Mise en oeuvre du calorimètre électromagnétique d'ATLAS et de la reconstruction des électrons avec les premières données du collisionneur de protons LHC. Détermination du potentiel de découverte d'un boson de jauge lourd chargé W^(' )→ev

ATLAS is a general purpose particle detector based at the Large Hadron Collider which has been delivering collisions since the beginning of 2010, with an energy in the centre of mass of 7 TeV. The electron and the discovery potential it carries is the subject of my thesis. The electromagnetic calorimeter is a crucial sub-detector for the measurement of electrons kinematic properties. In order to verify its functioning, I contributed to the first in situ data analysis, cosmic muons in 2008 and LHC beam data in 2009. These analyses showed the electromagnetic calorimeter was operational and efficient over its whole coverage. The knowledge of the electrons energy losses before they reach the calorimeter is mandatory to achieve precise measurements. For that purpose, I contributed to a method evaluating the amount of material upstream using Monte Carlo simulations of high transverse momentum electrons. The information from the electron allows mapping of the material from the inner tracker to the calorimeter entrance. In 2009 and 2010, the LHC collisions at 900 GeV et 7 TeV collisions provided ATLAS with its very first electron candidates and enabled the verification of their reconstruction performance. In this prospect, I compared the electron identification variables of data and simulation. Finally, I prepared the search for a charged heavy gauge boson W' decaying in an electron and a neutrino, using a calorimetric only definition of missing transverse energy in order to improve the method's robustness in the perspective of an early data analysis.