117742966
Non-equilibrium dynamics in heavy ion collisions at low SIS energies
The Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model, a microscopic transport model, is used to study the directed and elliptic collective flows and the nuclear stopping in Au+Au collisions at incident energies covered by INDRA and lower-energy FOPI experiments. It is seen clearly that these observables are sensitive to both, the potential terms (including iso-scalar and iso-vector parts as well as the momentum dependent term) in the equation of state (EoS) and the collision term (including the Pauli-blocking and the medium-modified nucleon-nucleon elastic cross section (NNECS)). The momentum modifications of both, the mean-field potentials and the density dependent NNECS, are found to be sensitive to the collectivity of heavy-ion collisions. At INDRA energies ($\le 150$~MeV/nucleon), the dynamic transport with a soft EoS with momentum dependence and with the momentum-modified density-dependent NNECS describes the directed flow exhibited by hydrogen isotopes ($Z=1$) emitted at mid-rapidity fairly well.
119408968
Isospin dependence of nucleon-nucleon elastic cross section
The in-medium neutron-proton, proton-proton (neutron-neutron) scattering cross sections (sigma(np)*, sigma(pp(nn))*) are studied based on QHD-II type Lagangian within the framework of the microscopic transport theory. The results demonstrate that, for free nucleon-nucleon scattering cross sections, the isospin dependence is dominantly caused by the rho meson field. The medium correction of nucleon-nucleon scattering cross sections is also isospin dependent, sigma(np)*, depends on the baryon density weakly and sigma(pp(nn))* depends on the baryon density significantly, which is due to the different effects of the medium correction of nucleon mass and rho meson mass on sigma(np) and sigma(pp(nn)), respectively.
8355559
Improved quantum molecular dynamics model and its applications to fusion reaction near barrier
An improved quantum molecular dynamics model is developed. By using this model, the properties of ground state of nuclei from Li-6 to Pb-208 are described very well with one set of parameters. The fusion reactions for Ca-40+Zr-90, Ca-40+Zr-96, and Ca-48+Zr-90 at energies near the barrier are studied by this model. The experimental data of the fusion cross sections for Ca-40+Zr-90,Zr-96 at energies near the barrier are reproduced remarkably well without introducing any new parameters. The mechanism for the enhancement of the fusion cross sections for neutron-rich nuclear reaction near barrier is analyzed.
55892113
In-medium NN cross sections determined from stopping and collective flow in intermediate-energy heavy-ion collisions
In-medium nucleon-nucleon scattering cross sections are explored by comparing results of quantum molecular dynamics simulations to data on stopping and on elliptic and directed flow in intermediate-energy heavy-ion collisions. The comparison points to in-medium cross sections which are suppressed at low energies but not at higher energies. Positive correlations are found between the degree of stopping and the magnitudes of elliptic and directed flows. PACS numbers: 25.70.-z, 24.10.Lx, 21.65.+f
121143863
THE DYNAMICAL ISOSPIN EFFECT ON PROTON-INDUCED REACTIONS ON Sn ISOTOPES
In this talk we present a model, Improved Quantum Molecular Dynamics (ImQMD05) model incorporated with a Statistical Decay Model (SDM), to describe intermediate energy proton induced spallation reactions. A good agreement with experimental data of double differential cross sections of emitted neutrons is obtained. We further apply this model to study the isospin effect in proton induced spallation reactions on a series Sn isotope targets. We find that the systematic behavior of the reaction cross sections for Sn isotope targets deviates from the empirical expression obtained by fitting the experimental data for proton induced spallation reactions on target nuclei along β-stability line. The extent of the deviation depends on the density dependence of the symmetry energy strongly. We also find an obvious shift of the elastic scattering angular distribution of emitted protons when the symmetry energy is taken into account for neutron-rich Sn isotope targets and the angle shifted strongly depends on the stiffness of the symmetry energy. The attractive effect of the symmetry potential of target on incident proton directly influences the motion of the incident proton leading to strong isospin effect on the reaction dynamics and thus on these reaction observables. We conclude that the measurement of reaction cross sections and the elastic scattering angular distributions in proton induced spallation reactions on Sn isotopes can provide clear constraint for the density dependence of symmetry energy.
124137012
Study of in-medium Delta Delta elastic scattering cross section
118832552
Validity of the relativistic impulse approximation for elastic proton-nucleus scattering at energies lower than 200 MeV
We present the first study to examine the validity of the relativistic impulse approximation (RIA) for describing elastic proton-nucleus scattering at incident laboratory kinetic energies lower than 200 MeV. For simplicity we choose a (208)Pb target, which is a spin-saturated spherical nucleus for which reliable nuclear structure models exist. Microscopic scalar and vector optical potentials are generated by folding invariant scalar and vector scattering nucleon-nucleon (NN) amplitudes, based on our recently developed relativistic meson-exchange model, with Lorentz scalar and vector densities resulting from the accurately calibrated PK1 relativistic mean field model of nuclear structure. It is seen that phenomenological Pauli blocking (PB) effects and density-dependent corrections to sigma N and omega N meson-nucleon coupling constants modify the RIA microscopic scalar and vector optical potentials so as to provide a consistent and quantitative description of all elastic scattering observables, namely, total reaction cross sections, differential cross sections, analyzing powers and spin rotation functions. In particular, the effect of PB becomes more significant at energies lower than 200 MeV, whereas phenomenological density-dependent corrections to the NN interaction also play an increasingly important role at energies lower than 100 MeV.
119563640
Microscopic description of quantum shape fluctuation in C isotopes
Covariant density functional theory is used to investigate quantum shape fluctuation in {sup 16}C and other even-even carbon isotopes. Long-range correlations beyond the mean-field approximation are taken into account by configuration mixing of wave functions with triaxial shapes and by restoring the spontaneously broken rotational symmetry through a three-dimensional angular-momentum projection. The systematics of the excitation energy of the 2{sub 1}{sup +} state and the B(E2:2{sub 1}{sup +}{yields}0{sub 1}{sup +}) values in carbon isotopes are reproduced rather well. Decoupled structures with rather different deformations for neutrons and protons have been found in {sup 16,18,20}C. In addition, the effects of shape fluctuations in {beta} and {gamma} deformations on the low-lying excited states of these nuclei are examined.
16718501
The Kaon-Photoproduction Of Nucleons In The Chiral Quark Model
In this paper, we develop a general framework to study the mesonphotoproductions of nucleons in the chiral quark model. The S and U channel resonance contributions are expressed in terms of the ChewGoldberger-Low-Nambu (CGLN) amplitudes. The kaon-photoproduction processes, γp → K+Λ, γp → K+Σ0, and γp → K0Σ+, are calculated. The initial results show that the quark model provides a much improved description of the reaction mechanism for the kaon-photoproductions of the nucleon with less parameters than the traditional phenomenological approaches. PACS numbers: 13.75.Gx, 13.40.Hq, 13.60.Le,12.40.Aa
18644940
Meson Photoproductions Off Nucleons In The Chiral Quark Model
The meson photoproductions off nucleons in the chiral quark model are described. The role of the S-wave resonances in the second resonance region is discussed, and it is particularly important for the Kaon, η and η photoproductions. Meson photoproductions of nucleons have always been a very important field to study the structure of hadrons. It was the early investigations by Copley, Karl and Obryk[1] and Feynman, Kisslinger and Ravndal[2] in the pion photoproduction that provided the first evidence of an underlying SU(6) ⊗ O(3) symmetry for the baryon structure in the quark model. Extensive calculations and discussions of the photoproduction of baryon resonances later have not changed the conclusion in Refs. 1 and 2 significantly. These calculations in the framework of the quark models have been limited on the transition amplitudes that are extracted from the photoproduction data by the phenomenological models, thus it is less model independent. The challenge is whether one could go one step further to confront the photoproduction data directly with the quark model. Such a step is by no means trivial, since it requires that the transition amplitudes in the quark model have correct off-shell behavior, which are usually evaluated on shell. More importantly, it also requires that the model with explicit quark and gluon degrees of freedom give a good description of the contributions to the photoproductions from the non-resonant background, which are usually used to evaluate the contributions from schannel resonances. The low energy theorem in the threshold pion photoproduction[3] is a ∗E-mail: ZPLI@ibm320h.phy.pku.edu.cn
59485768
Microscopic description of spherical to γ-soft shape transitions in Ba and Xe nuclei
The rapid transition between spherical and γ-soft shapes in Ba and Xe nuclei in the mass region A>130 is analyzed using excitation spectra and collective wave functions obtained by diagonalization of a five-dimensional Hamiltonian for quadrupole vibrational and rotational degrees of freedom, with parameters determined by constrained self-consistent relativistic mean-field calculations for triaxial shapes. The results reproduce the characteristic evolution of excitation spectra and E2 transition probabilities, and in general, a good agreement with available data is obtained. The calculated spectra display fingerprints of a second-order shape phase transition that can approximately be described by analytic solutions corresponding to the E(5) dynamical symmetry.