Altas Energias

G. VUJANOVIC: G. S. DENICOL; M. LUZUM; S. JEON; C. GALE

PHYSICAL REVIEW C, v. 98, p. 014902, 2018

Abstract

This work reports on investigations of the effects on the evolution of viscous hydrodynamics and on the flow coefficients of thermal dileptons, originating from a temperature-dependent specific shear viscosity η/s(T) at temperatures beyond 180 MeV formed at the Relativistic Heavy-Ion Collider (RHIC). We show that the elliptic flow of thermal dileptons can resolve the magnitude of η/s at the high temperatures, where partonic degrees of freedom become relevant, whereas discriminating between different specific functional forms will likely not be possible at RHIC using this observable.

10.1103/PhysRevC.98.014902

Orlando Oliveira, T. Frederico, W. de Paula, J. P. B. C. de Melo

The European Physical Journal C, July 2018, 78:553

ABSTRACT

The soft gluon limit of the longitudinal part of the quark-gluon vertex is studied by resorting to non-perturbative approaches to quantum chromodynamics (QCD). Based on a Slavnov–Taylor identity (STI), the longitudinal form factors is expressed in terms of the quark-ghost kernel, the quark self energy and the quark wave function. An exact relation between the non-vanishing longitudinal form factors is derived for the soft gluon limit and explored to understand the behaviour of the vertex. Within a Ball–Chiu vertex, the form factor  λ1λ1  was analysed using recent lattice simulations for full QCD for the soft gluon limit. The lattice data shows that the gluon propagator resumes the momentum dependence of such component of the vertex. This connection is understood via a fully dressed one-loop Bethe–Salpeter equation. The behaviour of the remaining longitudinal form factors  λ2(p2)λ2(p2)  and  λ3(p2)λ3(p2)  is investigated combining both the information of lattice simulations and the derived relations based on the STI.

DOI:10.1140/epjc/s10052-018-6037-0

Giorgio Torrieri

Phys. Rev. C 98, 014901

Abstract

I argue that, because of the peculiar properties of the η’ meson, it is a promising probe of chiral dynamics. In particular, I show that a rotating gluon-dominated plasma might lead to an enhanced production of η’ with respect to statistical model expectations. The presence of a strong topological susceptibility might give a similar effect. In both cases, unlike the statistical model, I expect a nontrivial dependence on event geometry, such as initial volume and impact parameter. Hence, an observation of η’/π ratio depending strongly on impact parameter might be a good indication of chiral effects, either from vorticity or topological phases of QCD.

10.1103/PhysRevC.98.014901

Fernando G. Gardim, Frédérique Grassi, Pedro Ishida, Matthew Luzum, Pablo S. Magalhães, and Jacquelyn Noronha-Hostler

Phys. Rev. C 97, 064919

Abstract

An open question in the field of heavy-ion collisions is to what extent the size of initial inhomogeneities in the system affects measured observables. Here we present a method to smooth out these inhomogeneities with minimal effect on global properties, to quantify the effect of short-range features of the initial state. We show a comparison of hydrodynamic predictions with original and smoothened initial conditions for four models of initial conditions and various observables. Integrated observables (integrated vn, scaled vn distributions, normalized symmetric cumulants, event-plane correlations) as well as most differential observables [vn(pT) ] show little dependence on the inhomogeneity sizes and instead are sensitive only to the largest-scale geometric structure. However, other differential observables such as the flow factorization ratio and subleading principal components are more sensitive to the granularity and could be a good tool to probe the short-scale dynamics of the initial stages of a heavy-ion collision, which are not currently well understood.

10.1103/PhysRevC.97.064919

Danuce M. Dudek, Wei-Liang Qian, Chen Wu, Otávio Socolowski, Sandra S. Padula, Gastão Krein, Yogiro Hama and Takeshi Kodama

International Journal of Modern Physics E (no momento online apenas,
publicado em 2018/6/24)

ABSTRACT

We perform an extensive study of the role played by the equation of state (EoS) in the hydrodynamic evolution of the matter produced in relativistic heavy ion collisions. By using the same initial conditions and freeze-out scenario, the effects of different equations of state are compared by calculating their respective hydrodynamical evolution, particle spectra, harmonic flow coefficients v2v2, v3v3 and v4v4 and two-pion interferometry radius parameters. The equations of state investigated contain distinct features, such as the nature of the phase transition, as well as strangeness and baryon density contents, which are expected to lead to different hydrodynamic responses. The results of our calculations are compared to the data recorded at two RHIC energies, 130GeV and 200GeV. The three equations of state used in the calculations are found to describe the data reasonably well. Differences can be observed among the studied observables, but they are quite small. In particular, the collective flow parameters are found not to be sensitive to the choice of the EOS, whose implications are discussed.

DOI:10.1142/S0218301318500581

M. GREIF; J. A. FOTAKIS; G. S. Denicol; C. GREINER

PHYSICAL REVIEW LETTERS, v. 120, p. 242301, 2018

Abstract

We demonstrate that the diffusion currents do not depend only on gradients of their corresponding charge density, but that the different diffusion charge currents are coupled. This happens in such a way that it is possible for density gradients of a given charge to generate dissipative currents of another charge. Within this scheme, the charge diffusion coefficient is best viewed as a matrix, in which the diagonal terms correspond to the usual charge diffusion coefficients, while the off-diagonal terms describe the coupling between the different currents. In this Letter, we calculate for the first time the complete diffusion matrix for hot and dense nuclear matter, including baryon, electric, and strangeness charges. We find that the baryon diffusion current is strongly affected by baryon charge gradients but also by its coupling to gradients in strangeness. The electric charge diffusion current is found to be strongly affected by electric and strangeness gradients, whereas strangeness currents depend mostly on strange and baryon gradients.

10.1103/PhysRevLett.120.242301

M.Broilo, E.G.S.Luna and M.J.Menon

Physics Letters B. Volume 781, p. 616-620. 10 June 2018.

ABSTRACT

Recent data from LHC13 by the TOTEM Collaboration on and ρ have indicated disagreement with all the Pomeron model predictions by the COMPETE Collaboration (2002). On the other hand, as recently demonstrated by Martynov and Nicolescu (MN), the new datum and the unexpected decrease in the ρ value are well described by the maximal Odderon dominance at the highest energies. Here, we discuss the applicability of Pomeron dominance through fits to the most complete set of forward data from pp and scattering. We consider an analytic parameterization for consisting of non-degenerated Regge trajectories for even and odd amplitudes (as in the MN analysis) and two Pomeron components associated with double and triple poles in the complex angular momentum plane. The ρ parameter is analytically determined by means of dispersion relations. We carry out fits to pp and data on and ρ in the interval 5 GeV–13 TeV (as in the MN analysis). Two novel aspects of our analysis are: (1) the dataset comprises all the accelerator data below 7 TeV and we consider three independent ensembles by adding: either only the TOTEM data (as in the MN analysis), or only the ATLAS data, or both sets; (2) in the data reductions to each ensemble, uncertainty regions are evaluated through error propagation from the fit parameters, with 90% CL. We argument that, within the uncertainties, this analytic model corresponding to soft Pomeron dominance, does not seem to be excluded by the complete set of experimental data presently available.

10.1016/j.physletb.2018.04.045