A thermodynamic model of the quark-gluon plasma using quasiparticle degrees of freedom based on the hard thermal loop self-energies is introduced. It provides a connection between an established phenomenological quasiparticle model – following from the former using a series of approximations – and QCD – from which the former is derived using the Cornwall-Jackiw-Tomboulis formalism and a special parametrization of the running coupling. Both models allow for an extrapolation of first-principle QCD results available at small chemical potentials using Monte-Carlo methods on the lattice to large net baryon densities with remarkably similar results. They are used to construct equations of state for heavy-ion collider experiments at SPS and FAIR as well as quark and neutron star interiors. A mixed-phase construction allows for a connection of the SPS equation of state to the hadron resonance gas. An extension to the weak sector is presented as well as general stability and binding arguments for compact stellar objects are developed. From the extrapolation of the most recent lattice results [Baz09, Bor10b] the existence of bound pure quark stars is not suggested. However, quark matter might exist in a hybrid phase in cores of neutron stars.

No description available.

L'expérience ALICE, qui utilise les collisions d'ions lourds ultra-relativistes produites par le LHC au CERN, est dédiée à l'étude d'un nouvel état de la matière nucléaire, qui pourrait se présenter sous la forme d'un plasma de quarks et de gluons (QGP). Parmi les sondes portant des informations sur les propriétés de ce milieu, celles relatives à la production des jets de grande impulsion transverse sont particulièrement intéressantes. L'analyse présentée dans cette thèse s'intéresse aux évènements photon-jet, qui comportent un photon de grande impulsion transverse avec un jet émis dans la direction opposée. Ce dernier est issu de la fragmentation d'un parton, une fois qu'il a traversé le QGP. La thèse comprend une étude des observables pertinentes pour la mesure des corrélations photon-hadron ainsi qu'une analyse des premières données du LHC en collisions proton-proton. Des résultats préliminaires sur l'impulsion transverse des partons incidents et la fonction de corrélation ont ainsi été obtenus. / The ALICE experiment, which uses the ultra-relativistic heavy-ions collisions produced by the LHC at CERN, is dedicated to the study of a new state of nuclear matter, which could be composed of a Quark-Gluon Plasma (QGP). Among the probes sharing information on the medium properties, those relative to the production of high transverse momentum jets are very interesting. The analysis presented in this thesis is focused on photon-jet events, which contain one photon of high transverse momentum and one jet emitted in the opposite direction. The jet comes from the fragmentation of the initial parton, after passing through the medium. The thesis includes a simulation study of the relevant observables for the photon-hadron correlation measurement and an analysis of first data from LHC in proton-proton collisions. Preliminary results on the transverse momentum of incident partons and on the correlation function have been obtained.

Diese Arbeit untersucht im Rahmen der Gittereichtheorie verschiedene Aspekte der QCD in der Landau-Eichung, insbesondere solche, die mit den Gluon- und Geist-Propagatoren bei kleinen Impulsen zusammenhängen. Die Eichgruppe ist SU(3). Wir analysieren den Einfluss unterschiedlicher systematischer Effekte. Wir zeigen, dass der Formfaktor des Geist-Propagators bei kleinen Impulsen systematisch von der Wahl der Eichkopien (Gribov-Kopien) abhängt. Hingegen können wir einen solchen Einfluss auf den Gluon-Propagator nicht feststellen. Ebenfalls wird die Verteilung der kleinsten Eigenwerte des Faddeev-Popov-Operators durch die Wahl der Eichkopien beeinflusst. Wir zeigen außerdem, dass der Einfluss dynamischer Wilson-Fermionen auf den Geist-Propagator für die untersuchten Impulse vernachlässigbar ist. Für den Gluon-Propagator können wir jedoch einen deutlichen Einfluss für große und mittlere Impulse feststellen. Zusätzlich wurden beide Propagatoren auf asymmetrischen Gittern gemessen und mit den Daten von symmetrischen Gittern verglichen. Wir vergleichen unsere Ergebnisse mit denen aus Studien von Dyson-Schwinger-Gleichungen für den Gluon- und Geist-Propagator. Wir zeigen, dass das in dieser Arbeit gefundene Niedrigimpulsverhalten im Einklang mit verschiedenen Kriterien für Confinement (Einschluss von Farbladungen) ist. Wir berechnen die laufende Kopplung, die sich als eine renormierungsgruppeninvariante Kombination der Gluon- und Geist-Formfaktoren ergibt. Unsere Ergebnisse zeigen, dass im Bereich kleiner Impulse die laufende Kopplung kleiner wird und so vermutlich kein endlicher Infrarot-Fixpunkt im Grenzfall Impuls Null angestrebt wird. Wir präsentieren außerdem eine erste nichtstörungstheoretische Berechnung der Renormierungskonstante des SU(3) Ghost-Gluon-Vertex. Wir berichten über Untersuchungen zu spektralen Eigenschaften des Faddeev-Popov-Operators. Dazu haben wir eine Reihe der kleinsten Eigenwerte und Eigenvektoren dieses Operators berechnet. / Within the framework of lattice QCD we investigate different aspects of QCD in Landau gauge using Monte Carlo simulations. In particular, we focus on the low momentum behavior of gluon and ghost propagators. The gauge group is SU(3). Different systematic effects on the gluon and ghost propagators are studied. We demonstrate the ghost dressing function to systematically depend on the choice of Gribov copies at low momentum, while the influence on the gluon dressing function is not resolvable. Also the eigenvalue distribution of the Faddeev-Popov operator is sensitive to Gribov copies. We show that the influence of dynamical Wilson fermions on the ghost propagator is negligible at the momenta available to us. On the contrary, fermions affect the gluon propagator at large and intermediate momenta. In addition, we analyze data for both propagators obtained on asymmetric lattices and compare these results with data obtained on symmetric lattices. We compare our data with results from studies of Dyson-Schwinger equations for the gluon and ghost propagators. We demonstrate that the infrared behavior of both propagators, as found in this thesis, is consistent with different criteria for confinement. However, the running coupling constant, given as a renormalization-group-invariant combination of the gluon and ghost dressing functions, does not expose a finite infrared fixed point. Rather the data are in favor of an infrared vanishing coupling constant. We also report on a first nonperturbative computation of the SU(3) ghost-gluon-vertex renormalization constant. We present results of an investigation of the spectral properties of the Faddeev-Popov operator. For this we have calculated the low-lying eigenvalues and eigenmodes of the Faddeev-Popov operator.

La chromodynamique quantique (QCD), théorie actuellement utilisée pour décrire l’interaction forte, a prédit l’existence d’une transition de phase, à très haute température et/ou densité, vers un état de la matière nucléaire où les quarks et les gluons sont déconfinés : le Plasma de Quarks et de Gluons (QGP). Un tel milieu peut être produit en laboratoire, et la mesure de ses propriétés permet d’apporter un éclairage nouveau sur les mécanismes sur les mécanismes d’interactions entre les constituants ainsi que de tester la QCD dans des domaines inexplorés.Les collisions d’ions lourds ultra-relativistes délivrées par l’accélérateur LHC au CERN permettent d’obtenir les conditions thermodynamiques nécessaires à la formation du QGP. À l’aide d’une instrumentation diversifiée, l’expérience ALICE permet d’accéder à un grand nombre d’observables permettant de caractériser le QGP. Parmi celles-ci, la mesure de la fragmentation des partons (quarks et gluons) permet d’étudier en détail les mécanismes de perte d’énergie des partons dans le milieu et de sa redistribution dans l’état final, et peut également être comparée à des calculs théoriques modélisant, à partir de la QCD, l’interaction d’un parton énergétique avec le QGP qu’il traverse.Le travail de thèse présenté dans ce manuscrit s’articule autour de l’étude de la fonction de fragmentation par la mesure des corrélations photon-hadron en collisions proton-proton et proton-Plomb. Dans un premier temps, un travail de calibration en énergie du calorimètre électromagnétique de l’expérience ALICE a été réalisé, accompagné de la caractérisation des incertitudes de cette calibration. Dans un second temps, les corrélations photon-hadron, dont la difficulté majeure réside en l’identification des photons directs, ont été étudiées. Les résultats obtenus dans les deux systèmes de collisions démontrent la faisabilité de l’analyse qui pourra être étendue facilement aux collisions Plomb-Plomb périphériques. Enfin, ce travail montre que les incertitudes dominantes de la mesure seront réductibles avec les données prochainement délivrées par le LHC. / The quantum chromodynamics (QCD), the theory used at present to describe the strong interaction, predicts the existence of a phase transition, at very high temperature and/or density, towards a state of nuclear matter where quarks and gluons are deconfined : the Quark-Gluon Plasma (QGP). Such a medium can be produced in laboratory, and the measurement of its properties allows to give a new perspective on the mechanisms of interactions between the constituents as well as to test the QCD in unexplored domains.Ultra-relativistic heavy ion collisions delivered by the accelerator LHC at CERN allow to obtain the thermodynamical conditions necessary for the QGP to be formed. By means of a diversified instrumentation, the ALICE experiment allows to reach a large number of observables allowing to characterize the QGP. Among these, the measurement of the fragmentation of the partons (quarks and gluons) allows to study in detail the mechanisms of energy loss in the medium and its redistribution in the final state, and can also be compared with theoretical calculations, based on QCD, that model the interaction of an energetic parton with the QGP which is passing through.The work presented in this manuscript is articulated around the study of the fragmentation function via the measurement of the photon-hadron correlations in proton-proton and proton-Lead collisions. At first, a work on energy calibration of the ALICE experiment’s electromagnetic calorimeter was realized, along with the characterization of the uncertainties of this calibration. Secondly, the photon-hadron correlations, whose main difficulty is the identification of the direct photons, were studied. The results obtained in both systems of collisions demonstrate the feasibility of the analysis which can be easily widened to the peripheral Lead-Lead collisions. Finally, this work shows that the dominant uncertainties of the measurement will be reducible with the new data delivered by the LHC.

We investigate phase transitions in holographic models of QCD. In chapter I, we explore the effect of constant external U(1) fields on the physics of chiral symmetry breaking, as realized in the D3/D7 model. We discover that this model exhibits the phenomenon of magnetic catalysis, which is what one would expect from a weakly coupled field theory intuition. In chapter II, we continue exploring the effect of external U(1) fields but now on the backreacted D3/D7 model, where the backreaction is obtained via a smearing procedure. We again find the magnetic catalysis effect, however the results differ from the previous case depending on the backreaction parameters. In chapter III, we investigate lattices of instantons in the D4/D8 model of chiral symmetry breaking. These instanton lattices can change dimensionality, and in particular we investigate the 1D [right arrow] 2D transition as a simpler case of the more complicated 3D [right arrow] 4D transition which is conjectured to be holographically dual to the baryonic to quarkyonic phase transition. Besides this interpretation, one could also view this as a hypothetical condensed matter system. We have a lattice of instantons dominated by two-body forces, whose interactions depend not only on their mutual distance in physical space but also on their relative orientations in the internal isospace. We obtain a rich variety of instanton crystals whose description could serve to be useful beyond holography. / text

A altas energias o n\\\'ucleon (ou o n\\\'ucleo) pode ser visto como um sistema denso de gl\\\'uons, o condensado de vidro de cor. Neste trabalho estudamos a intera\\c\\~ao deste sistema com dipolos de cor. Esta intera\\c\\~ao \\\'e representada pela se\\c\\~ao de choque dipolo-alvo, a qual \\\'e modelada. Utilizamos alguns dos modelos propostos na literatura para descrever os dados do HERA e do RHIC e propusemos uma nova parametriza\\c\\~ao que \\\'e capaz de descrever estes dados simultaneamente, demonstrando a propriedade de universalidade do condensado de vidro de cor. Generalizamos o modelo proposto por Iancu, Itakura e Munier para o caso nuclear e o aplicamos ao estudo de espalhamento el\\\'etron-n\\\'ucleo. Estimamos a influ\\^encia dos efeitos de satura\\c\\~ao nos observ\\\'aveis que ser\\~ao medidos no futuro eRHIC. Conclu\\\'imos entre outras coisas, que uma grande fra\\c\\~ao dos eventos observados ser\\~ao do tipo difrativo. Finalmente usamos a id\\\'eia de dipolo de cor para estudar a se\\c\\~ao de choque charmonium-h\\\'adron. / At high energies a nucleus (and even a nucleon) becomes a dense gluonic system called the color glass condensate. In this work we study the interaction of this dense system with color dipoles. This interaction is represented by the dipole-target cross section, which has to be modeled. We have used, without success, some of the existing models to try to reproduce the data obtained at HERA and RHIC. It was not possible to obtain a global agreement between the models and the two sets of data. We have then proposed a different parametrization of the dipole cross section, which is now compatible with all the available data. In the case of deep inelastic scattering, we have extended the Iancu-Itakura-Munier model to nuclear targets and made predictions for observables to be measured in the future electron-ion collider eRHIC. Among other things, we have concluded that a large fraction of the events will be of the diffractive type. Finally, we have used the color dipole approach to build a simple model for the charmonium-hadron interaction at high energies.

O principal objetivo deste trabalho foi obter a produção das partículas estranhas K0, e em colisões entre íons pesados relativísticos para ÖsNN = 62.4 GeV, bem como estudar o comportamento sistemático dessa produção em função da energia. Para isso, utilizamos os dados provenientes da colisão de íons pesados relativísticos obtidos pelo experimento STAR do RHIC. O objetivo deste trabalho também foi o de estudar dois estágios específicos da evolução do fireball formado nessas colisões: os chamados freeze-out químico e térmico. Estes estágios (ou fases) foram estudadas a partir das razões entre diversas partículas e da distribuição de momento transversal das mesmas, comparando os resultados com previsões e ajustes de modelos térmicos, a fim de avaliar possíveis efeitos da formação de um Plasma de Quarks e Gluons (QGP) em equilíbrio térmico sobre os hádrons medidos pelo experimento. O freeze-out químico foi estudado a partir das razões entre abundâncias de partículas produzidas na colisão, que foram comparadas a ajustes de um modelo térmico que trata o fireball como um gás de hádrons em equilíbrio (THERMUS) e aos resultados de um modelo que não assume esse equilíbrio (SHM). Com essa abordagem, verificamos que o modelo THERMUS ajusta bem os dados experimentais para uma ampla faixa de energias de colisão, principalmente para 62.4 GeV. Os parâmetros termodinâmicos obtidos foram estudados em função da energia para verificarmos se há um comportamento suave do sistema ou mudanças abruptas. O estudo indicou que esse comportamento é suave com a energia. Ainda neste estudo do freeze-out químico, comparamos os resultados do modelo THERMUS com os resultados do modelo que considera o não ? equilíbrio químico, o SHM. Nesta comparação, a razão apresentou um comportamento interessante, sugerindo que a energias mais baixas o sistema se comporta conforme a prescrição do modelo SHM, enquanto que o modelo que considera o fireball como um gás de hádrons em equilíbrio, novamente, demonstrou melhor compatibilidade a energias mais altas, reafirmando aqui a indicação de uma possível formação de um sistema termalizado. O freeze-out cinético/térmico foi estudado com os espectros de momento transversal, considerando um modelo fenomenológico inspirado na hidrodinâmica. Os resultados mostram que eventos mais centrais apresentam uma velocidade de expansão maior e uma temperatura menor, condizente com uma fonte que tem um gradiente de pressão maior. Também foi observado que a partícula ? apresenta sempre uma temperatura maior que as outras partículas (p, ?, ?) indicando um desacoplamento anterior dessas partículas em relação às outras. Finalmente, estudamos a utilização do SVT para a reconstrução de V0s, procurando compreender a maneira correta de se utilizar este detector na análise. Os resultados mostram que a utilização desse detector pode levar a uma melhora na eficiência e na pureza durante a reconstrução dessas partículas. / The main goal of this work was to measure the production of the singly strange particles, such as K0, and in Au+Au collisions at ?sNN = 62.4 GeV, inserting these results in a systematic energy scan study. The data were obtained from the STAR detector, one of the RHIC experiments. In addition, we have used the particle production in these collision to study two specific stages of the fireball evolution: the chemical and kinetic freeze-outs. These two stages were studied comparing the ratio between different particles (strange or not) and also the transverse momentum distribution with thermal models fits in order to check possible effects of equilibrated Quark Gluon Plasma (QGP) in the hadron production. The chemical freeze-out was studied comparing the ratios between particles produced in the collision with two different thermal models: one which assumes a equilibrated hadron gas (THERMUS) and another one which assumes a possible non-equilibrated system (SHM). The experimental data were well described by the THERMUS model fit in a great range of energy collisions, mainly at 62.4 GeV. The thermodynamic parameters had been studied as function of the energy in order to verify if it has a smooth or abrupt behavior. The result indicated that this behavior is very smooth with energy. We also compared these results with SHM\'s predictions and, in this comparison, the ratio presented an interesting behavior, suggesting that at low energies the fireball consists of a non-equilibrated system, such as described by SHM model, whereas the model that considers the fireball as a equilibrated hadron gas. The kinetic freeze-out was studied with the transverse momentum spectra using a hydrodynamics inspired model. The results indicate that for the most central events there is a higher expanding velocity and a lower freeze-out temperature. It was also observed that for the particle, the freeze-out temperature is higher than the one for other particles (?, K, p) indicating an earlier decoupling of these particles from the fireball. Finally, we have studied the inclusion for the SVT in the V0 reconstruction analysis, trying to optimize this detector usage in the analysis. The results show that the inclusion of this detector in the analysis can improve the efficiency and purity of the V0 reconstruction in the STAR experiment.

The aim of relativistic heavy-ion collisions is to investigate the properties of the Quark-Gluon Plasma (QGP) phase, that is achieved at high-enough temperatures and/or densities. In this context, light on heavy-ion collisions (e. g. p-Pb) are used to assess Cold Nuclear Matter effects (CNM), while elementary hadronic collisions (e. g. proton-proton) provide tests for QCD (Quantum Chromodynamics) based calculations and baseline for studies with heavy- ions. Heavy quarks, i. e. charm and beauty, are very convenient in the characterization of the QGP. They are produced via initial hard parton-parton scatterings at the early stages of the collision and, therefore, they are a self-generated probe for the system created in the reaction. In this work the angular correlation between electrons from heavy-flavour hadron decays and charged particles was studied in pp (2.76 and 7 TeV) and p-Pb (5.02 TeV) collisions at the CERN Large Hadron Collider, using the ALICE detector. The correlation strengths were evaluated as a function of multiplicity in p-Pb collisions. In pp collisions the relative beauty (and charm) contribution to the total heavy-flavour decay electron yield was estimated using the measured correlation distribution and Monte Carlo templates. / O próposito de colisões entre íons pesados relativísticos é investigar as propriedades do plasma de quarks e gluons (QGP, do inglês Quark-Gluon Plasma). A transição de fase, de um estado hadrônico para o QGP, ocorre em regimes onde a temperatura e/ou densidade atingem um valor suficientemente alto. Neste contexto, colisões entre íons pesados e leves (por exemplo, p-Pb) permitem acessar efeitos devido à matéria nuclear fria (CNM, do inglês Cold Nuclear Matter) e colisões elementares (por exemplo, próton-próton) são usadas como referência para estudos com íons pesados, além de proporcionarem testes para cálculos de QCD perturbativa. Quarks pesados, isto é charm e bottom, são ferramentes muito convenientes no estudo e caracterização do QGP. Essas partículas são produzidas através de espalhamento duro nos instantes iniciais da colisão e, portanto, elas atuam como uma sonda externa para o sistema criado na reação. Esse trabalho consiste no estudo da correlação angular entre elétrons oriundos de quarks pesados e partículas carregadas, em colisões pp (2.76 e 7 TeV) e p-Pb (5.02 TeV), no acelerador LHC (do inglês Large Hadron Collider) do CERN, usando o detector ALICE (do inglês A Large Ion Collider Experiment). A distribuição angular mencionada foi medida em função da multiplicidade do evento, no caso de colisões p-Pb. Em colisões pp, a contribuição relativa de quarks charm e bottom para o total de elétrons provenientes de quarks pesados foi estimada usando a função de correlação obtida.

Neste trabalho são reportadas medidas realizadas no detector PHENIX do RHIC sobre J/Psi em colisões p+p e Au+Au a s^(1/2) = 200 GeV na região de rapidez central e Psi\' em colisões p+p nas mesmas condições. As medidas incluem a dependência com o momento transverso da produção de charmônio e o fator de modificação nuclear de J/Psis para vários regimes de centralidade de colisão. / This work reports measurements done by the PHENIX detector at RHIC about J/Psi in p+p and Au+Au collisions at s^(1/2) = 200 GeV in the mid-rapidity range and Psi\' in p+p collisions in the same conditions. The measurements include the transverse momentum dependence of charmonium production and J/Psi nuclear modification factor in different centrality regimes.