Mass measurements with the ISOLTRAP mass spectrometer at CERN-ISOLDE improve mass uncertainties of neutron-deficient tin isotopes towards doubly magic ${}^{100}\mathrm{Sn}$. The mass uncertainty of ${}^{103}\mathrm{Sn}$ was reduced by a factor of 4, and the new value for the mass excess of $-67104\left(18\right)\mathrm{k}\mathrm{e}\mathrm{V}$ is compared with nuclear ab initio and density functional theory calculations. Based on these results and local trends in the mass surface, the masses of ${}^{101,103}\mathrm{Sn}$, as determined through their $Q_{\text{EC}}$ values, were found to be inconsistent with the new results. From our measurement for ${}^{103}\mathrm{Sn}$, we extrapolate the mass excess of ${}^{101}\mathrm{Sn}$ to $-60005\left(300\right)\mathrm{k}\mathrm{e}\mathrm{V}$, which is significantly less bound than previously suggested. By correcting the mass values for ${}^{101,103}\mathrm{Sn}$, we also adjust the values of ${}^{104}\mathrm{Sb}, {}^{105,107}\mathrm{Te}, {}^{108}\mathrm{I}, {}^{109,111}\mathrm{Xe}$, and ${}^{112}\mathrm{Cs}$ near the proton drip line which are connected through their $\alpha$ and proton $Q$ values. The results show an overall smoothening of the mass surface, suggesting the absence of deformation energy above the $N=50$ shell closure.

The equation of state of nuclear matter, momentum dependence of the effective interaction and in-medium modification of elastic nucleon-nucleon cross sections are studied by comparing theoretical predictions for stopping, directed, and elliptic flows of protons and light clusters in intermediate-energy heavy-ion collisions of beam energy between 150 and 800 MeV per nucleon to experimental data gathered by the FOPI Collaboration. To that end, the dcQMD transport model was upgraded by implementing medium modifications of differential elastic cross sections guided by microscopical model calculations, a medium modification factor of elastic transition amplitudes that depends on the local density, isospin asymmetry, and isospin projection of the scattering particles, a MST coalescence algorithm applied at the local freeze-out rather than at the end of simulation and threshold effects for elastic scattering. A multivariate analysis that takes into account systematic uncertainties induced on model predictions by the coalescence afterburner leads to the following constraint for the equation of state at 68% confidence level: compressibility modulus of isospin symmetric matter $K_0={230}_{-11}^{+9}\mathrm{MeV}$ and slope of the symmetry energy $L={63}_{-13}^{+10}\mathrm{MeV}$. The momentum dependence of the isoscalar potential is found to be similar to that of the empirical optical potential, with an effective isoscalar mass $m^{*}=0.{695}_{-0.018}^{+0.014}$. The isovector potential displays a momentum dependence corresponding to a positive neutron-proton effective mass difference $\mathrm{\Delta }{m}_{np}^{*}=(0.{17}_{-0.09}^{+0.10})\delta$, close to the world average for this quantity. A suppression of elastic nucleon-nucleon cross sections in symmetric nuclear matter at saturation by about $60\%$ relative to vacuum values is deduced, in qualitative agreement with microscopical results. A strong dependence of the suppression factor on isospin asymmetry is evidenced, experimental data for isospin symmetric systems proving crucial for this last conclusion.

The PHENIX experiment measured the centrality dependence of two-pion Bose-Einstein correlation functions in $\sqrt{s_{NN}}=200\mathrm{GeV} \mathrm{Au}+\mathrm{Au}$ collisions at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The data are well represented by Lévy-stable source distributions. The extracted source parameters are the correlation-strength parameter $\lambda$, the Lévy index of stability $\alpha$, and the Lévy-scale parameter $R$ as a function of transverse mass $m_T$ and centrality. The $\lambda \left(m_T\right)$ parameter is constant at larger values of $m_T$, but decreases as $m_T$ decreases. The Lévy-scale parameter $R\left(m_T\right)$ decreases with $m_T$ and exhibits proportionality to the length scale of the nuclear overlap region. The Lévy exponent $\alpha \left(m_T\right)$ is independent of $m_T$ within uncertainties in each investigated centrality bin, but shows a clear centrality dependence. At all centralities, the Lévy exponent $\alpha$ is significantly different from that of Gaussian ($\alpha =2$) or Cauchy ($\alpha =1$) source distributions. Comparisons to the predictions of Monte-Carlo simulations of resonance-decay chains show that, in all but the most peripheral centrality class (50%–60%), the obtained results are inconsistent with the measurements, unless a significant reduction of the in-medium mass of the ${\eta }^{\prime }$ meson is included. In each centrality class, the best value of the in-medium ${\eta }^{\prime }$ mass is compared to the mass of the $\eta$ meson, as well as to several theoretical predictions that consider restoration of ${\text{U}}_A\left(1\right)$ symmetry in hot hadronic matter.

A comparative study of the equation of state for pure neutron matter and symmetric nuclear matter is presented using three ab initio methods based on diagrammatic expansions: coupled-cluster theory, self-consistent Green's functions, and many-body perturbation theory. We critically evaluate these methods by employing different chiral potentials at next-to-next-to-leading-order (NNLO)—all of which include both two- and three-nucleon contributions—and by exploring various many-body truncations. Our investigation yields highly precise results for pure neutron matter and robust predictions for symmetric nuclear matter, particularly with soft interactions. Moreover, the new calculations demonstrate that the ${\mathrm{NNLO}}_{\mathrm{sat}}\left(450\right)$ and $\mathrm{\Delta }{\mathrm{NNLO}}_{\mathrm{go}}\left(394\right)$ potentials are consistent with the empirical constraints on the saturation point of symmetric nuclear matter. Additionally, this benchmark study reveals that diagrammatic expansions with similar architectures lead to consistent many-body correlations, even when applied across different methods. This consistency underscores the robustness of the diagrammatic approach in capturing the essential physics of nucleonic systems.

We present quantum Monte Carlo calculations of magnetic moments, form factors, and densities of $A\le 10$ nuclei within a chiral effective field theory approach. We use the Norfolk two- and three-body chiral potentials and their consistent electromagnetic one- and two-nucleon current operators. We find that two-body contributions to the magnetic moment can be large (up to $\approx 33\%$ in $A=9$ systems). We study the model dependence of these observables and place particular emphasis on investigating their sensitivity to using different cutoffs to regulate the many-nucleon operators. Calculations of elastic magnetic form factors for $A\le 10$ nuclei show excellent agreement with the data out to momentum transfers $q\approx 3{\mathrm{fm}}^{-1}$.

Nuclear fission at barrier-top energies is conventionally modeled by a one-dimensional Schrödinger equation applied to internal fission channels, but that treatment is hard to justify in the configuration-interaction approach to nuclear Hamiltonians. Here we show that inclusion of states of finite momentum by the generator coordinate method (GCM) considerably extends the range of energies at which GCM-based Hamiltonians could reproduce the Schrödinger treatment. The transmission probabilities for crossing the barrier are calculated by a discrete version of Kohn's variational method, which may also be useful for other systems of interacting fermions.

Radiative corrections are essential for an accurate determination of $V_{ud}$ from superallowed $\beta$ decays. In view of recent progress in the single-nucleon sector, the uncertainty is dominated by the theoretical description of nucleus-dependent effects, limiting the precision that can currently be achieved for $V_{ud}$. In this work, we provide a detailed account of the electroweak corrections to superallowed $\beta$ decays in effective field theory (EFT), including the power counting, potential and ultrasoft contributions, and factorization in the decay rate. We present a first numerical evaluation of the dominant corrections in light nuclei based on quantum Monte Carlo methods, confirming the expectations from the EFT power counting. Finally, we discuss strategies how to extract from data the low-energy constants that parametrize short-distance contributions and whose values are not predicted by the EFT. Combined with advances in ab initio nuclear-structure calculations, this EFT framework allows one to systematically address the dominant uncertainty in $V_{ud}$, as illustrated in detail for the ${}^{14}\mathrm{O}\to {}^{14}\mathrm{N}$ transition.

We present event-by-event simulations for central asymmetric $\text{light}+\text{heavy}$ and $\mathrm{Au}+\mathrm{Au}$ collisions to investigate the formation and evolution of vortex-ring structures in the longitudinal flow velocity profile. The production-plane polarization of $\mathrm{\Lambda }$ hyperons, defined with respect to the $\mathrm{\Lambda }$ momentum and the beam, can track the “vortex-ring” feature in the event, a characteristic vortical structure generated by longitudinal flow gradients. We make comprehensive model predictions for the rapidity-dependent vortex-ring observables for different collision system sizes at $\sqrt{s_{NN}}=200$ and 72 GeV. Our predictions at the latter energy can be explored in the future LHCb fixed-target experiment at the Large Hadron Collider.

We investigate the charge and point-proton radii of Ca nuclei in detail using a density functional theory framework. The Fayans energy density functional (EDF) provides a characteristic $N$ dependence, successfully describing the parabolic behavior of the differential charge radii in $20\le N\le 28$. We focus on its physical origin by decomposing it into radial and orbital contributions. The results are compared with those of the Skyrme plus normal pairing functional, which is considered as a representative of the usual EDFs. The enhancement of the differential charge radii in $N<20$ with the Fayans functional, which contradicts the data, has the origin common to the parabolic behavior in $20\le N\le 28$. It is important to describe both $N$ regions simultaneously.

We calculate the magnetic dipole $\gamma$-ray strength functions in a chain of even-mass neodymium isotopes ${}^{144–152}\mathrm{Nd}$ in the framework of the configuration-interaction (CI) shell model. We infer the strength function by applying the maximum entropy method (MEM) to the exact imaginary-time response function calculated with the shell-model Monte Carlo (SMMC) method. The success of the MEM depends on the choice of a good strength function as a prior distribution. We investigate two choices for the prior strength function: the static path approximation (SPA) and the quasiparticle random-phase approximation (QRPA). We find that the QRPA is a better approximation at low temperatures (i.e., near the ground state), while the SPA is a better choice at finite temperatures. We identify a low-energy enhancement (LEE) in the MEM deexcitation $M1$ strength functions of the even-mass neodymium isotopes and compare with recent experimental results for the total deexcitation $\gamma$-ray strength functions. The LEE is already seen in the SPA strength function but not in the QRPA strength function, indicating the importance of large-amplitude static fluctuations around the mean field in reproducing the LEE. Our method is currently the only one that can reproduce LEE in heavy open-shell nuclei where conventional CI shell-model calculations are prohibited. With the onset of deformation as number of neutrons increases along the chain of neodymium isotopes, we observe that some of the LEE strength transfers to a low-energy excitation, which we interpret as a finite-temperature scissors mode. We also observe a finite-temperature spin-flip mode.

This work presents a Bayesian inference study for relativistic heavy-ion collisions in the beam energy scan program at the BNL Relativistic Heavy-Ion Collider. The theoretical model simulates event-by-event $(3+1)$-dimensional $\left[(3+1)\text{D}\right]$ collision dynamics using hydrodynamics and hadronic transport theory. We analyze the model's 20-dimensional posterior distributions obtained using three model emulators with different accuracy and demonstrate the essential role of training an accurate model emulator in the Bayesian analysis. Our analysis provides robust constraints on the quark-gluon plasma's transport properties and various aspects of $(3+1)\text{D}$ relativistic nuclear dynamics. By running full model simulations with 100 parameter sets sampled from the posterior distribution, we make predictions for $p_{\mathrm{T}}$-differential observables and estimate their systematic theory uncertainty. A sensitivity analysis is performed to elucidate how individual experimental observables respond to different model parameters, providing useful physics insights into the phenomenological model for heavy-ion collisions.

Nuclear excitation by electron capture (NEEC) is a theoretically envisioned yet experimentally unverified process that intricately links nuclear and electronic degrees of freedom. For nearly five decades, the experimental validation of NEEC has remained elusive, primarily hindered by challenges in excitation and detection methodologies. This study proposes a laser-based strategy for verifying NEEC, exploiting the isomeric excitation of the ${}^{235}\mathrm{U}$ nucleus within a laser-cluster interaction scheme. With proper laser parameters, NEEC overwhelmingly dominates, constituting over 99.9% of the isomeric excitation yield. The long lifetime of the ${}^{235}\mathrm{U}$ isomer allows detection without interfering atomic background. Additionally, distinctive dependencies of isomeric excitation yield on laser parameters provide further confirmation for the NEEC mechanism.

We investigate the dynamics of dilute systems composed of nucleons and light clusters within a linear response approach, taking into account the in-medium Mott effects on cluster appearance, through a density-dependent momentum cut-off. We find that spinodal instabilities and associated growth rates are severely affected by the presence of light clusters and, in particular, by the treatment of in-medium effects, foreshadowing intriguing consequences for fragment formation in heavy-ion collisions and in the broader astrophysical context.

We study dark matter, assumed to be composed of weak interacting massive particles (WIMPs), scattering off ${}^2\mathrm{H}$ and ${}^4\mathrm{He}$ nuclei. In order to parametrize the WIMP-nucleon interaction, the chiral effective field theory approach is used. Considering only interactions invariant under parity, charge conjugation, and time reversal, we examine five interaction types: scalar, pseudoscalar, vector, axial, and tensor. Scattering amplitudes between two nucleons and a WIMP are determined up to second order of chiral perturbation theory. We apply this program to calculate the interaction rate as a function of the WIMP mass and of the magnitude of the WIMP-quark coupling constants. From our study, we conclude that the scalar nuclear response functions is much greater than the others due to their large combination of low energy constants. We verify that the leading order contributions are dominant in these low energy processes. We also provide an estimate for the background due to atmospheric neutrinos.

We report on the observation of the previously unknown isotope ${}^{21}\mathrm{Al}$, the first unbound aluminum isotope located beyond the proton dripline. The ${}^{21}\mathrm{Al}$ nucleus decays by one-proton ($1p$) emission, and its in-flight decays were detected by tracking trajectories of the decay products with silicon microstrip detectors. The $1p$-emission processes were studied by analyzing the measured angular correlations of decay products ${}^{20}\mathrm{Mg}+p$. The $1p$-decay energies of the ground and low-lying excited states of ${}^{21}\mathrm{Al}$, its mass excess, and the proton separation energy value $S_p=-1.{15}_{-0.07}^{+0.10}$ MeV were determined.

The possibility that nuclear matter might be quarkyonic is considered. Quarkyonic matter is high baryon density matter that is confined but can be approximately thought of as a filled Fermi sea of quarks surrounded by a shell of nucleons. Here, nuclear matter is described by the IdylliQ sigma model for quarkyonic matter, generalizing the noninteracting IdylliQ model [Y. Fujimoto et al., Phys. Rev. Lett. 132, 112701 (2024)] to include interactions with a $\sigma$ meson and a pion. When such interactions are included, we find that isospin-symmetric nuclear matter binds with acceptable values of the compressibility and other parameters for nuclear matter at saturation. The energy per nucleon and sound velocity of such matter is computed, and the isospin dependence is determined. Nuclear matter is formed at a density close to but slightly above the density at which quarkyonic matter forms. Quarkyonic matter predicts a strong depletion of nucleons in normal nuclear matter at low momentum. Such a depletion for nucleon momenta $k\lesssim 120$ MeV is shown to be consistent with electron scattering data.

The spectral $\gamma$ ray emission from the reaction ${}^3\mathrm{H}({}^2\mathrm{H},\gamma ){}^5\mathrm{He}$ has been measured for the first time in a magnetic confinement deuterium-tritium plasma experiment at the Joint European Torus. A custom developed gamma ray spectrometer system based on a $\mathrm{La}{\mathrm{Br}}_3$ scintillator combined to a LiH neutron attenuator and a zero dead time fast digital data acquisition allowed to measure the weak $\gamma$ ray emission under the $\approx {10}^5$ more intense $14\mathrm{MeV}$ neutron field. The $R$-matrix analysis of the ${}^5\mathrm{He}$ nucleus has been used to predict the expected gamma ray spectrum which has been compared with the measurement, but cannot predict the relative intensity of the $\gamma$ lines. The data analysis has identified the energy and width of the known 16.75 MeV $\gamma$ ray emission (${\gamma }_0$), from the second excited state to the ground state of the formed ${}^5\mathrm{He}$ nucleus, and confirmed the presence of a second emission (${\gamma }_1$) at $\approx 14\mathrm{MeV}$ due to the transition from the second to the first excited state. The analysis has shown that the ${\gamma }_1$ emission is broad and has assessed for the first time in a magnetic confinement experiment the relative yield ${\gamma }_1$ to ${\gamma }_0$ equal to $1.09\pm 0.25$.

For light nuclei, ab initio many-body methods such as the no-core shell model are the tools of choice for predictive, high-precision nuclear structure calculations. The applicability and the level of precision of these methods, however, is limited by the model-space truncation that has to be employed to make such computations feasible. We present a universal framework based on artificial neural networks to predict the value of observables for an infinite model-space size based on finite-size no-core shell model data. Expanding upon our previous ansatz of training the neural networks to recognize the observable-specific convergence pattern with data from few-body nuclei, we improve the results obtained for ground-state energies and show a way to handle excitation energies within this framework. Furthermore, we extend the framework to the prediction of converged root-mean-square radii, which are more difficult due to the much less constrained convergence behavior. For all observables robust and statistically significant uncertainties are extracted via the sampling over a large number of network realizations and evaluation data samples.

Nuclei around $N\approx Z\approx 40$ are strongly deformed and exhibit coexistence of shapes. These phenomena have challenged nuclear models. Here, we perform ab initio coupled-cluster computations of low-lying collective states and electromagnetic quadrupole transitions of the even-even nuclei ${}^{72}\mathrm{Kr}, {}^{76,78}\mathrm{Sr}, {}^{78,80}\mathrm{Zr}$, and ${}^{84}\mathrm{Mo}$ starting from chiral nucleon-nucleon and three-nucleon forces. Our calculations reproduce the coexistence of oblate and prolate shapes in these nuclei, yield rotational bands and strong electromagnetic transitions, but are not accurate for some observables and nuclei. These results highlight the advances and challenges of ab initio computations of heavy deformed nuclei.

Observations of anomalies in the electron-positron angular correlations in high-energy decays in ${}^4\mathrm{He}, {}^8\mathrm{Be}$, and ${}^{12}\mathrm{C}$ have been reported recently by the ATOMKI collaboration. These could be explained by the creation and subsequent decay of a new boson with a mass of $\approx 17\mathrm{MeV}$. Theoretical understanding of pair creation in the proton capture reactions used in these experiments is important for the interpretation of the anomalies. We apply the ab initio no-core shell model with continuum (NCSMC) to the proton capture on ${}^7\mathrm{Li}$. The NCSMC describes both bound and unbound states in light nuclei in a unified way with chiral two- and three-nucleon interactions as the only input. We investigate the structure of ${}^8\mathrm{Be}$, the $p+{}^7\mathrm{Li}$ elastic scattering, the ${}^7\mathrm{Li}(p,\gamma ){}^8\mathrm{Be}$ cross section, and the internal pair creation ${}^7\mathrm{Li}(p,e^{+}{e}^{-}){}^8\mathrm{Be}$. We discuss the impact of a proper treatment of the initial scattering state on the electron-positron angular correlation spectrum and compare our results to available ATOMKI data sets. Finally, we calculate ${}^7\mathrm{Li}(p,X){}^8\mathrm{Be}$ cross sections for several proposed models of the hypothetical X17 particle.