WQ（沈文庆） Shen

Isospin influences on particle emission and critical phenomena in nuclear dissociation

Features of particle emission and critical point behavior are investigated as functions of the isospin of disassembling sources and temperature at a moderate freeze-out density far medium-size Xe isotopes in the framework of the isospin-dependent lattice gas model. Multiplicities of emitted light particles, isotopic, and isobaric ratios of light particles show the strong dependence on the isospin of the dissociation source, but double ratios of light isotope pairs and the critical temperature determined by the extreme values of some critical observables are insensitive to the isospin of the systems. Values of the power law parameter of cluster mass distribution, mean multiplicity of intermediate mass fragments (IMF), information entropy, and Campis second moment also show a minor dependence on the isospin of Xe isotopes at the critical point. In addition, the slopes of the average multiplicities of the neutrons (N-n), protons (N-p), charged particles (N-CP), and IMFs (N-IMF), slopes of the largest fragment mass number (A(max)), and the excitation energy per nucleon of the disassembling source (E*/A) to temperature are investigated as well as variances of the distributions of N-n, N-p, N-CP, N-IMF, A(max), and E*/A. It is found that they can be taken as additional judgements to the critical phenomena. [S0556-2813(99)302108-1].

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

Abstract 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 T trig 6 GeV / c and 0.15 p T assoc 3 GeV / c (soft), or 2.5 p T trig 4 GeV / c and 1 p T assoc 2.5 GeV / c (hard) in Au + Au collisions at s N N = 200 GeV . A Mach-like structure has been observed in correlation functions for central collisions. By comparing scenarios with and without parton cascade and hadronic rescattering, we show that both partonic and hadronic dynamical mechanisms contribute to the Mach-like structure of the associated particle azimuthal correlations. The contribution of hadronic dynamical process cannot be ignored in the emergence of Mach-like correlations of the soft scattered associated hadrons. However, hadronic rescattering alone cannot reproduce experimental amplitude of Mach-like cone on away-side, and the parton cascade process is essential to describe experimental amplitude of Mach-like cone on away-side. In addition, both the associated multiplicity and the sum of p T decrease, while the 〈 p T 〉 increases, with the impact parameter in the AMPT model including partonic dynamics from string melting scenario.

Isospin effect in 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 the GEMINI code, isoscaling behavior is observed and the dependences of isoscaling parameters alpha and beta on emission fragment size, source size, source isospin asymmetry and excitation energies are studied. Results show that alpha and beta neither depends on light fragment size nor on source size. A good linear dependence of alpha and beta on the inverse of temperature T is manifested and the relationship of alpha=4C(sym)[(Z(s)/A(s))(1)(2)-(Z(s)/A(s))(2)(2)]/T and beta=4C(sym)[(N-s/A(s))(1)(2)-(N-s/A(s))(2)(2)]/T from different isospin asymmetry sources is satisfied. The symmetry energy coefficient C-sym extracted from simulation results is similar to 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.

Surveying the nucleon-nucleon momentum correlation function in the framework of quantum molecular dynamics model

Momentum correlation functions of nucleon-nucleon pairs are presented for reactions with C isotopes bombardinga 12 Ctargetwithintheframeworkoftheisospin-dependentquantummolecular 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 equations 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.

RMF calculation and phenomenological formulas for the rms radii of light nuclei

The RMF (Relativistic Mean Field) calculations are performed systematically for light isotopes (A < 40) with NL-SH parameter set. The calculated binding energies and root mean square (rms) radii of light nuclei are discussed. On the basis of the theoretical calculations and the experimental data, we have suggested a group of phenomenological formulas for the neutron, proton and matter rms radii for nuclei with A < 40, including the drip-line nuclei. In these formulas, the effects of binding energies, isospin and separation energies are considered. These formulas not only agree to the experimental data for stable nuclei well, but also reproduce the abnormal large radii of nuclei near the drip-line that the previous empirical models fail to reproduce them

Scaling of anisotropy flows in intermediate energy heavy ion collisions

Anisotropic flows ( v 1 , v 2 and v 4 ) of light nuclear clusters are studied by a nucleonic transport model in intermediate energy heavy ion collisions. The number-of-nucleon scalings of the directed flow ( v 1 ) and elliptic flow ( v 2 ) are demonstrated for light nuclear clusters. Moreover, the ratios of v 4 / v 2 2 of nuclear clusters show a constant value of 1/2 regardless of the transverse momentum. The above phenomena can be understood by the coalescence mechanism in nucleonic level and are worthy to be explored in experiments.

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 protons flow. (c) 2008 Elsevier B.V. All rights reserved.

Neutron Halos in the Excited States of Spherical Nuclei Near the β-Stable Line

The newly discovered neutron halos in the excited states of nuclei B-12, C-13, and Pb-209 are studied by the relativistic mean-field theory. The calculated binding energies are very close to the experimental ones. The experimentally extracted root-mean-square radii of the last neutron with different occupations in nuclei are well reproduced by calculations. New candidates for the neutron halos in excited states are predicted and are useful for further search of neutron halos in the excited states of stable nuclei.

Strange-quark collectivity of the φ-meson at RHIC

Abstract.Based on A Multi-Phase Transport (AMPT) model, the elliptic flow v2 of φ-mesons which is reconstructed from K+K- at the Relativistic Heavy-Ion Collider (RHIC) energy has been studied. The results show that the reconstructed v2 of the 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 v2 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.

Possible exotic structure in light proton-rich nuclei

Radioactive ion beams were produced through the projectile fragmentation induced by 69MeV/nucleon 36Ar primary beam on a 9Be target. Measurements of reaction cross section (σR) for some proton-rich nuclei on carbon target at intermediate energies around 30MeV/nucleon have been performed on RIBLL of HIRFL by transmission method and transmission plus transportation method. The experimental σR values for 23Al and 27P are abnormally large compared with their neighboring nuclei and that of 17F has an enhancement compared with the neighboring isotopes. It suggests anomalously large matter root-mean-square radii and proton halo structure in 23Al and 27P. The experimental σR values and momentum distribution of fragmentation reaction product for 31Cl, 32Cl, 33Cl, 28S, 29S were performed also on RIBLL by transmission and transportation method. These data are in analyzing. The calculation of relativistic density-dependent Hartree shows that the nuclei 23Al, 27P, 31Cl may have proton-halo structure and 17F, 32Cl may ...