Atsushi Umeya

Tensor-optimized shell model for the Li isotopes with a bare nucleon-nucleon interaction

We study the Li isotopes systematically in terms of the tensor-optimized shell model (TOSM) by using a bare nucleon-nucleon interaction as the AV8 ′ interaction. The short-range correlation is treated in the unitary correlation operator method (UCOM). Using the TOSM+UCOM approach, we investigate the role of the tensor force on each spectrum of the Li isotopes. It is found that the tensor force produces quite a characteristic effect on various states in each spectrum and those spectra are affected considerably by the tensor force. The energy difference between the spin-orbit partner, the p1/2 and p3/2 orbits of the last neutron, in 5 Li is caused by opposite roles of the tensor correlation. In 6 Li, the spin-triplet state in the LS coupling configuration is favored energetically by the tensor force in comparison with jj coupling shell model states. In 7,8,9 Li, the low-lying states containing extra neutrons in the p3/2 orbit are favored energetically due to the large tensor contribution to allow the excitation from the 0s-orbit to the p1/2 orbit by the tensor force. Those three nuclei show the jj coupling character in their ground states which is different from 6 Li.

Production of doubly strange hypernuclei via Ξ− doorways in the O16(K−,K+) reaction at 1.8 GeV/c

Abstract We examine theoretically production of doubly strange hypernuclei, C Ξ − 16 and 16ΛΛC, in double-charge exchange O 16 ( K − , K + ) reactions using a distorted-wave impulse approximation. The inclusive K + spectrum at the incident momentum p K − = 1.8 GeV / c and scattering angle θ lab = 0 ° is estimated in a one-step mechanism, K − p → K + Ξ − via Ξ − doorways caused by a Ξ − p – Λ Λ coupling. The calculated spectrum in the Ξ − bound region indicates that the integrated cross sections are on the order of 7 – 12 nb / sr for significant 1 − excited states with C 14 ( 0 + , 2 + ) ⊗ s Λ p Λ configurations in 16ΛΛC via the doorway states of the spin-stretched N 15 ( 1 / 2 − , 3 / 2 − ) ⊗ s Ξ − in C Ξ − 16 due to a high momentum transfer q Ξ − ≃ 400 MeV / c . The Ξ − admixture probabilities of these states are on the order of 5–9%. However, populations of the 0 + ground state with C 14 ( 0 + ) ⊗ s Λ 2 and the 2 + excited state with C 14 ( 2 + ) ⊗ s Λ 2 are very small. The sensitivity of the spectrum on the Ξ N – Λ Λ coupling strength enables us to extract the nature of Ξ N – Λ Λ dynamics in nuclei, and the nuclear ( K − , K + ) reaction can extend our knowledge of the S = − 2 world.

Structures in 9,10Be and 10B studied with the tensor-optimized shell model

Structures in 9,10Be and 10B studied with the tensor-optimized shell model Takayuki Myo1,2,∗, Atsushi Umeya3, Hiroshi Toki2, and Kiyomi Ikeda4 1General Education, Faculty of Engineering, Osaka Institute of Technology, Osaka, Osaka 535-8585, Japan 2Research Center for Nuclear Physics (RCNP), Osaka University, Ibaraki, Osaka 567-0047, Japan 3Human Science and Common Education, Faculty of Engineering, Nippon Institute of Technology, Saitama 345-8501, Japan 4RIKEN Nishina Center, Wako, Saitama 351-0198, Japan ∗E-mail: myo@ge.oit.ac.jp, takayuki.myo@oit.ac.jp

Shell and alpha cluster structures in 8Be with tensor-optimized shell model

We study the shell and alpha cluster structures in the ground and excited states of 8Be in terms of the tensor-optimized shell model (TOSM). In TOSM, the tensor correlation is optimized in the full space of 2p2h configurations involving high-momentum components. The short-range correlation is treated with the unitary correlation operator method (UCOM). We use the effective interaction based on the bare nucleon-nucleon interaction AV8

Structures and productions of typical sd-shell hypernuclei in shell-model calculations

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Doublet-spacing enhancement caused by {Lambda}N-{Sigma}N coupling in {sub {Lambda}L}i hypernuclear isotopes

. The 8Be states consist of two groups of ground band states and highly excited states with the isospin T=0 and T=1. It is found that the tensor contributions of the ground band states are stronger than the highly excited states and that the kinetic energies and the central contributions of the ground band states are almost twice the 4He values. These features suggest two-alpha clustering for the ground band states in 8Be. We also estimate the correlation energy of the

Monopole Interaction and Single‐Particle Energies

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Monopole and quadrupole interactions in binding energies of sd-shell nuclei

clustering using the alpha cluster model. In the highly excited states, the calculated spectrum in TOSM reproduces the experimental level order and the relative energies of each level. This agreement suggests that those states can be interpreted as shell-like states. The level order is found to be sensitive to the presence of the tensor force in comparison with the results using the Minnesota effective interaction without the tensor force. It is also found that the tensor contributions in the T=0 states are stronger than the T=1 states, which is consistent with the state dependence of the tensor force.

EFFECTIVE CHARGES OF E2 TRANSITIONS FOR CARBON ISOTOPES

As one of the typical sd-shell hypernuclei, the positive- and negative-parity energy levels of 20ΛNe are calculated to investigate structures of low-lying states within the shell model calculations. In addition to the conventional NN effective interactions, the ΛN G-matrix interactions derived from the Nijmegen NSC97f potentials are employed. The production cross sections of (π+,K+) and (K−,π−) reactions are estimated using the calculated shell-model wave functions.

Role of the tensor interaction in He isotopes with a tensor-optimized shell model

We theoretically investigate energy spacings of doublets in {sub {Lambda}L}i hypernuclear isotopes with A=7-10 in shell-model calculations with a {Lambda}N-{Sigma}N coupling effect. The calculated results show that the energy shifts are {Delta}{epsilon}=0.09-0.28 MeV and the {Sigma}-mixing probabilities are P{sub {Sigma}}=0.10%-0.34% in {Lambda} ground states for the isotopes because of the {Lambda}N-{Sigma}N coupling in the first-order perturbation. It is found that the energy spacing of the doublet is enhanced as a neutron number N increases; the contribution of the {Lambda}N-{Sigma}N coupling interaction is comparable to that of the {Lambda}N interaction in the neutron-rich {Lambda} hypernuclei. The coherent mechanism of this doublet-spacing enhancement is also discussed in terms of Fermi-type and Gamow-Teller-type {Lambda}N-{Sigma}N couplings.