By generating heavy-ion collision data with the ultrarelativistic quantum molecular dynamics (UrQMD) model, a multiphase transport (AMPT) model, and the JAM model, the impact parameter $b$ in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=4$ and 11 GeV is reconstructed using supervised learning and unsupervised learning in machine learning (ML). In supervised learning, the performance of ML algorithm is cross-checked by using data obtained from these three transport models. It is found that the typical mean absolute error (MAE), which measures the average magnitude of the absolute difference between the true and predicted $b$, is between 0.2–0.4 fm, even when training ML algorithm with data generated from one model but testing with data from others. While the conventional method (i.e., a polynomial fit to multiplicity as a function of $b$) only works for data generated from the same model. In the classification task, the present ML-based method also shows significantly superior results compared to the traditional approach. In unsupervised learning, the $K$-means clustering algorithm is used to partition collision events directly from experimental-style observables, showing that the algorithm autonomously identifies six clusters corresponding to different centrality classes without relying on predefined model-based binning. Our study demonstrates the strong robustness of using an ML algorithm trained on transport-model data for impact-parameter determination, and indicates that this method has the potential to be generalized to handle real experimental data.

We investigate the impacts of intrinsic nuclear deformation and orientation on the yield suppression and momentum anisotropy of charmonia in $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{U}+\mathrm{U}$ collisions at the Relativistic Heavy-Ion Collider (RHIC). The deformed nucleon density is parametrized via a modified Woods-Saxon distribution, which self-consistently determines the initial spatial distributions of both the heavy quarkonia and the bulk medium. A well-established Boltzmann-type transport equation is then utilized to describe the dynamical evolution of charmonia within this anisotropic medium. Using $\mathrm{Au}+\mathrm{Au}$ collisions as a baseline, we find that the momentum-integrated charmonium yield suppression in $\mathrm{U}+\mathrm{U}$ collisions is relatively insensitive to the initial nuclear geometry. In contrast, the elliptic flow ($v_2$) of charmonia is more sensitive to the nuclear deformation, which is inherently driven by specific collision configurations (e.g., tip-tip, body-body-$x$, and body-body-$y$ orientations). These configuration studies elucidate how the spatial orientation of deformed nuclei relative to the impact parameter dictates the initial geometric eccentricity, which subsequently translates into the final-state momentum anisotropy of charmonia. Notably, this orientation-induced effect is enhanced for the excited $\psi \left(2S\right)$ state, as its larger dissociation rate amplifies the azimuthal asymmetry in the path-integrated survival probability.

We employ physics-informed neural networks (PINNs) to investigate the dynamical evolution of heavy quarks within the expanding hot QCD medium generated in relativistic heavy-ion collisions. The heavy quark dynamics are first modeled under the assumption of complete kinetic thermalization, followed by a more realistic study of nonthermal diffusion governed by the Fokker-Planck (FP) equation. In both scenarios, the background evolution of the hot QCD medium is encoded into the coefficients of the diffusion equations. These equations are solved within the PINN framework, where the initial conditions, physical constraints from the dynamical equation, and probability conservation are incorporated into the loss function. We also compare the performance of the FP-PINN with a supervised five-dimensional DNN trained on labeled data generated from Langevin-based reference distributions. This work provides a valuable reference for applying PINN-based models to particle diffusion in phase space, laying the foundation for future studies of heavy quarkonium production via realistic nonthermal heavy quark coalescence.

We present the yield, average transverse momentum, and collective flow calculations of $K^{*0}$ resonances in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=19.6$, 14.5, and 7.7 GeV using the AMPT model. It is found that, due to hadronic rescattering, the decay daughters of $K^{*0}$ interact with other particles in the medium, causing the yield of reconstructable $K^{*0}$ to be significantly suppressed, especially at low transverse momentum. The model results are compared with recent experimental data from Phase-II of the Beam Energy Scan (BES-II) program at the Relativistic Heavy-Ion Collider. The string-melting version of the AMPT model successfully reproduces the measured $K^{*0}/K$ ratios at all three analyzed collision energies. Interestingly, AMPT calculations that exclude the hadronic phase nevertheless provide a reasonable description of the data, thereby challenging the conventional interpretation that hadronic rescattering is the primary mechanism responsible for suppressing the $K^{*0}/K$ ratio in central heavy-ion collisions. In addition, we find that the $K^{*0}/K$ ratio appears to be largely insensitive to the lifetime of the hadronic phase, whereas the average transverse momentum, $\langle p_T\rangle$, of the $K^{*0}$ shows a strong dependence, increasing significantly as the lifetime of the hadronic phase becomes longer. We further show that the directed flow $\left(v_1\right)$ of $K^{*0}$ mesons is strongly influenced by hadronic rescattering, whereas the elliptic flow $\left(v_2\right)$ exhibits only weak sensitivity to hadronic effects. These results establish $K^{*0}$ directed flow as a sensitive probe of the late-stage hadronic medium in heavy-ion collisions. These model calculations therefore provide valuable insight into the underlying physics governing the observed experimental results at RHIC.

In this work, we have extracted the nuclear level density (NLD) and $\gamma$-ray strength function ($\gamma \mathrm{SF}$) using the Oslo method on particle-$\gamma$ coincidence data from the ${}^{90}\mathrm{Zr}(p,p^{\prime }\gamma ){}^{90}\mathrm{Zr}$ reaction. We have applied the shape method to the same data set, providing a model-independent $\gamma \mathrm{SF}$ and a cross-check on the slope of the Oslo-method NLD and $\gamma \mathrm{SF}$. Further, we have combined the $\gamma \mathrm{SF}$ from this work with photonuclear data, thus covering the $2.5<E_{\gamma }<18\mathrm{MeV}$ energy range. We see an increase in strength in the region around $E_{\gamma }\approx 9\mathrm{MeV}$, consistent with previous $(\gamma ,{\gamma }^{\prime })$ and $(\gamma ,n)$ data. On the other hand, surprisingly, we do not observe a strong low-energy increase at low transition energies. The resulting NLD and $\gamma \mathrm{SF}$ were used as inputs to the nuclear reaction code talys to estimate the cross sections and astrophysical reaction rates for the ${}^{89}\mathrm{Zr}(n,\gamma ){}^{90}\mathrm{Zr}$ and ${}^{89}\mathrm{Y}(p,\gamma ){}^{90}\mathrm{Zr}$ reactions. We find good agreement with available experimental cross sections and JINA calculations for the ${}^{89}\mathrm{Y}(p,\gamma )$ results, but not for the ${}^{89}\mathrm{Zr}(n,\gamma )$ reaction rate for stellar temperatures above 0.7 GK. Based on our data, we provide a much more narrow uncertainty band for the ${}^{89}\mathrm{Zr}(n,\gamma )$ cross section and reaction rate.

We have developed a systematic approach to calculate the correlation function for spin-1/2 particles, incorporating both central and noncentral components of the interparticle interaction. This is achieved by extending the variable phase method to accommodate noncentral potentials and numerically solving the Schrödinger equation. Within this framework, the partial-wave contributions to the nucleon-nucleon correlation functions adopting the Reid soft-core potential are evaluated. The resulting correlation functions are then compared for Gaussian sources of different sizes.

The effects of triaxial softness on wobbling motion are investigated within the framework of the core-quasiparticle coupling model. By coupling a high-$j$ valence nucleon located in low shell or middle shell to a $\gamma$-rigid and $\gamma$-soft core, we compare energy spectra and electromagnetic transitions of odd-mass nuclei in the four characteristic scenarios. It is revealed that the wobbling motion also appears in nuclei with $\gamma$-soft cores, however, exclusively as longitudinal wobbling. Only a rigid triaxial core supports the appearance of transverse wobbling at low spin which changes to longitudinal wobbling at higher spin states. The differences in interband $B{\left(E2\right)}_{\text{out}}$ transitions provide clear signatures for distinguishing the softness of core, which may serve as the experimental probes. These findings offer clearer light on wobbling motion, thereby expanding our understanding of this fundamental collective mode.

The isomers in the very neutron-deficient isotopes ${}^{179m,181m}\mathrm{Hg}$ and ${}^{179m}\mathrm{Tl}$ were populated via fusion-evaporation reaction ${}^{78}\mathrm{Kr}+{}^{107}\mathrm{Ag}\to {}^{185}\mathrm{Bi}^{*}$. Using the gas-filled recoil separator SHANS (Lanzhou), the nuclei of interest were efficiently transported and separated from scattered beam particles and unwanted reaction products. In this study, conversion electrons (CEs) associated with isomeric transitions (ITs) of these isomers were observed for the first time. The CE-$\alpha$ correlation measurements provided crucial insights into their decay properties. For ${}^{179m}\mathrm{Tl}$, a previously unknown IT branch was identified, and a tentative IT decay scheme was proposed. For ${}^{179m,181m}\mathrm{Hg}$, the analysis of CEs served to validate and update their IT decay pathways.

Background: The synthesis of superheavy elements (SHEs) beyond Oganesson, such as $Z=119$, remains a formidable challenge, primarily because the dominant quasifission (QF) channel severely hinders the formation of compound nuclei. A microscopic understanding of the QF dynamics is therefore essential for guiding future experiments.

Purpose: We investigate the microscopic mechanisms of QF in the ${}^{54}\mathrm{Cr}+{}^{243}\mathrm{Am}$ reaction, a key candidate system for synthesizing SHE 119, with particular emphasis on the roles of projectile orientation and incident energy.

Method: The calculations are performed using the fully microscopic time-dependent Hartree-Fock theory based on the Skyrme energy density functional. We perform systematic simulations covering a broad set of initial orientations of the deformed ${}^{54}\mathrm{Cr}$ and ${}^{243}\mathrm{Am}$ nuclei, together with a finely spaced range of incident energies extending from below to well above the Coulomb barrier.

Results: Our fixed-energy simulations show that projectile side collisions are strongly shell driven, with heavy and light fragments tending toward the spherical $Z=82$ and deformed $N=52–56$ shell regions, respectively, whereas tip collisions exhibit weaker shell influence. These shell-driven reactions are associated with shorter contact times, consistent with faster neck rupture caused by the enhanced rigidity of shell-stabilized fragments. In the tip-tip channel, the energy dependence further reveals a transition from an octupole-deformed region around $Z\approx 88$ to a spherical shell-driven regime at higher energy, while shell steering is comparatively weak in a near-barrier region at a center-of-mass energy of approximately 226 MeV.

Conclusions: Our microscopic study demonstrates that the manifestation of shell effects in the final QF fragment distributions is a dynamical outcome sensitively dependent on both the initial collision geometry and the incident energy. This pronounced energy dependence indicates that the competition between QF and fusion may be affected by the beam energy. The comparatively weak shell steering found in the near-barrier tip-tip region therefore suggests a possible low-energy window of potential interest for SHE synthesis.

Background: Experimental setups commonly used to study fission properties of nuclei in the exotic neutron-deficient ${}^{180}\mathrm{Hg}$ region are based on the time-of-flight technique for the fission-product identification. In best cases, the obtained fragments mass (FFMD) and total kinetic energy (TKE) resolution does not exceed 2 u and 6 MeV, respectively. In addition, the nuclei of interest are created via fusion reactions and at excitation energies of several tens of MeV. The deduced final FFMDs are in general structureless, which makes the identification of fission modes, along with their properties, ambiguous and analysis dependent.

Purpose: To develop a robust analysis approach aiming at identification of a number of major fission modes in FFMDs from fusion-fission reactions.

Method: FFMD data with known composition are used to calculate the second derivative which is then inspected for presence of minima. Number of detected minima is relevant to the number of fission modes present in the FFMD and thus determines the structure of the fit function to use for the FFMD and TKE data description.

Results: The resolution effect is found to broaden the simulated FFMD and TKE data, as well as to smear structures in the second derivatives thus limiting the sensitivity of the method to a few per-cent level in the fission-mode weight. Direct fit of the resolution-affected FFMD data is shown unable to find the asymmetric-mode positions nor to reproduce the modes weights, especially if the used fit-function composition does not correspond to the input data. The fission-modes characteristic TKE values are also not reproduced in a non-constrained fit. In contrario, the simulated data could be safely reproduced with fit functions constructed with help of the second derivative curves, the detected minima being the signature of number of fission modes detectable in the resolution-affected data. The power of the derivative method is demonstrated on example of real experimental FFMDs for the ${}^{180}\mathrm{Hg}$ nucleus.

Conclusions: The derivative analysis applied to limited-resolution FFMDs appears to provide consistent results on the number and parameters of fission modes, even in cases of strong symmetric-mode dominance, i.e., for Gaussian-like FFMD shapes. The method is shown to work also on data sets with limited statistics (real experimental data with integral of a few tens of thousands of events).

We compute the transport coefficient $\widehat{q}$ which quantifies the transverse momentum broadening of hard probes passing through the evolving glasma from the earliest stage of relativistic heavy-ion collisions. We use a proper-time expansion method which is designed to study the glasma at very early times. In our earlier calculations of $\widehat{q}$ we used an approximation that greatly simplifies the complexity of the calculation but introduces a violation of gauge invariance. Based on these results we argued that the glasma plays an important role in jet quenching. In this paper we have used a gauge invariant formulation to calculate $\widehat{q}$. The results for the momentum broadening coefficient are quantitatively very close to those of our previous simplified version of the calculation and confirm our earlier conclusion about the importance of the glasma contribution to jet quenching.

The production of ${\mathrm{\Lambda }}_c^{+}$ baryons in $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=5.02$ TeV is investigated within the quark recombination framework, including the energy loss of light and charm quarks inside the hot and dense medium. The model simultaneously describes the transverse momentum ($p_T$) spectra of ${\mathrm{\Lambda }}_c^{+}$ baryons, ${\mathrm{\Lambda }}_c^{+}/D^0$ yield ratio, which is attributed to the dominance of the quark recombination mechanism in the quark-gluon plasma), and the second harmonic coefficient of ${\mathrm{\Lambda }}_c^{+}$ baryons with emphasis on the effects of minijets on the azimuthal anisotropy. Furthermore, we extend the theoretical calculation to $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=2.76$ TeV and make predictions for ${\mathrm{\Lambda }}_c^{+}$ baryons and ${\mathrm{\Lambda }}_c^{+}/D^0$ yield ratio. The simultaneous description of the yield, baryon-to-meson ratio, and azimuthal anisotropy further validates that the recombination model is an effective hadronization mechanism in heavy-ion collisions.

Relativistic heavy-ion collisions produce femtometer-scale sources whose space-time structure can be constrained using two-particle femtoscopic correlations. Standard implementations rely on the smoothness and on-shell approximations, which effectively remove the relative momentum dependence of the particle emission function. We explore the validity of these approximations by deriving model-independent expansions that quantify the leading corrections for femtoscopy and coalescence with arbitrary sources and final-state interactions. The resulting first- and second-order correction terms can be evaluated with essentially the same numerical complexity as the usual Koonin-Pratt expressions; for angle-averaged correlations the first-order contributions vanish by symmetry. We illustrate the framework with explicit calculations in a blast-wave source model; for blast-wave parameter sets representative of pp and PbPb fits at LHC energies, the corrections are at or below the percent level for pp correlations and deuteron coalescence. These corrections are potentially subdominant compared to other effects, for example, corrections to the equal time approximation.

We investigate the forces acting on a proton vortex in superconducting neutron-star matter composed of neutrons, protons, and electrons, accounting for Fermi-liquid interactions in the neutron-proton subsystem. While the force arising from electron scattering by the vortex magnetic field is well known, we demonstrate that normal neutrons also exert a force on proton vortices due to Fermi-liquid coupling with superconducting protons. Using a kinetic approach based on Landau Fermi-liquid theory, we show that neutron quasiparticles scatter off a proton vortex through the spatially varying condensate momentum, giving rise to a longitudinal force proportional to the relative neutron-vortex velocity. In contrast with the electron contribution, this force has no transverse component and vanishes in the absence of neutron-proton Fermi-liquid interaction. Within a simple model, we analyze the main properties of this force and provide physically motivated estimates of its magnitude.

The charge-dependent nucleon-nucleon $\left(NN\right)$ interaction plays a crucial role in understanding the nuclear structure and reaction problems. In this work, we explore the charge-dependent $NN$ interaction in covariant chiral effective field theory. By incorporating the isospin-breaking contributions, we derive the charge-dependent covariant chiral $NN$ potential up to next-to-next-to-leading order. The calculated $np$ and $pp$ phase shifts are in satisfactory agreement with the PWA93 partial wave analysis. Our results contribute to a deeper understanding of isospin-breaking effects in nuclear forces and provide a solid foundation for future studies of nuclear structure and reactions within the covariant framework.

The lowest states of the ${}^{52,54}\mathrm{Cr}$ isotopes are investigated for the presence of the shape coexistence phenomenon. The ground state deformation is extracted using the covariant density functional theory with a density-dependent point-coupling X parametrization, while the properties of the excited states are described involving the Bohr-Mottelson collective Hamiltonian with a sixth order anharmonic oscillator. A coexistence between near-spherical and well-deformed shapes is found in ${}^{52}\mathrm{Cr}$, and shape fluctuations of the ground state in ${}^{54}\mathrm{Cr}$. Moreover, the presence of coexisting shapes in ${}^{52}\mathrm{Cr}$ indicates that the $4^{+}$ state at 2768 keV would fit better the ground band than the $4^{+}$ state at 2370 keV. This latter assumption, in turn, implies that ${}^{52}\mathrm{Cr}$ could be a good candidate for the manifestation of the so-called $B_{4/2}$ anomaly.

A detailed investigation of the structural evolution of mercury (Hg) isotopes with mass numbers $A=174$–266 is carried out within the Skyrme Hartree-Fock-Bogoliubov (SHFB) framework using the UNEDF2 energy density functional. The study encompasses both bulk nuclear properties, such as binding energies, two-neutron separation energies, potential energy surfaces, root-mean-square radii, nuclear deformation parameters, and single-particle energy levels, as well as isospin-sensitive observables relevant to neutron-rich systems. To explore the isospin dependence, the coherent density fluctuation model (CDFM) is employed, using SHFB results as input to extract the symmetry energy and its volume and surface components. These quantities are particularly crucial for understanding the behavior of nuclei near the neutron drip line. The results reproduce the established shell closures at neutron numbers $N$ = 82 and 126 across both bulk and isospin-dependent observables. In addition, several calculated observables exhibit features consistent with a possible shell or subshell closure around $N$ = 184, although its presence remains model dependent and less robust than the traditional magic numbers. These findings suggest enhanced stability in extremely neutron-rich Hg isotopes and motivate further theoretical and experimental investigations in this region. The consistency between SHFB and CDFM predictions highlights the robustness of the combined theoretical framework in capturing both microscopic and macroscopic aspects of nuclear structure. The present work contributes to a deeper understanding of shell evolution, the role of the symmetry energy, and the stability of heavy isotopes far from the valley of stability.

The most stringent laboratory-based experimental limits on the existence of submegaelectronvolt sterile neutrinos are currently set by decay spectroscopy of radioactive ${}^7\mathrm{Be}$ embedded into superconducting sensors. The systematic uncertainties are dominated by the modeling of the electron shakeup and shakeoff spectra that are not based on state-of-the-art atomic theory and do not include electron correlations or relativistic effects. We have used the multiconfiguration Dirac-Fock formalism to obtain correlated wave functions ab initio and compute all single and double shake processes in the electron capture decay of atomic ${}^7\mathrm{Be}$. The simulations can explain some but not all of the observed spectral features, likely because the wave functions are modified by the Ta sensor material that the ${}^7\mathrm{Be}$ is embedded into. The new models also show that the $L/K$ electron capture ratio of ${}^7\mathrm{Be}$ in Ta has previously been slightly underestimated revising the previous value of 0.070(7) to a new value of 0.0756(20).

The inelastic scattering of ${}^{12}\mathrm{C}$ from ${}^{208}\mathrm{Pb}$ at an incident energy of 98 MeV exhibits a curious anomaly. While the shape of the angular distribution for populating the 4.086-MeV $2_1^{+}$ level of ${}^{208}\mathrm{Pb}$ is well reproduced by distorted wave Born approximation (DWBA) calculations, a coupling strength approximately double that of the accepted value is required. The inelastic scattering of a 270-MeV ${}^3\mathrm{He}$ beam from a ${}^{208}\mathrm{Pb}$ target exhibits similar behavior. This minor mystery has remained unsolved for the past 50 years. A solution is suggested based on the high level density of ${}^{208}\mathrm{Pb}$ in the region of 4-MeV excitation energy and the possibility that the measured $2_1^{+}$ angular distributions contain contributions from a number of unresolved levels, in particular the 4.324-MeV $4_1^{+}$. The coupling strengths for these levels, required as input for DWBA calculations, were obtained from an analysis of existing high-resolution ${}^{208}\mathrm{Pb}$($p,p^{\prime }$) scattering data, while the $2_1^{+}$ coupling strength was fixed by the adopted value of the $B\left(E2\right)$. Using these strengths a consistent description of a wide range of light-ion scattering data is obtained, in addition to the “anomalous” ${}^{12}\mathrm{C}$ and ${}^3\mathrm{He}$ data. While the individual contributions of the levels other than the $2_1^{+}$ and $4_1^{+}$ are negligible, their sum makes a significant contribution to the total angular distribution.