W. Q. Shen

Elliptic flow of phi mesons and strange quark collectivity

Based on a multiphase transport model, we have studied the elliptic flow v{sub 2} of {phi} mesons from the reconstructed K{sup +}K{sup -} decay channel at the top Relativistic Heavy Ion Collider energy at Brookhaven National Laboratory. The dependences of v{sub 2} on transverse momentum p{sub T} and collision centrality are presented and the rescattering effect of {phi} mesons in the hadronic phase is also investigated. The results show that experimental measurement of v{sub 2} for {phi} mesons can retain the early collision information before the {phi} decays and that the {phi} v{sub 2} value obeys the constituent quark number scaling that has been observed for other mesons and baryons. Our study indicates that the {phi} v{sub 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.

Study of halo nuclei with phenomenological relativistic mean field approach

Abstract The properties of halo nuclei are studied in the framework of the relativistic mean field approach. Single particle wave functions for last neutron configurations are obtained by using renormalized mean field potentials which reproduce experimental rms radii of halo nuclei. The extracted experimental density distributions and separation energies of loosely-bound neutrons of halo nuclei 11Li and 11Be are well described by the calculated results.

Examining the exotic structure of the proton-rich nucleus {sup 23}Al

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

A Future Laser Compton Scattering (LCS) γ-Ray Source: SLEGS at SSRF

The Shanghai Synchrotron Radiation Facility (SSRF) is a third-generation synchrotron radiation light source and will come into commission in April 2009. The project Shanghai Laser Electron Gamma Source (SLEGS), which is a high intensity γ-ray beamline based on Laser Compton Scattering (LCS) between relativistic electron bunches and a laser, has been proposed at the SSRF. According to our simulations, the SLEGS is expected to generate a polarized γ-ray beam of up to 22 MeV and 109–10 photons/s if using 3.5 GeV, 200–300 mA relativistic electrons and a 500 W CO2 polarized laser. Here we describe the status and the application prospects of SLEGS and its developed prototype.

Isoscaling behavior in 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

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 (Zproj − Z)/Zproj 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 is 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.

Theoretical study on the properties of some superheavy nuclei

Abstract The structures of some superheavy nuclei are investigated using self-consistent relativistic mean-field (RMF) model. The calculated binding energies and alpha-decay energies are in good agreement with experimental data. The theoretical lifetime reasonably agrees with the data. The properties of some unknown superheavy nuclei are predicted. A discussion on the deformed shell around Z=108 is made.

Effect of neutron skin thickness on projectile fragmentation

The fragment production in collisions of Ca-48,Ca-50+C-12 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 sizes, the effects of neutron skin thickness (delta(np)) on projectile-like fragments (PLFs) are investigated. The sensitivity of isoscaling behavior to neutron skin size is studied, from which it is found that the isoscaling parameter a has a linear dependence on delta(np). A linear dependence between delta(np) and the mean N/Z [N (Z) is neutron (proton) number] of the PLF is obtained as well. The results show that thicker neutron skin will lead to smaller isoscaling parameter alpha and N/Z. Therefore, it may be probable to extract information of neutron skin thickness from isoscaling parameter alpha and N/Z.

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 anticorrelated 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.

Directed and elliptic flows in heavy ion collisions at intermediate energies

A theoretical investigation of directed and elliptic flows for different light particles and fragments in collisions of 40Ca + 40Ca and 112Sn + 112Sn is conducted below 100 MeV/nucleon in the isospin-dependent quantum molecular dynamics model. With increasing incident energy, the directed flow rises from negative to positive, while the elliptic flow decreases with the increasing incident energies. The directed flow for 40Ca + 40Ca system is not sensitive to the nuclear equation of states (EOS), but the directed flow for 112Sn + 112Sn system is sensitive to the EOS. However, the elliptic flows for both 40Ca + 40Ca and 112Sn + 112Sn systems are not sensitive to EOS. A study of the dependence of directed and elliptic flows on fragment charge (mass) is also performed. The information on EOS can be extracted by investigating the directed flow at intermediate energies when the combined mass is large or small.