119107991
Transport model study of nuclear stopping in heavy-ion collisions over the energy range from 0.09A to 160A GeV
Nuclear stopping in heavy-ion collisions over a beam energy range from SIS and AGS up to SPS is studied in the framework of the modified Ultrarelativistic Quantum Molecular Dynamics transport model, in which mean field potentials of both formed and "preformed" hadrons (from string fragmentation) and medium-modified nucleon-nucleon elastic cross sections are considered. It is found that nuclear stopping is influenced by both the stiffness of the equation of state and medium modifications of nucleon-nucleon cross sections at SIS energies. At high SPS energies, a two-bump structure is shown in the experimental rapidity distribution of free protons, which can be understood by considering the preformed hadron potentials.
9051613
Mass and isotope dependence of limiting temperatures for hot nuclei
The mass and isotope dependence of limiting temperatures for hot nuclei are investigated. The predicted mass dependence of limiting temperatures is in good agreement with data derived from the caloric curve data. The predicted isotope distribution of limiting temperatures appears to be a parabolic shape and its centroid is not located at the isotope on the beta-stability line (T=0) but at neutron-rich side. Our study shows that the mass and isotope dependence of limiting temperatures depend on the interaction and the form of surface tension and its isospin dependence sensitively.
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.
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.
124137012
Study of in-medium Delta Delta elastic scattering cross section
120003352
Study of the baryon resonances structure via η photoproduction
Abstract Within a quark model the process γp → ηp , for E γ lab D 13 (1520), F 15 (1680), and to a lesser extent from P 13 (1720) in addition to those from the dominant S 11 (1535) resonance, implied by the Mainz differential cross-section data. The contributions from the resonances S 11 (1650), D 13 (1700) and D 15 (1675) are found consistently small but sensitive to the polarized target asymmetry measured recently at ELSA. These results are shown to be consistent with the quark model predictions.
55468935
Microscopic analysis of order parameters in nuclear quantum phase transitions
Microscopic signatures of nuclear ground-state shape phase transitions in Nd isotopes are studied 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. As a function of the physical control parameter, the number of nucleons, energy gaps between the ground state and the excited vibrational states with zero angular momentum, isomer shifts, and monopole transition strengths exhibit sharp discontinuities at neutron number N=90, which is characteristic of a first-order quantum phase transition.
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
211839122
DRESSING METHOD FOR A GENERALIZED FOCUSING NLS EQUATION VIA LOCAL RIEMANN–HILBERT PROBLEM∗
will be studied by dressing method via local Riemann–Hilbert (RH) problem [1,2,3,4,5,6,7,8,9], where ε > 0 and β is a real constant. Equation (1) can be transformed to the classical NLS equation [10, 11, 12, 13, 14] which describes the self-modulation of one-dimensional waves in a nonlinear dispersive medium. It is well known that the solution of focusing NLS equation with rapidly decreasing type [10,12] can be transformed into the solution of the defocusing NLS equation with finite density type [3,15,16]. It is readily verified that the solution of GFNLS equation becomes that of generalized defocusing NLS equation (ε < 0) under the transformation
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.