[en] The Standard Model (SM) is the theoretical framework that describes the interplay between the fundamental blocks of the Nature. Within the SM, Quantum Chromodynamics (QCD) is used to study the strong interaction of the elementary particles. At sufficiently high temperatures and pressure, QCD predicts that ordinary nuclear matter undergoes a phase transition. This new state of matter is called Quark Gluon Plasma (QGP) and is characterized by deconfined quarks and gluons. High energy heavy-ion collisions are used in the laboratory to satisfy the conditions of energy density and temperature necessary to recreate the QGP. A direct observation of the plasma is not possible, among the possible probes of the QGP, heavy quarks are of particular interest because they are produced in the initial hard-scattering processes and experience the whole evolution of the system. In particular the quarkonium family has been proposed as a tool to characterize the QGP: color screening of the heavy quarks potential, due to the deconfined state, would lead to a suppression of quarkonium production. However recent theoretical models indicate that recombination of charm quarks can lead to an enhanced J/ψ production, provided that the overall charm density of the medium at hadronization time is sufficiently high. The Large Hadron Collider (LHC), located under the French-Swiss border, is the largest and most powerful particle accelerator in the world. There are four main experiments located in the LHC, out of these, A Large Ion Collider Experiment (ALICE) is the only one that was specifically designed and built to focus on the study of heavy-ion collisions. Its goal is to characterize the physics of the QGP, but its program also includes the study of proton-proton, proton-nucleus and lighter ions collisions. The ensemble of detectors present in the ALICE experiment can be divided in three groups: the central barrel, forward detectors and the muon spectrometer. The latter is located at forward rapidity (2.5 < y < 4) and was designed to measure the quarkonia and low-mass vector mesons production via their dimuon decay channel, but also open heavy flavours through their semi-muonic disintegration. The muon spectrometer is made out of absorbers, a dipole magnet, tracking and trigger chambers. The first set of results in this thesis presents the efficiency of the tracking chambers computed, both in real data and simulations, in Pb-Pb and pp collisions at √s_NN = 2.76 TeV. The results are available in a run-per-run basis and integrated over the whole data taking period. For the Pb-Pb collisions the efficiency is also measured for different collision centralities and, for the 2011 heavy-ion period only, as a function of the transverse momentum and rapidity. In all cases the effects due to correlated inefficiencies in the tracking chambers are quantified. The comparison of the results obtained in data and simulation are used to assess the systematic uncertainties on the tracking apparatus. Finally, the second group of results contain the main physics output of the thesis. It describes the complete analysis performed on the 2011 Pb-Pb collisions: signal extraction, acceptance times efficiency corrections, normalization of the data and determination of the systematic uncertainties that arise from difference sources. The results present the J/ψ R_AA, T> and T²> together with a comparison to theoretical models and other experiments. (author)

[fr]

 La Chromodynamique Quantique predit que la matiere chaude et dense produite en collisions d'ions lourds ultra-relativistes, le Plasma de Quarks et de Gluons (QGP), se conduit comme un etat deconfine de quarks et gluons. ALICE est la seule experience au LHC qui a ete concue et construite pour caracteriser la physique du QGP. Le spectrometre a muons, un des detecteurs d'ALICE, est utilise pour mesurer la production de quarkonia a haut rapidite. Dans la these suivante, l'efficacite des chambres de trajectographie du spectrometre a muons est etudiee durant une annee de prise des donnees. Les resultats obtenus des donnees reelles sont comparees aux simulations pour calculer les incertitudes systematiques des chambres de trajectographie. Une analyse complete de la production inclusive de J/ψ → μ⁺μ^- dans les collisions Pb-Pb 2011 est egalement presentee. L'etude inclut l'extraction du signal, la normalisation et les corrections d'acceptance et d'efficacite. Une partie importante est consacree a quantifier les incertitudes systematiques liees aux differentes sources. Les resultats, R_AA et < p_T>, sont compares aux mesures de plus basse energie et aux modeles theoriques. (auteur)