Production of (4)(double Lambda)H hypernuclei

An experiment demonstrating the production of double-Lambda hypernuclei in (K(-),K(+)) reactions on (9)Be was carried out at the D6 line in the BNL alternating-gradient synchrotron. The technique was the observation of pions produced in sequential mesonic weak decay, each pion associated with one unit of strangeness change. The results indicate the production of a significant number of the double hypernucleus (4)(double Lambda)H and the twin hypernuclei (4)(Lambda)H and (3)(Lambda)H. The relevant decay chains are discussed and a simple model of the production mechanism is presented. An implication of this experiment is that the existence of an S = -2 dibaryon more than a few MeV below the double Lambda mass is unlikely.     

The formation of hypernuclei by K− capture

K^? capture leading to the formation of hypernuclei takes place with the kaon either in a Bohr orbit (capture at rest), or in flight. We analyze both situations in the framework of the distorted-wave impulse approximation (DWIA), derive cross sections and formation rates, and compare the results with experimental data on the reaction ¹²C(K^?, π^?)¹²_ΛC¹. Corrections to the DWIA which arise from rescattering, from binding energy effects and from the intermediate formation of a ∑-hyperon, are estimated and found not to be negligible.     

Asymmetry in the nonmesonic weak decay of polarized (5)(Lambda)He hypernuclei

We have measured the asymmetric emission of protons from the nonmesonic decay of polarized (5)(Lambda)He produced by the (pi(+), K+) reaction. (5)(Lambda)He is an s-shell hypernucleus and its polarization is due to the Lambda. One expects to obtain direct information on the elementary weak Lambda-->p-->np process. The asymmetry parameter has been determined to be 0.24+/-0.22. The implication of the result is discussed.     

Double-lambda compound nucleus and the formation of double hypernuclei

The formation probabilities of single- and double- compound nuclei from ^– following the (K^–, K⁺) reaction are calculated, showing that double- hypernuclei are formed with a fairly large probability through a hyperon compound process involving ^– directly after the (K^–, K⁺) reaction.We dedicate this paper to the late Professor Jan ofka with whom we enjoyed nice friendship and collaboration. We also thank the late Professor H. Bando and Professors K. Yazaki, Y. Akaishi and T. Fukuda for stimulating discussions.     

The formation of,and the γ-radiation from,the p-shell hypernuclei

The physical factors relevant for the production of various low-lying Λ-hypernuclear states ${}_{\mathrm{\Lambda }}{}^{\mathrm{A}}\text{Z}{}^1$ through the K^? → π^? and K^? → π⁰ reactions, in flight or from rest, on the corresponding target nuclei ^AZ and ^A(Z + 1) are discussed, on the basis of the shell model for these nuclei and hypernuclei, together with the characteristics of the dominant γ-transitions resulting from the excited states thus produced. Detailed consideration is given for a number of hypernuclei of specific interest, including the cases of _Λ⁷He, _ΛLi for A = 7, 9 and 10, _ΛBe for A = 9 and 10, _ΛB for A = 10, 11, and 12, _ΛC for A = 12, 13, 14, and 15, _ΛN for A = 14 and 15, and _Λ¹⁶O. The importance of (γ, π^?) correlation studies for the determination of hypernuclear spin values is stressed, with the discussion of several examples.     

Strangeness violating lambda-nucleon cross-section from hypernuclei life times

It is shown that the recently obtained hypernuclei life-times can be explained in term of a weak strangeness violating lambda-nucleon interaction with a cross section close to 6.0 10^?15 barns.     

Decay of hypernuclei

We present a nonrelativistic transition potential for the weak strangeness-changing reaction ΛN → NN. The potential is based on a one meson exchange model (OME), where, in addition to the long-ranged pion, the exchange of the pseudoscalar K, η, as well as the vector ,ω, K^* mesons is considered. Results obtained for different hypernuclear decay observables are compared to the available experimental data.     

Light deformed hypernuclei

In the Hartree-Fock scheme, the influence of the added -hyperon is studied on theN= Z even-evenA40 nuclei. The emphasis is put on the shape polarizability, which is related to the bulk properties of the potentials used. Possible experimental connections are commented.Dedicated to Academician Václav Votruba on the occasion of his seventieth birthday.Some of the results have been presented preliminarily at the Balaton 79 Conference on Large Amplitude Collective Motions [35], Discussions with L. Majling, M. Sotona and V. N. Fetisov are greatly acknowledged. Special thanks are due to Miloslav Sotona for constructing Si interactions.     

Pionic decay of hypernuclei

The mass number dependence of the total pionic decay rate of hypernuclei is evaluated under the closure approximation by using DDHF single-particle wave functions and taking into account the pion distortion and absorption. The effect ofNN andN correlations are then incorporated and found to give a drastic enhancement especially in heavy hypernuclei. More detailed features are discussed for partial and total decay rates of typical light hypernuclei.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

Excited states of hypernuclei

A two-body model of a hypernucleus with realistic N potentials is used to calculate the energies of the excited states of the particle in heavy hypernuclei. The positions of the levels are investigated as functions of: a) the form of the N potential, b) the size of the core nucleus and the form of the nucleon density, and c) the mass number A.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 33–37, April, 1980.     

Neutron halos in hypernuclei

Properties of single- Λ and double- Λ hypernuclei for even-N Ca isotopes ranging from the proton dripline to the neutron dripline are studied using the relativistic continuum Hartree-Bogoliubov theory with a zero-range pairing interaction. Compared with ordinary nuclei, the addition of one or two Λ-hyperons lowers the Fermi level. The predicted neutron dripline nuclei are, respectively, ⁷⁵ _ΛCa and ⁷⁶ _2ΛCa, as the additional attractive force provided by the Λ-N interaction shifts nuclei from outside to inside the dripline. Therefore, the last bound hypernuclei have two more neutrons than the corresponding ordinary nuclei. Based on the analysis of two-neutron separation energies, neutron single-particle energy levels, the contribution of continuum and nucleon density distribution, giant halo phenomena due to the pairing correlation, and the contribution from the continuum are suggested to exist in Ca hypernuclei similar to those that appear in ordinary Ca isotopes. Received: 21 October 2002 / Accepted: 11 January 2003 / Published online: 8 April 2003     

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.     

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.