K+Λ photoproduction provides the best possibility for a model independent extraction of the photoproduction process and contributing resonances. To do this, it is vital that cross section measurements are well understood. This thesis presents pγ K+Λ differential cross sections from the reaction threshold, to an invariant centre of mass energy of 1.87 GeV. The data was taken at MAMI-C electron microtron facility in Mainz, Germany, during July 2007 and April 2009. The 1.5 GeV MAMI-C electron beam was used to produce an energy tagged bremsstrahlung photon beam with a maximum energy of 1.4 GeV and an intensity of 105γs-1MeV-1. The beam impinged upon a liquid hydrogen target, with reaction products detected in two segmented calorimeter arrays; the Crystal Ball detector and TAPS. This work pioneers a new method of K+ detection in segmented calorimeters, in which the K+ was identified from the signature of its weak decay inside the crystals of the calorimeter. This proved to be an excellent method of isolating K+ and accessing strangeness photoproduction channels, with good agreement between experimental and Geant4 simulated data. A novel method in seperating K+Λ and K+Σ0 final states was also developed by identifying the photon from the decay: Σ0 → Λγ. The intense photon beam at the MAMI-C facility enabled differential cross section data with greater invariant mass resolution than previous measurements. The new measurement near threshold imposes important constraints to effective field theories based on the approximate chiral symmetry of QCD. At higher centre of mass energies it also addresses the current problem of discrepant data sets and will form an important constraint on partial wave analysis for the nucleon excitation spectrum. As such, this work contributes to a major world wide programme aiming to extract the excitation spectrum of the nucleon and to understand the dynamics and interactions of its constituents. The greater statistics near threshold, and particularly at backwards K+ centre of mass angles will give new valuable constraints to contributions from meson and hyperonic resonances on the reaction mechanism. The high resolution of the photon beam (approximately 2 MeV) also allows the first search for narrow resonances coupling to KΛ final states. The differential cross sections give good agreement with Kaon-MAID partial wave solutions, apart from at backward angles close to threshold, where the data is lower. Near threshold, the data agrees with calculations from the chiral unitary framework of Borasoy et al, tending to be in better accordance with the model than previous data. No strong structure from potential narrow resonance states was observed over the centre of mass energy region of 1650-1700 MeV, where narrow structure has been observed in recent η photoproduction of the neutron.

Orientador: Prof. Dr Pedro Galli Mercadante / Tese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, 2015. / We present a search in the CMS detector for a high-mass and narrow resonance decaying into a Higgs and a Z SM bosons in the final state with a pair of tau leptons and a pair of quarks. We analyze 19:7=fb of integrated luminosity of? s = 8 TeV proton-proton collisions from LHC. In the resonance mass range of interest (1:0 .. 2:5 TeV), the Z and Higgs bosons are produced with large momentum compared with their masses, which implies that the final products of the two quarks and the two taus must be detected within a small angular separation (boosted topology). Jet substructure techniques are used to identify the boosted Z boson decaying hadronically and a modified approach is considered to reconstruct very collimated pairs of tau leptons from boosted Higgs decay. From a combination of all possible decay modes of the tau lepton, heavy spin-1 resonances production cross sections are excluded at 95% C.L. in a range between 0:9 and 27:8 fb, depending on the resonance mass. We consider as benchmark model an effective description of a strongly coupled theory based on the Minimal Composite Higgs Model, which predicts heavy resonances with suppressed branching fractions into fermions. Comparing the experimental limits with analytical expressions of the parameters of a simplified model Lagrangian we obtain observed limits on these parameters, which are directly connected with the heavy resonance production and decay. / Apresentamos uma busca no detector CMS por ressonâncias massivas decaindo em um bóson de Higgs e um boson Z do Modelo Padrão no estado final com um par de leptons tau e um par de quarks. Analisamos 19; 7=fb de luminosidade integrada em colisões próton-próton com energia no centro de massa de 8 TeV no LHC. No intervalo de massa da ressonância entre 1; 0 .. 2; 5 TeV, os bósons Z e Higgs são produzidos com um momento grande comparado a suas massas, isso implica que os produtos finais provenientes de cada par de taus ou quarks devem ser detectados dentro de pequenas regiões espaciais. Técnicas de subestrutura de jatos são utilizadas para identificar o boson Z que decai em quarks. Para o Higgs decaindo em taus é definido um metodo modificado de reconstrução de pares de taus com alto momento e colimados. Combinando os resultados das análises de cada modo de decaimento do tau, são excluidas com 95% de confiança seções de choque de produção de ressonâncias com spin-1 no intervalo de 0; 9..27; 8 fb, dependendo da massa da ressonância. Consideramos como modelo de referência uma teoria efetiva de Higgs composto, que prediz ressonâncias massivas com pequena razão de ramificação em férmions. Comparando os limites experimentais com expressões analíticas dos parâmetros de uma Lagrangeana de um modelo simplificado, obtemos limites sobre esses parâmetros, os quais estão diretamente relacionados com a produção e decaimento das ressonâncias.

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