부산대학교 도서관

This thesis has been development in the framework of the ATLAS experiment, one of the main general-purpose detectors of the Large Hadron Collider (LHC) located at CERN. This work has to differentiated parts, starting with the basic description of the physic that involve LHC studies, centred in the top quark. The pair production of the top quark is one of the dominant processes in the proton-proton interactions, after QCD jets and the production of W and Z bosons. Also, the tau particle is described, one of the main ingredients of the physic analysis. After this, the fundamental parts of the LHC accelerator and the ATLAS detector are showed. The next is dedicated to TileCal sub-detector, describing mainly the electronic and the data quality assessment performed during commissioning. This is completed with the description of the TileMUID algorithm, based on TileCal and implemented in the second muon level trigger of ATLAS. These studies contributed to the commissioning of TileCal using cosmic muons taken during the previous period of collisions, showing the correct operation of the detector. The main part of this work is the physic analysis, with research concerned to the top quark physic. It starts with the selection of common objects for the whole analysis and the description of the samples used. This is followed by tau identification studies, with the calculation of tau-misidentification probabilities using γ +jets samples. The purpose of this study is to choice the best tau identification algorithm for the measurement of the cross-section. In the next, the calculation of the scale factors of Z background is performed, in order to obtain a better agreement between data and Monte Carlo (MC). These numbers are necessaries for the measurement of the cross-section. The description of the event selections and the cutflow study is also shown, with the goal of study the background and maximize the number of events in the signal against the background. Finally, it is presented the measurement of the top quark pair production cross-section in the lepton + tau channel, applying the fitting method to 4,73 fb-1 samples. This method use the TauID technique to separate process from tau leptons (signal) from those with jets that can be misidentified as taus (fake taus), applying a χ2 fit to signal and background samples, allowing to obtain the number of events from the samples and calculate the cross-section. The study of the main systematic uncertainties is also presented, in order to measure with more precision the cross-section in the lepton + tau channel. The result of the measurement agrees with the Standard Model predictions and the previous measurements in the same channel.