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Contribution to construction and performance tests of the ALFA/ATLAS/LHC
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ATLAS é um dos quatro detectores principais de partículas instalados no acelarador LHC. Foi projetado e construído para estudar colisões protão-protão e colisões entre iões pesados. É um detector de partículas que tem como objectivo geral a procura de novas partículas relacionadas com o mecanismo de quebra espontânea de simetria e investigar teorias para além do Modelo Padrão. Uma peça essencial para as medidas do programa de física de ATLAS é a determinação precisa da luminosidade integrada, ∫ Ldt, onde L é a luminosidade instantânea. O trabalho apresentado nesta tese foi realizado no âmbito do Grupo Português de ATLAS e dentro da colaboração com o Grupo de Trabalho de ALFA. Esta tese descreve o trabalho realizado para projetar, construir e testar um sistema de oito detectores para medir a dispersão elástica de protões a ângulos muito pequenos (3:5 µrad), atingindo a região de interferência coulombiana e, desta forma, permitir a medição da luminosidade absoluta utilizando a secção eficaz eletromagnética. Com este sistema de detectores, chamado ALFA, a sigla para Luminosity Absolute For ATLAS, esperamos alcançar uma precisão na medição de luminosidade de cerca de 97%. O ALFA é um detector de traços de fibra ópticas cintilantes que detecta partículas que atravessam o detector e induzem o processo de cintilação. As fibras ópticas, necessárias para a construção do detector, foram polidas e aluminizadas numa das faces laterais para melhorar o rendimento de colecção de luz de cintilação. Durante esta fase eu contribuí para o controle de qualidade (CQ) das fibras cintilantes classificando-as em termos de rendimento de colecção de luz para disponibilizar essa informação durante a colagem das fibras no detector. Após o CQ e a separação das fibras ópticas foi obtido um RMS < 5%. Depois da construção, os detectores ALFA foram sujeitos a testes com feixes de partículas de altas energias. Foi usado um detector de silício, chamado EUDET, para determinar a resolução espacial dos detectores ALFA. Nos testes com feixe a minha contribuição em 2009 foi na análise dos dados e em 2010 a realização do teste e a análise de dados. Na análise de 2009, reconstruí traços no telescópio EUDET que foram usados em estudos posteriores pela colaboração ALFA, estudei o desempenho do telescópio EUDET e testei o seu alinhamento interno. Foi obtida uma resolução espacial de 3 - 4 µm para o telescópio EUDET na posição do ALFA e aproximadamente um traço por evento, condições optimas para o estudo do desempenho do detector ALFA. Em 2010 a minha contribuição para análise foi focada no desempenho do detector ALFA, nomeadamente no estudo da eficiência de cada camada, na multiplicidade de hits por camada, no varrimento de parâmetros do MAPMT, no estudo da contribuição do ruído para o sinal em cada camada e na resolução espacial. Foi encontrada uma eficiência de 93%, uma multiplicidade perto de um (1) e um ruído na ordem de 0.3%. Foi obtida uma resolução espacial de ~23 µm utilizando o método stand-alone, que é melhor que a resolução mínima requerida (30 µm).
ATLAS is one of the four independent particle detectors designed and built to exploit the proton-proton and heavy ions collisions physics at the LHC. It is a general purpose particle detector mainly designed to search for new particles related to the symmetry breaking mechanism and to investigate theories beyond the SM. An essential ingredient to the measurements of the ATLAS physics program is the accurate determination of the integrated luminosity, R ∫Ldt, where L is the instantaneous luminosity. The work presented in this thesis was done in the framework of the Portuguese ATLAS Group and within its collaboration with the ATLAS ALFA Working Group. It outlines the work done to design, build and test a system of eight position sensitive detectors to measure the elastically scattered protons down to very small angles (3:5 µrad), reaching the Coulomb interference region and in this way getting an absolute calibration of the luminosity using the computable electromagnetic cross section. With this system of detectors, called ALFA, the acronym for Absolute Luminosity For ATLAS, we expect to achieve a precision in the luminosity measurement of around 97%. The ALFA is a tracking detector based in scintillating optical fiber which detects particles through the scintillation process. The optical fibers needed for the detector construction were polished and aluminized at one of the fibers end to improve the light yield. During this phase I contribute to the optical and visual Quality Control (QC) of the scintillating fibers classifying them in terms of light yield for information during the gluing of the fibers in the detector. In this task and after separation of the fibers a displacement in RMS was < 5%. After ALFA detector construction and before its installation in the LHC tunnel the detector was submitted to test beam to study its performance with the held of a silicon tracking detector, named EUDET, with a better spatial resolution. I contributed in 2009 test beam analysis and in the 2010 test beam campaign and analysis. In the 2009 test beam analysis I reconstructed track with EUDET telescope that were used in later studies by the ALFA Collaboration, studied the EUDET performance and tested the EUDET internal alignment. From the studies a spatial resolution of 3 - 4 µm at ALFA position and a track multiplicity near one (1) was obtained which is suitable to study ALFA. The 2010 test beam analysis was focused in the ALFA detector performance with the study of the layer efficiency, layer hit multiplicity, MAPMT parameter scan, noise contribution to the layer signal and spatial resolution. This study reveal an efficiency of 93% and a multiplicity close to one (1) with a noise of order of 0.3%. A spatial resolution of ~ 23 µm using a stand-alone method was obtained that is better than 30 µm, the minimum resolution required.
ATLAS is one of the four independent particle detectors designed and built to exploit the proton-proton and heavy ions collisions physics at the LHC. It is a general purpose particle detector mainly designed to search for new particles related to the symmetry breaking mechanism and to investigate theories beyond the SM. An essential ingredient to the measurements of the ATLAS physics program is the accurate determination of the integrated luminosity, R ∫Ldt, where L is the instantaneous luminosity. The work presented in this thesis was done in the framework of the Portuguese ATLAS Group and within its collaboration with the ATLAS ALFA Working Group. It outlines the work done to design, build and test a system of eight position sensitive detectors to measure the elastically scattered protons down to very small angles (3:5 µrad), reaching the Coulomb interference region and in this way getting an absolute calibration of the luminosity using the computable electromagnetic cross section. With this system of detectors, called ALFA, the acronym for Absolute Luminosity For ATLAS, we expect to achieve a precision in the luminosity measurement of around 97%. The ALFA is a tracking detector based in scintillating optical fiber which detects particles through the scintillation process. The optical fibers needed for the detector construction were polished and aluminized at one of the fibers end to improve the light yield. During this phase I contribute to the optical and visual Quality Control (QC) of the scintillating fibers classifying them in terms of light yield for information during the gluing of the fibers in the detector. In this task and after separation of the fibers a displacement in RMS was < 5%. After ALFA detector construction and before its installation in the LHC tunnel the detector was submitted to test beam to study its performance with the held of a silicon tracking detector, named EUDET, with a better spatial resolution. I contributed in 2009 test beam analysis and in the 2010 test beam campaign and analysis. In the 2009 test beam analysis I reconstructed track with EUDET telescope that were used in later studies by the ALFA Collaboration, studied the EUDET performance and tested the EUDET internal alignment. From the studies a spatial resolution of 3 - 4 µm at ALFA position and a track multiplicity near one (1) was obtained which is suitable to study ALFA. The 2010 test beam analysis was focused in the ALFA detector performance with the study of the layer efficiency, layer hit multiplicity, MAPMT parameter scan, noise contribution to the layer signal and spatial resolution. This study reveal an efficiency of 93% and a multiplicity close to one (1) with a noise of order of 0.3%. A spatial resolution of ~ 23 µm using a stand-alone method was obtained that is better than 30 µm, the minimum resolution required.
Descrição
Tese de mestrado em Engenharia Física, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2011
Palavras-chave
ATLAS ALFA Luminosidade Fibra óptica Resolução Multiplicidade Eficiência Teses de mestrado - 2011