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The electroweak standard model (Salam-Weinberg) is well-known to be a satisfactory and consistent theoretical description of all the experimental data we have obtained so far. In this thesis, we discuss possible phenomenology which goes beyond the standard model, with particular emphasis on the neutral current effects. First of all, the left-right symmetric extension of the standard model is discussed and we find limits on its parameters. We show that this model cannot explain certain newly reported and highly speculative events at the CERN collider [3], which in principle could be caused by the decay into two W's of a new heavy Z. We then discuss composite models where there is a strong expectation that there should be two neutral Z's of similar mass. We study the effects of these on neutral current phenomenology and show that in general the extra Z would be very hard to detect. A comparison of our model with a particular superstring model [6] is also made.

The standard model of particle physics is introduced, and extensions of it, which may be of cosmological relevance, are considered. The inflationary paradigm is reviewed as an extension of the standard cosmological model. In particular, the natural inflation mechanism resulting from a thermal phase change in a field theory with a spontaneous symmetry breaking potential, is examined. The question of when thermal equilibrium is likely to be a valid assumption in the early universe is considered in some detail. For inflation models, this question is answered by a self-consistency argument involving the total number of interactions per inflaton particle. In order to describe thermal-phase-change inflation models further, the temperature-dependent effective potential resulting from finite-temperature field theory is reviewed. The self-consistency test is developed into a numerical procedure which may be used to discuss the likelihood of thermal state generation in specific inflation models in a quantitative way. Alternatively, the method can be used to provide bounds on the parameters in the inflation potential from the requirement that a thermal state should occur. This procedure is applied to several example potentials and in particular it is easily verified that the "new inflation" model (relying on a phase change) is not viable. The method is quite general and can be applied to any inflation model for which a finite temperature effective potential can be defined. The procedure is generalised to the recently proposed extended inflation. Bounds on the extra free parameters which must be introduced in extended inflation are discussed. It is concluded that despite these extra free parameters the difficulties of generating a thermal state are just as great as they are in conventional inflation.

This thesis comprises two parts. In the first part an overview is given of the Standard Model, Supersymmetry and R-hadrons. R-hadrons are predicted within the framework of the Split-SUSY theory, in which the gluino can have a sufficiently long lifetime to hadronise into so-called R-hadrons. These will then propagate through the ATLAS detector as (meta)stable particles. The R-hadrons, which interact strongly, have the property of changing electric charge in interactions as they move through matter. In this thesis a strategy to search for R-hadrons with the ATLAS detcector is developed. The second part describes the ATLAS detector and the developement of the digitizer system of the ATLAS hadronic calorimeter. The digitizer system is the digitial readout system, in which data is read out from the detector to data buffers via an optical link. In the LHC environment, the operation of radiation-hard circuitry is essential. Therefore a quality control program was used to control that the design conforms to the requirements of radiation tolerance. An important part of the work was to test the devices to study their functionality and properties. This work is described in this thesis.

Feedback On Nanosecond Timescales (FONT) is a feedback system being developed to correct the beam position jitter in the extraction line and final focus system at the Accelerator Test Facility (ATF2), Tsukuba, Japan. FONT5 is currently being tested and is used to correct the intra-train jitter for a 3-bunch train; the bunch spacing is 154ns. This system measures the position of an electron bunch, using beam position monitors (BPMs). From this measurement, digital feedback electronics calculate the required correction, and sends a pulse to a feedback kicker. The feedback kicker then deflects the next bunch in the train in order to correct its position. Stripline BPMs are used at ATF2, and analogue processors manipulate the BPM signals before they are interpreted by the feedback electronics. The BPM system has been modelled and tested so that it can be parameterised and optimised. The BPMs are calibrated regularly, and the resolution of the system measured. Both of these properties have been analysed and modelled. This has allowed the resolution to be minimised. The resolution is an important factor which limits the achievable feedback correction. Several other factors have also been investigated; these include the feedback gain and the bunch-bunch correlation. To allow the feedback electronics to be controlled remotely, several data acquisition systems (DAQs) have been developed to allow data flow both to and from the digital board. The DAQs have been designed specically for the firmware on the FONT digital board.

Desenvolvemos uma nova técnica de equações de movimento para excitações nucleares partícula-partícula. Para isso, foi estendido o formalismo de duplos-comutadores de Rowe, relaxando-se a condição de aniquilação do estado-pai, violada no presente caso. As equações foram testadas para estados com senioridade nula de 2, 4 e 6 partículas sujeitas a uma força de emparelhamento, estando os resultados em excelente concordância com a solução exata. Foram também calculados, usando-se as novas equações e uma hamiltoniana realística, os estados de baixa energia com J = 0+, 2+, 4+, 6+ e 8+ para o 210,212,214Pb e 0+, 2+, 4+ e 6+ para o 206,204,202Pb. Tanto as energias de excitação como as taxas de transição (t,p) ou (p ,t) para esses estados concordam bem com as obtidas por um cálculo convencional de modelo de camadas de McGrory e Kuo e com os dados experimentais. O formalismo deverá ser útil para a análise de reações de transferência de dois núcleons. / A new equations-of-motion technique for particle-particle excitations in nuclei is developed. To this end Rowe\'s double-commutator formalism was extended, relaxing the condition of annihilation of the parent state, which is violated in the present case. The new equations were tested for seniority-zero states of 2, 4 and 6 particles interacting with a pairing force, and the results are in excellent agreement with the existing exact solution. Also computed, using the new equations and a realistic Hamiltonian, were the low energy states with J = 0+, 2+, 4+, 6+ and 8+ the case of 210,212,214 Pb and 0+, 2+, 4+ and 6+ in the case of 206, 204,202Pb. Both the excitation energies and the transition rates for the (t,p) or (p,t) \"reaction leading to those states are in as good an agreement with the experimental data as those obtained in a conventional shell-model calculation performed by McGrory and Kuo for some the above isotopes. The present formalism should be of interest for the analysis of two-nucleon transfer reactions.

Mostra-se que a atribuição de uma estrutura não puntiforme para uma partícula segue da exigência de uma formulação consistente do movimento da mesma quando se leva em conta a reação da radiação. Apresenta-se um esquema que permite a determinação da estrutura das partículas elementares (ou qualquer outro sistema quântico), em termos de densidades de carga e magnetização, a partir do conhecimento dos seus fatores de forma eletromagnéticos. As novas conexões entre estas grandezas levam a uma descrição correta dos raios médios de carga. A densidade de matéria hadrônica é obtida, adotando o modelo de Chou-Yang, a partir dos dados experimentais de colisões próton-próton a altas energias. Verificamos que, se a parte imaginária de amplitude elástica for positiva, a densidade de matéria hadrônica é muito semelhante à densidade de magnetização no interior do prótin, o mesmo valendo para o nêutron. / It is shown how the attribution of a structure to a particle follows from the requirement of a consistent formulation of the motion of such a system when one takes into account the radiation reaction. A scheme is presented which allows us to determine the structure of an elementary particle (or any other quantum system) in terms of charge and magnetization densities, out of its electromagnetic Form Factors. The new connection between these quantities leads us to a correct description of the mean charge-radius. The hadronic matter density is obtained, by assuming the Chou-Yang model, out of the experimental data on pp collisions at high energies. It is shown that, under the hypothesis that the imaginary part of scattering amplitude be always positive, the hadronic matter density is very similar to the magnetization density within the proton. The same is true for the neutron.

Mostra-se que a atribuição de uma estrutura não puntiforme para uma partícula segue da exigência de uma formulação consistente do movimento da mesma quando se leva em conta a reação da radiação. Apresenta-se um esquema que permite a determinação da estrutura das partículas elementares (ou qualquer outro sistema quântico), em termos de densidades de carga e magnetização, a partir do conhecimento dos seus fatores de forma eletromagnéticos. As novas conexões entre estas grandezas levam a uma descrição correta dos raios médios de carga. A densidade de matéria hadrônica é obtida, adotando o modelo de Chou-Yang, a partir dos dados experimentais de colisões próton-próton a altas energias. Verificamos que, se a parte imaginária de amplitude elástica for positiva, a densidade de matéria hadrônica é muito semelhante à densidade de magnetização no interior do prótin, o mesmo valendo para o nêutron. / It is shown how the attribution of a structure to a particle follows from the requirement of a consistent formulation of the motion of such a system when one takes into account the radiation reaction. A scheme is presented which allows us to determine the structure of an elementary particle (or any other quantum system) in terms of charge and magnetization densities, out of its electromagnetic Form Factors. The new connection between these quantities leads us to a correct description of the mean charge-radius. The hadronic matter density is obtained, by assuming the Chou-Yang model, out of the experimental data on pp collisions at high energies. It is shown that, under the hypothesis that the imaginary part of scattering amplitude be always positive, the hadronic matter density is very similar to the magnetization density within the proton. The same is true for the neutron.

<p>This thesis comprises two parts. In the first part an overview is given of the Standard Model, Supersymmetry and R-hadrons. R-hadrons are predicted within the framework of the Split-SUSY theory, in which the gluino can have a sufficiently long lifetime to hadronise into so-called R-hadrons. These will then propagate through the ATLAS detector as (meta)stable particles. The R-hadrons, which interact strongly, have the property of changing electric charge in interactions as they move through matter. In this thesis a strategy to search for R-hadrons with the ATLAS detcector is developed.</p><p>The second part describes the ATLAS detector and the developement of the digitizer system of the ATLAS hadronic calorimeter. The digitizer system is the digitial readout system, in which data is read out from the detector to data buffers via an optical link. In the LHC environment, the operation of radiation-hard circuitry is essential. Therefore a quality control program was used to control that the design conforms to the requirements of radiation tolerance. An important part of the work was to test the devices to study their functionality and properties. This work is described in this thesis.</p>

Ce travail consiste en l'étude des événements diffractifs avec production de jets pour lesquels le proton diffusé est détecté dans le spectromètre à protons, VFPS, au sein de l'expérience H1 auprès du collisionneur HERA. L'objectif est de mesurer la section efficace de ce processus et de la confronter aux prédictions théoriques de la Chromo Dynamique Quantique (QCD). Ces prédictions reposent sur le théorème de factorisation collinéaire, via l'universalité des densités de partons (PDF). Les analyses précédentes de la Collaboration H1 ont montré un bon accord entre les données et les prédictions dans le domaine de l'électro-production supportant la factorisation. Cependant, en photo-production, une brisure de la factorisation a été observée. Dans ce travail, le nouveau spectromètre à protons VFPS a été utilisé afin de détecter le proton diffusé lors de l'interaction diffractive, permettant de supprimer le bruit de fond dominant dans les mesures précédentes et de réduire d'autres sources d'incertitudes expérimentales. La section efficace de production de jets dans le domaine de l'électro-production est extraite et comparée aux prédictions QCD au NLO. Ces prédictions sont basées sur les fonctions de distribution de partons (PDF) extraites des mesures antérieures par la Collaboration H1. Les sections efficaces obtenues dans ce travail sont en accord tant d'un point de la normalisation que de celui de la dépendance en les différentes variables cinématiques avec les prédictions théoriques. Nous pouvons en conclure l'universalité des PDF telle que prédite par le théorème de factorisation. De plus, l'analyse des sections efficaces différentielles permet de montrer que les prédictions basées sur des PDF extraites à partir d'une combinaison de mesures en diffraction inclusive et de production de jets semble être favorisée. La production de jets en diffraction dans le domaine de la photo-production est également étudiée dans cette thèse. On y traite de la mise en place d'un nouveau sous-déclencheur permettant de sauvegarder les données sur banques. Les données en photo-production ont été comparées aux données simulées par un programme par Monte Carlo. Le bon accord entre les deux échantillons permet de s'assurer que les différents effets détecteurs ont été correctement pris en compte et montre que la mesure de la section efficace est faisable.