A New Determination of the Lambda-Nucleon Coupling Constants in Relativistic Mean Field Theory

A new determination of the Lambda-nucleon coupling constants in relativistic mean field theory is presented by optimizing both hyperon binding energy and spin-orbit splitting. Hypernuclear single particle spectra with the new coupling constants suggest the good agreement between the calculation and available data. The spin-orbit splitting of hyperon in medium mass hypernuclei is systematically larger than that in light- or heavy-mass hypernuclei. The sensitivity of the Lambda spin-orbit splitting to the omega-Lambda-Lambda tensor coupling term is also explored.     

A New Determination of the Lambda-Nucleon Coupling Constants in Relativistic Mean Field Theory

A new determination of the Lambda-nucleon coupling constants in relativistic mean field theory is presented by optimizing both hyperon binding energy and spin-orbit splitting.Hypernuclear single particle spectra with the new coupling constants suggest the good agreement between the calculation and available data.The spin-orbit splitting of hyperon in medium mass hypernuclei is systematically larger than that in light-or heavy-mass hypernuclei.The sensitivity of the Lambda spin-orbit splitting to the omega-Lambda-Lambda tensor coupling term is also explored.     

Shell-model calculation of strangeness exchange reactions on nuclei

We analyse recent experiments in which medium heavy hypernuclei 40 A 12 are produced. The shell model is used to describe the structure of these hypernuclei, and cross sections are calculated in the framework of the distorted-wave impulse approximation. Information about the Λ-nucleus interaction is then extracted, particularly on the depth of the central potential and on the spin-orbit term. Comparison with sum-rule calculations for the cross sections is made and good agreement with experimental spectra is found for both shape and magnitude.     

Spin-orbit coupling in Σ-hypernuclei

Single-particle energies of Σ-hyperons in _Σ¹⁶O are calculated within a relativistic mean-field theory. This model predicts a small spin-orbit splitting for Σ-hyperons in _Σ¹⁶O compared to ordinary nucleons in nuclei. Half of the small spin-orbit splitting is due to the anomalous magnetic moment of the Σ-hyperon. K and K¹ exchange terms are negligible. This is to be seen in contrast to a previous quark-model prediction of a strong spin-orbit splitting for hyperons.     

Tensor-Optimized Shell Model for s-Shell Hypernuclei

The explicit ΛN ? ΣN coupling in s-shell hypernuclei is studied by using the tensor-optimized shell model. We show the obtained results of s-shell hypernuclei, ${_{\Lambda}^{4}{\rm H}}$ and ${_{\Lambda}^{5}{\rm He}}$ , and investigate the roles of the ΛN ? ΣN coupling interaction in those hypernuclei.     

The Role of One Single Lambda Hyperon on Binding Energy Difference of Hypernuclear Mirror Pair

Investigation on isospin symmetry in light Lambda hypernuclei is one of the most important issues in hypemuclear physics.In order to know the influences introduced by a single Lambda hyperon,we study the binding energy difference of mirror hypemuclear pair with mass A = 16,18,28,40,and 42 using a time-odd triaxial relativistic mean field theory.Effects as the spin-orbit interaction,the time-odd component of vector fields,the core polarization,the proton-neutron mass difference,and the center-of-mass energy correction are self-consistently considered.Compared to the reported results of ordinary nuclei,the binding energy difference of mirror hypernuclei shows trivial change.With core polarization modified by an impurity hyperon,the isospin nonconserving effect between proton and neutron is hardly reduced for nuclei in study.     

The Role of One Single Lambda Hyperon on Binding Energy Difference of Hypernuclear Mirror Pair

Investigation on isospin symmetry in light Lambda hypernuclei is one of the most important issues in hypernuclear physics. In order to know the influences introduced by a single Lambda hyperon, we study the binding energy difference of mirror hypernuclear pair with mass A=16, 18, 28, 40, and 42 using a time-odd triaxial relativistic mean field theory. Effects as the spin-orbit interaction, the time-odd component of vector fields, the core polarization, the proton-neutron mass difference, and the center-of-mass energy correction are self-consistently considered. Compared to the reported results of ordinary nuclei, the binding energy difference of mirror hypernuclei shows trivial change. With core polarization modified by an impurity hyperon, the isospin nonconserving effect between proton and neutron is hardly reduced for nuclei in study.     

Structure of neutron-rich Λ hypernuclei

Properties of light neutron-rich Λ hypernuclei (¹⁶ _ΛC, ¹² _ΛBe, and ¹¹ _ΛLi) are calculated within the Skyrme-Hartree-Fock approach. Interplay between hypernuclear interaction features and properties of these hypernuclei is studied. Response of weakly bound neutron states to hyperon addition depends generally on core distortion by hyperon, and it is essentially different for the different states. This response is especially sensitive to details of the ΛN interaction for 1p _1/2 states. Implications of the nuclear spin-orbit potential and nuclear incompressibility in the neutron-rich system properties are inferred. Dependence of the Λ binding energies in hypernuclei on Z at fixed A is discussed. Received: 16 December 1998     

Average Λ-nucleus potentials

A few model Λ-nucleus potentials are proposed which explain the ground state binding energy data of⁵He and thep-shell hypernuclei satisfactorily. Potential-II is capable of distinguishing the hypernuclei of the same mass number but of differentN andZ values. The dependence of this potential on (N ? Z) term indicates that there is a charge symmetry breaking component in ΛN force. Alongwith the earlier density dependent effective Λ-nucleus interaction, these potentials may be used to determine approximately the density distributions of light nuclei. From these potentials an estimate ofD _Λ is also made. It is found to be in conformity with the earlier estimates.     

Strangeness exchange reactions and hypernuclear spectroscopy

Recent data obtained by the strangeness exchange reactions on p and s-shell nuclei are analyzed. Using the shell-model to describe the structure of the hypernuclei information about the Λ-nuclues interaction is extracted and compared to previous knowledge. In particular, spin-orbit coupling is found to be much smaller than in the nucleon-nucleus case.     

Hypernuclei and in-medium chiral dynamics

A recently introduced relativistic nuclear energy density functional, constrained by features of low-energy QCD, is extended to describe the structure of hypernuclei. The density-dependent mean field and the spin-orbit potential of a Λ-hyperon in a nucleus, are consistently calculated using the SU(3) extension of in-medium chiral perturbation theory. The leading long-range ΛN interaction arises from kaon-exchange and 2π-exchange with a Σ-hyperon in the intermediate state. Scalar and vector mean fields, originating from in-medium changes of the quark condensates, produce a sizeable short-range spin-orbit interaction. The model, when applied to oxygen as a test case, provides a natural explanation for the smallness of the effective Λ spin-orbit potential: an almost complete cancellation between the background contributions (scalar and vector) and the long-range terms generated by two-pion exchange.     

Σ-N相互作用的研究及 4ΣHe结合能的计算

基于SU(3)夸克模型， 用共振群方法研究了两种理论下的Σ-N相互作用， 得到了它们的相互作用非定域位以及Σ超子与3He壳心核的相互作用势， 并在此基础上计算了4ΣHe基态结合能。 计算结果表明， SU(3)夸克模型能较好地描述两种理论下的Σ N相互作用及Σ超子与3He壳心核的相互作用势， 同时由其得到的 4ΣHe基态结合能也与实验值基本相吻合。     

Baryon-baryon spin-orbit and tensor interactions from quark-exchange kernels

Dibaryon quark-exchange kernels are constructed in explicit analytic form for the tensor and spin-orbit terms of the one-gluon-exchange quark-quark Breit interaction and for spin-orbit terms generated by quark-confinement mechanisms. The spin operators needed are defined through their spin-reduced matrix elements including those needed for interactions coupling NN, NΔ, and ΔΔ channels. Effective baryon-baryon spin-orbit potentials, generated through the Wigner transforms of the quark-exchange kernels with the use of a local momentum approximation, show that the NN spin-orbit interaction derived from the symmetric spin-orbit term of the one-gluon-exchange quark-quark interaction is in general agreement with the short-range part of phenomenological potentials derived from NN scattering. With the inclusion of the antisymmetric spin-orbit one-gluon-exchange terms and spin-orbit terms generated by confining potentials the full triplet-odd NN spin-orbit potential is greatly reduced in the 0.5–1 fm range. The uncertainties associated with spin-orbit terms generated by quark-confinement mechanisms are emphasized. The relative importance of various possible quark-gluon exchange terms is studied and shows that models which neglect some types of exchange terms are open to question. An SU(3)-flavor symmetric model for N-hyperon spin-orbit potentials leads to an NΛ spin-orbit potential only slightly weaker than the NN spin-orbit potential.     

What does the free space Lambda Lambda interaction predict for Lambda Lambda hypernuclei?

Data on LambdaLambda hypernuclei provide a unique method to learn details about the strangeness S = -2 sector of the baryon-baryon interaction. From the free space Bonn-Jülich potentials, determined from data on baryon-baryon scattering in the S = 0,-1 channels, we construct an interaction in the S = -2 sector to describe the experimentally known LambdaLambda hypernuclei. After including short-range (Jastrow) and RPA correlations, we find masses for these LambdaLambda hypernuclei in a reasonable agreement with data, taking into account theoretical and experimental uncertainties. Thus, we provide a natural extension, at low energies, of the Bonn-Jülich one-boson exchange potentials to the S = -2 channel.     

Hypernuclei with A ⩾ 12

We analyse recent experiments in which medium heavy hypernuclei 40 ? A ? 12 are produced. The depth of the lambda-nucleus shell-model potential is found to be D_gL = 28 ± 3 MeV. We see no significant spin-orbit term. The magnitude of the strangeness exchange cross section is not understood in all respects.     

Hyperon properties in finite nuclei using realistic YN interactions

Single-particle energies of Λ and Σ hyperons in several nuclei are obtained from the relevant self-energies. The latter are constructed within the framework of a perturbative many-body approach employing present realistic hyperon-nucleon interactions such as the models of the Jülich and Nijmegen groups. The effects of the non-locality and energy dependence of the self-energy on the bound states are investigated. It is also shown that, although the single-particle hyperon energies are well reproduced by local Woods-Saxon hyperon-nucleus potentials, the wave functions from the non-local self-energy are far more extended. Implications of this behavior for the mesonic weak decay of Λ hypernuclei are discussed.     

Progress in p-shell A hypernuclear spectroscopy

The strangeness nuclear physics is an important branch of nuclear physics. The spectroscopic study of A hypernuclei has been used as a tool for investigating the A-N interaction as well as probing the nuclear interior structure. In this paper some high-lights and open questions in the spectroscopic study of p-shell A hypernuclei are presented.     

The quark-meson coupling model for Λ, Σ and Ξ hypernuclei

The quark-meson coupling (QMC) model, which has been successfully used to describe the properties of both infinite nuclear matter and finite nuclei, is applied to a systematic study of Λ, Σ and Ξ hypernuclei. Assumptions made in the present study are, (i) the (self-consistent) exchanged scalar, and vector, mesons couple only to the u and d quarks, and (ii) an SU(6) valence quark model for the bound nucleons and hyperon. The model automatically leads to a very weak spin-orbit interaction for the Λ in a hypernucleus. Effects of the Pauli blocking at the quark level, particularly in the open, coupled, ΣN-ΛN chanel (strong conversion), is also taken into account in a phenomenological way.     

相对论平均场理论对∧,Ξ和∑超核的研究(英文)

基于相对论平均场理论,系统地研究了单∧,Ξ和∑超核,超子-核子相互作用通过拟合实验数据以及参照之前理论工作来确定。以16O为核芯,通过加入不同类型超子（∧,Ξ0,-和∑+,0,-）,比较了超子的平均势场和单粒子能级,并研究了对核芯的杂质效应。整体上看,∧和Ξ0超子在大块性质上类似;Ξ0超子平均势场最浅;库仑相互作用对于带电超子Ξ-,∑+和∑-非常重要。作为杂质,原子核中加入超子会使整个体系更束缚。然而,不同超子对原子核的半径有不同效应。此外,讨论了ωYY张量耦合,发现其对超子的能级劈裂有显著影响,甚至导致Ξ超子中出现能级反转现象。Single ∧, Ξ, and ∑ hypernuclei are systematically studied within the framework of relativistic mean-field (RMF) model with YN interactions being constrained according to the experimental data and previous theoretical efforts. By adding a hyperon to 16O, the mean-field potentials and single-particle levels for hyperons (∧, Ξ0,-, and ∑+,0,-) are compared and the impurity effects on the nuclear core are examined. In general, the ∧ and ∑0 hyperons show similar behaviors in bulk properties since both of them are electroneutral and with similar coupling constants; Ξ0 hyperon owns the shallowest mean-field potential well; and Coulomb interactions play vital roles in the charged Ξ-, ∑-, and ∑+ hyperons. As an impurity, the intruded single-hyperon makes the nuclear system more bound in most cases due to the attractive NY interaction. However, very different effects on the nucleon radii are observed for different hyperons. Besides, the effects of the ωYY tensor couplings on the spin-orbit splitting are discussed, and remarkable influences are found which even change the level ordering of Ξ hyperon.