Nuclear Theory·nucl-th

Friday·February 27, 2026

17 papers—9 primary·8 cross-listed

01
Impact of Geometric Inflation on Nucleon Size Sensitivity in Relativistic Heavy-Ion Collisions
Jian-fei Wang🇨🇳 · Hao-jie Xu🇨🇳
The intrinsic transverse size of nucleons, parameterized by a Gaussian width $w$ , is a critical yet uncertain input in the initial-state modeling of relativistic heavy-ion collisions. Using a finite $w$ in standard initial geometry models introduces an unintentional ``geometric inflation'' that alters the initial nuclear density profile. In this study, we implement a self-consistent density correction to eliminate this artifact and investigate its impact on final-state observables. Through hybrid (viscous hydrodynamics + hadronic transport) simulations of $^{208}$ Pb+ $^{208}$ Pb collisions at the LHC, we demonstrate that removing geometric inflation significantly modifies the sensitivity of observables to the nucleon width $w$ . While elliptic flow and mean transverse momentum ( $⟨[p_{T}]⟩$ ) become less sensitive to variations in $w$ , the Pearson correlation coefficient $ρ (v_{n}^{2}, δ p_{T})$ , $[p_{T}]$ fluctuations, and triangular flow exhibit enhanced sensitivity to fluctuations in nucleon positions. Our results indicate that uncorrected geometric inflation can bias the extraction of nucleon structure and quark-gluon plasma properties. This underscores the necessity of a self-consistent initial-state geometry for reliable Bayesian inference in heavy-ion collisions.
nucl-thnucl-ex0 citations
02
The shape of transverse momentum spectra in hybrid hydrodynamic models
Thiago S. Domingues🇧🇷 · Fernando G. Gardim🇧🇷 · Cicero D. Muncinelli🇧🇷 · Andre V. Giannini🇵🇹 · Gabriel S. Denicol🇧🇷 · Tiago Nunes da Silva🇧🇷 · David D. Chinellato🇦🇹 · Giorgio Torrieri🇧🇷 · Mauricio Hippert🇧🇷 · Jun Takahashi🇧🇷 · Matthew Luzum🇧🇷
We study the scaled transverse momentum spectra over a wide parameter space of state-of-the-art hydrodynamic simulation models in order to learn what information can be obtained from the shape of identified-particle spectra -- previously observed to be surprisingly universal across centrality and collision systems in both experimental data and hydrodynamic simulations. We study its sensitivity to each of 17 model parameters in the context of 4 different models for particlization when switching from the hydro description to the kinetic theory afterburner. We find that the strongest sensitivity is to parameters relating to bulk viscosity, free-streaming time, and the $\texttt{T$ _\mathrm{R} $ENTo}$ nucleon width parameter $w$ . However, we find that the model generally has surprisingly little flexibility in describing the scaled spectrum observable, despite the large number of parameters. Within this small range of parameter dependence, we further find significant tension in a simultaneous description of momentum-integrated observables. In particular, while the mean transverse momentum prefers a large value of the nucleon width parameter $w$ , a small value is required to obtain scaled spectra that are consistent with experimental measurements. We speculate on the origin of these model tensions and possible missing physics in the commonly-used $\texttt{T$ _\mathrm{R} $ENTo}$ +free streaming+hydro+afterburner simulation model.
nucl-thhep-phhep-th2 citations
03
Symmetry-imposed correlation in nuclear level statistics: The spin distribution
Junchao Guo · Yang Sun
Despite long-term research, the origin of spin cutoff in the angular-momentum (spin) distribution of nuclear level densities remains incompletely elucidated. We demonstrate that this problem can be traced back to Bethe's assumption that nucleons in finite Fermi systems are independent random variables. By constructing a statistical ensemble that enforces rotational invariance through angular-momentum coupling, we obtain an analytical expression for the spin cutoff parameter, which includes a previously unidentified finite-population correction. Our results show that, even in the absence of interactions, nuclear many-body states exhibit non-negligible correlations arising from fermionic antisymmetry and angular-momentum coupling. From this perspective, spin cutoff may be interpreted as a quantitative measure of correlation imposed by symmetry in nuclear level statistics.
nucl-th0 citations
04
Statistical properties of non-flow correlations in pp and heavy-ion collisions at RHIC energies
Satya Ranjan Nayak🇮🇳 · Akash Das🇮🇳 · B.K. Singh🇮🇳
In this work, we have studied the two-particle cumulant in pp, d-Au, and Au-Au collisions. The two-particle cumulant was treated as an event-by-event distribution, and its skewness and kurtosis were analyzed. The non-flow correlations, like jets and decays, constantly produced a skewed distribution, regardless of the model used. On the contrary, HYDJET++ produced a smooth Gaussian distribution at higher $η$ windows in fixed impact parameter collisions. The skewness increased consistently for higher $η$ windows in all non-QGP models like PYTHIA, PHOJET, QGSJET, and DPMJET. The kurtosis of the distribution also increased with $η$ windows in non-QGP models. The skewness and kurtosis of the distributions produced by HYDJET++ decreased with $Δ η$ and eventually reached zero at higher $Δ η$ .
nucl-thhep-ph0 citations
05
Space-time regions of high baryon density and baryon stopping in heavy-ion collisions
Yuri B. Ivanov🇷🇺
Four-volumes ( $V_{4} =$ spatial-3-volume $\times$ lifetime) are calculated within the model of three-fluid dynamics (3FD) and compared with those of the the JET AA Microscopic Transport Model (JAM). The calculations are performed for central Au+Au collisions at energies $s_{N N} =$ 3 -- 19.6 GeV. These $V_{4}$ indicate optimal collision-energy ranges for realizing macroscopic high baryon-density matter. It is found that the 3FD four-volumes noticeably exceed those in the JAM, which indicates a stronger baryon stopping in the 3FD model as compared to that JAM. It is argued that this difference in the baryon stopping correlates with stiffness of the EoS implemented in these models. Contrary to JAM, the four-volume, where a baryon density ( $n_{B}$ ) exceeds three times the normal nuclear density ( $n_{0}$ ), does not exhibit a maximum as a function of $s_{N N}$ . It decreases monotonically with increasing $s_{N N}$ , remaining at a fairly macroscopic level (i.e. $V_{4} \geq 5. 5^{4}$ fm $^{4}$ /c). For higher baryon densities, $V_{4}$ exhibits maxima in its dependence on $s_{N N}$ . The optimal energy range for densities $n_{B} / n_{0} >$ 4 is located at $s_{N N} =$ 3.2 -- 8 GeV. Even for $n_{B} / n_{0} >$ 6, the four-volume remains quite macroscopic ( $V_{4} \geq 4^{4}$ fm $^{4}$ /c) at $s_{N N} =$ 4.5 -- 9 GeV contrary to the JAM.
nucl-thhep-phPRC(2026)·1 citation
06
CREX and PREX-II reconciled within energy-density functional theory
P. Papakonstantinou
The CREX and PREX-II measurements of the neutron-skin thickness of 48Ca and 208Pb challenge standard nuclear energy-density functional (EDF) descriptions of nuclei and nuclear matter. We show that the apparent tension arises from an implicit constraint in EDF theory, which ties the density dependence of the functional at the dilute nuclear surface to that of uniform matter near saturation. Relaxing this surface-bulk coupling and independently constraining the dilute-density sector, while preserving realistic saturation and high-density behavior, yields EDFs that simultaneously reproduce the neutron skins of both nuclei, their electric dipole polarizabilities, and neutron-star mass-radius relations. The established correlation between the neutron-skin thickness and the symmetry-energy slope parameter L at saturation is retained but becomes substantially broader. The results show that current neutron-skin data do not require extreme values of L and highlight an underconstrained degree of freedom associated with low-density nuclear matter.
nucl-th1 citation
07
Towards a microscopic description of 12C+12C fusion at stellar energies
P. Descouvemont
I present a fully microscopic description of the 12C+12C fusion reaction at stellar energies. Utilizing the multichannel Resonating Group Method (RGM), my model explicitly includes 12C+12C and alpha+20Ne reaction channels (with excited states). This approach provides a consistent, simultaneous, description of fusion, elastic scattering, and 24Mg spectroscopy. Results for 12C+12C elastic scattering show excellent agreement with experimental data, significantly improving the single-channel approximations. Spectroscopic analysis reveals that 24Mg states and resonances are highly mixed configurations, contradicting the concept of pure "molecular states." The calculated fusion S-factor is consistent with available experimental data and predicts both narrow and broad resonances near the Coulomb barrier. Main resonance widths originate primarily from the alpha+20Ne exit channels. The S-factor exhibits a decrease at low energies, providing a microscopic support for the hypothesis of fusion hindrance. This work is a first step towards a reliable theoretical extrapolation of the 12C+12C reaction to deep stellar burning temperatures. Future works should include the neutron and proton channels to provide a complete description of the 12C+12C fusion.
nucl-thnucl-exPRC(2026)·3 citations
08
The Delta-isobar masquerade: intrahadronic phase transitions and their quark-mimicking signatures in neutron stars
Martin O. Canullan-Pascual🇦🇷 · Germán Lugones🇧🇷 · Ignacio F. Ranea-Sandoval🇦🇷 · Milva G. Orsaria🇦🇷
We investigate the conditions under which $Δ (1232)$ isobars trigger a first-order phase transition within purely hadronic neutron-star matter, using the SW4L relativistic mean-field parametrization. For scalar-vector coupling differences $0.15 ≲ x_{σ Δ} - x_{ω Δ} ≲ 0.2$ and $x_{σ Δ} ≳ 1.3$ , the onset of $Δ^{-}$ resonances produces a van der Waals-like instability driven by a self-amplifying feedback in the scalar meson sector, in which the $Δ^{-}$ particle fraction acts as the order parameter of a Landau-type transition. A Maxwell construction yields a sharp density discontinuity at baryon densities $n_{b} \sim (1.3$ - $2) n_{0}$ , separating a $Δ$ -free outer core from a $Δ$ -rich inner core. The resulting neutron-star sequences satisfy all current multimessenger constraints: maximum masses $M_{max} \approx 2.15$ - $2.25 M_{⊙}$ , radii $R_{1.4} \approx 11$ - $12$ km, and tidal deformabilities $Λ_{1.4} \approx 190$ - $480$ , compatible with NICER observations and GW170817. We compute, for the first time for a $Δ$ -induced interface, the $ℓ = 2$ composition $g$ -mode eigenfrequencies, obtaining $ν_{g} \sim 400$ - $1100$ Hz with gravitational-wave damping times $τ_{g} \sim 1 0^{3}$ - $1 0^{9}$ s. These frequencies overlap quantitatively with those predicted for hadron-quark phase-transition interfaces, demonstrating that the mass-radius ``knee'', reduced tidal deformability, and $g$ -mode spectrum conventionally regarded as signatures of quark deconfinement can be reproduced by a purely intrahadronic mechanism. This extends the masquerade problem from static observables to the domain of gravitational-wave asteroseismology, implying that a future detection of a discontinuity $g$ -mode alone would not suffice to identify quark matter in neutron-star cores.
nucl-thastro-ph.HE1 citation
09
Nuclear binding, correlations, and the $A$ -dependence of the EMC effect
Omar Benhar🇮🇹 · Alessandro Lovato🇺🇸
The measurements of inclusive electron scattering from nuclear targets carried out at the Thomas Jefferson National Accelerator Facility in the mid 2000s have provided valuable novel information on the $A$ -dependence of the modifications of nuclear structure functions known as EMC effect. We argue that these data are best described in terms of the scaling variable $y$ , designed to take into account dynamical effects in interacting many-particle systems, and analyse the $A$ -dependence of the slope of the inclusive cross section ratios, $R_{A} = (σ_{A} / A) / (σ_{2} /2)$ , providing a measure of the size of the EMC effect in the region where nuclear binding plays a leading role. The results of our study clearly hint at a linear correlation between $d R_{A} (y) / d y$ and the average nucleon removal energy $⟨ E_{A} ⟩$ . The role of correlation effects in the determination of $⟨ E_{A} ⟩$ is highlighted.
nucl-th0 citations

Affiliations

first authorsco-authorsvia INSPIRE