arXiv subjects

Xin-Li Zhao

Publications and source records attributed to Xin-Li Zhao.

10 recordsLinked to original sources

arXiv2026

Sensitivity of anisotropic flow in Pb+Pb collisions to the neutron skin of $^{208}$Pb at energies available at the CERN Large Hadron Collider

We study the sensitivity of anisotropic flow in Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$~TeV to the neutron skin of $^{208}$Pb using the improved string-melting version of a multiphase transport (AMPT) model. By varying the neutron surface diffuseness, we trace the impact of several neutron-skin scenarios from the initial nuclear density profiles and eccentricities to final-state charged-particle production and flow cumulants. A systematic response is observed in both the initial eccentricities and the anisotropic flow, indicating that the neutron-skin-induced geometric effects can survive the full transport evolution. A model-to-data comparison with ALICE measurements disfavors the most compact and most diffuse density profiles within the tested AMPT setup, while the reference and moderate-skin configurations give comparable descriptions. Their similarity reflects a geometric degeneracy in large Pb+Pb collision systems, where the inclusive anisotropic flow is dominated by the effective collision geometry and nuclear size, making it only weakly sensitive to the detailed structure of the neutron surface. These results clarify both the sensitivity and the limitations of using anisotropic flow in relativistic heavy-ion collisions to probe neutron-skin effects.

nucl-th↗

arXiv2026

Nuclear cluster structure effect in $^{16}$O+$^{16}$O collisions at the top RHIC energy

Using the improved string-melting version of a Multi-Phase Transport model, we investigated the impact of nuclear geometry of $^{16}$O on anisotropic flows in O+O collisions at $\sqrt{s_{\rm NN}} = 200$ GeV. To evaluate the influence of nuclear structure and potential alpha clustering, we implemented four candidate configurations: Woods-Saxon, tetrahedron, square, and Nuclear Lattice Effective Field Theory. Initial-state geometry is quantified via the eccentricity cumulant ratio $\varepsilon_{2}\{4\}/\varepsilon_{2}\{2\}$, which provides a robust and evolution-independent measure sensitive to configuration differences. The model reproduces $v_{2}(p_{\rm T})$ at low $p_{\rm T}$ and $v_{3}(p_{\rm T})$ across the full $p_{\rm T}$ range, with integrated $v_{2}\{2\}$ and $v_{3}\{2\}$ matching the STAR data, demonstrating that transport dynamics captures the essential collectivity in this intermediate-size system. These findings establish a baseline for extending nuclear-structure studies in O+O collisions to other energies and differential observables within a unified transport model framework.

nucl-th↗

arXiv2025

Constraining the chiral magnetic effect using spectator and participant planes across Au+Au and isobar collisions at $\sqrt{s_{_{\rm NN}}} = 200$ GeV

We investigate the chiral magnetic effect (CME) in relativistic heavy-ion collisions through an improved two-plane method analysis of the $Δγ$ observable, probing $\mathcal{CP}$-symmetry breaking in strong interactions and topological properties of the QCD vacuum. Using a multiphase transport model with tunable CME strengths, we systematically compare Au+Au and isobar collisions at $\sqrt{s_{_{\rm NN}}} = 200$ GeV. We observe a reduced difference in the CME signal-to-background ratio between the spectator and participant planes for Au+Au collisions compared to isobar collisions. A comprehensive chi-square analysis across all three collision systems reveals stronger CME signatures in Au+Au collisions relative to isobar collisions, particularly when measured with respect to the spectator plane. Our findings demonstrate an enhanced experimental reliability of the two-plane method for the CME detection in Au+Au collisions.

nucl-th↗

arXiv2024

Difference between signal and background of the chiral magnetic effect relative to spectator and participant planes in isobar collisions at $\sqrt{s_{_{\rm NN}}} = 200$ GeV

The search for the chiral magnetic effect (CME) in relativistic heavy-ion collisions helps us understand the $\mathcal{CP}$ symmetry breaking in strong interactions and the topological nature of the QCD vacuum. Since the background and signal of the CME have different correlations with the spectator and participant planes, a two-plane method has been proposed to extract the fraction of the CME signal inside the CME observable of $Δγ$ from the experimental measurements relative to the two planes. Using a multiphase transport model with different strengths of the CME, we reexamine the two-plane method in isobar collisions at $\sqrt{s_{_{\rm NN}}} = 200$ GeV. The ratios of the CME signals and the elliptic flow backgrounds relative to the two different planes are found to be different, which is inconsistent with the assumptions made in the current experimental measurements. This difference arises from the decorrelation effect of the chiral magnetic effect relative to the spectator and participant planes caused by final state interactions. Our finding suggests that the current experimental measurements may overestimate the fraction of the CME signal in the CME observable in the final state of relativistic heavy-ion collisions.

nucl-th↗

arXiv2022

Search for the chiral magnetic effect in collisions between two isobars with deformed and neutron-rich nuclear structures

Isobar collisions which were thought to have the same background and different magnetic fields provide an opportunity to verify the chiral magnetic effect (CME) in relativistic heavy-ion collisions. However, the first result from the RHIC-STAR isobar experiment did not observe the CME signal, but discovered that the backgrounds are different between $_{44}^{96}\textrm{Ru}+_{44}^{96}\textrm{Ru}$ and $_{40}^{96}\textrm{Zr}+_{40}^{96}\textrm{Zr}$ collisions. We test eighteen cases of Woods-Saxon parameter settings resulting from different nuclear deformation or nuclear structure effects using a mutiphase transport model. We find out that seven cases can reasonably reproduce three reference ratios measured by the STAR experiment. Considering both the halo-type neutron skin structure and CME-like charge separation, we demonstrate that it is difficult for the CME observables ($Δδ$, $Δδ$ ratio, $Δγ$ and $Δγ$ ratio) to distinguish the presence or absence of the CME, if the CME strength is weak in isobar collisions. It is because the final state interactions significantly weaken the initial CME signal, resulting in non-linear sensitivities of the CME observables to the CME strength. Therefore, more sensitive observables are required to search for the possible small CME signal in isobar collisions.

nucl-th↗

arXiv2022

A transport model study of multiparticle cumulants in $p+p$ collisions at 13 TeV

Flow-like signals including the ridge structure observed in small collision systems that are similar to those in large collision systems have led to questions about the onset of collectivity in nuclear collisions. In this study, we use the string melting version of a multi-phase transport (AMPT) model with or without the sub-nucleon geometry for the proton to study multiparticle cumulants in $p+p$ collisions at 13 TeV. Both versions of the model produce negative $c_{2}\{4 \}$ values at high multiplicities. In addition, the dependence of $c_{2}\{4 \}$ on the parton cross section is non-monotonous, where only a range of parton cross section values leads to negative $c_{2} \{4 \}$. Furthermore, the AMPT model with sub-nucleon geometry better describes the multiplicity dependence of $c_{2} \{4 \}$, demonstrating the importance of incorporating the sub-nucleon geometry in studies of small collision systems.

nucl-th↗

arXiv2020

Validation and improvement of the ZPC parton cascade inside a box

Cascade solutions of the Boltzmann equation suffer from causality violation at large densities and/or scattering cross sections. Although the particle subdivision technique can reduce the causality violation, it alters event-by-event correlations and fluctuations and is also computationally expensive. Here we evaluate and then improve the accuracy of the ZPC parton cascade for elastic scatterings inside a box without using parton subdivision. We first test different collision schemes for the collision times and ordering time and find that the default collision scheme does not accurately describe the equilibrium momentum distribution at large opacities. We then find a specific collision scheme that can describe very accurately the equilibrium momentum distribution as well as the time evolution towards equilibrium, even at large opacities. We also calculate the shear viscosity and the $η/s$ ratio of the parton systems and confirm that the new collision scheme is more accurate. In addition, we use a novel parton subdivision method to obtain the "exact" evolution of the system. This subdivision method is valid for such box calculations and is so much more efficient than the standard subdivision method that we use a subdivision factor of $10^6$ in this study.

nucl-th↗

arXiv2019

Novel mechanism for electric quadrupole moment generation in relativistic heavy-ion collisions

We present the spatial distributions of electromagnetic fields ($\bf E$ and $\bf B$) and electromagnetic anomaly $ \bf E \cdot B$ in Au+Au collisions at the RHIC energy $\sqrt{s}$=200 GeV based on a multi-phase transport model. A dipolar distribution of $\bf E \cdot B$ is observed in non-central collisions. We find that the coupling of the $\bf E \cdot B$ dipole and magnetic field $\bf B$ can induce an electric quadrupole moment which can further lead to the difference in elliptic flows between positive charged particles and negative charged particles through final interactions. The centrality dependence of the density of $\bf E \cdot B$ is similar to the trend of the slope parameter $r$ measured from the difference in elliptic flows between positive pions and negative pions by the STAR collaboration. Therefore, the novel mechanism for electric quadrupole moment generation can offer a new interpretation of the observed charge-dependent elliptic flow of pions, but without the formation of chiral magnetic wave.

hep-ph↗

arXiv2019

Impact of magnetic-field fluctuations on measurements of the chiral magnetic effect in collisions of isobaric nuclei

We investigate the properties of electromagnetic fields in isobaric $_{44}^{96}\textrm{Ru}+\,_{44}^{96}\textrm{Ru}$ and $_{40}^{96}\textrm{Zr}+\,_{40}^{96}\textrm{Zr}$ collisions at $\sqrt{s}$ = 200 GeV by using a multiphase transport model, with special emphasis on the correlation between magnetic field direction and participant plane angle $Ψ_{2}$ (or spectator plane angle $Ψ_{2}^{\rm SP}$), i.e. $\langle{\rm cos}\ 2(Ψ_B - Ψ_{2})\rangle$ [or $\langle{\rm cos}\ 2(Ψ_B - Ψ_{2}^{\rm SP})\rangle$]. We confirm that the magnetic fields of $_{44}^{96}\textrm{Ru}+\,_{44}^{96}\textrm{Ru}$ collisions are stronger than those of $_{40}^{96}\textrm{Zr}+\,_{40}^{96}\textrm{Zr}$ collisions due to their larger proton fraction. We find that the deformation of nuclei has a non-negligible effect on $\langle{\rm cos}\ 2(Ψ_B - Ψ_{2})\rangle$ especially in peripheral events. Because the magnetic-field direction is more strongly correlated with $Ψ_{2}^{\rm SP}$ than with $Ψ_{2}$, the relative difference of the chiral magnetic effect observable with respect to $Ψ_{2}^{\rm SP}$ is expected to be able to reflect much cleaner information about the chiral magnetic effect with less influences of deformation.

hep-ph↗

arXiv2018

Electromagnetic fields in small systems from a multiphase transport model

We calculate the electromagnetic fields generated in small systems by using a multiphase transport (AMPT) model. Compared to $A+A$ collisions, we find that the absolute electric and magnetic fields are not small in $p$+Au and $d$+Au collisions at energies available at the BNL Relativistic Heavy Ion Collider and in $p$+Pb collisions at energies available at the CERN Large Hadron Collider. We study the centrality dependencies and the spatial distributions of electromagnetic fields. We further investigate the azimuthal fluctuations of the magnetic field and its correlation with the fluctuating geometry using event-by-event simulations. We find that the azimuthal correlation $\left\langle \cos2(Ψ_B - Ψ_{2}) \right\rangle$ between the magnetic field direction and the second harmonic participant plane is almost zero in small systems with high multiplicities, but not in those with low multiplicities. This indicates that the charge azimuthal correlation, $\left\langle \cos(ϕ_α+ϕ_β - 2Ψ_{RP}) \right\rangle$, is not a valid probe to study the chiral magnetic effect (CME) in small systems with high multiplicities. However, we suggest searching for possible CME effects in small systems with low multiplicities.

hep-ph↗