arXiv subjects

Masaaki Kimura

Publications and source records attributed to Masaaki Kimura.

At least 19 recordsLinked to original sources

arXiv2026

Intruder-driven mirror energy differences between $^{29}$Cl and $^{29}$Mg studied with antisymmetrized molecular dynamics

To clarify the mirror energy differences (MEDs) of the proton-unbound nucleus $^{29}$Cl and their microscopic origins, we investigate the low-lying states of the $^{29}$Cl-$^{29}$Mg mirror pair using antisymmetrized molecular dynamics. The calculation reasonably reproduces the normal and intruder states of $^{29}$Mg, while suggesting alternative spin-parity assignments for $^{29}$Cl. The $1/2^+$ and $3/2^+$ states are predicted to form a nearly degenerate ground-state doublet with a small MED because of their similar intrinsic structures. In contrast, the $3/2^-$ and $7/2^-$ intruder states exhibit large negative MEDs and are assigned to the observed resonances at approximately 500~keV and 1.1~MeV, respectively. Their large MEDs originate from the reduced Coulomb energies associated with the stronger deformation and spatially extended proton distributions in the intruder configurations.

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arXiv2026

Growth of quartet correlations in neutron-rich tellurium isotopes within quartet Bardeen-Cooper-Schrieffer theory

Quartet correlations in neutron-rich Te isotopes are investigated within the quartet Bardeen-Cooper-Schrieffer (BCS) framework. Taking $^{100}$Sn as an inert core, we consider two valence protons and valence neutrons occupying the $2d_{5/2} \oplus 1g_{7/2}$ model space, and solve the quartet BCS variational equations with a charge-independent isovector pairing interaction. The effective pairing strength is constrained from empirical neutron pairing gaps in the Te isotopic chain. We find that the valence quartet number increases as the valence neutron number is enlarged from $N_{\rm val}=2$ to $14$. The same increasing behavior is also found for the condensed quartet component. The proton occupation of the $1g_{7/2}$ orbit is strongly enhanced relative to the conventional like-particle BCS reference and is driven close to the degeneracy-weighted limit. These results suggest that additional valence neutrons enhance the quartet admixture in the correlated quartet BCS state, while redistributing the fixed proton weight from pair-like configurations to quartet configurations.

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arXiv2026

Strong Evidence for Three-$α$ Clustering in the Ground State of $^{12}\mathrm{C}$

The ground state of $^{12}\mathrm{C}$ has often been approximated by a mean-field picture. This conventional view has been challenged by recent nuclear theories suggesting non-negligible $α$-cluster formation, but experimental evidence remains inconclusive. Here, we show that existing $^{12}\mathrm{C}(p,pα)^{8}\mathrm{Be}$ data provide direct evidence for a pronounced $α$ cluster formation in the ground state of $^{12}\mathrm{C}$. We analyze the data with distorted-wave impulse approximation using $α$ preformation amplitudes from an unrestricted $3α$ cluster model and harmonic-oscillator-based models. The results show that the former reproduces the measured cross sections, whereas the latter underestimate them by more than an order of magnitude. Thus, contrary to conventional expectations, the data support a nearly fully developed three-$α$ cluster structure in the ground state of $^{12}\mathrm{C}$.

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arXiv2026

Oblate-prolate shape mixing and E0 transition in 28Si

Background: oblate-prolate shape coexistence in $^{28}$Si has been discussed for decades, but the degree of shape mixing between these configurations remains poorly constrained. Purpose: We constrain the oblate-prolate mixing amplitudes in $^{28}$Si using available experimental information and discuss the inter-band E0 transition strength. Methods: Oblate and prolate $0^+$ and $2^+$ configurations are obtained by antisymmetrized molecular dynamics combined with the generator coordinate method. Using these configurations as the basis states, we constrain the mixing amplitudes by simultaneously reproducing the measured charge radius, the quadrupole moment of the $2_1^+$ state, and the in-band and inter-band $B(\mathrm{E2})$ values. The strength of the density-dependent term in the Gogny interaction is also varied within a reasonable range. Results: In the ground state, the oblate component is dominant, and the prolate component in the ground state is limited to less than about $20\%$. For the $2_1^+$ state, the allowed prolate component is smaller than that in the ground state. The present analysis does not tightly constrain the corresponding E0 transition strength, but an upper limit of $ρ^2(\mathrm{E0};0_3^+\rightarrow0_1^+) \lesssim 0.206$ is obtained. Conclusions: The low-lying $0^+$ states of $^{28}$Si may exhibit substantial oblate-prolate mixing. A measurement of the inter-band E0 transition strength would provide a quantitative determination of the mixing amplitude.

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arXiv2026

Two-proton emission as source of spin-entangled proton pairs

We show that a two-proton emitter with a diproton-correlated initial state can act as a source of spin-correlated proton pairs. Using a time-dependent three-body model, we investigate the two-proton emission of $^{16}$Ne ($^{14}$O$+2p$) and analyze the spin correlation of the emitted protons. We find that, when the emission proceeds as a democratic three-body process from an initial state containing a spin-singlet diproton correlation, the emitted protons exhibit a pronounced spin-correlation pattern exceeding the local-hidden-variable bound. This spin correlation closely resembles that of a pure spin-singlet pair. In contrast, this pattern is lost when the process is dominated by the sequential emission or when the initial diproton correlation is absent. These results demonstrate that a certain class of two-proton emitters can deliver spin-entangled proton pairs, and their spin correlation reflects the diproton correlation embedded in the initial state.

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arXiv2026

Spectroscopic factors as a probe of nuclear shape in $^{44}$S via one-neutron knockout reaction

Background: Neutron-rich nucleus $^{44}$S lies in the region where traditional $N=28$ shell closure weakens, leading to the emergence of shape coexistence and large-amplitude collective motion (LACM). Understanding the nature and degree of shape mixing in this nucleus remains an important and fascinating problem. Purpose: We investigate the manifestation of shape fluctuations in $^{44}$S and examine how the electric transitions and the spectroscopic factors from one-neutron knockout reactions can serve as probes of shapes mixing. Method: The antisymmetrized molecular dynamics combined with the generator coordinate method (AMD+GCM) is used to study the structure of $^{44}$S and $^{43}$S. Calculations are performed by using Gogny effective interactions with two different parameter sets, D1S and D1M, to explore the interaction dependence of shape mixing. Monopole and quadrupole transition strengths and spectroscopic factors are evaluated. The cross sections for the $^{44}$S$(p,pn)^{43}$S reaction are calculated within the distorted wave impulse approximation (DWIA). Results: The calculations reveal a strong interaction dependence of shape fluctuation in $^{44}$S. The structural differences obtained from D1S and D1M interactions produce distinct patterns of the electric transitions, the spectroscopic factors, and the cross sections for $^{44}$S$(p,pn)^{43}$S knockout reaction. Conclusion: The population of $3/2^-$ and $7/2^-$ states of $^{43}$S is particularly sensitive to the underlying shape fluctuation in $^{44}$S. Thus, the measurement of $^{44}$S$(p,pn)^{43}$S reaction can provide a direct experimental probe.

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arXiv2026

Bridging Quantum Computing and Nuclear Structure: Atomic Nuclei on a Trapped-Ion Quantum Computer

We demonstrate quantum simulations of strongly correlated nuclear many-body systems on the RIKEN-Quantinuum Reimei trapped-ion quantum computer, targeting ground states of oxygen, calcium, and nickel isotopes. By combining a hard-core-boson representation of the nuclear shell model with a pair-unitary coupled-cluster doubles ansatz, we achieve sub-percent relative error in the ground-state energies compared to noise-free statevector simulations. Our approach leverages symmetry-aware state preparation and particle-number post-selection to efficiently capture pairing correlations characteristic of systems with same-species nucleons. These findings highlight the viability of high-fidelity trapped-ion platforms for nuclear physics applications and provide a foundation for scaling to more complex nuclear systems.

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arXiv2025

The universal size compression effect of nucleon pair in finite nuclei

We systematically investigate the size evolution of the di-neutron (2n), di-proton (2p), and deuteron (d) in 6He, 14Be, 17B, 6Be, 17Ne, and 6Li using microscopic calculations. Remarkably, all nucleon pairs exhibit a universal size compression at the nuclear surface, regardless of their species and binding energies. These features correspond to the BCS- and BEC-like nucleon pairs, which recent experimental techniques can further investigate.

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arXiv2025

One-proton emission of $^{102}$Sb and its sensitivity to proton-neutron interaction

One-proton emission from the $^{102}$Sb nucleus is discussed, assuming an inert $^{100}$Sn core and the valence proton and neutron. There are experimentally measured bound states in the $^{100}$Sn-neutron system, whereas no particle-bound $^{100}$Sn-proton state has been observed. With time-dependent three-body calculations, the $1^+$ ground state of $^{102}$Sb is suggested as a possible proton emitter. This conclusion is reached by assuming a weakening effect on the proton-neutron ($pn$) interaction with respect to a bare deuteron. An analogous phenomenon is necessary to reproduce the empirical binding energies of $^{42}$Sc and $^{18}$F. Continuous shift from the unbound to bound regions by changing the $pn$-interaction strength is demonstrated. The lower limit of lifetime is evaluated as $τ\gtrsim 4.4 \times 10^{-18}$ seconds in the no-$pn$-interaction limit. However, the actual lifetime is expected as longer with a finite $pn$ interaction. Observation of a resonant state in $^{102}$Sb and its decay would provide a benchmark of the $pn$-pairing correlation.

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arXiv2025

Analytic continuation in coupling constant applied to two-proton emitters

For quantum meta-stable problems with three particles, the $^{6}$Be and $^{16}$Ne nuclei as two-proton ($2p$) emitters provide a testing field. Considering the complexity of many-body meta-stable systems, a tractable solver has been on demand. We apply the analytic continuation in coupling constant (ACCC) to these nuclei, and confirm that this method can solve such problems consistently to the time-dependent results as well as to the experimental data. The sensitivity of the $2p$ energies and widths to the proton-proton interaction is also investigated. The $^{6}$Be shows a smooth shift from short-life to long-life systems according to the proton-proton interaction. Same is concluded for the $2^+$ resonance of $^{16}$Ne. In contrast, for the first and second $0^+$ resonances of $^{16}$Ne, their energies and widths show the avoid-crossing behaviour, due to the coupling of two configurations in the core-proton subsystem, $^{15}$F. Since it requires only the bound-state solvers, the ACCC can be a low-cost option to solve three or more-body resonances.

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arXiv2025

The correlation between the $α$-cluster separation and the neutron S-factor in $^{12}$Be

The reduced width amplitudes (RWA) and the spectroscopic factor (S-factor) of $α$-cluster and valence neutron in $^{12}$Be are calculated by the generator coordinates method (GCM) with the cluster model. By fixing the distance between the $α$-clusters' generated coordinates, we make a theoretical experiment to analyze the relationship between the $α$-clustering separation and the orbital occupation of the valence neutron in $^{12}$Be. The analysis of the results shows that the percentage of the $σ$ orbital occupation in $^{12}$Be is positively related to the clustering separation.

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arXiv2025

$ {}^{164} \mathrm{Pb} $: A possible heaviest $ N = Z $ doubly magic nucleus

We confirm by using the Skyrme Hartree-Fock-Bogoliubov calculation that $ {}^{164} \mathrm{Pb} $ is a possible heaviest $ N = Z $ doubly magic nucleus whose lifetime is long enough to be measured on accelerator experiments. We estimate the proton-emission and alpha-decay half-lives of $ {}^{164} \mathrm{Pb} $. The estimated proton-emission half-life ranges from $ 0.1 \, \mathrm{ps} $ to $ 10 \, \mathrm{ns} $, while the alpha decay can be safely neglected.

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arXiv2024

Exploring the nuclear momentum anisotropy based on intermediate-energy heavy-ion collisions

We simulate ultra-central collisions of prolate uranium-uranium nuclei at intermediate energies using the isospin-dependent Boltzmann-Uehling-Uhlenbeck model to investigate the impact of momentum anisotropy on spatial geometric effects. By defining the quadrupole deformation parameter in momentum space $β_\text{p}$, we establish an ellipsoidal Fermi surface, aligning its rotational symmetry axis with the one in coordinate space. It is found that oblate momentum density enhances elliptic flow $v_2$, while prolate momentum density has the opposite effect, particularly pronounced in the outer, high transverse momentum $p_\text{t}$ region. Momentum anisotropy also causes differences in the initial momentum mean projection along the beam direction, with larger projections producing more pion mesons. Additionally, significant effects on mean square elliptic flow are observed in non-polarized collisions. We further examine the relationship between the $v_2$-$p_\text{t}$ slope and $β_\text{p}$, eliminating systematic errors through the two-system ratio. These findings provide important references for experimentalists in heavy-ion collisions and valuable feedback to theorists regarding nuclear structure.

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arXiv2024

Interference of resonances in two-proton emission of $^{16}$Ne

We investigate the two-proton ($2p$) emission from $^{16}$Ne with the time-dependent $^{14}$O$+p+p$ three-body calculations. Two $0^+$ resonances are suggested to participate. For the $0^+_1$ resonance, the true emission of the spatially localized two protons is dominant, if the single-particle $s_{1/2}$ resonance locates above the $2p$ energy. By evaluating a time-evolution probability, the $0^+_2$ resonance is suggested at $\cong 3$ MeV from the $2p$ threshold. The inclusion of $0^+_2$ resonance makes the true-$2p$~emission more dominant in the time-dependent calculations.

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arXiv2024

Uncovering the sign of nuclear deformations: Determination of prolate or oblate shape via low-energy $α$ inelastic scattering

Background: Understanding nuclear shape is a crucial problem in nuclear physics. In particular, determining the sign of quadrupole deformation, i.e., whether prolate or oblate, remains a challenging problem. Purpose: Our aim is to propose a method for determining the sign of quadrupole deformation using $α$ inelastic scattering data and to demonstrate its effectiveness. Method: Our approach is the standard coupled-channel method based on the macroscopic model. We utilize the nuclear reorientation effect, a phenomenon associated with the self coupling of excited states, as a probe sensitive to the sign of deformation. Results: We first provide an overview of how the reorientation effect influences inelastic scattering cross sections, and numerically confirm its validity in realistic cases. We then demonstrate that the sign of deformation can be uniquely determined from inelastic scattering cross section data. Conclusion: Our technique offers a systematic approach for determining the sign of deformation in both stable and unstable nuclei. The broad applicability of $α$ inelastic scattering will make it a valuable tool to study shape of nuclei, especially unstable nuclei.

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arXiv2024

An implementation of nuclear many-body wave functions by the superposition of localized Gaussians

We introduce a new framework for the low-energy nuclear structure calculations, which describes the single-particle wave function as a superposition of localized Gaussians. It is a hybrid of the Hartree-Fock and antisymmetrized molecular dynamics models. In the numerical calculations of oxygen, calcium isotopes and 100Sn, the framework shows its potential by significantly improving upon AMD and yielding the results consistent with or even better than Hartree-Fock(-Bogoliubov) calculations based on harmonic oscillator expansions. In addition to the basic equations, general form of the matrix elements is also given.

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arXiv2024

Valuation methods for professional sports clubs: A historical review, a model development, and the application to Japanese football clubs

In the trend towards the globalization of football and the increasing commercialization of professional football clubs, a methodology for calculating the firm value of clubs in non-western countries has yet to be established. This study reviews the valuation methods for the club firm values in Europe and North America and how values are calculated at the time of changing ownership of Japanese clubs and develops regression models with higher explanatory power than before to estimate the more accurate firm value of Japanese football clubs. A review of the existing literature on methods for calculating the firm value of professional sports clubs in Europe and North America, as well as financial statements and registers relating to changes of ownership of Japanese clubs, was conducted. After that, multiple regression analyses were conducted using the firm value of European clubs as the explained variable. From the literature review and the Japanese case studies, it has become clear that European clubs' standard valuation methods are based on revenue and other factors, while in Japan, valuation is based solely on the par value of stocks or net assets. Multiple regression analysis revealed that the firm value of European clubs over the past three years is best explained by revenue or player market value and the number of SNS followers. Two models with high explanatory power were developed. The estimated firm value using the revenue-based formula was higher than the one based on player market value. However, in the J.League, the former was more than three times higher than the latter, while the former was only 1.2 times higher for European clubs. The discrepancy relates to differences in European and J.League clubs' revenues and asset structures. In either formula, the firm value of J.League clubs exceeded the actual transaction price when the change of ownership occurred in the past.

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arXiv2024

Accurate and precise quantum computation of valence two-neutron systems

Developing methods to solve nuclear many-body problems with quantum computers is an imperative pursuit within the nuclear physics community. Here, we introduce a quantum algorithm to accurately and precisely compute the ground state of valence two-neutron systems leveraging presently available Noisy Intermediate-Scale Quantum devices. Our focus lies on the nuclei having a doubly-magic core plus two valence neutrons in the $ p $, $ sd $, and $ pf $ shells, i.e. ${}^6$He, ${}^{18}$O, and ${}^{42}$Ca, respectively. Our ansatz, quantum circuit, is constructed in the pair-wise form, taking into account the symmetries of the system in an explicit manner, and enables us to reduce the number of qubits and the number of CNOT gates required. The results on a real quantum hardware by IBM Quantum Platform show that the proposed method gives very accurate results of the ground-state energies, which are typically within $ 0.1 \, \% $ error in the energy for ${}^6$He and ${}^{18}$O and at most $ 1 \, \% $ error for ${}^{42}$Ca. Furthermore, our experiments using real quantum devices also show the pivotal role of the circuit layout design, attuned to the connectivity of the qubits, in mitigating errors.

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