arXiv subjects

De-Xian Wei

Publications and source records attributed to De-Xian Wei.

11 recordsLinked to original sources

arXiv2026

Impact of spin polarization on the QCD equation of state

Spin polarization provides a novel probe of the rotational properties of the quark-gluon plasma formed in relativistic heavy-ion collisions. This work investigates the equation of state, particularly its transport and thermodynamic coefficients in noncentral O+O collisions, employing a parton distribution function that incorporates spin polarization induced by thermal vorticity. Within a kinetic theory framework, one finds that the magnitude of the squared speed of sound ($c_s^2$) is only weakly modified by spin polarization, whereas the specific shear viscosity ($η/s$), specific bulk viscosity ($ζ/s$), and mean free path ($λ$) show substantial changes. When spin polarization is included, both $c_s^2$ and $ζ/s$ develop a nonmonotonic dependence on the collision energy, with an inflection point near $\sqrt{s_{NN}}=27$ GeV, corresponding to an average parton chemical potential of $\langleμ_p\rangle=0.021$ GeV. These results suggest that spin polarization may serve as a useful probe for constraining the effective equation of state of QCD matter.

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arXiv2025

Impact of spin polarization on transport and thermodynamic coefficients

This work investigates the influence of parton spin polarization on effective transport and thermodynamic coefficients in noncentral light- and heavy-ion collisions. To model this influence, I consider two sources of spin polarization: thermal vorticity, induced by angular momentum, and thermal shear, arising from local velocity gradients. Using a novel kinetic theory framework, one finds that transport and thermodynamic coefficients -- including the speed of sound squared $c_{s}^{2}$, specific shear viscosity $η/s$, specific bulk viscosity $ζ/s$, and mean free path $λ$ -- are substantially modified by spin polarization effects. Among the two sources, thermal vorticity-induced spin polarization dominates the modifications to these coefficients. Moreover, both $c_{s}^{2}$ and $ζ/s$ exhibit a nonmonotonic dependence on the collision energy, and the associated scaling behaviors potentially serve as indicators of the critical phenomena of quantum chromodynamics.

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arXiv2025

Dynamical quark mass and finite volume effects in the Dyson-Schwinger Equations

Within the framework of Dyson-Schwinger equations(DSEs) and by means of the Multiple Reflection Expansion approximation, we study the finite volume effects of the constituent quark mass in a strong external magnetic field. Since the magnetic field has influence on the coupling constant, the coupling constant controls the strength of strongly interaction in QCD, so we adopt the magnetic-field-dependent running coupling constant in simulation. The results show that in addition to the magnetic field, the masses of constituent quarks also have a significant dependence on the volume and the running coupling constant. The model behaves close to the infinite volume limit for large size, but the effect of the finite volume is significant when the system size $R$ is about $2-6$ fm.The finite volume effects and the magnetic-field-dependent running coupling constant have considerable influence on the phase transition.

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arXiv2024

Volume fluctuations affect on transport and thermodynamic coefficients in p-Pb systems

We use A Multi-Phase Transport (AMPT) model to simulate the event-by-event p-Pb collisions at $\sqrt{s_{NN}}$=5.02 TeV. To study the space-time volume fluctuations, two different definitions of radius have been introduced in the calculation: One is weigh of event-by-event charged multiplicity (noted as set I), and the other one is weigh of energy density in a single event (notes as set II). Based on calculations of sets I and II, the transport and thermodynamic coefficients, such as the speed of sound squared, shear viscosity, bulk viscosity, and mean free path are both dependent on the radius and local temperature. By comparing results of sets I and II, we found that these transport and thermodynamic coefficients differed significantly in the results. These results imply that the transport and thermodynamic properties of the medium in small collisions significantly depend on the space-time volume fluctuations.

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arXiv2023

Quark condensate and magnetic moment in a strong magnetic field

This paper studies the quark condensate, magnetic moment, magnetic polarization, and magnetic susceptibility in a strong external magnetic field by employing the Dyson-Schwinger equations (DSE). The results show that these physical quantities as functions of the magnetic field. We note that the quark's spin polarizations are approximately proportional to the magnetic field magnitude. For comparison, we investigate the magnetic moments and susceptibility of the nucleon in the constituent quark model framework and demonstrate that both these quantities increase as the magnetic field rises.

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arXiv2022

Event-shaped-dependent cumulants in p-Pb collisions at 5.02 TeV

In this paper, we present a novel event-shaped cumulants (ESC) response approach, based on a multi-phase transport (AMPT) model simulations, to analyze p-Pb collisions at $\sqrt{s_{NN}}$= 5.02 TeV. We find that the Pearson coefficients between the subset cumulants of the final harmonics $v_{2}\{2k\}~(k=1,2,3,4)$ and the subset cumulants of initial eccentricity $\varepsilon_{2}\{2k\}$ in the ESC basis are significantly enhanced. These Pearson coefficients are strongly-dependent on the charged multiplicity, the set number of events (SNE), and only weakly-dependent on the order of the multi-particle cumulants (two-particles, four-particles, and so on). Our results show that the ESC method can suppress the event-by-event fluctuations.

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arXiv2021

Parton evolution time dependent transverse shape asymmetry in peripheral Pb-Pb and p-Pb collisions at 5.02 TeV

In this paper, we use a multi-phase transport model to simulate the parton evolution time-dependent transverse asymmetry in peripheral Pb-Pb (b=14-15 fm) and p-Pb (b=0-1 fm) collisions at $\sqrt{s_{NN}}$= 5.02 TeV, respectively. The simulated results showed that the initial spatial asymmetry depends on the collision system, while both the initial momentum asymmetry and final momentum asymmetry are independent on the collision system. It is also shown that the final momentum asymmetry is similar to the initial momentum asymmetry. Furthermore, the averaged transverse shape asymmetry, which includes the initial spatial asymmetry, the initial momentum asymmetry, and the final momentum asymmetry, is significantly dependent on the transverse momentum and particle species identity (PID). The PID scales ordering transverse asymmetry indicated that it provides a possible observation for studying the fluctuating droplet properties of quark-gluon plasma, which may produce in heavy-ion collisions.

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arXiv2020

Transverse momentum dependent decorrelation in Pb-Pb collisions at LHC

Based on A Multi-Phase Transport (AMPT) model simulations, the transverse momentum dependent decorrelation has been studied in Pb-Pb collisions at $\sqrt{s_{NN}}$= 2.76 and 5.02 TeV, respectively. It has been found that the mix-order factorization ratio $r_{m, n}$ value deviates significantly from unity in noncentral collisions. Such effect becomes stronger with an increase in the $p_{T}$ difference $p_{T}^{a}-p_{T}^{b}$. These decorrelations are not only between the same order harmonic but also between the different order harmonic, which as a result of the initial fluctuations appear between the different phase spaces. It has also been found that the correlations involving higher powers of the flow vector yield stronger decorrelation, $r_{m|n;3}<r_{m|n;2}<r_{m|n;1}~(m=2,3; n=2,3,4,5)$, except for the weighted factorization ratio $r_{3|4;k}$. The breaking phenomenon of these factorization ratios indicated that it provides a possible observation for studying the initial fluctuation properties of heavy-ion collisions.

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arXiv2020

Response relation in Pb-Pb and p-Pb collisions at 5.02 TeV

We carry out simulations using a multi-phase transport (AMPT) model to describe the response relation between $v_2$ and $\varepsilon_2$ in Pb-Pb and p-Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV, respectively. To simulate such relation, two methods have been introduced in the calculation: one is the directed response (DR) method, which correlates the outgoing particles with the initial anisotropy directly, and the other one is the cumulants response (CR) method, which is constructed from a cumulants correlation between outgoing particles. Based on calculations of the DR and CR methods, the response relations as a function of the transverse momentum are both shown in Pb-Pb and p-Pb collisions. By comparing the DR and CR methods, we found that the linear response relations are almost identical in all the present collisions. Similar results of linear+cubic response relations are also shown in the higher multiplicity systems, and it has become a significant difference in the lower multiplicity systems, i.e., the peripheral Pb-Pb collisions and p-Pb collisions. Throughout the whole $p_{T}$-dependent simulations, the $κ_2$ in the linear response and in the linear+cubic response are almost identical, except for in the lower multiplicity systems by the DR method. If one implements a pseudorapidity gap by the CR calculation, the $p_{T}$-dependent and $η$-independent response relations are similarly shown in peripheral Pb-Pb systems and p-Pb systems, which may imply that a collective response exists in the most central p-Pb collisions. These collective behaviors are dominantly produced on the stage of the medium expansions.

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arXiv2019

Thermal vorticity and spin polarization in heavy-ion collisions

The hot and dense matter generated in heavy-ion collisions contains intricate vortical structure in which the local fluid vorticity can be very large. Such vorticity can polarize the spin of the produced particles. We study the event-by-event generation of the so-called thermal vorticity in Au + Au collisions at energy region $\sqrt{s}=7.7-200$ GeV and calculate its time evolution, spatial distribution, etc., in a multiphase transport (AMPT) model. We then compute the spin polarization of the $Λ$ and $\barΛ$ hyperons as a function of $\sqrt{s}$, transverse momentum $p_T$, rapidity, and azimuthal angle. Furthermore, we study the harmonic flow of the spin, in a manner analogous to the harmonic flow of the particle number. The measurement of the spin harmonic flow may provide a way to probe the vortical structure in heavy-ion collisions. We also discuss the spin polarization of $Ξ^0$ and $Ω^-$ hyperons which may provide further information about the spin polarization mechanism of hadrons.

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arXiv2018

Hydrodynamic response in simulations within a multiphase transport model

We carry out simulations using a multiphase transport (AMPT) model to describe the observed flow signatures in $\sqrt{s_{NN}}=2.76$ TeV Pb-Pb collisions. Especially, we calculate the flow fluctuations of $v_2$ in terms of cumulant ratios and the standardized skewness. Based on event-by-event AMPT simulations, we study the linear and cubic response relation between $v_2$ and $\varepsilon_2$. We found that the observed response relation is compatible to what has been noticed in hydrodynamic modelings, with similar dependence on shear viscosity. Besides, this response relation is not sensitive to nonflow effects.

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