Partonic Phase Research Articles

Critical Opalescence and Its Impact on the Jet Quenching Parameter q^

Jet quenching parameter q^ is essential for characterizing the interaction strength between jet partons and nuclear matter. Based on the quark-meson model, we develop a new framework for calculating q^ at finite chemical potentials, in which q^ is related to the spectral function of the chiral order parameter. A mean field perturbative calculation up to the one-loop order indicates that the momentum broadening of jets is enhanced at both high temperature and high chemical potential, and approximately proportional to the parton number density in the partonic phase. We further investigate the behavior of q^ in the vicinity of the critical endpoint (CEP) by coupling our calculation with a recently developed equation of state that includes a CEP in the universality class of the Ising model, from which we discover the partonic critical opalescence, i.e., the divergence of scattering rate of jets and their momentum broadening at the CEP, contributed by scatterings via the σ exchange process. Hence, for the first time, jet quenching is connected with the search of CEP.

Transverse momentum distributions of the identified particles in mini–bias non-single diffracted p＋p collisions at 200 GeV

The transverse momentum (pT) distributions of hadrons stem from the probability distributions of deconfined colored partons known as pT distributions. This provides insights into various stages of nuclear collisions, ranging from the initial partonic phase to the later stages, including the directly measurable hadronization process. The objective is to analyze the pT distributions of identified particles: π+, π−, K+, K−, K0s, p, p̄, Λ, Λ̄, Σ+, Σ−. These analyses are conducted in mini-bias non-single diffracted p+p collisions at an energy of 200GeV. The goal is to accurately determine the kinetic freezeout parameters and the extent of statistical nonextensivity. The measurements from the STAR experiment are merged with simulations using DPMJET, PYTHIA, and Sibyll.3d Monte–Carlo Event Generators. The predictions from these models and the actual measurements are compared using statistical distributions employing the Tsallis-type of non-extensive statistics. While Pythia8 displays a closer alignment with the data in certain instances, it was observed that none of the event generators could accurately replicate the data for all charged particles across the entire range of pT. We examined how the effective temperature correlates with the rest mass of different particles. Our analysis revealed that the freezeout process for heavier particles tends to occur at lower temperatures. This suggests that heavier particles might reach an equilibrium state relatively rapidly during the freezeout stage. Additionally, we observed a pattern where the non-extensive parameter q decreases as the mass of the produced particles increases. This implies that lighter particles tend to reach equilibrium after the heavier ones. Furthermore, the average transverse momentum (<pT>) is greater for heavier particles, leading to an enhanced radial flow compared to lighter particles. This rising trend also indicates the likelihood of mini-jet production, contributing to color string fragmentation that becomes more pronounced with the increasing mass of the particles.

Elliptic flow of inclusive charged hadrons in Au+Au collisions at E lab = 35 A GeV using the PHSD model

Elliptic flow (v 2) of inclusive charged hadrons at mid-rapidity (∣η∣ < 1.0) in Au+Au collisions at E lab = 35 A GeV using the parton hadron string dynamics (PHSD) model are presented as a function of centrality, transverse momentum (p T) and pseudo-rapidity (η). The v 2 results are obtained using the η-sub event plane method with respect to the event plane angle (ψ 2) and participant plane angle (). p T-integrated charged hadron v 2 shows a strong centrality dependence in Au+Au collisions at E lab = 35 A GeV. The eccentricity-scaled elliptic flow (v 2/ε 2) also shows centrality dependence. The higher values of v 2/ε 2 in central collisions suggest the development of stronger collectivity. The calculations are compared with the results from Au+Au collisions at published by the STAR experiment at RHIC. We also compare the results of HSD and PHSD modes to investigate the contribution of hadronic and partonic phases of the medium on the calculated v 2. The current results serve as a prediction of the collective behavior of the matter produced in baryon-rich and moderate temperature conditions for the upcoming multi-purpose detector at the nuclotron-based Ion collider facility (NICA) and compressed baryonic matter experiment at the facility for antiproton and ion research. These predictions are also useful for interpreting data measured at relativistic heavy ion collider (RHIC) beam energy scan program.

QCD Phase Structure and In-Medium Modifications of Meson Masses in Polyakov Linear-Sigma Model with Finite Isospin Asymmetry

In the QCD-like effective model, the Polyakov linear-sigma model, the isospin sigma field (σ¯3=fK±−fK0) and the third generator of the matrix of the explicit symmetry breaking [h3=ma02fK±−fK0] are estimated in terms of the decay constants of the neutral (fK0) and charged Kaon (fK±) and the mass of a0 meson. Both quantities σ¯3 and h3 are then evaluated, at finite baryon (μB), isospin chemical potential (μI), and temperature (T). Thereby, the dependence of the critical temperature on isospin chemical potential could be mapped out in the (T−μI) phase diagram In the QCD-like effective model, the Polyakov linear-sigma model, the isospin sigma field (σ¯3=fK±−fK0) and the third generator of the matrix of the explicit symmetry breaking [h3=ma02fK±−fK0] are estimated in terms of the decay constants of the neutral (fK0) and charged Kaon (fK±) and the mass of a0 meson. Both quantities σ¯3 and h3 are then evaluated, at finite baryon (μB), isospin chemical potential (μI), and temperature (T). Thereby, the dependence of the critical temperature on isospin chemical potential could be mapped out in the (T−μI) phase diagram. The in-medium modifications of pseudoscalars (Jpc=0−+), scalars (Jpc=0++), vectors (Jpc=1−−), and axial-vectors (Jpc=1++) meson states are then analyzed in thermal and dense medium. We conclude that the QCD phase diagram (T−μI) is qualitatively similar to the (T−μB) phase diagram. We also conclude that both temperature and isospin chemical potential enhance the in-medium modifications of the meson states a0, σ, η′, π, f0, κ, η, K, ρ, ω, κ*, ϕ, a1, f1, K*, and f1*. Regarding their chemical potential, at high temperatures the various meson states likely dissolve into colored partonic phase. In this limit, the meson masses form a universal bundle. Thus, we conclude that the increase in the chemical potential similar to temperature derives the colorless confined meson states into the colored deconfined parton phase.

Exploring critical fluctuation phenomenon according to net-proton multiplicity information entropy in AMPT model

Information entropy can be used for investigating the critical fluctuation phenomenon by describing multiplicity fluctuations in heavy-ion collisions. In this study, a multiphase transport (AMPT) model in the default version (AMPT-DEF) and with the string melting (AMPT-SM) were used as event generators to simulate the Au+Au reaction at different incident energies. Owing to the influence of the distribution bin number in extracting its information entropy, two methods, i.e., data binning and weighting factors, were proposed to correct the information entropy analysis. The comparison between information entropy and kurtosis also reflects the necessity to correct the information entropy analysis. The corrected information entropy of net-proton multiplicity was analyzed in central Au+Au collisions at sNN= 4.7, 6.4, 7.7, 8.8, 11.5, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 140, 170, and 200 GeV with the impact parameter b=3 fm. The results indicated that the fluctuations of net-proton multiplicity were essentially identical at collision energies ranging from sNN= 4.7 GeV to sNN= 200 GeV in the same model. No critical fluctuation phenomenon was found in the central Au+Au collisions simulated using the AMPT models, similar to the case of the AMPT model, which does not have. Comparing the information entropy of AMPT-SM to AMPT-DEF, the effect of partonic phase leads to a bigger fluctuation, indicating that the corrected information entropy can be a useful probe to explore the phase transition. The mid-rapidity net-proton multiplicity information entropy was also calculated, and the results led to the same conclusion. The corrected information entropy may be useful for investigating critical fluctuations, which is important for exploring critical endpoint.

Effect of color reconnection and rope formation on resonance production in p\u2013p collisions in Pythia 8

Resonance production in proton–proton collisions at sqrt{s} = 7 TeV and 13 TeV have been investigated using a Pythia 8 event generator within the framework of microscopic processes including color reconnection and rope hadronization. Specifically, the observable effects of different modes of color reconnections on the ratio of yields of mesonic and baryonic resonances with respect to their stable counterpart have been explored as a function of mean charged particle multiplicity. A suppression in the ratio is observed as a function of the mean number of charged particles for mesonic resonances. The phi /mathrm {K} and {phi /pi } ratios show an enhancement for high-multiplicity events due to enhanced production of strange quarks via the microscopic process of rope hadronization in the partonic phase. The mechanism of the hadronization of color ropes together with the quark–gluon plasma (QCD)-based color reconnection of partons predicted an enhancement in the ratio for baryonic resonances to non-resonance baryons having similar quark content. The yield ratios of resonances are found to be independent of the collision energy and strongly dependent on event activity.

Elliptic flow splittings in the Polyakov–Nambu–Jona-Lasinio transport model

To incorporate the effect of gluons on the evolution dynamics of the quark matter produced in relativistic heavy-ion collisions, we extend the three-flavor Nambu--Jona-Lasinio (NJL) transport model to include the contribution from the Polyakov loops. Imbedding the resulting pNJL partonic transport model in an extended multiphase transport (extended AMPT) model, we then study the elliptic flow splittings between particles and their antiparticles in relativistic heavy-ion collisions at beam energy scan energies. We find that a weak quark vector interaction in the partonic phase is able to describe the elliptic flow splitting between protons and antiprotons in heavy-ion collisions at $\sqrt{{s}_{NN}}=7.7$ to 39 GeV. Knowledge of the quark vector interaction is useful for understanding the equation of state of quark matter at large baryon chemical potentials and thus the location of the critical point in the QCD phase diagram.

Chiral magnetic properties of QCD phase-diagram

The QCD phase-diagram is studied, at finite magnetic field. Our calculations are based on the QCD effective model, the SU(3) Polyakov linear-sigma model (PLSM), in which the chiral symmetry is integrated in the hadron phase and in the parton phase, the up-, down- and strange-quark degrees of freedom are incorporated besides the inclusion of Polyakov loop potentials in the pure gauge limit, which are motivated by various underlying QCD symmetries. The Landau quantization and the magnetic catalysis are implemented. The response of the QCD matter to an external magnetic field such as magnetization, magnetic susceptibility and permeability has been estimated. We conclude that the parton phase has higher values of magnetization, magnetic susceptibility, and permeability relative to the hadron phase. Depending on the contributions to the Landau levels, we conclude that the chiral magnetic field enhances the chiral quark condensates and hence the chiral QCD phase-diagram, i.e. the hadron-parton phase-transition likely takes place, at lower critical temperatures and chemical potentials.

Parton collisional effect on the conversion of geometry eccentricities into momentum anisotropies in relativistic heavy-ion collisions

We explore parton collisional effects on the conversion of geometry eccentricities into azimuthal anisotropies in Pb+Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV using a multi-phase transport model. The initial eccentricity $\varepsilon_{n}$ (n = 2,3) and flow harmonics $v_{n}$ (n = 2,3) are investigated as a function of the number of parton collisions ($N_{coll}$) during the source evolution of partonic phase. It is found that partonic collisions leads to generate elliptic flow $v_{2}$ and triangular flow $v_{3}$ in Pb+Pb collisions. On the other hand, partonic collisions also result in an evolution of the eccentricity of geometry. The collisional effect on the flow conversion efficiency is therefore studied. We find that the partons with larger $N_{coll}$ show a lower flow conversion efficiency, which reflect differential behaviors with respect to $N_{coll}$. It provides an additional insight into the dynamics of the space-momentum transformation during the QGP evolution from a transport model point of view.

Contribution of third generation quarks to two-loop helicity amplitudes for W boson pair production in gluon fusion

We compute the contribution of third generation quarks (t, b) to the two-loop amplitude for on-shell W boson pair production in gluon fusion gg → WW. We present plots for the amplitude across partonic phase space as well as reference values for two kinematic points. The master integrals are efficiently evaluated by numerically solving a system of ordinary differential equations.

Production of K(892)*0 mesons in 3He+Au collisions at

Collisions of small systems such as p/d/3He+Au are important for the investigation of quark-gluon plasma (QGP) in relativistic heavy ion collisions. These experiments distinguish the effects of the initial state of cold nuclear and the final state of hot matter. The research of light hadron production is one of the leading directions in the effects of the cold and hot nuclear matter studies. Due to a short lifetime and strange quark content, the K *0-meson is sensitive to the properties of the hot dense matter and strangeness production from an early partonic phase (i.e. QGP). This report presents invariant transverse momentum spectra and nuclear modification factors (RHeAu ) of K *0-meson as a function of pT measured in 3He+Au collisions at by the PHENIX experiment. In results, the nuclear modification factors for K *0-meson in d+Au and 3He+Au collisions are in a good agreement. Values of RHeAu for K *0, φ, and π 0 mesons are equal within uncertainties in all centrality bins in the whole pT range. In conclusion, the obtained results might indicate that CNM effects are not responsible for the differences of K *0 and φ to π 0 suppression level seen in heavy ion collisions.

Exploring the partonic phase at finite chemical potential within a covariant off-shell transport approach

We report on the extended Parton-Hadron-String Dynamics (PHSD) transport approach in the partonic sector by explicitly calculating the total and differential partonic scattering cross sections as a function of temperature T and baryon chemical potential μऔ on the basis of the effective propagators and couplings from the Dynamical QuasiParticle Model (DQPM). We calculated the ratio of shear viscosity η over entropy density s, i.e. η/s is evaluated using the collisional widths and compared to lQCD calculations for μB = 0 as well. We find that the ratio η/s does not differ very much from that calculated within the original DQPM on the basis of the Kubo formalism. Furthermore, there is only a very modest change of η/s with the baryon chemical μB as a function of the scaled temperature T/TC(μ B). This also holds for a variety of hadronic observables from central A+A collisions in the energy range 5 GeV GeV when implementing the differential cross sections into the PHSD approach. Accordingly, it will be difficult to extract finite μB-signals from the partonic dynamics based on bulk observables.

Exploring the partonic phase at finite chemical potential in and out-of equilibrium

We study the influence of the baryon chemical potential μB on the properties of the Quark–Gluon–Plasma (QGP) in and out-of equilibrium. The description of the QGP in equilibrium is based on the effective propagators and couplings from the Dynamical QuasiParticle Model (DQPM) that is matched to reproduce the equation-of-state of the partonic system above the deconfinement temperature Tc from lattice Quantum Chromodynamics (QCD). We calculate the transport coefficients such as the ratio of shear viscosity ɳ and bulk viscosity ¶ over entropy density s, i.e., η/s and ¶/s in the (T, μB ) plane and compare to other model results available at μB = 0. The out-of equilibrium study of the QGP is performed within the Parton–Hadron–String Dynamics (PHSD) transport approach extended in the partonic sector by explicitly calculating the total and differential partonic scattering cross sections (based on the DQPM propagators and couplings) evaluated at the actual temperature T and baryon chemical potential μB in each individual space-time cell of the partonic scattering. The traces of their μB dependences are investigated in different observables for relativistic heavy-ion collisions with a focus on the directed and elliptic flow coefficients in the energy range 7.7 GeV ≤ .

Elliptic Flow of Hadrons via Quark Coalescence Mechanism Using the Boltzmann Transport Equation for Pb+Pb Collision at sNN=2.76 TeV

Elliptic flow of hadrons observed at relativistic heavy ion collision experiments at relativistic heavy ion collider (RHIC) and large hadron collider (LHC) provides us an important signature of possible deconfinement transition from the hadronic phase to partonic phase. However, hadronization processes of deconfined partons back into final hadrons are found to play a vital role in the observed hadronic flow. In the present work, we use a coalescence mechanism also known as recombination (ReCo) to combine quarks into hadrons. To get there, we have used the Boltzmann transport equation in relaxation time approximation to transport the quarks into equilibration and finally to freeze-out the surface, before coalescence takes place. A Boltzmann-Gibbs blast wave (BGBW) function is taken as an equilibrium function to get the final distribution and a power-like function to describe the initial distributions of partons produced in heavy ion collisions. In the present work, we try to estimate the elliptic flow of identified hadrons such as π, K, and p, produced in Pb+Pb collisions at sNN=2.76 TeV at the LHC for different centralities. The elliptic flow (v2) of identified hadrons seems to be described quite well in the available pT range. After the evolution of quarks until freeze-out time has been calculated using BTE-RTA, the approach used in this paper consists of combining two or more quarks to explain the produced hadrons at intermediate momenta regions. The formalism is found to describe the elliptic flow of hadrons produced in Pb+Pb collisions to a large extent.

Exploring the Partonic Phase at Finite Chemical Potential in and out-of Equilibrium

We study the influence of the baryon chemical potential μ B on the properties of the Quark–Gluon–Plasma (QGP) in and out-of equilibrium. The description of the QGP in equilibrium is based on the effective propagators and couplings 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 Quantum Chromodynamics (QCD). We study the transport coefficients such as the ratio of shear viscosity η and bulk viscosity ζ over entropy density s, i.e., η / s and ζ / s in the ( T , μ ) plane and compare to other model results available at μ B = 0 . The out-of equilibrium study of the QGP is performed within the Parton–Hadron–String Dynamics (PHSD) transport approach extended in the partonic sector by explicitly calculating the total and differential partonic scattering cross sections based on the DQPM and the evaluated at actual temperature T and baryon chemical potential μ B in each individual space-time cell where partonic scattering takes place. The traces of their μ B dependences are investigated in different observables for symmetric Au + Au and asymmetric Cu + Au collisions such as rapidity and m T -distributions and directed and elliptic flow coefficients v 1 , v 2 in the energy range 7.7 GeV ≤ s N N ≤ 200 GeV.

Extracting jet transport parameter $$\hat{q}$$ from a multiphase transport model

Within a multi-phase transport model with string melting scenario, jet transport parameter $\hat{q}$ is calculated in Au+Au collisions at $\sqrt{s_{NN} } $= 200 GeV and Pb+Pb collisions at $\sqrt{s_{NN} } $= 2.76 TeV. The $\hat{q}$ increases with the increasing of jet energy for both partonic phase and hadronic phase. The energy and path length dependences of $\hat{q}$ in full heavy-ion evolution are consistent with the expectations of jet quenching. The correlation between jet transport parameter $\hat{q}$ and dijet transverse momentum asymmetry $A_{J}$ is mainly investigated, which discloses that a larger $\hat{q}$ corresponds to a larger $A_{J}$. It supports a consistent jet energy loss picture from the two viewpoints of single jet and dijet. It is proposed to measure dijet asymmetry distributions with different jet transport parameter ranges as a new potential method to study jet quenching physics in high energy heavy-ion collisions.

Flow and vorticity with varying chemical potential in relativistic heavy ion collisions

We study the vorticity patterns in relativistic heavy ion collisions with respect to the collision energy. The collision energy is related to the chemical potential used in the thermal — statistical models that assume approximate chemical equilibrium after the relativistic collision. We use the multiphase transport model (AMPT) to study the vorticity in the initial parton phase as well as the final hadronic phase of the relativistic heavy ion collision. We find that as the chemical potential increases, the vortices are larger in size. Using different definitions of vorticity, we find that vorticity plays a greater role at lower collision energies than at higher collision energies. We also look at other effects of the flow patterns related to the shear viscosity at different collision energies. We find that the shear viscosity obtained is almost a constant with a small decrease at higher collision energies. We also look at the elliptic flow as it is related to viscous effects in the final stages after the collision. Our results indicate that the viscosity plays a greater role at higher chemical potential and lower collision energies.

Exploring the partonic phase at finite chemical potential within an extended off‐shell transport approach

AbstractWe extend the parton‐hadron‐string dynamics (PHSD) transport approach in the partonic sector by explicitly calculating the total and differential partonic scattering cross sections as a function of temperature T and baryon chemical potential μB on the basis of the effective propagators and couplings from the dynamical quasiparticle model (DQPM) that is matched to reproduce the equation of state of the partonic system above the deconfinement temperature Tc from lattice quantum chromodynamics (QCD). We calculate the collisional widths for the partonic degrees of freedom at finite T and μB in the time‐like sector and conclude that the quasiparticle limit holds sufficiently well. Furthermore, the ratio of shear viscosity η over entropy density s, that is, η/s, is evaluated using the collisional widths and compared to lattice QCD(lQCD) calculations for μB = 0 as well. We find that the ratio η/s does not differ very much from that calculated within the original DQPM on the basis of the Kubo formalism. Furthermore, there is only a very modest change of η/s with the baryon chemical μB as a function of the scaled temperature T/Tc(μB). This also holds for a variety of hadronic observables from central A + A collisions in the energy range 5 GeV 200 GeV when implementing the differential cross sections into the PHSD approach. Accordingly, it will be difficult to extract finite μB signals from the partonic dynamics based on “bulk” observables.

Isospin splitting of pion elliptic flow in relativistic heavy-ion collisions

Based on the framework of an extended multiphase transport model with mean-field potentials in both the partonic phase and the hadronic phase, we explain the elliptic flow difference between π+ and π− in the beam-energy scan program at the relativistic heavy-ion collider by incorporating the vector-isovector potential for quarks and antiquarks with different flavors or isospins. It is found that the isospin splitting of pion elliptic flow favors a strong vector-isovector interaction, and thus serves as a probe of the quark matter equation of state as well as the QCD phase structure at finite baryon and isospin chemical potentials.

Exploring the partonic phase at finite chemical potential within an extended off-shell transport approach

We extend the Parton-Hadron-String Dynamics (PHSD) transport approach in the partonic sector by explicitly calculating the total and differential partonic scattering cross sections as a function of temperature $T$ and baryon chemical potential $\mu_B$ on the basis of the effective propagators and couplings 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. The ratio of shear viscosity $\eta$ over entropy density $s$, i.e. $\eta/s$, is evaluated using the collisional widths and compared to lQCD calculations for $\mu_B$ = 0 as well. We find only a very modest change of $\eta/s$ with the baryon chemical $\mu_B$. This also holds for a variety of hadronic observables from central A+A and C+Au collisions in the energy range 5 GeV $\leq \sqrt{s_{NN}} \leq$ 200 GeV when implementing the differential cross sections into the PHSD approach. We only observe small differences in the strangeness and antibaryon sector with practically no sensitivity of rapidity and $p_T$ distributions to the $\mu_B$ dependence of the partonic cross sections. Since we find only small traces of a $\mu_B$-dependence in heavy-ion observables - although the effective partonic masses and widths as well as their partonic cross sections clearly depend on $\mu_B$ - this implies that one needs a sizable partonic density and large space-time QGP volume to explore the dynamics in the partonic phase. These conditions are only fulfilled at high bombarding energies where $\mu_B$ is, however, rather low. On the other hand, when decreasing the bombarding energy and thus increasing $\mu_B$, the hadronic phase becomes dominant and accordingly, it will be difficult to extract signals from the partonic dynamics based on "bulk" observables.