Academic literature on the topic 'Quark-Gluon Plasma, transport theory, heavy quarks'

The validity of conventional Ohm’s law is tested in the context of a rapidly evolving quark–gluon plasma produced in heavy-ion collisions. Here, we discuss the electromagnetic response using an analytical solution in kinetic theory. As conjectured previously, after switching on an electric field in a nonexpanding plasma, the time-dependent current is given by J(t)=(1−e−t/τ0)σ0E, where τ0 is the transport relaxation time and σ0 is the steady-state electrical conductivity. Such an incomplete electromagnetic response reduces the efficiency of the magnetic flux trapping in the quark–gluon plasma, and may prevent the observation of the chiral magnetic effect. Here, we extend the study to the case of a rapidly expanding plasma. We find that the decreasing temperature and the increasing transport relaxation time have opposite effects on the electromagnetic response. While the former suppresses the time-dependent conductivity, the latter enhances it.

In this article, there are 18 sections discussing various current topics in the field of relativistic heavy-ion collisions and related phenomena, which will serve as a snapshot of the current state of the art. Section 1 reviews experimental results of some recent light-flavored particle production data from ALICE collaboration. Other sections are mostly theoretical in nature. Very strong but transient magnetic field created in relativistic heavy-ion collisions could have important observational consequences. This has generated a lot of theoretical activity in the last decade. Sections 2, 7, 9, 10 and 11 deal with the effects of the magnetic field on the properties of the QCD matter. More specifically, Sec. 2 discusses mass of [Formula: see text] in the linear sigma model coupled to quarks at zero temperature. In Sec. 7, one-loop calculation of the anisotropic pressure are discussed in the presence of strong magnetic field. In Sec. 9, chiral transition and chiral susceptibility in the NJL model is discussed for a chirally imbalanced plasma in the presence of magnetic field using a Wigner function approach. Sections 10 discusses electrical conductivity and Hall conductivity of hot and dense hadron gas within Boltzmann approach and Sec. 11 deals with electrical resistivity of quark matter in presence of magnetic field. There are several unanswered questions about the QCD phase diagram. Sections 3, 11 and 18 discuss various aspects of the QCD phase diagram and phase transitions. Recent years have witnessed interesting developments in foundational aspects of hydrodynamics and their application to heavy-ion collisions. Sections 12 and 15–17 of this article probe some aspects of this exciting field. In Sec. 12, analytical solutions of viscous Landau hydrodynamics in 1+1D are discussed. Section 15 deals with derivation of hydrodynamics from effective covariant kinetic theory. Sections 16 and 17 discuss hydrodynamics with spin and analytical hydrodynamic attractors, respectively. Transport coefficients together with their temperature- and density-dependence are essential inputs in hydrodynamical calculations. Sections 5, 8 and 14 deal with calculation/estimation of various transport coefficients (shear and bulk viscosity, thermal conductivity, relaxation times, etc.) of quark matter and hadronic matter. Sections 4, 6 and 13 deal with interesting new developments in the field. Section 4 discusses color dipole gluon distribution function at small transverse momentum in the form of a series of Bells polynomials. Section 6 discusses the properties of Higgs boson in the quark–gluon plasma using Higgs–quark interaction and calculate the Higgs decays into quark and anti-quark, which shows a dominant on-shell contribution in the bottom-quark channel. Section 13 discusses modification of coalescence model to incorporate viscous corrections and application of this model to study hadron production from a dissipative quark–gluon plasma.

The quark–gluon plasma (QGP) produced by collisions between ultrarelativistic heavy nuclei is well described in the language of hydrodynamics. Noncentral collisions are characterized by very large angular momentum, which in a fluid system manifests as flow vorticity. This rotational structure can lead to a spin polarization of the hadrons that eventually emerge from the plasma, and thus these collisions provide experimental access to flow substructure at unprecedented detail. Recently, the first observations of Λ hyperon polarization along the direction of collisional angular momentum were reported. These measurements are in broad agreement with hydrodynamic and transport-based calculations and reveal that the QGP is the most vortical fluid ever observed. However, there remain important tensions between theory and observation that might be fundamental in nature. In the relatively mature field of heavy-ion physics, the discovery of global hyperon polarization and 3D simulations of the collision have opened an entirely new direction of research. We discuss the current status of this rapidly developing area and directions for future research.

Relativistic magnetohydrodynamics (RMHD) provides an extremely useful description of the low-energy long-wavelength phenomena in a variety of physical systems from quark–gluon plasma in heavy-ion collisions to matters in supernova, compact stars, and early universe. We review the recent theoretical progresses of RMHD, such as a formulation of RMHD from the perspective of magnetic flux conservation using the entropy–current analysis, the nonequilibrium statistical operator approach applied to quantum electrodynamics, and the relativistic kinetic theory. We discuss how the transport coefficients in RMHD are computed in kinetic theory and perturbative quantum field theories. We also explore the collective modes and instabilities in RMHD with a special emphasis on the role of chirality in a parity-odd plasma. We also give some future prospects of RMHD, including the interaction with spin hydrodynamics and the new kinetic framework with magnetic flux conservation.

We apply the momentum integrated Boltzmann transport equation to study the time evolution of various quark flavors in the central region of ultrarelativistic heavy ion collisions. The effects of thermal masses for quarks and gluons are incorporated to take into account the in-medium properties of these ingredients of the putative quark gluon plasma. We find that even under very optimistic conditions, complete chemical equilibration in the quark gluon plasma appears unlikely.

Heavy quark transport coefficients in a strongly coupled Quark–Gluon Plasma can be evaluated using a gauge/string duality and lattice QCD. Via this duality, one can argue that for low momenta the drag coefficient for heavy quarks is proportional to the spatial string tension. Such a tension is well-studied on the lattice that allows one to straightforwardly make non-perturbative estimates of the heavy quark diffusion coefficients near the critical point. The obtained results are consistent with those in the literature.

J/ψ production is closely related to the production of the strongly interacting Quark-Gluon Plasma (sQGP) in relativistic heavy ion collisions. To study the effects of charm quark dynamics on J/ψ production, the phase space distributions of charm and anti-charm quarks are generated using A Multi-Phase Transport (AMPT) model. These charm quarks then coalesce into J/ψ particles. The production and flow of J/ψ show strong sensitivity to final state charm interactions. The results are compared to charm quark and D meson results from the AMPT model and recent predictions from other models.

We describe the propagation of Heavy quarks (HQs) in the quark-gluon plasma (QGP) within a relativistic Boltzmann transport (RBT) approach. The interaction between heavy quarks and light quarks is described within quasi-particle approach which is able to catch the main features of non-perturbative interaction as the increasing of the interaction in the region of low temperature near TC. In our calculations the hadronization of charm quarks in D mesons is described by mean of an hybrid model of coalescence plus fragmentation. We show that the coalescence play a key role to get a good description of the experimental data for the nuclear suppression factor RAA and the elliptic flow υ2(pT) at both RHIC and LHC energies. Moreover, we show some recent results on the direct flow υ1 and triangular flow υ3 of D meson.

Relativistic heavy ion collisions create a strongly coupled quark–gluon plasma. Some of the plasma's properties can be approximately understood in terms of a dual black hole. These properties include shear viscosity, thermalization time, and drag force on heavy quarks. They are hard to calculate from first principles in QCD. Extracting predictions about quark–gluon plasmas from dual black holes mostly involves solving Einstein's equations and classical string equations of motion. AdS/CFT provides a translation from gravitational calculations to gauge theory predictions. The gauge theory to which the predictions apply is [Formula: see text] super-Yang–Mills theory. QCD is different in many respects from super-Yang–Mills, but it seems that its high temperature properties are similar enough for us to make some meaningful comparisons.

The ultrarelativistic heavy-ion programs at the Relativistic Heavy Ion Collider and the Large Hadron Collider have entered an era of quantitative analysis of quantum chromodynamics (QCD) at high temperatures. The remarkable discovery of the strongly coupled quark–gluon plasma (sQGP), as deduced from its hydrodynamic behavior at long wavelengths, calls for probes that can reveal its inner workings. Charm- and bottom-hadron spectra offer unique insights into the transport properties and the microscopic structure of the QCD medium created in these collisions. At low momentum the Brownian motion of heavy quarks in the sQGP gives access to their diffusion constant, at intermediate momentum these quarks give insight into hadronization mechanisms, and at high momentum they are expected to merge into a radiative-energy loss regime. We review recent experimental and theoretical achievements on measuring a variety of heavy-flavor observables, characterizing the different regimes in momentum and extracting pertinent transport coefficients to unravel the structure of the sQGP and its hadronization.

Quantum Chromodynamics (QCD) is the non-abelian gauge field theory that within the Standard Model describes the strong interaction between quarks and gluons. QCD exhibits two main properties:confinement and asymptotic freedom. The former implies that in ordinary matter quarks and gluons are bounded within colorless hadrons. The latter is related to the decrease of the QCD strength coupling with increasing characteristic energy of the process. Asymptotic freedom implies that under extreme conditions of high temperature and density the interaction affecting quarks and gluons is so weakly that they are released from the bounding state to form a deconfined phase of matter known as the Quark-Gluon Plasma (QGP). Numerical solutions of QCD equations on lattice (lQCD) predict that such transition is properly a crossover at almost zero baryon density and with a critical temperature Tc=155 MeV. The study of nuclear matter under extreme conditions is the main program of the experiments at the Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) where ultrarelativistic Heavy-Ion Collisions (HICs) are conducted to create an almost baryon free QGP with initial T = 3Tc. In this scenario Heavy Quarks (HQs), mainly charm and bottom, play a unique role. Due to their large masses HQs are created at the initial stage of HICs by hard perturbative QCD scattering processes. Moreover, their thermalization time is comparable with the QGP lifetime. Hence HQs can probe the entire evolution of the fireball carrying more information about their initial properties. The most important observables in the HQ sector are the nuclear modification factor RAA and the elliptic flow v2. The challenge of each theoretical framework is to provide a simultaneous description of these two observables that have been measured both at RHIC and LHC energies. In this thesis we study the HQ dynamics within the QGP by means of a relativistic Boltzmann transport approach. In this framework we treat non-perturbative QCD effects by prescription of a Quasi-Particle Model (QPM) in which light quarks and gluons of the bulk are dressed with effective masses and the T dependence of the strength coupling is fitted to lQCD thermodynamics. In the first part of this thesis we discuss HQ transport coefficients by performing simulations in static QCD medium. We compare our extracted drag and diffusion coefficients with results obtained through a Montecarlo integration. Afterwards, we investigate charm suppression and compare the results among various theoretical models. In the second part, we focus on the dynamical evolution of HQs within the QGP by carrying out simulations of realistic HICs. We observe that within our QPM interaction, which implies a T-dependent drag coefficient almost constant near Tc, we are able to describe simultaneously the RAA and v2 of D mesons both at RHIC and LHC energies. In order to compare with the experimental measurements we couple the final HQ spectra to a hybrid coalescence plus fragmentation hadronization model which is suitable to describe the large magnitude of the observed charmed baryon-to-meson ratio. In the same framework, we provide our predictions for B meson RAA and v2 and compare our results with the available experimental data. A goal of this work is to include the effect of enhanced baryon production in HICs on the nuclear modification factor. Finally, we present our estimate of the HQ spatial diffusion coefficient Ds(T) within our Boltzmann approach. We show that our phenomenological predictions of Ds for charm quark are in agreement with lQCD expectations, meaning that through the study of HQ thermalization we can probe the QCD interaction within the present uncertainties of lQCD. We point out also that the possibility to calculate transport coefficients at the bottom mass scale allows to reduce uncertainties coming from the adopted transport model and to bring the estimate of Ds closer to the quenched lQCD.

The phase diagram of QCD is actually under exploration both theoretically and experimentally searching for the phase transition from ordinary matter to a deconfined phase of quarks and gluons, namely the Quark-Gluon Plasma. Being a very complex theory, such a task is very difficult however there are several indications that the phase transition occurs as indicated by Lattice QCD calculations, in the low baryon density region, at a critical temperature of Tc 155 MeV. The only way to access the QGP in a laboratory is to collide heavy ion collision at ultra-relativistic (uRHIC) energies as actually carry out at LHC at CERN and at RHIC at BNL. One of the most amazing discovery was that the system created in these collisions behaves like a perfect fluid. Indeed hydrodynamics calculations show that the large anisotropic flows measured are in agreement with a shear viscosity to entropy density ration eta/s close to the minimum value predicted by AdS/CFT eta/s = 1/4pi. In this thesis we discuss about two main subjects of QGP produced in uRHIC: transport coefficients, in particular shear viscosity and electric conductivity, and a modeling of initial fields and their early time dynamics of the system produced in uRHIC. Our challenge is to develop a very precise transport based approach with a fixed value of eta/s, being the physical quantity that describes a fluid in strong coupling. We compute the shear viscosity solving the Relativistic Boltzmann Transport (RBT) equation and using the Green-Kubo relation that, being not affected by any kind of approximation, gives us the possibility to find the correct formula among the analytical derivations in Relaxation Time Approximation and in Chapman-Enskog scheme. Using our numerical solution to the RTB equation we also compute the electric conductivity sigma-el of the QGP. This transport coefficient represents the response of the system to an applied external electric field and only very recently has captured the attention in the field of QGP due to the strong electric and magnetic fields present in the early stage of the collision. Our focus was to characterize the relation between the sigmael and the relaxation time tau . Moreover we study the relationship between eta and sigmael investigating the ratio between eta/s and sigma-el/T, taking into account the QCD thermodynamics, and predicting that the ratio supplies a measure of the quark to gluon scattering rates. Once we have developed a transport based approach describing a fluid with a given eta/s, our interest moved into describing, using a single consistent approach, the fireball created in uRHIC starting from the initial time. We modeled the early time dynamics considering only a color electric field which decays to pair particles thanks to the Schwinger mechanism. Our studies focused on the isotropization and thermalization of the system in the early stage in order to quantify the isotropization time, which is assumed to be tau-iso = 0.6 ÷ 0.8 f m/c in hydrodynamics calculations. We investigate in a sistematic way different systems: the static box, the longitudinal expanding system and the 3+1D expanding case. We compute the ratio PL/PT , with PL (PT ) the longitudinal (transverse) pressure, finding that for the relevant cases of 1+1D and 3+1D the system reaches PL/PT about 1, which characterizes the isotropization of the system, in about 1fm/c for eta/s = 1/4pi while for higher value of shear viscosity the ratio PL/PT is quite smaller than 1, meaning that the system does not isotropize. Moreover we study also the effects of eta/s on the elliptic flow v2. The first studies show that the final v2 developed by the system is not significantly affected by the strong early non-equilibrium dynamics. Hence, such a result provides a justification of the assumptions exploited in hydrodynamical approach.

The fundamental theory of strong interactions is the so called Quantum Chromo Dynamics (QCD) that is a quantum field theory with an extremely rich dynamical content. The main features of this theory are the asymptotic freedom and confinement. The study of QCD, under extreme conditions of temperature and density has been one of the most difficult problem in physics during the last decades, capturing increasing experimental and theoretical attention also in connection with its relation to the Early Universe physics.\\ In this work of thesis it is extensively discussed the effect of the primordial QCD phase transition during the first part of the evolution of our Universe: the Big Bang nucleosynthesis.\\ On the other hand, the Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) programs have been used to probe the properties of nuclear matter under such extreme condition. In the light of the experimental results accumulated in these years in these ultra relativistic heavy ion collisions, the main purpose of this thesis is to study the dynamical evolution of the Quark Gluon Plasma (QGP) in the framework of kinetic theory.\\ In particular, recent experimental data show that the momentum anisotropy of the emitted particles is an observable that encodes information about the transport properties of the matter created in these HIC and also that it is an observable sensitive to the shear viscosity to entropy density ratio $\eta/s$. Hence, in this work we have investigated within an event-by-event transport approach at fixed viscosity this elliptic flow $v_{2}$ and high order harmonics $v_{n}$.\\ The principal results presented in this thesis concern the different sensitivity to the $\eta/s(T)$ at different energies (RHIC and LHC) for both ultra-central and mid-peripheral collisions, especially in the cross over region of the transition. Moreover we highlighted the effect of the inclusion in our simulation code of a realistic kinetic freeze out. Finally, we discussed the correlation between the initial spatial anisotropies $\epsilon_{n}$ and flow coefficients $v_{n}$.

The fundamental theory of strong interactions is the so called Quantum Chromo Dynamics (QCD) that is a quantum field theory with an extremely rich dynamical content. The main features of this theory are the asymptotic freedom and confinement. The study of QCD, under extreme conditions of temperature and density has been one of the most difficult problem in physics during the last decades, capturing increasing experimental and theoretical attention also in connection with its relation to the Early Universe physics.\\ In this work of thesis it is extensively discussed the effect of the primordial QCD phase transition during the first part of the evolution of our Universe: the Big Bang nucleosynthesis.\\ On the other hand, the Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) programs have been used to probe the properties of nuclear matter under such extreme condition. In the light of the experimental results accumulated in these years in these ultra relativistic heavy ion collisions, the main purpose of this thesis is to study the dynamical evolution of the Quark Gluon Plasma (QGP) in the framework of kinetic theory.\\ In particular, recent experimental data show that the momentum anisotropy of the emitted particles is an observable that encodes information about the transport properties of the matter created in these HIC and also that it is an observable sensitive to the shear viscosity to entropy density ratio $\eta/s$. Hence, in this work we have investigated within an event-by-event transport approach at fixed viscosity this elliptic flow $v_{2}$ and high order harmonics $v_{n}$.\\ The principal results presented in this thesis concern the different sensitivity to the $\eta/s(T)$ at different energies (RHIC and LHC) for both ultra-central and mid-peripheral collisions, especially in the cross over region of the transition. Moreover we highlighted the effect of the inclusion in our simulation code of a realistic kinetic freeze out. Finally, we discussed the correlation between the initial spatial anisotropies $\epsilon_{n}$ and flow coefficients $v_{n}$.

Les collisions d'ions lourds ultra-relativistes ont pour objectif l'étude d'un état de matière en interaction forte dans des conditions extrêmes de densité d'énergie et température, le plasma de quarks et gluons (QGP). Les saveurs lourdes (charme et beauté) sont produites principalement lors de processus durs aux premiers instants de la collision et participent aux différentes étapes de la collision. Par conséquent, la mesure des saveurs lourdes ouvertes devrait permettre d'extraire des informations importantes concernant le système créé aux premiers instants de la collision. L'étude des collisions proton-proton (pp) fournit la référence indispensable pour la mesure des saveurs lourdes dans les systèmes lourds. Cette thèse est dédiée à l'étude de la production des muons de décroissance des hadrons charmés et beaux aux rapidités avant (2.5 < y < 4) dans les collisions pp sqrt (s) = 5.02 TeV, Pb-Pb à sqrt (sNN) = 2.76 et 5.02 TeV et Xe-Xe à sqrt (sNN) = 5.44 TeV enregistrées avec le détecteur ALICE au CERN-LHC. La mesure des sections efficaces différentielles de production des muons de décroissance des hadrons charmés et beaux dans les collisions pp à sqrt (s) = 5.02 TeV couvre un grand domaine en impulsion transverse de 2 à 20 GeV/c et ont une meilleure précision par rapport aux résultats publiés à sqrt (s) = 2.76 et 7 TeV. Les résultats sont en bon accord avec les calculs perturbatifs de QCD. Une importante suppression de la production des muons de décroissance des hadrons charmés et beaux est observée dans les collisions centrales (0-10%) Pb-Pb à sqrt (sNN) = 2.76 et 5.02 TeV. Cette suppression est attribuée au milieu dense et chaud formé dans ces collisions. L'influence de la taille du système est étudiée avec le système Xe-Xe à sqrt (sNN) = 5.44 TeV. La suppression est similaire à celle mesurée dans les collisions Pb-Pb. Les résultats obtenus dans les collisions Pb-Pb et Xe-Xe apportent des contraintes fortes aux paramètres des modèles
The study of ultra-relativistic heavy-ion collisions aims at investigating a state of strongly-interacting matter at high energy density and temperature, the Quark-Gluon Plasma (QGP). Heavy quarks (charm and beauty) are predominantly produced in initial hard scattering processes during the early stage of the collisions and experience the full evolution of the medium. Therefore, the measurement of open heavy flavours should provide essential information on the QGP properties. Similar measurements in small systems are also essential for a comprehensible understanding of the QGP properties. The study of open heavy flavours in proton-proton (pp) collisions provides the mandatory reference for measurements in heavy-ion collisions. This thesis presents measurements of the production of muons from heavy-flavour hadron decays at forward rapidity (2.5 < y < 4) in pp collisions at sqrt (s) = 5.02 TeV, Pb-Pb collisions at sqrt (sNN) = 2.76 and 5.02 TeV and Xe-Xe collisions at sqrt (sNN) = 5.44 TeV collected with the ALICE detector at the CERN-LHC. The differential production cross sections of muons from heavy-flavour hadron decays in pp collisions at sqrt (s) = 5.02 TeV are obtained in a wide transverse momentum interval, 2 < pT < 20 GeV/c, and with an improved precision compared to the previously published measurements at sqrt (s) = 2.76 and 7 TeV. The measurements are described within uncertainties by predictions based on perturbative QCD. A strong suppression of the yield of muons from heavy-flavour decays is observed in the 10% most central Pb-Pb collisions at both sqrt (sNN) = 2.76 and 5.02 TeV. This suppression is due to final-state effects induced by the hot and dense medium. The suppression in Xe-Xe collisions is similar to that observed with Pb-Pb collisions. The comparison in the two colliding systems provides insight in the path-length dependence of medium-induced parton energy loss. The results constrain model calculations

Les calculs de chromodynamique quantique sur réseau prévoient, que pour un potentiel baryonique nul et une température de T ∼ 173 MeV , il devrait être possible d'observer une transition de la phase de la matière hadronique vers un plasma de quarks et de gluons. Les collisions d'ions lourds ultra-relativistes devraient permettre de mettre en évidence ce changement de phase. Les saveurs lourdes peuvent être utilisées pour sonder les premiers instants des collisions pendant lesquels la température est la plus élevée. Le LHC va permettre d'étudier les collisions entre noyaux de plomb et les collisions entre protons à une énergie jamais égalée : √s = 5.5 TeV (√sNN = 14 TeV ) pour le plomb (les protons). Le détecteur ALICE est dédié à l'étude des collisions d'ions lourds mais peut également mesurer les collisions entre protons. Il est équipé d'un spectromètre à muons conçu pour l'étude des saveurs lourdes. Cette thèse présente les performances du spectromètre pour la mesure de la section efficace de production inclusive des hadrons beaux (B) et charmés (D) dans les collisions proton-proton. La première étape de cette mesure consiste à extraire les distributions des muons de décroissance des hadrons B et D. L'étape suivante consiste à extrapoler les distributions aux sections efficaces de production inclusive des hadrons. Cette thèse contient également une étude préliminaire des performances du spectromètre pour la mesure du rapport de modification nucléaire et de l'observable associée nommée RB=D dans les collisions plomb-plomb de centralité0−10%. L'accent est porté sur les incertitudes et l'intervalle en impulsion transverse sur lequel ces observables pourront être mesurées.

Relativistic hydrodynamics and kinetic theory play an increasing role in many areas of modern physics. Besides their traditional arenas, astrophysics and cosmology, relativistic fluids have recently attracted much attention also within the realm of high-energy and condensed matter physics, mostly in connection with quark-gluon plasmas experiments in heavy-ion colliders and electronic transport in graphene. This chapter describes the extension of the Lattice Boltzmann formalism to the case of relativistic fluids.