Etude du quark top avec ATLAS au LHC: Mise en route du calorimètre électromagnétique

The first proton-proton collisions in the Large Hadron Collider at CERN will take place on 2007. It aims at understanding the origins of mass, and it will also look for new physics. The ATLAS experiment will exploit all those physics potentialities, using a multilayer generalist detector. Quark top studies will be an important step in ATLAS physics program: its properties may reveal hints of new phenomena. One way to look for new physics is through quark top and W boson polarizations, which are studied here. This detailed simulation study has confirmed previous fast simulation results including extensive systematics estimation. ATLAS should thus yield a precision of a few percents with 10 fb-1 of data, that is a year of LHC working. This precision is sufficient to select among several new physics models. Among ATLAS subsystems, the electromagnetic calorimeter plays a crucial role in the characterisation of electrons and photons, which are used in particular for the Higgs boson search. This document deals with the calorimeter commissioning as the time of the first collisions approaches. The detector itself and its electronics will be described, as well as its installation and calibration. Cosmic muons observation will then be presented, as the first overall test of the reading and reconstruction electronics chain in actual working conditions.