Background subtraction for open heavy flavour studies in proton-proton collisions at √ s = 7 TeV with the ALICE Muon Spectrometer

With ultrarelativistic high energy heavy-ion collisions it is possible to reproduce, during a short time, the Quark Gluon Plasma : a dense and hot matter that existed in the early universe some microseconds after the big bang. Among the experiments at the LHC, ALICE is the only one that was designed and built to study heavy ion collisions. The muon spectrometer of the ALICE experiment studies open heavy flavours, quarkonium and low mass resonance through their semileptonic and leptonic decay into single muons and dimuons. The present report focuses on the study of open heavy flavours in proton-proton collisions as they can be used to test perturbative QCD calculations but also as a reference in Pb-Pb collision measurements. The first chapter introduces basic concepts of heavy ion collisions and open heavy flavour production in proton-proton collisions. The second chapter contains a description of the ALICE experiment and the muon spectrometer. Chapter three describes the method used to extract the single muon distribution coming from open heavy flavours and the associated systematic uncertainties to the background subtraction. Finally, chapter four is a summary of the most important results obtained.Avec les collisions des ions lourds à des énergies ultrarelativistes il est possible de reproduire, pendant un court laps de temps, un plasma de quarks et de gluons (QGP) : une matière dense et chaude qui existait dans l’univers primordial quelques microsecondes après le big bang. Parmi les expériences au LHC, ALICE est la seule qui a été conçue et construite pour étudier les collisions d’ions lourds. Le spectromètre à muons de l’expérience ALICE étudie les saveurs lourdes ouvertes, quarkonium et les résonances à faible masse à travers leurs désintégration leptonique et semileptonique en muons et dimuons. Le rapport actuel se concentre sur l’étude des saveurs lourdes ouvertes dans les collisions proton-proton comme ils peuvent être utilisés pour tester les calculs de la QCD perturbative mais aussi comme une référence dans les collisions Pb-Pb. Le premier chapitre introduit les concepts basiques des collisions des ions lourdes et la production des saveurs lourdes ouvertes dans les collisions protons-protons. Le deuxième chapitre contient une description de l’expérience ALICE et le spectromètre à muons. Le chapitre trois décrit la méthode utilisée pour extraire la distribution du muon provenant des saveurs lourdes ouvertes et les incertitudes systématiques associées à la soustraction du bruit de fonds. Finalement, le chapitre quatre est un résumé des résultats les plus importants obtenus

Azimuthal anisotropy of charged jet production in root s(NN)=2.76 TeV Pb-Pb collisions

We present measurements of the azimuthal dependence of charged jet production in central and semi-central root s(NN) = 2.76 TeV Pb-Pb collisions with respect to the second harmonic event plane, quantified as nu(ch)(2) (jet). Jet finding is performed employing the anti-k(T) algorithm with a resolution parameter R = 0.2 using charged tracks from the ALICE tracking system. The contribution of the azimuthal anisotropy of the underlying event is taken into account event-by-event. The remaining (statistical) region-to-region fluctuations are removed on an ensemble basis by unfolding the jet spectra for different event plane orientations independently. Significant non-zero nu(ch)(2) (jet) is observed in semi-central collisions (30-50% centrality) for 20 <p(T)(ch) (jet) <90 GeV/c. The azimuthal dependence of the charged jet production is similar to the dependence observed for jets comprising both charged and neutral fragments, and compatible with measurements of the nu(2) of single charged particles at high p(T). Good agreement between the data and predictions from JEWEL, an event generator simulating parton shower evolution in the presence of a dense QCD medium, is found in semi-central collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe

Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC

Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe

Forward-central two-particle correlations in p-Pb collisions at root s(NN)=5.02 TeV

Two-particle angular correlations between trigger particles in the forward pseudorapidity range (2.5 2GeV/c. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B. V.Peer reviewe

Event-shape engineering for inclusive spectra and elliptic flow in Pb-Pb collisions at root(NN)-N-S=2.76 TeV

Peer reviewe

Elliptic flow of muons from heavy-flavour hadron decays at forward rapidity in Pb-Pb collisions at root s(NN)=2.76TeV

The elliptic flow, v(2), of muons from heavy-flavour hadron decays at forward rapidity (2.5 <y <4) is measured in Pb-Pb collisions at root s(NN)= 2.76TeVwith the ALICE detector at the LHC. The scalar product, two- and four-particle Q cumulants and Lee-Yang zeros methods are used. The dependence of the v(2) of muons from heavy-flavour hadron decays on the collision centrality, in the range 0-40%, and on transverse momentum, p(T), is studied in the interval 3 <p(T)<10 GeV/c. A positive v(2) is observed with the scalar product and two-particle Q cumulants in semi-central collisions (10-20% and 20-40% centrality classes) for the p(T) interval from 3 to about 5GeV/c with a significance larger than 3 sigma, based on the combination of statistical and systematic uncertainties. The v(2) magnitude tends to decrease towards more central collisions and with increasing pT. It becomes compatible with zero in the interval 6 <p(T)<10 GeV/c. The results are compared to models describing the interaction of heavy quarks and open heavy-flavour hadrons with the high-density medium formed in high-energy heavy-ion collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V.Peer reviewe

Pseudorapidity and transverse-momentum distributions of charged particles in proton-proton collisions at root s=13 TeV

The pseudorapidity (eta) and transverse-momentum (p(T)) distributions of charged particles produced in proton-proton collisions are measured at the centre-of-mass energy root s = 13 TeV. The pseudorapidity distribution in vertical bar eta vertical bar <1.8 is reported for inelastic events and for events with at least one charged particle in vertical bar eta vertical bar <1. The pseudorapidity density of charged particles produced in the pseudorapidity region vertical bar eta vertical bar <0.5 is 5.31 +/- 0.18 and 6.46 +/- 0.19 for the two event classes, respectively. The transverse-momentum distribution of charged particles is measured in the range 0.15 <p(T) <20 GeV/c and vertical bar eta vertical bar <0.8 for events with at least one charged particle in vertical bar eta vertical bar <1. The evolution of the transverse momentum spectra of charged particles is also investigated as a function of event multiplicity. The results are compared with calculations from PYTHIA and EPOS Monte Carlo generators. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe

Centrality evolution of the charged-particle pseudorapidity density over a broad pseudorapidity range in Pb-Pb collisions at root s(NN)=2.76TeV

Peer reviewe

Corrélations angulaires azimutales entre les mésons D*+ et les hadrons chargés dans les collisions proton-proton à 13 TeV avec l'expérience ALICE au LHC

Collisions of heavy-ions at ultra-relativistic speeds allow for the creation of a new state of matter where quarks and gluons are deconfined in the so-called Quark-Gluon Plasma (QGP). It is believed that such a state of matter was present in our Universe a few microseconds after the Big Bang. The QGP properties are studied by means of probes. Heavy quarks (charm and beauty) are among the most suitable probes since, due to their large masses, are produced early in the collision and therefore they witness the full evolution of the system while losing energy in the QGP via collisional and radiative processes. The measurements of heavy quarks production and of their azimuthal correlation with lighter particles in small systems (proton-proton and proton-ion collisions) constitute a stringent test of perturbative Quantum Chromodynamics (pQCD) and a mandatory reference for the heavy-ion measurements in order to disentangle cold and hot nuclear matter effects. In this manuscript, we investigate the azimuthal correlations of charmed mesons (D*, D⁰, D⁺) with charged particles. The study is performed on real data and simulation for different collision energies. The proton-proton data used were collected by the ALICE Collaboration at CERN Large Hadron Collider while the simulation studies are performed with PYTHIA8 and EPOS3/EPOS@sHQ event generators. By means of correlation studies, we aim to shed light on the heavy-quarks production mechanisms setting constraints to pQCD calculations. At the same time, we build the necessary reference for future D mesons correlation studies in heavy-ion collisions targeted to investigate charm and beauty in medium energy loss.Les collisions d'ions lourds à des vitesses ultra-relativistes permettent la création d'un nouvel état de la matière où les quarks et les gluons sont déconfinés dans ce qu'on appelle le Plasma Quark-Gluon (QGP). On pense qu'un tel état de la matière était présent dans notre Univers quelques microsecondes après le Big Bang. Les propriétés QGP sont étudiées au moyen de sondes. Les quarks lourds (charme et beauté) sont parmi les sondes les plus appropriées car, en raison de leurs masses importantes, sont produits tôt dans la collision et par conséquent, ils témoignent à la pleine évolution du système tout en perdant de l'énergie dans le QGP via des processus collisionnels et radiatifs. Les mesures de la production de quarks lourds et de leur corrélation azimutale avec des particules plus légères dans de petits systèmes (collisions proton-proton et proton-ion) constituent un test rigoureux de Chromodynamique Quantique perturbatrice (pQCD) est une référence obligatoire pour les mesures d'ions lourds afin de démêler les effets de la matière nucléaire froide et chaude. Dans ce manuscrit, nous étudions les corrélations azimutales de mésons charmés (D*, D⁰, D⁺) avec des particules chargées. L'étude est réalisée sur des données réelles et une simulation pour différentes énergies de collision. Les données proton-proton utilisées ont été collectées par la collaboration ALICE au CERN Large Hadron Collider tandis que les études de simulation sont réalisées avec les générateurs d'événements PYTHIA8 et EPOS3/EPOS@sHQ. Au moyen d'études de corrélation, nous visons à faire la lumière sur les mécanismes de production de quarks lourds imposant des contraintes aux calculs de pQCD. Dans le même temps, nous construisons la référence nécessaire pour les futures études de corrélation des mésons D dans les collisions d'ions lourds visant à étudier le charme et la beauté dans la perte d'énergie moyenne