arXiv subjects

Manzi Nan

Publications and source records attributed to Manzi Nan.

6 recordsLinked to original sources

arXiv2025

Unlocking the initial neutron density distribution from the two-pion HBT correlation function in heavy-ion collisions

Revealing the neutron density distribution in the nucleus is one of the crucial tasks of nuclear physics. Within the framework of the ultrarelativistic quantum molecular dynamic model followed by a correlation afterburner program, we investigate the effects of the initial neutron density distribution on the charged-pion yield ratio $π^{-}/π^{+}$, the two-pion momentum correlation function, and the emission source dimension. It is found that the $π^{-}/π^{+}$ ratio is sensitive to the initial neutron density distribution and the impact parameter, especially for collisions at large impact parameter. However, the charge splitting in the correlation functions between positively $π^{+}π^{+}$ and negatively $π^{-}π^{-}$, as well as the source radii and volumes extracted exhibit a stronger dependence on the initial neutron density distribution, but a weaker dependence on the impact parameter. The present study highlights that $π^{+}π^{+}$ and $π^{-}π^{-}$ correlation functions in heavy-ion collisions could be used to probe the initial neutron density distribution of nuclei.

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arXiv2025

Temperature dependence of the nucleon-nucleon inelastic cross section in an isospin-asymmetric nuclear medium

The nucleon-nucleon ($NN$) inelastic cross section plays an important role in constraining the nuclear equation of state at high baryon density and in describing the formation and evolution of compact astrophysical objects. In this study, the temperature $T$ dependence of the $\Delta^{++}$ and $\Delta^{-}$ production cross sections in the isospin-symmetric and -asymmetric nuclear medium is investigated within the self-consistent and relativistic Boltzmann-Uehling-Uhlenbeck (RBUU) framework. Two relativistic mean-field parameterizations are employed: the density-dependent parameterization (called DD-ME$\delta$) and the nonlinear-dependent parameterization (called OMEG). Both parameterizations yield similar $T$-dependent baryon effective masses and mass splittings, although the OMEG set exhibits a stronger density dependence, particularly at higher densities ($> 1.5\rho_{0}$). Consequently, at lower densities, the energy, density, temperature, and isospin dependence of both $\Delta^{++}$ and $\Delta^{-}$ production cross sections are comparable for both sets, whereas at higher densities, the OMEG set predicts a stronger temperature and density sensitivity. Moreover, the $T$ dependence of the $NN$ inelastic cross section is enhanced with increasing density, but is suppressed in isospin-asymmetric nuclear matter compared to that in isospin-symmetric nuclear matter. The isospin dependence of the cross section remains nearly $T$-independent at small asymmetries, yet becomes more intricate in highly asymmetric systems. These findings provide valuable testing inputs for improving the thermal treatment of $\Delta$ related dynamical processes in transport models and offer insights into the behavior of $\Delta$ in astrophysical environments, such as core-collapse supernovae and binary neutron star mergers.

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arXiv2025

A novel filtering method for generating desired density profiles of colliding nuclei

Accurate modeling of the density profile is essential for studying heavy-ion collisions (HICs) with a transport model. Within the framework of the quantum molecular dynamics (QMD)-type model, a novel method for generating desired nuclear density distributions based on Fourier series expansion is proposed. This new initialization method is further incorporated into the ultrarelativistic quantum molecular dynamics model, and the bubble-like density distribution of $^{96}$Ru is constructed. Then, by simulating $^{96}$Ru+$^{96}$Ru collisions at $E_{\rm lab}=1500$ MeV/nucleon with different equations of state (EoS) and initialization methods, the effects of the initial density distribution on the final state observables and the constrained information of EoS are analyzed. It is found that $^{96}$Ru nuclei with a bubble density profile lead to an increased maximum compression during the collision, which in turn enhances the collective flow. Moreover, a relatively stiff EoS with $K_0>280$ MeV is favored for the conventional Woods-Saxon type density profile, whereas an EoS with $K_0$=200-280 MeV is supported when a bubble-like density profile is employed. These results demonstrate that the initial nuclear density distribution plays a non-negligible role in dynamical observables and EoS constraints. The proposed method thus provides a powerful tool for constructing exotic profiles and investigating nuclear structure effects in HICs.

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arXiv2025

Bayesian analysis of properties of nuclear matter with the FOPI experimental data

Based on the ultra-relativistic quantum molecular dynamics (UrQMD) transport model, combined with experimental data of directed flow, elliptic flow, and nuclear stopping power measured by FOPI in $\rm ^{197}Au+^{197}Au$ collisions at beam energies ($E_{lab}$) of 0.25 and 0.4 GeV/nucleon, the incompressibility of the nuclear equation of state $K_0$, the nucleon effective mass $m^*$, and the in-medium correction factor ($F$, with respect to free-space values) on the nucleon-nucleon elastic cross sections are studied by Bayesian analysis. It is found that both $m^*$ and $F$ can be tightly constrained with the uncertainty $\le$ 15\%, however, $K_0$ cannot be constrained tightly. We deduce $m^*/m_0 = 0.78^{+0.09}_{-0.10}$ and $F = 0.75^{+0.08}_{-0.07}$ with experimental data at $E_{lab}$ = 0.25 GeV/nucleon, and the obtained values increased to $m^*/m_0 = 0.88^{+0.03}_{-0.03}$ and $F = 0.88^{+0.06}_{-0.07}$ at $E_{lab}$ = 0.4 GeV/nucleon. The obtained results are further verified with rapidity-dependent flow data.

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arXiv2025

Nucleon-$Δ$ elastic cross section in isospin-asymmetric nuclear medium with inclusion of scalar-isovector $δ$ meson field

The production, dynamic evolution, and decay of $Δ$ particles play a crucial role in understanding the properties of high baryon density nuclear matter in intermediate-energy heavy-ion collisions. In this work, the energy-, density-, and isospin-dependent nucleon-$Δ$ elastic cross section ($σ^{*}_{N Δ}$) is studied within the relativistic Boltzmann-Uehling-Uhlenbeck framework, in which the $δ$ meson field is further considered. The results show that the $δ$ and $ρ$ meson related exchange terms have a nonnegligible contribution to the $σ^{*}_{N Δ}$ compared to only considering the $ρ$ meson exchange terms, although there is a significant cancellation on the cross section among these meson exchange terms. In addition, due to the different effects of the medium correction on the effective mass of neutrons, protons, and differently charged $Δ$s, the individual $σ^{*}_{N Δ}$ exhibits an ordered isospin-asymmetry ($α$) dependence, and $σ^{*}_{nΔ}$ and $σ^{*}_{pΔ}$ have opposite $α$ dependencies. And the $α$ dependence of the ratio $R(α)=σ^{*}(α)/σ^{*}(α=0)$ for $nΔ$ reaction channels follow $nΔ^{++}>nΔ^{+}>nΔ^{0}>nΔ^{-}$, while for $pΔ$ it is $pΔ^{-}>pΔ^{0}>pΔ^{+}>pΔ^{++}$. Moreover, the results also indicate that the isospin effect on the $σ^{*}_{N Δ}$, which is dominantly caused by the isovector $ρ$ and $δ$ meson fields, is still pronounced at densities up to 3 times normal nuclear density. Finally, a parametrization of the energy-, density-, and isospin-dependent $NΔ$ elastic cross section is proposed based on the microscopic calculated results, and the in-medium $σ^{*}_{N Δ}$ in the energy range of $\sqrt{s}$=2.3$\sim$3.0 GeV can be well described.

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arXiv2024

Isospin-dependent in-medium nucleon-Delta elastic cross section

In heavy-ion collisions at intermediate energies, the production and propagation of $Δ$ particles are crucial to understanding the nuclear equation of state and inferring the properties of nuclear matter at high densities. Based on the self-consistent relativistic Boltzmann-Uehling-Uhlenbeck (RBUU) transport theory, by introducing the isovector $ρ$ meson exchange into the effective Lagrangian and adopting the density-dependent coupling constants, the detailed expressions for isospin-dependent in-medium $NΔ\rightarrow NΔ$ elastic cross sections $σ_{NΔ}^{*}$ have been calculated. The energy and density dependence of the isospin-related $σ_{NΔ}^{*}$ as well as the total contributions of $σ$, $ω$ and $ρ$ meson fields are analyzed. It is found that the total $σ_{NΔ}^{*}$ has a sensitive center-of-mass energy dependence at lower energies while exhibiting a slight increase as the center-of-mass energy increases. The isospin effect between different isospin-separated channels weakens as the energy and/or density increases. The isospin effect on the density- and energy-dependent in-medium $NΔ$ elastic cross sections is dominantly caused by the delicate balance of the isovector $ρ$ meson exchange.

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