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Atlas jet trigger: performance and in-situ calibration studies

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Summary:The LHC at CERN will provide collisions of proton beams with a pioneer energy of 14TeV and an unprecedented luminosity of 1034cm−2s−1, extending the frontiers of Particle Physics. ATLAS is a general-purpose detector, designed to cover the widest range of physics possible by analyzing the myriad of particles produced by the LHC. Collision data from the LHC will be delivered to ATLAS at an unsustainable rate of 40MHz. Working in three steps, the ATLAS trigger system will effectively reject uninteresting events, still maintaining an excellent and unbiased efficiency for rare signals, in order to reduce the input rate to a manageable 200Hz.Hadronic jets will be among the most commonly produced objects at the LHC. They will represent, at the same time, signatures for many physics processes and background for nearly every physics analysis. Thus, the performance of the trigger system depends heavily on its ability to reconstruct jets. Moreover, precise jet reconstruction cannot be achieved without energy calibration, which is why the energy of trigger jet is calibrated at Level-2.The work presented in this thesis was developed in two steps. First, the performance of the ATLAS jet trigger system was evaluated using data from cosmic muon runs. This was done by comparing the properties of the jets reconstructed by the trigger and reconstructed offline. The analysis was simple but, nonetheless, powerful, since it allowed the identification of noisy cells and calibration problems. For the second study, a in-situ calibration method was applied to MonteCarlo simulated jets to evaluate if the method can be used with real collision data to validate and tune the calibration applied to Level-2 trigger jets. The method, named “intercalibration in η”, proved capable of improving theLevel-2 jet energy scale up to an uncertainty of 1% for jets with transverse momenta above 1TeV. Furthermore, the analysis strongly suggests that the method can be used with real data for the same purposes.
Main Authors:Miguéns, Joana Machado
Subject:CERN LHC ATLAS Jactos hadrónicos Trigger Calibração in-situ Teses de mestrado - 2009
Year:2009
Country:Portugal
Document type:master thesis
Access type:open access
Associated institution:Universidade de Lisboa
Language:English
Origin:Repositório da Universidade de Lisboa

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