Search

The structure of heavy hyperhydrogen 6 Λ H is studied within the framework of a t n n Λ four-body cluster model. Interactions among the constituent subunits are determined so as to reproduce reasonably well the observed low energy properties of the t n , t Λ and tnn subsystems. As long as we reproduce the energy and width of 5 H within the error bar, the ground state of 6 Λ H is obtained as a resonant state.

We have constructed the hyperon-nucleus optical potential based on the complex G -matrix folding model. The complex G -matrix interactions are derived from the extended-soft core (ESC) model interactions, ESC04a and ESC08. The elastic cross sections and analyzing powers are calculated using the folding-model potentials (FMPs) based on the complex G -matrix interactions. The strength functions for the ( π − , K + ) reaction are also obtained using the FMPs and are compared with the result calculated with a phenomenological repulsive optical potential. The ESC08 interaction gives a better result than does ESC04a.

The features of the new YN interaction model ESC08 are studied on the basis of the G-matrix theory.

By taking nuclear core excitations into account, detailed structure calculations of 89 ΛY have been performed as a function of the Λ spin–orbit splitting. The obtained wave functions have been used to estimate the ( π + , K + ) reaction cross sections within the distorted-wave impulse approximation (DWIA). A theoretical explanation is given quantitatively for the first time of how to understand the doublet substructure of each major peak observed in medium-heavy hypernuclear production. A small Λ spin–orbit splitting of around δ ( 0 f Λ ) = 0.2 MeV is deduced, a value consistent with the small ΛN two-body spin–orbit interactions deduced from γ-ray measurements in three light hypernuclei.

Structures of S=−2 many-body states (double-Λ and Ξ hypernuclei) are investigated on the basis of G-matrix interactions derived from the recently-developed extended-soft-core model (ESC04d). ΛΛ–ΞN mixing effects in 6ΛΛHe, 5ΛΛH and 5ΛΛHe are investigated with use of three-body models. Possible Ξ hypernuclei are investigated systematically with Ξ-core folding potentials derived from ΞN G-matrix interactions. A four-body narrow Ξ0–Ξ− mixed state, specific to ESC04d, is discussed.

Two spin-doublet, 3 / 2 + - 1 / 2 + and 7 / 2 + - 5 / 2 + , in 7ΛLi are studies on the basis of the α + Λ + n + p four-body model. The calculated energy splittings of 3 / 2 + - 1 / 2 + and 7 / 2 + - 5 / 2 + states in 7ΛLi are 0.69 MeV and 0.46 MeV, which are in good agreement with the recent observed data.

Three- and four-body structure calculations of single Λ hypernuclei such as Λ 7 He, Λ 9 Be and Λ 13 C and double Λ hypernuclei such as ΛΛ 4 H, ΛΛ 7 He, ΛΛ 7 Li, ΛΛ 8 Li, ΛΛ 9 Li, ΛΛ 9 Be and ΛΛ 10 Be are discussed. The energy levels of Λ 7 He whose core is a famous halo nucleus, Λ 6 He, are predicted based on Λ 5 He + 2 N three-body model. In the microscopic 2α + Λ(3α + Λ) model for Λ 9 Be( Λ 13 C), we predict the spin-orbit splittings of 5/2 1 + −3/2 1 + in Λ 9 Be and 3/2 1 − −1/2 1 − in Λ 13 C to be 0.08–0.16 MeV and 0.39–0.78 MeV, respectively, with the use of OBE-model NSC97a ∼f. On the other hand quark-model Λ N spin-orbit force gives rise to half of the splittings of the smallest OBE-model prediction. The experimental data were reported to be 31.4 −3.6 +2.5 keV for Λ 9 Be and to be 152 ± 54 ± 36 keV for Λ 13 C. By performing four-body calculation of ΛΛ 4 H with both NN ΛΛ and NNN Ξ channels, we show that the ΛΛ − Ξ N coupling potential plays an important role in making ΛΛ 4 H. Energy levels of the double-Λ hypernuclei, ΛΛ 7 He, ΛΛ 7 Li, ΛΛ 8 Li, ΛΛ 9 Li, ΛΛ 9 Be and ΛΛ 10 Be are predicted on the basis of an α + x + Λ + Λ four-body model, where x = n , p , d , t 3 He and α, respectively.

Hypernuclear physics has become very exciting owing to new epoch-making experimental data. Recent progress in theoretical and experimental studies of hypernuclei and future developments in this field are discussed.

Starting with the ( K − , K + ) reaction on nuclear targets of mass number 9–12 ( 9 Be, 10 B, 11 B, 12 C), the probabilities of producing double-Λ and single-Λ hyperfragments at the reaction points have been evaluated on the basis of the statistical model. First, the Ξ particle produced abundantly in the quasi-free region is shown to be well absorbed into the nucleus through the Ξ slowdown by knocking out a nucleon. Then the formation of a double-Λ compound nuclear system is assumed together with its subsequent breaking-up into various hyperfragments. The theoretical pion spectra are presented for the weak decays of the double-Λ and single-Λ hypernuclei produced efficiently in this scenario, which can be utilized for the identification of their hyperfragments production. It is proposed that the observation of ΛΛ 5 H with the 9 Be target is most feasible and promising.

Five kinds of G-matrix interactions derived from the Nijmegen and Julich hyperon-nucleon potentials have been applied to various hypernuclear structure calculations. Interesting results are discussed in connection with the interaction properties and also in view of the (π+, K) and (K−, π) reaction experiments.

In the first part, we present the structure calculations for double-Λ hypernuclei on the basis of the G-matrix ΛΛ interactions derived from the Nijmegen OBE models. In the second part, we discuss the production processes of double-Λ hypernuclei in Ξ − absorption.