核介质中强子性质的手征σ模型研究

采用手征σ模型描述核多体系统,考虑真空极化的影响,首先由核物质的饱和性质确定模型参数,进一步研究了强子性质在核介质中的变化。手征σ模型的研究结果给出,核子和ω介子的有效质量随核物质密度的增大而减小,但σ介子的有效质量随密度的增大而增大。这些结果与不满足手征对称性的Walecka模型结果进行了比较。计算中采用的重整化方法会对结果有一定的影响。The modification of hadron masses in nuclear medium is studied by using the chiral sigma model, which is extended to generate the omega meson mass by the sigma condensation in the vacuum in the same way as the nucleon mass. The chiral sigma model provides proper equilibrium properties of nuclear matter. It is shown that the effective masses of both nucleons and omega mesons decrease in nuclear medium, while the effective mass of sigma mesons increases at finite density in the chiral sigma model. The resuits obtained in the chiral sigma model are compared with those obtained in the Walecka model, which includes sigma and omega mesons in a non-chiral fashion.     

Nuclear Matter Properties from a Chiral Soliton Model

We present a recent investigation on properties of nuclear matter within a chrial soliton approach which includes the explicit scalar dilaton-quarkonium meson saturating the quark loop contribution to the scale anomaly of QCD. We discuss the binding energy per nucleon, the compressibility of nuclear matter and the behavior of meson–nucleon coupling constants according to the density variations in the system.     

Determination of Deuteron Dipole Moment in Nuclear Quark-Like Model

Using the quark-like model, we have improved the existing deviation between theoretical and experimental values of magnetic dipole moment of deuteron. Based upon Pauli Exclusion Principle, the constituent quarks form a ground state for l = 0. The expectation value of the deuteron magnetic dipole moment operator is determined to be equal to 0.861 597 8μ N in better agreement with the measured value of 0.857 437 6μ N as compared to the shell model calculations.     

Tetraneutron in the Chiral Quark Model

The tetraneutron state is studied in the framework of the chiral quark model with tetrahedron configuration. The universal attraction property of σ-meson exchange leads to a strong attraction in the effective potential of the system. It is possible to form a bound state. For comparison, the naive quark model is also employed to carry out the calculation. A weak attraction, which is too weak to bind the system, is obtained.     

A QCD-Inspired Model for the Deuteron Form Factors in the Intermediate-Q2 Region

Based on a perturbative QCD analysis of the deuteron form factors a QCD-inspired model is suggested. The contributions of helicity-flip matrix elements to the deuteron form factors are discussed. Our numerical results are consistent with the data in the intermediate-Q² region.     

Deuteron photodisintegration in the quark-hadron picture

The study of the two-body photodisintegration of the deuteron in the few GeV region is the ideal reaction to clarify the transition from the nucleonic degrees of freedom to the QCD picture of hadrons. The CLAS large-angle spectrometer of Hall B at JLab allowed for the first time the complete measurement of the angular distribution of the differential cross-section at photon energy between 0.5 and 3 GeV. Preliminary results of the E93-017 experiment from the analysis of the 30% of the total statistic accumulated show persistent forward-backward asymmetry and are well described by the recent calculation of the deuteron photodisintegration cross-section derived in the framework of the Quark-Gluon String Model.Received: 1 November 2002, Published online: 15 July 2003PACS: 21.45.+v Few-body systems - 24.85.+p Quarks, gluons, and QCD in nuclei and nuclear processes - 25.10.+s Nuclear reactions involving few-nucleon systems - 25.20.-x Photonuclear reactionsP. Rossi: For the CLAS Collaboration     

Optical Model Analysis for Elastic Deuteron Scattering on light Nuclei

An optical model analysis for the elastic deuteron scattering on light nuclei (⁷Li. ⁹Be, ¹¹B, ¹²B and ¹⁶O) is studied at energies about 28MeV. Satisfactory fits to the experimental data are found using the volume and the surface absorption nuclear potentials. The effect of varying the resulting parameters on the differential cross-section is discussed.     

Chiral Extension of the Quark Model

The chiral extension of the minimal standard model makes quarks with two chiralities present parallelly. Some interesting questions, such as the possibility of that the leptons are made of additional leptonic quarks and the proton decay are discussed.     

Deuteron Photodisintegration in the Diagrammatic Approach

Photodisintegration of the deuteron below the pion-photoproduction threshold is considered in the framework of the diagrammatic approach. The deuteron wave function, the final-state N–N interaction and meson-exchange currents are constructed from the nonrelativistic versions of the Bonn OBE potential. A detailed comparison with the existing data is made. It is shown that the model gives a satisfactory agreement with the experimental data. Possible sources for the remaining disagreements are discussed. Received June 10, 1994; revised September 25, 1994; accepted for publication November 18, 1994     

Deuteron photodisintegration in the Bethe-Salpeter formalism

A relativistically invariant analysis of the deuteron-photodisintegration reaction is performed. The reaction γd → pn is considered in the plane-wave approximation on the basis of the Bethe-Salpeter equation with a separable kernel. The results obtained in this way are compared with the results based on nonrelativistic models and on the quasipotential approximation. It is shown that the most important relativistic contributions to the relevant angular distributions are associated with the dependence of the Bethe-Salpeter amplitude on the relative energy of nucleons and on the boost transformation of this amplitude.     

Photoproduction of Vector Meson ø off Deuteron in QCD Inspired Model

Based on the quark-gluon contents of nucleon and strongly believing that the force mediators, Pomeron and its counterpart in the conventional approach of Regge theory, for high energy diffractive process would be the tensor glueball and Odderonrespectively, we discuss photo-production of vector meson ø off the deuteron at energy less than 3 GeV in the QCD inspired model in which the quark gluon degrees of freedom and glueball, Odderon exchange are taken into account. A calculation isperformed for γ+D → ø+D, and the theoretical predictions of the differential cross section dσ ^γD/dt, are presented and compared with available experimental data. Our QCD inspired model reproduces data quite well in the whole range of the experimental measurements up to |t|≌ 0.4~GeV. Our results can be used toextract γn →øn data, which cannot be measured in experiment.     

Properties of Deuteron Bound State from Meson and Quark Theories for the Nucleon-Nucleon Interaction

The properties of the nucleon-nucleon bound state in the deuteron are considered. Nucleonnucleon interactions of the Yukawa, Reid and Paris potential forms are used to describe the deuteron bound state. Also, the nudeon-nudeon interaction with different meson exchanges derived fiom the meson theory as well as the nudeon-nudeon interaction with quark exchange derived from the quark theory by introducing the quark-quark potential with one gluon exchange are used to investigate the deuteron properties. The deuteron binding energy, quadrupole moment, effective range, root-mean-square radius and the D/S ratio are calculated by using different nucleon-nucleon interactions. The obtained results of the present calculations are in good agreement with the experimental values.     

Deuteron photodisintegration within the Quark-Gluon Strings Model and QCD motivated nonlinear Regge trajectories

We investigate deuteron two-body photodisintegration within the framework of the Quark-Gluon Strings Model with nonlinear baryon Regge trajectories. Special attention is paid to the use of QCD motivated Regge trajectories of the logarithmic and square-root form. We find that the recent experimental data from TJNAF in the few-GeV region can be reasonably described by the model. Angular distributions at different γ-energies are presented and the effect of a forward-backward asymmetry is discussed. Predictions for the energy dependence of dσ/dt at higher energies and different Θ_c.m. are presented, too. Received: 12 March 2001 / Accepted: 19 March 2001     

A Study on the Chiral Bag Model

Within the framework of SU(2) chiral bag model, we determine the bag parameters and radii by fitting the mass spectra. In terms of these parameters we calculate the mean square root of the charged radius and the anomalous magnetic moments g_P and g_N. The ir values are obviousJy improved from that obtained from either the MIT bag model or the standard Skyrme model.     

Deuteron decay in the field of the nucleus

The amplitude of the A+d→n+p+A reaction was obtained on the basis of the diagram summation method for the particular configurations of the particle in the final state, when (i) the neutron and proton have a small relative energy, or (ii) one of the nucleons and the nucleus have a small relative energy. It was shown that from the analysis of the experimental data of the reaction A+d→n+p+A and by using the obtained formula the value of the spin-dependent and spin-independent parts of the nucleon-nucleus scattering amplitude can be found.     

Deuteron break-up in the field of the nucleus

The break-up of deuterons in Coulomb and nuclear fields is calculated in the framework of a distorted-wave Born approximation (DWBA). The matrix element in the post-interaction formulation is evaluated using a partial-wave decomposition. The results are in very good agreement with recent experiments, but only if nuclear forces are included. In addition, other theoretical models for the disintegration of deuterons are reviewed critically.