Two measurements of the Cabibbo-Kobayashi-Maskawa angle &gamma; using B &rarr; DK and B⁰ &rarr; DK^&ast;0 decays are presented in this thesis. The subsequent D meson decays to the K_S⁰&pi;⁺&pi;^− and K_S⁰K⁺K^− final states are studied using a binned Dalitz plot analysis. The D strong-phase variation over the Dalitz plot is taken from measurements performed at the CLEO-c experiment, making the analysis independent of a model to describe the D decay amplitude. Both measurements are performed using proton-proton collision data collected by the Large Hadron Collider beauty (LHCb) experiment in 2011 and 2012, corresponding to an integrated luminosity of 3 fb^−1 at centre-of-mass energies &radic;s = 7 TeV and 8 TeV. The value &gamma;= (62 ⁺¹⁵<sub style='position: relative; left: -1.7em;'>−14</sub>)° is measured using B⁰ &rarr; DK^&ast;0 decays and &gamma; = (71 ± 20)° is measured using B⁰ &rarr; DK^&ast;0 decays, with a second solution for each value corresponding to &gamma; + 180°. The measurements are consistent with the world average value of &gamma;.

This thesis describes the measurement of inclusive heavy flavor jet suppression in collisions between two lead nuclei with the center of mass energy per nucleon-nucleon pair of 2.76 TeV with the ATLAS detector at the Large Hadron Collider (LHC). The measurement of the heavy flavor jets and b-jet quenching at the LHC is important in the path towards the understanding of QGP. Parton showers initiated by heavy quarks are expected to be sensitive to the medium in a different way as the large quark mass suppresses the medium-induced radiation. This results in a different interplay between radiative and collisional energy loss. Therefore the analysis of the properties of jet associated with b hadrons (b-jet) is useful in understanding energy loss in the QGP. The inclusive b-jet suppression R AA has been measured using muons in jets, where a b-jet corresponds to a jet with at least one muon clustered with the anti-k t algorithm with parameter R = 0.2. The b-jets of p T between 30 GeV - 150 GeV are identified by the semileptonic decay of beauty hadrons. Muons originating from background sources, primarily Charm hadrons, pion and kaon decays, have been removed from the analysis using template fits to the distribution of a quantity(p T^rel) capable of statistically distinguishing between signal and background. The measured nuclear modification factor R AA has been presented in different centrality bins as a function of the b-jet transverse momentum p T.The results of R AA indicate that the yield of the most central event (0-10%) experiences more suppression compared to the most peripheral event (60-80%) by a factor of approximate 2.

Estágio realizado no CERN e orientado Eva Sanchez-Corral Mena / Tese de mestrado integrado. Engenharia Informática e Computação. Faculdade de Engenharia. Universidade do Porto. 2008

Estágio realizado na ATLAS Distributed Computing Group e orientado por Markus Elsing / Tese de mestrado integrado. Engenharia Informátca e Computação. Faculdade de Engenharia. Universidade do Porto. 2008

Grâce à l'exploitation du Large Hadron Collider, débutée en 2010, le monde de la physique des particules espère enfin avoir une compréhension plus précise du mécanisme de brisure de la symétrie électrofaible et résoudre certaines questions expérimentales et théoriques que soulèvent encore le modèle standard. S'inscrivant dans cette effervescence scientifique, nous allons présenter dans ce manuscrit une paramétrisation largement indépendante des modèles afin de caractériser les effets d'une éventuelle nouvelle physique sur les mécanismes de production et de désintégration du bosons de Higgs. Ce nouvel outil pourra aisément être utilisé dans les analyses des grandes expériences généralistes comme CMS et ATLAS afin de valider ou d'exclure de manière significative certaines théories au delà du modèle standard. Ensuite, dans une approche différente, fondée sur la construction de modèles, nous avons considéré un scenario où les champs du modèle standard peuvent se propager dans un espace plat possédant six dimensions. Les nouvelles directions spatiales supplémentaires sont compactifiées sur un Plan Projectif Réel. Cet orbifold original est l'unique géométrie à six dimensions qui présente des fermions chiraux et un candidat de matière noire dit naturel. Le photon scalaire, particule la plus légère du premier mode de Kaluza-Klein, est en effet stabilisé par une symétrie résiduelle de l'invariance de Lorentz à six dimensions. En utilisant les contraintes actuelles fournies par les observations cosmologiques, nous avons déterminé l'ordre de grandeur de la masse de cette particule aux alentours d'une centaine de GeV. De ce fait les nouveaux états présents dans cette théorie sont suffisamment légers pour produire des signatures claires et observables au Large Hadron Collider. Avec une étude plus poussée du spectre de masses et des couplages du modèle, incluant les corrections radiatives à une boucle, nous avons pu ainsi donner les premières prédictions et contraintes sur la phénoménologie attendue au Large Hadron Collider.

Dark matter has been shown to be extremely abundant in our universe. It comprises about 23 percent of the energy density of the entire universe, which is more than five times greater than the regular matter we already know about. Dark matter cannot be explained within the Standard Model of particle physics. However, models which extend the Standard Model, such as supersymmetry, can explain dark matter. This dissertation investigates the signals of some supersymmetry models in the context of collider physics. If dark matter particles or other supersymmetry particles are produced at some collider experiment, such as the Large Hadron Collider, it is important to know how we can find and measure the signatures and properties of these particles. This dissertation provides some measurement techniques for that exact purpose. These measurement techniques are also very general, making them useful for examining other models of particle physics as well. Lastly, if the supersymmetry model can be understood well enough from collider data, the connection back to cosmology can be made. Namely, it is possible to determine (from LHC data and using a standard cosmological calculation) the abundance of dark matter in the universe. Comparing this collider value with the value already measured will be a crucial step in understanding dark matter. This dissertation provides simulated results of this dark matter abundance calculation for a number of supersymmetry model points.

Over the last few decades, the Standard Model (SM) of particle physics has been used as a means of understanding the world around us. However, there is an increasing amount of data that suggests the SM of particle physics only describes nature up to energies of the electroweak scale. Extensions to the SM have been developed as a means of explaining experimental observation. If these extensions are indeed the correct mathematical descriptions of nature, the Large Hadron Collider (LHC), located at the European Center for Nuclear Research (CERN) near Geneva, Switzerland, is expected to produce new and exciting physics signatures that can shed light on the evolution of our universe since the early hypothesized Big Bang. Of particular interest are models that may lead to events with highly energetic tau lepton pairs. In this dissertation, focus is placed on a possible search for new heavy gauge bosons decaying to highly energetic tau pairs using a data sample corresponding to an integrated luminosity of 36 pb^-1 of proton-proton collisions at sqrt(s) = 7 TeV collected with the CMS detector at the CERN LHC. The number of observed events in the data is in good agreement with the predictions for SM background processes. In the context of the Sequential SM, a Z0 with mass less than 468 GeV/c^2 is excluded at 95 percent credibility level, exceeding the sensitivity by the Tevatron experiments at the Fermi National Accelerator Laboratory.

The Large Hadron Collider located at CERN is currently the most powerful particle accelerator and ATLAS is an experiment designed to exploit the high energy proton-proton collisions provided by the LHC. It opens a unique window to search for new physics at very high energy, such as supersymmetry, a postulated symmetry between fermions and bosons. Supersymmetry can provide a solution to the hierarchy problem and a candidate for Dark Matter. It also predicts the existence of new particles with masses around 1 TeV, thus reachable with the LHC. This thesis presents a new search for supersymmetry in a previously unexplored search channel, namely the production of charginos and neutralinos directly decaying to electroweak on-shell gauge bosons, with two leptons, jets, and missing transverse momentum in the final state. The search is performed with proton-proton collision data at a center of mass energy of √s = 8 TeV recorded with the ATLAS experiment in 2012. The design of a signal region sensitive to the new signal is presented and a data driven technique to estimate the Z+jets background is developed. Precise measurements of hadronic jet energies are crucial to search for new physics with ATLAS. A precise energy measurement of hadronic jets requires detailed knowledge of the pulse-shapes from the hadron calorimeter signals. Performance of the ATLAS Tile Calorimeter in this respect is presented using both pion test-beams and proton–proton collision data. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2 and Paper 4: Technical report from the  ATLAS experiment.</p>

No description available.

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.