Parton Plasma Research Articles

Confinement induced frustration in a one-dimensional lattice gauge theory

Coupling dynamical charges to gauge fields can result in highly non-local interactions with a linear confining potential. As a consequence, individual particles bind into mesons which, in one dimension, become the new constituents of emergent Luttinger liquids (LLs). Furthermore, at commensurate fillings, different Mott-insulating states can be stabilized by including nearest-neighbour (NN) interactions among charges. However, rich phase diagrams expected in such models have not been fully explored and still lack comprehensive theoretical explanation. Here, by combining numerical and analytical tools, we study a simple one-dimensional lattice gauge theory at half-filling, where U(1) matter is coupled to gauge fields and interacts through NN repulsion. We uncover a rich phase diagram where the local NN interaction stabilizes a Mott state of individual charges (or partons) on the one hand, and an LL of confined mesons on the other. Furthermore, at the interface between these two phases, we uncover a highly frustrated regime arising due to the competition between the local NN repulsion and the non-local confining interactions, realizing a pre-formed parton plasma. Our work is motivated by the recent progress in ultracold atom experiments, where such simple model could be readily implemented. For this reason we calculate the static structure factor which we propose as a simple probe to explore the phase diagram in an experimental setup.

Finite-size effects and finite-size scaling in time evolution during a colorless confining phase transition

The time evolution of the expanding colorless partonic matter, created in ultra-relativistic heavy ion collisions and undergoing the confining phase transition, is discussed in the context of our colorless QCD-MIT bag model with the boost invariant Bjorken expansion and using the -method. The direct extension of this method to the non-colorless case is clearly formulated. The hydrodynamic equation in the case of a longitudinal expansion scenario of a non-ideal relativistic medium in finite volume is solved using certain initial conditions . The evolution of the temperature T(τ,V) as a function of the proper time and of the volume is then obtained. Different times characterising the whole time evolution, like the time at which the confining phase transition begins τ P (V), the hadronic time at which the hadronization is completed, the lifetime of the Colorless Partonic Plasma and the lifetime of the confining phase transition are carefully extracted and their finite-size scaling properties are studied in detail and compared with the derived laws. The effects of the initial conditions (T i , τ i ) on different times and lifetimes are investigated in detail. We find that the time evolution of our system is really affected by the colorlessness requirement.

Dissipative phenomena in QCD plasma state created in heavy ion collisions

Modern heavy ion experiments reach collision energies that span the QCD phase diagram in the region of a partonic plasma state called the quark-gluon plasma (QGP). This relativistic QCD plasma is a strongly coupled hot/dense medium that lasts only a few fm/c. Being such a ephemeral state of matter, the only effective information about it is contained in the final particle shower collected by the experiment. Plethora of measurements show that the QGP behaves like a relativistic liquid with very small dissipative effects. Phenomenologically, a full theoretical framework of the QGP comprises of initial medium conditions, viscous hydrodynamics and particle shower (hadronization) phase. Each of these phases determines the predictive power of the model and puts a direct quantitative constrain on dissipative contributions when compared to data.

Detailed study of the QCD Equation of State of a colorless partonic plasma in finite volume

The color confinement in Quantum Chromodynamics (QCD) remains an interesting and intriguing phenomenon. It is considered as a very important nonperturbative effect to be taken into account in all models intended to describe the QCD many-parton system. During the deconfinement phase transition, the non-Abelian character of the partonic plasma manifests itself in an important manner. A direct consequence of color confinement is that all states of any partonic system must be colorless and the requirement of the colorlessness condition is more than necessary. Indeed, the colorless state is a result of the multiparton interactions, from which collective phenomena can emerge, inducing strong correlations and giving rise to a long-range order of liquid-like phase, a behavior fundamentally different from that of a conformal ideal gas. Within our Colorless QCD MIT-Bag Model and using the [Formula: see text]-method, three Thermal Response Functions, related to the Equation of State, like pressure [Formula: see text], sound velocity [Formula: see text] and energy density [Formula: see text] are calculated and studied as functions of temperature [Formula: see text] and volume [Formula: see text]. Also and in the same context, two relevant correlation forms [Formula: see text] and [Formula: see text] are calculated and studied intensively as functions of [Formula: see text] at different volumes. A detailed comparative study between our results and those obtained from lattice QCD simulation, hot QCD and other phenomenological models is carried out. We find that the Liquid Partonic Plasma Model is the model which fits our Equation of State very well, in which the Bag constant term is revealed very important. Our Colorless Partonic Plasma, just beyond the finite volume transition point, is found in a state where the different partons interact strongly showing a liquid behavior in agreement with the estimate of the plasma parameter [Formula: see text] and supporting the result obtained from the fitting work. This allows us to understand experimental observations in Ultra-Relativistic Heavy-Ion Collisions and to interpret lattice QCD results.

Charmonium suppression in a baryon rich quark-gluon plasma

We have investigated the survival probability of different charmonium states, in a high baryon density parton plasma, expected to be produced in nuclear collisions at FAIR. Charmonia are assumed undergo complete dissociation by color screening, if the in-medium Debye radius becomes comparable to the spatial size of the corresponding bound state. Results indicate a non-trivial dependence of the suppression pattern on the plasma evolution dynamics.

Charmonium suppression in a baryon-rich quark-gluon plasma

We have investigated the survival probability of different charmonium states in a high baryon density parton plasma, expected to be produced in nuclear collisions at the Facility for Antiproton and Ion Research. Charmonia are assumed to undergo complete dissociation by color screening if the in-medium Debye radius becomes comparable to the spatial size of the corresponding bound state. Results indicate a nontrivial dependence of the suppression pattern on the plasma evolution dynamics. A much larger magnitude of suppression is foreseen induced by cold nuclear matter compared to that due to plasma screening.

Dilepton production in proton-proton and Pb+Pb collisions atsNN=2.76TeV

We study ${e}^{+}{e}^{\ensuremath{-}}$ pair production in proton-proton and central $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=2.76$ TeV within two models: an extended statistical hadronization model (SHM) and the Parton-Hadron-String Dynamics (PHSD) transport approach. We find that the PHSD calculations roughly agree with the dilepton spectrum from hadronic sources with the ``cocktail'' estimates from the statistical hadronization model matched to available data at Large Hadron Collider energies. The dynamical simulations within the PHSD show a moderate increase of the low-mass dilepton yield essentially due to the in-medium modification of the $\ensuremath{\rho}$ meson. Furthermore, pronounced traces of the partonic degrees of freedom are found in the PHSD results in the intermediate-mass regime. The dilepton production from the strongly interacting quark-gluon plasma (sQGP) exceeds that from the semileptonic decays of open charm and bottom mesons. Additionally, we observe that a transverse momentum cut of 1 GeV/$c$ further suppresses the relative contribution of the heavy-meson decays to the dilepton yield, such that the sQGP radiation strongly dominates the spectrum for masses from 1 to 3 GeV, allowing a closer look at the electromagnetic emissivity of the partonic plasma in the early phase of $\mathrm{Pb}+\mathrm{Pb}$ collisions.

Baryon deceleration and partonic plasma creation by strong chromofields in ultrarelativistic heavy-ion collisions

Strong chromofields generated at early stages of ultrarelativistic nuclear collisions may explain not only creation of the quark-gluon plasma but also collective deceleration of net baryons. This is demonstrated by solving classical equations of motion for baryonic slabs under the action of a time-dependent chromofield. We have studied sensitivity of the slab trajectories and their final rapidities to the initial strength and decay time of the chromofield, as well as to the back reaction of the produced plasma. By proper choice of the initial chromofield energy density we can reproduce significant baryon stopping, an average rapidity loss of about two units, observed for Au + Au collisions at RHIC. Using a Bjorken-like hydrodynamical model with the particle production source, we also study the evolution of partonic plasma produced as the result of the chromofield decay. Due to the delayed formation and expansion of plasma its maximum energy density is significantly lower than the initial energy density of the chromofield. It is shown that the fluctuations of the chromofield due to the stochastic distribution of color charges help to populate the midrapidity region in the net-baryon distribution. To fit the midrapidity data we need the chromofields with initial energy densities in the range of 30 to 60 GeV/fm3. Predictions of baryon stopping for Pb + Pb collisions at LHC energies are made.

Baryon stopping and partonic plasma production by strong chromofields

Strong chromofields developed at early stages of relativistic heavy-ion collisions give rise to the collective deceleration of net baryons from colliding nuclei. We have solved classical equations of motion for baryonic slabs under the action of a time-dependent chromofield. We have studied the sensitivity of the slab trajectories and their final rapidities to the initial strength and decay pattern of the chromofield as well as to the back-reaction of produced plasma. This mechanism can naturally explain significant baryon stopping observed at Relativistic Heavy Ion Collider corresponding to an average rapidity loss $\ensuremath{\langle}\ensuremath{\delta}y\ensuremath{\rangle}\ensuremath{\approx}2$. Using a Bjorken-like hydrodynamical model with a particle production source term, we also study the evolution of partonic plasma produced as the result of chromofield decay. Due to the delayed formation and expansion of plasma, its maximum energy density is much lower than the initial energy density of the chromofield. Predictions of baryon stopping for $\text{Pb}\phantom{\rule{4.pt}{0ex}}\text{+}\phantom{\rule{4.pt}{0ex}}\text{Pb}$ collisions at Large Hadron Collider energies were made.

PHOTON EMISSION FROM OUT OF EQUILIBRIUM DISSIPATIVE PARTON PLASMA

Using the second order Israel–Stewart hydrodynamics we discuss the effect of viscosity on photon production in a parton plasma created in relativistic heavy ion collisions. We find that photon production rates can be enhanced by several factors due to the viscous effect in a chemically nonequilibrated plasma.

Formation and decay of hadronic resonances in the QGP

Hadronic resonances can play a pivotal role in providing experimental evidence for partial chiral symmetry restoration in the deconfined quark–gluon phase produced at RHIC and the LHC. Their lifetimes, which are comparable to the lifetime of the partonic plasma phase, make them an invaluable tool to study medium modifications to the resonant state due to the chiral transition. In this Letter we show that the heavier, but still abundant, light and strange quark resonances K∗, ϕ, Δ and Λ∗ have large probability to be produced well within the plasma phase due to their short formation times. We demonstrate that, under particular kinematic conditions, these resonances can be formed and will decay inside the partonic state, but still carry sufficient momentum to not interact strongly with the hadronic medium after the QCD phase transition. Thus, K∗, ϕ, Δ and Λ∗ should exhibit the characteristic property modifications which can be attributed to chiral symmetry restoration, such as mass shifts, width broadening or branching ratio modifications.

Baryon deceleration by strong chromofields in ultrarelativistic nuclear collisions

It is assumed that strong chromofields are generated at early stages of ultrarelativistic heavy-ion collisions which give rise to a collective deceleration of baryons from colliding nuclei. We have solved classical equations of motion for baryonic slabs under the action of a time-dependent longitudinal chromoelectric field. It is demonstrated that the slab final rapidities are rather sensitive to the strength and decay time of the chromofield as well as to the back reaction of the produced partonic plasma. The net-baryon rapidity loss $\ensuremath{\langle}\ensuremath{\delta}y\ensuremath{\rangle}=2.0$, found for most central Au-Au collisions at RHIC, can be explained by the action of chromofields with the initial energy density of about 50 GeV/fm${}^{3}$. Predictions of the baryon stopping for the LHC energy are made.

QCD COLLISIONAL ENERGY LOSS IN AN INCREASINGLY INTERACTING QUARK–GLUON PLASMA

The discovery of the jet quenching in central Au + Au collisions at the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory has provided clear evidence for the formation of strongly interacting dense matter. It has been predicted to occur due to the energy loss of high energy partons that propagate through the quark–gluon plasma. In this paper we investigate the dependence of the parton energy loss due to elastic scatterings in a parton plasma on the value of the strong coupling and its running with the evolution of the system. We analyze different prescriptions for the QCD coupling and calculate the energy and length dependence of the fractional energy loss. Moreover, the partonic quenching factor for light and heavy quarks is estimated. We found that the predicted enhancement of the heavy to light hadrons (D/π) ratio is strongly dependent on the running of the QCD coupling constant.

Elastic energy loss in an expanding QGP

The discovery of the jet quenching in central Au + Au collisions at the Relativistic Heavy-ion Collider (RHIC) has provided clear evidence for the formation of strongly interacting dense matter. It has been predicted to occur due to the energy loss of high energy partons that propagate through the quark gluon plasma. Since the medium is not static and it cools while expands, the strong coupling is not fixed, running with the evolution of the system. In this work, we present an investigation of the dependence on the value of the strong coupling in the parton energy loss due to elastic scatterings in a parton plasma. We analyze different prescriptions for the QCD coupling and calculate the energy and length dependence of the fractional energy loss. Moreover, the quenching factor for light and heavy quarks is estimated. We found that the predicted enhancement of heavy to light hadrons (D/pi) ratio is strongly dependent on the running of the QCD coupling constant.

Local Thermalization in d+Au Collisions

The extent of a locally equilibrated parton plasma in d + Au collisions at sqrt(s_NN) = 200 GeV is investigated as a function of centrality in a nonequilibrium-statistical framework. Based on a three-sources model, analytical solutions of a relativistic diffusion equation are in precise agreement with recent data for charged-particle pseudorapidity distributions. The moving midrapidity source indicates the size of the local thermal equilibrium region after hadronization. In central d + Au collisions it contains 19% of the produced particles.

EOS of nonequilibrium parton plasma in an expanding flux tube

We investigate a new version of the flux-tube model based on joint action of two different processes responsible for vacuum creation of the parton plasma: the dynamical Schwinger mechanism and the geometrical mechanism linked to the dynamical Casimir effect. These two mechanisms act at different time scales. The Casimir mechanism provides the abundant generation of partons from the sea at the very early stage after the fusion of colliding nuclei and release of color degrees of freedom. Then the created plasma initiates the backreaction mechanism via the standard Schwinger scenario. This process apparently leads to fast thermalization of secondary partons. The model allows for the self-consistent description of preequilibrium evolution of the plasma, fully determined by the total energy and the total number of valence quarks of colliding nuclei. The Equation of State of the created parton plasma is discussed.

$J/\psi$ gluonic dissociation revisited: II. Hydrodynamic expansion effects

We explicitly take into account the effect of hydrodynamic expansion profile on the gluonic breakup of $J/\psi$'s produced in an equilibrating parton plasma. Attention is paid to the space-time inhomogeneities as well as Lorentz frames while deriving new expressions for the gluon number density $n_g$, average dissociation rate $<\tilde{\Gamma}>$, and $\psi$ survival probability $S$. A novel type of partial wave {\em interference} mechanism is found to operate in the formula of $<\tilde{\Gamma}>$. Nonrelativistic longitudinal expansion fro small length of the initial cylinder is found to push the $S(p_T)$ graph above the no flow case considered by us earlier \cite{rev1}. However, relativistic flow corresponding to large length of the initial cylinder pushes the curve of $S(p_T)$ downwards at LHC but upwards at RHIC. This mutually different effect on $S(p_T)$ may be attributed to the different initial temperatures generated at LHC and RHIC.

Local thermalization in the [formula omitted] system

The extent of a locally equilibrated parton plasma in d+Au collisions at sNN=200 GeV is investigated as a function of collision centrality in a nonequilibrium-statistical framework. Based on a three-sources model, analytical solutions of a relativistic diffusion equation are in precise agreement with recent data for charged-particle pseudorapidity distributions. The moving midrapidity source indicates the size of the local thermal equilibrium region after hadronization. In central d+Au collisions it contains about 19% of the produced particles, and its relative importance rises with decreasing centrality.

Chromodynamic Weibel instabilities in relativistic nuclear collisions

Employing a previously derived formulation, and extending the treatment from purely transverse modes to wave vectors having a longitudinal component, we discuss the prospects for the occurrence of Weibel-type color-current filamentation in high-energy nuclear collisions. Numerical solutions of the dispersion equation for a number of scenarios relevant to RHIC and LHC suggest that modes with (predominantly transverse) wave numbers of several hundred MeV may become moderately agitated during the early collision stage. The emergence of filamentation helps to speed up the equilibration of the parton plasma and it may lead to nonstatistical azimuthal patterns in the hadron final state.

Closed-time path integral formalism and medium effects of nonequilibrium QCD matter

We apply the closed-time path integral formalism to study the medium effects of non-equilibrium gluon matter. We derive the medium modified resummed gluon propagator to the one loop level in non-equilibrium in the covariant gauge. The gluon propagator we derive can be used to remove the infrared divergences in the secondary parton collisions to study thermalization of minijet parton plasma at RHIC and LHC.