Heavy-ion physics: freedom to do hot, dense, exciting QCD
Maria Elena Tejeda-Yeomans
备注：
These lectures were given at the 2019 CERN Latin-American School of High-Energy Physics in Cordoba, Argentina, 13 - 26 March 2019 and the notes have been submitted to proceedings of CLASHEP 2019. These lecture notes are based on previous Heavy-Ion and extreme QCD lectures given at CLASHEP by A. Ayala (2017), E. Fraga (2015) and J. Takahashi (2013)
In these two lectures I review the basics of heavy-ion collisions at relativistic energies and the physics we can do with them. I aim to cover the basics on the kinematics and observables in heavy-ion collider experiments, the basics on the phenomenology of the nuclear matter phase diagram, some of the model building and simulations currently used in the heavy-ion physics community and a selected list of amazing phenomenological discoveries and predictions.
In quenched QCD, on lattices with $\nt=4$, the absence of a pole in the pseudoscalar meson channel for $T>T_c$ is demonstrated. A set of effective 4-fermi couplings is extracted. It is observed that this coupling is small in the vector channel for all $T>T_c$, but not in the pseudoscalar channel. The temperature dependence of hadronic parameters below \tc{} is found to be small. NOTE: Latex source, no figures, needs espcrc2.sty from hep-lat macros.
We investigate the equation of state of hadronic matter at finite values of baryon density and temperature reachable in high energy heavy ion collisions. The analysis is performed by requiring the Gibbs conditions on the global conservation of baryon number, electric charge fraction and zero net strangeness. We consider an effective relativistic mean-field model with the inclusion of Delta-isobars, hyperons and lightest pseudoscalar and vector mesons degrees of freedom. In this context, we study the influence of the Delta-isobars degrees of freedom in the hadronic equation of state and, in con…
We present a general approach to incorporate hadronic as well as quark degrees of freedom in a unified approach. This approach implements the correct degrees of freedom at high as well as low temperatures and densities. An effective Polyakov loop field serves as the order parameter for deconfinement. We employ a well-tested hadronic flavor-SU(3) model based on a chirally symmetric formulation that reproduces properties of ground state nuclear matter and yields good descriptions of nuclei and hypernuclei. Excluded volume effects simulating the finite size of the hadrons drive the transition to …
Explosive astrophysical systems - such as supernovae or compact star binary mergers - provide conditions where exotic degrees of freedom can be populated. Within the covariant density functional theory of nuclear matter we build several general purpose equations of state which, in addition to the baryonic octet, account for $Δ(1232)$ resonance states. The thermodynamic stability of $Δ$-admixed nuclear matter is investigated in the limiting case of vanishing temperature for charge fractions $Y_Q=0.01$ and $Y_Q=0.5$ and wide ranges of the coupling constants to the scalar and vector mesonic field…
Collisions between heavy atomic nuclei at ultra-relativistic energies are carried out at particle colliders to produce the quark-gluon plasma, a state of matter where quarks and gluons are not confined into hadrons, and colour degrees of freedom are liberated. This state is thought to be produced as a transient phenomenon before it fragments into thousands of particles that reach the particle detectors. Despite two decades of investigations, one of the big open questions is to obtain an experimental determination of the temperature reached in a heavy-ion collision, and a simultaneous determina…
The change in the energy of the moving heavy (charm and bottom) quarks due to field fluctuations present in the hot QCD medium has been studied. A finite quark chemical potential has been considered while modeling the hot QCD medium counting the fact that the upcoming experimental facilities such as Anti-proton and Ion Research (FAIR) and Nuclotron-based Ion Collider fAcility (NICA) are expected to operate at finite baryon density and moderate temperature. The effective kinetic theory approach has been adopted where the collisions have been incorporated using the well defined collisional kerne…
In high neutron flux environments where isomers can be strongly populated by nucleonic reactions, isotope abundances from reaction network chains can be affected by the population of nuclear isomers. At high temperatures and densities there is the additional possibility of populating these isomers electromagnetically. Here we examine the rates for electromagnetic excitation of the isotopes of several isomers of interest both in astrophysics and applied physics (e.g. 235U, 193Ir, and 87Y,88Y). We consider six possible electromagnetic processes, namely, photo-absorption, inverse internal convers…
We study the hadron production at finite values of temperature and baryon density by means of an effective relativistic mean-field model with the inclusion of the full octet of baryons, the Delta-isobar degrees of freedom and the lightest pseudoscalar and vector mesons. These last particles are considered in the so-called one-body contribution, taking into account of an effective chemical potential and mass depending on the self-consistent interaction between baryons. The analysis is performed by requiring the Gibbs conditions on the global conservation of baryon number, electric charge fracti…
The response of the hot QCD medium in the presence of external time dependent electromagnetic fields has been studied within the relativistic Boltzmann transport theory. The impact of the time dependence of the electromagnetic fields and collisional aspects of the medium to the induced electric and Hall current densities has been explored. The non-equilibrium momentum distribution of degrees of freedom has been obtained in the presence of space-time varying electromagnetic fields. Further, the analysis has been extended to an anisotropic QCD medium while incorporating the in-medium interaction…
A production mechanism of highly excited nuclei formed in violent collisions in the Fermi energy domain is investigated. The collision of two nuclei is decomposed into several stages which are treated separately. Simplified exciton concept is used for the description of pre-equilibrium emission. A modified spectator-participant scenario is used where motion along classical Coulomb trajectories is assumed. The participant and one of the spectator zones undergo incomplete fusion. Excitation energies of both cold and hot fragment are determined. Results of the calculation are compared to recent e…
The effects of longitudinal bulk viscous pressure on the heavy quark dynamics have been estimated in a strongly magnetized quark-gluon plasma within the Fokker-Planck approach. The bulk viscous modification to the momentum distribution of bulk degrees of freedom has been obtained in the presence of a magnetic field while incorporating the realistic equation of state of the hot magnetized QCD medium. As the magnetic field breaks the isotropy of the medium, the analysis is done along the directions longitudinal and transverse to the field. The longitudinal bulk viscous contribution is seen to ha…
Ultra-relativistic heavy ion collisions at RHIC and the LHC open exciting new possibilities for jet physics studies in the presence of hot and dense nuclear matter. Recent theoretical advances in understanding the QCD multi-parton dynamics provide a good description of the quenching in the single and double inclusive high-pT hadron spectra. Measurement of the redistribution of the lost energy and the corresponding increase in the soft hadron multiplicities is the next critical step in elucidating the modification of the jet properties in the nuclear environment.
One of the more promising observables to probe the high energy regime of the QCD dynamics in the future Electron-Ion Colliders (EIC) is the exclusive vector meson production cross section in coherent and incoherent interactions. Such processes measure the average spatial distribution of gluons in the target as well the fluctuations and correlations in the gluon density. In this paper we present a comprehensive analysis of the energy, photon virtuality, atomic number and momentum transfer dependencies of the coherent and incoherent cross sections considering two different models for the nuclear…
Transport coefficients serve as important probes in characterizing the QCD matter created in high-energy heavy-ion collisions. Thermal and electrical conductivities as transport coefficients have got special significance in studying the time evolution of the created matter. We have adopted color string percolation approach for the estimation of thermal conductivity ($κ$), electrical conductivity ($σ_{el}$) and their ratio, which is popularly known as Wiedemann-Franz law in condensed matter physics. The ratio $κ/σ_{el}T$, which is also known as Lorenz number ($\mathbb{L}$) is studied as a funct…
An extended chiral SU(3) model is applied to the description of dense, hot and strange hadronic matter. The degrees of freedom are the baryon octet and decuplet and the spin-0 and spin-1 meson multiplets. The parameters of the model are fitted to the hadron masses in vacumm, infinite nuclear matter properties and soft pion theorems. At high densities the appearance of density isomers cannot be ruled out and extrapolation to finite temperature exhibits a first order phase transition at $T \approx 150 MeV$. The predicted dropping baryon masses lead to drastically changed particle ratios compared…
Hot QCD medium effects have been studied in the effective quasi-particle description of quark-gluon plasma. This model encodes the collective excitation of gluons and quarks/anti-quarks in the thermal medium in terms of effective quarks and gluons having non-trivial energy dispersion relation. The present investigation involves the extension of the effective quasi-particle model in strong magnetic field limit. Realizing, hot QCD medium in the strong magnetic field as an effective grand canonical system in terms of the modified quark, anti-quark and gluonic degrees of freedom, the thermodynamic…
The temperature of the chiral restoration phase transition at 130 MeV as well as the temperature of the center symmetry ("deconfinement") phase transition in a pure glue theory at 300 MeV are two independent temperatures and their interplay determines a structure of different regimes of hot QCD. Given a chiral spin symmetry of the color charge and of the chromoelectric interaction we can conclude from observed symmetries of spatial and temporal correlators of N_F=2 QCD with domain wall Dirac operator at physical quark masses that above the chiral symmetry restoration crossover around T_pc but …
Collective excitations of a hot QCD medium are the main focus of the present article. The analysis is performed within semi-classical transport theory with isotropic and anisotropic momentum distribution functions for the gluonic and quark-antiquark degrees of freedom that constitutes the hot QCD plasma. The isotropic/equilibrium momentum distributions for gluons and quarks are based on a recent quasi-particle description of hot QCD equations of state. The anisotropic distributions are just the extensions of isotropic ones by stretching or squeezing them in one of the directions. The hot QCD m…
We present calculations for the shear viscosity of the hot and dense quark-gluon plasma (QGP) using the partonic scattering cross sections as a function of temperature $T$ and baryon chemical potential $μ_B$ from the dynamical quasiparticle model (DQPM) that is matched to reproduce the equation of state of the partonic system above the deconfinement temperature $T_c$ from lattice QCD. To this aim we calculate the collisional widths for the partonic degrees of freedom at finite $T$ and $μ_B$ in the time-like sector and conclude that the quasiparticle limit holds sufficiently well. Furthermore, …
We explore the presence of thermodynamic instabilities and, con\-se\-quen\-tly, the realization of a pure hadronic phase transition in the hot and finite baryon density nuclear matter. The analysis is performed by means of an effective relativistic mean-field model with the inclusion of hyperons, $Δ$-isobars, and the lightest pseudoscalar and vector meson degrees of freedom. The Gibbs conditions on the global conservation of baryon number and zero net strangeness in symmetric nuclear matter are required. Similarly to the liquid-gas phase transition, we show that a phase transition, characteriz…
The hot nuclear matter created at the Relativistic Heavy Ion Collider (RHIC) has been characterized by near-perfect fluid behavior. We demonstrate that this stands in contradiction to the identification of QCD quasi-particles with the thermodynamic degrees of freedom in the early (fluid) stage of heavy ion collisions. The empirical observation of constituent quark ``$n_q$'' scaling of elliptic flow is juxtaposed with the lack of such scaling behavior in hydrodynamic fluid calculations followed by Cooper-Frye freeze-out to hadrons. A ``quasi-particle transport'' time stage after viscous effects…
We investigate transverse hadron spectra from relativistic nucleus-nucleus collisions which reflect important aspects of the dynamics - such as the generation of pressure - in the hot and dense zone formed in the early phase of the reaction. Our analysis is performed within two independent transport approaches (HSD and UrQMD) that are based on quark, diquark, string and hadronic degrees of freedom. Both transport models show their reliability for elementary $pp$ as well as light-ion (C+C, Si+Si) reactions. However, for central Au+Au (Pb+Pb) collisions at bombarding energies above $\sim$ 5 A$\c…
