Nuclear Theory·nucl-th

Wednesday·April 8, 2026

14 papers—7 primary·7 cross-listed

01
Species-dependent viscous corrections at particlization: A novel relaxation time approximation approach
I. Aguiar🇧🇷 · T. Nunes da Silva🇧🇷 · G. S. Denicol🇧🇷 · M. Luzum🇧🇷 · G. S. Rocha🇧🇷 · C. Shen🇺🇸
We assess the effects of a recently proposed generalized relaxation time approximation (RTA) for multi-species relativistic gases within a realistic numerical hybrid framework and study its phenomenological consequences in p-Pb and Pb-Pb collisions. The novel approximation introduces counter-terms to the collision kernel, allowing for momentum-dependent relaxation times $τ_{i} (p)$ while preserving local energy-momentum conservation. As a consequence, the resulting first-order viscous corrections $δ f_{i}$ 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 ( $π, K, p$ ) are significantly affected, leading to modifications of relative particle yields such as the $K / π$ and $p / π$ 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.
nucl-thhep-ph0 citations
02
Equilibrated fraction of QCD matter in high-energy oxygen--oxygen collisions
Naoya Ito🇯🇵 · Tetsufumi Hirano🇯🇵
We quantify to what degree the QCD matter created in high-energy oxygen--oxygen ( $O + O$ ) collisions at $s_{N N} = 5.36$ TeV reaches a locally equilibrated state. For this purpose, we employ a novel framework based on the core--corona picture that describes the dynamics of both locally equilibrated fluids (the core) and nonequilibrium particles (the corona). Contributions from the core become larger than those from the corona above charged-particle multiplicity at midrapidity, $⟨ d N_{ch} / d η ⟩_{∣ η ∣ < 0.5} \approx 20$ . We also find that nonnegligible contributions from the corona still remain even in central $O + O$ collisions. The yield ratios of strange baryons to charged pions exhibit an increasing behavior with increasing multiplicity at midrapidity. However, these ratios are smaller than those obtained when assuming that QCD matter has reached complete chemical equilibrium. These results demonstrate that a purely hydrodynamic approach is insufficient and that the inclusion of a corona component is essential for describing the dynamics of intermediate-size systems such as $O + O$ collisions.
nucl-thhep-phnucl-exPRC(2026)·2 citations
03
Predictions of charge density distributions for nuclei with $Z \geq 8$
Yun Dong Wang · Tian Shuai Shang · Hui Hui Xie · Peng Xiang Du · Jian Li · Haozhao Liang
A deep neural network (DNN) has been developed to accurately predict nuclear charge density distributions for nuclei with proton numbers $Z \geq 8$ . By incorporating essential nuclear structure features, the model achieves a significant improvement in predictive accuracy over conventional methods. The charge density distributions are analyzed using a Fourier-Bessel (FB) series expansion, and the DNN is trained on a comprehensive dataset derived from relativistic continuum Hartree-Bogoliubov (RCHB) theory calculations. The model demonstrates exceptional performance, with root-mean-square deviations of 0.0123 fm and 0.0198 fm for charge radii on the training and validation sets, respectively, remarkably surpassing the precision of the original RCHB calculations. Beyond advancing nuclear physics research, this high-precision model provides critical data for applications in atomic physics, nuclear astrophysics, and related fields.
nucl-thcs.LGphysics.atom-phNucl.Sci.Tech.(2026)·5 citations
04
Impact of neutron-proton pairing on the nucleon high-momentum distribution in symmetric nuclear matter
Guo-peng Li · Ji-you Fu · Jin Zhou · Xin-le Shang · Jian-min Dong · Wei Zuo
The effect of neutron-proton ( $n p$ ) pairing on the high-momentum tail (HMT) of nucleon momentum distributions in symmetric nuclear matter is investigated within a combined framework of the extended Brueckner-Hartree-Fock approach with off-shell BCS theory. The HMT ratio, quantifying the high-momentum fraction in the BCS state relative to the normal state, reaches about $1.06$ around the density of $0.052 fm^{- 3}$ , indicating that the maximal contribution of the $n p$ pairing, amounts to approximately 6\% that from short-range correlations (SRCs). This contribution exhibits a density dependence that closely follows the squared relative pairing gap $Δ_{F} = Z_{F} Δ (k_{F})$ with respect to the kinetic energy $E_{k_{F}}^{*}$ evaluated using the effective mass, suggesting that $Δ_{F}^{2} / E_{k_{F}}^{* 2}$ provides a qualitative measure of the $n p$ pairing effect on the HMT. These findings highlight the significant role of $n p$ pairing and its interplay with SRCs in shaping nucleon momentum distributions in nuclear matter.
nucl-thPRC(2026)·1 citation
05
Channel couplings redirect absorbed flux from peripheral loss to fusion in weakly bound nuclear reactions
Hao Liu · Jin Lei · Zhongzhou Ren
In reactions of weakly bound nuclei, the absorption cross section mixes two physically distinct contributions: inner capture associated with compound-nucleus formation, and peripheral losses from breakup, transfer, and other direct reactions. Within a framework that combines an ingoing-wave boundary condition (IWBC) at an inner radius with a complex potential in the external region, we derive the exact flux identity $σ_{abs} = σ_{fusion} + σ_{W}$ from the radial continuity equation. The resulting partition is exact within the adopted CC/CDCC model space and provides a practical diagnostic of where absorbed flux is removed. Applied to $^{6}$ Li+ $^{209}$ Bi, the analysis reveals that channel couplings qualitatively reorganize the absorbed flux: the dominant absorption mechanism shifts from peripheral loss at sub-barrier energies to inner capture above the barrier, whereas the single-channel baseline remains peripheral-loss dominated throughout. The resulting IWBC-defined inner-capture cross section tracks the measured complete-fusion excitation function with only a modest dependence on the chosen boundary radius. Together with the exact identity $σ_{abs} = σ_{fusion} + σ_{W}$ , this agreement supports interpreting the peripheral term $σ_{W}$ as a major spatial contributor to the well-known CF suppression in weakly bound systems.
nucl-thPLB(2026)·2 citations
06
Beam energy dependence of identified particle production in heavy-ion collisions using a parton-hadron string dynamics model
Towseef Bhat🇮🇳 · Vipul Bairathi🇨🇱 · Lokesh Kumar🇮🇳 · Sonia Kabana🇨🇱
We report predictions for the transverse momentum ( $p_{T}$ ) spectra of $π^{\pm}$ , $K^{\pm}$ , $p$ , and $p ˉ$ in various collision centrality from Au + Au collisions at beam energies ( $E_{l ab}$ ) of 6.7, 8, 11, and 25 A~GeV using a parton-hadron string dynamics (PHSD) transport model. We studied the dependence of particle yields ( $d N / d y$ ), mean transverse momenta ( $⟨ p_{T} ⟩$ ), and particle ratios on collision energy and centrality to understand the underlying mechanisms of particle production. A comparison of the PHSD model results with available experimental measurements provides a qualitative description of these observables. Our results highlight the importance of baryon stopping, strangeness production, pair production, and baryon-antibaryon annihilation in the high baryon density region. These findings also provide theoretical insights relevant to the ongoing beam energy scan program at RHIC and the future heavy-ion programs at FAIR and NICA.
nucl-thhep-exhep-phnucl-ex0 citations
07
Uncertainty quantified three-body model applied to the two-neutron halo $^{22}$ C
Patrick McGlynn🇺🇸 · Chloë Hebborn🇺🇸
Two-neutron halo nuclei offer a fascinating probe into the behaviour of quantum few-body systems at the limits of binding. Although few nuclei have already been clearly identified, many of their properties remain poorly constrained. $^{22}$ C, one of the heaviest, still lacks a precise identification of its static and dynamic properties, such as its mass and dipole strength in the continuum. One main difficulty is that properties of two-neutron halo nuclei are inferred from experimental data using a theoretical model. Therefore, accurately determining the characteristics of two-neutron halo nuclei requires an accurate theoretical model and careful quantification of the uncertainties. In this work, we examine $^{22}$ C with a three-body model, seeing $^{22}$ C as a $^{20}$ C core and two halo neutrons, and quantify for the first time the uncertainties associated with the $^{20}$ C- $n$ interaction using a Bayesian approach. We propagate these uncertainties to properties of bound and scattering states of $^{22}$ C, as well as its dipole strength. The comparison of our prediction for the matter radius to experimentally-derived values suggests that $^{22}$ C is bound by less than 0.35~MeV and is dominated by a $(s_{1/2})^{2}$ configuration. Our analysis of the dipole strength shows that final-state interaction needs to be included for an accurate description, the uncertainties on the strength function are about 50\% and are mostly influenced by uncertainties on the ground-state properties, and partial-wave occupation of $^{22}$ C depends on the scattering length and the $d_{3/2}$ resonance energy of the $^{20}$ C- $n$ unbound system. Such sensitivity of the dipole strength to the properties of both $^{21}$ C and $^{22}$ C properties motivates a precise measurement of the $^{22}$ C dipole strength function, that will allow to precisely and accurately resolve the spectroscopy of these nuclei.
nucl-thPLB(2026)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE

Species-dependent viscous corrections at particlization: A novel relaxation time approximation approach

Equilibrated fraction of QCD matter in high-energy oxygen--oxygen collisions

Predictions of charge density distributions for nuclei with Z≥8

Impact of neutron-proton pairing on the nucleon high-momentum distribution in symmetric nuclear matter

Channel couplings redirect absorbed flux from peripheral loss to fusion in weakly bound nuclear reactions

Beam energy dependence of identified particle production in heavy-ion collisions using a parton-hadron string dynamics model

Uncertainty quantified three-body model applied to the two-neutron halo 22C

Affiliations

Predictions of charge density distributions for nuclei with $Z \geq 8$

Uncertainty quantified three-body model applied to the two-neutron halo $^{22}$ C