the existing one are highlighted. The analysis of the existing system takes into account present operational conditions and addresses the sensitivity to settings previously not considered, updating and extending past studies. The work carried out on the upgraded system represents the first extensive characterisation of a multi-turn cleaning system based on a magnetic bump. Results have been obtained with the Fluka-SixTrack coupling, developed during this PhD activity from its initial version to being a state-of-art tracking tool for cleaning studies in circular machines. Relevant contributions to the development involve the handling of time-varying impact conditions. An extensive benchmark against a test of the scraper blades with beam has been carried out, to verify the reliability of results. Effcts induced in the tested blades confirm the high values of energy deposition predicted by the simulation. Moreover, the comparison with the time profile of the beam intensity measured during scraping allowed the reconstruction of the actual settings of the blades during the test. Finally, the good agreement of the quantitative benchmark against readouts of beam loss monitors finally proves the quality of the analyses and the maturity of the coupling.