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

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

Study of J/psi polarization in proton-proton collisions with the ALICE detector at the LHC

The main purpose of the ALICE experiment is the study and characterization of the Quark Gluon Plasma (QGP), a state of nuclear matter in which quarks and gluons are deconfined. Quarkonia (bound states of a heayvy quark Q and its anti-quark Q) constitute one of the most interesting probes of the QGP. Besides this motivation, the study of quarkonium production is very interesting since it can contribute to our understanding of Quantum Chromodynamics, the theory of strong interactions. The formation of quarkonium states in hadronic collisions is not yet completely understood. The two main theoretical approaches to describe the production of quarkonium states, the Color Singlet Model and the Non-Relativistic QCD framework (NRQCD), have historically presented problems to simultaneously describe the production cross section and polarization of such states. On the experimental side, quarkonium polarization measurements have not always been complete and consistent between them. So, neither from the theoretical nor from the experimental point of view the situation was clear.Improved methods for the measurement of quarkonium polarization have been recently proposed, highlighting the necessity to perform the measurements of all polarization parameters with respect to different reference axes. In this context, new measurements could help to improve and set new constraints to the calculations. ALICE has measured the J/ψ polarization in pp collisions at √8= 7 TeV. The higher statistics of the 8 TeV data with respect to the 7 TeV data allows to extend the pT range of the measurements. This thesis presents a complete measurement of J/ψ polarization, i.e. the three polarization parameters, in two polarization frames : the Collins-Soper and Helicity frames. The results show no significant J/ψ polarization in the kinematic domain studied: 2.5 < y < 4.0 and 2 < pT < 15 GeV/c. The measurement of a frame invariant parameter λ, was also performed to ensure that no bias was present in the analysis procedure. The comparison with different theoretical predictions shows that there is not yet a satisfactory description of quarkonium production. None of the present theoretical approaches is able to describe both, the cross section and polarization measurement

Etude de la polarisation du J/ψ dans les collisions proton-proton avec le détecteur ALICE au LHC

The main purpose of the ALICE experiment is the study and characterization of the Quark Gluon Plasma (QGP), a state of nuclear matter in which quarks and gluons are deconfined. Quarkonia (bound states of a heayvy quark Q and its anti-quark Q) constitute one of the most interesting probes of the QGP. Besides this motivation, the study of quarkonium production is very interesting since it can contribute to our understanding of Quantum Chromodynamics, the theory of strong interactions. The formation of quarkonium states in hadronic collisions is not yet completely understood. The two main theoretical approaches to describe the production of quarkonium states, the Color Singlet Model and the Non-Relativistic QCD framework (NRQCD), have historically presented problems to simultaneously describe the production cross section and polarization of such states. On the experimental side, quarkonium polarization measurements have not always been complete and consistent between them. So, neither from the theoretical nor from the experimental point of view the situation was clear.Improved methods for the measurement of quarkonium polarization have been recently proposed, highlighting the necessity to perform the measurements of all polarization parameters with respect to different reference axes. In this context, new measurements could help to improve and set new constraints to the calculations. ALICE has measured the J/ψ polarization in pp collisions at √8= 7 TeV. The higher statistics of the 8 TeV data with respect to the 7 TeV data allows to extend the pT range of the measurements. This thesis presents a complete measurement of J/ψ polarization, i.e. the three polarization parameters, in two polarization frames : the Collins-Soper and Helicity frames. The results show no significant J/ψ polarization in the kinematic domain studied: 2.5 < y < 4.0 and 2 < pT < 15 GeV/c. The measurement of a frame invariant parameter λ, was also performed to ensure that no bias was present in the analysis procedure. The comparison with different theoretical predictions shows that there is not yet a satisfactory description of quarkonium production. None of the present theoretical approaches is able to describe both, the cross section and polarization measurements.L’expérience ALICE a pour principal objectif l’étude et la caractérisation du plasma de quarks et de gluons (QGP), un état de la matière nucléaire dans lequel les quarks et les gluons sont déconfinés. Les quarkonia constituent l’une des plus intéressantes sondes (des états liés d’un quark lourd Q et de son anti-quark Q) du QGP. De plus, l’étude de la production des quarkonia est très intéressante puisqu’elle peut contribuer à une meilleure compréhension de la Chromodynamique Quantique, la théorie décrivant l’interaction forte. La formation d’états de quarkonia lors de collisions hadroniques n’est pas bien comprise. Les deux principales approches théoriques décrivant la production d’états de quarkonia, le ‘Color Singlet Model’ (CSM) et la QCD non-relativiste (NRQCD), ont montré des difficultés à décrire simultanément la section efficace de production et la polarisation de tels états. Expérimentalement, les mesures de la polarisation des quarkonia n’ont pas toujours été compatibles entre elles. Ainsi, que ce soit du point de vue expérimental ou théorique, l’étude des quarkonia est restée inachevée.De nouvelles méthodes récemment proposées ont souligné la nécessité de mesurer tous les paramètres de la polarisation, dans les différents systèmes de référence. Dans ce contexte, de nouvelles mesures peuvent améliorer les contraintes actuelles, voire apporter de nouvelles contraintes sur les prédictions. ALICE a mesuré la polarisation du J/ψ lors de collisions pp à √8 = 7 TeV. La plus grande statistique des données à 8 TeV par rapport aux données à 7 TeV permet d’étendre les mesures à une gamme de pT plus large. Cette thèse présente une mesure complète de la polarisation de J/ψ, i.e. les trois paramètres de polarisation, dans deux systèmes de référence différents: le système Collins-Soper et le système d’hélicité. Les résultats ne montrent aucune polarisation significative pour le J/ψ dans le domaine cinématique étudié : 2.5 < y < 4.0 et 2 < pT < 15 GeV/c. Le paramètre invariant λ a également été mesuré afin d’écarter le risque d’un biais dans la procédure d’analyse. La comparaison de ces résultats avec les prédictions théoriques montre que la production de quarkonia n’est pas encore correctement décrite. Aucun de ces modèles théoriques n’est capable de décrire à la fois les mesures de sections efficaces et de polarisation

Charmonium production in pp, p—Pb and Pb—Pb collisions at forward rapidity with ALICE at the LHC

International audienceThis contribution presents recent ALICE measurements on charmonium production at forward rapidity in pp collisions at √s = 7 TeV, p-Pb at √sNN = 5.02 TeV and Pb-Pb at √sNN = 2.76 TeV. The charmonium production cross sections in pp collisions are in good agreement with calculations within the NRQCD approach. The comparison between J/Ψ and Ψ(2S) yields in p-Pb collisions indicates the presence of Cold Nuclear Matter effects on charmomium production in the final state. In Pb-Pb collisions the measured J/Ψ suppression is in agreement with models that introduce J/Ψ regeneration mechanisms through the recombination of cc̅ pairs produced in the medium