Nuclear Theory·nucl-th

Thursday·January 29, 2026

8 papers—5 primary·3 cross-listed

01
Exploring the properties of the Hadronic Phase in Heavy-Ion Collisions at RHIC Energies via Partial Chemical Equilibrium
Rishabh Sharma · Chitrasen Jena · Volodymyr Vovchenko
The hadronic phase in heavy-ion collisions plays a crucial role in shaping the final-state hadron abundances. In this work, we study Au+Au collisions at $s_{NN}$ = 7.7-200 GeV using the Hadron Resonance Gas model in Partial Chemical Equilibrium (HRG-PCE). By fitting the yields of stable hadrons and short-lived resonances such as K $^{*} (892)^{0}$ , we extract both chemical and kinetic freeze-out temperatures as functions of center-of-mass energy and centrality. The analysis, performed using the Thermal-FIST package, avoids assumptions about radial flow profile or freeze-out hypersurfaces. Furthermore, we estimate the baryon annihilation freeze-out temperature from the experimentally measured $p ˉ /$ p ratio, using the HRG-PCE framework extended to include $B B ˉ \leftrightarrow nπ$ reactions. The inferred annihilation freeze-out temperature lies between the chemical and kinetic freeze-out temperatures, suggesting that baryon annihilation remains active in the early hadronic phase but ceases prior to kinetic freeze-out. These results provide a consistent picture of the sequential decoupling of hadronic processes and demonstrate that inelastic hadronic interactions significantly influence the chemical composition of the system between chemical and kinetic freeze-outs at RHIC energies.
nucl-thhep-exhep-ph0 citations
02
Baryon Transition Form Factors from Dynamical Coupled-Channel Analyses
Yu-Fei Wang🇨🇳
In this talk, the electromagnetic transition form factors from the nucleon ground state to twelve $N^{*}$ and $Δ$ states are exhibited and discussed. Those results are extracted through a comprehensive coupled-channel approach -- the Juelich-Bonn-Washington model, with the center-of-mass energy ranging from $1.13$ GeV to $1.8$ GeV, and the photon virtuality up to $8$ GeV $^{2}$ . The extraction is based on $1 0^{5}$ electroproduction data points of $π N$ , $η N$ , and $K Λ$ channels, with additionally about $5 \times 1 0^{4}$ data points in the hadronic sector as well as photoproductions as boundary conditions. The form factors are defined from the residues at the corresponding resonance poles in the multipole amplitudes. Uncertainties are also estimated by the exploration of the parameter space. The qualitative behavior of the transition form factors of $N (1440)$ and $Δ (1232)$ here are in agreement with the previous studies, while for the other states, there has not been literature results that are also defined at the resonance poles.
nucl-thhep-phnucl-exPoS(2026)·0 citations
03
From first to second minimum: Parity-dependent level densities in $^{240, 242}$ Pu
A. Rahmatinejad · T. M. Shneidman · N. Jovancevic
We calculate the parity-dependent level density ratios for $^{240, 242}$ Pu across a broad range of quadrupole deformations, from the spherical configuration up to the superdeformed region, explicitly including both the ground-state minimum and the second minimum (fission isomer). The parity-equilibration energy, defined as the excitation energy at which positive- and negative-parity level densities approach equilibrium, is compared between configurations. A significant reduction is observed near the second minimum, indicating a faster equilibration process in this region.
nucl-th0 citations
04
Effects of the centrality determination method for the equation of state and nucleonic observables from Au+Au collisions at $s_{N N}$ = 2.4 GeV
Xiaoqing Yue🇨🇳 · Pengcheng Li🇨🇳 · Yongjia Wang🇨🇳 · Qingfeng Li🇨🇳 · Fuhu Liu🇨🇳
Centrality determination remains one of the major sources of systematic uncertainty in intermediate-energy heavy-ion collision analyses, especially for probing the nuclear equation of state (EoS) at supra-saturation densities. To quantitatively assess the uncertainties associated with different centrality determination methods and to investigate their effects on final-state EoS-sensitive observables. Within the ultra-relativistic quantum molecular dynamics (UrQMD) model, Au+Au collisions at $s_{N N}$ =2.4 GeV are performed within a soft and a hard EoS. Event centrality is determined using the multiplicity of all charged particles ( $M_{ch}$ ) and two impact parameter-based centrality filters, one based on a geometrical interpretation and the other based on the Glauber Monte Carlo (MC) model, denoted as $b_{f}$ and $b_{r}$ , respectively. It is shown that there exist significant differences between the real impact parameter distributions of event samples selected by $M_{ch}$ , $b_{f}$ , and $b_{r}$ , particularly between $M_{ch}$ and $b_{r}$ . When the $b_{f}$ is employed, uncertainties associated with centrality selection have a weaker influence on observables than the effects induced by the EoS. In contrast, when the $b_{r}$ is used, the influence of centrality-related uncertainties becomes more pronounced than that of the EoS. These results demonstrate that a rigorous and consistent mapping between $M_{ch}$ and impact parameter is essential to impose quantitative constraints on the high-density nuclear EoS. Furthermore, our study indicates that the geometrical interpretation of centrality remains valid and consistent with dynamical multiplicity selection, whereas the Glauber MC-based centrality determination becomes unreliable at the investigated energy.
nucl-thPRC(2026)·2 citations
05
De-excitation effects on entanglement in multi-nucleon transfer reactions
Y. C. Yang · D. D. Zhang · D. Vretenar · B. Li · T. Nikšić · P. W. Zhao · J. Meng
This study quantifies the impact of nuclear de-excitation on correlations in multi-nucleon transfer (MNT) reactions. To bridge the gap between initial collision dynamics and final experimental observables, we introduce a hybrid TDCDFT+GEMINI approach, integrating time-dependent covariant density functional theory (TDCDFT) with the statistical de-excitation model GEMINI++. Applied to the $^{40}$ Ca + $^{208}$ Pb reaction, our method demonstrates that the de-excitation is essential for reconciling theoretical cross sections with experimental data. Analysis of the cross-section Shannon entropy reveals that new reaction channels open abruptly at a specific energy threshold. By employing mutual information, we show that the de-excitation process significantly degrades the initial quantum entanglement between the projectile-like and the target-like fragments, revealing a key mechanism through which fundamental quantum correlations are lost.
nucl-thPRC(2026)·1 citation
06
The 2025 Evaluation of Experimental Thermonuclear Reaction Rates (ETR25)
Christian Iliadis · Richard Longland · Kiana Setoodehnia · Caleb Marshall · Peter Mohr · Athanasios Psaltis
This work describes the formalism for estimating thermonuclear reaction rates for astrophysical applications, emphasizing modern statistical approaches such as Monte-Carlo sampling and Bayesian models. We discuss related topics including the calculation of resonance energies from nuclear Q values, indirect estimates of particle partial widths, and matching of reaction rates at elevated temperatures to statistical-model results. We have evaluated available experimental data on cross sections, resonance energies and strengths, partial widths, life-times, spin-parities, and spectroscopic factors. Based on these results, we have estimated numerical values of 78 experimental charged-particle thermonuclear reaction rates for target nuclei in the A = 2 to 40 mass region, for temperatures ranging from 1 MK to 10 GK. For each reaction, three rate values are provided: low, median, and high, corresponding to the 16th, 50th, and 84th percentiles, respectively, of the cumulative reaction rate probability density distribution. Additionally, we present the factor uncertainty of each rate at each temperature grid point. These results enable users to sample the reaction rate probability density in nucleosynthesis calculations, facilitating uncertainty estimates of nuclidic abundances. The rates presented here refer to their laboratory values. For use in stellar model simulations, these values need to be corrected for the effects of thermal excitations of the interacting nuclei. For each reaction, we include graphs that illustrate the fractional contributions to the overall reaction rate along with the associated uncertainty. These visuals are designed to assist both stellar modelers and nuclear experimentalists by identifying the primary sources of rate uncertainty at specific stellar temperatures. A graphical comparison with earlier Monte-Carlo rates is also provided.
↳ astro-ph.SRnucl-exnucl-thAstrophys.J.Suppl.(2026)·3 citations
07
Toward a Unified Picture of Confinement and Baryon Structure
Fan Lin🇨🇳 · Xinyang Wang🇨🇳
In this work, we investigate the infrared structure of quantum chromodynamics from the perspective of the Cho-Faddeev-Niemi decomposition and the Faddeev-Niemi effective theory of Yang-Mills fields. We argue that the topological solitons of the Faddeev-Niemi theory, namely gluon knots characterized by the Hopf invariant, should be regarded as the relevant ground-state degrees of freedom of Yang-Mills theory in the deep infrared region. In this framework, gluon knots provide a unified description of monopole condensation and the center-vortex confinement mechanism. We further propose that baryons are composite objects consisting of quarks immersed in a gluon-knot background. The monopole condensate associated with the gluon knot realizes dual superconductivity, squeezes color-electric flux into flux tubes, and naturally generates the $Y$ -shaped confinement structure of baryons. Simultaneously, the strong local color-magnetic field generated by the gluon knot induces chiral symmetry breaking through magnetic catalysis and topological vacuum fluctuations. We show that the Hopf invariant of the gluon knot is closely related to the topology of Yang-Mills vacua and discuss its connection with the axial anomaly and instanton-induced chiral symmetry breaking. Furthermore, the topological current associated with gluon knots provides a natural carrier of gluon angular momentum and may account for a substantial fraction of the proton spin. The resulting picture establishes a possible connection between the infrared topology of Yang-Mills theory and the internal structure of baryons, providing a unified framework for confinement, chiral symmetry breaking, and baryon structure in QCD.
↳ hep-thhep-phnucl-th0 citations
08
Bjorken Initial Energy Density and Viscous Longitudinal Hydrodynamic Evolution in Xe-Xe Collisions
S. Biswal🇮🇳 · M. A. Bhat🇮🇳 · A. Nayak🇮🇳 · S. I. Sahoo🇮🇳 · D. Dutta🇮🇳 · D. K. Mishra🇮🇳 · P. K. Sahu🇮🇳
We present a systematic study of the Bjorken initial energy density in Xe-Xe collisions at $s_{N N} = 5.44$ TeV, estimated using charged-particle multiplicity data and a generalized transverse overlap geometry applicable beyond the most central collisions. The dependence of the extracted energy density is examined by adopting both a constant formation time and a centrality-dependent formation time derived from Pb-Pb collisions at $s_{N N} = 5.02$ TeV. Corresponding Bjorken energy density estimates for Pb-Pb collisions are also presented for comparison. Taking the Bjorken energy density and formation time as initial conditions, the subsequent longitudinal evolution of the quark-gluon plasma (QGP) formed in these collisions is studied. Both ideal and first-order viscous boost-invariant hydrodynamics are employed to assess the influence of dissipation. We observe that viscous effects slow the longitudinal expansion and lead to entropy production dominated by early-time dynamics. The lifetime of the QGP is observed to increase with centrality and is substantially enhanced by viscous effects. These effects are highly sensitive to the choice of formation time, particularly in peripheral collisions. A comparative analysis of Xe-Xe and Pb-Pb collisions demonstrates that the longitudinal evolution is primarily controlled by the initial energy density scale set by the Bjorken prescription. Consequently, when this scale is comparable, both systems exhibit nearly identical evolution patterns, while appreciable distinctions emerge in peripheral collisions due to system-size and geometric effects.
↳ hep-phnucl-th0 citations

Affiliations

first authorsco-authorsvia INSPIRE