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Étude de la production de saveurs lourdes et de la multiplicité de particules chargées dans le cadre du formalisme du Color Glass Condensate pour les collisions p+p et p+Pb dans l'expérience ALICE au LHC

Abstract : The classical nuclear matter is characterized by an energy density of the order of " = 0.17 GeV/fm3. For the critical values of the energy density (5 -10 ") or the temperature (150 - 200 MeV), the Lattice QuantumChromo Dynamics (LQCD) calculations predict a phase transition from the classical to a new form of nuclear matter called the Quark Gluon Plasma (QGP) in which quarks and gluons are deconfined. Heavy ion collisions allow to create the thermodynamical conditions needed for the QGP formation. The LHC will collide p+p and Pb+Pb nuclei at ultrarelativistic energies, reaching a few TeV per nucleon. At such ultra-relativistic energies, new theoretical approaches of QCD developed to understand high energy hadronic collisions can be tested experimentally. One of the most discussed topic is the Color Glass Condensate (CGC) approach allowing the description of the initial conditions of the heavy ion collision. The CGC approach predicts the saturation of the parton density of the nucleus for small values of the Bjorken-x variable, i.e. large pseudorapidity. The comprehension of the initial conditions for heavy ion collisions is mandatory to understand the system evolution toward the QGP. ALICE is one of the LHC experiment dedicated to the study of heavy ion collisions and especially to probe the QGP properties. One of the possible signatures of the QGP formation is the quarkonia (J/ , ) suppression due to the color screening in the deconfined medium. The ALICE muon spectrometer covering the pseudorapidity domain -4 < < -2.5 allows to measure the quarkonia production via their dimuon decay. The saturation effects, more visible in the large pseudorapidity region, can be studied with the muon spectrometer detector. The first part of this report presents the preparation and commissioning of the muon spectrometer. The results of the tests of the frontal electronics and of the spectrometer tracking chambers show that the first station of the tracking system works correctly and thus is ready to register the first physics data. The second part describes the study of the Color Glass Condensate effects using two experimental methods : the heavy quark production (charm and beauty) and the charged particle multiplicity.We show that the final state of the collision is affected by the existence of the CGC in the initial stage of the collision.We conclude that the LHC will allow the study of the new Physics never explored before.
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Submitted on : Tuesday, January 26, 2010 - 10:57:58 AM
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M. Malek. Étude de la production de saveurs lourdes et de la multiplicité de particules chargées dans le cadre du formalisme du Color Glass Condensate pour les collisions p+p et p+Pb dans l'expérience ALICE au LHC. Physique Nucléaire Théorique [nucl-th]. Université Paris Sud - Paris XI, 2009. Français. ⟨tel-00450342⟩

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