arXiv subjects

Yoshiko Kanada-En'yo

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

At least 55 records · Page 3Linked to original sources

arXiv2018

Investigation of the pairing effect in 10B nucleus compared with 10Be and 10C nuclei by using the extended THSR wave function

In order to study the nucleon-nucleon pairing effects in clustering nuclei, we formulate a superposed Tohsaki-Horiuchi-Schuck-Roepke (THSR) wave function, which includes both molecular-orbit and pairing configurations explicitly. With this new wave function, we investigate the abnormal deuteron-like pn-pairing effect in 10B with T=0 and S=1 (isoscalar) by comparing with isovector NN pairs (T=1, S=1) in 10Be and 10C. Energies are calculated for the ground states of 10Be, 10B and 10C nuclei, and the 1+ excited state of 10B. These energies are essentially improved comparing with studies using previous version of THSR wave function. Further more, overlaps between the total wave function and the pairing component indicate that the NN pairing effect is more visible in 10B than in 10Be and 10C. By analyzing the energies and the overlaps between wave function components, we observe two different mechanisms enhancing the formation of deuteron-like pairs in 10B. We also discuss the pairing effect by showing average distances between components in each nucleus and density distributions of valance nucleons.

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arXiv2018

Investigation of $α$ clustering with knockout reactions

Our goal is to reveal how the $α$ cluster amplitude is probed through $α$ knockout reactions depending on reaction conditions, e.g., the incident energy. We consider $^{20}$Ne($p$,$pα$)$^{16}$O and $^{120}$Sn($p$,$pα$)$^{116}$Cd at 100-400 MeV within the distorted wave impulse approximation (DWIA) framework. We introduce a masking function which shows how the reaction amplitude in the nuclear interior is suppressed and defines the probed region of the $α$ cluster wave function. It is clearly shown by means of the masking function that the $α$ knockout reaction probes the $α$ cluster amplitude in the nuclear surface region, which is the direct measure of well-developed $α$ cluster states. A simplified form of the masking function is introduced and the incident energy dependence of the masking effect is investigated. $α$ knockout reaction can probe the $α$ cluster amplitude in the nuclear surface region by choosing proper kinematics owing to the masking effect originated from absorptions of distorting potentials, and is a suitable method to investigate how $α$ cluster states are spatially developed.

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arXiv2018

Microscopic Clustering in Light Nuclei

We review recent experimental and theoretical progress in understanding the microscopic details of clustering in light nuclei. We discuss recent experimental results on $α$-conjugate systems, molecular structures in neutron-rich nuclei, and constraints for ab initio theory. We then examine nuclear clustering in a wide range of theoretical methods, including the resonating group and generator coordinate methods, antisymmetrized molecular dynamics, Tohsaki-Horiuchi-Schuck-Röpke wave function and container model, no-core shell model methods, continuum quantum Monte Carlo, and lattice effective field theory.

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arXiv2018

Low-Energy Gamow-Teller Transitions in deformed $N = Z$ odd-odd Nuclei

We have investigated the Gamow-Teller transitions from ${}^{22}\textrm{Ne}$ to ${}^{22}\textrm{Na}$ by applying the isospin projected antisymmetrized molecular dynamics combined with generator coordinate method. We have found that the GT strength from $^AZ(J^πT)={}^{22}\textrm{Ne}(0_1^+1)$ is fragmented into two final states ${}^{22}\textrm{Na}(1_{1,2}^+0)$, which belong to $K=0$ and $K=1$ bands constructed by a prolately deformed $^{20}$Ne core with a $S=1$ proton-neutron ($pn$) pair. Coupling of the intrinsic-spin of the $pn$ pair with the core deformation play an important role in the GT fragmentation. The symmetry breaking in the intrinsic-spin rotation leads to the $SU(4)$-symmetry breaking of the $NN$ pair and causes the GT fragmentation. We have compared the features of the GT transitions with those for ${}^{10}\textrm{Be}\to{}^{10}\textrm{B}$ and discuss the link of the $SU(4)$-symmetry and the GT fragmentation in the deformed systems.

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arXiv2018

Manifestation of α-clustering in $^{10}$Be via α-knockout reaction

Background: Proton-induced α-knockout reactions empower direct experimental manifestations of α-clustering in nuclei. This is obtained by relating the theoretical descriptions of clustering states with experimental reaction observables. It is desired to introduce microscopic structure models into the theoretical frameworks for α-knockout reactions. Purpose: Our goal is to probe the α-clustering in $^{10}$Be nucleus by proton-induced α-knockout reaction observables. Method: We adopt an extended version of the Tohsaki-Horiuchi-Schuck-Röpke (THSR) wave function of $^{10}$Be and integrate it with the distorted wave impulse approximation (DWIA) framework for the calculation of (p,pα) knockout reactions. Results: We make the first calculation for the $^{10}$Be(p,pα)$^{6}$He reaction at 250 MeV implementing a microscopic α-cluster wave function and predict the triple differential cross sections (TDX). Furthermore, by constructing artificial states of the target nucleus $^{10}$Be with compact or dilute spatial distributions, the TDX is found to be highly sensitive to the extent of clustering in the target nuclei. Conclusions: These results provide reliable manifestation of the α-clustering in $^{10}$Be.

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arXiv2018

Energy spectra in $p$-shell $Λ$ hypernuclei and $^{19}_Λ\textrm{F}$ and spin-dependent $ΛN$ interactions

Energy spectra of $0s$-orbit $Λ$ states in $p$-shell $Λ$ hypernuclei ($^{A}_ΛZ$) and those in $^{19}_Λ\textrm{F}$ are studied with the microscopic cluster model and antisymmetrized molecular dynamics using the $G$-matrix effective $ΛN$ ($ΛNG$) interactions. Spin-dependent terms of the ESC08a version of the $ΛNG$ interactions are tested and phenomenologically tuned to reproduce observed energy spectra in $p$-shell $^{A}_ΛZ$. Spin-dependent contributions of the $ΛN$ interactions to spin-doublet splitting and excitation energies are discussed. Energy spectra for unobserved excited states in $p$-shell $^{A}_ΛZ$ and $^{19}_Λ\textrm{F}$ are predicted with the modified $ΛNG$ interactions.

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arXiv2018

Structures of $p$-shell double-$Λ$ hypernuclei studied with microscopic cluster models

$0s$-orbit $Λ$ states in $p$-shell double-$Λ$ hypernuclei ($^{\ \,A}_{ΛΛ}Z$), $^{\ \,8}_{ΛΛ}\textrm{Li}$, $^{\ \,9}_{ΛΛ}\textrm{Li}$, $^{10,11,12}_{\ \ \ \ \ ΛΛ}\textrm{Be}$, $^{12,13}_{\ \ ΛΛ}\textrm{B}$, and $^{\,14}_{ΛΛ}\textrm{C}$ are investigated. Microscopic cluster models are applied to core nuclear part and a potential model is adopted for $Λ$ particles. The $Λ$-core potential is a folding potential obtained with effective $G$-matrix $Λ$-$N$ interactions, which reasonably reproduce energy spectra of $^{A-1}_{\,Λ}Z$. System dependence of the $Λ$-$Λ$ binding energies is understood by the core polarization energy from nuclear size reduction. Reductions of nuclear sizes and $E2$ transition strengths by $Λ$ particles are also discussed.

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arXiv2017

Excitation energy shift and size difference of low-energy levels in $p$-shell $Λ$ hypernuclei

We investigated structures of low-lying $0s$-orbit $Λ$ states in $p$-shell $Λ$ hypernuclei ($^A_ΛZ$) by applying microscopic cluster models for nuclear structure and a single-channel folding potential model for a $Λ$ particle. For $A>10$ systems, the size reduction of core nuclei is small, and the core polarization effect is regarded as a higher-order perturbation in the $Λ$ binding. The present calculation qualitatively describes the systematic trend of experimental data for excitation energy change from $^{A-1} Z$ to $^A_ΛZ$, in $A>10$ systems. The energy change shows a clear correlation with the nuclear size difference between the ground and excited states. In $^7_Λ\textrm{Li}$ and $^9_Λ\textrm{Be}$, the significant shrinkage of cluster structures occurs consistently with the prediction of other calculations.

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arXiv2017

Cluster and toroidal aspects of isoscalar dipole excitations in $^{12}$C

We investigated cluster and toroidal aspects of isoscalar dipole excitations in $^{12}$C based on the shifted basis antisymmetrized molecular dynamics combined with the generator coordinate method, which can describes 1p-1h excitations and $3α$ dynamics. In the $E=10-15$ MeV region, we found two low-energy dipole modes separating from the giant dipole resonance. One is the developed $3α$-cluster state and the other is the toroidal dipole mode. The cluster state is characterized by the large amplitude cluster motion beyond the 1p-1h model space, whereas the toroidal dipole mode is predominantly described by 1p-1h excitations on the ground state. The low-energy dipole states are remarkably excited by the toroidal dipole operator, which can measure the nuclear vorticity. For compressive dipole transition strengths, a major part is distributed in the $30-50$ MeV region for the giant dipole resonance, and 5\% of the total energy weighted sum exist in the $E<20$ MeV region.

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arXiv2017

Tetrahedral $4α$ and $^{12}\textrm{C}+α$ cluster structures in $^{16}$O

We have investigated structures of the ground and excited states of $^{16}\textrm{O}$ with the method of variation after spin-parity projection in the antisymmetrized molecular dynamics model combined with the generator coordinate method of $^{12}\textrm{C}+α$ cluster. The calculation reasonably reproduces the experimental energy spectra, $E2$, $E3$, $E4$, $IS1$ transitions, and $α$-decay properties. The formation of 4 $α$ clusters has been confirmed from nucleon degrees of freedom in the AMD model without assuming existence of any clusters. They form "tetrahedral" $4α$- and $^{12}\textrm{C}+α$-cluster structures. The $^{12}\textrm{C}+α$ structure constructs the $K^π=0^+$ band consisting of the $0^+_2$, $2^+_1$, and $4^+_1$ states and the $K^π=0^-$ band of the $1^-_2$, $3^-_2$, and $5^-_1$ states. The $0^+_1$, $3^-_1$, and $4^+_2$ states are assigned to the ground band constructed from the tetrahedral 4$α$ structure. The $0^+_1$ and $3^-_1$ are approximately interpreted as $T_d$ band members with the ideal tetrahedral configuration. The ground state $4α$ correlation plays an important role in enhancement of the $E3$ transition strength to the $3^-_1$. The $4^+_2$ state is not the ideal $T_d$ member but constructed from a distorted tetrahedral $4α$ structure. Moreover, significant state mixing of the tetrahedral $4α$ and $^{12}\textrm{C}+α$ cluster structures occurs between $4^+_1$ and $4^+_2$ states, indicating that the $T_d$ configuration of $4α$ is rather fragile at $J^π=4^+$.

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arXiv2017

Toroidal, compressive, and $E1$ properties of low-energy dipole modes in $^{10}$Be

We studied dipole excitations in $^{10}$Be based on an extended version of the antisymmetrized molecular dynamics, which can describe 1p-1h excitations and large amplitude cluster modes. Toroidal and compressive dipole operators are found to be good proves to separate the low-energy and high-energy parts of the isoscalar dipole excitations, respectively. Two low-energy $1^-$ states, the toroidal dominant $1^-_1$ state at $E\sim 8$ MeV and the $E1$ dominant $1^-_2$ state at $E\sim 16$ MeV, were obtained. By analysis of transition current densities, the $1^-_1$ states is understood as a toroidal dipole mode with exotic toroidal neutron flow caused by rotation of a deformed $^6\textrm{He}$ cluster, whereas the $1^-_2$ state is regarded as a neutron-skin oscillation mode, which are characterized by surface neutron flow with inner isoscalar flow caused by the surface neutron oscillation against the $2α$ core.

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arXiv2017

Gamow-Teller transitions and proton-neutron pair correlation in $N=Z=$ odd $p$-shell nuclei

We have studied the Gamow-Teller (GT) transitions from $N=Z+2$ neighbors to $N=Z=$ odd nuclei in $p$-shell region by using isospin-projected and $βγ$-constraint antisymmetrized molecular dynamics combined with generator coordinate method. The calculated GT transition strengths from $0^+1$ states to $1^+0$ states such as ${}^{6} \textrm{He}(0_1^+1)\rightarrow{}^{6} \textrm{Li}(1_1^+0)$, ${}^{10} \textrm{Be}(0_1^+1)\rightarrow{}^{10} \textrm{B}(1_1^+0)$, and ${}^{14} \textrm{C}(0_1^+1)\rightarrow{}^{14} \textrm{N}(1_2^+0)$ exhaust more than 50\% of the sum rule. These $N=Z+2$ initial states and $N=Z=$ odd final states are found to dominantly have $S=0,T=1$ $nn$ pairs and $S=1,T=0$ $pn$ pairs, respectively. Based on two-nucleon ($NN$) pair picture, we can understand the concentration of the GT strengths as the spin-isospin-flip transition $nn(S=0,T=1)\rightarrow pn(S=1,T=0)$ in $LS$-coupling scheme. The GT transition can be a good probe to identify the spin-isospin partner states with $nn$ pairs and $pn$ pairs of $N=Z+2$ and $N=Z=$ odd nuclei, respectively.

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arXiv2016

3$α$-cluster structure and monopole transition in $^{12}$C and $^{14}$C

3$α$-cluster structures and monopole transitions of $0^+$ states in $^{12}$C and $^{14}$C were investigated with $3α$- and $^{10}$Be+$α$-cluster models. A gas-like $3α$ state and a bending-chain $3α$ state were obtained in the $0^+_2$ and $0^+_3$ states of $^{12}$C, respectively. In $^{14}$C, a linear-chain 3$α$ structure is found in the $0^+_4$ state near the $^{10}$Be+$α$ threshold, but a cluster gas-like state does not appear because valence neutrons attract $α$ clusters and suppress spatial development of 3$α$ clustering. It was found that the linear-chain state in $^{14}$C is stabilized against the bending and $α$ escaping modes by valence neutrons. The monopole transition strengths in $^{12}$C are enhanced by $3α$-cluster developing, whereas, those in $^{14}$C are not enhanced so much because of the tight binding of $α$ clusters by valence neutrons.

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arXiv2016

Tetrahedral shape and surface density wave of $^{16}$O caused by $α$-cluster correlations

$α$-cluster correlations in the $0^+_1$ and $3^-_1$ states of $^{12}$C and $^{16}$O are studied using the method of antisymmetrized molecular dynamics, with which nuclear structures are described from nucleon degrees of freedom without assuming existence of clusters. The intrinsic states of $^{12}$C and $^{16}$O have triangle and tetrahedral shapes, respectively, because of the $α$-cluster correlations. These shapes can be understood as spontaneous symmetry breaking of rotational invariance, and the resultant surface density oscillation is associated with density wave (DW) caused by the instability of Fermi surface with respect to particle-hole correlations with the wave number $λ=3$. $^{16}$O($0^+_1$) and $^{16}$O($3^-_1$) are regarded as a set of parity partners constructed from the rigid tetrahedral intrinsic state, whereas $^{12}$C($0^+_1$) and $^{12}$C($3^-_1$) are not good parity partners as they have triangle intrinsic states of different sizes with significant shape fluctuation because of softness of the $3α$ structure. $E3$ transition strengths from the $3^-_1$ to $0^+_1$ states in $^{12}$C and $^{16}$O are also discussed.

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arXiv2016

Colored-hadron distribution in hadron scattering in SU(2) lattice QCD

In color SU(2) lattice QCD, we investigate colored-diquark distributions in two-hadron scatterings by means of Bethe-Salpeter amplitudes on the lattice. With colored-diquark operators in the Coulomb gauge, we measure components of two colored diquarks realized as intermediate states via one gluon exchange (OGE) processes in hadron scattering. From the colored-diquark distributions, we estimate the dominant range of gluon (color) exchanges between closely located two hadrons. We find that the colored-diquark components are enhanced at the short range ($\leq$0.2 fm) and their tails show the single-exponential damping. In order to distinguish the genuine colored-diquark components originating in the color exchange processes from trivial colored two-quark components contained in two color-singlet hadrons as a result of simple transformation of hadronic basis, we repeat the analyses on the artificially constructed gauge fields, where low- and high-momentum gluon components are decoupled and only restricted pair of quarks can share and exchange low-momentum gluons. We observe qualitatively the same behaviors and confirm that the short-range enhancement of the colored-diquark distributions is the genuine OGE-origin color excitation in hadron scattering.

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arXiv2016

Isospin Projected Antisymmetrized Molecular Dynamics and its Application to ${}^{10}$B

To investigate $pn$ pair correlations in $N=Z=\textrm{odd}$ nuclei, we develop a new framework based on the generator coordinate method of the $βγ$ constraint antisymmetrized molecular dynamics. In the framework, the isospin projection is performed before the energy variation to obtain the wave function optimized for each isospin. We apply the method to ${}^{10} \textrm{B}$ and show that it works well to describe coexistence of $T=0$ and $T=1$ states in low-energy spectra. Structures of low-lying states and $pn$ correlations are investigated. Strong $M1$($0^+_1\rightarrow 1^+_1$) and $E2$($1^+_1\rightarrow 1^+_2$) transitions are understood by the spin excitation of the $pn$ pair and the rotation of a deformed core, respectively.

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arXiv2016

Monopole transitions to cluster states in $^{10}$Be and $^9$Li

Isoscalar monopole transitions from the ground states to cluster states in $\Be$ and $\Li$ are investigated with $\He+α$ and $\He+t$ cluster models, respectively. In $\Be$, significant monopole strengths to $\He+α$ cluster resonances of $\Be(0^+_{3,4})$ above the $α$-decay threshold are obtained, whereas those to $\He+t$ cluster resonances in $^9$Li are not enhanced because of the large fragmentation of the strengths in the corresponding energy region. The monopole transition to $\Be(0^+_2)$ having the molecular orbital structure is relatively weak compared with those to $\He+α$ cluster resonances. Monopole strength distributions do not directly correspond to distributions of $\He(0^+)+α$ and $\He(0+)+t$ components but they reflect component of the deformed $\He$ cluster with a specific orientation, which is originally embedded in the ground state.

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arXiv2016

Probing surface distributions of $α$ clusters in $^{20}$Ne via $α$-transfer reaction

Direct evidence of the $α$-cluster manifestation in bound states has not been obtained yet, although a number of experimental studies were carried out to extract the information of the clustering. In particular in conventional analyses of $α$-transfer reactions, there exist a few significant problems on reaction models, which are insufficient to qualitatively discuss the cluster structure. We aim to verify the development of the $α$-cluster structure from observables. As the first application, we plan to extract the spatial information of the cluster structure of the $^{20}$Ne nucleus in its ground state through the cross section of the $α$-transfer reaction $^{16}$O($^6$Li,~$d$)$^{20}$Ne. For the analysis of the transfer reaction, we work with the coupled-channel Born approximation (CCBA) approach, in which the breakup effect of $^6$Li is explicitly taken into account by means of the continuum-discretized coupled-channel method based on the three-body $α+ d + {}^{16}$O model. The two methods are adopted to calculate the overlap function between $^{20}$Ne and $α+ {}^{16}$O; one is the microscopic cluster model (MCM) with the generator coordinate method, and the other is the phenomenological two-body potential model (PM). We show that the CCBA calculation with the MCM wave function gives a significant improvement of the theoretical result on the angular distribution of the transfer cross section, which is consistent with the experimental data. Employing the PM, it is discussed which region of the cluster wave function is probed on the transfer cross section. It is found that the surface region of the cluster wave function is sensitive to the cross section. The present work is situated as the first step in obtaining important information to systematically investigate the cluster structure.

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