Experimental study of the test module of the electromagnetic end-cap calorimeter for the ATLAS experiment. Study of the spin correlation in the production of pairs tt-bar / Experimental study of the ATLAS electromagnetic endcap calorimeter module 0 performances: spin correlation study in the t t-bar pair production at the LHC

LHC, the future CERN proton collider, will start in 2006. It will be devoted to a better understanding of the Standard Model and new physics research. With a 10 ∫b^-1 per year at low luminosity during the first three years, then 100 ∫b^-1 per year, and energy of 14 TeV in the center of mass, the LHC is designed to discover the Standard or SUSY Higgs boson, or probe signature of new physics. ATLAS, one of the four experiments at the LHC, can study a large physics range, as Higgs boson, top and bottom, gauge bosons and new particles expected by SUSY model or other models beyond the Standard Model. The CPPM laboratory is responsible of a part of the electromagnetic end-cap calorimeter for the ATLAS experiment. In 1999, an ATLAS-like prototype of module was stacked in Marseille and intensively tested at CERN. Description of the calorimeter and a part of test-beam results are presented in this PhD manuscript. In parallel, a study about potentiality of the tt-bar spin correlation measurement was done. The high tt-bar statistic produced at the LHC allows to explore the quark top properties in details and being sensitive to new physics phenomena. Signatures of such physics can be extracted from tt-bar decay product angular distributions which are sensitive to tt-bar spin correlation. (authors)