La physique des (di)muons dans ALICE au LHC : analyse en collisions pp $\sqrt{s}$ = 7 TeV) et Pb-Pb ($\sqrt{s_NN}$ = 2.76 TeV) des résonances de basses masses ($\rho, \omega, \phi$) et étude d'un trajectographe en pixels de Silicium dans l'ouverture du spectromètre

ALICE experiment at LHC studies the Quark Gluon Plasma (QGP), a particular state of matter where quarks and gluons are deconfined. A probe to explore this state is the study of several resonances ($\rho$, $\omega$, $\phi$, J/$\psi$ and $\Upsilon$) through their dimuon decay channel, with a muon spectrometer covering pseudo-rapidity -4 < $\eta$ < -2.5. In the first part of this thesis, the focus is on light vector mesons ($\rho$, $\omega$ and $\phi$) and their analysis in the 2010 data, in pp collisions at $\sqrt{s}$ = 7 TeV and Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. Light vector mesons are powerful tools to probe the QGP due to their short lifetime and their dimuon decay channel. Indeed, leptons have negligible final state interactions. Production rates and spectral functions of those mesons are modified by the hot hadronic and QGP medium. Chiral symmetry restoration study is done thanks to the study of $\rho$ spectral function. Strangeness enhancement is accessed via the ratio of $\phi$ over $\rho$+$\omega$ yields as a function of the centrality of the collision. In pp analysis, the emphasis is on background understanding and on first physics results such as $\phi$ yield over $\rho$+$\omega$ yield as a function of $p_{\rm \hspace{0.05 cm} T}$, and $p_{\rm \hspace{0.05 cm} T}$ distributions of $\phi$ and $\rho$ + $\omega$. Cross sections and $p_{\rm \hspace{0.05 cm} T}$-differential cross sections of light mesons will also be shown. The Pb-Pb analysis and its prospects will be presented. The second part of the thesis concerns ALICE upgrade plans of year 2017. A feasibility study for a Muon Forward Tracker (MFT) in Silicon pixels located upstream of the hadronic absorber in the spectrometer acceptance was performed. This upgrade is mainly motivated by the improvement of the dimuon invariant mass resolution and secondary vertex measurement. This gives access to open charm and beauty direct study in single muon channel. Prompt J/$\psi$ can also be distinguished from B feed-down J/$\psi$, allowing a better study of a QGP signature: the "J/$\psi$ suppression" in ultra-relativistic heavy ion collisions. MFT performances on those different topics were established in simulations. The track matching algorithm to match MFT tracks with spectrometer tracks (a crucial step for the feasibility of the project) and its results are presented.