Structure Of Hypernuclei Research Articles

The structure of hypernuclei and hyperon mixing in neutron-star matter

We review our recent studies of the structure of Λ hypernuclei within the framework of the Gaussian expansion method for s- and p-shell hypernuclei and the mean-field approach for sd-shell hypernuclei. Specifically, we focus on the structures of (i) the energy splittings of the – and – levels in Be and within the framework of and , three- and four-body cluster models for the hyperon–nucleon (Y–N) spin–orbit force; (ii) the system for coupling; (iii) the weakly bound states or resonant states of neutron-rich Λ hypernuclei such as and He within the framework of and four-body models; and (iv) the tensor correlation effect and super-deformation structure of Λ hypernuclei based on sd-shell nuclei with mass using the deformed Skyrme–Hartree–Fock model and the antisymmetrized molecular dynamics model. As an extreme limit of nuclei including multiple hyperons, we review hyperon effects in neutron-star matter in the high-density region using recent Y–N interactions.

EXPERIMENTAL OVERVIEW AND CHALLENGE IN STRANGENESS NUCLEAR PHYSICS — STRANGENESS IN THE PAST AND COMING DECADES

A great progress has been made in strangeness nuclear physics in the past decade. Examples are; 1) The "hyperfine" structure of hypernuclei were measured with the Hyperball, and ΛN spin dependent interactions in p -shell hypernuclei were determined. 2) The "complete measurements" of the weak decay of hypernuclei were made and the np ratio puzzle in the non-mesonic decay was solved. 3) The discovery of a clean event of "Lambpha" and determination of its binding energy concluded that the Λ-Λ interaction is weak attractive. However, we still have important questions to be answered in this field, especially in relation with QCD and nuclear physics. For the future strangeness nuclear physics, we have and will have facilities such as JLab, SPring-8, Daphne, J-PARC, FAIR. We discuss experimental challenges in the strangeness nuclear physics and related fields in the next decade.

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.

Baryon-baryon interactions with strangeness studied from hypernuclei

Structure of hypernuclei provides valuable information on baryon-baryon interactions. We have studied the Λ N spin-dependent interactions from precise level structure of p- shell Λ hypernuclei by means of a recently-developed technique of hypernuclear γ -ray spectroscopy with the germanium detector array, Hyperball. The strengths of the spin-spin, spin-orbit, and tensor interactions have been experimentally determined from Li Λ 7 , Be Λ 9 , and O Λ 16 hypernuclear level energies. Consistency check of the strength parameters has been also made with more p -shell hypernuclear data. Experimental results on double Λ hypernuclei and Σ hypernuclei have also provided information on ΛΛ and Σ N interactions.

Gaussian expansion method for few-body systems

We review our method of calculation, Gaussian Expansion Method (GEM), for bound and scattering states of few-body systems. The method was proposed in 1988 and has been applied to a variety of few-body systems. The understanding on the structure and the mechanisms of reactions of those systems obtained from such applications is discussed together with some useful techniques for the calculations. A well-chosen set of Gaussian basis functions forms an approximate complete set in a finite coordinate space so that it can describe accurately short-range corielations and long-range asymptotic behavior as well as highly oscillatory character of wave functions in the bound and the scattering states of the systems. Examples of applications of GEM include i) the latest determination of antiproton mass by the analysis of laser spectroscopic data for antiprotonic helium atoms, ii) predictions and experimental verifications on the structure of hypernuclei and hyperon-nucleon interactions, iii) Coulomb three-body calculations of bound and resonant states of muonic molecules as well as muon transfer reactions in muon catalyzed fusion cycles, iv) a new treatment of CDCC (continuum-discretized coupled channels) method for three- and four-body breakup processes, and v) benchmark test calculations for three- and four-nucleon bound states using realistic interactions.

Diffraction scattering of Λ 3 H and Λ 6 He hypernuclei on nuclei with allowance for edge diffuseness, the structure of hypernuclei, and multiple-scattering effects

General formulas for the amplitudes of the diffraction scattering of two-and three-cluster loosely bound nuclei on spherical nuclei for an arbitrary dependence of the profile functions on the impact parameter are represented in a form that is convenient for calculations. The differential cross sections for the elastic scattering of Λ 3 H and Λ 6 He hypernuclei and the total cross sections are obtained with allowance for the diffuseness of the target-nucleus edge, the binding energy of incident hypernuclei, the ranges of nuclear forces between the clusters in the hypernuclei, and multiple (double and triple) scattering. Changes in the behavior of the cross sections in response to a transition from the two-cluster to the three-cluster model of the aforementioned nuclei are revealed.

ΛN and ΛΛ interaction and structure of hypernuclei

Parameters of ΛN and ΛΛ interactions have been found from the binding energies of hypernuclei 4He Λ, 5He Λ, 6He ΛΛ . A possibility is discussed of multiplet state existence of hypernuclei, which exist due to the proximity of ΛN interactions in singlet and triplet spin states.