Recent years have witnessed an expanding interest in experimental studies of $\beta$ electrons (electrons emitted in ${\beta }^{-}$ decay transitions) and their energy distributions, the so-called $\beta$-electron spectra. These experiments have been focused mainly on $\beta$ transitions with electron spectra sensitive to the effective value of the weak axial coupling $g_{\mathrm{A}}$. In the present paper we make an extensive search for $g_{\mathrm{A}}$ sensitive $\beta$ spectral shapes in the $A=86–99$ region using the nuclear shell model with the well established Hamiltonians glekpn and jj45pnb, designed to render a good description of the spectroscopic properties of nuclei in this mass region. We have found eight ${\beta }^{-}$ decay transitions with various degrees of $g_{\mathrm{A}}$ sensitivity. Moreover, these transitions are also important in pinning down the value of the so-called small relativistic vector nuclear matrix element. In addition, some of the corresponding mother nuclei are important contributors to the antineutrino flux from nuclear reactors. All this means that the found $\beta$ transitions are potentially of great interest for future rare-events experiments.

$\alpha +\alpha$ scattering has a long history since the first experiment by Rutherford and Chadwick in 1927 and has been studied thoroughly experimentally and theoretically. However, $\alpha +\alpha$ scattering has never been paid attention from the viewpoint of refractive scattering. I have successfully analyzed the experimental angular distributions in $\alpha +\alpha$ scattering systematically over a wide range of incident energies $E_L=53.4–280\mathrm{MeV}$ using a phenomenological optical model with a deep real potential. The existence of a farside-dominant quasinuclear rainbow with no well-defined rainbow angle and no supernumerary bow in the lit side followed by the shadow, which is not a genuine rainbow but a refractive scattering from a marginally small droplet at high energies, is found for the first time in $\alpha +\alpha$ scattering. The refraction due to the deep potentials with an attractive core at short distances are discussed from the viewpoint of the Luneburg. The deep vs shallow problem of the potential and the nuclear rainbow scattering in inelastic channels are also discussed.

A linear Boltzmann transport (LBT) Monte Carlo model has been developed to describe jet propagation and interaction with the quark-gluon plasma (QGP) in relativistic heavy-ion collisions. A complete set of elastic-scattering processes and medium-induced gluon emissions based on the higher-twist formalism are incorporated for both jet shower and medium recoil partons. It has been employed to describe experimental data on large transverse momentum hadron and jet spectra, correlation and jet substructures in high-energy heavy-ion collisions. We document in detail the structure of the model and validation of the Monte Carlo implementations of the physics processes in LBT, in particular, the inelastic process of medium-induced gluon radiation. We carry out a comprehensive examination of the jet-medium interaction as implemented in LBT through energy loss and momentum broadening of a single hard parton, the energy and transverse momentum transfer from leading partons to medium-induced gluons and jet-induced medium excitation, and medium modification of reconstructed jets in a static and uniform medium. With realistic and event-by-event hydrodynamic medium in heavy-ion collisions, we compute and compare with experimental data on the jet cone-size dependence of the single inclusive jet suppression at both the BNL Relativistic Heavy-Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC), the dijet asymmetry at the LHC and $\gamma$-jet correlation at RHIC. Effects of medium-induced gluon emissions and jet-induced medium excitation on jet observables are systematically examined. Rescatterings of the radiated gluons and recoil partons with the QGP are found essential to account for the enhancement of soft particle yield toward the edge of the jet cone.

We have employed both unpaired (cranked Nilsson-Strutinsky) and paired (cranked Nilsson-Strutinsky-Bogoliubov) cranked Nilsson-Strutinsky calculations to explore the properties of observed and potential isomers within the shape-transitional osmium $(Z=76)$ isotopes and $N=116$ isotones. Our analyses reveal the prevalence of multiquasiparticle prolate and broken-pair triaxial structures in even-even osmium isotopes $(N=112–118)$ and $N=116$ isotones $(Z=72–80)$. In addition, our exploration of $N=116$ isotones identifies potential isomeric states, systematically, including noncollective ${10}^{-}$ and collective ${12}^{+}$ states, constructed upon specific neutron configurations.

Neural networks have been proposed as efficient numerical wave function Ansätze, which can be used to variationally search a wide range of functional forms for ground-state solutions. These neural network methods are also advantageous in that more variational parameters and system degrees of freedom can be easily added. We benchmark the methodology by using neural networks to study several different integrable bosonic quantum systems in one dimension and compare our results to the exact solutions. While testing the scalability of the procedure to systems with many particles, we also introduce using symmetric function inputs to the neural network to enforce exchange symmetries of indistinguishable particles.

The low-energy structure and $\beta$-decay properties of the neutron-rich even-mass nuclei near the neutron number $N=60$ that are experimentally of much interest are investigated within the framework of the nuclear density functional theory and the interacting boson-fermion-fermion model. By using the results of the constrained self-consistent mean-field calculations based on the relativistic energy density functional, the interacting-boson Hamiltonian describing the even-even core nuclei, the boson-fermion, and the fermion-fermion interactions are determined. The Gamow-Teller transition strengths, with the corresponding operator being constructed without introducing further phenomenological adjustment, are computed by using the wave functions of the initial and final nuclei of the $\beta$ decay. The triaxial quadrupole potential energy surfaces computed for the $N=60$ even-even isotones suggest a pronounced $\gamma$ softness. The calculated energy spectra for the even-even and odd-odd nuclei in the Rb to Cd isotopic chains exhibit an abrupt change in nuclear structure around $N=60$, as suggested experimentally. The predicted $\beta$-decay ${log}_{10}ft$ values underestimate the measured values for the nuclei with low $Z$ and with $N⩽60$, exhibit a rapid increase for $N>60$, reflecting the nuclear structure evolution, and agree rather well with the measured values for those nuclei with $Z$ being not far from the proton major shell closure $Z=50$. Sensitivity of the predicted $\beta$-decay properties to the model assumptions and parameters employed in the nuclear structure calculations is discussed, specifically, by comparing results obtained based on the different choices of the underlying energy density functional.

We incorporate a microscopic relativistic nuclear potential obtained from the recently developed relativistic R3Y $NN$ potential in the coupled-channels code ccfull to study fusion dynamics. The R3Y $NN$ potential and the densities of interacting nuclei are obtained for the relativistic mean-field approach for the $\mathrm{NL}{3}^{*}$ parameter set. Note that the R3Y $NN$ potential can be expressed in terms of masses of the mesons and their couplings by considering the meson degrees of freedom within the relativistic mean field, which has a form similar to the widely used M3Y potential. We focused on the fusion cross sections for oxygen-based reactions with targets from different mass regions of the periodic table, i.e., ${}^{16}\mathrm{O}+{}^{24}\mathrm{Mg}, {}^{18}\mathrm{O}+{}^{24}\mathrm{Mg}, {}^{16}\mathrm{O}+{}^{148}\mathrm{Sm}, {}^{16}\mathrm{O}+{}^{176}\mathrm{Hf}, {}^{16}\mathrm{O}+{}^{176}\mathrm{Yb}, {}^{16}\mathrm{O}+{}^{182}\mathrm{W}$, and ${}^{16}\mathrm{O}+{}^{186}\mathrm{W}$. A comparison is also made with the cross sections calculated using the nuclear potential obtained from the traditional Woods-Saxon potential and the widely used M3Y $NN$ potential within ccfull. The coupled-channels calculations are performed with shape and rotational degrees of freedom to examine the fusion enhancement at below-barrier energies. It is observed from the calculations that the fusion cross sections obtained using the R3Y $NN$ potential with rotational degrees of freedom are found to be more consistent with the experimental data than those for the M3Y and Woods-Saxon potentials, mainly at below barrier energies.

Ultrarelativistic heavy-ion collisions will first realize many nucleon-nucleon scatterings, happening instantaneously and therefore necessarily in parallel, due to the short collision time. An appropriate quantum mechanical tool to treat that problem is S-matrix theory, and it has been known for a long time how to derive a simple geometric probabilistic picture, still widely used, and here the Abramovskii-Gribov-Kancheli (AGK) theorem plays a crucial role. All this is done in a scenario where energy conservation is not taken care of, but this is needed, in particular for Monte Carlo simulations. When introducing energy-momentum sharing properly, the AGK theorem does not apply anymore, nor do simple geometric concepts such as binary scaling. I will discuss this (very serious) problem, and how it can be solved, in the EPOS4 framework. When connecting the multiple-Pomeron approach (for parallel scatterings) and perturbative QCD, one is actually forced to implement in a very particular way saturation scales in order to get an approach free of contradictions. One recovers a generalized AGK theorem (gAGK), valid at large $p_t$ (larger than the relevant saturation scales). I discuss how gAGK is related to factorization (in proton-proton scatterings) and binary scaling (in heavy-ion collisions). I will show some applications, using this new approach as an initial condition for hydrodynamical evolutions, for heavy-ion collisions at $\sqrt{s_{NN}}$ of 5.02 TeV and 200 GeV, to get some idea about the energy dependence.

Upcoming studies at the CERN Large Hadron Collider (LHC) aim to extend the rapidity coverage in measurements of the production cross section of antinuclei $\overline{d}$ and $\overline{{}^3\mathrm{He}}$. I illustrate the impact of such studies on cosmic ray (CR) flux predictions, important, in turn, for the interpretation of results from CR experiments. I show that, in terms of the rapidity effect, covering the range $\left|y\right|<1.5$ at the LHC should be sufficient for the astrophysical CR calculation. Important extrapolation remains in other aspects of the problem, notably, $\sqrt{s}$.

The Green's function Monte Carlo (GFMC) method provides accurate solutions to the nuclear many-body problem and predicts properties of light nuclei starting from realistic two- and three-body interactions. Controlling the GFMC fermion sign problem is crucial, as the signal-to-noise ratio decreases exponentially with imaginary time, requiring significant computing resources. Inspired by similar scenarios in lattice quantum field theory and spin systems, in this work, we employ integration contour deformations to improve the GFMC signal-to-noise ratio. Machine learning techniques are used to select optimal contours with minimal variance from parametrized families of deformations. As a proof of principle, we consider the deuteron binding energies and Euclidean density response functions. We only observe mild signal-to-noise improvement for the binding energy case. On the other hand, we achieve an order of magnitude reduction of the variance for Euclidean density response functions, paving the way for computing electron- and neutrino-nucleus cross sections of larger nuclei.

The binding energy or mass is one of the most fundamental properties of an atomic nucleus. Precise binding energies are vital inputs for many nuclear physics and nuclear astrophysics studies. However, due to the complexity of atomic nuclei and the nonperturbative strong interaction, up to now, no conventional physical model can describe nuclear binding energies with a precision below 0.1 MeV, the accuracy needed by nuclear astrophysical studies. In this work, artificial neural networks (ANNs), the so-called “universal approximators”, are used to calculate nuclear binding energies. We show that the ANN can describe all the nuclei in AME2020 with a root-mean-square deviation (RMSD) around 0.2 MeV, better than the best macroscopic-microscopic models, such as FRDM and WS4. The success of the ANN is mainly due to the proper and essential input features we identify, which contain the most relevant physical information, i.e., shell, paring, and isospin-asymmetry effects. We show that the well-trained ANN has excellent extrapolation ability and can predict binding energies for those nuclei inaccessible experimentally. In particular, we highlight the important role of “feature engineering” for physical systems where data are relatively scarce, such as nuclear binding energies.

There must be electromagnetic fields created during high-energy heavy-ion collisions. As the quark-gluon plasma (QGP) starts to evolve hydrodynamically, although these fields may become weak compared to the energy scales of the strong interaction, they are potentially important to some electromagnetic probes. In this work, we focus on the dissipative corrections in QGP due to the presence of a weak external magnetic field, and calculate accordingly the induced photon radiation in the framework of viscous hydrodynamics. By event-by-event hydrodynamical simulations, the experimentally measured direct photon elliptic flow can be well reproduced. Correspondingly, the direct photon elliptic flow implies a magnetic field strength around $0.1m_{\pi }^2\approx {10}^{16}$ G. This is indeed a weak field in heavy-ion physics that is compatible to the theoretical predictions, however, it is still an ultrastrong magnetic field in nature.

We examine in detail two alternative descriptions of a system of $\alpha$ particles interacting via local interactions of different character, highlighting the fact that a faithful microscopic description of such systems demands a consistent treatment of both short- and long-range correlations. In preparation, we examine four different versions of modern microscopic many-body theory and conclude by emphasizing that these approaches, although a priori very different, actually lead to the same equations for their efficient application. The only quantity that depends on the formulation of many-body theory chosen is an irreducible interaction correction. In the language of Green's functions and Feynman diagrams, it is the set of both particle-particle and particle-hole irreducible diagrams, and in variational Jastrow-Feenberg theory it is determined by multipartite correlations and elementary diagrams. We apply these theoretical methods to the calculation of the energetics, structure, thermodynamics, and dynamics of $\alpha$ matter, as well as its condensate fraction. In dimensionless units, $\alpha$ matter appears to be remarkably similar to the much-studied ${}^4\mathrm{He}$ quantum fluid, its low-temperature properties now basically solved in the Jastrow-Feenberg framework. Accordingly, one can have confidence in the results of application of the same procedure to $\alpha$ matter. Even so, closer examination reveals significant differences between the physics of the two systems. Within an infinite nuclear medium, $\alpha$ matter is subject to a spinoidal instability. Extended mixtures of nucleons and $\alpha$ particles are yet to be given rigorous consideration in a corresponding theoretical framework.

Background: In the framework of nuclear energy density functional (EDF) methods, many nuclear phenomena can be related to the deformation of intrinsic states. Their accurate modeling relies on the correct description of the change of nuclear binding energy with deformation. The two most important contributions to the deformation energy have their origin in shell effects and the surface energy coefficient of nuclear matter.

Purpose: It has been pointed out before that the choices made for the center-of-mass (c.m.) correction energy and the effective mass during the parameter adjustment influence the deformation properties of nuclear EDFs. We study the impact of these two properties by means of a set of purpose-built parametrizations of the standard Skyrme EDF at next-to-leading (NLO) order in gradients.

Methods: In a first step, we build nine series of parametrizations with a systematically varied surface-energy coefficient $a_{\text{surf}}$ for three frequently used options for the c.m. correction (none, one-body term only, full one-body and two-body contributions) combined with three values for the isoscalar effective mass $m_0^{*}/m$ (0.7, 0.8, 0.85) and analyze how well each of these parametrizations can be adjusted to the properties of spherical nuclei and infinite nuclear matter. In a second step, we performed additional fits without the constraint on surface energy, adding one “best-fit” parametrization to each of the nine series. We then benchmark these parametrizations to the deformation properties of heavy nuclei by means of three-dimensional Hartree-Fock-Bogoliubov calculations that allow for nonaxial and/or nonreflection symmetric configurations.

Results: We perform a detailed correlation analysis between surface and volume properties of nuclear matter using the nine series of parametrizations. The best fits out of each series are then benchmarked on the fission barriers of ${}^{240}\mathrm{Pu}$ and ${}^{180}\mathrm{Hg}$, as well as on the properties of deformed states at normal and superdeformation for actinides and nuclei in the neutron-deficient Hg region.

Conclusions: The main conclusions are as follows: (i) Each combination of choices for c.m. correction and $m_0^{*}/m$ leads to a significantly different optimal value of $a_{\text{surf}}$, reason being that the effective interaction has to absorb the contribution of the c.m. correction to the total binding energy. (ii) Many properties of symmetric and asymmetric infinite nuclear matter of Skyrme NLO EDFs are strongly correlated to the value of $a_{\text{surf}}$. (iii) Omitting the c.m. correction results in values of $a_{\text{surf}}$ that are systematically too small. On the other hand, including the one-body term but neglecting the computationally expensive two-body term means $a_{\text{surf}}$ will be too large. Both choices result in unrealistic predictions for fission barriers and superdeformed states of heavy nuclei. Only by incorporating the complete c.m. correction does one obtain quite realistic surface properties from an adjustment protocol that only constrains properties of infinite nuclear matter and spherical nuclei. (iv) Lowering $a_{\text{surf}}$ increases the susceptibility of finite nuclei to take an exotic shape.

Background: Multinucleon transfer (MNT) reactions are considered now as a possible tool to produce new isotopes of heavy and superheavy elements.

Purpose: Experimental study of MNT fragments formed in the ${}^{136}\mathrm{Xe}+{}^{238}\mathrm{U}$ reaction at ${}^{136}\mathrm{Xe}$ beam energy of 1.11 GeV and comparison with theoretical calculations.

Methods: Primary and secondary mass and energy distributions of projectilelike fragments (PLF) formed in the ${}^{136}\mathrm{Xe}+{}^{238}\mathrm{U}$ reaction have been experimentally investigated independently and in coincidence with survived heavy targetlike fragments (TLF) using the CORSET setup. Since the heavy fragments formed in the reactions are highly excited the masses, energies, and angles of both fragments as products of the sequential fission of heavy MNT fragments have been measured.

Results: The cross sections for PLFs at $27.2^{\circ }\le {\theta }_{\mathrm{lab}}\le 32.8^{\circ }$ along with survived TLFs and TLFs undergoing fission have been obtained. The mass loss during the deexcitation process of excited PLFs has been found using the measured primary and secondary masses. The excitation energies of light and heavy MNT fragments have been estimated from the mass loss and total kinetic energies. An overall good agreement with theoretical calculations increases reliability of performed analysis.

Conclusions: The transfer of about 27 nucleons from the projectile to target nucleus has been found. The cross section of the heaviest observed fragment with the mass of 265 u is about few hundred microbarns. The survival probabilities of transtarget nuclei formed in the reaction drop rapidly from $\approx 7\times {10}^{-1}$ for the fragment mass of 240 u to $\approx 1.8\times {10}^{-3}$ for 255 u.

The isotopes ${}^{261,262}\mathrm{Bh}$ were reinvestigated by using the cold fusion reaction ${}^{54}\mathrm{Cr}+{}^{209}\mathrm{Bi}$. The evaporation residues were separated by the gas-filled recoil separator SHANS2 (Spectrometer for Heavy Atoms and Nuclear Structure-2) and identified by means of the recoil-$\alpha$-correlation method. The $\alpha$-decay properties of ${}^{261,262}\mathrm{Bh}$ were measured and the results are consistent with the previously reported values. Based on the measured half-lives, the existence of two distinct states of ${}^{262}\mathrm{Bh}$ was confirmed, whereas ${}^{261}\mathrm{Bh}$ lacked any isomer with $\alpha$-decay properties. Two spontaneous fission events potentially from ${}^{262}\mathrm{Bh}$ and/or ${}^{261}\mathrm{Bh}$ were detected and the production cross sections at beam energies of 264.1 and 270.4 MeV were obtained.

We suggest that the angular momentum in fission fragments is generated by statistical excitation at scission. The magnitude of the angular momentum is determined by excitation energy and shell structure in the level density. Treating the prescission shape evolution as a diffusive process, implemented as a Metropolis walk on a five-dimensional potential-energy surface, the average magnitudes of the fission fragment angular momenta are calculated for ${}^{235}\mathrm{U}(n_{\mathrm{th}},\mathrm{f})$, assuming that they are perpendicular to the fission axis. The sawtooth behavior of the average angular momentum magnitude as function of mass number is discussed in connection with the similar observed behavior of the average neutron multiplicity, and a good understanding is achieved. The magnitudes of the angular momenta of light and heavy fragments are found to have a weak negative correlation, in accordance with recent experimental results. This correlation arises from the microcanonical sharing of excitation energy by the fragments at scission, where each energy provides a distribution of angular momenta.