We calculate the $k$-particle $\left(k=2,4,6,8\right)$ azimuthal cumulants resulting from the conservation of transverse momentum. We find that $c_2\left\{k\right\}>0$ and, depending on the transverse momenta, $c_2\left\{k\right\}$ can reach substantial values even for a relatively large number of particles. The impact of our results on the understanding of the onset of collectivity in small systems is emphasized.

In order for a Sullivan-like process to provide reliable access to a meson target as $t$ becomes spacelike, the pole associated with that meson should remain the dominant feature of the quark-antiquark scattering matrix and the wave function describing the related correlation must evolve slowly and smoothly. Using continuum methods for the strong-interaction bound-state problem, we explore and delineate the circumstances under which these conditions are satisfied: for the pion, this requires $-t\lesssim 0.6{\mathrm{GeV}}^2$, whereas $-t\lesssim 0.9{\mathrm{GeV}}^2$ will suffice for the kaon. These results should prove useful in planning and evaluating the potential of numerous experiments at existing and proposed facilities.

Background: Nuclear astrophysics centers on the role of nuclear physics in the cosmos. In particular, nuclear masses at the limits of stability are critical in the development of stellar structure and the origin of the elements.

Purpose: We aim to test and validate the predictions of recently refined nuclear mass models against the newly published AME2016 compilation.

Methods: The basic paradigm underlining the recently refined nuclear mass models is based on existing state-of-the-art models that are subsequently refined through the training of an artificial neural network. Bayesian inference is used to determine the parameters of the neural network so that statistical uncertainties are provided for all model predictions.

Results: We observe a significant improvement in the Bayesian neural network (BNN) predictions relative to the corresponding “bare” models when compared to the nearly 50 new masses reported in the AME2016 compilation. Further, AME2016 estimates for the handful of impactful isotopes in the determination of $r$-process abundances are found to be in fairly good agreement with our theoretical predictions. Indeed, the BNN-improved Duflo-Zuker model predicts a root-mean-square deviation relative to experiment of ${\sigma }_{\mathrm{rms}}\simeq 400$ keV.

Conclusions: Given the excellent performance of the BNN refinement in confronting the recently published AME2016 compilation, we are confident of its critical role in our quest for mass models of the highest quality. Moreover, as uncertainty quantification is at the core of the BNN approach, the improved mass models are in a unique position to identify those nuclei that will have the strongest impact in resolving some of the outstanding questions in nuclear astrophysics.

The anomalous large radii are exotic phenomena observed around the neutron dripline. Around the neutron dripline, the weak binding of the last bound neutron(s) causes the drastic increase of the radius, which is called the neutron halo structure. Although the nucleus ${}^{24}\mathrm{O}$ is located at the dripline of oxygen isotopes, the separation energies of one and two neutron(s) are 4.19 MeV and 6.92 MeV, respectively. In spite of this sufficient binding, the enhancement of the matter radius is observed. In this study, we microscopically describe the structure change of the ${}^{22}\mathrm{O}$ core in ${}^{24}\mathrm{O}$ and explain the observed large radius based on the cluster model. Two degrees of freedom for the large radius, the relative distances among four $\alpha$ clusters and the size of each $\alpha$ cluster, are examined, where the Tohsaki interaction, which has finite range three-body terms, is employed. The nucleus ${}^{22}\mathrm{O}$ has smaller $\alpha \text{−}\alpha$ distance compared with ${}^{16}\mathrm{O}$ owing to the gluelike effect of six valence neutrons around four $\alpha$ clusters. When two neutrons are added at the center of ${}^{22}\mathrm{O}$, the expansion of each $\alpha$ cluster is energetically more favored than increasing the $\alpha \text{−}\alpha$ distances for reducing the kinetic energy of the neutrons. The calculated rms matter radii of ${}^{22}\mathrm{O}$ and ${}^{24}\mathrm{O}$ are 2.75 fm and 2.92 fm, respectively. Although these are slightly smaller than the experimental values, the jump at ${}^{24}\mathrm{O}$ from ${}^{22}\mathrm{O}$ is reproduced.

Background: Precise fitting of scattering observables suggests that the nucleon-nucleus interaction is $l$ dependent. Such $l$ dependence has been shown to be $S$-matrix equivalent to an undulatory $l$-independent potential. The undulations include radial regions where the imaginary term is emissive.

Purpose: To study the dynamical polarization potential (DPP) generated in proton-${}^{16}\mathrm{O}$ and neutron-${}^{16}\mathrm{O}$ interaction potentials by coupling to pickup channels. Undulatory features occurring in these DPPs can be compared with corresponding features of empirical optical model potentials (OMPs). Furthermore, the additional inclusion of coupling to vibrational states of the target will provide evidence for dynamically generated nonlocality.

Methods: The fresco code provides the elastic channel $S$-matrix $S_{lj}$ for chosen channel couplings. Inversion, $S_{lj}\to V\left(r\right)+\mathbf{l}·\mathbf{s}{V}_{\mathrm{SO}}\left(r\right)$, followed by subtraction of the bare potential, yields an $l$-independent and local representation of the DPP due to the chosen couplings.

Results: The DPPs have strongly undulatory features, including radial regions of emissivity. Certain features of empirical DPPs appear, e.g., the full inverted potential has emissive regions. The DPPs for different collective states are additive except near the nuclear center, whereas the collective and reaction channel DPPs are distinctly nonadditive over a considerable radial range, indicating dynamical nonlocality. Substantial differences between the DPPs due to pickup coupling for protons and neutrons occur; these imply a greater difference between proton and neutron OMPs than the standard phenomenological prescription.

Conclusions: The onus is on those who object to undularity in the local and $l$-independent representation of nucleon elastic scattering to show why such undulations do not occur. This work suggests that it is not legitimate to halt model-independent fits to high-quality data at the appearance of undularity.

In this paper, we investigate the noncritical fluctuations of (net) charges and (net) protons in Au+Au collisions at $\sqrt{s_{\mathit{NN}}}=7.7$, 39, and 200 GeV, using iebe-vishnu hybrid model with Poisson fluctuations added in the particle event generator between hydrodynamics and urqmd. Various effects, such as volume fluctuations hadronic evolution and scatterings, resonance decays, as well as realistic centrality cuts and acceptance cuts have been embedded in our model calculations. With properly tuned parameters, iebe-vishnu roughly describes the centrality-dependent moments and cumulants of (net) charges and (net) protons measured in experiment. Further comparison simulations show that the volume fluctuation is the dominant factor to influence the multiplicity fluctuations, which makes the higher moments of (net) charges largely deviate from the Poisson baselines. We also find that the effects from hadronic evolutions and resonance decays are rather small or even negligible for the multiplicity fluctuations of both (net) charges and (net) protons.

${}^{146}\mathrm{Nd}$ is one of only four (over a total of 35 existing) $2{\beta }^{-}$-decay isotope candidates whose half-lives currently lack experimental limits. The $\alpha$ activity of the ${}^{146}\mathrm{Sm}$ daughter nuclide allows placement of limits on the $2\beta$ decay using the ${}^{146}\mathrm{Nd}/{}^{142}\mathrm{Nd}$ abundance ratio $(T_{1/2}^{\beta \beta }\gtrsim 3\times {10}^9$ yr) or direct search for ${}^{146}\mathrm{Sm}$ with accelerator mass spectrometers $(T_{1/2}^{\beta \beta }\gtrsim 4.5\times {10}^{19}$ yr). With a similar approach, a modest $(\sim \text{Gyr})$ first limit on half-lives for the other unexplored $2\beta$ unstable isotopes and competitive limits (few $10{}^{13}\mathrm{yr})$ for ${}^{98}\mathrm{Mo}$ and ${}^{122}\mathrm{Sn}$ are also given. Finally, it is shown how the limit $T_{1/2}^{0\nu \epsilon {\beta }^{+}}\gtrsim {10}^{15}$ yr for the unexplored ${}^{144}\mathrm{Sm}0\nu \epsilon {\beta }^{+}$ decay may be obtained from the data of a GSO crystal scintillator.

The nonleptonic weak interaction in the few-nucleon system at very low energies is studied with the calculation of the photon circular polarization in the $pd\to {}^3\mathrm{He}\gamma$ reaction ($P_{\gamma }^{pd}$). For very low energies, one may treat the pion as heavy and integrate it out from the QCD symmetry-based model-independent effective field theory, leaving only short-range strong interactions which are introduced in term of pionless effective field theory formulation. We investigate a complete set of the parity-violating electromagnetic transitions in the $pd\to {}^3\mathrm{He}\gamma$ process. In this paper the interferences of strong, electromagnetic, Coulomb, and parity-violating weak interactions are presented with the calculation of a full set of appropriate diagrams at the leading order. We have obtained energy-dependent $P_{\gamma }^{pd}$ results as a function of the laboratory energy values $0.5\le E_{\mathrm{Lab}}\le 3$ MeV in terms of the low-energy coupling constants. The contributions of the initial $S$- and $P$-wave proton-deuteron systems have been considered to make the final ${}^3\mathrm{He}$ ground state in this energy region.

The tensor contribution can be directly incorporated in the cluster model in a simplified way. In conventional $\alpha$ cluster models, the contribution of the noncentral interactions exactly cancels because of the antisymmetrization effect and spatial symmetry of $\alpha$ clusters. The mixing of breaking components of $\alpha$ clusters to take into account the spin-orbit and tensor effects is needed. Previously, we proposed a simplified method to include the spin-orbit effect, and also for the tensor part, a simplified model to directly take into account the contribution of the tensor interaction (called SMT) was introduced; however, the contribution of the tensor interaction was quite limited. Here we improve SMT, which is called $i\mathrm{SMT}$. Using newly proposed $i\mathrm{SMT}$, the contribution of the tensor interaction in ${}^4\mathrm{He}$ is more than $-40$ MeV, four times larger than the previous version. The method is applied to four-$\alpha$ cluster structure of ${}^{16}\mathrm{O}$. In ${}^{16}\mathrm{O}$, the tensor contribution is also large, and this is coming from the finite size effect for the distances among $\alpha$ clusters with a tetrahedral configuration.

High-spin states of ${}^{138}\mathrm{Pm}$ have been populated using the ${}^{124}\mathrm{Te}({}^{19}\mathrm{F},5\mathrm{n}){}^{138}\mathrm{Pm}$ reaction at a beam energy of 105 MeV. A new positive-parity side band with the same $\pi h_{11/2}\otimes \nu h_{11/2}$ configuration as that of the yrast band is observed in ${}^{138}\mathrm{Pm}$. The properties of the two positive-parity bands show general agreement with the fingerprints of chiral rotation and thus these two bands are suggested to be candidates for near degenerate chiral doublet bands. Besides, odd-even spin staggering of the $\pi h_{11/2}\otimes \nu h_{11/2}$ bands is studied systematically in odd-odd Cs, La, Pr, and Pm isotopes. As a result of this study we suggest that the spin value of lowest observed state of the yrast band be reassigned as 9 in ${}^{138}\mathrm{Pm}$. This new spin assignment is also supported by the argument of alignment additivity.

The elastic $\alpha \text{−}{}^{12}\mathrm{C}$ scattering for $l=0,1,2,3$ channels at low energies is studied, including the energies of excited bound states of ${}^{16}\mathrm{O}$, in effective field theory. A new renormalization method is introduced due to the large suppression factor produced by the Coulomb interaction when the effective range parameters are fitted to the phase sift data. After fitting the parameters, the asymptotic normalization constants of the $0_2^{+},1_1^{-},2_1^{+},3_1^{-}$ states of ${}^{16}\mathrm{O}$ are calculated. The uncertainties when the amplitudes are interpolated to the stellar energy region of the ${}^{12}\mathrm{C}(\alpha ,\gamma ){}^{16}\mathrm{O}$ reaction are also discussed.

Excitation-energy spectra of ${}^{11}\mathrm{C}$ nuclei near the ${\eta }^{\prime }$-meson production threshold have been measured by missing-mass spectroscopy using the ${}^{12}\mathrm{C}(p,d)$ reaction. A carbon target has been irradiated with a 2.5 GeV proton beam supplied by the synchrotron SIS-18 at GSI to produce ${\eta }^{\prime }$-meson bound states in ${}^{11}\mathrm{C}$ nuclei. Deuterons emitted at $0^{\circ }$ in the reaction have been momentum analyzed by the fragment separator (FRS), used as a high-resolution spectrometer. No distinct structure due to the formation of ${\eta }^{\prime }$-mesic states is observed although a high statistical sensitivity is achieved in the experimental spectra. Upper limits on the formation cross sections of ${\eta }^{\prime }$-mesic states are determined, and thereby a constraint imposed on the ${\eta }^{\prime }$-nucleus interaction is discussed.

We study $\alpha$-cluster structure based on the geometric configurations with a microscopic framework, which takes full account of the Pauli principle, and which also employs an effective internucleon force including finite-range three-body terms suitable for microscopic $\alpha$-cluster models. Here, special attention is focused upon the $\alpha$ clustering with a hollow structure; all the $\alpha$ clusters are put on the surface of a sphere. All the platonic solids (five regular polyhedra) and the fullerene-shaped polyhedron coming from icosahedral structure are considered. Furthermore, two configurations with dual polyhedra, hexahedron-octahedron and dodecahedron-icosahedron, are also scrutinized. When approaching each other from large distances with these symmetries, $\alpha$ clusters create certain local energy pockets. As a consequence, we insist on the possible existence of $\alpha$ clustering with a geometric shape and hollow structure, which is favored from Coulomb energy point of view. Especially, two configurations, that is, dual polyhedra of dodecahedron-icosahedron and fullerene, have a prominent hollow structure compared with the other six configurations.

Carbon burning is a critical phase for nucleosynthesis in massive stars. The conditions for igniting this burning stage, and the subsequent isotope composition of the resulting ashes, depend strongly on the reaction rate for ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$ fusion at very low energies. Results for the cross sections for this reaction are influenced by various backgrounds encountered in measurements at such energies. In this paper, we report on a new measurement of ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$ fusion cross sections where these backgrounds have been minimized. It is found that the astrophysical $S$ factor exhibits a maximum around $E_{\mathrm{cm}}=3.5–4.0$ MeV, which leads to a reduction of the previously predicted astrophysical reaction rate.

The photon emission from a nonequilibrium quark-gluon plasma is analyzed. We derive an integral equation that describes photon production through quark-antiquark annihilation and quark bremsstrahlung. It includes coherence between different scattering sites, also known as the Landau-Pomeranchuk-Migdal effect. These leading-order processes are studied for the first time together in an out-of-equilibrium field theoretical treatment that enables the inclusion of viscous corrections to the calculation of electromagnetic emission rates. In the special case of an isotropic, viscous, plasma the integral equation only depends on three constants, which capture the nonequilibrium nature of the medium.

We investigate cluster and toroidal aspects of isoscalar dipole excitations in ${}^{12}\mathrm{C}$ based on the shifted basis antisymmetrized molecular dynamics combined with the generator coordinate method, which can describe 1p-1h excitations and $3\alpha$ dynamics. In the $E=10\text{−}15\mathrm{MeV}$ region, we find two low-energy dipole modes separating from the giant dipole resonance. One is the developed $3\alpha$-cluster state and the other is the toroidal dipole mode. The cluster state is characterized by the high-amplitude cluster motion beyond the 1p-1h model space, whereas the toroidal dipole mode is predominantly described by 1p-1h excitations in the ground state. The low-energy dipole states are remarkably excited by the toroidal dipole operator, which can measure the nuclear vorticity. For compressive dipole transition strengths, a major part is distributed in the 30- to 50-MeV region for the giant dipole resonance, and 5% of the total energy-weighted sum exists in the $E<20$ MeV region.

The thermodynamical ground-state properties and static response in both cold atoms at or close to unitarity and neutron matter are determined using a recently proposed density functional theory (DFT) based on the $s$-wave scattering length $a_s$, effective range $r_e$, and unitary gas limit. In cold atoms, when the effective range may be neglected, we show that the pressure, chemical potential, compressibility modulus, and sound velocity obtained with the DFT are compatible with experimental observations or exact theoretical estimates. The static response in homogeneous infinite systems is also obtained and a possible influence of the effective range on the response is analyzed. The neutron matter differs from unitary gas due to the noninfinite scattering length and to a significant influence of effective range, which affects all thermodynamical quantities as well as the static response. In particular, we show for neutron matter that the latter response recently obtained in auxiliary-field diffusion Monte Carlo (AFDMC) can be qualitatively reproduced when the $p$-wave contribution is added to the functional. Our study indicates that the close similarity between the exact AFDMC static response and the free-gas response might stem from the compensation of the $a_s$ effect by the effective range and $p$-wave contributions. We finally consider the dynamical response of both atoms or neutron droplets in anisotropic traps. Assuming the hydrodynamical regime and a polytropic equation of state, a reasonable description of the radial and axial collective frequencies in cold atoms is obtained. Following a similar strategy, we estimate the equivalent collective frequencies of neutron drops in anisotropic traps.

The $\beta$-decay process of the ${}^6\mathrm{He}$ halo nucleus into the $\alpha +d$ continuum is studied in an updated three-body model. The ${}^6\mathrm{He}$ nucleus is described as an $\alpha +n+n$ system in hyperspherical coordinates on a Lagrange mesh. The shape and absolute values of the transition probability per time and energy units of new experiments are reproduced with a modified $\alpha +d$ potential. The obtained total transition probabilities are $(2.48\pm 0.16)\times {10}^{-6}{\mathrm{s}}^{-1}$ for the full energy region and $(2.40\pm 0.16)\times {10}^{-6}{\mathrm{s}}^{-1}$ for the cut-off $E>150$ keV. The strong cancellation between the internal and halo parts of the $\beta$ decay matrix element is a challenge for future ab initio calculations.

Using the stochastic Langevin model, we investigate the influence of dissipation on first-chance fission properties of nuclei ${}^{220}\mathrm{Th}$ and ${}^{240}\mathrm{Cf}$ by calculating the drop of their first-chance fission probability caused by friction over their standard statistical-model value, $P_{f0}^{\mathrm{drop}}$, as a function of the presaddle friction strength ($\beta$) at different angular momenta and excitation energies. It is shown that the first-chance fission probability may be affected more largely at low angular momentum and that it is sensitive to $\beta$ and the sensitivity is significantly larger than that of the total fission probability. Furthermore, we find that for heavy ${}^{240}\mathrm{Cf}$, while the total fission probability is insensitive to $\beta$, the first-chance fission probability depends sensitively on $\beta$. Our findings suggest that, to more stringently constrain the presaddle friction strength, the measurement of the first-chance fission probability from those heavy fissioning systems could provide a more sensitive and suitable experimental approach.