arXiv subjects

X. G. Deng

Publications and source records attributed to X. G. Deng.

13 recordsLinked to original sources

arXiv2025

Dual-polarization structure and nuclear structure effect on $Λ$ polarization

We report a novel manifestation of spin-vorticity interplay in relativistic heavy-ion collisions. Using $^{16}$O+$^{197}$Au at $\sqrt{s_{\rm NN}}=7.7$ GeV as a test case, we show that the $Λ$ hyperon exhibits a clear dual-polarization structure, observed here in central $^{16}$O + $^{197}$Au collisions for the first time. The polarization is further highly sensitive to the intrinsic nuclear geometry: different $α$-cluster configurations of $^{16}$O, ranging from chain-like to tetrahedral, lead to distinct polarization patterns across centralities. In particular, the backward rapidity region and peripheral events display striking structure-dependent variations, including opposite angular distributions of local polarizations $P_x$ and $P_y$ compared with a spherical reference. These findings reveal that nuclear clustering leaves measurable imprints on hyperon spin alignment in relativistic collisions. Our results open a promising avenue for probing nuclear structure in short-lived systems and highlight a new spin-sensitive mechanism relevant for upcoming experiments at RHIC and future facilities.

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arXiv2025

Bayesian inference of nuclear incompressibility from collective flow in mid-central Au+Au collisions at 400--1500 MeV/nucleon

The incompressibility $K$ of symmetric nuclear matter (SNM) is determined through a Bayesian analysis of collective flow data from Au + Au collisions at beam energies $E = 400 -1500$ MeV/nucleon. This analysis utilizes a Gaussian process (GP) emulator applied to the isospin-dependent quantum molecular dynamics (IQMD) model for heavy-ion collisions, both with and without incorporating the momentum dependence of the single-nucleon potentials. Specifically, the inferred incompressibility values are $K=188.9^{+2.9}_{-4.5}$ MeV and $256.1^{+8.2}_{-8.7}$ MeV at $E = 400$ MeV/nucleon, respectively, at the 68\% confidence level using rapidity and transverse velocity dependence of proton elliptic flow data, with and without consideration of the momentum dependence. When the transverse momentum dependence of proton-like directed flow data is included, the inferred incompressibility values become $K=222.3^{+9.0}_{-9.9}$ MeV and $K=285.5^{+6.7}_{-7.3}$ MeV, respectively. Furthermore, we found that the value of $K$ derived from observables of proton elliptic flow increases with beam energy. This indicates that the equation of state (EoS) of nuclear matter hardens at higher densities and temperatures in reactions with higher beam energies.

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arXiv2025

Influence of Cluster Configurations and Nucleon--Nucleon Scattering Cross-Section on Stopping Power in Heavy-Ion Collisions

We investigate the impacts of nuclear $α$-clustering structures and nucleon--nucleon cross-section on nuclear stopping power for ${}^{16}\text{O}$ + ${}^{40}\text{Ca}$ collisions below 300 MeV/nucleon using an extended quantum molecular dynamics (EQMD) model. Our results show that the specific $α$-clustering configurations of ${}^{16}\text{O}$--including chain, square, kite, and tetrahedron--have a significant effect on collision dynamics. Among them, the tightly bound tetrahedral structure exhibits the highest stopping power. Moreover, the repulsive Coulomb interaction is found to reduce the stopping power of protons in the Fermi-energy domain. At higher energies, the decreasing trend is influenced by both the nucleon--nucleon cross-section and the mean field.

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arXiv2023

Effect of initial-state geometric configurations on the nuclear liquid-gas phase transition

Within the framework of an extended quantum molecular dynamics model, we simulated $^{40}$Ca + $^{16}$O collisions at beam energies ranging from 60 to 150 MeV/nucleon for $^{16}$O with different $α$-cluster configurations. Results imply that different $α$-cluster configurations lead to different yields of deuteron, triton, $^3$He and $^4$He, but not for proton and neutron. We discuss the effect of geometric fluctuations which are presented by double ratios of light nuclei, namely $\mathcal{O}_\text{p-d-t}$ and $\mathcal{O}_\text{p-d-He}$. It is found that magnitude hierarchy of geometric fluctuations is chain, kite, square and tetrahedron structure of $^{16}$O. $\mathcal{O}_\text{p-d-t}$ has maximum value around 80 -- 100 MeV/nucleon which could be related to liquid-gas phase transition, that is consistent with results from the charge distribution of the heaviest fragments in the collisions.

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arXiv2021

Green-Kubo formula for Boltzmann and Fermi-Dirac statistics

Shear viscosity of nuclear matter is extracted via the Green-Kubo formula and the Gaussian thermostated SLLOD algorithm (the shear rate method) in a periodic box by using an improved quantum molecular dynamic (ImQMD) model without mean field, also it is calculated by a Boltzmann-type equation. Here a new form of the Green-Kubo formula is put forward in the present work. For classical limit at nuclear matter densities of $0.4ρ_{0}$ and $1.0ρ_{0}$, shear viscosity by the traditional and new form of the Green-Kubo formula as well as the SLLOD algorithm are coincident with each other. However, for non-classical limit, shear viscosity by the traditional form of the Green-Kubo formula is higher than those obtained by the new form of the Green-Kubo formula as well as the SLLOD algorithm especially in low temperature region. In addition, shear viscosity from the Boltzmann-type equation is found to be less than that by the Green-Kubo method or the SLLOD algorithm for both classical and non-classical limits.

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arXiv2021

Determining the temperature in heavy-ion collisions with multiplicity distribution

By relating the charge multiplicity distribution and the temperature of a de-exciting nucleus through a deep neural network, we propose that the charge multiplicity distribution can be used as a thermometer of heavy-ion collisions. Based on an isospin-dependent quantum molecular dynamics model, we study the caloric curve of reaction $^{103}$Pd + $^9$Be with the apparent temperature determined through the charge multiplicity distribution. The caloric curve shows a characteristic signature of nuclear liquid-gas phase transition around the apparent temperature $T_{\rm ap}$ $=$ $6.4~\rm MeV$, which is consistent with that through a traditional heavy-ion collision thermometer, and indicates the viability of determining the temperature in heavy-ion collisions with multiplicity distribution.

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arXiv2020

Light nuclei production in Au + Au collisions at $\sqrt{s_{NN}}$ = 7.7-80 GeV from UrQMD model

Light nuclei production in relativistic $^{197}$Au + $^{197}$Au collisions from 7.7 to 80 GeV is investigated within the Ultra-relativistic-Quantum-Molecular-Dynamics model (UrQMD) with a naive coalescence approach. The results of the production of light nuclei at midrapidity can essentially match up the experimental data and a slight enhancement of combined ratio of ${N_{p}N_{t}}/{N_{d}^{2}}$ where $N_p, N_d$ and $N_t$ represent respectively the yields of proton, deuteron and triton, which is sensitive to the neutron density fluctuations, occurs around 20 GeV. However, this enhanced ${N_{p}N_{t}}/{N_{d}^{2}}$ ratio should not be over-understood considering that the present UrQMD model is a cascade version without equation of state (EoS), i.e. there is an absence of critical end point mechanism. Furthermore, within different rapidity regions, the kinetic temperatures of different light nuclei are extracted by the Blast-wave model analysis and ratios among different light nuclei are also discussed.

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arXiv2020

Magnetic field effects in peripheral heavy-ion collisions around 1 GeV/nucleon

Magnetic field effects on free nucleons are studied in peripheral collisions of $^{197}$Au + $^{197}$Au at energies ranging from 600 to 1500 MeV/nucleon by utilizing an isospin-dependent quantum molecular dynamics (IQMD) model. With the help of angular distributions and two-particle angular correlators, the magnetic field effect at an impact parameter of 11 fm is found to be more obvious than at an impact parameter of 8 fm. Moreover, the results suggest that with an increase in the number of peripheral collisions, protons are more easily condensed with the magnetic field. Magnetic field effects are further investigated by the ratio of free neutrons to free protons as functions of a two-particle correlator $C_{2}$, four-particle correlator $C_{4}$ and six-particle correlator $C_{6}$ of angle $ϕ$, rapidity $Y$ and transverse momentum $p_{T}$. The results show that weak magnetic field effects could be revealed more clearly by these multiple-particle correlators, with the larger number of particle correlators demonstrating a clear signal. The results highlight a new method to search for weak signals using multi-particle correlators.

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arXiv2019

Yield ratio of neutrons to protons in $^{12}C(d,n)^{13}$N and $^{12}C(d,p)^{13}$C from 0.6 MeV to 3 MeV

The neutron yield in $^{12}$C(d,n)$^{13}$N and the proton yield in $^{12}C(d,p)^{13}$C have been measured by deuteron beam from 0.6 MeV to 3 MeV which is delivered from a 4-MeV electro static accelerator bombarding on the thick carbon target. The neutrons are detected at $0\degree$, $24\degree$, $48\degree$ and the protons at $135\degree$ in the lab frame. The ratios of the neutron yield to the proton one have been calculated and can be used as an effective probe to pin down the resonances. The resonances are found at 1.4 MeV, 1.7 MeV, 2.5 MeV in $^{12}C(d,p)^{13}$C and at 1.6 MeV, 2.7 MeV in $^{12}$C(d,n)$^{13}$N. This method provides a way to reduce the systematic uncertainty and helps to confirm more resonances in compound nuclei.

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arXiv2019

Nuclear probes of an out-of-equilibrium plasma at the highest compression

We report the highest compression reached in laboratory plasmas using eight laser beams, E$_{laser}$$\approx$12 kJ, $τ_{laser}$=2 ns in third harmonic on a CD$_2$ target at the ShenGuang-II Upgrade (SGII-Up) facility in Shanghai, China. We estimate the deuterium density $ρ_D$= 2.0 $\pm$ 0.9 kg/cm$^{3}$, and the average kinetic energy of the plasma ions less than 1 keV. The highest reached areal density $Λρ_{D}$=4.8 $\pm$ 1.5 g/cm$^{2}$ was obtained from the measured ratio of the sequential ternary fusion reactions (dd$\rightarrow$t+p and t+d$\rightarrow$$α$+n) and the two body reaction fusions (dd$\rightarrow$$^3$He+n). At such high densities, sequential ternary and also quaternary nuclear reactions become important as well (i.e. n(14.1 MeV) + $^{12}$C $\rightarrow$ n'+$^{12}$C* etc.) resulting in a shift of the neutron (and proton) kinetic energies from their birth values. The Down Scatter Ratio (DSR-quaternary nuclear reactions) method, i.e. the ratio of the 10-12MeV neutrons divided by the total number of 14.1MeV neutrons produced, confirms the high densities reported above. The estimated lifetime of the highly compressed plasma is 52 $\pm$ 9 ps, much smaller than the lasers pulse duration.

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arXiv2018

Mean free path and shear viscosity in central $^{129}$Xe+$^{119}$Sn collisions below 100 MeV/nucleon

Thermal and transport properties of hot nuclear matter formed in central $^{129}$Xe + $^{119}$Sn collisions at the Fermi energy are investigated using the isospin-dependent quantum molecular dynamical (IQMD) model. Temperature ($T$), average density ($ρ$), chemical potential ($μ$), mean momentum ($P$), shear viscosity ($η$) and entropy density ($s$) are obtained from the phase-space information. The mean free path ($λ_{nn}$) and the in-medium nucleon-nucleon cross section ($σ_{nn}$) in the highest compressible stage at different incident energies are deduced and compared with the experimental results from Phys. Rev. C $\bf{90}$ (2014) 064602. The result shows that $λ_{nn}$ and $σ_{nn}$ have the same trend and similar values as the experimental results when the beam energy is greater than 40 MeV/u at maximum compressed state. Furthermore, the derived shear viscosity over entropy density ($η/s$) shows a decreasing behaviour to a saturated value around $\frac{3}{4π}$ as a function of incident energy.

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arXiv2017

Iso-vector dipole resonance and shear viscosity in low energy heavy-ion collision

The ratio of shear viscosity over entropy density in low energy heavy-ion collision has been calculated by using the Green-Kubo method in the framework of an extended quantum molecular dynamics model. After the system almost reaching a local equilibration for a head-on $^{40}$Ca+$^{100}$Mo collision, thermodynamic and transport properties are extracted. Meanwhile, iso-vector giant dipole resonance (IVGDR) of the collision system is also studied. By the Gaussian fits to the IVGDR photon spectra, the peak energies of IVGDR are extracted at different incident energies. The result shows that the IVGDR peak energy has a positive correlation with the ratio of shear viscosity over entropy density. This is a quantum effect and indicates a difference between nuclear matter and classical fluid.

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arXiv2016

Thermal and transport properties in central heavy-ion reactions around a few hundred MeV/nucleon

Thermalization process of nuclear matter in central fireball region of heavy-ion collisions is investigated by employing an extension model of Boltzmann-Uehling-Uhlenbeck, namely the Van der Waals Boltzmann-Uehling-Uhlenbeck (VdWBUU) model. Temperature ($T$) is extracted by the quantum Fermion fluctuation approach and other thermodynamic quantities, such as density ($ρ$), entropy density ($s$), shear viscosity ($η$), isospin diffusivity ($D_{I}$) and heat conductivity ($κ$), are also deduced. The liquid-like and gas-like phase signs are discussed through the behavior of shear viscosity during heavy-ion collisions process with the VdWBUU model.

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