arXiv subjects

W. Q. Shen

Publications and source records attributed to W. Q. Shen.

At least 19 recordsLinked to original sources

arXiv2018

The role of the Heisenberg principle in Constrained Molecular Dynamics model

We implement the Heisenberg principle into the Constrained Molecular Dynamics (CoMD) model with a similar approach to the Pauli principle using the one-body occupation probability $\bar{f}_i$. Results of the modified and the original model with comparisons to data are given. The binding energies and the radii of light nuclei obtained with the modified model are more consistent to the experimental data than the original one. The collision term and the density distribution are tested through a comparison to p+$^{12}$C elastic scattering data. Some simulations for fragmentation and superheavy nuclei production are also discussed.

nucl-th↗

arXiv2017

Giant dipole resonance in proton capture reactions using an extended quantum molecular dynamics model

Proton capture reaction is an important process concerning the astrophysical origin of the elements. In present work, we focus on giant dipole resonance (GDR) in proton capture reactions, such as $^{11}$B$(p, γ)^{12}$C, $^{27}$Al$(p, γ)^{28}$Si, $^{39}$K$(p, γ)^{40}$Ca, and $^{67}$Co$(p, γ)^{68}$Ni in a framework of an extended quantum molecular dynamics model. The systematic properties of GDR parameters including the peak energy, the strength and full width at half maximum (FWHM) have been studied. The dependence of FWHM on temperature has also been discussed. Some comparisons with experimental data have been presented.

nucl-th↗

arXiv2015

Effect of neutron skin thickness on projectile fragmentation

The fragment production in collisions of $^{48,50}$Ca+$^{12}$C at 50 MeV/nucleon are simulated via the Isospin-Dependent Quantum Molecular Dynamics (IQMD) model followed by the {GEMINI code}. {By changing the diffuseness parameter of neutron density distribution to obtain different neutron skin size, the effects of neutron skin thickness ($δ_{np}$) on projectile-like fragments (PLF) are investigated. The sensitivity of isoscaling behavior to neutron skin size is studied, from which it is found that the isoscaling parameter $α$ has a linear dependence on $δ_{np}$. A linear dependence between $δ_{np}$ and the mean $N/Z$ [N(Z) is neutron(proton) number] of PLF is obtained as well.} The results show that thicker neutron skin will lead to smaller {isoscaling parameter} $α$ and N/Z. Therefore, it may be probable to extract information of neutron skin thickness from {isoscaling parameter} $α$ and N/Z.

nucl-th↗

arXiv2014

Correlation between elliptic flow and shear viscosity in intermediate-energy heavy-ion collisions

The correlation between the elliptic flow $v_2$ scaled by the impact parameter $b$ and the shear viscosity $η$ as well as the specific viscosity $η/s$, defined as the ratio of the shear viscosity to the entropy density $s$, is investigated for the first time in intermediate-energy heavy-ion collisions based on an isospin-dependent quantum molecular dynamic model. The elliptic flow is calculated at balance energies to exclude the geometric influence such as the blocking effect from the spectators. Our study shows that $v_{2}/b$ decreases almost linearly with increasing $η$, consistent with that observed in ultra-relativistic heavy-ion collisions. On the other hand, $v_{2}/b$ is found to increase with increasing $η/s$.

nucl-th↗

arXiv2013

Symmetry-energy dependence of the dynamical dipole mode in the Boltzmann-Uehling-Uhlenbeck model

Using an isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model, we have studied the connection between the symmetry energy and features of the dynamical dipole mode in fusion reactions with charge-asymmetric entrance channel. The yield and angular distribution of the prompt photon emission are extracted by a bremsstrahlung approach. The experimental data of $^{36}$Ar+$^{96}$Zr at 16 MeV/nucleon and $^{32}$S + $^{100}$Mo at 9.3 MeV/nucleon are compared with IBUU model calculations, and the soft symmetry energy is found to describe the data reasonably well.

nucl-th↗

arXiv2012

Hard photon flow and photon-photon correlation in intermediate energy heavy-ion collisions

Hard photons emitted from energetic heavy ion collisions are very interesting since they do not experience nuclear interaction, and therefore they are useful to explore properties of nuclear matter. We investigated hard photon production and its properties in intermediate energy heavy-ion collisions with the help of the Blotzmann-Uehling-Ulenbeck model. Two components of hard photons are discussed: direct and thermal. The positive directed flow parameter and negative elliptic flow parameter of direct photons are demonstrated and they are anti-correlated to the flows of free protons. The dependencies of hard photon production and anisotropic parameters on impact parameter, beam energy, nuclear equation of state and symmetry energy are also discussed. Furthermore, we investigated the two-photon momentum correlation function from which the space-time structure information of the photon source could be extracted as well as the two-photon azimuthal correlation which could provide another good method to determine the elliptic flow parameter $v_{2}$ of direct hard photons.

nucl-th↗

arXiv2009

Viscosity and dilepton production of a chemically equilibrating quark-gluon plasma at finite baryon density

By considering the effect of shear viscosity we have investigated the evolution of a chemically equilibrating quark-gluon plasma at finite baryon density. Based on the evolution of the system we have performed a complete calculation for the dilepton production from the following processes: $q\bar{q}{\to}l\bar{l}$, $q\bar{q}{\to}gl\bar{l}$, Compton-like scattering ($qg{\to}ql\bar{l}$, $\bar{q}g{\to}{\bar{q}}l\bar{l}$), gluon fusion $g\bar{g}{\to}c\bar{c}$, annihilation $q\bar{q}{\to}c\bar{c}$ as well as the multiple scattering of quarks. We have found that quark-antiquark annihilation, Compton-like scatterring, gluon fusion, and multiple scattering of quarks give important contributions. Moreover, we have also found that the dilepton yield is an increasing function of the initial quark chemical potential, and the increase of the quark phase lifetime because of the viscosity also obviously raises the dilepton yield.

nucl-th↗

arXiv2008

Azimuthal asymmetry of direct photons in intermediate energy heavy-ion collisions

Hard photon emitted from energetic heavy ion collisions is of very interesting since it does not experience the late-stage nuclear interaction, therefore it is useful to explore the early-stage information of matter phase. In this work, we have presented a first calculation of azimuthal asymmetry, characterized by directed transverse flow parameter $F$ and elliptic asymmetry coefficient $v_2$, for proton-neutron bremsstrahlung hard photons in intermediate energy heavy-ion collisions. The positive $F$ and negative $v_2$ of direct photons are illustrated and they seem to be anti-correlated to the corresponding free proton's flow.

nucl-ex↗

arXiv2007

Phenomenological Scaling of Rapidity Dependence for Anisotropic Flows in 25 MeV/nucleon Ca + Ca by Quantum Molecular Dynamics Model

Anisotropic flows ($v_1$, $v_2$, $v_3$ and $v_4$) of light fragments up till the mass number 4 as a function of rapidity have been studied for 25 MeV/nucleon $^{40}$Ca + $^{40}$Ca at large impact parameters by Quantum Molecular Dynamics model. A phenomenological scaling behavior of rapidity dependent flow parameters $v_n$ (n = 1, 2, 3 and 4) has been found as a function of mass number plus a constant term, which may arise from the interplay of collective and random motions. In addition, $v_4/{v_2}^2$ keeps almost independent of rapidity and remains a rough constant of 1/2 for all light fragments.

nucl-th↗

arXiv2007

Systematic study of isoscaling behavior in projectile fragmentation by the statistical abrasion-ablation model

The isospin effect and isoscaling behavior in projectile fragmentation have been systematically investigated by a modified statistical abrasion-ablation (SAA) model. The normalized peak differences and reduced isoscaling parameters are found to decrease with ($Z_{proj}-Z$)/$Z_{proj}$ or the excitation energy per nucleon and have no significant dependence on the size of reaction systems. Assuming a Fermi-gas behavior, the excitation energy dependence of the symmetry energy coefficients are tentatively extracted from $α$ and $β$ which looks consistent with the experimental data. It is pointed out that the reduced isoscaling parameters can be used as an observable to study excitation extent of system and asymmetric nuclear equation of state in heavy ion collisions.

nucl-th↗

arXiv2007

Comparison of elastic electron or positron scattering from proton-rich nuclei

We investigate the cross sections of the elastic electron or positron scattering from $^{208}$Pb, $^{12}$C, $^{12,16}$O and $^{28, 32}$S by the relativistic partial-wave expansion method using the static charge density distribution from the self-consistent relativistic mean field model and also calculate the charge form factor for $^{12, 16}$O and $^{28, 32}$S. The numerical results are compared with the available data. Calculations indicate that the extended charge density distributions of $^{12}$O and $^{28}$S have observable effects on the cross sections of the electron or positron scattering as well as the charge form factors.

nucl-th↗

arXiv2007

Scaling of Anisotropic Flows and Nuclear Equation of State in Intermediate Energy Heavy Ion Collisions

Elliptic flow ($v_2$) and hexadecupole flow ($v_4$) of light clusters have been studied in details for 25 MeV/nucleon $^{86}$Kr + $^{124}$Sn at large impact parameters by Quantum Molecular Dynamics model with different potential parameters. Four parameter sets which include soft or hard equation of state (EOS) with/without symmetry energy term are used. Both number-of-nucleon ($A$) scaling of the elliptic flow versus transverse momentum ($p_t$) and the scaling of $v_4/A^{2}$ versus $(p_t/A)^2$ have been demonstrated for the light clusters in all above calculation conditions. It was also found that the ratio of $v_4/{v_2}^2$ keeps a constant of 1/2 which is independent of $p_t$ for all the light fragments. By comparisons among different combinations of EOS and symmetry potential term, the results show that the above scaling behaviors are solid which do not depend the details of potential, while the strength of flows is sensitive to EOS and symmetry potential term.

nucl-th↗

arXiv2007

Examining exotic structure of proton-rich nucleus $^{23}$Al

The longitudinal momentum distribution (P_{//}) of fragments after one-proton removal from ^{23} Al and reaction cross sections (σ_R) for ^{23,24} Al on carbon target at 74A MeV have been measured. The ^{23,24} Al ions were produced through projectile fragmentation of 135 A MeV ^{28} Si primary beam using RIPS fragment separator at RIKEN. P_{//} is measured by a direct time-of-flight (TOF) technique, while σ_R is determined using a transmission method. An enhancement in σ_R is observed for ^{23} Al compared with ^{24} Al. The P_{//} for ^{22} Mg fragments from ^{23} Al breakup has been obtained for the first time. FWHM of the distributions has been determined to be 232 \pm 28 MeV/c. The experimental data are discussed by using Few-Body Glauber model. Analysis of P_{//} demonstrates a dominant d-wave configuration for the valence proton in ground state of ^{23} Al, indicating that ^{23} Al is not a proton halo nucleus.

nucl-ex↗

arXiv2007

Isospin effect in the statistical sequential decay

Isospin effect of the statistical emission fragments from the equilibrated source is investigated in the frame of statistical binary decay implemented into GEMINI code, isoscaling behavior is observed and the dependences of isoscaling parameters $α$ and $β$ on emission fragment size, source size, source isospin asymmetry and excitation energies are studied. Results show that $α$ and $β$ neither depends on light fragment size nor on source size. A good linear dependence of $α$ and $β$ on the inverse of temperature $T$ is manifested and the relationship of $α=4C_{sym}[(Z_{s}/A_{s})_{1}^{2}-(Z_{s}/A_{s})_{2}^{2}]/T$ and $β=4C_{sym}[(N_{s}/A_{s})_{1}^{2}-(N_{s}/A_{s})_{2}^{2}]/T$ from different isospin asymmetry sources are satisfied. The symmetry energy coefficient $C_{sym}$ extracted from simulation results is $\sim$ 23 MeV which includes both the volume and surface term contributions, of which the surface effect seems to play a significant role in the symmetry energy.

nucl-th↗

arXiv2007

Transverse momentum and pseudorapidity dependences of $'\bm{Mach-like}'$ correlations for central Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV

The transverse momentum and pseudorapidity dependences of partonic {`\it{Mach-like}'} shock wave have been studied by using a multi-phase transport model (AMPT) with both partonic and hadronic interactions. The splitting parameter $D$, i.e. half distance between two splitting peaks on away side in di-hadron azimuthal angular ($Δϕ$) correlations, slightly increases with the transverse momentum of associated hadrons ($p^{assoc}_T$), which is consistent with preliminary experimental trend, owing to different interaction-lengths/numbers between wave partons and medium in strong parton cascade. On the other hand, the splitting parameter $D$ as a function of pseudorapidity of associated hadrons ($η^{assoc}$), keeps flat in mid-pseudorapidity region and rapidly drops in high-pseudorapidity region, which is as a result of different violent degrees of jet-medium interactions in the medium that has different energy densities in the longitudinal direction. It is proposed that the research on the properties of {`\it{Mach-like}'} correlation can shed light on the knowledge of both partonic and hadronic interactions at RHIC.

nucl-th↗

arXiv2007

Three-Particle Correlations from Parton Cascades in Au+Au Collisions

We present a study of three-particle correlations among a trigger particle and two associated particles in Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV using a multi-phase transport model (AMPT) with both partonic and hadronic interactions. We found that three-particle correlation densities in different angular directions with respect to the triggered particle (`center', `cone', `deflected', `near' and `near-away') increase with the number of participants. The ratio of `deflected' to `cone' density approaches to 1.0 with the increasing of number of participants, which indicates that partonic Mach-like shock waves can be produced by strong parton cascades in central Au+Au collisions.

nucl-th↗

arXiv2006

The Proto Type of Shanghai Laser Electron Gamma Source at 100 MeV LINAC

The design for the proto type of the Shanghai Laser Electron Gamma Source (SLEGS) at the Shanghai Synchrotron Radiation Facility (SSRF) is introduced. Some detailed descriptions for design of related instruments are provided. The proto type can produce X-ray with energy of 10 keV order. A description of the kinematics of Compton backscattering mechanism and the related simulation results are presented and discussed. The backgrounds from dipole magnet and bremsstrahlung are estimated and the signal-noise ratio is also given.

nucl-ex↗

arXiv2006

Nucleon-nucleon momentum correlation function for light nuclei

Nucleon-nucleon momentum correlation function have been presented for nuclear reactions with neutron-rich or proton-rich projectiles using a nuclear transport theory, namely Isospin-Dependent Quantum Molecular Dynamics model. The relationship between the binding energy of projectiles and the strength of proton-neutron correlation function at small relative momentum has been explored, while proton-proton correlation function shows its sensitivity to the proton density distribution. Those results show that nucleon-nucleon correlation function is useful to reflect some features of the neutron- or proton-halo nuclei and therefore provide a potential tool for the studies of radioactive beam physics.

nucl-th↗