Neutron-rich Hypernuclei Research Articles

Prediction of exotic hyperon halos in neutron-rich Zr hypernuclei

Abstract We study the single- and double-Λ hypernuclei in Zr isotopes with the Hartree–Fock–Bogoliubov model and Skyrme-type nucleon–nucleon, Λ–nucleon, and Λ–Λ interactions. We found two peculiar features of the Λ hyperon halo phenomena that have never been found in nuclei without the strangeness degree of freedom. One is the d-wave halo, and the other is a bunch of three halo orbits just below the Λ hyperon threshold in $^{137}_\Lambda$Zr and also in $^{138}_{\Lambda \Lambda }$Zr. We name these exotic halo phenomena giant hyperon halos in hypernuclei whose core nucleus 136Zr was predicted to have a “giant neutron halo.” The interaction between Λ hyperons and the neutrons is responsible for inducing giant hyperon halo phenomena in the single- and double-Λ nuclei $^{137}_\Lambda$Zr and $^{138}_{\Lambda \Lambda }$Zr.

Time-of-Flight System of HyperNIS Spectrometer

The main goal of the HyperNIS experiment is the search for the lightest neutron-rich hypernuclei, in particular, $$_{{\Lambda }}^{{\text{6}}}{\text{H}}$$ and the poorly studied $$_{{\Lambda }}^{{\text{6}}}{\text{He}}{\text{,}}$$ and to measure the lifetimes and production cross sections of these hypernuclei. In order to measure the masses of the hypernuclei, it is necessary to determine the momenta of their decay products, including pions. The time-of-flight (TOF) method is planned to be used to measure the pion momenta. Simulation results show that this method provides sufficient accuracy for recovering the masses of the hypernuclei. The structure of the TOF system detectors and the results of the study of their characteristics are presented.

Light neutron-rich hypernuclei from the importance-truncated no-core shell model

We explore the systematics of ground-state and excitation energies in singly-strange hypernuclei throughout the helium and lithium isotopic chains — from HeΛ5 to HeΛ11 and from LiΛ7 to LiΛ12 — in the ab initio no-core shell model with importance truncation. All calculations are based on two- and three-baryon interaction from chiral effective field theory and we employ a similarity renormalization group transformation consistently up to the three-baryon level to improve the model-space convergence. While the absolute energies of hypernuclear states show a systematic variation with the regulator cutoff of the hyperon–nucleon interaction, the resulting neutron separation energies are very stable and in good agreement with available data for both nucleonic parents and their daughter hypernuclei. We provide predictions for the neutron separation energies and the spectra of neutron-rich hypernuclei that have not yet been observed experimentally. Furthermore, we find that the neutron drip lines in the helium and lithium isotopic chains are not changed by the addition of a hyperon.

Examination of experimental conditions for the production of proton-rich and neutron-rich hypernuclei

After the demonstration of the feasibility of hypernuclear spectroscopy with heavy-ion beams, the HypHI Collaboration will next focus on the study of proton- and neutron-rich hypernuclei. The use of a fragment separator for the production and separation of rare isotope beams is a crucial aspect to producing hypernuclei far from the stability line. Precise spectroscopy of exotic hypernuclei is planned to be carried out at the GSI and later at the FAIR facility with the FRS and Super-FRS fragment separators. A systematic study and an optimization analysis were performed in order to determine optimal experimental conditions for producing hypernuclei with high isospin. The optimal conditions are obtained based on theoretical models for the heavy-ion induced reaction and hypernuclei production. Experimental efficiencies for the production of exotic secondary beams were also taken into account via Monte Carlo simulations of the fragment separator. The developed methodology is presented to deduce the expected yields of $^8_\Lambda$Be and subsequently other proton-rich and neutron-rich hypernuclei.

Study of Neutron-Rich Λ Hypernuclei

We discuss neutron-rich hypernuclei based on the first observation of \({^{10}_\Lambda{\rm Li}}\) in the KEK-E521 experiment as well as theoretical analyses. We also discuss recent experimental results on the production of an extremely neutron-rich hypernucleus, \({^{6}_\Lambda {\rm H}}\).

Study of Neutron-Rich Hypernuclei by the (π −, K +) Reaction at J-PARC

We are planning to perform an experiment at J-PARC and produce new neutron-rich Λ hypernuclei by using the (π−, K+) reaction (J-PARC E10). As the first step, we are planning to produce \({^6_{\Lambda}{\rm H}}\) hypernuclei with a 6Li target. To conduct this experiment, we are developing new detectors, those are scintillating fiber tracker, and silicon strip detector, for high rate operation to aim at increasing beam intensity up to 107/spill. As a result of beam test in Jun 2012, we are going to use high-rate beam at least 107/spill.

Neutron-rich hypernuclei in the chiral soliton model

The binding energies of neutron-rich strangeness S = −1 hypernuclei are estimated in the chiral soliton approach using the bound state rigid oscillator version of the SU(3) quantization model. Additional binding of strange hypernuclei in comparison with nonstrange neutron-rich nuclei takes place at not large values of atomic (baryon) numbers, A = B ≤ ∼10. This effect becomes stronger with increasing isospin of nuclides, and for the “nuclear variant” of the model with rescaled Skyrme constant e. Binding energies of Λ 8 He and recently discovered Λ 6 H satisfactorily agree with data. Hypernuclei Λ 7 H, Λ 9 He are predicted to be bound stronger in comparison with their nonstrange analogues 7H, 9He; hypernuclei Λ 10 Li, Λ 11 LI, Λ 12 Be, Λ 13 Be, etc. are bound stronger in the nuclear variant of the model.

HYPERNUCLEAR SPECTROSCOPY WITH HEAVY ION BEAMS: THE HypHI PROJECT AT GSI AND FAIR

The HypHI experiment for precise hypernuclear spectroscopy with induced reactions of stable heavy ion beams and rare isotope beams is currently under preparation at GSI. The main goal of the HypHI project is to study neutron and proton rich hypernuclei and to measure directly hypernuclear magnetic moments at GSI and FAIR. In the first HypHI experiment (Phase 0) planned in 2009, the feasibility of precise hypernuclear spectroscopy with heavy ion beams will be demonstrated by observing π- decay channels of [Formula: see text], [Formula: see text] and [Formula: see text] with 6 Li projectiles at 2 A GeV impinging on a 12 C target. An overview of the HypHI project and the details of the Phase 0 experiment will be discussed.

HYPERNUCLEI WITH A MICROSCOPIC LAMBDA-NUCLEON FORCE

We study properties of Λ hypernuclei in an extended Skyrme-Hartree-Fock model employing recent modern nucleonic Skyrme forces together with a microscopic lambda-nucleon interaction derived from Brueckner-Hartree-Fock calculations of hypernuclear matter with the Nijmegen soft-core hyperon-nucleon potentials. We show in particular recent results of deformed and neutron-rich hypernuclei close to the dripline.

Hypernuclei with a Microscopic Lambda-Nucleon Force

We study properties of Λ hypernuclei in an extended Skyrme-Hartree-Fock model employing recent modern nucleonic Skyrme forces together with a microscopic lambda-nucleon interaction derived from Brueckner-Hartree-Fock calculations of hypernuclear matter with the Nijmegen soft-core hyperon-nucleon potentials. We confront with experimental data on single-particle levels of single-Λ hypernuclei and bond energies of double-Λ hypernuclei, and present also recent results for deformed and neutron-rich hypernuclei close to the dripline.

Σ-admixture in neutron-rich Li Λ hypernuclei in a microscopic shell-model calculation

We systematically investigate the structures of the Λ hypernuclei Λ Li with the mass number A = 7–10 in shell-model calculations considering the ΛN -ΣN coupling in the first-order perturbation method. We find that the calculated Σ -mixing probabilities and energy shifts due to the ΛN -ΣN coupling increase with the neutron number. The Fermi-type and Gamow-Teller-type couplings, which are related to the β-transition properties of the nuclear core state, coherently contribute to the energy shift in neutron-rich hypernuclei.

THE HYPHI PROJECT: HYPERNUCLEAR SPECTROSCOPY WITH STABLE HEAVY ION BEAMS AND RARE ISOTOPE BEAMS AT GSI AND FAIR

The HypHI collaboration aims to perform a precise hypernuclear spectroscopy with stable heavy ion beams and rare isotope beams at GSI and FAIR in order to study hypernuclei at extreme isospin, especially neutron rich hypernuclei to look insight hyperon-nucleon interactions in the neutron rich medium, and hypernuclear magnetic moments to investigate baryon properties in the nuclei1,2. We are currently preparing for the first experiment with 6 Li and 12 C beams at 2 A GeV to demonstrate the feasibility of a precise hypernuclear spectroscopy by identifying [Formula: see text], [Formula: see text] and [Formula: see text]. The first physics experiment on these hypernuclei is planned for 2009. In the present document, an overview of the HypHI project and the details of this first experiment will be discussed.

Strangeness at J-PARC

Strangeness nuclear physics is one of the main fields to be explored at the J-PARC Hadron Hall. The K − and π± beams at the K1.8 beam line will be used mostly for hypernuclear experiments. The γ-spectroscopy of Λ hypernuclei using the K −,π − reaction and the spectroscopy of neutron-rich hypernuclei via the π −,K + reaction are planned to be studied. As for Strangeness = − 2 systems, experiments for Ξ hypernuclear spectroscopy via the K −,K + reaction, double Λ hypernuclei by the hybrid emulsion method, and Ξ−-atomic X rays will be carried out.

Studying of hypernuclei with nuclotron beams

A spectrometer is created to study relativistic hypernuclei produced with beams of accelerated nuclei from the Nuclotron facility (Dubna, JINR). Test runs have been carried out and the conclusion is drawn that the properties of the facility meet the requirements of the task of searching for unknown and studying poorly known neutron-rich hypernuclei.

Light hypernuclei in FINUDA

The FINUDA experiment produces Λ-hypernuclei stopping in thin targets the K−’s coming from the decay of the Φ particle inside the DAΦNE e+-e− collider machine. The Λ-hypernucleus formation is detected by measuring the momentum of the outgoing π− coming from the strangeness-exchange reaction (K−, π−) inside the targets. Experimental results related to few-body issues, such as hypernuclear spectroscopy, hypernuclear decays, and neutron-rich hypernuclei will be presented.

What can we learn about baryon-baryon interaction from hypernuclei Λ 6 H and Λ 8 H?

At the LHE JINR, an original approach to hypernuclear experiments was elaborated to produce relativistic hypernuclei. The production cross sections and lifetimes, τ, of Λ 3 H and Λ 4 H were measured successfully. The results of recent experiments on 5H and 7H nuclei suggest that the hypernucleus Λ 6 H might be stable and that this may be the case even for Λ 8 H. The unique quality of the spectrometer SPHERE may be used to identify unambiguously the isotopes of hyperhydrogen—through their pionic decay Λ H → π − + A He—including the new hypernuclei Λ 6 H and Λ 8 H with extreme values of N/Z of 4 and 6, respectively. The confirmation of the very existence of these neutron-rich hypernuclei would be a strong motivation to search for their spectra in strangeness and double-charge-exchange reactions (K stop − , π +) at FINUDA or (π −, K +) at J-PARC. It is very probable that, similarly as in Λ 4 H, there is a low-lying state 1+ also in Λ 6 H and Λ 8 H. If their electromagnetic width (M1) is small enough, we could see two different values of τ for Λ 6 H and/or Λ 8 H. We investigate the spacings of the 1+ and 0+ states of Λ 4 H, Λ 6 H, and Λ 8 H. The understanding of the structure of isospin asymmetric systems plays a key role in the description of systems as diverse as neutron-rich nuclei and neutron matter.

PHYSICS RESULTS FROM FINUDA AT DAΦNE

Physics results achieved with the use of the FINUDA detector at DAΦNE are presented and discussed. They span from Hypernuclear Spectroscopy to the search for neutron rich Hypernuclei and to the solution of the puzzle about the existence of narrow Deeply Bound [Formula: see text] States.

First results from the FINUDA experiment

This paper provides a summary of the first results obtained by the FINUDA Collaboration in the field of hypernuclear physics. They range from the spectroscopic study of several A-hypernuclei to the observation of some non-mesonic decay modes. Hints on rare hypernuclear two-body decays, on neutron-rich hypernuclei and on deeply-bound kaonic nuclei are also reported.

Hypernuclear physics at DAΦNE2

The FINUDA experiment begun its first data taking period at DAΦNE, the INFN Frascati Φ-factory, in October 2003, working with a peak luminosity L p ∼ 0 , 5 × 10 32 cm −2 s −1 . Its Scientific Program in based on the study of spectroscopy and decay modes of Λ-hypernuclei produced by stopping slow K − in thin nuclear targets. The possibility of extending this program to particular very interesting items, like neutron-rich hypernuclei research, 2 N induced non-mesonic decays investigation and coincidence γ-ray spectroscopy of low-lying hypernuclear levels, is discussed in this paper in the hypothesis of a future improvement the DAΦNE peak luminosity up to L p = 10 35 cm −2 s −1 , proposed for a second version of the machine, called DAΦNE2.

First results from the FINUDA experiment at DAΦNE

In spring 2003 the FINUDA detector was installed at the ϕ factory DAΦNE in the Laboratori Nazionali di Frascati of INFN (Italy). In October 2003 the commissioning of the apparatus was accomplished and the first data taking started with a set of nuclear targets 6Li, 7Li, natC, 27Al, 51V. The data collection will continue until a total integrated luminosity of 250 pb −1 is recorded. Light and medium A hypernuclei will be abundantly produced by the strangeness exchange reaction induced by the stopped K − coming from the decay of ϕ ( 1020 ) mesons. The aim of the experiment is to simultaneously measure the excitation energy spectra of the produced hypernuclei, with a resolution better than 1 MeV, the lifetime of the Λ embedded in the different hypernuclei and the partial widths Γ π , Γ n p and Γ n n for mesonic and non-mesonic hypernuclear decays. Information on neutron-rich hypernuclei and rare hypernuclear two-body decays might be available too, with the statistics that will be collected at the end of the run. In the present paper, first results concerning in-beam detector calibration, spectrometer performances and very preliminary hypernuclear formation and decay spectra will be presented.