Since He et al. [J. J. He et al., Phys. Lett. B 725, 287 (2013)] postulated the existence of a new, low-lying, broad resonance in the ${}^6\mathrm{Li}(p,\gamma ){}^7\mathrm{Be}$ reaction, there have been several studies that have looked to further investigate this assertion. However, none of these approaches has utilized the stringent constraint imposed by the unitarity of the scattering matrix. That is, the corresponding compound nucleus state must produce a corresponding resonance in ${}^3\mathrm{He}(\alpha ,\alpha ){}^3\mathrm{He}$ and ${}^6\mathrm{Li}(p,p){}^7\mathrm{Li}$ scattering and the ${}^6\mathrm{Li}(p,\alpha ){}^3\mathrm{He}$ reaction. Since precision data are readily available in the literature, the level of consistency can be tested using a phenomenological $R$-matrix analysis. In addition, remaining discrepancies with the description of the ${}^6\mathrm{Li}(p,\gamma ){}^7\mathrm{Be}$ reaction are discussed.

A dedicated isochronous storage ring, named the Rare-RI Ring, was constructed at the RI Beam Factory of RIKEN, aiming at precision mass measurements of nuclei located in uncharted territories of the nuclear chart. The Rare-RI Ring employs the isochronous mass spectrometry technique with the goal to achieve a relative mass precision of ${10}^{-6}$ within a measurement time of less than 1 ms. The performance of the facility was demonstrated through mass measurements of neutron-rich nuclei with well-known masses. Velocity or magnetic rigidity is measured for every particle prior to its injection into the ring, wherein its revolution time is accurately determined. The latter quantity is used to determine the mass of the particle, while the former one is needed for nonisochronicity corrections. Mass precisions on the order of ${10}^{-5}$ were achieved in the first commissioning, which demonstrates that the Rare-RI Ring is a powerful tool for mass spectrometry of short-lived nuclei.

The interplay between the ${}^{22}\mathrm{Ne}(\alpha ,\gamma ){}^{26}\mathrm{Mg}$ reaction and the competing ${}^{22}\mathrm{Ne}(\alpha ,n){}^{25}\mathrm{Mg}$ reaction determines the efficiency of the latter as a neutron source at the temperatures of stellar helium burning. In both cases, the rates are dominated by the $\alpha$-cluster resonance at 830 keV. This resonance plays a particularly important role in determining the strength of the neutron flux for both the weak and main $s$ process as well as the $n$ process. Recent experimental studies based on transfer reactions suggest that the neutron and $\gamma$-ray strengths for this resonance are approximately equal. In this study, the ${}^{22}\mathrm{Ne}(\alpha ,n){}^{25}\mathrm{Mg}$ resonance strength has been remeasured and found to be similar to the previous direct studies. This reinforces an 830 keV resonance strength that is approximately a factor of 3 larger for the ${}^{22}\mathrm{Ne}(\alpha ,n){}^{25}\mathrm{Mg}$ reaction than for the ${}^{22}\mathrm{Ne}(\alpha ,\gamma ){}^{26}\mathrm{Mg}$ reaction.

The exploration of nuclear mass or binding energy, a fundamental property of atomic nuclei, remains at the forefront of nuclear physics research due to limitations in experimental studies and uncertainties in model calculations, particularly when moving away from the stability line. In this work, we employ two machine learning (ML) models, support vector regression (SVR) and Gaussian process regression (GPR), to assess their performance in predicting nuclear mass excesses using available experimental data and a physics-based feature space. We also examine the extrapolation capabilities of these models using newly measured nuclei from AME2020 and by extending our calculations beyond the training and test set regions. Our results indicate that both SVR and GPR models perform quite well within the training and test regions when informed with a physics-based feature space. Furthermore, these ML models demonstrate the ability to make reasonable predictions away from the available experimental data, offering results comparable to the model calculations. Through further refinement, these models can be used as reliable and efficient ML tools for studying nuclear properties in the future.

A global Bayesian analysis of relativistic $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=2.76\mathrm{TeV}$ is performed, using a multistage model consisting of an ip-glasma initial state, a viscous fluid dynamical evolution, and a hadronic transport final state. The observables considered are from the soft sector hadronic final state. Posterior and maximum a posteriori parameter distributions that pertain to the ip-glasma and hydrodynamic phases are obtained, including the shear and bulk specific viscosity of strong interacting matter. The first use of inference with transfer learning in heavy-ion analyses is presented, together with Bayes model averaging.

We sample the posterior probability distributions of the low-energy constants (LECs) in $\mathrm{\Delta }$-full chiral effective field theory $\left(\chi \mathrm{EFT}\right)$ up to third order. We use eigenvector continuation for fast and accurate emulation of the likelihood and Hamiltonian Monte Carlo to draw effectively independent samples from the posteriors. Our Bayesian inference is conditioned on the Granada database of neutron-proton ($np$) cross sections and polarizations. We use priors grounded in $\chi \mathrm{EFT}$ assumptions and a Roy-Steiner analysis of pion-nucleon scattering data. We model correlated EFT truncation errors using a two-feature Gaussian process, and find correlation lengths for $np$ scattering energies and angles in the ranges 45–83 MeV and 24–39 degrees, respectively. These correlations yield a nondiagonal covariance matrix and reduce the number of independent scattering data with factors of 8 and 4 at the second and third chiral orders, respectively. The relatively small difference between the second- and third-order predictions in $\mathrm{\Delta }$-full $\chi \mathrm{EFT}$ suppresses the marginal variance of the truncation error and the effects of its correlation structure. Our results are particularly important for analyzing the predictive capabilities in ab initio nuclear theory.

From the observation of both heavy neutron stars and light ones with small radii, one anticipates a steep rise in the speed of sound of nuclear matter as a function of baryon density up to values close to the causal limit. A question follows whether such behavior of the speed of sound in neutron-rich matter is compatible with the equation of state extracted from low-energy heavy-ion collisions. In this work, we consider a family of neutron-star equations of state characterized by a steep rise in the speed of sound, and use the symmetry energy expansion to obtain equations of state applicable to the almost-symmetric nuclear matter created in heavy-ion collisions. We then compare collective flow data from low-energy heavy-ion experiments with results of simulations obtained using the hadronic transport code smash with the mean-field potential reproducing the density-dependence of the speed of sound. We show that equations of state featuring a peak in the speed of sound squared occurring at densities between $2\text{–}3$ times the saturation density of normal nuclear matter, producing neutron stars of nearly $M_{\text{max}}\approx 2.5M_{\odot }$, are consistent with heavy-ion collision data.

Background: The inner crust of neutron stars consists of a Coulomb lattice of neutron-rich nuclei, immersed in a sea of superfluid neutrons with background relativistic electron gas. A proper quantum-mechanical treatment for such a system under a periodic potential is the band theory of solids. The effect of band structure on the effective mass of dripped neutrons, the so-called entrainment effect, is currently in a debatable situation, and it has been highly desired to develop a microscopic nuclear band theory taking into account neutron superfluidity in a fully self-consistent manner.

Purpose: The main purpose of the present work is twofold: (1) to develop a formalism of the time-dependent self-consistent band theory, taking fully into account nuclear superfluidity, based on time-dependent density-functional theory (TDDFT) extended for superfluid systems, and (2) to quantify the effects of band structure and superfluidity on the entrainment phenomenon, applying the formalism to the slab phase of the inner crust of neutron stars.

Methods: The fully self-consistent time-dependent band theory, proposed in a previous work [Phys. Rev. C 105, 045807 (2022)], is extended to superfluid systems. To this end, a superfluid TDDFT with a local treatment of pairing, known as time-dependent superfluid local density approximation, is formulated in the coordinate space with a Skyrme-type energy density functional, adopting the Bloch's boundary condition. A real-time method is employed to extract the collective masses of a slab and of protons, which in turn quantify the conduction neutron number density and the neutron effective mass, i.e., the entrainment effect.

Results: Static calculations have been performed for a range of baryon number density ($n_{\text{b}}=0.04\text{–}0.07{\mathrm{fm}}^{-3}$) under the $\beta$-equilibrium condition with and without superfluidity, for various interslab spacings. From the results, we find that the system gains energy through the formation of Cooper pairs for all densities examined, which supports the existence of superfluidity in the inner crust of cold neutron stars. From a response of the system to an external potential, we dynamically extract the collective masses of a slab and of protons immersed in neutron superfluid. The obtained results show the collective mass of a slab is substantially reduced by 57.5%–82.5% for $n_{\text{b}}=0.04\text{–}0.07{\mathrm{fm}}^{-3}$, which corresponds to an enhancement of conduction neutron number density and, thus, to a reduction of the neutron effective mass, which we call the anti-entrainment effect. A comparison of the results with and without superfluidity reveals that superfluidity slightly enhances the anti-entrainment effects for the slab phase of neutron-star matter. We discuss a novel phenomenon associated with superfluidity, that is, quasiparticle resonances in the inner crust, which are absent in normal systems.

Conclusions: Our fully self-consistent, microscopic, superfluid band theory calculations based on (TD)DFT showed that the effective mass of dripped neutrons is reduced by about 20%–40% for $n_{\text{b}}=0.04\text{–}0.07{\mathrm{fm}}^{-3}$ because of the band-structure effects, and superfluidity slightly $\mathit{enhances}$ the reduction.

The presence of ${}^{240}\mathrm{Pu}$ in nuclear fuels for reactors has resulted in high uncertainties in the results of reactor and nuclear transmutation calculations because of deficiencies in ${}^{240}\mathrm{Pu}$-related nuclear data. Specifically for the prompt fission neutron spectrum (PFNS) of ${}^{240}\mathrm{Pu}$, there is only one neutron-induced, ($n,f$), measurement at 0.85 MeV incident neutron energy and only one complete spontaneous fission, (sf), measurement. This limited availability of data does not sufficiently guide nuclear data evaluations of these quantities. Here, we report on a measurement of both the ${}^{240}\mathrm{Pu}$(sf) and the ${}^{240}\mathrm{Pu}(n,f$) PFNS, both over the emitted neutron energy range of 0.79–10.0 MeV, and from incident neutron energies of 1.0–20.0 MeV for the ($n,f$) reaction. Measurements were made with a hemispherical array of liquid scintillators at the high-energy Los Alamos Neutron Science Center white neutron source at the Weapons Neutron Research facility as part of the joint LANL-LLNL Chi-Nu experimental campaign to measure actinide fission neutron spectra. These measurements are the first of their kind, and provide clear experimental evidence for second-chance fission, third-chance fission, and pre-equilibrium neutron emission processes in neutron-induced fission of ${}^{240}\mathrm{Pu}$, and are the first ever measurements above 1 MeV incident neutron energy.

A relativistic microscopic optical model potential for nucleon-nucleus scattering is developed based on the ab initio relativistic Brueckner-Hartree-Fock (RBHF) theory with the improved local density approximation, which is abbreviated as the RBOM potential. Both real and imaginary parts of the single-particle potentials in symmetric and asymmetric nuclear matter at various densities are determined uniquely in the full Dirac space. The density distributions of the target nuclei are calculated by the covariant energy density functional theory with the density functional PC-PK1. The central and spin-orbit terms of the optical potentials are quantitatively consistent with the relativistic phenomenological optical potentials. The performance of the RBOM potential is evaluated by considering proton scattering with incident energy $E\le 200$ MeV on five target nuclei, ${}^{208}\mathrm{Pb}, {}^{120}\mathrm{Sn}, {}^{90}\mathrm{Zr}, {}^{48}\mathrm{Ca}$, and ${}^{40}\mathrm{Ca}$. Scattering observables including the elastic scattering angular distributions, analyzing powers, spin rotation functions, and reaction cross sections are analyzed. Theoretical predictions show good agreements with the experimental data and the results derived from phenomenological optical potentials. We anticipate that the RBOM potential can provide reference for other phenomenological and microscopic optical model potentials, as well as reliable descriptions for nucleon scattering on exotic nuclei in the era of rare-isotope beams.

Reaction processes in muon catalyzed fusion ($\mu \mathrm{CF}$), ${\left(dt\mu \right)}_{J=v=0}\to \alpha +n+\mu +17.6\mathrm{MeV}$ or ${\left(\alpha \mu \right)}_{nl}+n+17.6\mathrm{MeV}$ in a deuterium-tritium (D-T) mixture were comprehensively studied by Kamimura, Kino, and Yamashita [Phys. Rev. C 107, 034607 (2023)] by solving the $dt\mu \text{−}\alpha n\mu$ coupled channel (CC) Schrödinger equation under a boundary condition where the muonic molecule ${\left(dt\mu \right)}_{J=v=0}$ was set as the initial state and the outgoing wave was in the $\alpha n\mu$ channel. We approximate this CC framework and propose a considerably more tractable model using the $T$-matrix method based on the Lippmann-Schwinger equation. Nuclear interactions adopted in the $T$-matrix model are determined by reproducing the cross section of the reaction $d+t\to \alpha +n+17.6\mathrm{MeV}$ at low energies. The cross section of the strong-coupling rearrangement reaction is presented in a simple closed form based on our new model. This $T$-matrix model has reproduced most of the calculated results on the above $\mu \mathrm{CF}$ reaction reported by Kamimura et al. (2023) and is applicable to other $\mu \mathrm{CF}$ systems such as $\left(dd\mu \right), \left(tt\mu \right), {\left(dt\mu \right)}^{*}, {\left(dd\mu \right)}^{*}$.

Recent discussions about the origin of the so-called gallium anomaly have motivated a remeasurement of the half-life of ${}^{71}\mathrm{Ge}$. We have conducted three separate measurements using dedicated planar Ge detectors—one with ${}^{55}\mathrm{Fe}$ as a standard, one with ${}^{57}\mathrm{Co}$ as a standard, and one standalone ${}^{71}\mathrm{Ge}$ measurement. Our results yield a half-life of $11.468\pm 0.008$ days, which is consistent with, but significantly more precise than, the currently accepted value. With this experiment, the potential explanation of the gallium anomaly being due to an unexpectedly long ${}^{71}\mathrm{Ge}$ half-life has been ruled out, leaving the anomaly's origin as an open question.

Exact solutions to the equations of hydrodynamics provide valuable benchmark tests for numerical hydrodynamic codes and also provide useful insights into the nature of hydrodynamic flow. In this paper, we introduce two novel, closely related exact solutions with nontrivial rapidity dependence which are generalizations of the well-known Gubser flow solution to conformal hydrodynamics. We then use one of our solutions to explore the consequences of choosing between two different criteria for implementing the freeze-out process in fluid dynamical simulations of nuclear collisions: freeze-out at constant temperature vs freeze-out at constant Knudsen number. We find that, employing our exact solution, the differences between these freeze-out criteria are heavily influenced by the presence of strong collective flow. Our results highlight the importance of accurately describing the freeze-out process in collisions with large flow gradients, particularly in small systems.

We report on the first experimental measurements made at a magnetic confinement fusion device of the tritium(T)-tritium(T) reaction $\text{T}+\text{T}\to {}^4\mathrm{He}+2n$ indicating the presence of the intermediate two-body resonant reaction $\text{T}+\text{T}\to {}^5\mathrm{He}+n$. During the second deuterium-tritium campaign (DTE2) at the Joint European Torus, measurements of fusion plasmas with high tritium concentrations, $n_{\text{T}}/(n_{\text{T}}+n_{\text{D}})\approx 0.99$, heated with tritium neutral beam injection, were performed using the neutron time-of-flight (TOF) spectrometer TOFOR. We detect a peak in the neutron emission TOF spectrum consistent with the two-body resonant reaction. The TT neutron emission energy spectrum is modeled using an $R$-matrix framework where the distributions of the most likely model parameters given our experimental TOF data are determined utilizing a Markov chain Monte Carlo approach. We compare our best estimate of the $\text{T}+\text{T}$ neutron emission energy spectrum with results obtained at inertial confinement fusion experiments at the OMEGA facility and find a spectral shape that is consistent with the energy dependency in the neutron spectrum observed at OMEGA.

A new data set for the helicity-dependent differential cross section of the single-meson photoproduction reaction $\gamma p\to p{\pi }^0$ was obtained for the photon energy interval 150–400 MeV. The experiment was performed at the A2 tagged photon facility of the Mainz Microtron MAMI using a circularly polarized photon beam and a longitudinally polarized proton target. The reaction products were detected with the large-acceptance Crystal Ball and TAPS calorimeters covering 97% of the full solid angle. These new results, obtained with a fine energy and polar angle binning, greatly increase both the existing quantity and quality of the data available for this observable. A moment analysis, based on a finite expansion in Legendre polynomials, was applied to these data by using a bootstrap-based fitting method to correctly account for their systematic uncertainties. From the resulting decomposition of the differential cross sections, the $E2/M1$ ratio for the $N\to \mathrm{\Delta }\left(1232\right)$ transition was determined to be $[-2.38\pm 0.16(\mathrm{stat}.+\mathrm{sys}.)\pm 0.10\text{(model)}]\%$. Combining this value with previous results also allowed us to evaluate the most precise available estimate of the $E2/M1$ ratio to be used for all further reference and model comparisons.

We present a comprehensive reevaluation of the $ft$ values in superallowed nuclear $\beta$ decays crucial for the precise determination of $V_{ud}$ and low-energy tests of the electroweak standard model. It consists of the first, fully data-driven analysis of the nuclear $\beta$ decay form factor, that utilizes isospin relations to connect the nuclear charged weak distribution to the measurable charge distributions. This prescription supersedes previous shell-model estimations, and allows for a rigorous quantification of theory uncertainties in $f$ which is absent in the existing literature. Our new evaluation shows an overall downward shift of the central values of $f$ at the level of 0.01%.

Neutron transmission experiments can offer a new type of highly sensitive search for time-reversal invariance violating (TRIV) effects in nucleon-nucleon interactions via the same enhancement mechanism observed for large parity violating (PV) effects in neutron-induced compound nuclear processes. In these compound processes, the TRIV cross section is given as the product of the PV cross section, a spin factor $\kappa$, and a ratio of TRIV and PV matrix elements. We determined $\kappa$ to be $0.59\pm 0.05$ for ${}^{139}\mathrm{La}+n$ using both $(n,\gamma )$ spectroscopy and ($\vec{n}+{}^{139}\overrightarrow{\mathrm{La}}$) transmission. This result quantifies for the first time the high sensitivity of the ${}^{139}\mathrm{La}$ 0.75-eV $p$-wave resonance in a future search for effects of $P$-odd/$T$-odd interactions in ($\vec{n}+{}^{139}\overrightarrow{\mathrm{La}}$) forward transmission.

We calculate the ${}^{16}\mathrm{O}$ spectral function by combining coupled-cluster theory with a Gaussian integral transform and by expanding the integral kernel in terms of Chebyshev polynomials to allow for a quantification of the theoretical uncertainties. We perform an analysis of the spectral function and employ it to predict lepton-nucleus scattering. Our results well describe the ${}^{16}\mathrm{O}$ electron-scattering data in the quasielastic peak for momentum transfers $\left|\mathbf{q}\right|⪆500$ MeV and electron energies up to 1.2 GeV, extending, therefore, the so-called first-principles approach to lepton-nucleus cross sections well into the relativistic regime. To prove the applicability of this method to neutrino-nucleus cross sections, we implement our ${}^{16}\mathrm{O}$ spectral functions in the nuwro Monte Carlo event generator and provide a comparison with recently published T2K neutrino data.

We adapt the proton-neutron finite-amplitude method, which in its original form is an efficient implementation of the Skyrme quasiparticle random phase approximation, to include the coupling of quasiparticles to like-particle phonons. The approach allows us to add beyond-quasiparticle random-phase approximation correlations to computations of Gamow-Teller strength and $\beta$-decay rates in deformed nuclei for the first time. We test the approach in several deformed isotopes for which measured strength distributions are available. The additional correlations dramatically improve agreement with the data, and will lead to improved global $\beta$-decay rates.

Examination of high-resolution, experimental fusion excitation functions for ${}^{16,17,18}\mathrm{O}+{}^{12}\mathrm{C}$ reveals a remarkable irregular behavior that is rooted in the structure of both the colliding nuclei and the quasimolecular composite system. The impact of the $\ell$-dependent fusion barriers is assessed using a time-dependent Hartree-Fock model, viewed as a mean-field reference. Barrier penetrabilities, taken directly from a density-constrained calculation, provide a significantly improved description of the experimental data as compared to the standard Hill-Wheeler approach. The remaining deviations between the parameter-free theoretical mean-field predictions and experimental fusion cross sections are exposed and discussed.