Title: Study of strange particle production in jets with the ALICE experiment at the LHC Author: Vít Kučera Institute: Institute of Particle and Nuclear Physics Supervisors: RNDr. Jana Bielčíková, Ph.D., Nuclear Physics Institute of the CAS; Dr. Christian Kuhn, Institut Pluridisciplinaire Hubert CURIEN Abstract: Quark-gluon plasma is a state of matter existing under extreme energy densities and temperatures where quarks and gluons are deconfined. Complex phenomena occurring in the plasma emerge from the strong interaction of its constituents. This hot and dense strongly interacting matter can be created in ultra-relativistic heavy-ion collisions and its properties can be studied by measuring particles produced in the collisions. Partons produced in hard scatterings interact with the medium which modifies the production of particles in jets. Measurements of spectra of identified particles produced in jets represent an important tool for understanding the interplay of various hadronization mechanisms which contribute to the particle production in the medium created in heavy-ion collisions. In this thesis, we present the measurement of the pT spectra of Λ baryons and K0 S mesons produced in charged jets in central Pb-Pb collisions at the energy √ sNN = 2.76 TeV, measured in the ALICE experiment at the LHC. The...

O principal objetivo de experimentos envolvendo colisões de íons pesados relativísticos é estudar a matéria nuclear sob condições extremas de temperatura e densidade. Sob tais condições, acredita-se que a matéria transite para um novo estado no qual quarks e glúons deixem de estar confinados, o plasma de quarks e glúons (PQG). A produção de partículas estranhas é uma importante ferramenta para a caracterização desse novo estado. O aumento da produção dessas partículas já era considerado como sendo um possível sinal para a existência do plasma de quarks e glúons mesmo antes da obtenção dos primeiros resultados experimentais do RHIC. Nesse trabalho, é feita a determinação da produção das partículas estranhas neutras K0s , e em colisões Cu+Cu ap sNN = 62:4 GeV, utilizando o intervalo de rapidez y < j0:75j. Em seguida, esses dados são comparados a modelos teóricos (estatístico -termodinâmicos, coalescência e core-corona) para entender o processo de produção dessas partículas em colisões de íons pesados relativísticos. / The main goal of relativistic heavy ion collisions is to study nuclear matter under extreme conditions of temperature and density. It is under these conditions that it is believed that a phase transition to a new state of matter where quarks and gluons are no loger conned takes place, the so called Quarks and Gluon Plasma. Strange particle production is an important tool for the characterization of this new state of matter. Strangeness enhancement was considered as a possible evidence for the formation QGP even before the rst RHIC experimental results. In this thesis, it is determined a production of neutral strange particles K0 s and in Cu+Cu collisions at p sNN = 62:4 GeV, using a rapidity range y < j0:75j. These data are compared to theoretical models (statistical-thermodynamic, coalescence and core-corona) in order to understand the hadronization process in relativistic heavy ions collisions.

Nesta tese estudamos o fluxo dirigido, a primeira componente na expansão de Fourier da distribuição azimutal das partículas emitidas. Diferente do fluxo elíptico, que é muito bem estudado e descrito na literatura, a física que gera este observável ainda não é muito conhecida. Mostramos que este observável é altamente sensível a condições iniciais, comparando vários resultados numéricos para diferentes condições iniciais, entre analíticas e numéricas. Propomos que o fluxo dirigido também é sensível à aceleração longitudinal e formulamos um modelo analítico baseado nesta hipótese. Este modelo sugere quais ingredientes são relevantes para o fluxo dirigido. Ele é confrontado com sucesso com cálculos numéricos, resultados experimentais e cálculos que não incluem a aceleração longitudinal. / In this thesis we study the directed flow, the first component in the Fourier\'s expansion of the azimuthal distribution of emitted particles. Unlike the elliptic flow, which is well studied and described in the literature, the physics that generates this observable is not yet well described. We show that this observable is highly sensible to the initial conditions, comparing several numeric results with different initial conditions, between analytic and numeric ones. We propose that the directed flow is also sensitive to the longitudinal acceleration and we formulate an analytic model based in this hypothesis. This model suggests which ingredients are relevant to the directed flow. It is confronted with success against numeric calculus, experimental results, and calculus that do not include the longitudinal acceleration.

Quarks charm são criados em estágios iniciais da colisão de íons pesados em processos de espalhamento duro. Portanto eles são sondas ideais para o Plasma de Quarks e Glúons (QGP), que é um estado da matéria em que os partons contidos em hadrons, em condições de alta temperatura (150 MeV) ou densidade (cerca de cinco vezes a densidade da matéria ordinária), passam para um estado livre de quarks e glúons. A fragmentação de quarks charm pode produzir mésons D. Jatos contendo um méson D como um de seus constituentes podem ser identificados como originados de uma fragmentação de quark pesado. Jatos contendo mésons D são valiosas ferramentas para caracterizar interações de quarks charm com o plasma. Jatos de charm podem fornecer informações para o estudo da perda de energia dependente da massa pela medida da modificação da produção de jatos de charm em colisões de núcleos de chumbo com respeito a colisões entre prótons em função do momento transversal dos jatos. Além disso, uma visão mais profunda pode ser obtida com a medida da distribuição da fração de momento, que é de particular interesse para investigar a possível influência do meio na fragmentação de quarks charm em jatos. Mésons D são reconstruídos através da análise de massa invariante de seu canal de decaimento hadrônico, rejeitando uma grande quantidade de fundo combinatório com seleções topológicas e explorando o tempo de vida relativamente longo de mésons D e as capacidades de identificação de partículas do detector ALICE. Jatos são reconstruídos com o algoritmo anti-kT usando candidatos a mésons D e partículas carregadas. A medida do espectro de momento transversal de jatos contendo mésons D em colisões de núcleos de chumbo a energias de sNN = 5.02 TeV será apresentada. Esses resultados levam a novas possibilidades de sondagem das propriedades do QGP quando comparados com medidas de referência. Por fim, os métodos desenvolvidos podem ser empregados no estudo das funções de fragmentação de quarks charm em colisões de íons pesados. / Charm quarks are created in the early stages of heavy-ion collisions in hard-scattering processes. Therefore, they are ideal probes of the Quark-Gluon Plasma (QGP), which is a state of matter where partons contained in hadrons, at high temperatures (150 MeV) or density (about five times the density of ordinary matter), change to a deconfined state of quarks and gluons. The fragmentation of charm quarks can produce D mesons. Jets containing a D meson as one of their constituents can be identified as originating from heavy-quark fragmentation. These jets are a valuable tool to characterize the charm interaction with the QGP. Charmed jets can provide information to the study the mass-dependent energy loss by the measurement of the modification of the charm-jet yield in Pb-Pb collisions with respect to pp collisions as a function of the jet transverse momentum. Moreover, a further insight can be obtained with the measurement of the momentum-fraction distribution, which is of particular interest to investigate the possible influence of the medium in the charm-jet fragmentation. D mesons are reconstructed through an invariant mass analysis of their hadronic decay channels, rejecting the large combinatorial background with topological selections exploiting the relatively large lifetime of D mesons and the particle identification capabilities of the ALICE detector. Jets are reconstructed with the anti-kT algorithm using D-meson candidates and charged tracks. The measurement of the transverse momentum spectrum of jets containing D mesons in Pb-Pb collisions at sNN = 5.02 TeV will be presented. These results lead to new possibilities of probing the QGP properties when compared to baseline measurements. Furthermore, the methods developed can be employed in the study of charm-quark fragmentation functions in heavy-ion collisions.

Le plasma de quarks et de gluons est un état de matière obtenu lors de températures et de densités d’énergie extrêmes où les quarks et les gluons sont libres. Cette matière chaude et dense peut être créée dans les collisions d’ions lourds ultra-relativistes. Les mesures des spectres des particules identifiées produites dans des jets représentent un outil majeur permettant d'étudier les propriétés du plasma créé dans les collisions et d'ainsi comprendre les relations entre divers mécanismes contribuant à la production de particules dans ce milieu. Cette thèse présente une analyse des spectres en impulsion transverse des baryons Λ et mésons K0S produits dans des jets chargés lors de collisions Pb–Pb centrales à l'énergie sqrt(sNN) = 2.76 TeV mesurées avec ALICE au LHC. Les résultats sont utilisés pour discuter l'origine de l'augmentation du rapport entre baryons et mésons observée pour la production inclusive des particules dans les collisions d’ions lourds ultra-relativistes. / Quark–gluon plasma is a state of matter existing under extreme energy densities and temperatures where quarks and gluons are deconfined. This hot and dense strongly interacting matter can be created in ultra-relativistic heavy-ion collisions. Measurements of spectra of identified particles produced in jets represent a major tool for studying properties of the plasma created in the collisions and for understanding the interplay of various mechanisms which contribute to the particle production in this medium. In this thesis, we present the measurement of the transverse-momentum spectra of Λ baryons and K0S mesons produced in charged jets in central Pb–Pb collisions at the centre-of-mass energy sqrt(sNN) = 2.76 TeV, measured with ALICE at the LHC. The results of the analysis are used to discuss the origin of the enhancement of the baryon-to-meson ratio observed for the inclusive production of light-flavour particles in ultra-relativistic heavy-ion collisions.

Les collisions d'ions lourds ultra-relativistes sont considérées comme un outil unique pour produire, enlaboratoire, un milieu chaud et dense interagissant fortement, le Plasma de Quarks etde Gluons (PQG). Cette thèse est dédiée à l’étude de deux sondes, les J/ψ et les bosons Z, qui peuvent aider àatteindre une meilleure compréhension des propriétés du PQG.Dans les collisions d’ions lourds, il existe une observable importante pour étudier la formation du PQG, c’est lamesure de la production des J/ψ. L’importance des différents effets qui peuvent augmenter ou supprimer cetteproduction varie avec l’énergie de la collision. Dans cette thèse, la production des J/ψ est mesurée avec lescollisions Pb-Pb à √sNN =5.02 TeV, en utilisant principalement le spectromètre à muons du détecteur ALICE. Lefacteur de modification nucléaire des J/ψ est présenté en fonction de la centralité des collisions, la rapidité etl’impulsion transversale (pT). En outre, les résultats sur le pT moyen du J/ψ sont présentés. La comparaison entreles résultats expérimentaux et divers calculs théoriques suggère que la production du J/ψ est affectée dans le milieupar deux processus concurrents : le dissociation et le régénération.Dans les collisions d’ions lourds, l'état initial de la collision peut aussi affecter les résultats, en l'absence deformation du PQG. La compréhension et la quantification des tels effets est crucial pour les séparer de ceuxprovoqués par la présence du PQG. Un de ces effets est la modification nucléaire des fonctions de distribution despartons (PDFs). La mesure de production du boson Z dans les collisions d’ions lourds est un outil puissant pourétudier la modification nucléaire des PDFs car il n’est pas affectés par la présence d'une matière en forteinteraction. La seconde partie de cette thèse est dévolue à la mesure de la production des bosons Z, pour lapremière fois dans ALICE, avec les collisions p-Pb et Pb-Pb à √sNN =5.02 TeV. Dans les collisions Pb-Pb où laprécision de la mesure est plus élevée, l'accord entre les données et des calculs théoriques est meilleur lorsque cesderniers prennent en compte la modification nucléaire des PDFs. / Ultra relativistic heavy-ion collisions are considered as a unique tool to produce, in the laboratory, thehot and dense strongly-interacting medium, the Quark-Gluon Plasma (QGP). This thesis is dedicated to the studyof two powerful probes, the J/ψ and Z-boson, that can help reaching a better understanding of the properties of theQGP.An important observable to study the QGP formation in heavy-ion collisions is the measurement of the J/ψproduction. The sizes of the different effects that can enhance or suppress this production vary with the collisionenergy. In this thesis, the J/ψ production is measured in Pb-Pb collisions at √sNN = 5.02 TeV using mainly themuon spectrometer of the ALICE detector. The J/ψ nuclear modification factor is presented as a function ofcollision centrality, rapidity and transverse momentum (pT). In addition, results on the J/ψ average pT and squaredaverage pT are also obtained. The comparison between the results and various theoretical calculations suggests thatthe J/ψ production is affected in the medium by an interplay between dissociation and regeneration mechanisms.In heavy-ion collisions, the initial state of the collision can affect the results even in the absence of the QGP.Understanding and quantifying such effects is crucial in order to separate them from the ones caused by thepresence of the QGP. One of these effects is the nuclear modification of the parton distribution functions (PDFs).The measurement of Z-boson production in heavy-ion collisions is a powerful tool to study the nuclearmodification of PDFs since it is not affected by the presence of the strongly-interacting medium. The second partof this thesis is devoted to measure the Z-boson production, for the first time with ALICE, in p-Pb and Pb-Pbcollisions at √sNN = 5.02 TeV. In Pb-Pb collisions where the precision of the measurement is higher, the agreementbetween data and theoretical calculations is better when the latter take into account the nuclear modification of thePDFs.

L’équation d’état de la matière nucléaire est un outil primordial dans la description des collisions entreions lourds, mais également dans la description de la formation d’objets ou de phénomènes astrophysiques(structure des étoiles à neutrons, fusion d’étoiles à neutron). Établir l’équation d’état de la matière nucléairerequiert de définir de manière précise les conditions thermodynamiques (densité, température, asymétrie pro-ton/neutron) dans lesquelles le systèmes évolue. Dans ce travail, nous abordons la problématique de l’étatd’équilibration maximal qui est atteint dans les collisions entre ions lourds, en terme d’énergie et d’isospin.Pour cela, nous utilisons la base de données expérimentale du multi-détecteur INDRA construite par lacollaboration au cours de ces 25 dernières années, en nous intéressant plus particulièrement aux collisionscentrales dans le domaine de l’énergie de Fermi, entre 10 et 100 MeV/nucléon. Nous présentons ainsi dansce document, comment à l’aide de simulation dédiées, il nous a été possible de relier le pouvoir d’arrêt de lamatière nucléaire à la section efficace de collision nucléon-nucléon dans la matière nucléaire. Nous apportonségalement des éléments de réponse au regard du transport de l’isospin dans les collisions centrales à l’aidedes rapports isobariques A = 3 construits à partir des tritons et des hélium-3. Ces différents résultats nouspermettent de mettre en avant le nouveau dispositif expérimental mis en place par les collaborations INDRAet FAZIA : le multi-détecteur FAZIA. Ce dernier est le résultat d’une période de recherche et développementde dix ans, ayant abouti à un multi-détecteur embarquant son électronique numérique sous vide, avec desperformances d’identification accrues (mesure de la charge Z et de la masse A jusqu’à Z = 25) par rapportaux multi-détecteurs des générations précédentes. / The nuclear matter equation of the state is an essential tool in the description of heavy ion collisions,but also in the description of the formation of astrophysical objects or phenomena (neutron star structure,neutron stars fusion). Establishing the nuclear matter equation of state requires a proper definition of thethermodynamic conditions (density, temperature, proton/neutron asymmetry) in which the system evolves.In this work, we address the issue of equilibration reached in heavy ion collisions, in terms of energy andisospin. To do this, we use the experimental database of the INDRA array built by the collaboration over thepast 25 years, focusing on central collisions in the Fermi energy domain, between 10 and 100 MeV/nucleon.In this document, we present how, with the help of dedicated simulations, it has been possible to link thestopping power of nuclear matter to the in-medium nucleon-nucleon cross-section. We also provide someanswers regarding isospin transport in central collisions using the isobaric ratios A = 3 based on the tritonsand helium-3 particles. These different results allow us to highlight the new experimental apparatus devel-loped by the INDRA and FAZIA collaborations : the FAZIA array. The latter is the result of a ten-yearperiod of research and development, resulting in an array embedded its digital electronic under vacuum, withincreased identification performance (measurement of the Z charge and A mass up to Z = 25) compared tothe previous generations arrays.

Title: Study of proton-proton and heavy-ion collisions with the ATLAS experi- ment at the LHC Author: Mgr. Petr Balek Department: Institute of Particle and Nuclear Physics Supervisor: Doc. RNDr. Jiří Dolejší, CSc. Abstract: The presented results show a suppression in a production of charged hadrons in heavy-ion collisions with respect to the production measured in proton- proton collisions. Lead-lead data at √ sNN = 2.76 TeV were recorded by the AT- LAS experiment at the LHC in 2010 and 2011 and they have a total integrated luminosity of 0.15 nb−1 , and proton-proton data at √ s = 2.76 TeV were recorded in 2011 and 2013 having an integrated luminosity of 4.2 nb−1 . The results are presented in wide transverse momentum (0.5 < pT < 150 GeV) and pseudorapid- ity (|η| < 2) ranges, and also in different centrality intervals of Pb+Pb collisions. Nuclear modification factor RAA shows a clear pT-dependence with a minimum at around 7 GeV, however above 60 GeV, it reaches a plateau with no significant pT-dependence. As a function of |η|, the RAA is flat over whole pT region. Keywords: ATLAS detector, heavy-ion collisions, charged-hadron spectra, nuclear modification factor RAA

In relativistischen Schwerionenkollisionen spielen seltsame Teilchen bei der Untersuchung heißer und dichter Materie eine wichtige Rolle. Dazu wird die Produktion von Hadronen mit Strangeness-Inhalt mit Hilfe eines Transportmodells vom Boltzmann-Ühling-Uhlenbeck (BUU)-Typ numerisch behandelt. Aktuelle Messungen der HADES-Kollaboration bezüglich K+- - und phi-Spektren bilden dabei den entsprechenden experimentellen Rahmen. Darüber hinaus wird das doppelt-seltsame Hyperon Xi- unterhalb der freien NN-Produktionsschwelle analysiert. Hadronische Multiplizitäten, Transversalimpuls- und Rapiditätsspektren werden mit neuen experimentellen Ergebnissen verglichen. Weiterhin werden Massenverschiebungen im Medium, die nukleare Zustandsgleichung sowie das mittlere Feld der Nukleonen berücksichtigt. Neben der Untersuchung von Kern-Kern-Stößen bietet sich in Proton-Kern-Kollisionen ein Vergleich mit jüngsten ANKE-Daten im Hinblick auf die phi-Ausbeute an. Mit Hilfe des BUU-Transportcodes wurden Tranzparenzverhältnisse ermittelt und die Absorption von phi-Mesonen untersucht. Dabei sind sekundäre phi-Produktionskanäle, Isospin-Asymmetrie und Detektorakzeptanzen von Bedeutung und werden systematisch für verschiedene Systemgrößen analysiert. Die impulsintegrierten Boltzmann-Gleichungen dienen im Rahmen einer kinetischen Nichtgleichgewichtsdynamik der Beschreibung hochkomprimierter nuklearer Materie auf hadronischem Niveau, wie sie sowohl beim Urknall als auch bei ultra-relativistischen Schwerionenkollisionen auftritt. Diese Theorie wird am Beispiel von Antiprotonen untersucht und unter Berücksichtigung verschiedener Expansionsmodelle numerisch ausgewertet. Dabei wird die Evolution der Proton- und Antiprotondichten bis zum Ausfrieren für SPS- und RHIC-Energien mittels eines hadro-chemischen Resonanzgasmodells als möglicher Lösungsansatz des "Antiproton-Puzzles" analysiert. Diskutiert wird darüber hinaus das Verhalten baryonischer Materie und Antimaterie im frühen Universum und der adiabatische Pfad kosmischer Materie im QCD-Phasendiagramm. / Strange particles play an important role as probes of relativistic heavy-ion collisions where hot and dense matter is studied. The focus of this thesis is on the production of strange particles within a transport model of Boltzmann-Ühling-Uhlenbeck (BUU) type. Current data of the HADES Collaboration concerning K+- and phi spectra provide the appropriate experimental framework. Moreover, the double-strange hyperon Xi- is analyzed below the free NN production threshold. Hadron multiplicities, transverse-momentum and rapidity spectra are compared with recent experimental data. Further important issues are in-medium mass shifts, the nuclear equation of state as well as the mean field of nucleons. Besides the study of AA collisions a comparison with recent ANKE data regarding the phi yield in pA collisions is done. Transparency ratios are determined and primarily investigated for absorption of phi mesons by means of the BUU transport code. Thereby, secondary phi production channels, isospin asymmetry and detector acceptance are important issues. A systematic analysis is presented for different system sizes. The momentum integrated Boltzmann equations describe dense nuclear matter on a hadronic level appearing in the Big Bang as well as in little bangs, in the context of kinetic off-equilibrium dynamics. This theory is applied to antiprotons and numerically calculated under consideration of various expansion models. Here, the evolution of proton- and antiproton densities till freeze-out is analyzed for ultra-relativistic heavy-ion collisions within a hadrochemic resonance gas model acting as a possible ansatz for solving the "antiproton puzzle". Furthermore, baryonic matter and antimatter is investigated in the early universe and the adiabatic path of cosmic matter is sketched in the QCD phase diagram.

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