Study of the flavor symmetry breaking in the nucleon light quarks sea using the Drell-Yan process

The aim of the NA51 experiment, realized at CERN, is to make the first direct measurement of the flavor asymmetry in the light quark sea of the nucleon. To do this, it studies the production difference of the Drell-Yan process in the proton-hydrogen and proton-deuterium collisions at 450 GeV/c. This thesis describes the experimental apparatus and especially the target systeme which allows to realize this measurement. The wished precision on the final result leads to change periodically the target during the data taking to minimise the sources of systematical errors and to have a great statistic on the number of Drell-Yan events with a mass greater than 4.3 GeV/c2. The cross section asymmetry of the Drell-Yan production in the proton-proton and proton-neutron interactions allows to calculate the ratio of the number of antiquarks u on the number of antiquarks d. This result is a clear indication of the flavor symmetry breaking in the light quark sea of the nucleon. The J/ψ asymmetry is also measured and leads to the same conclusion. These results are compared to different theoretical models. Finally the ratio ψ'/J/ψ is calculated for the interactions proton-hydrogen and proton-deuterium. The result is in very good agreement with those done by other experiments. It confirms the independence of the ratio ψ'/J/ψ versus the length of nuclear matter through which the ψ' and the J/ψ go in proton-nucleus collisions. (author). 47 refs., 57 figs., 10 tabs., 2 annexes