Top quark mass measurement in the dilepton electron-muon channel with the matrix element method in the ATLAS experiment at LHC

The LHC produced proton-proton collisions data at 7 TeV of center of mass energy in 2011 and 8 TeV in 2012, corresponding to an integrated luminosity of, respectively, 5 fb^-1 and 23 fb^-1. Data acquired by ATLAS have led to a better understanding of the detector and its performance, to many measurements of physical quantities and the discovery of the Higgs boson. Top quark is involved in many processes beyond the Standard Model. Its mass is an important parameter for the Standard Model and any New Physics theory, thus measuring its mass accurately is necessary. After a description of the Standard Model of Particle Physics, and the role of the top quark in it, the first half of this thesis describes the ATLAS detector and its electromagnetic calorimeter, for which a study of the calibration constant patching is detailed. The second half details top quark physics events detected in ATLAS and their selection. Theoretical aspects of the matrix element method and its implementation for the top quark mass measurement in the dilepton electron-muon channel in the experimental framework of ATLAS are discussed. The measurement calibration and optimisation studies for the analysis are presented. Finally, systematic uncertainties are described and estimated. This measurement yields a top quark mass of (173.65 ± 0.70 ± 2.36) GeV ; showing no discrepancy with current worldwide measurements. (author)