Etude de la production de mesons $\phi$ , $\rho$ et $\omega$ dans les collisions d'ions lourds ultra-relativistes au SPS du CERN (dans l'experience NA50)

The NA50 experiment is one of the experiment using the SPS beam at CERN. One the common aim of the SPS experiment is to look for the existence of a new state of the nuclear matter : the quark-gluon plasma. Among the proposed signatures of the quark-gluon plasma is the enhanced production of particles containing strange quarks. In the current work the NA50/NA38 experiment data are analysed and the relative production of the $\phi$ and $\rho$ + $\omega$ mesons are obtained from Pb-Pb collisions at 158 and S-U at 200 GeV per nucleon.