In ab initio nuclear structure theory, accurately predicting electromagnetic observables, such as moments and transition rates, is essential for a comprehensive understanding of nuclear properties. However, computational limitations and conceptual difficulties often hinder the precise calculation of these observables. In this work, we extend machine learning methods for model-space extrapolations to electric quadrupole moments. We further present a new machine learning approach that leverages the correlations between energies, radii, and electromagnetic observables. By learning these correlations from no-core shell model calculations in accessible model spaces, this new model enables the prediction of electromagnetic observables in the full Hilbert space from predictions of full-space energies and radii, which can be obtained with established machine learning extrapolation tools. An essential property of our approach is the capability of uncertainty quantification, allowing for reliable predictions with combined statistical error estimates for many-body and interaction uncertainties. Being solely built upon the physical correlations of different observables, it can be generalized across different ab initio methods. We demonstrate the power of this new extrapolation scheme through a precision study of electric quadrupole moments across a wide range of $p$-shell nuclei.

The onset of collective nuclear behavior in the $N=60$, $A\approx 100$ region is examined through high-precision mass measurements of ${}^{96-98}\mathrm{Kr}$, performed with the ISOLTRAP mass spectrometer at ISOLDE, CERN. Our results for ${}^{96-97}\mathrm{Kr}$ agree with previous measurements, with our new ${}^{97}\mathrm{Kr}$ Penning-trap mass value being three times more precise. The mass value of ${}^{98}\mathrm{Kr}$ is measured for the first time. The new mass surface, together with comparisons to beyond-mean-field theoretical predictions, suggests that collectivity persists for the $Z=36$ isotopes, blurring the apparent “low-$Z$ boundary” of this deformed region.

We report on empirical parameterizations of longitudinal (${\mathcal{R}}_L$) and transverse (${\mathcal{R}}_T$) nuclear electromagnetic form factors for elastic scattering and the excitations of nuclear states in ${}^{27}\mathrm{Al}$ and ${}^{40}\mathrm{Ca}$. The parameterizations are needed for the calculations of radiative corrections in measurements of electron scattering cross sections on ${}^{27}\mathrm{Al}$ and ${}^{40}\mathrm{Ca}$ in the quasielastic, resonance, and inelastic continuum regions, provide the contribution of nuclear excitations in investigations of the Coulomb sum rule, and test theoretical model predictions for excitation of nuclear states in electron and neutrino interactions on nuclear targets at low energies.

Background: The $0_2^{+}$ state of ${}^8\mathrm{He}$ has been discovered by a recent experiment, which suggested a developed cluster structure of spatially correlated neutron pairs, called “dineutrons” (${}^{2}n$).

Purpose: We aim to investigate the structure of ${}^8\mathrm{He}\left(0_1^{+}\right)$ and ${}^8\mathrm{He}\left(0_2^{+}\right)$ to clarify the monopole excitation mode in ${}^8\mathrm{He}$ system while focusing on the $\alpha +{}^{2}n+{}^{2}n$ cluster structures and the breaking of ${}^{2}n$ clusters.

Methods: We apply a microscopic cluster model with the generator coordinate method for the $\alpha +{}^{2}n+{}^{2}n$ cluster and ${}^6\mathrm{He}+{}^{2}n$ cluster dynamics. The $p_{3/2}$-closure component, which is induced by the spin-orbit force, is also incorporated.

Results: The present calculation reasonably reproduces the experimental data of the properties of ${}^8\mathrm{He}$, such as $2n$ and $4n$ separation energies, energy spectra, and radii. The spatially developed cluster structure of the $0_2^{+}$ state is obtained. The $0_1^{+}$ and $0_2^{+}$ states have dominant components of $\alpha +{}^{2}n+{}^{2}n$ 3-body cluster, but contain significant ${}^{2}n$ breaking components which contribute to the energy gain and size shrinking of the ${}^8\mathrm{He}$ system. The monopole excitation in ${}^8\mathrm{He}$ is regarded as a radial excitation, which is similar to that in ${}^{12}\mathrm{C}$.

Conclusions: The $\alpha +{}^{2}n+{}^{2}n$ cluster structures play a dominant role in ${}^8\mathrm{He}\left(0_{1,2}^{+}\right)$, and the mixing of the dineutron breaking contributes to significant structural effects.

We present the first forward-rapidity measurements of elliptic anisotropy of open-heavy-flavor muons at the Relativistic Heavy Ion Collider. The measurements are based on data samples of $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{{}_{NN}}}=200\mathrm{GeV}$ collected by the PHENIX experiment in 2014 and 2016 with integrated luminosity of $14.5{\mathrm{nb}}^{-1}$. The measurements are performed in the pseudorapidity range $1.2<\left|\eta \right|<2$ and cover transverse momenta $1<p_T<4\mathrm{GeV}/c$. The elliptic flow of charged hadrons as a function of transverse momentum is also measured in the same kinematic range. We observe significant elliptic flow for both charged hadrons and heavy-flavor muons. The results show clear mass ordering of elliptic flow of light- and heavy-flavor particles. The magnitude of the measured $v_2$ is comparable to that in the midrapidity region. This indicates that there is no strong longitudinal dependence in the quark-gluon-plasma evolution between midrapidity and the rapidity range of this measurement at $\sqrt{s_{{}_{NN}}}=200\mathrm{GeV}$.

Charge sum rules for quark fragmentation functions are studied. The simultaneous implementation of the conservation of electric and baryon charges, strangeness, and isospin symmetry is achieved when the fragmentation to both mesons and baryons is considered. The results are compatible to Gell-Mann–Nishijima formulas and may be the new manifestation of superconformal symmetry between mesons and baryons. The numerical estimates are performed and compared with phenomenological models. The recently suggested violations of sum rules due to Wilson line contributions are discussed.

Accurate modeling of the neutron star crust is essential for interpreting multimessenger observations and constraining the nuclear equation of state (EOS). However, standard phenomenological EOS models often rely on heuristic extrapolations in the low-density regime, which are inconsistent with microscopic predictions. In this work, we refine a unified metamodeling framework for the EOS by incorporating low-density corrections based on energy density functionals constrained by ab initio neutron-matter calculations. Using Bayesian inference to combine information from astrophysical observations, nuclear theory, and experiments, we assess the impact of these corrections on key crustal properties, including the crust-core transition density and pressure, crustal composition, and moment of inertia. The improved model reduces uncertainties in the inner crust and emphasizes the importance of low-density physics in EOS modeling, highlighting the value of integrating both theoretical and observational constraints across densities to robustly describe the EOS. Moreover, the adopted approach can be readily applied to any existing EOS model to provide a solid framework for interpreting upcoming high-precision multimessenger data.

The multinucleon transfer process is regarded as a promising pathway for producing the stable superheavy elements. However, the underlying mechanism, especially the possible transfer channels for sailing to the “island of stability” are poorly known. In this work, the time-dependent Hartree-Fock theory is used to investigate the collision dynamics of ${}^{136}\mathrm{Xe}, {}^{198}\mathrm{Pt}, {}^{238}\mathrm{U}+{}^{238}\mathrm{U}$ reactions. A novel reaction channel of the concentrated valence nucleons (CVN) transferring is found in the collisions heading on the tips of ${}^{238}\mathrm{U}$. These nucleons are transferred with relatively short relaxation time and break the symmetry of nucleon exchange in the early reaction stage. In consequence, the mass equilibrium with relaxation time is deviated from the systematic behavior based on the macroscopic-microscopic potential energy surface. The CVN transfer channel shows promising prospect for producing neutron-rich superheavy nuclei. In this case, we also investigated the angular distributions of products from the CVN transfer channel in the reaction ${}^{238}\mathrm{U}+{}^{238}\mathrm{U}$ with tip-side configuration, and the optimal detection angles are predicted.

Calculations for electron capture rates on nuclei with atomic numbers between $Z=20$ and $Z=52$ are performed in a self-consistent finite-temperature covariant energy density functional theory within the relativistic quasiparticle random-phase approximation. Electron captures on these nuclei contribute most to reducing the electron fraction during the collapse phase of core-collapse supernovae. The rates include contributions from allowed (Gamow-Teller) and first-forbidden (FF) transitions, and it is shown that the latter become dominant at high stellar densities and temperatures. Temperature-dependent effects such as Pauli unblocking and transitions from thermally excited states are also included. The new rates are implemented in a spherically symmetric one-dimensional simulation of the core-collapse phase. The results indicate that the increase in electron capture rates, due to inclusion of FF transitions, leads to reductions of the electron fraction at nuclear saturation density, the peak neutrino luminosity, and enclosed mass at core bounce. The new rates reaffirm that the most relevant nuclei for the deleptonization situate around the $N=50$ and 82 shell closures, but, compared to previous simulations, nuclei are less proton rich. The new rates developed in this work are available, and will be of benefit to improve the accuracy of multidimensional supernova simulations.

The changes in the mean-squared charge radii relative to ${}^{209}\mathrm{Bi}_{126}$ ($\delta {\langle r^2\rangle }^{N,126}$) and the magnetic dipole and electric quadrupole moments in ${}^{214-218}\mathrm{Bi}$ have been measured using the in-source resonance-ionization spectroscopy technique at ISOLDE (CERN). Magnetic moments of odd-odd bismuth nuclei have been analyzed by the additivity relation. Previous tentative spin-parity and configuration assignments based on the $\beta$-decay feeding patterns have been supported. A normal odd-even staggering in charge radii of bismuth isotopes with $N>126$ has been observed. The new data for the $\delta \langle r^2\rangle$ of bismuth isotopes allow a study of the isotonic dependencies in the charge radii, revealing jumps in $\delta {\langle r^2\rangle }^{132,126}$ and $\delta {\langle r^2\rangle }^{134,126}$ at $Z=84$. This pattern could be explained by a sudden onset of octupole deformation at $N=132$ and 134 when going from polonium ($Z=84$) to astatine ($Z=85$).

We have investigated the role of isospin asymmetry of the NN effective interaction in the context of NA elastic scattering. To this purpose we represent the in-medium $g$ matrix as an admixture of isospin-symmetric nuclear matter and pure neutron matter solutions of Brueckner-Hartree-Fock equations for infinite nuclear matter, denoted as $g[\rho ,\beta ]$. We use the Argonne $v_{18}$ bare potential to represent the NN interaction in free space, due to its ability to describe the NN scattering amplitudes up to 350 MeV. The density-dependent isospin-asymmetric $g$ matrices are then used to calculate optical model potentials for elastic nucleon scattering off closed-shell nuclei. For this aim, we make use of the Arellano-Bauge $\delta g$-folding approach suited for an explicit treatment of nonlocal density matrices. This approach allows one to account for the local isospin-asymmetry and density dependence of the in-medium NN interaction. The resulting optical potentials are nonlocal since the entire nonlocal structure of the $g$ matrix is retained. We observe that including the isospin asymmetry in the $g$ matrix allows for a reasonable description of differential cross sections at nucleon beam energies between 40 and 200 MeV. In the case of proton scattering at energies below $\approx 65$ MeV, at momentum transfers $q$ below $\approx 1{\mathrm{fm}}^{-1}$, the inclusion of neutronic-matter $g$ matrices yields better agreement with the data as compared to the case when symmetric nuclear matter $g$ matrices are used. These results provide evidence that the isospin-asymmetry in the NN effective interaction yield non-negligible effects in nucleon scattering off isospin-asymmetric targets at beam energies below 65 MeV.

The production cross sections of neutron-rich nuclei for elements just above ${}^{60}\mathrm{Ca}$ were measured at the Facility for Rare Isotope Beams (FRIB). Four previously unobserved isotopes (${}^{63}\mathrm{Sc}, {}^{65,66}\mathrm{Ti}$, and ${}^{68}\mathrm{V}$) were produced, separated, and identified for the first time using the Advanced Rare Isotope Separator (ARIS). One event was found to be consistent with ${}^{61}\mathrm{Ca}$. The new isotopes were created through the interaction of an ${}^{82}\mathrm{Se}$ beam with a carbon target at an energy of $228\mathrm{MeV}/u$ and a primary beam current of $1.07\mathrm{p}\mu \mathrm{A}$. The event-by-event particle identification of the mass number ($A$), atomic number ($Z$), and ionic charge state ($q$) for the reaction products was achieved by combining measurements of energy loss, time of flight, magnetic rigidity, and total kinetic energy. This successful search for new isotopes, conducted at the beginning of FRIB's third year of operation, highlights the facility's discovery potential, which will continue to grow as the beam current increases. The production cross sections were analyzed in the context of the newly developed $\mathrm{\Delta }BE$ systematics that provides trends in neutron-rich regions and increased sensitivity to nuclear binding, an important nuclear structure observable. The new systematics addresses gaps in $Q_g$-based methods commonly used to interpret the production cross sections of light neutron-rich elements, and provides an efficient empirical approach to describe cross-section trends across isotopic chains. Good agreement with the measured data was obtained when the $\mathrm{\Delta }BE$ systematics and abrasion-ablation calculations were performed using the Hartree-Fock-Bogoliubov (HFB-22) mass table.

We present the first threefold differential measurement for neutral-pion multiplicity ratios produced in semi-inclusive deep-inelastic electron scattering on carbon, iron, and lead nuclei normalized to deuterium from CLAS at Jefferson Lab. We found that the neutral-pion multiplicity ratio is maximally suppressed for the leading hadrons (energy fraction $z\to$ 1), suppression varying from 25% in carbon up to 75% in lead. An enhancement of the multiplicity ratio at low $z$ and high $p_T^2$ is observed, suggesting an interconnection between these two variables. This behavior is qualitatively similar to the previous twofold differential measurement of charged pions by the HERMES Collaboration and, recently, by CLAS Collaboration. The largest enhancement was observed at high $p_T^2$ for heavier nuclei, namely, iron and lead, while the smallest enhancement was observed for the lightest nucleus, carbon. This behavior suggests a competition between partonic multiple scattering, which causes enhancement, and hadronic inelastic scattering, which causes suppression.

In the first part of the article we present the identification of ${\mathrm{C}}_{2\mathrm{v}}$ (water molecule) symmetry in ${}^{236}\mathrm{U}$ nucleus employing existing experimental information using a model-independent approach. This represents for the first time experimental evidence of the molecular symmetry in very heavy nuclei and promotes further exploration of molecular symmetries in subatomic physics. The second part describes the realistic phenomenological mean-field theory approach as the background of the large-scale mesh calculations in multidimensional deformation spaces aiming at the theory indications for the nuclear ${\mathrm{C}}_{2\mathrm{v}}$ symmetry. We discuss and illustrate the strong and the weak points of the algorithms, the uncertainties of the theory predictions as well as the issue of the most probable (dynamical equilibrium) deformations obtained by employing the Bohr collective model and deformation-dependent collective inertia tensor.

The cross sections (${\sigma }_{\mathrm{th}}$) of one-proton removal from ${}^{10-13,15}\mathrm{B}$ and ${}^{12-16,18}\mathrm{C}$ near $400\text{MeV/nucleon}$ are calculated using Glauber model with shell-model spectroscopic factors as structural inputs, and compared with the corresponding experimental measurements ${\sigma }_{\exp }$. The reduction factors of the spectroscopic strengths $R_{\mathrm{s}}={\sigma }_{\exp }/{\sigma }_{\mathrm{th}}$ plotted against the nucleon separation energy difference $\mathrm{\Delta }S=S_p-S_n$ of the projectile largely conform to the former $R_{\mathrm{s}}\text{−}\mathrm{\Delta }S$ systematics established upon one-nucleon removal data mainly over beam energies of $100–240\text{MeV/nucleon}$, yet with signs of a dampened $R_{\mathrm{s}}\text{−}\mathrm{\Delta }S$ dependence for boron isotopes and an odd-even staggering of $R_{\mathrm{s}}$ with projectile mass number $A$ for carbon isotopes. With the linear representation of the $R_{\mathrm{s}}\text{−}\mathrm{\Delta }S$ systematics $R_{\mathrm{s}}\left(\mathrm{\Delta }S\right)=0.61–0.016\mathrm{\Delta }S\pm 0.1$ given by Tostevin and Gade, we have also tried applying $R_{\mathrm{s}}\left(\mathrm{\Delta }S\right)$ to a phenomenological correction of ${\sigma }_{\mathrm{th}}$. The $R_{\mathrm{s}}\left(\mathrm{\Delta }S\right)$-corrected cross sections ${\sigma }_{\mathrm{th}}^{\mathrm{cor}}=R_{\mathrm{s}}\left(\mathrm{\Delta }S\right)·{\sigma }_{\mathrm{th}}$ demonstrate a much higher overall predictive power than the empirical parametrizations EPAX 2, EPAX 3, and FRACS.

To solve the Cd puzzle (spherical nucleus puzzle), I have proposed a new spherical-like $\gamma$-soft nucleus. Since shape coexistence often occurs in such nuclei, explicit spherical-like $\gamma$-soft spectra are not easily identified. In this paper, I finally find the direct evidence for the existence of the new spherical-like $\gamma$-soft nucleus. ${}^{106}\mathrm{Pd}$ is in fact a typical spherical-like $\gamma$-soft nucleus. The low-lying parts, up to the ${10}_1^{+}$ state, under 4000 keV, of the spherical-like $\gamma$-soft spectra are verified. The $B$(2) values and the quadrupole moments of the low-lying levels are also studied. By comparison, the new spherical-like $\gamma$-soft mode is confirmed. Moreover ${}^{104,108}\mathrm{Pd}$ are also discussed. These results completely disprove the possibility of the phonon excitations of the spherical nucleus in the Cd-Pd nuclei region.

Although pseudospin partner (PSP) bands have been experimentally reported in about 20 nuclei, their structures and properties have not yet been systematically discussed. In the present work, the typical characteristics of PSP bands with the configuration $(g_{7/2},d_{5/2})$ have been studied systematically based on the particle rotor model in comparison with the well-known signature partner bands. It is found that the energies $E\left(I\right)$ of the $\pi g_{7/2}$ bands and $E(I-1)$ of the $\pi d_{5/2}$ bands are nearly degenerate, which could be a fingerprint of the PSP bands. The interband $M1$ and $E2$ transitions are in general hindered between PSP bands but allowed between the signature partner bands. The $B\left(M1\right)$ values of the $\pi g_{7/2}$ bands are much smaller than those of $\pi d_{5/2}$ bands. The model's wave functions are analyzed quantitatively to understand the band structure. The typical characteristics of PSP bands predicted by the model are also consistent with the available data in ${}^{125}\mathrm{Cs}$ and ${}^{175}\mathrm{Re}$.

The effects of nuclear surface dynamics on both fusion and multinucleon transfer reactions are investigated simultaneously within the framework of the improved quantum molecular dynamics model. The capture processes of ${}^{40}\mathrm{Ca}+{}^{40}\mathrm{Ca}$ and ${}^{40}\mathrm{Ar}+{}^{208}\mathrm{Pb}$ systems are simulated using different surface energy coefficients. It is found that a larger surface energy coefficient reduces the Coulomb barrier height, thereby enhancing the capture cross section. For the multinucleon transfer reactions of ${}^{58}\mathrm{Ni}+{}^{208}\mathrm{Pb}$ and ${}^{64}\mathrm{Ni}+{}^{208}\mathrm{Pb}$, we find that a strong surface energy significantly inhibits isospin diffusion processes between the collision partners and reduces the probability of fusion-fission events. Furthermore, an enhanced surface energy extends the lifetime of the dinuclear system, resulting in larger deflection angles for projectile-like fragments in deep-inelastic collisions.

We present a model for the distribution of the number of forward neutrons emitted in soft (minimum bias) and hard inelastic proton-nucleus ($pA$) scattering at the CERN Large Hadron Collider. It is based on the Gribov-Glauber model for the distribution over the number of inelastic collisions (wounded nucleons) combined with a parametrization of cross section (color) fluctuations in the projectile proton, which depend on the parton momentum fraction $x_p$, and the assumption of independent neutron emissions. We observe that, while the effect of soft color fluctuations is modest, a reduction of the interaction strength with increasing $x_p$ provides the dominant effect. It allows us to qualitatively describe the trend of the ATLAS data on the zero degree calorimeter (ZDC) energy spectra of forward neutrons emitted in dijet production in inelastic $pA$ scattering at $\sqrt{s_{NN}}=8.16$ TeV.

The photoproduction of ${\pi }^{+}{\pi }^{-}$ meson pairs off the proton has been studied in the reaction $\gamma p\to p{\pi }^{+}{\pi }^{-}$ using the CEBAF Large Acceptance Spectrometer (CLAS) and the frozen-spin target (FROST) in Hall B at the Thomas Jefferson National Accelerator Facility. For the first time, the beam and target asymmetries, $I^{s,c}$ and $P_{x,y}$, have been measured along with the beam-target double-polarization observables, $P_{x,y}^{s,c}$, using a transversely polarized target with center-of-mass energies ranging from 1.51 GeV up to 2.04 GeV. These data and additional $\pi \pi$ photoproduction observables from CLAS and experiments elsewhere were included in a partial-wave analysis within the Bonn-Gatchina framework. Significant contributions from $s$-channel resonance production are observed in addition to $t$-channel exchange processes. The data indicate significant contributions from $N^{*}$ and ${\mathrm{\Delta }}^{*}$ resonances in the third and fourth resonance regions.