Recently, the $n{}^3\mathrm{He}$ Collaboration reported a measurement of the parity-violating (PV) proton directional asymmetry $A_{\mathrm{PV}}=[1.55\pm 0.97\left(\mathrm{stat}\right)\pm 0.24\left(\mathrm{sys}\right)]\times {10}^{-8}$ in the capture reaction of ${}^3\mathrm{He}(\vec{n},p){}^3\mathrm{H}$ at meV incident neutron energies. The result increased the limited inventory of precisely measured and calculable PV observables in few-body systems required to further understand the structure of hadronic weak interaction. In this Letter, we report the experimental and theoretical investigation of a parity conserving (PC) asymmetry $A_{\mathrm{PC}}$ in the same reaction (the first ever measured PC observable at meV neutron energies). As a result of S- and P-wave mixing in the reaction, the $A_{\mathrm{PC}}$ is inversely proportional to the neutron wavelength $\lambda$. The experimental value is $(\lambda \times A_{\mathrm{PC}})\equiv \beta =[-1.97\pm 0.28\left(\mathrm{stat}\right)\pm 0.12\left(\mathrm{sys}\right)]\times {10}^{-6}\AA$. We present results for a theoretical analysis of this reaction by solving the four-body scattering problem within the hyperspherical harmonic method. We find that in the ${}^3\mathrm{He}(\vec{n},p){}^3\mathrm{H}$ reaction, $A_{\mathrm{PC}}$ depends critically on the energy and width of the close $0^{-}$ resonant state of ${}^4\mathrm{He}$, resulting in a large sensitivity to the spin-orbit components of the nucleon-nucleon force and even to the three-nucleon force. The analysis of the accurately measured $A_{\mathrm{PC}}$ and $A_{\mathrm{PV}}$ using the same few-body theoretical models gives essential information needed to interpret the PV asymmetry in the ${}^3\mathrm{He}(\vec{n},p){}^3\mathrm{H}$ reaction.

The entanglement and coherence of the wobbling mode are studied in the framework of the particle plus triaxial-rotor model for the one-quasiparticle nucleus ${}^{135}\mathrm{Pr}$ and the two-quasiparticles nucleus ${}^{130}\mathrm{Ba}$. The focus lies on the coupling between the total and the particle angular momenta. Using the Schmidt decomposing, it is quantified in terms of the von Neumann entropy of the respective subsystems, which measures their mutual entanglement. The entropy and the entanglement increase with spin $I$ and number of wobbling quanta $n$. The coherence of the wobbling mode is studied by means of the eigenstate decomposition of its reduced density matrix. To a good approximation, the probability distributions of the total angular momentum can be interpreted as the incoherent combination of the coherent contributions from the first two pairs of eigenvectors with the largest weight of the reduced density matrix. Decoherence measures are defined, which, in accordance, scatter between 0.1 to 0.2 at low spin and between 0.1 and 0.3 at high spin. Entanglement in the framework of the adiabatic approximation is further analyzed. In general, the coherent eigenstates of the effective collective Hamiltonian approximate the reduced density matrix with the limited accuracy of its pair of eigenstates with the largest weight. As the adiabatic approximation becomes more accurate with decreasing excitation energy, the probability distribution of the angle of the total angular momentum around a principal axis approaches the one of the full reduced density matrix. The $E2$ transition probabilities and spectroscopic quadrupole moments reflect this trend.

The shell model Monte Carlo method is a powerful method for calculating exactly (up to statistical errors) thermal observables and statistical properties of atomic nuclei. However, its application has been limited by a sign problem at low temperatures that arises from the projection onto odd number of particles even for good-sign interactions. Here, we develop a technique—the partition function extrapolation method (PFEM)—to extract the ground-state energy of an odd-mass nucleus from the excitation partition function calculated at temperatures at which this sign problem is moderate. We validate the PFEM in heavy even-mass nuclei and systematically calculate ground-state energies for isotopic chains of heavy odd-mass nuclei. The PFEM can be extended to other finite-size quantum many-body systems.

A comprehensive level scheme of ${}^{114}\mathrm{Te}$, including 35 newly observed $\gamma$ transitions, has been established by using in-beam $\gamma$-ray spectroscopy techniques. The excited states were populated by using the ${}^{112}\mathrm{Sn}({}^4\mathrm{He},2\mathrm{n}\gamma ){}^{114}\mathrm{Te}$ fusion-evaporation reaction at a beam energy of 37 MeV. The deexciting $\gamma$ rays were detected with the help of the Indian National Gamma Array. Furthermore, the presence of octupole correlation is verified in this nucleus through the presence of several enhanced E1 transitions. To understand the microscopic structure of the excited levels, the kshell code within the framework of the shell model and the covariant density functional theory were used.

The spontaneous fission analysis of even mass (${}^{230}\mathrm{U}$ to ${}^{264}\mathrm{Hs}$) nuclei is carried out using the quantum mechanical fragmentation theory (QMFT) based preformed cluster model (PCM). The effect of deformations and orientations is investigated in view of the spontaneous fission of the considered nuclei. The PCM treats the spontaneous emission in terms of the barrier tunneling process where the fragments are preformed with a relative probability within the QMFT framework. The addition of deformation effects, i.e., ${\beta }_2$ (elongated)-deformed and ${\beta }_2$ (compact)-deformed, considerably modify the fragmentation potential, penetration path, and related barrier characteristics, resulting in significant change in the mass and charge of emitting fragments. The half-life time calculated using compact ${\beta }_2$ deformed fragments find better comparison with experimental data. For this configuration, the transition from asymmetric fission to nearly symmetric fission takes place with an increase in the mass/charge number of the considered nuclei. The effect of deformations on the decay of $A=230–264$ parent nuclei is also analyzed in terms of barrier characteristics such as barrier height, barrier position, and fissility parameter, and the most probable fragments operating in spontaneous fission process are identified. In addition to this, the substructure of fission fragments and the isobaric behavior is analyzed within the collective clusterization approach.

The identity method is a statistical technique developed to reconstruct moments of multiplicity distributions of particles produced in high-energy nuclear collisions. The method leverages principles from fuzzy logic, allowing for a more nuanced representation of particle identification by assigning degrees of membership to different particle types based on detector signals. In this contribution, a new framework, based on a multivariate moment generating function, is developed that allows the derivation of the formulas used in the identity method in a more robust way. Moreover, within the introduced framework, the identity method is easily extended to cope with arbitrarily higher-order moments. The techniques developed here offer significant potential for improving the accuracy of multiplicity distribution analyses in high-energy nuclear collisions. While the primary focus of the work presented is on applications in high-energy particle and nuclear physics, it can also be applied in other areas where signal identification is probabilistic and data are noisy, such as in medical imaging, remote sensing, and various other fields of experimental science.

We discuss the modeling of the hadronic phase of QCD at finite magnetic field in the framework of hadron resonance gas (HRG). We focus on the statistical description of particle yields that include contribution from resonance decays. We demonstrate that the swift increase in the number of protons with magnetic field predicted in the HRG is due to the assumption of structureless resonances. We discuss fluctuations of conserved charges and show that at present the qualitative comparison of the model predictions with the lattice QCD data should be treated with care. We also discuss the principle of detailed balance which allows us to study the magnetic field dependence of neutral resonances.

The ADAPT-VQE (adaptive derivative-assembled pseudo-Trotter Ansatz variational quantum eigensolver) approach is used to solve the neutron-proton pairing problem in atomic nuclei. This variational approach is considered today to be one of the most powerful methods to iteratively find the ground state of a many-body problem, provided a performing set of operators, called the pool of operators, is used to explore the Hilbert space of many-body wave-functions. Three different pools of operators, which might eventually break one or several symmetries of the Hamiltonian during the descent to the ground state, are tested for the neutron-proton pairing problem. We observe that the breaking of some symmetries during the optimization of the trial wave function might, in general, help to speed up the convergence towards the ground state. Still, we rejected the pool of operators that might explicitly break the total particle number because they become uncontrollable during the optimization process. Overall, we observed that the iterative optimization process rapidly becomes a delicate problem when the number of parameters to build the Ansatz increases, and the energy might get stuck at energies higher than the ground state energy. To improve the convergence in this case, several techniques have been proposed, with some better controlling the symmetries during the energy minimization. Among the proposed methods, two have proved effective: one based on an embedding technique and the other on a randomized preparation of the initial state. We conclude that the ADAPT-VQE, complemented by these techniques, can provide a very accurate description of the neutron-proton pairing problem, and can outperform other standardly used techniques that break the particle number symmetry and restore afterwards.

Background: Single-charge-exchange reactions are among the most appropriate nuclear tools to study the response of nuclear systems to isovector interaction. Nowadays, the availability of powerful experimental setups and advanced nuclear models bring the possibility of the complete study of the reaction mechanisms involved in the nuclear reactions, also in the case of heavy projectiles. This new possibility allows one to access valuable information on key nuclear structure aspects, including those embedded in the widely searched neutrinoless double-$\beta$ decay.

Purpose: We intend to elucidate the main nuclear structure and reaction features involved in the ${}^{18}\mathrm{O}$ $+$ ${}^{12}\mathrm{C}$ collision at 275 MeV beam incident energy. In this paper, the main focus is to quantify the competition between the sequential two-step transfer and the direct meson-exchange reaction mechanisms.

Methods: The energy spectra and cross-section angular distributions for the ${}^{12}\mathrm{C}({}^{18}\mathrm{O},{}^{18}\mathrm{F}){}^{12}\mathrm{B}$ single-charge-exchange reaction are measured by the MAGNEX magnetic spectrometer in the same experimental setup of the elastic and inelastic scattering and the one-nucleon transfer reaction channels. The cross sections for the sequential two-step transfer and the direct meson-exchange single-charge-exchange reaction mechanisms are evaluated in a single coherent theoretical calculation, using state-of-the-art nuclear structure and reaction theories.

Results: The energy resolution achieved in the study of the ${}^{12}\mathrm{C}({}^{18}\mathrm{O},{}^{18}\mathrm{F}){}^{12}\mathrm{B}$ single-charge-exchange reaction allows one to separate the ground-to-ground-state transition and to identify other structures in the measured energy spectra. The coherent sum of the distorted wave Born approximation cross sections of the direct and sequential reaction mechanisms well describes the experimental cross-section angular distributions. The crucial role of the optical model distortion in the scattering of the incoming and outgoing waves was taken into account via the introduction of the coupled-channel local equivalent effective potential.

Conclusions: Advanced nuclear structure and reaction models turned out to be appropriate tools for the detailed analysis of single-charge-exchange reactions originating in heavy-ion collisions. This is of particular relevance in several fields of nuclear physics. Moreover, it is inherent to the challenging project to provide valuable information on neutrinoless double-$\beta$ decay nuclear matrix elements from single- and double-charge-exchange cross-section measurements.

The equation of state describes the emergent physical properties of matter. Experimental data is needed to help constrain the equation of state for nuclear matter. These constraints can help distinguish between an “asy-stiff” and an “asy-soft” equation of state, which has astrophysical implications. One path to help constrain the models is to analyze the nuclear caloric curve; some experiments have shown dependence on neutron excess, and may thus be sensitive to the asymmetry. A difference in the caloric curve based on the asymmetry of the reconstructed quasiprojectile (QP) had been observed using ${}^{70}\mathrm{Zn}$ on ${}^{70}\mathrm{Zn}$ at 35 MeV/nucleon taken with the NIMROD array. Antisymmetrized molecular dynamics calculations were performed for the same system and deexcited with gemini$++$. Both Gogny (asy-soft) and Gogny-as (asy-stiff) data sets were generated. The particles were then filtered based on detector geometric acceptance and thresholds. From the accepted particles, the excitation energy and temperature were calculated in the same way as for experimental data. Additionally, filter effects on the observed nuclear caloric curves were investigated. A tendency for the asy-stiff nuclear caloric curves to have higher temperatures than their asy-soft counterparts was observed for a number of probes. In addition, some probes may show sensitivity to the reconstructed composition of the QP, but this is inconclusive due to high statistical fluctuations and a large dependence on the exact method of event selection.

Background: Nuclear fission is a large-amplitude collective motion of quantum many-body systems. A microscopic description of fission remains a challenge for nuclear theories. The tensor force, a key ingredient of the nucleon-nucleon interaction, has attracted great interest in nuclear physics. Its crucial effects have been revealed in many aspects of both nuclear structure and low-energy heavy-ion reactions. However, the role of the tensor force in fission is still not well known.

Purpose: We study how the tensor force affects the static fission pathway, the dynamical evolution from saddle to scission points, the mass and charge distributions, and the total kinetic energies (TKEs) of fission fragments of the induced fission of ${}^{240}\mathrm{Pu}$.

Methods: Based on the Skyrme density functionals SLy5 and SLy5t, the constrained Hartree-Fock (CHF) method with BCS pairing has been applied to generate a two-dimensional potential energy surface (PES) by constraining quadrupole and octupole mass moments. We then use the time-dependent Hartree-Fock (TDHF) approach with double particle number projection (PNP) for dynamical calculations. The TDHF approach is used to simulate the dynamical process until the formation of fission fragments and the properties of fragments can be obtained, in particular their mass, charge, and TKE. The double PNP is used to calculate the mass and charge distributions of fragments from each single TDHF fission trajectory, and then a Gaussian kernel estimation is introduced to give a proper description of fragment distributions. The changes caused by the tensor force are analyzed by comparing the SLy5 calculations with those of SLy5t.

Results: We find that the tensor force affects the height of fission barriers and the double-humped structure of the fission path of ${}^{240}\mathrm{Pu}$. On the PES, the fission valley becomes larger in the $(Q_{20},Q_{30})$ plane, and the triaxial deformation is suppressed around the outer barrier after considering the tensor force. Incorporating the tensor force into the dynamical process enhances the difference in shape evolution between two asymmetric channels. More interestingly, the charge distribution from TDHF with double PNP calculations shows a strong odd-even effect after including the tensor force. In addition, the total mass and charge distributions of fission fragments show a slight shift towards larger asymmetry and are more consistent with experiments when tensor components are included. We also find that the tensor force enhances energy gaps of the deformed shells for heavy fragments. Moreover, the TKEs of fragments are in accord with experiments, and, after incorporating the tensor force, we observe a higher concentration of the calculated TKEs for heavy fragments at $Z=52$ and $Z=56$.

Conclusions: The tensor force plays a role in both static and dynamical processes in nuclear fission, improving the accuracy of theoretical descriptions within the current framework. Our calculations have shown that the fission-barrier height with SLy5t is closer to the empirical value than that of SLy5. Additionally, the inclusion of the tensor force not only reveals the odd-even effect in charge distribution but also improves the description of total mass and charge distributions.

In this study, the effects of the nucleon's intrinsic electromagnetic (EM) structure on the nuclear charge radius have been explored within the framework of the relativistic Hartree-Bogoliubov theory. It is found that the intrinsic EM structure corrections could make an effect for accurately describing the evolution of nuclear charge radius. After taking into account the intrinsic EM structure corrections, the descriptions of the evolution of charge radii for Pb, Sn, and Cd isotopes have been improved within relativistic density functional theory. Using the Pb isotopic chain as an example, the improvement in charge radii can be primarily attributed to the intrinsic neutron and neutron spin-orbit terms of the intrinsic EM structure. Additionally, nuclear charge densities and corresponding isotopic evolution in Pb isotopes have been discussed.

Using an $\alpha +\alpha +N$ three-body model, we describe the ground and excited unbound states above the three-body threshold of $A=9$ mirror nuclei. We investigate the energy levels of low-lying and highly excited resonances below $\approx 10\mathrm{MeV}$ excitation energy of ${}^9\mathrm{Be}$ and ${}^9\mathrm{B}$ mirror nuclei with the complex-scaling method. The same number of solutions are found for both mirror nuclei, namely, thirteen resonances, $3/2_{1-4}^{-}$, $5/2_{1-3}^{-}$, $1/2_{1-3}^{-}$, $7/2_{1,2}^{-}$, and $9/2^{-}$, including the ground state for odd parity states, and eight resonances $5/2_{1,2}^{+}$, $3/2_{1,2}^{+}$, $7/2_{1,2}^{+}$, and $9/2_{1,2}^{+}$, for even-parity states with the exception of the low-lying $1/2^{+}$ state. These results are compared with experimentally observed and other theoretically calculated results. The band structures of odd and even parity states for both ${}^9\mathrm{Be}$ and ${}^9\mathrm{B}$ mirror nuclei are discussed in relation to the effect of the Coulomb energy difference.

We present a self-consistent quasiparticle random-phase approximation (QRPA) plus quasiparticle-vibration coupling (QPVC) approach, based on the Skyrme Hartree-Fock-Bogoliubov (HFB) model within the spherical assumption. Isovector giant dipole resonances (IVGDRs) and isoscalar giant quadrupole resonances (ISGQRs) are studied by taking Ca, Sn, and Pb isotopes as examples. We demonstrate that the $\mathrm{QRPA}+\mathrm{QPVC}$ approach is very powerful for the description of giant resonances and, in particular, describes their widths well. By using the experimental measurements of the ISGQR in ${}^{120}\mathrm{Sn}$ and ${}^{208}\mathrm{Pb}$, we discuss the extraction of an empirical value for the nucleon isoscalar effective mass $m^{*}/m$.

Molecular dynamics approaches use wave packets as nucleon wave functions to simulate the time evolution of nuclear reactions. It is crucial to activate the momentum fluctuation inherent in each wave packet so that it properly affects the time evolution. In the antisymmetrized molecular dynamics (AMD) model, this has traditionally been done by splitting the wave packets, i.e., by introducing a random fluctuation to the wave packet center of each particle. The present work proposes an improved approach to activate the fluctuation in both the one-body mean-field propagation and the two-nucleon collision processes, consistently based on the gradual or sudden change of the degree of isolation, which is derived from the fragment number function used for the zero-point energy subtraction. This new method is applied to the ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$ and ${}^{12}\mathrm{C}+p$ reactions at about 100 MeV/nucleon, focusing on the momentum distribution of the ${}^{11}\mathrm{B}$ fragments produced by one-proton removal from the ${}^{12}\mathrm{C}$ projectile. The results show that, with the momentum fluctuation suitably activated, the method correctly accounts for the recoil from the removed nucleon to the residue and the ${}^{11}\mathrm{B}$ momentum distribution is significantly improved, while without activating the fluctuation the distribution is too narrow compared to the experimental data. Furthermore, the AMD results indicate that the momentum distribution consists of two components; one is the high $P_z$ component with a small shift from the beam velocity, resulting from the simple removal of a proton after an energetic collision with a target particle; the other is the low $P_z$ component with a larger peak shift resulting from the decay of an excited ${}^{12}\mathrm{C}$ nucleus in a longer time scale. The activation of momentum fluctuation mainly affects the high $P_z$ component to broaden it. The role of cluster correlations in this problem is also investigated.

We compute the ${}^{63}\mathrm{Ga}(p,\gamma ){}^{64}\mathrm{Ge}$ and ${}^{64}\mathrm{Ge}(p,\gamma ){}^{65}\mathrm{As}$ thermonuclear reaction rates using the latest experimental input supplemented with theoretical nuclear spectroscopic information. The experimental input consists of the latest proton thresholds of ${}^{64}\mathrm{Ge}$ and ${}^{65}\mathrm{As}$ and the nuclear spectroscopic information of ${}^{65}\mathrm{As}$, whereas the theoretical nuclear spectroscopic information for ${}^{64}\mathrm{Ge}$ and ${}^{65}\mathrm{As}$ are deduced from the full $pf$-shell space configuration-interaction shell-model calculations with the GXPF1A Hamiltonian. Both thermonuclear reaction rates are determined with known uncertainties at the energies that correspond to the Gamow windows of the temperature regime relevant to type I x-ray bursts, covering the typical temperature range of the thermonuclear runaway of the GS $1826-24$ periodic bursts and SAX $\mathrm{J}1808.4-3658$ photospheric radius expansion bursts.

The ${}^{78}\mathrm{Se}(n,\gamma ){}^{79}\mathrm{Se}$ cross section has a high impact on the abundances of ${}^{78}\mathrm{Se}$ produced during the slow neutron capture process ($s$ process) in massive stars. A measurement of the ${}^{78}\mathrm{Se}$ radiative neutron capture cross section has been performed at the Neutron Time-of-Flight facility at CERN using a set of liquid scintillation detectors that have been optimized for a low sensitivity to neutrons. We present resonance capture kernels up to 70 keV and cross section from 70 to 600 keV. Maxwellian-averaged cross section (MACS) values were calculated for stellar temperatures between $kT=5$ and 100 keV, with uncertainties between 4.6% and 5.8%. The new MACS values result in substantial decreases of 20–30% of ${}^{78}\mathrm{Se}$ abundances produced in the $s$ process in massive stars and AGB stars. Massive stars are now predicted to produce subsolar ${}^{78}\mathrm{Se}/{}^{76}\mathrm{Se}$ ratios, which is expected since ${}^{76}\mathrm{Se}$ is an $s$-only isotope, while solar ${}^{78}\mathrm{Se}$ abundances have also contributions from other nucleosynthesis processes.

Shell quenching phenomena in nuclear charge radii are typically observed at the well-established neutron magic numbers. However, the recent discovery of potential new magic numbers at the neutron numbers $N=32$ and $N=34$ has sparked renewed interest in this mass region. This work further inspects into the charge radii of nuclei around the $N=28$ shell closure using the relativistic Hartree-Bogoliubov model. We incorporate meson-exchange and point-coupling effective nucleon-nucleon interactions alongside the Bogoliubov transformation for pairing corrections. To accurately capture the odd-even staggering and shell closure effects observed in charge radii, neutron-proton correlations around Fermi surface are explicitly considered. The charge radii of Ca and Ni isotopes are used to test the theoretical model and show an improvement with neutron-proton pairing corrections, in particular for neutron-rich isotopes. Our calculations reveal a inverted parabolic-like trend in the charge radii along the $N=28$ isotones for proton numbers $Z$ between 20 and 28. Additionally, the shell closure effect of $Z=28$ persists across the $N=28,30,32$, and 34 isotonic chains, albeit with a gradual weakening trend. Notably, the significantly abrupt changes in charge radii are observed across $Z=22$ along both the $N=32$ and $N=34$ isotonic chains. This kink at $Z=22$ comes from the sudden decrease of the neuron-proton correlation around Fermi surfaces across $Z=22$ for $N=30$, 32, and 34 isotones and might provide a signature for identifying the emergence of neutron magic numbers $N=32$ and 34. Furthermore, the calculated charge radii for these isotonic chains ($N=28$, 30, 32, and 34) can serve as reliable guidelines for future experimental measurements.