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Shung-Ichi Ando

Publications and source records attributed to Shung-Ichi Ando.

At least 19 recordsLinked to original sources
arXiv2026

Joint cluster-EFT analysis of $^{16}$N $β$-delayed $α$ spectra and $α$-$^{12}$C scattering

The $β$-delayed $α$ decay (BDAD) of $^{16}$N probes the $p$-wave $α$-$^{12}$C continuum relevant to the low-energy $E1$ transition of $^{12}$C$(α,γ)^{16}$O. We analyze the spectra of Azuma \textit{et al.} and Tang \textit{et al.} within cluster effective field theory, fitting each independently together with the same elastic-scattering data. The baseline eight-parameter fits yield $χ^2_{\rm A}/N_{\rm A} = 1.732$ for the Azuma spectrum and $χ^2_{\rm T}/N_{\rm T} = 2.028$ for the Tang spectrum, substantially improving upon the corresponding fixed-propagator values of 4.06 and 3.56, respectively. The raw simultaneous fit yields $χ^2_{\rm A}/N_{\rm A} = 4.319$, $χ^2_{\rm T}/N_{\rm T} = 10.901$, and $χ^2_{\rm el}/N_{\rm el}= 6.366$ for the Azuma, Tang, and elastic-scattering data, respectively. With sector-balanced weighting, the corresponding values are 3.308, 8.993, and 6.466, respectively. Thus, reducing the relative elastic weight improves the BDAD sectors but does not recover the quality of the independent fits. The common strong parameters and normalization ratio remain stable, whereas the fitted weak-current coefficients depend on the objective. The two spectra are separately compatible with a common strong continuum, but the minimal common weak-current amplitude does not reproduce them simultaneously; its fitted coefficients also depend on the objective. These results define the experimental and model sensitivities that must be propagated in a future unified analysis including radiative capture.

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arXiv2026

$S$ matrices of elastic $n$-$^{16}$O scattering at low energies in cluster effective field theory

Elastic $n$-$^{16}$O scattering at low energies is studied in the framework of cluster effective field theory. An evaluated data set of the total cross section of elastic $n$-$^{16}$O scattering at neutron energy, $0\le E_n\le 4$~MeV, is adopted from Evaluated Nuclear Data File (ENDF/B-VIII.0). We derive an expression for the $S$ matrices of the elastic scattering for seven spin-partial wave channels, $lj=s_{1/2}$, $p_{1/2}$, $p_{3/2}$, $d_{3/2}$, $d_{5/2}$, $f_{5/2}$, $f_{7/2}$, including one excited state and nineteen resonant states of $^{17}$O. Thirty-four parameters of the theory are fitted to the ENDF data, and we find that a plotted line, by using the fitted parameters, reproduces the ENDF data well. We discuss the uncertainties that may appear in the present approach from the fitted parameters of the resonant states with widths, larger than $Γ= 90$~keV. We also discuss the implications of the fitted values of energies and widths of the resonant states in the estimate of the astrophysical $S$ factor of $^{13}$C($α$,$n$)$^{16}$O reaction at stellar energies.

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arXiv2026

Analysis of elastic $α$-$^{12}$C scattering with global optimization in the cluster effective field theory

We analyze the elastic $α$-$^{12}$C scattering including the contribution of resonance states below the $p$-$^{15}$N breakup threshold energy. We use the cluster effective field theory in which scattering amplitude is expanded in terms of the effective range expansion parameters for the angular momentum states from $l=0$ to $l=6$. The amplitude contains 37 parameters, which are determined by fitting to 11 392 differential cross section data points of the elastic $α$-$^{12}$C scattering. To optimize the fitting process, we implement the differential evolution (DE) algorithm, which performs a global search over the high-dimensional parameter space and consistently converges to the same minimum $χ^{2}$ value across independent runs, suggesting proximity to the global minimum within the explored domain. In parallel, the Markov chain Monte Carlo (MCMC) method is used to crosscheck the DE results and to estimate the parameter uncertainties. The best fit yields $χ^{2}/N\!\simeq\!6.2$ for the elastic scattering data. Using the determined 37 parameters, we calculate the differential cross sections and the phase shifts of the elastic $α$-$^{12}$C scattering and compare the results with experimental data and those of an $R$-matrix analysis. Our result of the cross section agrees with the experimental data as accurately as an $R$-matrix analysis. The results demonstrate that the cluster effective field theory, combined with global optimization and uncertainty quantification based on DE-MCMC methods, provides a reliable and systematic framework for applications to low energy phenomena relevant to stellar evolution and nucleosynthesis.

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arXiv2026

$S$ factor of $^{13}$C($α$,$n$)$^{16}$O at low energies in cluster effective field theory

The $^{13}$C($α$,$n$)$^{16}$O reaction at low energies is studied by constructing an effective field theory. We choose a separation scale at $E=1$~MeV, where $E$ is the initial $α$-$^{13}$C energy in center-of-mass frame, just below the sharp resonant $5/2^+$ state of $^{17}$O, and include two open channels, $α$-$^{13}$C and $n$-$^{16}$O, and resonant $1/2^+$, $5/2^-$, $3/2^+$ states of $^{17}$O in the study. Parameters of the theory are fitted to experimental data, $S$ factor of $^{13}$C($α$,$n$)$^{16}$O at the energies below $E=1$~MeV, including the data sets recently reported by the LUNA and JUNA collaborations, and the $S$ factor of $^{13}$C($α$,$n$)$^{16}$O is extrapolated to the Gamow peak energy $E_G= 0.19$~MeV in the low mass AGB stars. We discuss an uncertainty in the estimate of the $S$ factor and confirm that the main part of the uncertainty emerges from the parameter fit of the near-breakup threshold $1/2^+$ state of $^{17}$O.

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arXiv2025

Radiative $α$ capture on $^{12}$C in cluster effective field theory: short review

Study of radiative $α$ capture on $^{12}$C, $^{12}$C($α$,$γ$)$^{16}$O, in cluster effective field theory (EFT) is reviewed. A low energy EFT for $^{12}$C($α$,$γ$)$^{16}$O at the Gamow-peak energy, $E_G=0.3$~MeV, is constructed, and the theory is first applied to the study of elastic $α$-$^{12}$C scattering at low energies. The effective range parameters are fitted to the precise phase shift data of the elastic scattering and the astrophysical $S_{E1}$ factor of the $E1$ transition of $^{12}$C($α$,$γ$)$^{16}$O at $E_G$ is estimated. For the study of the $E2$ transition of $^{12}$C($α$,$γ$)$^{16}$O, we discuss a difficulty to determine the asymptotic normalization coefficient (ANC) of the subthreshold $2_1^+$ state of $^{16}$O from the elastic scattering data, and demonstrate the difficulty with the estimate of the astrophysical $S_{E2}$ factor of $^{12}$C($α$,$γ$)$^{16}$O at $E_G$. We discuss the uncertainty in the estimate of the $S$ factors at $E_G$ in the present approach.

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arXiv2023

ANCs of the bound states of $^{16}$O deduced from elastic $α$-$^{12}$C scattering data

Asymptotic normalization coefficients (ANCs) of the $0_1^+$, $0_2^+$, $1_1^-$, $2_1^+$, $3_1^-$ ($l_{i th}^π$) bound states of $^{16}$O are deduced from the phase shift data of elastic $α$-$^{12}$C scattering at low energies. $S$ matrices of elastic $α$-$^{12}$C scattering are constructed within cluster effective field theory (EFT), in which both bound and resonant states of $^{16}$O are considered. Parameters in the $S$ matrices are fitted to the precise phase shift data below the $p$-$^{15}$N breakup energy for the partial waves of $l=0,1,2,3,4,5,6$, and the ANCs are calculated by using the wave function normalization factors of $^{16}$O propagators for $l=0,1,2,3$. We review the values of ANCs, which are compared with other results in the literature, and discuss uncertainties of the ANCs obtained from the elastic $α$-$^{12}$C scattering data in cluster EFT.

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arXiv2023

Radiative decay of the sub-threshold $1_1^-$ and $2_1^+$ states of $^{16}$O in cluster effective field theory

Radiative decay of the sub-threshold $1_1^-$ and $2_1^+$ states of $^{16}$O is studied in cluster effective field theory. The wave function normalization factors for initial and final states of the radiative decay amplitudes are deduced by using the phase shift data of elastic $α$-$^{12}$C scattering for $l=0,1,2$, which are related to the asymptotic normalization coefficients of $0_1^+$, $1_1^-$, $2_1^+$ states of $^{16}$O for the two-body $α$-$^{12}$C channel; then only one unfixed parameter remains in each of the radiative decay amplitudes. We fit the parameters to the experimental radiative decay rates and apply the fitted parameters to the study of radiative $α$ capture on $^{12}$C, $^{12}$C($α$,$γ$)$^{16}$O. The order of magnitude of astrophysical $S$ factors of $E1$ and $E2$ transitions of $^{12}$C($α$,$γ$)$^{16}$O is reproduced compared to the experimental data, and we discuss an improvement in the calculation of $S$ factors of $^{12}$C($α$,$γ$)$^{16}$O.

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arXiv2023

The $S$ matrices of elastic $α$-$^{12}$C scattering at low energies in effective field theory

The elastic $α$-$^{12}$C scattering at low energies for $l=0,1,2,3,4,5,6$ is studied in effective field theory. We discuss the construction of the $S$ matrices of elastic $α$-$^{12}$C scattering in terms of the amplitudes of sub-threshold bound and resonant states of $^{16}$O, which are calculated from the effective Lagrangian. The parameters appearing in the $S$ matrices are fitted to the phase shift data below the $p$-$^{15}$N breakup threshold energy, and we find that the phase shifts are well described within the theory.

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arXiv2022

Radiative proton capture on $^{15}\mathrm{N}$ within effective field theory

The astrophysical $S$ factor for the radiative proton capture process on the $^{15}\mathrm{N}$ nucleus, i.e., $^{15}\mathrm{N}(p, γ)^{16}\mathrm{O}$, at stellar energies are studied within the framework of the cluster effective field theory. The thermonuclear $^{15}\mathrm{N}(p, γ)^{16}\mathrm{O}$ reaction links the type-I to type-II cycles of the carbon-nitrogen-oxygen cycle and affects the abundances of elements in the univere. For investigating this reaction in the effective field theory formalism, we first construct an effective Lagrangian that is appropriate for this reaction at low-energies. Since the intermediate excited states of the $^{16}\mathrm{O}$ nucleus have a crucial role in this reaction, we include these resonances in the formalism. The corresponding radiative capture amplitudes and cross section are calculated, which lead to the astrophysical $S$ factor. The low energy constants introduced in the effective Lagrangian are determined by fitting the theoretical results to the observed $S$ factors in the range of $130~\mathrm{keV} < E_p < 2500~\mathrm{keV}$ using three different experimental data sets. Considering the recent data sets, we obtain $S(0) = 29.8\mbox{-}34.1~\mathrm{keV\ b}$, which is in a good agreement with the estimates from $R$-matrix approaches in the literature. The values of $S$ at the Gamow energy are found to be larger than $S(0)$ values by about $10\%$.

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arXiv2022

Elastic $α$-$^{12}$C scattering at low energies with the resonant $2_2^+$ and $2_3^+$ states of $^{16}$O

The elastic $α$-$^{12}$C scattering for $l=2$ at low energies is studied in an effective Lagrangian approach. We explicitly include two resonant $2_2^+$ and $2_3^+$ states of $^{16}$O in the scattering amplitudes and construct an $S$ matrix assuming that three amplitudes, the non-resonant part of the amplitude which has the sub-threshold $2_1^+$ state of $^{16}$O and those of the two resonant states, are represented by the summation of corresponding parts of the phase shift. Then, we fit the parameters in the $S$ matrix to the phase shift data by imposing three conditions at very low energies where the phase shift data are not available. By using the fitted parameters, we calculate the asymptotic normalization coefficients (ANC) of the $2_1^+$ state of $^{16}$O and find that the previously reported small and large values of the ANC can be reproduced depending on the imposed conditions, but we obtain large error bars for the large ANC values which are reported from the $α$ transfer reactions.

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arXiv2020

Cluster effective field theory and nuclear reactions

An effective field theory (EFT) for a nuclear reaction at low energies is studied. The astrophysical $S$-factor of radiative $α$ capture on $^{12}$C at the Gamow-peak energy, $T_G=0.3$ MeV, is a fundamental quantity in nuclear-astrophysics, and we construct an EFT for the reaction. To fix parameters appearing in the effective Lagrangian, the EFT is applied to the study for three reactions: elastic $α$-$^{12}$C scattering at low energies, $E1$ transition of radiative $α$ capture on $^{12}$C, and $β$ delayed $α$ emission from $^{16}$N. We report an estimate of the $S_{E1}$-factor of the reaction through the $E1$ transition at $T_G$ by employing the EFT. We also discuss applications of EFTs to nuclear reactions at low energies.

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arXiv2020

Elastic $α$-$^{12}$C scattering at low energies with the sharp resonant $0_3^+$ state of $^{16}$O

An inclusion of sharp resonant $0_3^+$ state of $^{16}$O and first excited $2_1^+$ state of $^{12}$C in a study of $s$-wave elastic $α$-$^{12}$C scattering at low energies is investigated in an effective Lagrangian approach. The elastic scattering amplitude is parted into two; one is for the sharp resonant $0_3^+$ state of $^{16}$O parameterized by Breit-Wigner formula, and the other is for a non-resonant part of the amplitude parameterized by effective range expansion. In the non-resonant part of the amplitude, a contribution from the $2_1^+$ state of $^{12}$C is included. We discuss a large correlation between a coupling for the $2_1^+$ state of $^{12}$C and an effective range parameter $Q_0$ as well as a necessity of inclusion of a vertex correction for the initial and final $α$-$^{12}$C states. After fixing parameters appearing in the amplitudes by using experimental data, we calculate asymptotic normalization coefficients for ground $0_1^+$ state and first excited $0_2^+$ state of $^{16}$O and compare them to previous results found in literature.

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arXiv2020

Neutrino-Deuteron Reactions at Solar Neutrino Energies in Pionless Effective Field Theory with Dibaryon Fields

We study breakup of the deuteron induced by neutrinos in the neutral $νd\to νnp$, $\barν d\to \barν np$ and the charged $\barν d\to e^+ n n$, $νd\to e^- pp$ processes. Pionless effective field theory with dibaryon fields is used to calculate the total cross sections for neutrino energies $E_ν$ from threshold to 20 MeV. Amplitudes are expanded up to next-to-leading order, and the partial wave is truncated at $P$-waves. The Coulomb interaction between two protons is included nonperturbatively in the reaction amplitudes, and an analytic expression of the amplitudes is obtained. The contribution of the next-to-leading order to the total cross section is in the range of 5.2$-$9.9\% in magnitude, and that of the $P$-wave is 2.4$-$2.8\% at $E_ν= 20$ MeV. Uncertainty arising from an axial isovector low-energy constant is estimated to be on the order of 1\%.

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arXiv2019

The $S_{E1}$ factor of radiative $α$ capture on $^{12}$C in cluster effective field theory

The $S_{E1}$-factor of radiative $α$-capture on $^{12}$C is studied in effective field theory up to next-to-leading order. A modification of the counting rules for the radiative capture amplitudes is discussed. We find that only two unfixed parameters remain in the amplitudes, and those two parameters are fitted to the experimental $S_{E1}$ data. An $S_{E1}$ factor is calculated at the Gamow-peak energy as $S_{E1}=59\pm 3$ keV$\cdot$b, and the result is found to be about 30% smaller than the estimates reported recently. An uncertainty of the estimate in the present work is also discussed.

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arXiv2018

Universal physics of the few-body system of two neutrons and one flavored meson

We investigate the $s$-wave three-body system of two neutrons and one flavored meson with total spin-isospin $J=0,I=3/2$. The meson-neutron scattering length can become infinitely large in an unphysical region of the quark mass when extrapolated from strangeness to charm in the so-called zero coupling limit. Using a low-energy cluster effective field theory, we demonstrate that the Efimov effect is manifest in the three-body system when the meson-neutron scattering length is extrapolated to the unitary limit of the two-body interaction. We thereby discuss the consequence of universal physics in the physical $K^{-}nn$ and $D^{0}nn$ systems.

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arXiv2017

Elastic $α$-$^{12}$C scattering at low energies with the bound states of $^{16}$O in effective field theory

The elastic $α$-$^{12}$C scattering for $l=0,1,2,3$ channels at low energies is studied, including the energies of excited bound states of $^{16}$O, in effective field theory. We introduce a new renormalization method due to the large suppression factor produced by the Coulomb interaction when fitting the effective range parameters to the phase sift data. After fitting the parameters, we calculate asymptotic normalization constants of the $0_2^+$, $1_1^-$, $2_1^+$, $3_1^-$ states of $^{16}$O. We also discuss the uncertainties of the present study when the amplitudes are interpolated to the stellar energy region of the $^{12}$C($α$,$γ$)$^{16}$O reaction.

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arXiv2017

Spin polarization observables of the deuteron photodisintegration at low energies in pionless effective field theory

Spin polarization observables of the deuteron photodisintegration at low energies are studied in a pionless effective field theory up to next-to-next-to-leading order (NNLO). The total and differential cross sections, induced neutron polarization $P_{y'}$, and tensor analyzing powers $T_{20}$ and $T_{22}$ of the process are calculated at photon energies from the breakup threshold to 20~MeV. We find that the NNLO corrections in the cross sections and $P_{y'}$ converge well whereas they turn out to be important contributions in $T_{20}$ and $T_{22}$. We discuss the discrepancy between theory and experiment in $P_{y'}$ still persisting as well as an implication of our result to the first measurement of $T_{20}$ at low energies in the HIGS facility.

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