Background: In recent years, extensive research has been conducted on heavy-ion (HI) reactions to understand the mechanisms involved. Current studies on HI interactions have highlighted the existence of incomplete fusion (ICF) processes in addition to complete fusion (CF) reactions, even at energies $\approx$4–7 MeV/nucleon.

Purpose: As of now, no theoretical model has been developed that can explain the breakup fusion processes at low energies. In the absence of such a model, the systematics developed for a large number of projectile-target combinations are likely to be useful.

Method: The $\gamma$-ray spectroscopy technique has been employed in the present work to obtain the excitation functions (EFs) of several reaction residues in the system ${}^{16}\mathrm{O}+{}^{174}\mathrm{Yb}$ at $E/V_b\approx 1.01$ to 1.35, which are populated via both complete and/or incomplete fusion events. The statistical model code PACE4 has been used to analyze the measured EFs. The fusion cross-section data were also analyzed within the universal fusion function (UFF) approach to get information about the fusion suppression.

Results: The measured EFs of reaction residues populated via the $xn$ and $pxn$ channels are found to agree well with those predicted by the statistical model code PACE4. This confirms that the production of these residues is exclusively due to the complete fusion (CF) process. However, in comparison to theoretical predictions, a notable enhancement was observed in the measured cross sections of residues populated via $\alpha$-emitting channels. The incomplete fusion strength function was deduced to provide a better understanding of its onset and strength. The parameters impacting the dynamics of ICF process were studied. For the presently studied system, fusion suppression of about 16% compared to the UFF was observed at energies above the Coulomb barrier.

Conclusions The observed enhancement in the cross sections for $\alpha$-emitting channels is ascribed to the ICF processes. The $F_{\mathrm{ICF}}$ is found to strongly depend on the energy of the projectile and also on the product of the charges of the projectile and target nuclei. The observed fusion suppression is primarily attributed to the prompt breakup of the projectile and is found to be strongly related to the breakup threshold energy of the projectile.

Background: In the last decade, uncertainty quantification (UQ) for optical model potentials (OMPs) has become a focal point for nuclear reaction theory, and several competing approaches for OMP UQ have recently been developed.

Purpose: We clarify recent efforts to compare frequentist and Bayesian approaches in the context of OMP UQ [G. B. King et al., Phys. Rev. Lett. 122, 232502 (2019)].

Method: We replicate a portion of that OMP UQ study but use independent statistical tools. Specifically, we compare two methods for OMP parameter inference from elastic scattering data: the Levenberg-Marquardt algorithm for ${\chi }^2$ minimization on one hand and Markov chain Monte Carlo (MCMC) sampling on the other. Separately, we assess the common practice of using a renormalized likelihood (${\chi }^2/N$), $N$ being the number of data points, instead of the canonical weighted-least-squares likelihood (${\chi }^2$), as a way of accounting for unknown data correlations.

Results: We show that for a generic linear model and for a five-parameter OMP analysis, frequentist and uniform-prior Bayesian approaches recover the same optimum and uncertainty estimates—not systematically larger uncertainties for the Bayesian approach, as was concluded in G. B. King et al., Phys. Rev. Lett. 122, 232502 (2019). Further, we show that if an additional, near-degenerate parameter is introduced into the same OMP analysis such that the parameter posterior becomes non-Gaussian, then covariance-based estimates of uncertainty become unreliable. Finally, we show that regardless of optimization approach, if ${\chi }^2/N$ is used for the likelihood, the resulting parametric uncertainties increase by $\sqrt{N}$, and that this is responsible for the conclusions drawn in the revisited study.

Conclusions: Based on our replication results, we find that a fortuitous cancellation of unreported errors and the renormalization factor can lead to improvement in empirical coverages, as was the case in the original comparative study. We emphasize that developing and applying a realistic likelihood function is an essential task in a UQ analysis, and that several recent UQ studies that employed a renormalized likelihood (i.e., including a $1/N$ factor) may have yielded unrealistically large uncertainties for elastic-scattering observables. If the parameter posterior deviates from multivariate-normal, a sampling-based approach like MCMC has a clear advantage over methods that assume the Laplace approximation holds. We note that empirical coverage can serve as an important internal check for the analyst whose model or data may have additional, unaccounted-for uncertainties.

There have long been questions about the limits to the validity of relativistic fluid dynamics and whether it is being used outside its regime of validity in modern simulations of relativistic heavy-ion collisions. An important new tool for answering this question is a causality analysis in the nonlinear regime—if the solutions of the evolution equations do not respect relativistic causality, then they are not a faithful representation of the underlying relativistic theory (in this case, quantum chromodynamics). Using this nonlinear criterion, it has recently been shown that hydrodynamics is indeed being used outside its regime of validity in simulations, at least sometimes. Here we explore the phenomenological implications, particularly the quantitative effects of demanding limits on acausality in modern Bayesian parameter estimation. We find that, while typically only a small fraction of the system's energy is initially in an acausal regime, placing strict limits on the allowed energy fraction significantly changes the preferred properties of the initial condition, which in turn alters the extracted medium properties such as bulk viscosity, where large values are no longer favored. These findings highlight the importance of developing better theoretical descriptions of the early-time, out-of-equilibrium dynamics of relativistic heavy-ion collisions.

A primary objective in high-energy heavy-ion collisions is to investigate the phase transition between confined and deconfined color matter. Complementary to the cumulants of conserved charges integrated over the full azimuth, we introduce a novel experimental approach to explore particle fluctuations in azimuthal partitions, which are potentially sensitive to the first-order phase transition in heavy-ion collisions. We evaluate proton multiplicity $\left(N_w\right)$ fluctuations in azimuthal partitions of width $w$ to quantitatively estimate the clustering tendency among these protons. The $\mathrm{\Delta }{\sigma }^2$ observable is defined as the normalized difference between the variance of the $N_w$ distribution and the binomial baseline. We demonstrate the feasibility and characteristics of this observable through simulations using a multiphase transport (AMPT) and $\mathrm{MUSIC}+\mathrm{FIST}$ models. We also use a Gaussian correlation model to illustrate that the dependence of $\mathrm{\Delta }{\sigma }^2$ on $w$ can be parameterized to accurately extract the strength and the range of the input interaction among protons.

The rod phase as it is expected in the bottom layers of neutron-star crusts is analyzed within the Hartree-Fock-Bogoliubov framework. To well describe the interplay between band structure and superfluidity, periodicity of the lattice is taken into account using Bloch boundary conditions. A relative flow between the rods and the surrounding neutron gas is introduced in a time-independent way. This induces a nontrivial phase of the complex order parameter, leading to a counterflow between neutrons inside and outside the rods. With the resulting current, we compute the actual neutron superfluid fraction. For the latter our results are significantly larger than previous ones obtained in normal band theory, indicating that the normal band theory overestimates the entrainment effect.

Recently, Oganessian et al. successfully synthesized the new superheavy isotope ${}^{275}\mathrm{Ds}$ through a ${}^{48}\mathrm{Ca}$-induced reaction with a ${}^{232}\mathrm{Th}$ target [Oganessian et al., Phys. Rev. C 109, 054307 (2024)]. Several other newly synthesized heavy and superheavy nuclides have also been reported in various works. Despite these experimental advancements, theoretical studies into the $\alpha$-decay properties of these newly discovered nuclides remain limited and insufficiently explored. In this study, we conduct an investigation on the newly reported or updated $\alpha$-decay data from recent experiments, focusing on the heavy neutron-deficient nuclei and superheavy nuclei. Utilizing an improved density-dependent cluster model ($\mathrm{DDCM}+$) of our recent work [Wang et al., Phys. Rev. C 105, 024327 (2022)], most of these experimental $\alpha$-decay half-lives are well reproduced with an average factor of approximately 2, which indicate that the $\mathrm{DDCM}+$ model remains robust and reliable across these newly explored mass regions. Notably, based on the theoretical results given by $\mathrm{DDCM}+$, we propose the possible $\alpha$-decay schemes for the newly observed ${}^{273}\mathrm{Ds}$ and ${}^{275}\mathrm{Ds}$ decay chains, incorporating minor modifications to the previously suggested schemes proposed by Oganessian et al. These theoretical results are expected to serve as valuable references for future experimental studies, contributing to a deeper understanding of the $\alpha$-decay properties and nuclear structures in heavy and superheavy nuclei.

Cross sections for the ${}^{197}\mathrm{Au}(\gamma ,n)$ reaction are broadly used in nuclear physics as a standard for normalizing photonuclear reaction cross-section data at photon beam energies above approximately 8 MeV. In this paper, we report cross-section measurements for the ${}^{197}\mathrm{Au}{(\gamma ,n)}^{196}{\mathrm{Au}}^{g+m1}$ reaction at beam energies from 13 to 31 MeV. Our measurements provide the first cross-section data for this reaction at beam energies above 20 MeV, enabling the use of this reaction as a cross-section standard up to 30 MeV. Also, this work provides first cross-section measurements for the ${}^{197}\mathrm{Au}(\gamma ,n){}^{196}\mathrm{Au}^{m2}$ reaction. In addition, we measured cross-section data for the ${}^{197}\mathrm{Au}(\gamma ,3n){}^{194}\mathrm{Au}$ reaction, which can be used as a cross-section standard above about 25 MeV. These measurements were performed using a new target activation method that is based on the angle-energy correlation of the laser Compton-scattered photon beams at the High Intensity Gamma-ray Source ($\mathrm{HI}\gamma \mathrm{S}$). The technique enables measuring photonuclear reaction cross-sections at several discrete beam energies concurrently via a single irradiation on a stack of different targets. Measurements were carried out by irradiating a stack of concentric-ring targets consisting of Au, ${\mathrm{TiO}}_2$, Zn, Os, and Au (in order of the $\gamma$-ray beam direction). Our data for the ${}^{197}\mathrm{Au}(\gamma ,n){}^{196}\mathrm{Au}^{g+m1}$ reaction in the energy range of 13 to 20 MeV are in good agreement with existing ones measured using monoenergetic $\gamma$-ray beams, but differ from data acquired using a bremsstrahlung $\gamma$-ray beam. Also, above 18 MeV, our data for the ${}^{197}\mathrm{Au}(\gamma ,n){}^{196}\mathrm{Au}^{g+m1}$ and ${}^{197}\mathrm{Au}(\gamma ,n){}^{196}\mathrm{Au}^{m2}$ reactions differ significantly from the most recent TENDL and JENDL evaluations, suggesting a need to update these data libraries. The TENDL evaluation and existing data are consistent with our data for the ${}^{197}\mathrm{Au}(\gamma ,3n)$ reaction, but differ significantly from the JENDL evaluation above 26 MeV.

We present calculations of dielectron anisotropic flow in heavy-ion collisions at HADES beam energies from a hadronic transport approach. The ongoing experimental analysis employs the traditional reaction plane method to evaluate the flow coefficients $v_n$ and claims to see isotropic radiation from the thermal quark-gluon plasma. We show in this paper that in the region above the pion mass, the dilepton flow measurement might suffer from cancellation effects that mask the complicated underlying dynamics. Contributions from different baryonic and mesonic resonances show collective behavior with different signs and lead to an overall vanishing elliptic flow. To differentiate the different contributions, we propose to employ the scalar product method, which exploits the previously measured hadronic flow to create different reference planes. As a proof of concept, we calculate the $v_2$ of dielectrons for $\mathrm{Ag}+\mathrm{Ag}$ collisions at $\sqrt{s_{NN}}=2.55\mathrm{GeV}$ with both methods and investigate the contribution of each source, concluding that the scalar product method provides the proton and pion tagged flow coefficients as two distinct measurements, disentangling the various dilepton sources.

The resonant states in ${}^{20}\mathrm{Mg}$ and ${}^{19}\mathrm{Mg}$ have been studied by the invariant-mass reconstruction of ${}^{18}\mathrm{Ne}+2p$ and ${}^{17}\mathrm{Ne}+2p$ events, respectively. Two new resolved states ($4_1^{+}$ and $2_2^{+}$) in ${}^{20}\mathrm{Mg}$ are found to decay through ${}^{19}\mathrm{Na}$ intermediate states to the ground state of ${}^{18}\mathrm{Ne}$ from the examination of the decay-energy spectra for ${}^{18}\mathrm{Ne}+1p$ subsystems. The deduced $R_{42}=E^{*}\left(4_1^{+}\right)/E^{*}\left(2_1^{+}\right)$ ratio of 2.10(1) is close to the expected harmonic-vibrator value and reveals a spherical or weakly deformed shape for ${}^{20}\mathrm{Mg}$. Systematic comparison of $E^{*}\left(2_1^{+}\right)$ and $R_{42}$ along isotopic and isotonic chains with shell model calculations, using the YSOX interaction, suggest the persistence of $N=8$ shell around the proton drip-line. The relatively higher $2_1^{+}$ excitation energy in ${}^{18}\mathrm{Mg}$ relative to ${}^{20}\mathrm{Mg}$ can be ascribed to different excitation characters of the valence protons. The $1/2_1^{+}$ state in ${}^{19}\mathrm{Mg}$ has been observed for the first time. The energy differences between the $1/2_1^{-}$ and $1/2_1^{+}$ states in ${}^{19}\mathrm{Mg}$ and its isotones manifest the magnitude of the $N=8$ shell gap on the proton-rich side.

Flow coefficients ($v_2$ and $v_3$) are measured in high-multiplicity $p+\mathrm{Au}, d+\mathrm{Au}$, and ${}^3\mathrm{He}+\mathrm{Au}$ collisions at a center-of-mass energy of $\sqrt{s_{{}_{NN}}}=200$ GeV using the STAR detector. The measurements utilize two-particle correlations with a pseudorapidity requirement of $\left|\eta \right|<$ 0.9 and a pair gap of $\left|\mathrm{\Delta }\eta \right|>1.0$. The primary focus is on analysis methods, particularly the subtraction of nonflow contributions. Four established nonflow subtraction methods are applied to determine $v_n$, validated using the HIJING event generator. $v_n$ values are compared across the three collision systems at similar multiplicities; this comparison cancels the final-state effects and isolates the impact of initial geometry. While $v_2$ values show differences among these collision systems, $v_3$ values are largely similar, consistent with expectations of subnucleon fluctuations in the initial geometry. The ordering of $v_n$ differs quantitatively from previous measurements using two-particle correlations with a larger rapidity gap, which, according to model calculations, can be partially attributed to the effects of longitudinal flow decorrelations. The prospects for future measurements to improve our understanding of flow decorrelation and subnucleonic fluctuations are also discussed.

Motivated by the recent progress in developing high-precision relativistic chiral nucleon-nucleon interactions, we study the antinucleon-nucleon interaction in a hybrid approach where the real part of the potential is constructed in the leading-order covariant chiral effective field theory, and the imaginary part is described following the procedure adopted in the heavy baryon chiral effective field theory. The phase shifts and inelasticities with $J\le 1$ are obtained and compared to those calculated in the next-to-leading-order heavy baryon chiral effective field theory. For most partial waves, the descriptions of phase shifts and inelasticities in the hybrid approach are comparable to those in the next-to-leading-order heavy baryon chiral effective field theory, confirming the relatively faster convergence of the relativistic approach observed in the nucleon-nucleon sector. In addition, we search for bound states/resonances near the $\overline{N}N$ threshold and find several structures that can be associated with those states recently observed by the BESIII Collaboration.

The tensor force effect on the two-proton radioactivity of ${}^{18}\mathrm{Mg}$ and ${}^{20}\mathrm{Si}$, including the two-proton halos, spectroscopic factors, decay energies, and diproton potentials, are investigated within the Skyrme-Hartree-Fock-Bogoliubov theory using the SAMi-T, $\mathrm{SLy}5+\mathrm{T}$, T36, $\mathrm{SLy}5+\mathrm{Tw}, \mathrm{SLy}5+\mathrm{ta}$, and $\mathrm{SLy}5+\mathrm{tb}$ interactions. It is shown that ${}^{18}\mathrm{Mg}$ and ${}^{20}\mathrm{Si}$ are the nuclei with an evident two-proton halo. Furthermore, a pronounced linear correlation between the spectroscopic factors and the halo sizes is found. More specifically, the spectroscopic factor becomes larger with the increase of the $2p$ halo size due to the tensor force of the $\mathrm{SLy}5+\mathrm{Tw}, \mathrm{SLy}5+\mathrm{ta}$, and T36 interactions. As a result, the decay mode may prefer to the ${}^2\mathrm{He}$ emission. As to the $\mathrm{SLy}5+\mathrm{T}$ and $\mathrm{SLy}5+\mathrm{tb}$ interactions, the results are opposite to those within the $\mathrm{SLy}5+\mathrm{Tw}, \mathrm{SLy}5+\mathrm{ta}$, and T36 interactions. Then, the half-lives are calculated using the diproton potentials extracted from various interactions. It is found that the increment of the half-lives does not exceed one order of magnitude caused by the tensor force of the $\mathrm{SLy}5+\mathrm{T}, \mathrm{SLy}5+\mathrm{Tw}, \mathrm{SLy}5+\mathrm{ta}$, and $\mathrm{SLy}5+\mathrm{tb}$ interactions although the tensor force has a certain influence on the spectroscopic factors, decay energies, and diproton potentials. However, the half-life decreases by a factor of 17.75 caused by the tensor force of the T36 interaction. As to the SAMi-T interaction, the structure and decay properties are not influenced by the tensor force.

Influences of the octupole shape degree of freedom on low-energy spectra of neutron-rich odd-mass xenon isotopes are studied within the interacting boson-fermion model that is based on the nuclear density functional theory. The interacting-boson Hamiltonian describing low-energy quadrupole and octupole collective states of the even-even nuclei ${}^{140,142,144}\mathrm{Xe}$, single-particle energies, and occupation probabilities for an unpaired neutron in the odd-mass nuclei ${}^{141,143,145}\mathrm{Xe}$, are determined based on the axially symmetric quadrupole-octupole deformation-constrained self-consistent mean-field calculations with a choice of the energy density functional and pairing interaction. Strength parameters of the boson-fermion interactions are empirically determined to reproduce a few low-lying levels of each odd-mass nucleus. The mean-field calculation predicts for ${}^{142}\mathrm{Xe}$ a potential energy surface that is notably soft in the octupole deformation with a nonzero octupole global minimum. The octupole correlations are shown to be relevant in positive-parity excited states of ${}^{143,145}\mathrm{Xe}$.

A possible signature of the $d^{*}\left(2380\right)$ dibaryon in the reaction $\gamma d\to {\pi }^0{\pi }^{0}d$ is explored. To calculate the conventional coherent ${\pi }^0{\pi }^0$ photoproduction on a deuteron, the $2\pi \mathrm{MAID}$ model has been updated by fitting its parameters to the set of the modern $\gamma N\to \pi \pi N$ data. Besides the Born and the resonance terms the new model includes additional background in the partial waves with the spin-parity $J^{\pi }={\frac{3}{2}}^{\pm }$ and isospin $I=\frac{1}{2}$. The radiative $d^{*}\to \gamma d$ width and the contribution of the $d^{*}\left(2380\right)$ component to the $\gamma d\to {\pi }^0{\pi }^{0}d$ amplitude are evaluated by comparing the resulting theoretical cross section with the data. The sensitivity of some polarization observables to the $d^{*}\left(2380\right)$ contribution is investigated.

We study charged particles in three dimensions interacting via a short-range potential in addition to the Coulomb potential. When the Bohr radius and the scattering length are much larger than the potential range, low-energy physics of the system becomes independent from details of the short-range potential. We develop the zero-range theory to describe such universal physics in terms of the Bohr radius and the scattering length by generalizing the Bethe-Peierls boundary condition, which is then applied to two charged particles to reveal their bound states and resonances. Infinite resonances are found for a repulsive Coulomb potential, one of which turns into a bound state with increasing inverse scattering length, whereas infinite bound states exist for an attractive Coulomb potential with no resonances at any scattering length. The zero-range theory is also applied to three equally charged particles at infinite scattering length under the variational Born-Oppenheimer approximation. We find that the effective potential between two heavy particles induced by a light particle is an inverse-square attraction at distances shorter than the Bohr radius, leading to infinite deep bound states, whereas shallow ones successively turn into resonances with increasing Coulomb repulsion.

The first spectroscopy of ${}^{52}\mathrm{K}$ was investigated via in-beam $\gamma$-ray spectroscopy at the RIKEN Radioactive Isotope Beam Factory after one-proton and one-neutron knockout from ${}^{53}\mathrm{Ca}$ and ${}^{53}\mathrm{K}$ beams impinging on a 15-cm liquid hydrogen target at $\approx 230$ MeV/nucleon. The energy level scheme of ${}^{52}\mathrm{K}$ was built using single $\gamma$ and $\gamma \text{−}\gamma$ coincidence spectra. The spins and parities of the excited states were established based on momentum distributions of the fragment after the knockout reaction and based on exclusive cross sections. The results were compared to state-of-the-art shell model calculations with the SDPF-Umod interaction and ab initio in-medium similarity renormalization group calculations with chiral effective field theory nucleon-nucleon and three-nucleon forces.

Background: ${}^{15}\mathrm{Be}$ is an unbound nuclide that has been observed to decay by one-neutron emission. Shell model calculations predict two low-lying states in its energy spectrum; however, only a single resonance has been observed from coincident measurements of ${}^{14}\mathrm{Be}+n$. It has been suggested that the yet unobserved state may decay sequentially through the first excited state in ${}^{14}\mathrm{Be}$ followed by a two-neutron emission to ${}^{12}\mathrm{Be}$.

Purpose: The ground state of ${}^{15}\mathrm{Be}$ has yet to be confirmed. A search for this predicted ${}^{15}\mathrm{Be}$ state by reconstructing ${}^{12}\mathrm{Be}+3n$ events allows a possible determination of its ground state properties.

Methods: A neutron-pickup reaction was performed with a ${}^{14}\mathrm{Be}$ beam on a ${\mathrm{CD}}_2$ target (where D denotes ${}^2\mathrm{H}$) to populate unbound ${}^{15}\mathrm{Be}$ states. Decay energies were reconstructed using invariant mass spectroscopy by detecting ${}^{12}\mathrm{Be}$ daughter nuclei in coincidence with up to three neutrons.

Results: Evidence for at least one resonance in ${}^{15}\mathrm{Be}$ is presented based on the reconstruction of ${}^{12}\mathrm{Be}+3n$ events. Through comparison with simulations, the energy of the strongest resonance in the analyzed reaction and decay channel is determined to be $E_{{12}_{\mathrm{Be}}+3n}=330\left(20\right)\mathrm{keV}$.

Conclusions: The inclusion of a new ${}^{15}\mathrm{Be}$ state among the ${}^{12}\mathrm{Be}+3n$ events lower in relative decay energy than the previous ${}^{14}\mathrm{Be}+\mathrm{n}$ observations provides the best fit to the data. Because this suggested new state would be lower in energy than the previously observed state, it is a candidate for the ground state of ${}^{15}\mathrm{Be}$.

Background: The nuclear structure of low-lying excited states in ${}^{139}\mathrm{I}$, a neutron-rich nucleus with $Z=53$ and $N=86$ above ${}^{132}\mathrm{Sn}$ and in the proximity of $A\sim 140$, is investigated.

Purpose: The decay scheme for ${}^{139}\mathrm{I}$ is obtained after the first $\beta$-decay measurement of ${}^{139}\mathrm{Te}$. Transitions in ${}^{138}\mathrm{I}$ are detected after the $\beta$-delayed neutron emission of ${}^{139}\mathrm{Te}$. The $P_n$ ratio is investigated based on the $\gamma$-ray emissions.

Methods: $\beta$-delayed $\gamma$-ray spectroscopy is employed to study excited states in ${}^{139}\mathrm{I}$, populated in the decay of a mass-separated beam of ${}^{139}\mathrm{Te}$, produced in the in-flight fission of ${}^{235}\mathrm{U}$ on a ${}^9\mathrm{Be}$ target.

Results: The new level scheme of ${}^{139}\mathrm{I}$ with 26 new transitions, established for the first time in $\beta$ decay, is reported. Two new transitions are observed also in ${}^{138}\mathrm{I}$. The $\beta$-delayed neutron emission probability $P_n$ of ${}^{139}\mathrm{Te}$ is deduced to be 17.6(48)%. New and/or more restrictive spin/parity assignments of states in the daughter ${}^{138}\mathrm{I}$ nucleus are reported as well.

Conclusions: The experimental results are an important input to the theoretical description of nuclei in the region, being well interpreted within large-scale shell-model calculations, and provide essential information on the first-forbidden transitions beyond $N=82$ and $Z=50$.