Quark-gluon Plasma Phase Research Articles

Magnetic Susceptibility of Strongly Interacting Matter across the Deconfinement Transition

We propose a method to determine the total magnetic susceptibility of strongly interacting matter by lattice QCD simulations and present numerical results for the theory with two light flavors, which suggest a weak magnetic activity in the confined phase and the emergence of strong paramagnetism in the deconfined, quark-gluon plasma phase.

Thermal QCD deconfining phase transition in a finite volume within color-singletness and excluded volume effects: a finite size scaling analysis using cumulants

We study the properties of the deconfining phase transition for a finite-volume system in which the hadronic and quark–gluon plasma phases coexist and the finite extensions of the hadrons are taken into account. Finite-size effects are examined by probing the behavior of some useful response functions near the transition, and scaling exponents are determined using a finite-size scaling (FSS) analysis. For the shift scaling exponent, the finite-size transition point is determined from several definitions, and we propose new ways of defining this quantity, using cumulants of the probability distribution. Our study shows that the deconfining phase transition stays first-order, the scaling exponents being equal to unity. This result is consistent with the predictions of the standard FSS theoretical approaches to a first-order phase transition, and with results using Monte Carlo methods in lattice QCD and other models in statistical physics.

Shear viscosity in the Nambu–Jona-Lasinio model withΦ-derivable approximations

Within the Nambu--Jona-Lasinio model the temperature dependence of the shear viscosity is calculated to the first nontrivial order in the $1/{N}_{c}$ expansion with $\ensuremath{\Phi}$-derivable approximations. The two-particle irreducible effective action is computed to next-to-leading order, from which the integral equations for the 3- and 4-point vertices are obtained. These sum infinite sets of diagrams contributing to the shear viscosity at the same order in the $1/{N}_{c}$ expansion. We find that the shear viscosity decreases rapidly when the chiral crossover is approached. Comparing with the hadron phase, the quark-gluon plasma phase has a low shear viscosity, which is consistent with the measurements. The ratio of the shear viscosity to entropy density is also calculated.

Viscosity, wave damping, and shock-wave formation in cold hadronic matter

We study linear and nonlinear wave propagation in a dense and cold hadron gas and also in a cold quark-gluon plasma, taking viscosity into account and using the Navier-Stokes equation. The equation of state of the hadronic phase is derived from the nonlinear Walecka model in the mean-field approximation. The quark-gluon plasma phase is described by the MIT equation of state. We show that in a hadron gas viscosity strongly damps wave propagation and also hinders shock-wave formation. This marked difference between the two phases may have phenomenological consequences and lead to new quark-gluon plasma signatures.

An effective model of QCD thermodynamics

A combined effective model reproducing the equation of state of hadronic matter as obtained in recent lattice QCD simulations is presented. The model reproduces basic physical characteristics encountered in dense hadronic matter in the quark-gluon plasma (QGP) phase and the lower temperature hadron resonance gas phase. The hadronic phase is described by means of an extended Mott-Hagedorn resonance gas while the QGP phase is described by the extended PNJL model. The dissociation of hadrons is obtained by including the state dependent hadron resonance width.

STRONGLY INTERACTING MATTER AT FINITE CHEMICAL POTENTIAL: HYBRID MODEL APPROACH

Search for a proper and realistic equation of state (EOS) for strongly interacting matter used in the study of the QCD phase diagram still appears as a challenging problem. Recently, we constructed a hybrid model description for the quark–gluon plasma (QGP) as well as hadron gas (HG) phases where we used an excluded volume model for HG and a thermodynamically consistent quasiparticle model for the QGP phase. The hybrid model suitably describes the recent lattice results of various thermodynamical as well as transport properties of the QCD matter at zero baryon chemical potential (μB). In this paper, we extend our investigations further in obtaining the properties of QCD matter at finite value of μB and compare our results with the most recent results of lattice QCD calculation.

Improved Polyakov-loop potential for effective models from functional calculations

We investigate the quark backreaction on the Polyakov loop and its impact on the thermodynamics of quantum chromodynamics. The dynamics of the gluons generating the Polyakov-loop potential is altered by the presence of dynamical quarks. However, this backreaction of the quarks has not yet been taken into account in Polyakov-loop extended model studies. In the present work, we show within a 2+1 flavour Polyakov-quark-meson model that a quark-improved Polyakov-loop potential leads to a smoother transition between the low-temperature hadronic phase and the high-temperature quark-gluon plasma phase. In particular, we discuss the dependence of our results on the remaining uncertainties that are the critical temperature and the parametrisation of the Polyakov-loop potential as well as the mass of the sigma-meson.

Heavy quark energy loss and thermalization in hot and dense nuclear matter

We study heavy quark energy loss and thermalization in hot and dense nuclear medium. The diffusion of heavy quarks is calculated via a Langevin equation, both for a static medium as well as for a quark-gluon plasma (QGP) medium generated by a (3+1)-dimensional hydrodynamic model. We investigate how the initial configuration of the QGP and its properties affect the final state spectra and elliptic flow of heavy flavor mesons and non-photonic electrons. It is observed that both the geometric anisotropy of the initial profile and the flow profile of the hydrodynamic medium play important roles in the heavy quark energy loss process and the development of elliptic flow. Within our definition of the thermalization criterion and for reasonable values of the diffusion constant, we observe thermalization times that are longer than the lifetime of the QGP phase.

Beam energy dependence of elliptic and triangular flow with the AMPT model

A beam energy scan has been carried out at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory to search for the onset of deconfinement and a possible critical point where the transition from a Quark Gluon Plasma to a hadronic phase changes from a rapid cross-over to a first order phase transition. Anisotropy in the azimuthal distribution of produced particles such as the second and third harmonics v2 and v3 are expected to be sensitive to the existence of a Quark Gluon Plasma phase and the Equation of State of the system. For this reason, they are of great experimental interests. In this Letter we report on calculations of v2 and v3 from the AMPT model in the Default (Def.) and String Melting (SM) mode to provide a reference for the energy dependence of v2 and v3 for sNN from 7.7 GeV to 2.76 TeV. We expect that in the case that collisions cease to produce QGP at lower colliding energies, data will deviate from the AMPT String Melting calculations and come in better agreement with the Default calculations.

Some aspects of QGP phase in a hQCD model

We continue to study the holographic QCD (hQCD) model, proposed in a previous paper, in an Einstein-Maxwell-Dilaton (EMD) system. In this paper we discuss some aspects of quark gluon plasma (QGP) in the hQCD model, such as drag force, jet quenching parameter and screening length. The results turn out to be consistent with those as expected in QCD qualitatively. By calculating free energy of the background black hole solution, we find that there exists a Hawking-Page phase transition between small black hole and big black hole when chemical potential $\mu $ is less than a critical one $ \mu_c$, and the phase transition is absent when chemical potential is beyond the critical one.

Event-by-Event Anisotropic Flow in Heavy-ion Collisions from Combined Yang-Mills and Viscous Fluid Dynamics

Anisotropic flow coefficients v(1)-v(5) in heavy ion collisions are computed by combining a classical Yang-Mills description of the early time Glasma flow with the subsequent relativistic viscous hydrodynamic evolution of matter through the quark-gluon plasma and hadron gas phases. The Glasma dynamics, as realized in the impact parameter dependent Glasma (IP-Glasma) model, takes into account event-by-event geometric fluctuations in nucleon positions and intrinsic subnucleon scale color charge fluctuations; the preequilibrium flow of matter is then matched to the music algorithm describing viscous hydrodynamic flow and particle production at freeze-out. The IP-Glasma+MUSIC model describes well both transverse momentum dependent and integrated v(n) data measured at the Large Hadron Collider and the Relativistic Heavy Ion Collider. The model also reproduces the event-by-event distributions of v(2), v(3) and v(4) measured by the ATLAS Collaboration. The implications of our results for better understanding of the dynamics of the Glasma and for the extraction of transport properties of the quark-gluon plasma are outlined.

Quantifying Initial State Fluctuations in Heavy Ion Collisions

Author(s): Petersen, H; Coleman-Smith, CE; Wolpert, RL | Abstract: Quantum fluctuations induce interesting structures in the initial state profiles for hydrodynamic calculations of the hot and dense quark-gluon plasma phase of heavy ion collisions. Especially, after the discovery of non-zero odd higher flow coefficients, there has been a lot of theoretical effort to quantify the correlation lengths of energy density fluctuations. A new method to characterize initial state profiles based on a 2D Fourier analysis is presented and an outlook on how this analysis can lead to a better quantitative understanding of the properties of hot and dense nuclear matter is given.

Electromagnetic signals from Au + Au collisions at RHIC energy, [formula omitted] and Pb + Pb collisions at LHC energy, [formula omitted

We analyse the recently available experimental data on direct photon productions from Au+Au collisions at sNN=200 GeV RHIC and from Pb+Pb collisions at sNN=2.76 TeV LHC energies. The transverse momentum (pT) distributions have been evaluated with the assumption of an initial quark gluon plasma phase at energy densities ϵi=41 and 70 GeV/fm3 with initial thermalisation times τi=0.2 and 1.0 fm/c respectively for RHIC and LHC energies. The theoretical evaluations agree well with the experimental observations. The thermal radiations dominate within the pT range 1.5⩽pT(GeV)⩽3.5. The ratio of thermal photons to dileptons (Rem=[d2Nγ/d2pTdy]/[d2Nγ⁎/d2pTdy]) determines more precisely the window, as mentioned above.

Structure of a thermal quasifermion in the QCD/QED medium

In this paper we carried out a nonperturbative analysis of a thermal quasifermion in the chiral symmetric thermal QCD/QED medium by studying its self-energy function through the Dyson-Schwinger equation with the hard-thermal-loop resummed improved ladder kernel. Our analysis reveals several interesting results, two in some of which may force us to change the image of thermal quasifermions: (1) The thermal mass of a quasifermion begins to decrease as the strength of the coupling gets stronger and finally disappears in the strong coupling region, thus showing a property of a massless particle, and (2) its imaginary part (i.e., the decay width) persists to have $O({g}^{2}T\mathrm{log}(1/g))$ behavior. These results suggest that in the recently produced strongly coupled quark-gluon plasma, the thermal mass of a quasiquark should vanish. Taking into account the largeness of the imaginary part, it seems very hard for a quark to exist as a qausiparticle in the strongly coupled quark-gluon plasma phase. Other important findings are as follows: (3) The collective plasmino mode disappears also in the strongly coupled system, and (4) there exists an ultrasoft third peak in the quasifermion spectral density at least in the weakly coupled QED/QCD plasma, indicating the existence of the ultrasoft fermionic mode.

Hybrid model for QCD deconfining phase boundary

Intensive search for a proper and realistic equations of state (EOS) is still continued for studying the phase diagram existing between quark gluon plasma (QGP) and hadron gas (HG) phases. Lattice calculations provide such EOS for the strongly interacting matter at finite temperature ($T$) and vanishing baryon chemical potential (${\ensuremath{\mu}}_{B}$). These calculations are of limited use at finite ${\ensuremath{\mu}}_{B}$ due to the appearance of notorious sign problem. In the recent past, we had constructed a hybrid model description for the QGP as well as HG phases where we make use of a new excluded-volume model for HG and a thermodynamically-consistent quasiparticle model for the QGP phase and used them further to get QCD phase boundary and a critical point. Since then many lattice calculations have appeared showing various thermal and transport properties of QCD matter at finite $T$ and ${\ensuremath{\mu}}_{B}=0$. We test our hybrid model by reproducing the entire data for strongly interacting matter and predict our results at finite ${\ensuremath{\mu}}_{B}$ so that they can be tested in future. Finally we demonstrate the utility of the model in fixing the precise location, the order of the phase transition and the nature of $CP$ existing on the QCD phase diagram. We thus emphasize the suitability of the hybrid model as formulated here in providing a realistic EOS for the strongly interacting matter.

Bottomonia in the quark-gluon plasma and their production at RHIC and LHC

We study the production of bottomonium states in heavy-ion reactions at collider energies available at RHIC and LHC. We employ an earlier constructed rate equation approach which accounts for both suppression and regeneration mechanisms in the quark-gluon plasma (QGP) and hadronization phases of the evolving thermal medium. Our previous predictions utilizing two limiting cases of strong and weak bottomonium binding in the QGP are updated by i) checking the compatibility of the pertinent spectral functions with lattice-QCD results for euclidean correlators, ii) adapting the initial conditions of the rate equation by updating bottom-related input cross-sections and the charged-particle multiplicity of the fireball, and iii) converting our calculations into observables as recently measured by the STAR and CMS experiments. Our main findings are a preference for strong ϒ binding as well as a significant regeneration component at the LHC.

PRIMORDIAL STRANGE QUARK MATTER

Strange quark nuggets (SQNs) could be the relics of the cosmological QCD phase transition, and they could very likely be the candidate of cold dark matter if survived the cooling of the later Universe, although the formation and evolution of these SQNs depend on the physical state of the hot QGP (quark-gluon plasma) phase and the state of cold quark matter. We reconsider the possibility of SQNs as cold dark matter, and discuss the astrophysical consequences of primordial SQNs in the early and present universe. In the early Universe, the formation of black holes inside primordial halos could be faster than that in the standard scenario, and speed up the formation of the supermassive black holes at high redshift. In the present Universe, the capture of SQNs by pulsars could trigger star-quakes, which could be the mechanism for pulsar-glitches.

Meson spectra andmTscaling inp+p,d+ Au, and Au + Au collisions atsNN=200GeV

The meson spectra provide insight into the particle production mechanism and interaction in the hadronic and quark gluon plasma (QGP) phases. The detailed study of systematics of meson spectra is important also because it acts as an ingredient for estimating the hadronic decay backgrounds in the photon, single lepton, and dilepton spectra which are the penetrating probes of quark gluon plasma. In this work, we parametrize experimentally measured pion spectra and then obtain the spectra of other light mesons using a property known as ${m}_{T}$ scaling. The ${m}_{T}$ scaled spectra for each meson is compared with experimental data for $p+p$, $d$ + Au, and Au + Au systems at $\ensuremath{\surd}{s}_{NN}$ = 200 GeV. The agreement of the ${m}_{T}$ scaled and experimental data shapes are excellent in most cases and their fitted relative normalization gives ratio of meson to pion ${m}_{T}$ spectra. These ratios are useful to obtain the hadronic decay contribution in photonic and leptonic channels but also point to the quantitative changes in the dynamics of the heavy ion collision over $p+p$ collisions. It is shown that, the particles with charm contents behave differently as compared to pions in $d$ + Au systems and particles either with strange or charm contents behave differently from pions in Au + Au systems. For Au + Au system, three centrality classes have been studied which reveal that for the particles, such as kaon and $\ensuremath{\varphi}$, peripheral collision data are better reproduced as compared to central collision data and their relative ratios with pions also increase as the collisions become more central.

Thermal QCD sum rules study of vector charmonium and bottomonium states

We calculate the masses and leptonic decay constants of the heavy vector quarkonia, $J/\psi$ and $\Upsilon$ mesons at finite temperature. In particular, considering the thermal spectral density as well as additional operators coming up at finite temperature, the thermal QCD sum rules are acquired. Our numerical calculations demonstrate that the masses and decay constants are insensitive to the variation of temperature up to $T\cong 100 ~MeV$, however after this point, they start to fall altering the temperature. At deconfinement temperature, the decay constants attain roughly to 45% of their vacuum values, while the masses are diminished about 12%, and 2.5% for $J/\psi$ and $\Upsilon$ states, respectively. The obtained results at zero temperature are in good consistency with the existing experimental data as well as predictions of the other nonperturbative models. Considerable decreasing in the values of the decay constants can be considered as a sign of the quark gluon plasma phase transition.

Finite-size scaling as a tool in the search for the QCD critical point in heavy ion data

Given the short lifetime and the reduced volume of the quark-gluon plasma (QGP) formed in high-energy heavy ion collisions, a possible critical endpoint (CEP) will be blurred in a region and the effects from criticality severely smoothened. Nevertheless, the non-monotonic behavior of correlation functions near criticality for systems of different sizes, given by different centralities in heavy ion collisions, must obey finite-size scaling. We apply the predicting power of scaling plots to the search for the CEP of strong interactions in heavy ion collisions using data from RHIC and SPS. The results of our data analysis exclude a critical point below chemical potentials $\mu\sim 450 $MeV. Extrapolating the analysis, we speculate that criticality could appear slightly above $\mu\sim 500 $MeV. Using available data we extrapolate our scaling curves to predict the behavior of new data at lower center-of-mass energy, currently being investigated in the Beam Energy Scan program at RHIC. If it turns out that the QGP phase is no longer achievable in heavy ion experiments before the CEP is reached, FSS might be the only way to experimentally estimate its position in the phase diagram.