Temperature Of Quark-gluon Plasma Research Articles

Viscous QCD medium effects on the bottom quark transport coefficients

The bottom quark transport coefficients, i.e., drag and diffusion coefficients, have been studied for the collisional and soft gluon radiative processes within the viscous QCD medium. The thermal medium effects are incorporated using the effective fugacity quasiparticle model (EQPM). Both the shear and bulk viscous effects at leading order are embedded through the near-equilibrium distribution functions of the quark–gluon plasma (QGP) constituent quasiparticles. The transport coefficients’ dependence on the bottom quark’s initial momentum and QGP temperature have been investigated. The relative dominance of the radiative over the collisional process for the bottom quark seems to occur at a higher initial momentum compared to that of the charm quark. In contrast, the effect of the viscous corrections seems to be more for the charm quark. Furthermore, we also investigate the validity of the Einstein fluctuation–dissipation theorem for our analysis.

Waves in magnetized quark matter

We study wave propagation in a non-relativistic cold quark-gluon plasma immersed in a constant magnetic field. Starting from the Euler equation we derive linear wave equations and investigate their stability and causality. We use a generic form for the equation of state, the EOS derived from the MIT bag model and also a variant of the this model which includes gluon degrees of freedom. The results of this analysis may be relevant for perturbations propagating through the quark matter phase in the core of compact stars and also for perturbations propagating in the low temperature quark-gluon plasma formed in low energy heavy ion collisions, to be carried out at FAIR and NICA.

Parton energy loss and momentum broadening at NLO in high temperature QCD plasmas

We present an overview of a perturbative-kinetic approach to jet propagation, energy loss, and momentum broadening in a high temperature quark–gluon plasma. The leading-order kinetic equations describe the interactions between energetic jet-particles and a non-abelian plasma, consisting of on-shell thermal excitations and soft gluonic fields. These interactions include [Formula: see text] scatterings, collinear bremsstrahlung, and drag and momentum diffusion. We show how the contribution from the soft gluonic fields can be factorized into a set of Wilson line correlators on the light-cone. We review recent field-theoretical developments, rooted in the causal properties of these correlators, which simplify the calculation of the appropriate Wilson lines in thermal field theory. With these simplifications lattice measurements of transverse momentum broadening have become possible, and the kinetic equations describing parton transport have been extended to next-to-leading order in the coupling [Formula: see text].

Dilepton production from RHIC to the LHC

The goal of ultrarelativistic heavy-ion collisions at RHIC and the LHC is to study the properties of the quark-gluon plasma (QGP), a phase of matter with partonic degrees of freedom. Electromagnetic radiation, in form of photons or lepton pairs, is a penetrating probe that allows the investigation of the full time evolution and dynamics of the produced matter as it does not undergo strong interaction in the final state. The dilepton spectrum is extremely rich in physics sources: Thermal black-body radiation is of particular interest as it carries information about the QGP temperature. Modifications of the spectral functions of light vector mesons are linked to the potential restoration of chiral symmetry in the QGP phase. Correlated lepton pairs from semi-leptonic charm and beauty decays provide additional information about the heavy-quark energy loss. Finally, the suppression of quarkonia in the QGP give access to an independent temperature measurement. In this proceedings, dilepton results from RHIC are reviewed and the status as well as prospects of low-mass dilepton measurements at the LHC are given.

Electrical conductivity of the quark-gluon plasma and soft photon spectrum in heavy-ion collisions

I extract the electrical conductivity ${\ensuremath{\sigma}}_{0}$ of the quark gluon plasma (QGP) and study the effects of magnetic field and chiral anomaly on soft photon azimuthal anisotropy, ${v}_{2}$, based on the thermal photon spectrum at $0.4\phantom{\rule{0.16em}{0ex}}\mathrm{GeV}\phantom{\rule{4pt}{0ex}}<{p}_{\ensuremath{\perp}}<0.6\phantom{\rule{0.16em}{0ex}}\mathrm{GeV}$ at the Brookhaven Relativistic Heavy Ion Collider energy. As a basis for my analysis, I derive the behavior of retarded photon self-energy of a strongly interacting neutral plasma in hydrodynamic regime in the presence of magnetic field and chiral anomaly. By evolving the resulting soft thermal photon production rate over the realistic hydrodynamic background and comparing the results with the data from the PHENIX Collaboration, I found that the electrical conductivity at QGP temperature is in the range: $0.4<{\ensuremath{\sigma}}_{0}/({e}^{2}T)<1.1$, which is comparable with recent studies on lattice. I also compare the contribution from the magnetic field and chiral anomaly to soft thermal photon ${v}_{2}$ with the data. I argue that at the CERN Large Hadron Collider, the chiral magnetic wave would give negative contribution to photon ${v}_{2}$.

Strangeness at high temperatures

We use up to fourth order cumulants of net strangeness fluctuations and their correlations with net baryon number fluctuations to extract information on the strange meson and baryon contribution to the low temperature hadron resonance gas, the dissolution of strange hadronic states in the crossover region of the QCD transition and the quasi-particle nature of strange quark contributions to the high temperature quark-gluon plasma phase.

Equation of state and initial temperature of quark gluon plasma at RHIC

Abstract In gold-gold collisions of the Relativistic Heavy Ion Collider a perfect fluid of strongly interacting quark gluon plasma (sQGP) is created. The time evolution of this fluid can be described by hydrodynamical models. After an expansion, hadrons are created during the freeze-out period. Their distribution reveals information about the final state. To investigate the time evolution one needs to analyze penetrating probes: e.g. direct photon observations. In this paper we analyze a 1+3 dimensional solution of relativistic hydrodynamics. We calculate momentum distribution, azimuthal asymmetry and momentum correlations of direct photons. Based on earlier fits to hadronic spectra, we compare photon calculations to measurements to determine the equations of state and the initial temperature of sQGP. We find that the initial temperature in the center of the fireball is 507±12 MeV, while for the sound speed we get c s=0.36±0.02. We also estimate a systematic error of these results. We find that the measured azimuthal asymmetry is also compatible with this model. We also predict a photon source that is significantly larger in the out direction than in the side direction.

Thermal bottomonium suppression at RHIC and LHC

In this paper we consider the suppression of bottomonium states in ultrarelativistic heavy ion collisions. We compute the suppression as a function of centrality, rapidity, and transverse momentum for the states Upsilon(1s), Upsilon(2s), Upsilon(3s), chi_b1, and chi_b2. Using this information, we then compute the inclusive Upsilon(1s) suppression as a function of centrality, rapidity, and transverse momentum including feed down effects. Calculations are performed for both RHIC sqrt(s_NN)=200 GeV Au-Au collisions and LHC sqrt(s_NN)=2.76 TeV Pb-Pb collisions. From the comparison of our theoretical results with data available from the STAR and CMS Collaborations we are able to constrain the shear viscosity to entropy ratio to be in the range 0.08 < eta/S < 0.24. Our results are consistent with the creation of a high temperature quark-gluon plasma at both RHIC and LHC collision energies.

Energy loss of a heavy quark produced in a finite-size quark–gluon plasma

We study the energy loss of an energetic heavy quark produced in a high temperature quark–gluon plasma and travelling a finite distance before emerging in the vacuum. While the retardation time of purely collisional energy loss is found to be of the order of the Debye screening length, we find that the contributions from transition radiation and the Ter–Mikayelian effect do not compensate, leading to an energy loss, the reduction of the zeroth-order (in an opacity expansion) energy loss.

Retardation effect for collisional energy loss of hard partons produced in a QGP

We study the collisional energy loss suffered by an energetic parton travelling the distance L in a high temperature quark-gluon plasma and initially produced in the medium. We find that the medium-induced collisional loss -Delta E(L) is strongly suppressed compared to previous estimates which assumed the collisional energy loss rate -dE/dx to be constant. The large L linear asymptotic behaviour of -Delta E(L) sets in only after a quite large retardation time. The suppression of -Delta E(L) is partly due to the fact that gluon bremsstrahlung arising from the initial acceleration of the energetic parton is reduced in the medium compared to vacuum. The latter radiation spectrum is sensitive to the plasmon modes of the quark-gluon plasma and has a rich angular structure.

Collisional energy loss of high energy jets in the quark-gluon plasma

The collisional energy loss dE dx for a high energy light quark or gluon propagating through a high temperature quark-gluon plasma is estimated. Implications for jet quenching in ultrarelativistic heavy ion collisions are discussed.

Mass-effect of Quarks in Freeze-out from Quark-gluon Plasma

The effects of masses of quarks and light gluions on the temperature of Quark-Gluon Plasma (QGP) is taken into account in Massachusetts Institute of Technology (MIT) bag model while freeze-out of quarks from QGP is discussed in the break-up model. It turns out that in the last stage of development of QGP, quark species will freeze-out in the heavier to lighter order, which may not be changed by unavoidable production of other particles (e.g., gluions).

J/ψ rapidity density and its suppression in ultrarelativistic heavy-ion collisions

The production of charm quark-antiquark pairs and their hadronization are taken into account by the semi-local duality model. The thermalJ/ψ production rate is analysed in the framework of the Bjorken's scaling hadrodynamical picture and theJ/ψ yield as a function of the initial temperature of quark-gluon plasma is calculated in the case of the central region of untrarelativistic nucleus-nucleus collisions. In view of the ideal of the Debye screening an alternativeJ/ψ suppression mechanism is suggested and the thermalJ/ψ yield with and without the suppression mechanism are evaluated numerically, respectively.