We analyze the effect of the $\sigma$ potential on the characteristics of pure nucleonic and hyperon-rich neutron star matter with recently proposed, well-constrained relativistic mean field model. The $\sigma$-cut potential is recognized for diminishing the influence of the $\sigma$ field, leading to a stiffer equation of state at high densities. This ultimately results in increased neutron star masses without altering the characteristics of nuclear matter at nuclear saturation density. We further examined the impact of the $\sigma$-cut potential on symmetric nuclear matter, symmetry energy as well as neutron star matter with pure nucleonic and hyperon-rich cores, and compared it to the existing theoretical, experimental, and observational data.

The level scheme of semimagic nucleus ${}^{93}\mathrm{Tc}$ has been reinvestigated via the ${}^{90}\mathrm{Zr}$(${}^6\mathrm{Li}$, $3n$) ${}^{93}\mathrm{Tc}$ reaction. Nine transitions together with five states are identified for the first time by the $\gamma \text{−}\gamma$ coincidence measurement. The shell-model calculation employing the JUN45 interaction has been performed to interpret the experimental level scheme of ${}^{93}\mathrm{Tc}$. The calculated results well describe the low-lying states, and deviations happen for the states with energies higher than 6.0 MeV, which could be ascribed to the $N=Z=50$ core excitation beyond the model space of the JUN45 interaction. Newly found states at energies of 2215 and 2305 keV belong to the multiplets formed by the valence proton in $g_{9/2}$ orbits coupled with the $5^{-}$ state of the even-even core, ${}^{92}\mathrm{Mo}$. A 669.1-keV $\gamma$-ray was determined to be an $E3$ transition in ${}^{93}\mathrm{Tc}$ with the $B\left(E3\right)$ value of 0.41(5) W.u. Systematical investigation on the $B\left(E3\right)$ tendency among $N=50$ isotones and $Z=40$ isotopes has been performed in the current work, in order to interpret the effect of valence protons or neutrons in the $g_{9/2}$ orbit on the octupole correlation in the region.

The $\beta$-delayed neutron emission in the ${}^{85,86}\mathrm{As}\beta$ decays has been measured at the Ion Guide Isotope Separator On Line facility of the Accelerator Laboratory of the University of Jyväskylä. The complete $\beta$ decays have been studied with a complex setup that consists of a plastic scintillator for $\beta$ particles, MONSTER—the MOdular Neutron time-of-flight SpectromeTER—for neutrons, and a high-purity germanium and four ${\mathrm{LaBr}}_3$ crystals for $\gamma$ rays. The $\beta$-delayed neutron energy distributions have been determined by unfolding the time-of-flight spectra with an innovative methodology based on the iterative Bayesian unfolding method and accurate Monte Carlo simulations. The results obtained for ${}^{85}\mathrm{As}$ are in excellent agreement with the existing evaluated data, validating the proposed methodology. In the case of ${}^{86}\mathrm{As}$, a stronger neutron intensity at higher energies than previously predicted is discovered.

In this work, we investigate the photon strength function (PSF) of ${}^{57}\mathrm{Fe}$ derived from thermal neutron capture on ${}^{56}\mathrm{Fe}$, with a focus on the low-energy photon strength below the neutron separation energy. We show that the PSF derived from primary $\gamma$ transitions does not support the significant low-energy enhancement previously reported in the Oslo method. The role of secondary $\gamma$ transitions and $E2$ transitions in the total PSF is discussed. Averaging the $E2$ primary transitions following thermal neutron capture on ${}^{56}\mathrm{Fe}$, we obtained an estimate for the E2 strength function for primary gamma transitions in radiative capture, $f_{E2}=2\times {10}^{-11}{\mathrm{MeV}}^{-5}$.

The proton-deuteron correlation function measured by the ALICE collaboration in high multiplicity $\mathrm{p}+\mathrm{p}$ collisions shows a momentum dependence which is in contradiction with the predictions of the Lednický-Lyuboshitz formalism of the two-body interaction. This result motivated a more sophisticated three-body description in terms of a composite deuteron. Encouraged by the good description of other deuteron observables in the context of heavy-ion collisions, we revisit this correlation function under the two-body approximation without relying on the Lednický-Lyuboshitz approximation, but using the solution of the Schrödinger equation by incorporating both strong and Coulomb interactions. The two-body description provides a reasonable agreement to ALICE data for natural values of the source size. Interpreting the previously assumed attractive character of the $(L,S)=(0,3/2)$ channel of the $pd$ interaction into a more likely repulsion, the results agree better not only with the ALICE measurements but also with recent STAR data in $\mathrm{Au}+\mathrm{Au}$ collisions.

The study of shell structure evolution in nuclei with extreme $N/Z$ ratios, particularly in those near the doubly magic nucleus ${}^{78}\mathrm{Ni}$, is a significant topic in nuclear structure. In this work, we employed the realistic shell model to calculate the low-lying spectra of neutron-rich odd-mass ${}^{6\text{9–7}9}\mathrm{Cu}$ isotopes and $N=49$ isotones, including ${}^{77}\mathrm{Ni}$, ${}^{79}\mathrm{Zn}$, ${}^{81}\mathrm{Ge}$, ${}^{83}\mathrm{Se}$, and ${}^{85}\mathrm{Kr}$, all situated in the vicinity of ${}^{78}\mathrm{Ni}$. Our calculations successfully reproduced the low-lying spectra of neutron-rich Cu isotopes, especially for the ground state inversion from $3/2^{-}$ to $5/2^{-}$ states when transitioning from ${}^{69}\mathrm{Cu}$ to ${}^{79}\mathrm{Cu}$. Moreover, the shell evolution related to the proton $1p_{3/2}$ and $0f_{5/2}$ orbits is investigated via the calculated effective single-particle energies. The low-lying intruder states and shape coexistence that appear in $N=49$ isotones are also well reproduced in our calculations. Additionally, the average occupations of valence neutrons and the $g$ factors of low-lying states are presented to further investigate the exotic properties of $N=49$ isotones. The results are in good agreement with experimental data and suggest a weakening of the $N=50$ shell closure around $Z=32$ and 34.

The nucleon-pair approximation (NPA) of the shell model, with collective pairs projected from unconstrained Hartree-Fock states as well as a number of so-called noncollective pairs, is applied to study the low-lying states, both the yrast and a few non-yrast, of the ${}^{144}\mathrm{Ba}$ nucleus. There are the most sophisticated NPA calculations ever performed. The calculated electric quadrupole transition rates are very consistent with experimental data. Our calculations demonstrate robustness of intrinsic quadrupole moment for the yrast states. In addition, our calculations also reproduce an octupole band and a prolate band in low-lying states of ${}^{144}\mathrm{Ba}$. With consideration of two major shells both for valence protons and neutrons, our calculations yield a sizable $B(E1,J^{-}\to {(J-1)}^{+})$.

We propose first-chance fission as a new avenue to probe the temperature-dependent nuclear dissipation mechanism. To this end, stochastic dynamical approaches are applied to calculate the drop of first-chance fission probability caused by friction over their standard statistical-model value, $P_{f1}^{\mathrm{drop}}$, as a function of the dissipation strength $\left(\beta \right)$ for ${}^{28}\mathrm{Si}+{}^{209}\mathrm{Bi}$, ${}^{30}\mathrm{S}+{}^{204}\mathrm{Pb}$, and ${}^{30}\mathrm{S}+{}^{209}\mathrm{Bi}$ at different bombarding energies $\left(E_{\mathrm{lab}}\right)$. It is shown that $P_{f1}^{\mathrm{drop}}$ of each neutron-deficient system ${}^{237}\mathrm{Bk}$, ${}^{234}\mathrm{Cf}$, and ${}^{239}\mathrm{Es}$, populated in these reactions, rapidly rises with increasing $\beta$, but it exhibits a quite weak dependence on $E_{\mathrm{lab}}$. This indicates that first-chance fission probability is more sensitive to friction and less sensitive to bombarding energy, revealing that it is a robust probe of $\beta$. Our results therefore suggest that in experiments, to more stringently constrain $\beta$ and to more clearly illustrate the dependence of dissipation on temperature, it is optimal to measure first-chance fission probability of neutron-deficient heavy fissioning systems produced via stable or radioactive nuclear beams induced reactions.

Conservation laws play a crucial role in the modeling of heavy-ion collisions, including those for charges such as baryon number (B), strangeness (S), and electric charge (Q) (hereafter referred to as BSQ charges). In this study, we present a new (2+1)-dimensional relativistic viscous hydrodynamic code called ccake which uses the smoothed particle hydrodynamics formalism to locally conserve BSQ charges, together with an extended description of the multidimensional equation of state obtained from lattice quantum chromodynamics. Initial BSQ charge distributions for ccake are supplied by iccing, an algorithm which samples gluon splittings into quark-antiquark pairs from a background energy distribution from the TRENTo model. We study correlations between the BSQ charges and find that local BSQ fluctuations remain finite during the evolution, with corresponding chemical potentials of $\approx 100–200\mathrm{MeV}$ at freeze-out. We find that our framework produces reasonable multiplicities of identified particles and that iccing has no significant effect on the collective flow of all charged particles nor of identified particles when only one particle of interest is considered. However, we show specifically for Pb $+$ Pb collisions at the LHC $\sqrt{s_{NN}}=5.02$ TeV that iccing does have an effect on collective flow of identified particles if two particles of interest are considered.

Background: Reaction mechanisms involved in charge-exchange reactions are heavily mixed. From an experimental perspective, separating the role of specific mechanisms from others is impossible due to quantum interference. To address this, rigorous theoretical studies must be applied. Refining the used quantum states is a key factor, not only for this purpose but also for reactions involving weak interactions, such as neutrinoless double-beta decay.

Purpose: The present study investigates the ${}^{40}\mathrm{Ca}({}^{18}\mathrm{O},{}^{18}\mathrm{F}){}^{40}\mathrm{K}$ reaction at an energy of 275 MeV. It is assumed that the reaction primarily proceeds through three mechanisms: direct meson exchange (DME), nucleon transfer—first a neutron, then a proton ($n\text{−}p$)—and the reverse ($p\text{−}n$). The main goal of the study is to compare the experimental data with the calculations for this reaction and to investigate the role of the different mechanisms in a coherent and consistent manner.

Methods: For the direct process, the distorted-wave Born approximation (DWBA) method was employed. The two-step DWBA procedure is used for the $n\text{−}p$ and $p\text{−}n$ mechanisms. In these calculations, the semi-microscopic optical potential is utilized, validated through comparisons of calculated cross sections for elastic, inelastic, and single-nucleon transfer channels with experimental data. Calculations to obtain information about nuclear structure, spectroscopic amplitudes, and onebody transition densities were performed using the large-scale shell model, employing a unified p-sd model space for projectile nuclei and an sd-pf model space for target nuclei.

Results: The ground state and the first ten excited states for both the target and projectile nuclei were included in the calculations. The differential cross sections, calculated considering three mechanisms, were compared with the experimental data across three available excitation energy regions of interest.

Conclusion: The differential cross-sections obtained using the DWBA method, considering the three mechanisms, show good agreement with the available experimental data. This result can be interpreted as evidence for the applicability of the nuclear-reaction and nuclear-structure models adopted in the present study. In particular the DME mechanism gives the dominant contribution to the cross section, indicating that the experimental conditions of the present work in terms of projectile/ejectile combination, incident energy, and explored angles are favorable to highlight the role of the direct meson-exchange mechanism.

The role of nucleon-nucleon collisions in heavy-ion fusion reactions is examined using the time-dependent Hartree-Fock (TDHF) approach combined with a relaxation-time approximation (RTA). The investigation focuses on energy dissipation and thermalization in the head-on fusion reaction ${}^{16}\mathrm{O}+{}^{16}\mathrm{O}$. The nucleus-nucleus interaction potential, obtained via the density-constraint method, reveals minimal dependence on nucleon-nucleon collisions. However, incorporation of nucleon-nucleon collisions significantly enhances the dissipation of collective kinetic energy, promotes thermalization, and increases the fusion threshold energy above which the system does not fuse. Comparisons with TDHF results indicate that nucleon-nucleon collisions are crucial for achieving equilibrium, a process that pure mean-field models fail to adequately capture. These findings highlight the necessity of beyond mean-field approaches for exploring energy dissipation and thermalization in nuclear-fusion dynamics.

The transport property of cold and dense nucleon matter is important for nuclear physics but is relatively less studied than that at finite temperatures. In this paper, we present a primary study of bulk and shear viscosities in the limit $T/{\mu }_B\ll 1$, where $T$ and ${\mu }_B$ are the temperature and the baryon chemical potential. The analysis is performed for a generic system where nucleons are dressed by the condensation of both scalar and vector interactions. Under the relaxation time approximation of the Boltzmann equation, we compute the viscosities of the system to leading power in $T/{\mu }_B$ expansion and establish a relation between the thermodynamic potential and transport coefficients, including bulk viscosity ($\zeta$) and shear viscosity ($\eta$). It is found that hydrodynamic stability ($\zeta >0$) imposes additional constraints on the thermodynamic potential. As an example, these relations are applied to the Walecka model. The fluid properties of the cold and dense nucleon matter are characterized by the dimensionless combination of viscosities times the quasi-Fermi momentum over the enthalpy. Furthermore, we discuss the implication of the stability condition on the range of applicability of the model.

High-resolution in-beam $\gamma$-ray spectroscopy was used to study excited states of the neutron-deficient nucleus ${}^{32}\mathrm{Ar}$ populated in fast-beam induced four- and six-nucleon removal reactions from ${}^{36,38}\mathrm{Ca}$. One new $\gamma$-ray transition and indications for an additional two were found, allowing for a glimpse at the level scheme beyond the $2_1^{+}$ state. The nature of the new $1900\left(4\right)$-keV transition is discussed in the context of the known energy spectrum of the mirror nucleus ${}^{32}\mathrm{Si}$ and shell-model calculations using the FSU and SDPF-M cross-shell effective interactions. Its resulting parent state at $3767\left(5\right)\mathrm{keV}$, more than 1.3 MeV above the proton separation energy, is tentatively assigned to have mixed $sd$-shell and $\text{2p-2h}$ character. It might either be the mirror of the $J^{\pi }=2_2^{+}$ state of ${}^{32}\mathrm{Si}$ at $4230.8\left(8\right)\mathrm{keV}$, but with a decay branch favoring a transition to the $2_1^{+}$ over the ground state, or the mirror of the $4983.9\left(11\right)$-keV state with quantum numbers $0^{+}$. The resulting mirror-energy differences of $-473\left(5\right)$ and $-1218\left(5\right)\mathrm{keV}$ are both sizable when compared to systematics; in the latter case the result would, in fact, be among the largest reported to date in the nuclear chart or suggest the potential existence of an additional, hitherto unidentified, low-lying $0^{+}$ state of ${}^{32}\mathrm{Si}$.

The density overlap between two interacting nuclei results in a change of the internal kinetic energy, which magnifies a repulsive contribution. We investigated to what extent the internal kinetic energy can be calculated using the extended Thomas-Fermi approximation (ETF) with inhomogeneous terms and with surface corrections. The complete fusion reactions involving light and heavy nuclei from ${}^{16}\mathrm{O}$ to ${}^{208}\mathrm{Pb}$ are considered as examples. The fusion excitation function is calculated in the framework of the extended quantum diffusion model, using a nucleus-nucleus interaction potential based on the Skyrme energy-density functional. We found that both the fixed strengths of the inhomogeneous terms of the ETF approximation and its semiclassical expansion up to ${\hslash }^2$ (ETF2) fail to correctly describe the complete fusion process and, thus, the Coulomb barrier parameters. The density and mass-number dependencies for the strengths of these inhomogeneous terms of the internal kinetic-energy density functions are suggested, with which the fusion cross sections are successfully reproduced.

Improved constraints on current model parameters in a heavy-ion collision model are established using the latest measurements from three distinct collision systems. Various observables are utilized from Au–Au collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV and Pb–Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV and $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV. Additionally, the calibration of centrality is now carried out separately for all parametrizations. The inclusion of an Au–Au collision system with an order of magnitude lower beam energy, along with separate centrality calibration, suggests a preference for smaller values of nucleon width, minimum volume per nucleon, and free-streaming time. The results with the acquired maximum a posteriori parameters show improved agreement with the data for the second-order flow coefficient, identified particle yields, and mean transverse momenta. This work contributes to a more comprehensive understanding of heavy-ion collision dynamics and sets the stage for future improvements in theoretical modeling and experimental measurements.

Here we publish three years of data from the UCNτ experiment performed at the Los Alamos Ultracold Neutron Facility at the Los Alamos Neutron Science Center. These data are in addition to our previously published data. Our goals in this paper are to better understand and quantify systematic uncertainties and to improve the lifetime statistical precision. We previously reported a value from our 2017–2018 data for the neutron lifetime of $877.75\pm 0.28$ (statistical) +0.22–0.16 (systematic) s. We have collected an additional three years of data reported here for the first time. When all the data from UCNτ are averaged for 2017, 2018, 2020, 2021, and 2022, we report an updated value for the lifetime of $877.83\pm 0.22$ (statistical)+0.20–0.17 (systematic) s. We utilized improved monitor detectors, reduced our correction due to UCN upscattering on residual gas, and employed four different UCN detector geometries both to reduce the correction required for rate dependence and to explore potential contributions due to phase space evolution.

Background: The collective properties of the neutron-deficient ${}^{154}\mathrm{Er}$ and ${}^{155}\mathrm{Er}$ nuclei remain poorly understood. To better characterize these properties, spectroscopic data, such as reduced quadrupole transition probabilities, are essential. These measurements help quantify the strength of collectivity in these isotopes, particularly near the $N=82$ shell closure. With such data, the shape evolution of neutron-deficient Er isotopes can be investigated within the framework of theoretical nuclear structure models.

Purpose: This paper aims to improve the understanding of the collective properties of neutron-deficient ${}^{154}\mathrm{Er}$ and ${}^{155}\mathrm{Er}$ isotopes by measuring reduced transition probabilities. These measurements provide key insights into the evolution of nuclear shapes near the $N=82$ shell closure. By comparing experimental $B\left(E2\right)$ values with theoretical predictions from the five-dimensional collective Hamiltonian (5DCH) and quasiparticle random-phase approximation (QRPA), this paper seeks to refine nuclear structure models and explore the role of quasiparticle excitations in shape transitions of rare-earth nuclei.

Methods: We report on the lifetime measurements of the first $2^{+}, 4^{+}, 6^{+}, 8^{+}$, and ${10}^{+}$ states in ${}^{154}\mathrm{Er}$, as well as the $17/2^{+}, 21/2^{+}$, and $25/2^{+}$ levels in ${}^{155}\mathrm{Er}$. These measurements were performed using the recoil distance Doppler shift method at the IFIN-HH 9 MV Tandem accelerator. Excited states were populated via the ${}^{144}\mathrm{Sm}({}^{13}\mathrm{C},\mathrm{Xn})$ fusion-evaporation reaction, and data were collected using the ROSPHERE array. The experimental results for ${}^{154}\mathrm{Er}$, along with previously published data for ${}^{156–164}\mathrm{Er}$ isotopes, are analyzed within the framework of the 5DCH implemented with the D1S Gogny force. Additionally, QRPA calculations are performed for ${}^{162}\mathrm{Er}$ and ${}^{164}\mathrm{Er}$ to compare experimental and theoretical $B\left(E2\right)$ values for interband transitions with those predicted by 5DCH.

Results: Reduced transition probability $B\left(E2\right)$ values have been obtained for the ground-state band transitions up to the ${10}^{+}$ state in ${}^{154}\mathrm{Er}$, alongside strong evidence for the gamma vibrational band. For ${}^{155}\mathrm{Er}, B$($E2$) values are obtained for the $17/2^{+}\to 13/2^{+}, 21/2^{+}\to 17/2^{+}$, and $25/2^{+}\to 21/2^{+}$ transitions. The evolution of nuclear structure from a quasispherical to a strongly deformed shape in the ${}^{154–164}\mathrm{Er}$ isotopes is analyzed based on the present 5DCH calculations. The $B$($E2$) strengths calculated for interband transitions using QRPA are weaker than those predicted by 5DCH but show better agreement with experimental $B$($E2$) values.

Conclusions: The measured $B$($E2$) values for intraband transitions in ${}^{154}\mathrm{Er}$ are significantly weaker than those predicted by 5DCH calculations. This suggests that more accurate $B$($E2$) predictions may require incorporating quasiparticle degrees of freedom into the collective structure model. The structure of neutron-deficient erbium isotopes undergoes a transition from quasispherical to strongly deformed shapes that is reasonably well described by the 5DCH calculations. Additionally, extending systematic QRPA calculations to deformed nuclei in the rare-earth region is suggested.

We analyze parameter sensitivities of the mapped interacting boson model (IBM) and boson-fermion-fermion model (IBFFM) in the description of $\beta$-decay properties of the even-mass neutron-deficient Ge and As, and neutron-rich Zr and Mo isotopes. Based on the self-consistent mean-field calculations with a given energy density functional and a pairing interaction, the IBM Hamiltonian for even-even nuclei, single-particle energies, and occupation probabilities for unpaired nucleons, which are necessary building blocks of the IBFFM Hamiltonian and Gamow-Teller and Fermi transition operators, are completely determined. A few coupling constants of the boson-fermion and residual neutron-proton interactions are only phenomenological parameters fitted to reproduce low-energy spectra of odd-mass and odd-odd nuclei. It is found that the calculated ${log}_{10}ft$ values for the ${\beta }^{+}$ decays ${}^{68}\mathrm{As}\to {}^{68}\mathrm{Ge}$ are particularly sensitive to the quadrupole-quadrupole boson interaction strength used for the parent $\left({}^{68}\mathrm{As}\right)$ nucleus. We further incorporate higher-order terms in the one-nucleon transfer operators in the boson system, and find that, while their effects are non-negligible, they do not significantly alter qualitative features of $\beta$-decay properties. We report a novel application of the mapped IBM framework to compute $\beta$-decay half-lives, and show that the observed trend along isotopic chains are reasonably reproduced.

An extended interacting boson model incorporating one-particle-one-hole (1p-1h) excitations to the next nearest shell and configuration mixing due to two-particle-two-hole (2p-2h) excitations from the nearest lower shell is applied to systematically describe the low-lying spectra and isoscalar giant monopole and quadrupole resonances (ISGMR and ISGQR) of the well-deformed nuclei ${}^{148,150,152,154}\mathrm{Sm}$. The model results are compared with experimental data and with those of the consistent-$Q$ formalism that includes 1p-1h excitations but lacks 2p-2h configuration mixing. The extended model shows improved agreement with both low-lying spectral properties and high-lying excitations associated with ISGMR and ISGQR compared to the original consistent-$Q$ formalism. Furthermore, the $X\left(5\right)$ critical point features are not only evident in the low-lying level energies and corresponding B(E2) ratios, but also reflected in the effective charge parameters and excitation energies associated with 1p-1h excitations.