Abstract : Ultra-relativistic heavy ion collisions are produced in order to observe the created hot and dense matter. One major goal is to probe the existence of the Quark Gluon Plasma (QGP). The QGP would be the state of matter in which temperature and density are high enough to break the quark confinement into hadrons. For that purpose, the RHIC collider has produced p+p and Au+Au collisions at the energy of $\sqrt(s_(NN))=$ 200 GeV. This thesis work is focused on the production of $\Lambda (1520)$ resonances in these collisions with the STAR experiment. In comparison with statistical prediction, the measured $\Lambda (1520)/\Lambda $ ratios show a significant lowering in ultra-relativistic heavy ion collisions. These results strongly support the decoupling of the system in two stages : a chemical freeze-out followed by a thermal freeze-out. This conclusion constitutes an important step to an understanding of the created matter in high energy heavy ion collisions.