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X. Z. Cai

Publications and source records attributed to X. Z. Cai.

At least 163 records · Page 9Linked to original sources

Di-hadron azimuthal correlation and Mach-like cone structure in parton/hadron transport model

In the framework of a multi-phase transport model (AMPT) with both partonic and hadronic interactions, azimuthal correlations between trigger particles and associated scattering particles have been studied by the mixing-event technique. The momentum ranges of these particles are $3< p^{trig}_T< 6$ GeV/$c$ and $0.15< p_{T}^{assoc} < 3$ GeV/$c$ (soft), or $2.5 $ increases, with the impact parameter in the AMPT model including partonic dynamics from string melting scenario.

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Elliptic flow of $ϕ$ meson and strange quark collectivity at RHIC

Based on A Multi-Phase Transport (AMPT) model, we have studied the elliptic flow $v_{2}$ of $ϕ$ mesons from reconstructed $K^{+}K^{-}$ decay channel at the top Relativistic Heavy Ion Collider energy at Brookhaven National Laboratory. The dependences of $v_{2}$ on transverse momentum $p_T$ and collision centrality are presented and the rescattering effect of $ϕ$ mesons in the hadronic phase is also investigated. The results show that experimental measurement of $v_{2}$ for $ϕ$ mesons can retain the early collision information before $ϕ$ decays and that the $ϕ$ $v_2$ value obeys the constituent quark number scaling which has been observed for other mesons and baryons. Our study indicates that the $ϕ$ $v_2$ mostly reflects partonic level collectivity developed during the early stage of the nucleus-nucleus collision and the strange and light up/down quarks have developed similar angular anistropy properties at the hadronization.

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Di-hadron and Tri-hadron correlation and Mach-like cone structure

In a framework of a multi-phase transport model with both partonic and hadronic interactions, azimuthal correlations between trigger particles and associated scattering particles in Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV/$c$ have been studied by the mixing-event technique. The Mach-like structure has been observed in correlation function for central collisions. It is shown that the Mach-like structure is basically born in the partonic process and further developed in hadronic rescattering process. However, hadronic rescattering alone cannot reproduce the amplitude of Mach-like cone on away side, therefore partonic cascade process is necessary to describe the amplitude of Mach-like cone on away side in experiment. In addition, three-particle correlations have been investigated in central Au + Au collisions with the AMPT model, and the results support the conclusion that partonic cascade processes enhance the opening angle of Mach-like cone structures.

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Strange baryon resonance production in $\sqrt{s_{NN}} = 200$ GeV $p+p$ and $Au+Au$ collisions

We report the measurements of $Σ(1385)$ and $Λ(1520)$ production in $p+p$ and $Au+Au$ collisions at $\sqrt{s_{NN}} = 200$ GeV from the STAR collaboration. The yields and the $p_{T}$ spectra are presented and discussed in terms of chemical and thermal freeze-out conditions and compared to model predictions. Thermal and microscopic models do not adequately describe the yields of all the resonances produced in central $Au+Au$ collisions. Our results indicate that there may be a time-span between chemical and thermal freeze-out during which elastic hadronic interactions occur.

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Strange quark collectivity of $ϕ$ meson at RHIC

Based on A Multi-Phase Transport model, the elliptic flow $v_{2}$ of $ϕ$ mesons which is reconstructed from $K^{+}K^{-}$ at the Relativistic Heavy Ion Collider (RHIC) energy has been studied. The results show that reconstructed $v_{2}$ of $ϕ$ meson can keep the earlier information before $ϕ$ decays and it seems to obey the number of constituent quark scaling as other mesons and baryons. This result indicates that the $ϕ$ $v_2$ mostly reflects the parton level collectivity developed during the early stage of the collisions and the strange and light up/down quarks have similar collectivity properties before the hadronization.

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Scaling of Anisotropic Flow and Momentum-Space Densities for Light Particles in Intermediate Energy Heavy Ion Collisions

Anisotropic flows ($v_2$ and $v_4$) of light nuclear clusters are studied by Isospin-Dependent Quantum Molecular Dynamics model for the system of $^{86}$Kr + $^{124}$Sn at intermediate energy and large impact parameters. Number-of-nucleon scaling of the elliptic flow ($v_2$) are demonstrated for the light fragments up to $A$ = 4, and the ratio of $v_4/v_2^2$ shows a constant value of 1/2. In addition, the momentum-space densities of different clusters are also surveyed as functions of transverse momentum, in-plane transverse momentum and azimuth angle relative to the reaction plane. The results can be essentially described by momentum-space power law. All the above phenomena indicate that there exists a number-of-nucleon scaling for both anisotropic flow and momentum-space densities for light clusters, which can be understood by the coalescence mechanism in nucleonic degree of freedom for the cluster formation.

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Surveying the Nucleon-Nucleon Momentum Correlation Function in the Framework of Quantum Molecular Dynamics Model

Momentum correlation functions of the nucleon-nucleon pairs are presented for reactions with C isotopes bombarding a $^{12} \rm C$ target within the framework of the isospin-dependent quantum molecular dynamics model. The binding-energy dependence of the momentum correlation functions is also explored, and other factors that have an influence on momentum correlation functions are investigated. These factors include momentum-dependent nuclear equation of state, in-medium nucleon-nucleon cross sections, impact parameters, total pair momenta, and beam energy. In particular, the rise and the fall of the strength of momentum correlation functions at lower relative momentum are shown with an increase in beam energy.

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Dynamical and sequential decay effects on isoscaling and density dependence of the symmetry energy

The isoscaling properties of the primary and final products are studied via isospin dependent quantum molecular dynamics (IQMD) model and the followed sequential decay model GEMINI, respectively. It is found that the isoscaling parameters $α$ of both primary and final products keep no significant change for light fragments, but increases with the mass for intermediate and heavy products. The dynamical effects on isoscaling are exhibited by that $α$ value decreases a little with the evolution time of the system, and opposite trend for the heavy products. The secondary decay effects on isoscaling are reflected in the increasing of the $α$ value for the final products which experiences secondary decay process. Furthermore the density dependence of the symmetry energy has also been explored, it is observed that in the low densities the symmetry energy coefficient has the form of $C_{sym}(ρ)\sim C_{0}(ρ/ρ_{0})^γ$, where $γ= 0.7 \sim 1.3$ for both primary and final products, but $C_{0}$ have different values for primary and final products. It is also suggested that it might be more reasonable to describe the density dependence of the symmetry energy coefficient by the $C_{sym}(ρ/ρ_{0})\approx C_{1}(ρ/ρ_{0})^{γ_{soft}} + C_{2}(ρ/ρ_{0})^{γ_{stiff}}$ with $γ_{soft}\leq 1$, $γ_{stiff}\geq 1$ and $C_{1}, C_{2}$ constant parameters.

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Isoscaling behavior in the Fission Dynamics

The fission processes of $^{112}$Sn + $^{112}$Sn and $^{116}$Sn + $^{116}$Sn are simulated with the combination of the Langevin equation and the statistical decay model. The masses of two fission fragments are given by assuming the process of symmetric fission or asymmetric fission by the Monte Carlo sampling with the Gaussian probability distribution. From the analysis to the isotopic/isotonic ratios of the fission fragments from both reactions, the isoscaling behavior has been observed and investigated in details. Isoscaling parameters $α$ and $β$ are extracted as a function of the charge number and neutron number, respectively, in different width of the sampling Gaussian probability distribution. It seems that $α$ is sensitive to the width of fission probability distribution of the mass asymmetrical parameter but $β$ is not. Both $α$ and $β$ drop with the increasing of beam energy and the reduced friction parameter.

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Isoscaling of projectile-like fragments

The isotopic and isotonic distributions of the projectile fragmentation products have been simulated by a modified statistical abrasion-ablation (SAA) model and the isoscaling behavior of projectile-like fragments has been discussed. The isoscaling parameters $α$ and $β$ for hot fragments before evaporation and cold fragments after evaporation have been extracted, respectively. It looks that the evaporation has strong effect on $α$. For cold fragments, a monotonic increase of $α$ and $|β|$ with the increasing of $Z$ and $N$ is observed. The relation between isoscaling parameter and the change of isospin content is demonstrated. In addition, the disappearance of the isospin effect of projectile fragmentation is also discussed in the viewpoint of isoscaling parameter.

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Effect of Hadronic Rescattering on Elliptic Flow Following Hydrodynamics Model

The effect of hadronic rescattering on the elliptic flow has been investigated by the Cooper-Frye hadronization model from hydrodynamic evolution following by the afterburner hadronic rescattering model for 200 GeV/c Au + Au at 20-40% centrality. It is found that the hadronic rescattering can suppress elliptic flow $v_2$ in momentum space especially in lower transverse momentum region. In addition, the hadronic rescattering effects on transverse momentum spectra and anisotropy coordinate space of hadrons are studied.

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Study on the One-Proton Halo Structure in $^{23}$Al

The Glauber theory has been used to investigate the reaction cross section of proton-rich nucleus $^{23}$Al. A core plus a proton structure is assumed for $^{23}$Al. HO-type density distribution is used for the core while the density distribution for the valence proton is calculated by solving the eigenvalue problem of Woods-Saxon potential. The transparency function in an analytical expression is obtained adopting multi-Gaussian expansion for the density distribution. Coulomb correction and finite-range interaction are introduced. This modified Glauber model is apt for halo nuclei. A dominate s-wave is suggested for the last proton in $^{23}$Al from our analysis which is possible in the RMF calculation.

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$Δ$-scaling and heat capacity in relativistic ion collisions

The $Δ$-scaling method has been applied to the total multiplicity distribution of the relativistic ion collisions of p+p, C+C and Pb+Pb which were simulated by a Monte Carlo package, LUCIAE 3.0. It is found that the $Δ$-scaling parameter decreases with the increasing of the system size. Moreover, the heat capacities of different mesons and baryons have been extracted from the event-by-event temperature fluctuation in the region of low transverse mass and they show the dropping trend with the increasing of impact parameter.

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Isoscaling behavior in the Isospin dependent Quantum Molecular Dynamics model

The isoscaling behavior is investigated in the frame of Isospin dependent Quantum Molecular Dynamics (IQMD) models. The isotopic yields ratio $Y_2$/$Y_1$ for reactions $^{48}Ca$+$^{48}Ca$ and $^{40}Ca+^{40}Ca$ at different entrance channels are simulated and presented, the relationship between the isoscaling parameter and the entrance channel is analyzed, the results show that $α$ and $β$ reduce with the rise of incident energies and increase with the impact parameter b, which can be attributed to the temperature varying of the pre-fragments in different entrance channels. The relation of $α$ and symmetry-term coefficient $C_{sym}$ reveals that the chemical potential difference $\triangleμ$ is sensitive to the symmetry-term coefficient $C_{sym}$.

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Parallel momentum distribution of the $^{28}$Si fragments from $^{29}$P

Distribution of the parallel momentum of $^{28}$Si fragments from the breakup of 30.7 MeV/nucleon $^{29}$P has been measured on C targets. The distribution has the FWHM with the value of 110.5 $\pm$ 23.5 MeV/c which is consistent quantitatively with Galuber model calculation assuming by a valence proton in $^{29}$P. The density distribution is also predicted by Skyrme-Hartree-Fock calculation. Results show that there might exist the proton-skin structure in $^{29}$P.

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Isoscaling of the Fission Fragments with Langevin Equation

Langevin equation is used to simulate the fission process of $^{112}$Sn + $^{112}$Sn and $^{116}$Sn + $^{116}$Sn. The mass distribution of the fission fragments are given by assuming the process of symmetric fission or asymmetric fission with the Gaussian probability sampling. Isoscaling behavior has been observed from the analysis of fission fragments of both reactions and the isoscaling parameter $α$ seems to be sensitive to the width of fission probability and the beam energy.

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Systematic studies of binding energy dependence of neutron - proton momentum correlation function

Hanbury Brown-Twiss (HBT) results of the neutron-proton correlation function have been systematically investigated for a series nuclear reactions with light projectiles with help of Isospin-Dependent Quantum Molecular Dynamics model. The relationship between the binding energy per nucleon of the projectiles and the strength of the neutron-proton HBT at small relative momentum has been obtained. Results show that neutron-proton HBT results are sensitive to the binding energy per nucleon.

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Radioactive Ion Beam Physics and Nuclear Astrophysics in China

Based on the intermediate energy radioactive Ion Beam Line in Lanzhou (RIBLL) of Heavy Ion Research Facility in Lanzhou (HIRFL) and Low Energy Radioactive Ion Beam Line (GIRAFFE) of Beijing National Tandem Accelerator Lab (HI13), the radioactive ion beam physics and nuclear astrophysics will be researched in detail. The key scientific problems are: the nuclear structure and reaction for nuclear far from $β$-stability line; the synthesize of new nuclides near drip lines and new super heavy nuclides; the properties of asymmetric nuclear matter with extra large isospin and some nuclear astro- reactions.

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