arXiv subjects

Y. F. Niu

Publications and source records attributed to Y. F. Niu.

At least 19 recordsLinked to original sources

arXiv2026

Nuclear landscape based on point-coupling density functional with localized exchange terms

Nuclear landscape is initially explored in the framework of relativistic Hartree-Bogoliubov theory under the spherical approximation, adopting the newly developed PCF-PK1 density functional. The functional effectively incorporates exchange terms via the Fierz transformation and explicitly includes the tensor coupling. We analyze the limits of the nuclear landscape and nuclear ground state properties including binding energies, charge radii, α-decay energies, compared with other functionals and experiment. In the present calculations, 7210 nuclei are predicted to be bound with the root-mean-square deviation of binding energies 7.170 MeV. The removal of spurious shell closure at Z = 58 and 92 is discussed by shell gaps and single-particle spectra. For superheavy nuclei, potential magic numbers beyond 208Pb are studied. The inclusion of the tensor coupling in PCF-PK1 helps restore the pseudospin symmetry, leading to a less pronounced shell closure at Z = 120.

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arXiv2026

Nuclear mass prediction using bidirectional recurrent neural networks with isotopic and isotonic chain correlations

Nuclear masses are fundamental quantities in nuclear physics, providing essential information for understanding nuclear structure, decay properties, and reaction processes. Here we develop a bidirectional recurrent neural network (Bi-RNN) that naturally incorporates sequential correlations along isotopic and isotonic chains for nuclear mass prediction. The model achieves a root-mean-square (rms) deviation of 78 keV for binding energies of 2339 nuclei with known masses, a 45% improvement over a conventional artificial neural network (ANN) with comparable parameter count. The Bi-RNN also delivers consistent accuracy across different odd-even parity groups and yields an rms of 99 keV for $Q_β$ values without explicit training, demonstrating that recurrent correlations encode physically relevant information beyond individual nuclear features. Extrapolation tests on 292 nuclei updated from AME2003 to AME2012 and on 109 nuclei updated from AME2012 to AME2020 reveal that the Bi-RNN maintains stable performance, substantially outperforming WS4, ANN, and earlier AME evaluations. These results demonstrate the power of recurrent architectures in capturing correlations along nuclear chains and suggest Bi-RNN as a robust tool for studying nuclear masses.

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arXiv2026

Isoscalar Giant Resonances in the even-A Pd Isotopes

Studies of the isoscalar giant monopole resonance (ISGMR) across the chart of nuclides provide insight into the incompressibility of nuclear matter near saturation density, K(infinity). Such studies had revealed a discrepancy between theoretical approaches: quasiparticle random phase approximation (QRPA) derived from Skyrme interactions reproduce the strength distributions of the ISGMR in the doubly-closed-shell nuclei 90Zr and 208Pb, but their descriptions of strength distributions in open-shell medium-heavy nuclei suggest higher centroid energies should be experimentally observed. The latter nuclei required a smaller K(infinity) and were thus deemed softer. The present work serves to add to this softness discourse by extracting ISGMR strength distributions for 104,106,108,110Pd via 386-MeV inelastic alpha-scattering. The extracted giant resonance strength distributions are consistent with expectations in this isotopic range. Additional Quasiparticle Vibration Coupling (QPVC) effects are included with the QRPA approach and compared to aforementioned ISGMR strength distributions.

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arXiv2026

Probing Vortex γ Photons via Nuclear Resonance Fluorescence

High-energy vortex γ photons offer unique prospects in nuclear physics, astrophysics, and strong-field physics, owing to their distinctive topological structure. Yet, their hallmark effects are erased in macroscopic targets, the only practical regime to date, when probed via the total transition probability of photoabsorption. Here we show that nuclear resonance fluorescence (NRF) circumvents this limitation. Using a Bessel-mode description, we demonstrate that for macroscopic targets, the target-averaged angular distribution of scattered photons retains a distinct dependence on the vortex polar angle, which emerges as the sole surviving vortex signature. Moreover, by scanning the vortex polar angle instead of the detector angle, we show that NRF can extract the angular momentum of nuclear excited states in a fixed-geometry setup. The vortex polar angle, a new degree of freedom in NRF, not only provides a direct quantitative diagnostic for vortex γ beams at the MeV energy scale, but also opens a new avenue for exploring orbital angular momentum-induced quantum phenomena in photonuclear physics.

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arXiv2026

Construction of Nuclear Covariant Energy Density Functional from A Physics-Guaranteed Neural Network Approach

Density functional theory is a practical approach for solving quantum many-body problems with available computational resources. The complexity of the nuclear force makes constructing an accurate nuclear energy density functional much more challenging. The feasibility of constructing a nuclear covariant energy density functional with deep neural networks is demonstrated. This physics-guaranteed neural network approach achieves high accuracy in predicting nuclear energy density and exhibits significantly better extrapolation abilities than traditional machine learning methods for binding energies. When combined with the existing covariant density functional, the neural network approach improves the binding energy accuracy from $644$ keV to $86$ keV in the known region and also effectively captures the microscopic shell effect. Furthermore, its extrapolation performance is also significantly enhanced, achieving an accuracy of approximately $5$ MeV even when extrapolating up to $30$ steps. This work paves the way for the construction of accurate nuclear energy density functionals through machine learning.

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arXiv2026

$β$-Decay Half-Lives Serve as Novel Evidence for the New Magic Number $N=32$

Conventional signatures of nuclear magic number, including low-lying quadrupole collectivity and mass systematics, face significant challenges when probing emergent shell closures near the drip line. However, $β$-decay half-lives are among the first experimental observables measurable following the discovery of neutron-rich isotopes. This letter demonstrates that $β$-decay half-lives provide evidence for the emergent magic number $N=32$. The observed half-life pattern around the $N=32$ can be attributed to the occupation probabilities of orbitals above this shell gap, which directly reflect the gap's magnitude. Our results reveal a pronounced $N=32$ shell gap in Ca isotopes and a weaker yet apparent gap in K isotopes, consistent with mass and electromagnetic transition data. Furthermore, the analysis indicates no prominent closed-shell signature at $N=32$ in Ar and Cl isotopes.

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arXiv2025

Photoabsorption Cross Sections studied within the axially deformed Relativistic Quasiparticle Finite Amplitude Framework

Photoabsorption cross sections for 235 stable nuclei, ranging from $^{40}$Ca to $^{209}$Bi, were investigated by the quasiparticle finite amplitude method (QFAM) based on the axially deformed relativistic Hartree-Bogoliubov (RHB) approach using relativistic point-coupling interaction DD-PC1, with extensions to odd-A nuclei. GDR parameters based on the standard Lorentzian (SLO) model were extracted from QFAM results and compared with those from experimental data recommended by IAEA. Good agreement was achieved for giant dipole resonance (GDR) peak energies, while resonance widths were underestimated and hence peak cross sections were overestimated due to the lack of higher-order many-body correlations. These discrepancies were much improved in deformed nuclei. The effects of deformation on photoabsorption cross sections were examined systematically. The comparison of photoabsorption cross sections among QFAM results and discrepant experimental data revealed the potential of QFAM calculations in the evaluation of photonuclear data.

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arXiv2025

Role of nuclear and electromagnetic fragmentation in the charge-changing reactions of 18O on carbon and lead targets at around 370 MeV/nucleon

Charge-changing cross sections (CCCSs) of 18O on carbon (C) and lead (Pb) targets have been measured with an uncertainty of less than 4% at around 370MeV/nucleon. We evaluate the contributions of nucleon-nucleon (NN) and electromagnetic (EM) interactions to CCCSs by considering the direct proton removal process, the charged particle evaporation (CPE) after neutron removal, and the EM excitation. We conclude that the CPE accounts for 12.3% and 5% of CCCSs on C and Pb, respectively. Only less than 1% of CCCSs of 18O is attributed to the EM excitation. Further investigation of projectiles from 18O to 197Au on C, silver (Ag) and Pb targets at 300 and 900MeV/nucleon show that the contribution of EM to CCCSs on Ag and Pb increases with projectile mass numbers and incident energies, and can reach 10% for 197Au on Pb at 900MeV/nucleon. In contrast, the EM contribution to CCCS is negligible for all projectiles on C at both energies.

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arXiv2025

$Z=14$ Magicity Revealed by the Mass of the Proton Dripline Nucleus $^{22}$Si

Using the $Bρ$-defined isochronous mass spectrometry technique, we conducted the first mass measurement of the proton dripline nucleus $^{22}$Si. We confirm that $^{22}$Si is bound against particle emission with $S_p/S_{2p}=+1412(114)/+229(54)$ keV, fixing the proton dripline location for the Si element. By analyzing the mass differences of the neighboring $sd$-shell nuclei, we find that $^{22}$Si exhibits a doubly-magic character similar to its mirror partner $^{22}$O, and that the mirror energy difference of $^{22}$Si-$^{22}$O deviates from the predictions assuming mirror symmetry. Gamow shell-model calculations reveal that the average occupations of valence protons in $^{22}$Si are nearly identical to those of valence neutrons in $^{22}$O, supporting the $Z=14$ magicity in $^{22}$Si. The observed mirror-symmetry breaking is attributed to the extended proton distribution in $^{22}$Si arising from a small contribution of the unbound $\pi2s_{1/2}$ orbital.

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arXiv2024

Nuclear structure of dripline nuclei elucidated through precision mass measurements of $^{23}$Si, $^{26}$P, $^{27,28}$S, and $^{31}$Ar

Using the B$ρ$-defined isochronous mass spectrometry technique, we report the first determination of the $^{23}$Si, $^{26}$P, $^{27}$S, and $^{31}$Ar masses and improve the precision of the $^{28}$S mass by a factor of 11. Our measurements confirm that these isotopes are bound and fix the location of the proton dripline in P, S, and Ar. We find that the mirror energy differences of the mirror-nuclei pairs $^{26}$P-$^{26}$Na, $^{27}$P-$^{27}$Mg, $^{27}$S-$^{27}$Na, $^{28}$S-$^{28}$Mg, and $^{31}$Ar-$^{31}$Al deviate significantly from the values predicted assuming mirror symmetry. In addition, we observe similar anomalies in the excited states, but not in the ground states, of the mirror-nuclei pairs $^{22}$Al-$^{22}$F and $^{23}$Al-$^{23}$Ne. Using $ab~ initio$ VS-IMSRG and mean field calculations, we show that such a mirror-symmetry breaking phenomeon can be explained by the extended charge distributions of weakly-bound, proton-rich nuclei. When observed, this phenomenon serves as a unique signature that can be valuable for identifying proton-halo candidates.

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arXiv2024

Electric dipole polarizability of $^{58}$Ni

The electric dipole strength distribution in $^{58}$Ni between 6 and 20 MeV has been determined from proton inelastic scattering experiments at very forward angles at RCNP, Osaka. The experimental data are rather well reproduced by quasiparticle random-phase approximation calculations including vibration coupling, despite a mild dependence on the adopted Skyrme interaction. They allow an estimate of the experimentally inaccessible high-energy contribution above 20 MeV, leading to an electric dipole polarizability $α_\mathrm{D}(^{58}{\rm Ni}) = 3.48(31)$ fm$^3$. This serves as a test case for recent extensions of coupled-cluster calculations with chiral effective field theory interactions to nuclei with two nucleons on top of a closed-shell system.

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arXiv2024

The axially-deformed relativistic quasiparticle random phase approximation based on point-coupling interactions

Collective nuclear excitations, like giant resonances, are sensitive to nuclear deformation, as evidenced by alterations in their excitation energies and transition strength distributions. A common theoretical framework to study these collective modes, the random-phase approximation (RPA), has to deal with large dimensions spanned by all possible particle-hole configurations satisfying certain symmetries. This work aims to establish a new theoretical framework to study the impact of deformation on spin-isospin excitations, that can provide fast and reliable solutions of the RPA equations. The nuclear ground state is determined with the axially-deformed relativistic Hartree-Bogoliubov (RHB) model based on relativistic point-coupling energy density functionals (EDFs). To study the excitations in the charge-exchange channel, an axially-deformed proton-neutron relativistic quasiparticle RPA (pnRQRPA) is developed in the linear response approach. After benchmarking the axially-deformed pnRQRPA in the spherical limit, a study of spin-isospin excitations including Fermi, Gamow-Teller (GT), and Spin-Dipole (SD) is performed for selected $pf$-shell nuclei. For GT transitions, it is demonstrated that deformation leads to considerable fragmentation of the strength function. A mechanism inducing the fragmentation is studied by decomposing the total strength to different projections of total angular momentum $K$ and constraining the nuclear shape to either spherical, prolate or oblate. A similar fragmentation is also observed for SD transitions, although somewhat moderated by the complex structure of these transitions, while the Fermi strength is almost shape-independent. The axially-deformed pnRQRPA introduced in this work opens perspectives for future studies of deformation effects on astrophysically relevant weak interaction processes, in particular beta decay and electron capture.

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arXiv2024

Neutron radius determination of 133Cs and its impact on the interpretation of CEvNS-CsI measurement

Proton-$^{133}$Cs elastic scattering at low momentum transfer is performed using an in-ring reaction technique at the Cooler Storage Ring at the Heavy Ion Research Facility in Lanzhou. Recoil protons from the elastic collisions between the internal H$_2$-gas target and the circulating $^{133}$Cs ions at 199.4 MeV/u are detected by a silicon-strip detector. The matter radius of $^{133}$Cs is deduced by describing the measured differential cross sections using the Glauber model. Employing the adopted proton distribution radius, a point-neutron radius of 4.86(21) fm for $^{133}$Cs is obtained. With the newly determined neutron radius, the weak mixing angle sin$^2 θ_W$ is independently extracted to be 0.227(28) by fitting the coherent elastic neutrino-nucleus scattering data. Our work limits the sin$^2 θ_W$ value in a range smaller than the ones proposed by the previous independent approaches, and would play an important role in searching new physics via the high precision CE$ν$NS-CsI cross section data in the near future.

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arXiv2022

Towards a Unified Description of Isoscalar Giant Monopole Resonances in a Self-Consistent Quasiparticle-Vibration Coupling Approach

"Why is the EoS for tin so soft?" is a longstanding question, which prevents us from determining the nuclear incompressibility $K_\infty$ accurately. To solve this puzzle, a fully self-consistent quasiparticle random phase approximation (QRPA) plus quasiparticle-vibration coupling (QPVC) approach based on Skyrme-Hartree-Fock-Bogoliubov is developed. We show that the many-body correlations introduced by QPVC, which shift the ISGMR energy in Sn isotopes by about 0.4 MeV more than the energy in $^{208}$Pb, play a crucial role in providing a unified description of the ISGMR in Sn and Pb isotopes. The best description of the experimental strength functions is given by SV-K226 and KDE0, which are characterized by incompressibility values $K_\infty=$ 226 MeV and 229 MeV, respectively, at mean field level.

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arXiv2022

Beyond-mean-field approaches for nuclear neutrinoless double beta decay in the standard mechanism

Nuclear weak decays provide important probes to fundamental symmetries in nature. A precise description of these processes in atomic nuclei requires comprehensive knowledge on both the strong and weak interactions in the nuclear medium and on the dynamics of quantum many-body systems. In particular, an observation of the hypothetical double beta decay without emission of neutrinos ($0νββ$) would unambiguously demonstrate the Majorana nature of neutrinos and the existence of the lepton-number-violation process. It would also provide unique information on the ordering and absolute scale of neutrino masses. The next-generation tonne-scale experiments with sensitivity up to $10^{28}$ years after a few years of running will probably provide a definite answer to these fundamental questions based on our current knowledge on the nuclear matrix element (NME), the precise determination of which is a challenge to nuclear theory. Beyond-mean-field approaches have been frequently adapted for the study of nuclear structure and decay throughout the nuclear chart for several decades. In this review, we summarize the status of beyond-mean-field calculations of the NMEs of $0νββ$ decay assuming the standard mechanism of an exchange of light Majorana neutrinos. The challenges and prospects in the extension and application of beyond-mean-field approaches for $0νββ$ decay are discussed.

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arXiv2022

Single-state or low-lying-states dominance mechanism of $2νββ$-decay nuclear matrix elements

The $2νββ$-decay nuclear matrix elements (NMEs) for 11 nuclei are studied with the self-consistent quasiparticle random phase approximation (QRPA) based on Skyrme Hartree-Fock-Bogoliubov (Skyrme HFB) model. As a common feature pointed out in https://journals.aps.org/prc/abstract/10.1103/PhysRevC.98.064325 Phys. Rev. C 98, 064325 (2018), negative contributions in the running sums of NMEs are found, and play important roles in the fulfillment of the single-state dominance or low-lying-states dominance hypothesis. By comparing the results of QRPA model and quasiparticle Tamm-Dancoff approximation (QTDA) model, we find that the negative contributions are due to the enhanced ground-state correlations, which are brought by the backward amplitude in QRPA model and tuned by strong isoscalar pairing interaction. The enhancement of ground-state correlations will change the signs of GT$^{+}$ transition amplitudes of higher-lying states and leads to the negative contributions in the running sum.

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arXiv2021

Evolution of $β$-decay half-lives at finite-temperatures

$β$-decay properties of nuclei are investigated within the relativistic nuclear energy density functional framework by varying the temperature and density, conditions relevant to the final stages of stellar evolution. Both thermal and nuclear pairing effects are taken into account in the description of nuclear properties and in the finite temperature proton-neutron relativistic quasiparticle random-phase approximation (FT-PNRQRPA) to calculate the relevant allowed and first-forbidden transitions in the $β$-decay. The temperature and density effects are studied on the $β$-decay half-lives between temperatures $T = 0-1.5$ MeV, and at densities $ρY_e = 10^7$ g/cm${}^3$ and $10^9$ g/cm${}^3$. The relevant Gamow-Teller transitions are also investigated for Ti, Fe, Cd, and Sn isotopic chains at finite temperatures. We find that the $β$-decay half-lives increase with increasing density $ρY_e$, whereas half-lives generally decrease with increasing temperature. It is shown that the temperature effects decrease the half-lives considerably in nuclei with longer half-lives at zero temperature, while only slight changes for nuclei with short half-lives are obtained. We also show the importance of including the de-excitation transitions in the calculation of the $β$-decay half-lives at finite temperatures. Comparing the FT-PNQRPA results with the shell-model calculations for $pf-$shell nuclei, a reasonable agreement is obtained for the temperature dependence of $β$-decay rates. Finally, large-scale calculations of $β$-decay half-lives are performed at temperatures $T_9(\text{K}) = 5$ and $T_9(\text{K}) = 10$ and densities $ρY_e = 10^7$ g/cm${}^3$ and $10^9$ g/cm${}^3$ for even-even nuclei in the range $8 \leq Z \leq 82$, relevant for astrophysical nucleosynthesis mechanisms.

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arXiv2021

Finite-temperature linear response theory based on relativistic Hartree Bogoliubov model with point-coupling interaction

The finite-temperature linear response theory based on the finite-temperature relativistic Hartree-Bogoliubov (FT-RHB) model is developed in the charge-exchange channel to study the temperature evolution of spin-isospin excitations. Calculations are performed self-consistently with relativistic point-coupling interactions DD-PC1 and DD-PCX. In the charge-exchange channel, the pairing interaction can be split into isovector ($T = 1$) and isoscalar ($T = 0$) parts. For the isovector component, the same separable form of the Gogny D1S pairing interaction is used both for the ground-state calculation as well as for the residual interaction, while the strength of the isoscalar pairing in the residual interaction is determined by comparison with experimental data on Gamow-Teller resonance (GTR) and Isobaric analog resonance (IAR) centroid energy differences in even-even tin isotopes. The temperature effects are introduced by treating Bogoliubov quasiparticles within a grand-canonical ensemble. Thus, unlike the conventional formulation of the quasiparticle random-phase approximation (QRPA) based on the Bardeen-Cooper-Schrieffer (BCS) basis, our model is formulated within the Hartree-Fock-Bogoliubov (HFB) quasiparticle basis. Implementing a relativistic point-coupling interaction and a separable pairing force allows for the reduction of complicated two-body residual interaction matrix elements, which considerably decreases the dimension of the problem in the coordinate space. The main advantage of this method is to avoid the diagonalization of a large QRPA matrix, especially at finite temperature where the size of configuration space is significantly increased. The implementation of the linear response code is used to study the temperature evolution of IAR, GTR, and spin-dipole resonance (SDR) in even-even tin isotopes in the temperature range $T = 0 - 1.5$ MeV.

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