Fission barrier of actinide nuclei with double-Λ particles within the Skyrme–Hartree–Fock method

Fission barrier of actinide nuclei including two Λ hyperons is studied in the framework of the Skyrme–Hartree–Fock approach at zero temperature. We adopt the zero-range Skyrme-type interaction between Λ–N and Λ–Λ. Fission barrier is investigated using several parameter sets for ΛΛ interactions. We obtain the result that the barrier height becomes higher as the number of Λ particle increases and the barrier width has a dependence on the ΛΛ interaction. A relation between Λ binding energy and density distribution of Λ particle inside a core nucleus is also discussed. We found that the both Λ particles are attracted into heavier fission fragment.     

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.     

Study of ΛΛ dynamics and ground state structure of low and medium mass double Λ hypernuclei

We critically review the ΛΛ dynamics by examining Λ - Λ and Λ-nucleon phenomenological potentials in the study of the bound state properties of double-Λ hypernuclei _ΛΛ ⁶ He, _ΛΛ ¹⁰ Be, _ΛΛ ¹⁴ C, _ΛΛ ¹⁸ O, _ΛΛ ²² Ne, _ΛΛ ²⁶ Mg, _ΛΛ ³⁰ Si, _ΛΛ ³⁴ S, _ΛΛ ³⁸ Ar, _ΛΛ ⁴² Ca, _ΛΛ ⁴⁶ Ti, _ΛΛ ⁵⁰ Cr, _ΛΛ ⁵⁴ Fe, _ΛΛ ⁵⁸ Ni, _ΛΛ ⁶² Zn, _ΛΛ ⁶⁶ Ge, _ΛΛ ⁷⁰ Se, _ΛΛ ⁷⁴ Kr, _ΛΛ ⁷⁸ Sr, _ΛΛ ⁸² Zr, _ΛΛ ⁸⁶ Mo, _ΛΛ ⁹⁰ Ru, _ΛΛ ⁹⁴ Pd, _ΛΛ ⁹⁸ Cd, _ΛΛ ¹⁰² Sn in the frame work of (core+Λ+Λ) three body model. An effective ΛN potential is obtained by folding the phenomenological ΛN potential into the density distribution of the core nuclei. The former two cases (i.e. _ΛΛ ⁶ He and _ΛΛ ¹⁰ Be) are revisited to justify the correctness of the present potential model. Assuming the same potential model we predicted some of the structural properties of heavier doubly Λ-hypernuclei. The hyperspherical harmonics expansion method, which is an essentially exact method has been employed for the three body system. A convergence in binding energy up to 0.15% for K _max=20 has been achieved. In our calculation we have made no approximation in restricting the allowed l-values of the interacting pairs.     

Necessity of extra repulsion in hypernuclear systems: Suggestion from neutron stars

Neutron star models with hyperon-mixed core are studied by a realistic approach to use the YN and the YY interactions consistent with hypernuclear data. From the compatibility of the theoretical maximum mass with the observed neutron star mass 1.44 M _⊙ of PSR1913+16, the necessity of some extra repulsion in hypernuclear systems, e.g., a repulsion from three-body force, is stressed. It is noted that the increase of baryon degrees of freedom to avoid the short-range repulsion effectively is an essential mechanism causing the Y-mixed phase. Received: 1 May 2001 / Accepted: 4 December 2001     

Strangeness at the international Facility for Antiproton and Ion Research

The project of the international Facility for Antiproton and Ion Research (FAIR), co-located to the GSI facility in Darmstadt, was officially started on November 7, 2007. An investment of about 1 billion euro will permit new physics programs in the areas of low and medium energy antiproton research, heavy ion physics complementary to LHC, as well as in nuclear structure and astrophysics. The facility will comprise about a dozen accelerators and storage rings, which will enable simultaneous operations of up to four different beams.     

Study of the proton weak decay of 12ΛCg.s. with FINUDA

The FINUDA experiment studies the Λ -hypernuclei formation and decay using the reaction ( K ^- _stop,π^- induced by the low-momentum K^- from the deacy of the φ -meson produced at the (e ⁺, e ^- collider DAφ NE at the Laboratory Nazionali di Frascati of INFN. In this paper we present new data on the proton spectra following the weak decay of ¹² _ΛC .     

γ -ray spectroscopy study of 11 ΛB and 12 ΛC

In this paper, a preliminary result from the latest hypernuclear γ -ray spectroscopy experiment (KEK-E566) is presented together with a short discussion. The experiment was performed at the KEK-PS K6 beam line in 2005. In this experiment, the ¹²C(π⁺, K ⁺)¹² _ΛC reaction was employed to populate ¹² _ΛC/¹¹ _ΛB hypernuclei. A germanium detector array, Hyperball2, was constructed to detect γ -rays emitted from the hypernuclei produced. Three hypernuclear γ -ray peaks were observed and assigned.     

The A(K-stop,Λd )A'' reaction, a tool to observe [ˉNNN] clusters

This work presents experimental results obtained from a study of the K ^- _stop A → ΛdA' reaction, where A = ⁶ Li . The study concerns the distributions of the Λd invariant mass, which allows us to determine the structure of bound [K ^- ppn] systems in nuclei. A candidate of such clusters is identified in the present measurement, and its mass (binding energy), decay width and yield are reported. The experiment was performed at the DAΦ NE φ -facility (LNF) by using the FINUDA spectrometer. The study depended on the capability of FINUDA to reconstruct the traces of all the particles involved in the decay of the nuclear cluster.     

Impurity nuclear physics

Using a germanium-detector array for hypernuclear γ spectroscopy (Hyperball), we measured B(E2) of the ⁷ _ΛLi hypernucleus and observed a significant shrinkage of the ⁶Li core induced by a Λ-particle. In this way, nuclear properties can be drastically changed by introducing a Λ-particle, which can be investigated by high-resolution hypernuclear γ spectroscopy. In the future neutron-rich hypernuclei will also be studied, where interesting modifications of nuclear structure by a Λ-particle are expected. Received: 1 May 2001 / Accepted: 4 December 2001     

Structure of light hypernuclei

The structure of light hypernuclei with strangeness S=−1 and −2 is investigated with the microscopic cluster model and the Gaussian expansion method (GEM). We emphasize that the cluster picture as well as the mean-field picture is invaluable to understand the structure of Λ hypernuclei, Σ hypernuclei and double Λ hypernuclei. A variety of aspects of Λ hypernuclei is demonstrated through a systematic study of p-shell hypernuclei (,, , , , , ) and sd-shell ones (, ): for example, the appearance of genuine hypernuclear states with new spatial symmetry which cannot be seen in ordinary nuclei, the glue-like role of the Λ particle which shrinks the size of nuclear core and thus reduces the B(E2) value, and the halo and skin structures in and etc. The typical light hypernucleus is thoroughly investigated, including its production, structure and decay. Precise three-body and four-body calculations of , and using GEM provide important information on the spin structure of the underlying ΛN interaction, by comparing with recent experimental data from γ-ray hypernuclear spectroscopy. The Λ–Σ coupling effect is studied in and . The binding mechanism of is discussed together with the possible existence of , emphasizing the fact that the study of is useful for extracting information on the ΣN interaction differing from that from . A systematic study of double-Λ hypernuclei, constrained by the NAGARA data () within a four-body cluster model indicates that the recently observed Demachi–Yanagi event can be interpreted as the 2⁺ state of . The effect of hyperon mixing in and is investigated using one-boson-exchange potentials and quark-cluster-model interactions for the S=−2 sector. A close relation between nuclear deep hole states and hypernuclei is discussed, emphasizing the selection rule for fragmentation of the s-hole in light nuclei, which is promising for understanding the production mechanism of double-Λ and twin-Λ hypernuclei via Ξ-atomic capture.