We have calculated a complete set of primary fission fragment mass yields, $Y\left(A\right)$, for heavy nuclei across the chart of nuclides, including those of particular relevance to the rapid neutron capture process ($r$ process) of nucleosynthesis. We assume that the nuclear shape dynamics are strongly damped, which allows for a description of the fission process via Brownian shape motion across nuclear potential-energy surfaces. The macroscopic energy of the potential was obtained with the Finite-Range Liquid-Drop Model (FRLDM), while the microscopic terms were extracted from the single-particle level spectra in the fissioning system by the Strutinsky procedure for the shell energies and the BCS treatment for the pairing energies. For each nucleus considered, the fission fragment mass yield, $Y\left(A\right)$, is obtained from 50 000 to 500 000 random walks on the appropriate potential-energy surface. The full mass and charge yield, $Y(Z,A)$, is then calculated by invoking the Wahl systematics. With this method, we have calculated a comprehensive set of fission-fragment yields from over 3800 nuclides bounded by $80\le Z\le 130$ and $A\le 330$; these yields are provided as an ASCII formatted database in the Supplemental Material. We compare our yields to known data and discuss general trends that emerge in low-energy fission yields across the chart of nuclides.

The kaonic system $NN\overline{K}$ is studied based on the configuration space Faddeev equations. We consider two models associated with isospin “natural” basis and isospin “charge” basis. One basis is related to another by a unitary transformation. We show that the “particle representation” for $NN\overline{K}(s_{NN}=0)$ system motivated by the charge basis does not describe the system in terms of coupled particle channels $pp{K}^{-}/pn{\overline{K}}^0$. The coupling is associated with the nondiagonal elements of the matrix representation for the $N\overline{K}$ potential in the charge basis. The matrix can be diagonalized by a simple unitary transformation. With this relation, the Kyoto potential is discussed. The particle configurations of the $NN\overline{K}$ system may be classified by the presence or absence of the Coulomb interaction according to an analogy with the $NNN$ system. The $NN\overline{K}(s_{NN}=0)$ system is represented by four particle configurations: $pp{K}^{-}$, $np{K}^{-}$, $np{\overline{K}}^0$, and $nn{\overline{K}}^0$.

Background: Nuclear pasta matter, emerging due to the competition between the long-range Coulomb force and the short-range strong force, is believed to be present in astrophysical scenarios, such as neutron stars and core-collapse supernovae. Its structure can have a high impact, e.g., on neutrino transport or the tidal deformability of neutron stars.

Purpose: We investigate the impact of nuclear pasta on neutrino interactions and compare the results to uniform matter.

Method: We calculate the elastic and inelastic static structure factors for nuclear pasta matter, using density functional theory (DFT), which contain the main nuclear input for neutrino scattering.

Results: Each pasta structure leaves a unique imprint in the elastic structure factor and it is largely enhanced. The inelastic structure factors are very similar for all configurations.

Conclusion: Nuclear pasta has a noticeable impact on neutrino neutral-current scattering opacities. While for inelastic reactions the cross section is reduced, the elastic coherent scattering increases dramatically. The effect can be of importance for the cooling of neutron stars as well as for core-collapse supernova models.

The $\alpha$ decays of exotic $N=125$, 126, and 127 isotones, including two new isotopes ${}^{219}\mathrm{Np}$ [Phys. Lett. B 777, 212 (2018)] and ${}^{220}\mathrm{Np}$ [Phys. Rev. Lett. 122, 192503 (2019)], are studied by using the improved Buck-Merchant-Perez cluster model with the charge-dependent $\alpha$-preformation factors. The experimental half-lives of $\alpha$ decays varying from $2.50\times {10}^{-5}$ to $6.00\times {10}^{26}\mathrm{s}$ are reproduced within a factor of $\approx 2$. Noticeably, the theoretical $\alpha$-decay half-lives of the new isotopes ${}^{219,220}\mathrm{Np}$ are also in good agreement with the experimental data. Furthermore, the $\alpha$-decay half-lives of some undiscovered $N=125$, 126 and 127 isotones are predicted, which could be useful for future experimental studies on the robustness of the magic number $N=126$.

The role of the short-range part (repulsive core) of the proton-neutron ($pn$) potential in deuteron elastic breakup processes is investigated. A simplified one-range Gaussian potential and the Argonne $\text{V4}{}^{\prime }$ ($\text{AV4}{}^{\prime }$) central potential are adopted in the continuum-discretized coupled-channels (CDCC) method. The deuteron breakup cross sections calculated with these two potentials are compared. The repulsive core is found not to affect the deuteron breakup cross sections at energies from 40 MeV to 1 GeV. To understand this result, an analysis of the peripherality of the elastic breakup processes concerning the $pn$ relative coordinate is performed. It is found that for the breakup processes populating the $pn$ continua with orbital angular momentum $\ell$ different from 0, the reaction process is peripheral, whereas it is not for the breakup to the $\ell =0$ continua (the $s$-wave breakup). The result of the peripherality analysis indicates that the whole spatial region of deuteron contributes to the $s$-wave breakup.

Detailed knowledge of the hadronic spectrum is still an open question, which has phenomenological consequences on the study of heavy-ion collisions. A previous lattice QCD study concluded that additional strange resonances are missing in the currently tabulated lists provided by the Particle Data Group (PDG). That study identified the list labeled $\text{PDG2016}+$ as the ideal spectrum to be used as an input in thermal-model-based analyses. In this work, we determine the effect of additional resonances on the freeze-out parameters of systems created in heavy-ion collisions. These parameters are obtained from thermal fits of particle yields and net-particle fluctuations. For a complete picture, we compare several hadron lists including both experimentally discovered and theoretically predicted states. We find that the inclusion of additional resonances mildly influences the extracted parameters—with a general trend of progressively lowering the temperature—but is not sufficient to close the gap in temperature between light and strange hadrons previously observed in the literature.

We consider the elastic constants of phases with nonspherical nuclei, so-called pasta phases, predicted to occur in the inner crust of a neutron star. First, we treat perfectly ordered phases and give numerical estimates for lasagna and spaghetti when the pasta elements are spatially uniform; the results are in order-of-magnitude agreement with the numerical simulations of Caplan, Schneider, and Horowitz, [Phys. Rev. Lett. 121, 132701 (2018)]. We then turn to pasta phases without long-range order and calculate upper (Voigt) and lower (Reuss) bounds on the effective shear modulus and find that the lower bound is zero, but the upper bound is nonzero. To obtain better estimates, we then apply the self-consistent formalism and find that this predicts that the shear modulus of the phases without long-range order is zero if the pasta elements are spatially uniform. In numerical simulations, the pasta elements are found to be modulated spatially and we show that this modulation is crucial to obtaining a nonzero elastic moduli for pasta phases without long-range order. In the self-consistent formalism we find that, for lasagna, the effective shear modulus is linear in the elastic constants that do not vanish when the pasta elements are spatially uniform while, for spaghetti, it varies as the square root of these elastic constants. We also consider the behavior of the elastic constant associated with a homologous strain (hydrostatic compression) of the structure of the pasta phases without long-range order.

Uncertainties in nuclear models have a major impact on simulations that aim at understanding the origin of heavy elements in the universe through the rapid neutron capture process ($r$ process) of nucleosynthesis. Within the framework of the nuclear density functional theory, we use results of Bayesian statistical analysis to propagate uncertainties in the parameters of energy density functionals to the predicted $r$-process abundance pattern, by way not only of the nuclear masses but also through the influence of the masses on $\beta$-decay and neutron capture rates. We point out the importance of the nonequilibrium end stage of the $r$ process in determining the width of the resulting abundance pattern uncertainty bands. We additionally make the first identifications of specific parameters of Skyrme-like energy density functionals which show tentative correlations with particular aspects of the $r$-process abundance pattern. While previous studies have explored the reduction in the abundance pattern uncertainties due to anticipated new measurements of neutron-rich nuclei, here we point out that an even larger reduction will occur when these new measurements are used to reduce the uncertainty of model predictions of masses, which are then propagated through to the abundance pattern. We make a quantitative prediction for how large this reduction will be.

The energy spectrum of two short-range interacting particles in a harmonic potential trap has previously been related to free-space scattering phase shifts. But the existing formula for systems with a nonzero interaction range is exact only in the limit of an infinitely shallow trap. Here I provide a systematically improved formula—describing the low-energy dynamics—that enables the use of finite traps. This paves the way for extracting nuclear scattering phase shifts from ab initio nuclear many-body structure calculations, a long-sought goal in nuclear physics. The derivation establishes effective field theory as a powerful framework for studying the connection between structure information of a trapped system (with two or more subclusters) and continuum physics in the fields of both nuclear and condensed-matter physics.

Reactor neutrino experiments have seen major improvements in precision in recent years. With the experimental uncertainties becoming lower than those from theory, carefully considering all sources of ${\overline{\nu }}_e$ is important when making theoretical predictions. One source of ${\overline{\nu }}_e$ that is often neglected arises from the irradiation of the nonfuel materials in reactors. The ${\overline{\nu }}_e$ rates and energies from these sources vary widely based on the reactor type, configuration, and sampling stage during the reactor cycle and have to be carefully considered for each experiment independently. In this article, we present a formalism for selecting the possible ${\overline{\nu }}_e$ sources arising from the neutron captures on reactor and target materials. We apply this formalism to the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory, the ${\overline{\nu }}_e$ source for the the Precision Reactor Oscillation and Spectrum Measurement (PROSPECT) experiment. Overall, we observe that the nonfuel ${\overline{\nu }}_e$ contributions from HFIR to PROSPECT amount to 1% above the inverse $\beta$ decay threshold with a maximum contribution of 9% in the 1.8–2.0 MeV range. Nonfuel contributions can be particularly high for research reactors like HFIR because of the choice of structural and reflector material in addition to the intentional irradiation of target material for isotope production. We show that typical commercial pressurized water reactors fueled with low-enriched uranium will have significantly smaller nonfuel ${\overline{\nu }}_e$ contribution.

The half-life of ${}^{15}\mathrm{O}$ was measured using the $\beta$-Counting Station at the University of Notre Dame's Nuclear Science Laboratory. Our new result, $t_{1/2}=122.308\left(49\right)$ s, is the most precise determination to date for ${}^{15}\mathrm{O}$, and improves the world average by a factor of 4, yielding $t_{1/2}^{\text{world}}=122.27\left(6\right)$ s. This more precise value will be important for future determinations of $V_{\text{ud}}$ using superallowed $T=1/2$ mirror transitions.

The ${}^7\mathrm{Li}(\gamma ,t){}^4\mathrm{He}$ ground state cross section was measured for the first time using monoenergetic $\gamma$ rays with energies between 4.4 and 10 MeV at the High Intensity Gamma-ray Source. The reaction is important for the primordial Li problem and for testing our understanding of the mirror $\alpha$-capture reactions ${}^3\mathrm{H}(\alpha ,\gamma ){}^7\mathrm{Li}$ and ${}^3\mathrm{He}(\alpha ,\gamma ){}^7\mathrm{Be}$. Although over the last 30 years most measurements of the ${}^3\mathrm{H}(\alpha ,\gamma ){}^7\mathrm{Li}$ reaction have concentrated in an energy range below $E_{\gamma }=3.65$ MeV, measurements at higher energies could potentially restrict the extrapolation to astrophysically important energies. The experimental arrangement for measuring the ${}^7\mathrm{Li}(\gamma ,t){}^4\mathrm{He}$ reaction included a large-area silicon detector array and several beam characterization instruments. The experimental astrophysical $S$ factor of ${}^3\mathrm{H}(\alpha ,\gamma )$ calculated from the present data was fitted using the $R$-matrix formalism. The results are in disagreement with previous experimental measurements in the same energy range but the extrapolated $S$ factor agrees with the potential model calculation and lower energy experimental data.

Anomalous event-by-event fluctuations of the relative yields of neutral ($K_s^0$) and charged kaon ($K^{\pm }$) have been predicted to yield a signature for the formation of disoriented chiral condensate (DCC) in relativistic heavy-ion collisions. In this work, we model the production and decay of DCCs in the context of heavy-ion collisions at the CERN Large Hadron Collider, and estimate the sensitivity of large acceptance detectors, such as the ALICE detector, towards the identification of such anomalous decays. Our study is based on the robust statistical observable, ${\nu }_{\mathrm{dyn}}$, known for its sensitivity to dynamical fluctuations. We first present simulations without DCCs, based on the HIJING and AMPT models, in order to establish an approximate reference for the magnitude of ${\nu }_{\mathrm{dyn}}(K^{\pm },K_s^0)$ and its centrality evolution in Pb-Pb collisions at the TeV energy scale. We next introduce simple phenomenological models of $K_s^0$ vs $K^{\pm }$ event-by-event yield fluctuations, which we use to study the feasibility and sensitivity of detection of the production of DCCs in heavy-ion collisions. Although the precision of models such as HIJING and AMPT limit their use as absolute references and thus render anomalous fluctuations difficult to define precisely, our studies demonstrate that the magnitude of ${\nu }_{\mathrm{dyn}}(K^{\pm },K_s^0)$ is in fact very sensitive to the presence of small admixture of DCCs in normal non-DCC events. Consequently, while large values of ${\nu }_{\mathrm{dyn}}(K^{\pm },K_s^0)$ may not be sufficient to identify the existence of DCCs, they nonetheless constitute a first and necessary condition to signal their possible production in heavy-ion collisions.

We report first measurements of the $\beta$-neutrino angular correlation based on the kinetic-energy shift of protons emitted in parallel or antiparallel directions with respect to the positron in the beta decay of ${}^{32}\mathrm{Ar}$. This proof of principle experiment performed at ISOLDE-CERN provided simultaneous measurements for both a superallowed $0^{+}\to 0^{+}$ transition and a Gamow-Teller transition followed by proton emission. The results, respectively ${\tilde{a}}_{\beta \nu }=1.007{\left(32\right)}_{\mathrm{stat}}{\left(25\right)}_{\mathrm{syst}}$ and ${\tilde{a}}_{\beta \nu }=-0.222{\left(86\right)}_{\mathrm{stat}}{\left(16\right)}_{\mathrm{syst}}$, are found in agreement with the standard model. The analysis of the data shows that future measurements can reach a precision level of ${10}^{-3}$ for both pure Fermi and pure Gamow-Teller decay channels, providing new constraints on exotic weak interactions.

Recent investigations have emphasized the importance of uncertainty quantification (UQ) in nuclear theory. We carry out UQ for configuration-interaction shell-model calculations in the $1s\text{−}0d$ valence space, investigating the sensitivity of observables to perturbations in the 66 parameters (matrix elements) of a high-quality empirical interaction. The large parameter space makes computing the corresponding Hessian numerically costly, so we compare a cost-effective approximation, using the Feynman-Hellmann theorem, to the full Hessian and find it works well. Diagonalizing the Hessian yields the principal components of the interaction: linear combinations of parameters ordered by sensitivity. This approximately decoupled distribution of parameters facilitates theoretical uncertainty propagation onto structure observables: electromagnetic transitions, Gamow-Teller decays, and dark matter-nucleus scattering matrix elements.

The $1^{+}$ spectrum of ${}^{130}\mathrm{In}$ populated in the $\beta$ decay of ${}^{130}\mathrm{Cd}$ is studied. The coupling between one- and two-phonon terms in the wave functions of $1^{+}$ states is taken into account within the microscopic model based on the Skyrme interaction. The approach enables one to perform the calculations in very large configurational spaces. The new calculation is extended by enlarging the variational space for the $1^{+}$ states with the inclusion of the two-phonon configurations. The dominant contribution to the additional $1^{+}$ states comes from the ${[3^{+}\otimes 2^{+}]}_{\text{QRPA}}$ two-phonon configurations constructed from the charge-exchange $3^{+}$ phonons. A correlation is found between the low-lying $E2$ transition strengths of the parent and daughter isobaric companions. Using the same set of parameters this correlation is studied also for ${}^{126,128}\mathrm{In}$ and ${}^{126,128}\mathrm{Cd}$.

Recent data on the production of $D$ mesons and ${\mathrm{\Lambda }}_c^{+}$ baryons in heavy ion collisions at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider exhibit a number of striking characteristics such as enhanced yield ratios $D_s^{+}/D^0$ and ${\mathrm{\Lambda }}_c^{+}/D^0$ and their transverse momentum dependencies. In this article, we derive the momentum dependence of open charm mesons and singly charmed baryons produced in ultrarelativistic heavy ion collisions via the equal-velocity quark combination. We present analytic expressions and numerical results of yield ratios and compare them with the experimental data available. We make predictions for other charmed hadrons.

We report the measurement of the parity-violating asymmetry for the inelastic scattering of electrons from the proton, at $Q^2=0.082{\mathrm{GeV}}^2$ and $W=2.23$ GeV, above the resonance region. The result $A_{\mathrm{Inel}}=-13.5\pm 2.0\left(\mathrm{stat}\right)\pm 3.9\left(\mathrm{syst}\right)$ ppm agrees with theoretical calculations, and helps to validate the modeling of the $\gamma Z$ interference structure functions $F_1^{\gamma Z}$ and $F_2^{\gamma Z}$ used in those calculations, which are also used for determination of the two-boson exchange $\gamma \text{−}Z$ box diagram (${\square }_{\gamma Z}$) contribution to parity-violating elastic scattering measurements. A positive parity-violating asymmetry for inclusive ${\pi }^{-}$ production was observed, as well as positive beam-normal single-spin asymmetry for scattered electrons and a negative beam-normal single-spin asymmetry for inclusive ${\pi }^{-}$ production.

The kernel ridge regression (KRR) approach is employed to improve the nuclear mass predictions for the first time, and more importantly, a careful study of the expected predictive power in the neutron-rich region of the nuclear chart is presented, which is crucial for astrophysical simulations of nucleosynthesis processes. The ridge penalty influences the optimized kernel function significantly and plays an essential role in reducing the risk of overfitting and improving the accuracy of the predictions. By taking the WS4 mass model as an example, the mass for each nucleus in the nuclear chart is predicted with the KRR network, which is trained with the mass model residuals, i.e., deviations between experimental and calculated masses, of other nuclei with known masses. The resultant root-mean-square mass deviation from the available experimental data for the 2353 nuclei with $Z\ge 8$ and $N\ge 8$ can be reduced to 199 keV. This is at the same level with other machine-learning-rooted approaches, such as the radial basis function and Bayesian neural network approaches. However, with the Gaussian kernel, the present KRR approach provides strikingly different extrapolated masses for nuclei with unknown masses, since it automatically identifies the limit of the extrapolation distance. Therefore, it avoids the risk of worsening the mass description for nuclei at large extrapolation distances.