arXiv subjects

Yoshiko Kanada-En'yo

Publications and source records attributed to Yoshiko Kanada-En'yo.

At least 109 records · Page 6Linked to original sources

arXiv2011

Cluster formations in deformed states for $^{28}$Si and $^{32}$S

We study cluster formation in strongly deformed states for $^{28}$Si and $^{32}$S using a macroscopic-microscopic model. The study is based on calculated total-energy surfaces, which are the sums of deformation-dependent macroscopic-microscopic potential-energy surfaces and rotational-energy contributions. We analyze the angular-momentum-dependent total-energy surfaces and identify the normal- and super-deformed states in $^{28}$Si and $^{32}$S, respectively. We show that at sufficiently high angular momenta strongly deformed minima appear. The corresponding microscopic density distributions show cluster structure that closely resemble the $^{16}$O+$^{12}$C and $^{16}$O+$^{16}$O configurations. At still higher deformations, beyond the minima, valleys develop in the calculated surfaces. These valleys lead to mass divisions that correspond to the target-projectile configurations for which molecular resonance states have been observed. We discuss the relation between the one-body deformed minima and the two-body molecular-resonance states.

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arXiv2011

Triaxial quadrupole deformation dynamics in sd-shell nuclei around 26Mg

Large-amplitude dynamics of axial and triaxial quadrupole deformation in 24,26Mg, 24Ne, and 28Si is investigated on the basis of the quadrupole collective Hamiltonian constructed with use of the constrained Hartree-Fock-Bogoliubov plus the local quasiparticle random phase approximation method. The calculation reproduces well properties of the ground rotational bands, and beta and gamma vibrations in 24Mg and 28Si. The gamma-softness in the collective states of 26Mg and 24Ne are discussed. Contributions of the neutrons and protons to the transition properties are also analyzed in connection with the large-amplitude quadrupole dynamics.

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arXiv2010

Hindrance of the excitation of the Hoyle state and the ghost of the $2^+_2$ state in $^{12}$C

While the Hoyle state (the isoscalar $0^+_2$ excitation at 7.65 MeV in $^{12}$C) has been observed in almost all the electron and $α$ inelastic scattering experiments, the second $2^+$ excited state of $^{12}$C at $E_{\rm x}\approx 10$ MeV, believed to be an excitation of the Hoyle state, has not been clearly observed in these measurements excepting the high-precision \aap experiments at $E_α=240$ and 386 MeV. Given the (spin and isospin zero) $α$-particle as a good probe for the nuclear isoscalar excitations, it remains a puzzle why the peak of the $2^+_2$ state could not be clearly identified in the measured \aap spectra. To investigate this effect, we have performed a microscopic folding model analysis of the \ac scattering data at 240 and 386 MeV in both the Distorted Wave Born Approximation (DWBA) and coupled-channel (CC) formalism, using the nuclear transition densities given by the antisymmetrized molecular dynamics (AMD) approach and a complex CDM3Y6 density dependent interaction. Although AMD predicts a very weak transition strength for the direct $(0^+_1\to 2^+_2)$ excitation, our detailed analysis has shown evidence that a weak \emph{ghost} of the $2^+_2$ state could be identified in the 240 MeV \aap data for the $0^+_3$ state at 10.3 MeV, when the CC effects by the indirect excitation of the $2^+_2$ state are taken into account. Based on the same AMD structure input and preliminary \aap data at 386 MeV, we have estimated relative contributions from the $2^+_2$ and $0^+_3$ states to the excitation of $^{12}$C at $E_{\rm x}\approx 10$ MeV as well as possible contamination by $3^-_1$ state.

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arXiv2010

Hadron-hadron interaction from SU(2) lattice QCD

We evaluate interhadron interactions in two-color lattice QCD from Bethe-Salpeter amplitudes on the Euclidean lattice. The simulations are performed in quenched SU(2) QCD with the plaquette gauge action at $β= 2.45$ and the Wilson quark action. We concentrate on S-wave scattering states of two scalar diquarks. Evaluating different flavor combinations with various quark masses, we try to find out the ingredients in hadronic interactions. Between two scalar diquarks ($u Cγ_5 d$, the lightest baryon in SU(2) system), we observe repulsion in short-range region, even though present quark masses are not very light. We define and evaluate the "quark-exchange part" in the interaction, which is induced by adding quark-exchange diagrams, or equivalently, by introducing Pauli blocking among some of quarks. The repulsive force in short-distance region arises only from the "quark-exchange part", and disappears when quark-exchange diagrams are omitted. We find that the strength of repulsion grows in light quark-mass regime and its quark-mass dependence is similar to or slightly stronger than that of the color-magnetic interaction by one-gluon-exchange (OGE) processes. It is qualitatively consistent with the constituent-quark model picture that a color-magnetic interaction among quarks is the origin of repulsion. We also find a universal long-range attractive force, which enters in any flavor channels of two scalar diquarks and whose interaction range and strength are quark-mass independent. The weak quark-mass dependence of interaction ranges in each component implies that meson-exchange contributions are small and subdominant, and the other contributions, {\it ex.} flavor exchange processes, color-Coulomb or color-magnetic interactions, are considered to be predominant, in the quark-mass range we evaluated.

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arXiv2010

Triaxial superdeformation in $^{40}$Ar

Superdeformed (SD) states in $^{40}$Ar have been studied using the deformed-basis antisymmetrized molecular dynamics. Low energy states were calculated by the parity and angular momentum projection (AMP) and the generator coordinate method (GCM). Basis wave functions were obtained by the energy variation with a constraint on the quadrupole deformation parameter $β$, while other quantities such as triaxiality $γ$ were optimized by the energy variation. By the GCM calculation, an SD band was obtained just above the ground state (GS) band. The SD band involves a $K^π= 2^+$ side band due to the triaxiality. The calculated electric quadrupole transition strengths of the SD band reproduce the experimental values appropriately. Triaxiality is significant for understanding low-lying states.

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arXiv2010

Quadrupole Deformation $β$ and $γ$ Constraint in a Framework of Antisymmetrized Molecular Dynamics

We propose a new method of the $β$-$γ$ constraint for quadrupole deformation in antisymmetrized molecular dynamics (AMD) to describe various cluster and shell-model structures in the ground and excited states of light nuclei. We apply this method to N=6 isotones, $^{10}$Be, $^{12}$C, $^{9}$Li, and $^{11}$B, and find various structures as functions of the deformation parameters, $β$ and $γ$. In these nuclei, shell-model-like structures appear in the small $β$ region, while cluster structures develop well in the large $β$ region where various geometric configurations of clusters are obtained depending on the $γ$ parameter. For $^{10}$Be and $^{12}$C, we superpose the basis AMD wave functions obtained by the $β$-$γ$ constraint method to calculate energy spectra, and prove the advantages of the present method of the two-dimensional $β$-$γ$ constraint in the framework of AMD.

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arXiv2009

Lambda(1405) N to Y N transition in nuclear medium for non-mesonic absorption of Kbar in nucleus

Non-mesonic transition of Lambda(1405) N to YN is investigated as one of the essential processes for the non-mesonic absorption of Kbar in nuclei. Using one-meson exchange model in the calculation of the transition, we find that the non-mesonic transition ratio Gamma_{Lambda N} / Gamma_{Sigma N} depends strongly on the ratio of the Lambda(1405) (Lambda^*) couplings to Kbar N and pi Sigma. Especially a larger Lambda^*-Kbar N coupling leads to enhancement of the transition to Lambda N. Using the chiral unitary model for the description of the Lambda^*, we obtain Gamma_{Lambda N} / Gamma_{Sigma^{0} N} is approximately 1.2 which is almost independent of the nucleon density, and find the total non-mesonic decay width of the Lambda^* in uniform nuclear matter to be 22 MeV at the normal density.

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arXiv2009

Cluster structures and superdeformation in $^{28}$Si

We have studied positive-parity states of $^{28}$Si using antisymmetrized molecular dynamics (AMD) and multi-configuration mixing (MCM) with constrained variation. Applying constraints to the cluster distance and the quadrupole deformation of the variational calculation, we have obtained basis wave functions that have various structures such as $α$-$^{24}$Mg and $^{12}$C-$^{16}$O cluster structures as well as deformed structures. Superposing those basis wave functions, we have obtained a oblate ground state band, a $β$ vibration band, a normal-deformed prolate band, and a superdeformed band. It is found that the normal-deformed and superdeformed bands contain large amounts of the $^{12}$C-$^{16}$O and $α$-$^{24}$Mg cluster components, respectively. The results also suggest the presence of two excited bands with the developed $α$-$^{24}$Mg cluster structure, where the inter-cluster motion and the $^{24}$Mg-cluster deformation play important roles.

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arXiv2009

Gamow-Teller transitions from $^{9,11}$Li to $^{9,11}$Be

Gamow-Teller(GT) transitions in the $β$ decays of $^9$Li and $^{11}$Li are investigated with theoretical calculations of antisymmetrized molecular dynamics. The calculated $B(GT)$ values are small for transitions to low-lying states in Be isotopes, while relatively large $B(GT)$ values are found for excited states at excitation energy $E_x\ge 10$ MeV. Sum of the $B(GT)$ values are discussed for each spin parity of final states. The calculated results seem to be inconsistent with the experimental report of the strongest GT-transition from $^9$Li to the $5/2^-$ state at 11.8 MeV of $^9$Be.

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arXiv2009

A new N* resonance as a hadronic molecular state

We report our recent work on a hadronic molecule state of the KbarKN system with I=1/2 and J^P=1/2^+. We assume that the Lambda(1405) resonance and the scalar mesons, f_{0}(980), a_{0}(980), are reproduced as quasi-bound states of KbarN and KbarK, respectively. Performing non-relativistic three-body calculations with a variational method for this system, we find a quasibound state of the KbarKN system around 1910 MeV below the three-body breakup threshold. This state corresponds to a new baryon resonance of N* with J^P=1/2^+. We find also that this resonance has the cluster structure of the two-body bound states keeping their properties as in the isolated two-particle systems. We also briefly discuss another hadronic molecular state composed by two Kbar and one N, which corresponds to a Xi^* resonance.

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arXiv2009

Lambda(1405)-induced non-mesonic decay in kaonic nuclei

Non-mesonic decay of kaonic nuclei is investigated under a Lambda(1405) doorway picture where the Kbar absorptions in nuclei take place through the Lambda(1405) resonance. Calculating Lambda(1405) N to YN transitions in one-meson exchange, we find that the non-mesonic decay ratio Gamma_{Lambda N} / Gamma_{Sigma^{0} N} depends strongly on the ratio of the couplings Lambda(1405)-Kbar N and Lambda(1405)-pi Sigma. Especially a larger Lambda(1405)-Kbar N coupling leads to enhancement of the decay to Lambda N. Using the chiral unitary approach for description of the Kbar N amplitudes, we obtain Gamma_{Lambda N} / Gamma_{Sigma ^{0} N} \approx 1.2 almost independently of the nucleon density, and find the total two-nucleon absorption of the Kbar in uniform nuclear matter to be 22 MeV at the normal density.

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arXiv2009

Dineutron correlations in quasi two-dimensional systems in a simplified model and possible relation to neutron-rich nuclei

Two-neutron correlation in the $^1S$ channel in quasi two-dimensional (2D) neutron systems at zero temperature is studied by means of the BCS theory with finite-range effective nuclear forces. The dineutron correlation in low density neutron systems confined in an infinite slab is investigated in a simplified model that neutron motion of one direction is frozen. When the slab is thin enough, two neutrons form a tightly bound dineutron with a small size in the quasi-2D system, and a Bose dineutron gas is found in low density limit. With increase of Fermi momentum, the neutron system changes from the Bose-gas phase to the superfluid Cooper pair phase. The density dependence of the neutron pairing shows the BCS-BEC crossover phenomena at finite low-density region. In the transition region, the size shrinking of neutron pair and enhancement of pairing gap are found. The relation to dineutron correlation at surface of neutron-rich nuclei is also discussed.

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arXiv2008

Deformations and clustering correlations in $p$- and $sd$-shell nuclei using the Gogny and Skyrme interactions

Structures of $p$- and $sd$-shell nuclei are studied with the deformed-basis antisymmetrized molecular dynamics method using the Gogny D1S and Skyrme SLy7 forces as effective interactions. By the energy variation with a constraint, energy curves as functions of quadrupole deformation parameter $β$ are obtained. The energy curves for $sd$-shell nuclei show structure change as a function of $β$, and suggest shape coexistence. Nuclear structures in the deformed region are discussed focusing on deformations and clustering. It is found that the deformations often involve cluster structures. Effective-interaction dependence is also discussed comparing the results obtained with the two effective interactions. Although the two forces give similar results when cluster structures do not develop clearly, they give different energies in the largely deformed region when an $α$ cluster develops.

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arXiv2008

K anti-K N molecule state with I=1/2 and J^P=1/2^+ studied with three-body calculation

A K \bar{K} N system with I=1/2 and J^P=1/2^+ is investigated with non-relativistic three-body calculations by using effective \bar K N, K \bar K and KN interactions. The \bar K N interaction describes the Lambda(1405) as a \bar K N molecule, and the K\bar K interaction is adjusted to give f_0(980) and a_0(980) states as K \bar K molecules. The present investigation suggests that a bound K \bar K N state can be formed below the K \bar K N threshold (1930 MeV) with a 90 ~ 100 MeV width of three-hadron decays, which are dominated by K bar K N -> K pi Sigma and pi eta N. It is found that the K \bar K N state is a weakly bound hadron molecular state with a size larger than an alpha particle because of the repulsive KN interactions.

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arXiv2008

anti-K anti-K N molecule state in three-body calculation

A $\bar{K}\bar{K}N$ system with $I=1/2$ and $J^P=1/2^+$ is investigated with non-relativistic three-body calculations by using effective $\bar{K}N$ and $\bar K \bar K$ interactions. The present investigation suggests that a weakly bound state for the $\bar{K}\bar{K}N$ system can be formed below the two-body threshold of $\bar{K}$ and quasibound $\bar{K}N$ with a $40 \sim 60$ MeV decay width of $\bar{K}\bar{K}N\to πY\bar{K}$. This corresponds to an excited $Ξ$ baryon with $J^P=1/2^+$ located around 1.9 GeV. Studying the wave function of the $\bar{K}\bar{K}N$ system obtained in this formulation, we find that the three-body bound system has a characteristic structure of $\bar K N$+$\bar K$ cluster with spatial extent.

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arXiv2007

Dineutron structure in $^{8}$He

The ground and excited states of $^{8}$He were investigated with a method of antisymmetrized molecular dynamics(AMD). We adopted effective nuclear interactions which systematically reproduce the binding energies of $^4$He, $^6$He and $^8$He. The ground state of $^8$He has both the $j$-$j$ coupling feature($p_{3/2}$ closure) and the $L$-$S$ coupling feature($^4$He$+2n+2n$) with a slight tail of dineutron at the long distance region. The theoretical results give an indication of the $0^+_2$ state with dineutron gas-like structure. The dineutron structure, $^4$He+$2n$+$2n$, of this state is similar to the $3α$-cluster structure of the $^{12}$C($0^+_2$) state which has been interpreted as an $α$ condensate state. Since the $^8$He($0^+_2$) state has a significant overlap with the dineutron condensate wave function where two dineutrons are moving in $S$ wave around the $α$ core with a dilute density, we suggest that this theoretically predicted $0^+_2$ state is a candidate of the dineutron condensate state.

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arXiv2007

Clustering and Triaxial Deformations of $^{40}$Ca

We have studied the positive-parity states of $^{40}$Ca using antisymmetrized molecular dynamics (AMD) and the generator coordinate method (GCM). Imposing two different kinds of constraints on the variational calculation, we have found various kinds of $^{40}{\rm Ca}$ structures such as a deformed-shell structure, as well as $α$-$^{36}$Ar and $^{12}$C-$^{28}$Si cluster structures. After the GCM calculation, we obtained a normal-deformed band and a superdeformed band together with their side bands associated with triaxial deformation. The calculated $B(E2)$ values agreed well with empirical data. It was also found that the normal-deformed and superdeformed bands have a non-negligible $α$-$^{36}$Ar cluster component and $^{12}$C-$^{28}$Si cluster component, respectively. This leads to the presence of an $α$-$^{36}$Ar higher-nodal band occurring above the normal-deformed band.

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arXiv2007

Largely deformed states of $^{13}$B

The excited states of $^{13}$B were studied with a method of antisymmetrized molecular dynamics(AMD). The theoretical results suggest that the intruder states with large deformations construct the rotational bands, $K^π=3/2^-$ and $K^π=1/2^+$, starting from 5 MeV and 8 MeV, respectively. The neutron structure of the $K^π=3/2^-$ is analogous to the intruder ground state of $^{12}$Be. In the predicted $K^π=1/2^+$ band, we found very exotic structure with a proton intruder configuration. This proton intruder state has a larger deformation than superdeformation. The band-head $1/2^+$ state is assigned to the $1/2^+$(4.83 MeV), which was experimentally suggested to be the proton intruder state because of the strong production via the proton-transfer to the $^{12}$Be($0^+$) state in the $^4$He($^{12}$Be,$^{13}$B$γ$)$X$ experiments.

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