$p_t$-differential quantity $v_2\left(p_t\right)$ is meant to measure elliptic flow manifested by a dense QCD medium formed in high-energy nucleus-nucleus collisions. Elliptic flow may be referred to more neutrally as a cylindrical quadrupole component of the transverse motion of particle sources within a collision. As defined, $v_2\left(p_t\right)$ relies on an implicit assumption that almost all produced particles emerge from a single source. This article describes a detailed study of the algebraic structure of $v_2\left(p_t\right)$. A procedure is developed to derive a common monopole boost (“radial flow”) value and quadrupole $p_t$ spectra for several hadron species. The method is applied to $v_2\left(p_t\right)$ data for four hadron species from 2.76-TeV Pb-Pb collisions. According to available $v_2\left(p_t\right)$ data the assumption of a single dominant particle source within $A\text{−}A$ collisions is unjustified. Combined with a previous study of quadrupole amplitude variation for 200-GeV $p\text{−}p$ collisions these results demonstrate that quadrupole structure is related to a novel QCD process separate from projectile-nucleon dissociation and jet production. Given quadrupole evolution it is unlikely that a hydrodynamic description is relevant to that process.

We assess the effects of a recently proposed generalized relaxation time approximation (RTA) for multispecies relativistic gases within a realistic numerical hybrid framework and study its phenomenological consequences in $p$-Pb and Pb-Pb collisions. The novel approximation introduces counterterms to the collision kernel, allowing for momentum-dependent relaxation times ${\tau }_i\left(p\right)$ while preserving local energy-momentum conservation. As a consequence, the resulting first-order viscous corrections $\delta f_i$ to the phase-space distribution functions depend explicitly on the particle species mass $m_i$. We systematically investigate the impact of these species-dependent corrections on particle production at particlization, focusing on identified hadron yields and transverse momentum ($p_T$) spectra obtained from Cooper-Frye sampling. We find that the yields and spectra of light hadrons ($\pi ,K,p$) are significantly affected, leading to modifications of relative particle yields such as the $K/\pi$ and $p/\pi$ ratios. We show that these effects persist, albeit with reduced magnitude, after the inclusion of the hadronic cascade stage. In contrast, the impact on inclusive charged-particle observables is strongly reduced due to compensating enhancements and suppressions among different species. This controlled deformation of identified hadron observables, which selectively modifies flavor-sensitive quantities, makes the new prescription particularly well suited for Bayesian inference, as it introduces new sensitivity directions without spoiling existing constraints. Overall, our results demonstrate that species-dependent viscous corrections arising from the generalized RTA can leave significant and observable imprints on identified hadron production and relative yields, while remaining fully consistent with the successful description of bulk collective flow observables.

We derive the long-range components of the nucleon-nucleon (NN) two-pion-exchange potential with an intermediate Roper resonance. Leading-order interactions in heavy-baryon chiral perturbation theory are considered. To assess the Roper contributions in a unified framework, we include the leading contributions from the Delta resonance, as well as mixed Delta-Roper effects. NN phase shifts with orbital angular momentum $L\ge 2$ are calculated in first-order perturbation theory and compared to those obtained without the Roper resonance. We find that the Delta sets the dominant scale of the resonance-induced corrections, while the Roper-dependent effects are smaller, strongly channel dependent, and most visible in the $D$ waves.

We analyze 67 heavy-ion fusion reactions with high-quality sub-barrier excitation functions using the single-Gaussian model of Jiang et al. [Phys. Rev. C 112, 034612 (2025)] and extract the barrier parameters $R_g,V_g,W_g,R_g^2{W}_g$. The reactions involve seven projectiles, ${}^{16,18}\mathrm{O}, {}^{28,30}\mathrm{Si}, {}^{32,34}\mathrm{S}$, and ${}^{40}\mathrm{Ca}$, on targets from ${}^{12}\mathrm{C}$ to ${}^{208}\mathrm{Pb}$. The mean barrier height $V_g$ scales linearly with $\eta =Z_1{Z}_2/(A_1^{1/3}+A_2^{1/3})$ ($r=0.999$), while $R_g^2{W}_g$ correlates strongly with $W_g$ ($r=0.95$). The $\eta$ dependence accounts for 45% of the variation in fusion strength. After removing this geometric dependence, the resulting structure ratio $r_{\eta }$ shows no correlation with static target deformation or neutron-transfer $Q$ value. For the 24 systems with at least one open transfer channel, however, $r_{\eta }$ correlates strongly with an effective transfer coupling strength $\mathrm{\Lambda }$ ($r=0.70, p=1.4\times {10}^{-4}$), whereas the $Q$ value alone does not. Thus, positive-transfer $Q$ values are necessary but not sufficient for fusion enhancement, with the transfer coupling strength playing a key role. Systems showing the largest deviations from the geometric trend provide promising candidates for detailed coupled-channels studies.

Evaluated nuclear databases currently in use for numerical simulations to develop new nuclear technology and design advanced nuclear reactors still present large uncertainties. Their improvement is necessary, in particular through better reaction models and experimental nuclear data. Among the reactions of interest, $(n,n^{\prime })$ reactions or inelastic scattering reactions are of great importance for the operation of a reactor as they modify the neutron spectrum, the neutron population, and produce radioactive species. Providing new data on inelastic scattering reactions can be done in several ways, looking at the emitted neutrons, or $\gamma$ rays. Here we present experimental data on $\left(n,n^{\prime }\gamma \right)$ reactions that provide strong constraints on the mechanism of inelastic scattering. Tungsten isotopes, being deformed like actinides but free of the fission channel, are of interest to test the models. We report on ${}^{182,184,186}\mathrm{W}$$(n,n^{\prime }\gamma )$ cross-section measurements. Seventy $\gamma$-production cross sections were measured. This large set of new experimental data offers a valuable opportunity to probe modeling of direct, preequilibrium and compound nucleus reaction mechanisms. The choice of major reaction ingredients and parameters can be refined thanks to comparison to partial $\left(n,n^{\prime }\gamma \right)$ cross sections, which allows to provide recommendations and highlight modeling aspects that may require further work.

Although coupled-channels (CC) calculations have been widely used to describe sub-barrier fusion cross sections, theoretical interpretations can be affected by ambiguities arising from the choice of input potential parameters and explicit coupling schemes. In this work, we systematically investigate this “parameter-coupling nonuniqueness” using the ccfull2 code. Starting from the empirical Akyüz–Winther (AW) parametrization, we perform a systematic grid-based scan for several representative heavy-ion systems. The above-barrier fusion cross sections are employed to map an AW-centered Woods–Saxon (WS) parameter space and to select representative phenomenological effective baselines, rather than to determine a unique bare nucleus-nucleus potential. By confronting these effective WS baselines, selected from an AW-centered parameter scan, with various coupling schemes adopted in the literature, we show that for some systems and under some comparison metrics, distinct combinations of potential parameters and coupling schemes can yield phenomenologically similar descriptions of fusion excitation functions. When fusion barrier distributions are further considered, this ambiguity can be more stringently constrained in a system-dependent manner, although not eliminated. Our results emphasize that the barrier distribution provides a more sensitive and complementary observable for testing the consistency of coupling schemes, rather than a unique determination of the coupling effects involved.

In low-energy heavy-ion collisions, baryon stopping is an important process, in which protons from the initial colliding nuclei are stopped at the midrapidity region. Quantifying such stopping can reveal information on the properties of the nuclear medium, such as net-baryon density. Although experimental measurement of net-proton rapidity spectra provides constraints, the microscopic origin of such protons is not fully accessible. Transport model studies can therefore provide deeper insight into the microscopic origin of protons that are transported from initial nuclei, complementing experimental measurements. This article presents an investigation of baryon stopping in minimum-bias $\mathrm{Au}+\mathrm{Au}$ collisions over a wide range of beam energies, $\sqrt{s_{NN}}=2.4–17.3$ GeV ($E_{\mathrm{lab}}=1.23A–158A$ GeV). Final-state protons are classified based on their origin by analyzing their interaction history in the UrQMD model. It is found that a significant fraction of transported protons at midrapidity originates from initial neutrons rather than initial protons, referred to as isospin-converted protons, and their contribution as a function of collision energy and centrality is quantified. Anisotropic flow coefficients of different proton categories are estimated and compared with experimental measurements. Furthermore, a comparison between the ${\pi }^{-}/{\pi }^{+}$ ratio and isospin conversion rate is performed. The isospin conversion rate is further compared with the $\alpha$ parameters of the Kitazawa-Asakawa formalism, revealing a significant deviation from the chemical equilibrium assumption ${\alpha }_N={\alpha }_{\pi }$ below $\sqrt{s_{NN}}\lesssim 10$ GeV. Finally, the saturation of the isospin conversion rate is found to coincide with the onset of nuclear transparency, demonstrating that isospin randomization and baryon stopping are coupled phenomena in hadronic transport across the NICA/FAIR energy range.

We investigate charm-quark dynamics in asymmetric $\mathrm{Cu}+\mathrm{Au}$ collisions at top energies available at the BNL Relativistic Heavy Ion Collider using a Langevin approach embedded in a realistic hydrodynamic background. The intrinsic asymmetry of the colliding nuclei leads to a spatially lopsided initial energy-density profile, which generates a dipolar flow structure in the transverse plane even at midrapidity. As charm quarks propagate through this medium, they acquire a finite directed flow, $v_1$. We find that the $p_T$-integrated heavy-quark $v_1$ is approximately an order of magnitude larger than that of charged hadrons. In addition, the $p_T$-differential $v_1$ exhibits strong sensitivity to the initial spatial distribution of heavy quarks, highlighting the potential impact of preequilibrium modifications of the heavy-quark phase-space distribution on final-state anisotropies. Beyond geometric effects, $v_1$ also provides direct sensitivity to medium interactions through the temperature-dependent drag coefficient. Its pronounced dependence on this transport input indicates that precision measurements of heavy-flavor directed flow could place meaningful constraints on heavy-quark transport coefficients, thereby improving Langevin-based descriptions and predictive power for heavy-flavor observables in heavy-ion collisions.

Higher-order cumulants between the mean transverse momentum and elliptic flow are calculated in a relativistic viscous hydrodynamic model of relativistic heavy-ion collisions. The results of the hydrodynamic simulations are compared with calculations using event-by-event predictors of the final collective observables constructed from the initial-state entropy distribution. The predictors describe quantitatively the centrality dependence of the higher cumulants considered in the paper. We derive quantitative relations between the cumulants of the mean transverse momentum and different moments of the harmonic flow. The hydrodynamic model results satisfy those relations very well. Those relations could be used to test experimentally the collective origin of the observed correlations between the mean transverse momentum and harmonic flow.

Background: The nuclear structure in the region southwest of the doubly magic ${}^{208}\mathrm{Pb}$ is important to benchmark theoretical models relevant for neutron-rich heavy element formation and for the origin of the $A\approx 195$ peak in the mass abundance distribution. Although neutron-rich Pb, Tl, and Hg ($Z=80\text{–}82$) isotopes are relatively well studied, experimental data for neutron-rich Au isotopes ($Z=79$) remain largely limited due to experimental challenges.

Purpose: The purpose of this work is to investigate the evolution of the high-spin structure in neutron-rich Au isotopes near the $N=126$ shell closure and to characterize the underlying shell-model configurations, with a particular focus on the roles of the high-$j$ unique-parity $\pi h_{11/2}$ and $\nu i_{13/2}$ orbitals.

Methods: Neutron-rich ${}^{195\text{–}202}\mathrm{Au}$ isotopes were produced using multinucleon transfer reactions of ${}^{198}\mathrm{Pt}({}^{136}\mathrm{Xe}, {}^x\mathrm{I}){}^y\mathrm{Au}$ at a beam energy of 7 MeV/nucleon. Prompt and delayed $\gamma$-ray spectroscopy of isotopically identified reaction products was performed with a unique experimental setup combining the $\mathrm{VAMOS}++$ large acceptance magnetic spectrometer, the AGATA high-purity germanium $\gamma$-ray tracking array, and the CATLIFE detection system.

Results: In even-$A {}^{196,198,200,202}\mathrm{Au}$ isotopes, prompt $\gamma$-ray transitions built on the ${12}^{-}$ isomer have been observed for the first time. The odd-$J$ band built on the ${11}^{-}$ state vanishes for $A\ge 196$. In odd-$A {}^{195,197,199,201}\mathrm{Au}$ isotopes, new prompt and delayed $\gamma$-ray transitions above the $11/2^{-}$ isomer were identified, confirming and extending the known level schemes. New isomeric states assigned to ($25/2^{+}$) have been established in ${}^{199}\mathrm{Au}$ and ${}^{201}\mathrm{Au}$. The minima in the excitation energies of the bands as a function of $N$ built on the $11/2^{-}$ and ${12}^{-}$ isomers occur at ${}^{198}\mathrm{Au}$ ($N=119$), showing a dip against an otherwise smooth evolution.

Conclusions: Large-scale shell-model calculations based on the Kuo-Herling hole effective interaction show an overall good agreement with experimental level schemes. However, the present calculations do not reproduce the minima in excitation energies at $N=119$ observed in both Au and Hg isotopes. A systematic analysis of $\pi h_{11/2}$ and $\nu i_{13/2}$ hole occupancies, together with spin contributions of protons and neutrons, sheds light on the role of these high-$j$ unique-parity orbitals in the generation of high-spin states. Part of the results of this work have been reported in another publication [Y. Cho et al., Phys. Lett. B 878, 140558 (2026)].

Monochromatic neutron emissions from photonuclear sources ${}^{88}\mathrm{Y}/\mathrm{Be}$ and ${}^{124}\mathrm{Sb}/\mathrm{Be}$ are employed to obtain the response of pure (undoped) cesium iodide at 80 K. The use of a low-noise, high-quantum-efficiency avalanche photodiode in combination with a novel wave shifter results in a 70 eV analysis threshold. This reach allows us to observe signals from sub-keV nuclear recoils originating in neutron scattering. The extracted quenching factor drops much faster towards low energy than the extrapolation of a model developed for room-temperature CsI[Na]. We comment on the impact of our measurement on planned use of cryogenic CsI in neutrino physics and dark matter experiments.

Cluster structure of atomic nuclei, which plays a crucial role in the reaction mechanism, can be probed using breakup and transfer followed by breakup processes. The reaction mechanism, including breakup and transfer breakup, involving the ${}^{10}\mathrm{B}$ nucleus has been investigated by performing charged particle coincidence measurements of $\alpha \text{−}{}^6\mathrm{Li}$ and $\alpha \text{−}{}^7\mathrm{Li}$ fragment pairs originating from the decay of resonant ${}^{10,11}\mathrm{B}^{*}$ states in the ${}^{10}\mathrm{B}+{}^{209}\mathrm{Bi}$ reaction at $E_{\mathrm{lab}}=53.7$ MeV $(E_{\mathrm{c}.\mathrm{m}.}/V_B\sim 1.02)$. Breakup from various resonant states of ${}^{10,11}\mathrm{B}$ above their respective $\alpha$-decay threshold have been investigated. Angular distributions were extracted and benchmarked with coupled-channels calculations. Angle integrated cross sections for breakup following inelastic excitation and neutron pickup are found to be of similar magnitude. Statistical model calculations for the compound nuclear evaporation along with inclusive and exclusive data suggest that cluster transfer and/or capture of ${}^{3,4}\mathrm{He}$ are important in addition to breakup processes.

The present investigation focuses on the improvement of the accuracy of the description of physical observables of interest in a moderately sized fermionic basis within the framework of covariant density functional theory. It extends the previous study [B. Osei et al., Phys. Rev. C 112, 054321 (2025)] to point coupling (PC) covariant energy density functionals (CEDFs) and to excited states. Using as a benchmark the solutions corresponding either to an infinite fermionic basis or those extrapolated to such a basis it is shown that the optimization of oscillator frequency $\hslash {\omega }_0$ of the harmonic oscillator (HO) basis leads to a substantial improvement in the description of different physical observables in the fermionic basis truncated at $N_F$. Globally optimized scaling factors $f_{\mathrm{opt}}\left(A\right)$ of the oscillator frequency and the sizes $N_F^{\varepsilon }$ of the HO bases providing the required accuracy $\varepsilon$ in the calculations of the binding energies are generated for the PC functionals. The optimization of the basis also significantly improves the accuracy of the description of potential energy curves, defining the fission barriers and fission isomers in actinides and superheavy nuclei, provided that the size of the basis is at least equal to $N_F=20$. The optimization of the HO basis improves the accuracy of the description of the energies of bound single-particle states: the only exceptions are weakly bound neutron states with low orbital momenta $l=0$, 1, and 2. It is demonstrated for the first time that the halo densities of neutron halo nuclei generated in the coordinate space calculations are well reproduced in the calculations with very large fermionic HO bases.

Coherent hard exclusive reactions on light nuclei provide access to their quark and gluon structure and enable three-dimensional tomography of these complex systems. We study deeply virtual Compton scattering on a helium-4 target, including both kinematic twist-3 and twist-4 corrections, as well as next-to-leading-order corrections to the twist-2 amplitude in the strong coupling ${\alpha }_s$. We show that these contributions are crucial for achieving a precise description of the data and, as a result, obtain the first tomographic image of the helium-4 nucleus at the quark-gluon level.

One of the outstanding challenges in nuclear physics is achieving a comprehensive understanding of the equation of state that governs dense nuclear matter, and, by extension, the internal composition and structure of compact astrophysical objects such as neutron stars and quark stars. The primary approach to addressing this problem has thus far been predominantly theoretical, involving the construction of equations of state based on plausible nuclear and particle physics theories. These theoretical predictions are subsequently evaluated against empirical results, which are obtained primarily from heavy-ion collision experiments and, increasingly, from astrophysical observations of compact objects. In recent years, several alternative analytical methodologies have been developed that integrate the aforementioned theoretical and empirical approaches. These methods incorporate advanced data analysis and processing techniques, including Bayesian inference, and machine-learning and deep-learning frameworks, to enhance the interpretation and constraining of the equation of state for dense nuclear matter. In this study, the aforementioned techniques, particularly machine learning and deep learning, are employed with the objective of enhancing our understanding of the equation of state by leveraging information derived from mass-radius diagrams of compact objects. More specifically, this study utilizes a large dataset of equations of state constructed using multimodal formulations of neutron stars, along with a corresponding dataset for quark stars. These equations of state are consistent with known physical constraints and have been developed to reflect the highest degree of physical plausibility. Through the application of machine-learning and deep-learning techniques, it becomes possible to infer or reconstruct the underlying equations of state based on input from mass-radius diagram data.

The low-energy $\mathrm{\Xi }$-deuteron scattering is investigated through the solution of Faddeev equations, employing three sets of the currently available representation of the $\mathrm{\Xi }$-nucleon interactions. One of these is the chiral next-to-leading order interaction specified by the Jülich group, and the other two are based on the calculations by the HAL QCD method. The $s$-wave phase shifts in the $J=3/2$ and $J=1/2$ states are presented. Three-body wave functions in coordinate space are constructed from the Faddeev amplitudes in momentum space. These functions are used in the calculation of $\mathrm{\Xi }d$ momentum correlation functions. The effects of the deuteron breakup are significant in the $J=3/2$ channel. The differences in the magnitude of the calculated correlation function show the quantitative difference of the $\mathrm{\Xi }N$ interactions in the spin-isospin channels. The prospective experimental data on the $\mathrm{\Xi }d$ momentum correlation function could contribute to a better description of the $\mathrm{\Xi }N$ interactions.

The identical charged-kaon correlations induced by quantum-statistics effects and final-state interactions are measured in Pb-Pb collisions at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$. The results of one- (1D) and three-dimensional (3D) analyses show that the obtained system-size parameters (radii) are smaller for more peripheral collisions and decrease with increasing pair transverse momentum $k_{\mathrm{T}}$. The 1D parameters agree within uncertainties with those obtained in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76\mathrm{TeV}$. The observed power-law dependence of the extracted 3D radii as a function of the pair transverse momentum is a signature of the collective flow in the particle-emitting system created in Pb-Pb collisions. This dependence is well reproduced by the integrated hydrokinetic model calculations except for the outward projection of the radius (measured in the longitudinally comoving system) for the most central collisions. The time of maximal emission for kaons is extracted from the 3D analysis in a wide collision centrality range from 0 to 90%. Its reduction with decreasing charged-particle multiplicity is well reproduced by the hydrokinetic model predictions, and means that kaons are emitted earlier in more peripheral events.