We have studied single-$\mathrm{\Lambda }$ finite hypernuclear systems spanning from light to heavy masses, employing a new microscopic $\mathrm{\Lambda }N$ interaction derived from in-medium interactions within relativistic Brueckner-Hartree-Fock calculations using the leading-order covariant chiral hyperon-nucleon force. Without any adjustable parameters, we have successfully reproduced the experimental results for the single-$\mathrm{\Lambda }$ binding energies. Although some discrepancies persist in light hypernuclei, the overall calculated binding energies show excellent agreement with the experimental data, and outperform other microscopic interactions. This study further demonstrates the validity of the leading-order covariant chiral hyperon-nucleon potential and provides a practical set of microscopic interactions for the Skyrme-Hartree-Fock framework.

The symmetric nuclear matter and pure neutron matter are investigated by the relativistic Brueckner-Hartree-Fock (RBHF) theory with the covariant chiral nuclear forces up to the next-to-leading order (NLO). A fitting scheme to ensure the naturalness of the low-energy constants is proposed, which plays a crucial role in the proper description of nuclear matter. With a momentum cutoff of $\mathrm{\Lambda }=590$ MeV, the empirical saturation energy and density, as well as the incompressibility coefficient at the saturation density, are reproduced well. The equations of state show less dependence on the momentum cutoff and become softer at densities above the saturation density, in comparison with the previous leading-order results. Given the good description of the saturation properties of nuclear matter, the present work encourages future studies of finite nuclei in the framework of the RBHF theory with the NLO covariant chiral nuclear forces.

We study quantum phase transitions (QPTs) involving octupole degrees of freedom within the $spdf$ interacting boson model ($spdf$-IBM) by examining the potential-energy surface (PES) in the thermodynamic limit. Our analysis of a transitional Hamiltonian allows us to map the phase diagram for paths between spherical, quadrupole-deformed, and octupole-deformed shapes, identifying their critical points and order. The results confirm the established nature of the ${\text{U}}_{pdf}\left(5\right)\to {\text{O}}_{spdf}\left(6\right)$ and ${\text{U}}_{pdf}\left(5\right)\to {\text{SU}}_{pdf}\left(3\right)$ transitions. Furthermore, we uncover novel phenomena, including a sequential transition with an intermediate phase for the ${\text{U}}_{pdf}\left(5\right)\to {\text{SU}}_{spdf}\left(3\right)$ path, as well as transitions occurring entirely within the octupole sector. Finally, we connect these ground-state QPTs to precursors in the excitation spectra of finite-$n$ systems.

This study introduces a quantum information perspective to analyze the internal structure of atomic nuclei, focusing on the quantum entanglement between $\alpha$ clusters in the $0^{+}$ state of ${}^8\mathrm{Be}$. A wave function based on angular momentum coupling is developed to transform the two-cluster wave function from the conventional center of mass and relative coordinate basis (${\mathcal{H}}_{R_{\mathrm{c}.\mathrm{m}.}}\otimes {\mathcal{H}}_r$) into the individual particle basis (${\mathcal{H}}_1\otimes {\mathcal{H}}_2$), which is essential for a precise quantification of entanglement. Within this method, the von Neumann entropy is employed to quantify the entanglement arising from the mixing of angular momentum channels. Additionally, we introduce the concept of spatially resolved entropy, which measures entanglement as a function of the radial separation between clusters. Our analysis reveals that the entanglement is strongly correlated with the spatial configuration at the femtometer scale. As the intercluster separation vanishes, the system approaches a separable $S$-wave state, indicating that entanglement is dynamically generated during the spatial separation of the clusters. This research provides a new tool for investigating nonlocal quantum correlations in nuclear structure, complementing existing descriptions.

A statistical method is presented to evaluate the uncertainty bands in the optical nucleus-nucleus potential and in differential cross sections. The starting point is the least square fit of a set of experimental values of elastic differential cross sections, varying the relevant optical potential parameters. This is done using standard ${\chi }^2$ minimization codes, that provide the covariance matrix of the parameters. A maximum likelihood exploration of the ${\chi }^2$ surface in parameter space allows us to determine the covariance matrix of the parameters associated to a contour of a given ${\chi }^2$ value. The Bayes theorem allows us to assign probabilities ($p$ values) to the regions in parameter space, characterized by ${\chi }^2$ contours. The method allows us to obtain uncertainty bands of an arbitrary observable associated to a given $p$ value using two approaches. The general approach determines the uncertainties from the extremes of the observables calculated in the region of parameter space associated to that $p$ value. This requires an adequate sampling of parameter space, and explicit calculations of the observables on all sampling points. The simplified approach considers uncertainty propagation of the observable in terms of the optical model parameters. This involves the least square covariance matrix, given by ${\chi }^2$ minimization codes, and analytically calculated enhancement factors for each $p$ value. The method, in the general and simplified approaches, is applied to recent measurements of the elastic differential cross sections of ${}^8\mathrm{Li}+{}^{58}\mathrm{Ni}$. $1\sigma$ and $2\sigma$ uncertainty bands are obtained for the optical potentials as a function of the distance, and for the differential cross sections as a function of the angle. The general and simplified approaches are very similar in this case. The application of the procedure to determine uncertainty bands of complex scattering calculations is discussed.

Recent research in machine learning has employed neural networks to learn mappings between function spaces on bounded domains termed “neural operators.” As such, these operators can provide alternatives to standard numerical methods for partial differential equation (PDE) solutions. In particular, the Fourier neural operator (FNO) has been shown to map solutions for classical fluid flow problems with accuracy competitive with traditional PDE solvers and with much greater computing speed. This paper explores the first application of FNOs to model ultrarelativistic hydrodynamic flow of the quark-gluon plasma (QGP) generated in relativistic heavy-ion collisions. The application in ultrarelativistic flow is novel relative to classical flow due to the hydrodynamic evolution of the QGP occurring in femtometer-scaled explosions characterized by rapid expansion and cooling. In this study, we investigate the applicability of FNOs as computationally fast alternatives to standard numerical PDE solvers. The FNO predictions are evaluated by comparing with standard PDE solutions, using music in the jetscape Monte Carlo event generator framework. The performance of calculating established experimental observables for flow and jet quenching using FNOs in the MC framework is also reported.

Using the Monte Carlo $\mathrm{HYDJET}++$ model, we investigate the transverse momentum ($p_T$) spectra of heavy-flavor hadrons, namely $D^0, {\overline{D}}^0, D^{+}, D^{-}$, and ${\mathrm{\Lambda }}_c$, along with the nuclear modification factors of $D^0$ and $D^{\pm }$ in Au $+$ Au collisions at $\sqrt{s_{NN}}=200$ GeV RHIC energy across various centrality bins. This work extends the earlier study by relaxing the assumption of identical chemical and thermal freezeout and by exploring the effect of a higher chemical freezeout temperature relative to thermal freezeout. The study also explores the centrality and mass dependence of the charm enhancement factor (${\gamma }_c$). Furthermore, we investigate medium-induced energy loss, particle-antiparticle asymmetry, and the role of fragmentation in the hadronization process. The $\mathrm{HYDJET}++$ model, with its default parameters, is unable to reproduce heavy hadron yields due to their early thermal freezeout and initial state production of heavy quarks. Therefore, a systematic tuning of model parameters is performed to improve the overall agreement with experimental data. Additionally, to assess the performance of the $\mathrm{HYDJET}++$ model relative to other theoretical approaches, its results are compared with the TAMU, SUBATECH, Torino, and Duke models, for which corresponding simulation data are available. This study shows a decreasing trend in ${\gamma }_c$ from central to peripheral collisions. Moreover, ${\gamma }_c$ increases with increasing charm-hadron mass. The model approximately reproduces the experimental data of $p_T$ spectra at low and intermediate $p_T$. However, it overestimates the data at high $p_T$, indicating a need for improvements in modeling the energy loss of heavy quarks. The nuclear modification factors ($R_{AA}$ and $R_{CP}$) for $D^0$ mesons exhibit significant suppression at high $p_T$. At low $p_T, R_{AA}$ results show deviations from the data, reflecting limitations in the model where coalescence becomes important. The antiparticle-to-particle ratios are consistent with experimental data, whereas mixed-particle ratios are underestimated, revealing the model's limitation in estimating the baryon-to-meson enhancement.

The early stage of a heavy-ion collision is marked by rapid entropy production and the transition from a gluon saturated initial condition to a plasma of quarks and gluons that evolves hydrodynamically. However, during the early times of the hydrodynamic evolution, the chemical composition of the QCD medium is still largely unknown. We present a study of quark chemical equilibration in the (Q)GP using a novel model of viscous hydrodynamic evolution in partial chemical equilibrium. Motivated by the success of gluon saturated initial condition models, we initialize the QCD medium as a completely gluon dominated state. Local quark production during the hydrodynamic phase is then simulated through the evolution of time-dependent fugacities for each independent quark flavor, with the timescales set as free parameters to compare different rates of equilibration. We present the results of complete heavy-ion collision simulations using this partial chemical equilibrium model, and show the effects on hadronic and electromagnetic observables. In particular, we show that the development of flow is sensitive to the equilibration timescale, providing an empirical way to probe the chemical equilibration of the QCD medium.

The evolution of nuclear excitation in electron-gold ($e+\mathrm{Au}$) collisions at the forthcoming Electron-Ion Collider (EIC) is investigated using the beagle event generator. The EIC's collider kinematics and detector-motivated rapidity selections enable a clear separation, in the laboratory frame, of the dominant reaction stages: hard scattering, intranuclear cascade (INC), and nuclear deexcitation. A systematic study of the event-by-event mean transverse momentum fluctuation observable $\kappa$ reveals strong sensitivity to the intranuclear-cascade formation time and to nuclear geometry, with only weak dependence on the electron-beam energy. These findings indicate that $\kappa$ can serve as an exploratory diagnostic for disentangling the cascade and deexcitation stages of nuclear excitation at the EIC. The pronounced sensitivity observed within the beagle framework underscores the model dependence of the present results while at the same time motivating systematic cross-model investigations to establish the broader applicability of $\kappa$. The results yield stage-resolved, testable predictions for early EIC measurements.

We propose a new method to investigate the existence and location of the conjectured high-temperature critical point of strongly interacting matter via contours of constant entropy density. By approximating these lines as a power series in the baryon chemical potential ${\mu }_B$, one can extrapolate them from first-principle results at zero net-baryon density, and use them to locate the quantum chromodynamics (QCD) critical point, including the associated first-order and spinodal lines. As a proof of principle, we employ currently available continuum-extrapolated lattice data from the Wuppertal-Budapest collaboration to find a critical point at a temperature and a baryon chemical potential of $T_c=114.3\pm 6.9$ MeV and ${\mu }_{B,c}=602.1\pm 62.1$ MeV, respectively, at expansion order $\mathcal{O}\left({\mu }_B^2\right)$. We advocate for a more precise determination of the required expansion coefficients via lattice QCD simulations as a means of pinpointing the location of the critical endpoint in the phase diagram of strongly interacting matter.

We construct the three-nucleon contact potentials in the Jacobi partial-wave basis. The potentials are built in the separable form as the products of the antisymmetrized three-nucleon states in which the nucleons are arbitrarily close to each other. We compile the three-nucleon contact potentials up to $O\left(Q^2\right)$. These contact potentials are by construction independent operators under exchanges of any nucleon pairs.

We investigate the accurate description of $\alpha$-decay half-lives across a wide range of nuclei by integrating physical modeling with machine learning techniques. A double-folding potential model (DPM), constructed using a Skyrme-type effective nucleon-nucleon interaction that neglects momentum and spin dependence, is employed to calculate the $\alpha$-decay half-lives of 498 nuclei with $Z=61–118$. The model yields a root-mean-square (RMS) deviation of 0.58 from experimental data. To improve predictive accuracy, a support vector regression (SVR) method is applied. The SVR is optimized using the artificial bee colony algorithm and trained with the same nuclear input features {$Z, A, Q_{\alpha }, l$}. This approach reduces the RMS deviation to 0.44. Furthermore, by incorporating the SVR-predicted preformation factor into the DPM, the SVR-optimized DPM achieves a further reduction in RMS deviation to 0.41. The predictive performance of all three models is evaluated in the superheavy nuclear region, and their results are used to estimate the $\alpha$-decay half-lives of isotopes with $Z$= 117 and 118. These results offer reliable theoretical references for future experimental exploration of superheavy elements.

Background: Neutron-rich nuclei around $Z\approx 40$ are well known for exhibiting multiple shape transitions. This region shows one of the sharpest shape transitions in the nuclear chart, evolving from a spherical vibrator at $N=58$ to a strongly deformed prolate shape at $N=60$. The largest deformations are observed for ${}_{38}\mathrm{Sr}$ and ${}_{40}\mathrm{Zr}$. This abrupt shape transition disappears at $Z=36$ and below, where a shape transition from spherical to oblate nuclei is predicted. On the other hand, for $Z\ge 42$ and $N\ge 60$, the shape is known to evolve from axial to triaxial. While the even-$Z$ nuclei in this region have already been extensively studied, new insights can be gained from the studies of odd-$Z$ isotopes for a better understanding of the underlying mechanisms driving these phenomena.

Purpose: The ${}_{41}\mathrm{Nb}$ nuclei lie at the boundary between axially deformed Zr and triaxially deformed Mo nuclei. This work investigates the nuclear structure of very neutron-rich Nb nuclei up to $N=68$. The goal is to understand how the nuclear shape evolves as a function of isospin in this isotopic chain and provide new insights into the emergence of triaxial deformation.

Methods: The structure of the neutron-rich Nb isotopes was investigated using state-of-the-art high-resolution $\gamma$-ray spectroscopy of fission fragments produced via two different fission reactions. The use of ${}^9\mathrm{Be}({}^{238}\mathrm{U},f)$ inverse kinematics, with a detection system comprising AGATA, EXOGAM, and $\mathrm{VAMOS}++$, enabled the measurement of prompt and delayed $\gamma$ rays from isotopically identified fission fragments, and $\gamma \text{−}\gamma \text{−}\gamma \text{−}\gamma$ highfold data were obtained from a spontaneous fission source of ${}^{252}\mathrm{Cf}$ using the Gammasphere array.

Results: The level scheme of ${}^{105}\mathrm{Nb}$ has been significantly extended, with the addition of two negative-parity bands observed for the first time. A new level scheme is proposed for ${}^{107}\mathrm{Nb}$, which is not in agreement with an earlier measurement, and new levels and transitions have been added to the very neutron-rich ${}^{109}\mathrm{Nb}$. The degree of triaxiality of the new bands is discussed on the basis of signature splitting analysis. The recently reported level scheme of ${}^{99}\mathrm{Nb}$ has been revised.

Conclusions: This systematic study on the Nb isotopic chain, compared to Zr and Mo, indicates that while the ground-state band exhibits a triaxial deformation, attributed to a proton hole coupled to a triaxially deformed Mo core, the negative-parity bands, based on isomeric bandheads, display an axially symmetric deformed structure, similar to that observed in the Zr isotopes, revealing the existence of a shape coexistence in the neutron-rich Nb nuclei.

Low- and intermediate-spin negative-parity band structures have been investigated in the ${}^{82}\mathrm{Kr}$ nucleus using the fusion-evaporation reaction ${}^{76}\mathrm{Ge}$ (${}^9\mathrm{Be}, 3n$) at $E_{\text{Lab}}\approx 31$ MeV. Lifetimes of the states of interest in ${}^{82}\mathrm{Kr}$ have been measured using the Doppler shift attenuation method with the help of the Indian National Gamma Array, and the parity of the states has been confirmed from polarization measurements. The deduced $B$($M1$) and $B$($E2$) values from the lifetime measurements in comparison with the particle rotor model and the total Routhian surfaces calculations reveal that the bands DB1 and DB2 are based on the collective oblate and prolate deformed core, respectively. The enhanced electric dipole strengths, $B\left(E1\right)\mathrm{s}$, and dipole moments, $|D_0|\mathrm{s}$, for the parity-changing transitions connecting the negative-parity bands DB1 and DB2 to the ground-state positive-parity band QB1 ensure the octupole correlation in ${}^{82}\mathrm{Kr}$.

Within the framework of Lanzhou quantum molecular-dynamics transport model, the correlation of initial configuration and symmetry energy is systematically investigated in collisions of ${}^{238}\mathrm{U}+{}^{238}\mathrm{U}$. The impacts of the collision centrality (angular momentum), beam energy, stiffness of symmetry energy, and initial configuration on the collective flows, neutron/proton, and ${\pi }^{-}/{\pi }^{+}$ ratios have been thoroughly analyzed. It is found that the broader neutron-rich region is formed in the body-body collisions in comparison with the ones in the tip-tip collisions. The neutron-star matter might be created in the density region of 0.2–0.5 ${\rho }_0$ (the normal nuclear density ${\rho }_0=0.165{\mathrm{fm}}^{-3}$) formed in the ${}^{238}\mathrm{U}+{}^{238}\mathrm{U}$ reaction at the incident energy of 500 MeV/nucleon. The elliptic flows of protons are related to the incident energy, collision centrality, symmetry energy, and collision orientation. The hard-symmetry energy enables the larger free neutron/proton ratio at the beam energy of 500 MeV/nucleon. However, the neutron/proton and ${\pi }^{-}/{\pi }^{+}$ ratios in the density regime of $1.2\le \rho /{\rho }_0\le 1.8$ are enhanced by the soft-symmetry energy with the slope parameter of $\mathrm{L}=42$ MeV.

Sapphire has mechanical and electrical properties that are advantageous for the construction of internal components of radiation detectors such as time projection chambers and bolometers. However, it has proved difficult to assess its ${}^{232}\mathrm{Th}$ and ${}^{238}\mathrm{U}$ content down to the picogram per gram level. This work reports an experimental verification of a computational study that demonstrates $\gamma \gamma \text{coincidence}\text{counting}$, coupled with neutron activation analysis (NAA), can reach ppt sensitivities. Combining results from $\gamma \gamma \text{coincidence}\text{counting}$ with those of earlier single-$\gamma$ counting based NAA shows that a sample of Saint Gobain sapphire has ${}^{232}\mathrm{Th}$ and ${}^{238}\mathrm{U}$ concentrations of $<0.26\text{ppt}$ and $<2.3$ ppt, respectively; the best constraints on the radiopurity of sapphire.

In this work we provide a new, well-controlled expansion of the equation of state of dense matter from zero to finite temperatures $\left(T\right)$ while covering a wide range of charge fractions $\left(Y_Q\right)$, from pure neutron to isospin symmetric nuclear matter. Our expansion can be used to describe neutron star mergers using the equation of state inferred from neutron star observations. We discuss how knowledge from low-energy nuclear experiments and heavy-ion collisions can be directly incorporated into the expansion. We also suggest new thermodynamic quantities of interest that can be calculated from theoretical models or directly inferred by experimental data that can be used to infer the finite temperature equation of state. With our new method, we can quantify the uncertainty in our finite $T$ and $Y_Q$ expansions without making assumptions about the underlying degrees of freedom. We can reproduce results from a microscopic equation of state up to $T=100$ MeV for baryon chemical potential ${\mu }_B\gtrsim 1100$ MeV $[\approx (1–2)n_{\mathrm{sat}}]$ within $5\%$ error, with even better results for larger ${\mu }_B$ and/or lower $T$. We investigate the sources of numerical and theoretical uncertainty and discuss future directions of study.

The STAR Collaboration reports measurements of acoplanarity using semi-inclusive distributions of charged-particle jets recoiling from direct photon and ${\pi }^0$ triggers, in central $\mathrm{Au}\text{–}\mathrm{Au}$ and $pp$ collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV. Significant medium-induced acoplanarity broadening is observed for large but not small recoil jet resolution parameter, corresponding to recoil jet yield enhancement up to a factor of $\approx 20$ for trigger-recoil azimuthal separation far from $\pi$. This phenomenology is indicative of the response of the quark-gluon plasma to excitation, but not the scattering of jets off of its quasiparticles. The measurements are not well described by current theoretical models which incorporate jet quenching.

A generalization of the phenomenological blast-wave-Tsallis-power model, recently proposed by the author for the hadrons' transverse momentum ($p_{\text{T}}$) spectra measured at the CERN Large Hadron Collider (LHC), is developed to also describe the hadrons' $p_{\text{T}}$-differential elliptic flow coefficients $v_2$ in identical nuclei collisions of different centralities. The model describes well the available data on $p_{\text{T}}$ spectra and $v_2$ for any $p_{\text{T}}$ of various particles, from pions to charmonia, in Pb-Pb collisions at $\sqrt{s_{NN}}=$ 2.76 and 5.02 TeV and in Xe-Xe collisions at $\sqrt{s_{NN}}=$ 5.44 TeV. Also, predictions for OO collisions at $\sqrt{s_{NN}}=$ 5.36 TeV are given. While the model is mainly targeting the energies available at the LHC, it also works at much lower energies available at the BNL Relativistic Heavy Ion Collider.

I reexamine the perturbative renormalizability of chiral two-pion exchange in two-nucleon scattering for coupled triplets when one-pion exchange has been fully iterated at leading order. Improving on previous works, it is shown that only two counterterms are required to obtain cutoff independent results, which is one less than in naive dimensional analysis. The explanation for this reduction is the existence of an attractive and repulsive eigenchannel in the one-pion exchange potential for the coupled triplets: the attractive eigenchannel can be renormalized like a regular attractive uncoupled triplet, while the repulsive eigenchannel is always finite regardless of whether there are counterterms or not. I discuss the implications of this finding for the power counting of the ${}^{3}S_1\text{−}{}^{3}D_1$ and ${}^{3}P_2\text{−}{}^{3}F_2$ partial waves.