arXiv subjects

Kazuyuki Ogata

Publications and source records attributed to Kazuyuki Ogata.

At least 19 recordsLinked to original sources

arXiv2026

Rotational Feshbach resonances in the deformed halo nucleus $^{31}$Ne

Background: The deformed halo nucleus $^{31}$Ne exhibits unique structural properties arising from the interplay between its halo neutron and the deformation of the $^{30}$Ne core. While previous studies have established the nature of its weakly-bound ground state through reaction cross sections and inclusive breakup measurements, the structure of its excited states in the low-energy continuum, which are expected to appear as resonances, remains largely unexplored. Purpose: We investigate the structure of these resonant states and clarify their rotational nature and formation mechanism. Method: The structure of $^{31}$Ne is described using the particle rotor model (PRM), which explicitly treats the coupling between core excitation and single-particle motion in both bound and continuum states. Results: The calculations predict the emergence of unbound rotational states in the low-energy continuum of $^{31}$Ne, which form a rotational sequence built on the weakly-bound Nilsson [321 3/2] configuration. As the total angular momentum increases along the rotational band, the intrinsic Nilsson structure is largely preserved, whereas the dominant core-spin component shifts to higher spins. These resonances are stabilized through the combined effects of coupling to higher-lying closed core-excited channels and reduced effective neutron relative energies, and can therefore be interpreted as rotational Feshbach resonances. Conclusion: The present study elucidates the formation mechanism of rotational Feshbach resonances in $^{31}$Ne. This mechanism is expected to be a general feature of weakly-bound deformed nuclei. Exclusive breakup measurements with coincident detection of $γ$ rays from the de-exciting core will provide crucial tests of the proposed formation mechanism of rotational Feshbach resonances.

nucl-th↗

arXiv2026

Description of nucleon elastic scattering off $^6$Li with the four-body continuum-discretized coupled-channels method

Background: Neutron reactions off lithium isotopes up to 50 MeV are important for nuclear data science, around the International Fusion Material Irradiation Facility (IFMIF) facility in particular. Purpose: We aim at constructing a semi-microscopic reaction model that describes neutron elastic scattering off $^6$Li up to 50 MeV taking the breakup channels of $^6$Li into account. Methods: We adopt the continuum-discretized coupled-channels method (CDCC) with an $α+p+n$ three-body model of $^6$Li. We employ the $g$-matrix effective interaction by Jeukenne, Lejeune, and Mahaux (JLM). The renormalization factors of the real and imaginary parts of the JLM interaction are treated as free parameters. Results: The renormalization parameter of the real part of the JLM interaction is found to be constant ($=1.1$), whereas that for the imaginary part has a smooth energy dependence. The four-body CDCC calculation with these parameters well describes the angular distributions of both proton and neutron elastic scatterings as well as the neutron total cross section and proton total reaction cross section. The applicable energy range is found to be from 7 MeV to 50 MeV. Conclusions: We have constructed a reliable reaction model for describing nucleon-$^6$Li scattering between 7 MeV and 50 MeV. This model can directly be applied to inelastic scattering and breakup reactions for $^6$Li with the help of the complex scaling method.

nucl-th↗

arXiv2026

Phenomenological refinement of $p$-$d$ elastic scattering descriptions towards the 3NF study in nuclei via the ($p,pd$) reaction

The ($p,pd$) reaction is expected to be a powerful tool for probing three-nucleon forces (3NFs) in nuclear medium since it can be essentially regarded as the $p$-$d$ elastic scattering inside nuclei. One of the important points in the theoretical description of the ($p,pd$) reaction is to calculate the $p$-$d$ scattering in a nucleus quantitatively using effective interactions. This work aims to develop a phenomenological approach to improve the quantitativity of the $p$-$d$ scattering cross section in free space calculated with effective interactions. The $p$-$d$ elastic amplitude is decomposed into a 2N part, described using 2N effective interactions, and a residual part, which the 2N part cannot describe. The latter is approximated by a superposition of Legendre polynomials, with coefficients treated as adjustable parameters. These parameters are determined to reproduce experimental $p$-$d$ differential cross-section data at various incident energies. The obtained parameters exhibit smooth energy dependence, which is approximated by quadratic functions. The numerical results with the analytic energy dependence also reproduce the experimental data. The developed approach works well for improving the $p$-$d$ scattering cross section in a wide range of incident energies. This work can be regarded as the first step toward the description of ($p,pd$) reactions taking 3NF effect in nuclear medium into account.

nucl-th↗

arXiv2026

Chirality in $(\vec{p},2p)$ reactions induced by proton helicity

It is shown that longitudinally polarized protons can be used to induce chirality in the final states of the $(\vec{p},pN)$ reaction at intermediate energies, when there exist three final-state particles with non-coplanar momentum vectors. The analyzing power $A_z$ is proposed as a measure of this effect. Theoretical descriptions to obtain $A_z$ based on an intuitive picture as well as a distorted wave impulse approximation are presented, showing that the helicity of incident protons is coupled to the chirality of the orbital motion of a single-particle wave function, resulting in the chirality of the final states and a large $A_z$ value.

nucl-th↗

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.

nucl-th↗

arXiv2026

Establishing the $^{40}$Ca$(p,p α)$ reaction at 392 MeV under quasi-free scattering conditions

The $(p,p α)$ reaction offers a direct means to probe preformed $α$-cluster structures in nuclei under quasi-free scattering conditions. Previous studies around 100 MeV provided valuable insights into $α$ clustering, but quantitative comparison with microscopic cluster wave functions remained limited due to strong distortion effects. At higher energies, the reaction mechanism becomes simpler and the distorted-wave impulse approximation (DWIA) provides a more reliable framework for quantitative analysis. In the present work, the $^{40}$Ca$(p,pα)$ reaction was measured at an incident energy of 392 MeV using the high-resolution Grand Raiden and LAS spectrometers at RCNP. Despite the small cross section in this energy region, the achieved resolution allowed clear separation of the ground and excited states of the residual $^{36}$Ar nucleus, and corresponding momentum distributions were extracted. DWIA calculations using a Woods-Saxon $α+ ^{36}$Ar bound-state wave function yielded an experimental spectroscopic factor of $ S_{\mathrm{FAC}}^{\mathrm{WS}} = 0.51 \pm 0.05 $, consistent with the previous result at 101.5 MeV $(0.52 \pm 0.23 )$. This agreement demonstrates that the reaction mechanism is well described across a wide energy range. The present study establishes the feasibility of high-precision $(p,pα)$ measurements at several hundred MeV and highlights their potential as a quantitative probe of $α$ clustering in medium-mass nuclei, forming the basis for systematic studies in both stable and unstable systems.

nucl-ex↗

arXiv2026

$ΞNN$ three-baryon force from SU(3) chiral effective field theory: A femtoscopic study

Background: The development of SU(3) chiral effective field theory has opened the way to a systematic exploration of three-baryon forces (3BFs), a key ingredient in hypernuclear and dense matter physics. However, $ΞNN$ 3BF based on SU(3) chiral EFT has not been studied until now. Purpose: We apply SU(3) chiral EFT to derive $ΞNN$ potentials in momentum space. Then, we investigate how the $ΞNN$ 3BF affects the correlation function of deuteron--$Ξ^-$ pair created through heavy-ion collisions. Methods: To reduce the number of low-energy constants involved in the $ΞNN$ potentials, we employ the decuplet saturation approximation, by which only two of them remain unconstrained. The deuteron--$Ξ^-$ scattering is treated as an effective two-body problem with the $ΞNN$ 3BF incorporated into the potential between the deuteron and $Ξ^-$. Results: We found that the effect of the $ΞNN$ 3BF on the deuteron--$Ξ^-$ correlation function is at most about 4\%. This small effect is not primarily due to the loosely-bound nature of the deuteron. Instead, this is because the deuteron and $Ξ^-$ interact with each other mainly at low momentum, corresponding to peripheral scattering, where the influence of the $ΞNN$ 3BF is limited. Conclusions: Since the correlation function shows limited sensitivity to the short-range 3BF, complementary approaches may be necessary.

nucl-th↗

arXiv2025

Systematic analysis of proton- and deuteron-induced one-proton knockout reactions

The ratios of the one-proton knockout cross sections by a deuteron to those by a proton are about 1.5, indicating that using deuteron is more efficient than proton in yielding large knockout cross sections. However, this ratio differs from the intuitive expectation, and its underlying mechanism remains unclear. The purpose of this study is to clarify the mechanism behind the observed ratio by theoretically describing and analyzing the deuteron- and proton-induced one-proton knockout reactions. Proton-induced one-proton knockout reactions are described within the standard distorted-wave impulse approximation (DWIA) framework, while deuteron-induced one-proton knockout reactions are treated with a new approach, DWIA-BU, that incorporates deuteron breakup into the DWIA. The ratios calculated with the DWIA-BU reproduce the experimental data reasonably, whereas those with the DWIA significantly underestimate them. The ratio of the corresponding elementary cross sections remains about 3.5 regardless of the energy, and the difference in absorption between the deuteron and the proton influences the ratios of knockout cross sections, resulting in agreement between the calculated ratios and the experimental data. It is found that the deuteron breakup is essential to reproduce the experimental ratio. The ratios of the knockout cross sections are primarily determined by the difference in the elementary cross sections and that in the absorption between the deuteron and the proton.

nucl-th↗

arXiv2025

Description of nucleon transfer reactions at intermediate energies within the impulse picture

Background: At intermediate energies, transfer reactions are suppressed because the momentum-matching condition is difficult to satisfy. In the standard distorted wave Born approximation (DWBA), a high momentum component of the transferred particle is required to match the large momentum transfer. Purpose: We investigate the applicability of the distorted wave impulse approximation (DWIA) for describing ($p,d$) transfer reactions at intermediate energies by performing a comparative study with the standard DWBA. DWIA, which has been successful for knockout reactions, is expected to provide an alternative reaction mechanism at this energy region. Methods: Both DWBA and DWIA formalisms are applied to the $^{16}$O($p,d$){}$^{15}$O reaction at 200~MeV. In DWBA, the reaction is described as a neutron pickup, while in DWIA, it is treated as a quasi-elastic scattering from a preformed deuteron cluster in the target. Results: The DWBA calculation is in good agreement with the experimental data, reproducing both the angular distribution and the absolute magnitude of the cross section with a reasonable spectroscopic factor. In contrast, the DWIA calculation, while qualitatively reproducing the trend of the angular distribution, severely underestimates the cross section by about two orders of magnitude. Conclusions: Our findings suggest that conventional DWBA provides a more suitable description for the $^{16}$O($p,d$){}$^{15}$O reaction at 200~MeV. The failure of DWIA in this case, unlike its success in knockout reactions, raises open questions about its applicability to transfer reactions. This motivates the need for systematic investigations to delineate the applicability of both reaction mechanisms under various conditions.

nucl-th↗

arXiv2025

Determination of $S_{18}$ from $^{9}$C breakup reaction within a four-body reaction model

The astrophysical factor $S_{18}$ for the $^{8}$B($p$,$γ$)$^{9}$C has indirectly been measured with the proton removal reactions from $^9$C, elastic breakup of $^9$C off a heavy target, and transfer reactions. Quite recently, the elastic breakup cross section data were reanalyzed with the continuum-discretized coupled channels method (CDCC) assuming a $p+{\rm ^{8}B}$ two-body model for $^9$C and the $S_{18}$ was modified. It was not well justified, however, to treat $^8$B as an inert nucleus given its proton separation energy is only 137~keV. We reexamine the elastic breakup of $^9$C by the four-body CDCC with a $p+p+{\rm ^{7}Be}$ three-body model for $^9$C and evaluate $S_{18}$. To achieve this, we propose a method to disentangle the $p+{\rm ^{8}B}+{\rm ^{208}Pb}$ three-body channel in the four-body CDCC calculation, for the first time. We calculate the elastic breakup cross section of $^9$C off a $^{208}$Pb target at 65~MeV/nucleon. The obtained breakup cross sections are decomposed into the contributions of the $p+{\rm ^{8}B}+{\rm ^{208}Pb}$ and $p+p+{\rm ^{7}Be}+{\rm ^{208}Pb}$ channels by using the solution of the complex-scaled Lippmann--Schwinger equation. The breakup cross section to the $p+{\rm ^{8}B}+{\rm ^{208}Pb}$ channel reproduces well the shape of the experimental data in the low breakup energy region, which is important for determining $S_{18}$. By fitting the theoretical result to the experimental data, the asymptotic normalization coefficient of $^9$C for the $p+{\rm ^{8}B}$ configuration is determined and we obtain $S_{18}=38.4\pm1.1$ eVb. This result is smaller than the previous value obtained with the three-body CDCC by about 45\%. Thus, our new results suggest the necessity of taking into account the fragile nature of $^{8}$B in the $^{9}$C breakup.

nucl-th↗

arXiv2025

Ab initio informed 20Ne(p, p$α$)16O reaction elucidates the emergence of alpha clustering from chiral potentials

We report on the first \textit{ab initio} informed $α$ knock-out reaction in the intermediate-mass region, with the aim to probe the underlying chiral potential and its impact on the emergence of alpha clustering in this mass region. The theoretical predictions of the $α+^{16}$O clustering in the $^{20}$Ne ground state, based on the \textit{ab initio} symmetry-adapted no-core shell model, yield a triple differential cross section for $^{20}$Ne(p, p$α$)$^{16}$O that is in a remarkable agreement with the data. This allows us to examine predictions of surface and in-medium $α$-cluster features from a chiral potential and to compare these to the successful antisymmetrized molecular dynamics approach.

nucl-th↗

arXiv2025

Three-body analysis reveals the significant contribution of minor $^{5}$He $s$-wave component in $^{6}$Li$(p,2p)^{5}$He cross section

$^6$Li is usually treated as an $α+p+n$ three-body system, and the validity of this picture is important for understanding $^6$Li reactions. The ($p$,$2p$) reaction is a powerful method to study the structure of valence nucleons in $^6$Li. Recently, the new experimental data of the $^{6}$Li($p$,$2p$)$^{5}$He reaction have been obtained and should be analyzed. We investigate the $^{6}$Li($p$,$2p$)$^{5}$He reaction using the $α+p+n$ three-body wave function of $^6$Li and study the validity of this model. We calculate the $^6$Li wave function by using Gaussian expansion method, and the function is used to obtain the relative wave function between $p$ and $^5$He. We combine the relative wave function with the distorted wave impulse approximation. Our results reproduce the experimental data of the triple differential cross section within about 10\% difference in the absolute values, and contributions from both $p$- and $s$-wave states of $^5$He in $^6$Li are found to be important. We can qualitatively understand the $^{6}$Li($p$,$2p$)$^{5}$He reaction by describing $^6$Li with the three-body model. Contribution from the $s$-wave component is important in reproducing the experimental data in the zero recoil-momentum region.

nucl-th↗

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.

nucl-th↗

arXiv2024

Significance of the refraction effect on the $p$-$d$ elementary process in the ($p$,$pd$) reaction

The proton-induced deuteron knockout reaction, ($p$,$pd$), is one of the interests in the studies for probing the deuteron-like $p$-$n$ correlation in nuclei. According to a recent study of the inclusive deuteron-induced reaction, $(d,d'x)$, the refraction effect of the deuteron has a significant effect on the elementary process, nucleon-deuteron ($N$-$d$) binary scattering inside a nucleus, of the reaction. In the paper, it is shown that proper treatment of the local $N$-$d$ relative momentum in the elementary process is crucial in $(d,d'x)$ reactions at $100$ MeV and below. In the present work, we investigate the deuteron refraction effect in the exclusive ($p$,$pd$) reactions. We also discuss the incident energy dependence of the refraction effect. The refraction effect on the $p$-$d$ elementary process is taken into account by the local semiclassical approximation to the distorted waves. The results are compared with those obtained with the asymptotic momentum approximation, which is standardly applied to the distorted wave impulse approximation framework. It is shown that the refraction effect drastically changes the energy sharing distribution of the $^{16}$O($p$,$pd$)$^{14}$N reaction at 101.3 MeV and gives a better agreement with experimental data. In contrast, it is confirmed that the effect is negligibly small at 250 MeV. We have clarified that the deuteron refraction effect is significant in the $^{16}$O($p$,$pd$)$^{14}$N reaction at 101.3 MeV and the experimental data are well reproduced. The refraction effect plays a significant role in both the shape and magnitude of the ($p$,$pd$) cross section, while the effect is negligible at 250 MeV.

nucl-th↗

arXiv2024

Difference in peripherality of the inclusive (p, p'x) and (d, d'x) reactions and its implications for phenomenological reaction model

Previous studies have revealed the importance of introducing surface correction into a phenomenological model for inclusive (n, n'x) and (p, p'x) reactions. These findings have contributed significantly to the improvement of nuclear data evaluation. However, the necessity for the surface correction in an inclusive (d, d'x) reaction has hardly been investigated. The purpose of this study is to investigate the difference in the peripherality of the (p, p'x) and (d, d'x) reactions by a theoretical analysis using a quantum mechanical model, and to obtain a theoretical basis on the surface correction in the (d, d'x) reaction. The energy spectra and their radial distributions for the (p, p'x) and (d, d'x) reactions are calculated by the one-step semiclassical distorted wave model. The radial distribution of the energy spectra for the (d, d'x) reaction is shifted toward the outer region of the nucleus compared to the (p, p'x) reaction. Based on this finding, we consider a larger surface correction into a phenomenological model for the (d, d'x) reaction than that for the (p, p'x) reaction, and calculated values reproduce the experimental (d, d'x) spectra well. The peripherality of the (d, d'x) reaction is more prominent than that of the (p, p'x) reaction. The stronger surface correction thus should be introduced for the (d, d'x) reaction than for the (p, p'x) reaction.

nucl-th↗

arXiv2023

Systematic analysis of the nuclear absorption effect on the cross section of the knockout reaction

Recent studies on nucleon and alpha knockout reactions have shown that the distorted-wave impulse approximation (DWIA) is a simple and accurate method to describe these reactions. As it has been argued for decades, the nuclear absorption is one of the most important ingredients of the DWIA calculation. In this work, we systematically investigate the absorption effects on the cross sections of the nucleon and alpha knockout reactions. To do this, we calculate the ratio of the cross sections of the DWIA and plane-wave impulse approximation (PWIA) and examine its dependence on the mass number and single-particle orbital of the knocked-out particles. We will discuss the specific characteristics of the absorption effect for each reaction.

nucl-th↗

arXiv2023

Description of inclusive $(d,d^{\prime}x)$ reaction with the semiclassical distorted wave model

The description of deuteron-induced inclusive reactions has been an important subject in direct nuclear reaction studies and nuclear data science. For proton-induced inclusive processes, the semiclassical distorted wave model (SCDW) is one of the most successful models based on quantum mechanics. We improve SCDW for deuteron-induced inclusive processes and clarify the importance of the proper treatment of the kinematics of the deuteron inside a nucleus. The double differential cross section (DDX) of the inclusive deuteron-emission process $(d,d^{\prime}x)$ is described by one-step SCDW. The changes in the kinematics due to the distortion effect, the refraction effect, is taken into account by the local semiclassical approximation (LSCA). The calculated DDXs of $(d,d^{\prime}x)$ reasonably reproduce experimental data in the small energy-transfer region and at forward and middle angles with some exceptions. The angular distributions of $(d,d^{\prime}x)$ are improved by including the refraction effect. The proper treatment of the changes in the kinematics of the deuteron inside a nucleus is necessary in describing the ($d$,$d'x$) reaction. The effect of the changes on the DDX of $(d,d^{\prime}x)$ is significant compared to on the proton-induced inclusive process $(p,p^{\prime}x)$ because of the stronger distortion effect on the deuteron.

nucl-th↗

arXiv2023

Systematic analysis of $t$ and $^3$He breakup reactions

Systematic measurement of $t$ and $^3$He knockout processes is planned. The weakly-bound nature of these nuclei may affect the interpretation of forthcoming knockout reaction data. Purpose: We aim at clarifying breakup properties of $t$ and $^3$He by investigating their elastic and breakup cross sections. We employ the four-body continuum-discretized coupled-channels method with the eikonal approximation to describe the $t$ and $^3$He reactions. The breakup cross section of $t$ is found to be almost the same as that of $^3$He and is about one-third of that of $d$. Coulomb breakup plays negligible role in the breakup of $t$ and $^3$He, in contrast to in the deuteron breakup reaction. It is found that $t$ and $^3$He tend to breakup into three nucleons rather than $d$ and a nucleon. It is shown that the breakup cross sections of $t$ and $^3$He are not as large as those of d but non-negligible. Because about 80% of them corresponds to the three-nucleon breakup process, a four-body breakup reaction model is necessary to quantitatively describe the breakup of $t$ and $^3$He.

nucl-th↗