The European Physical Journal A最新文献

We present a multi-species analysis of identified-hadron transverse-momentum spectra in high-multiplicity p-Pb collisions at (sqrt{s_{NN}}=5.02~textrm{TeV}) within the Unified Statistical Thermal Freeze-out Model. The spectra are described through Cooper-Frye emission from an expanding freeze-out hypersurface, with resonance feed-down included. ALICE measurements of light mesons, protons, strange and multi-strange baryons, and the (K^{*}(892)) and (phi (1020)) channels are fitted in the soft-(p_T) region using a standard (chi ^2) minimization. To study the residual hadron-species dependence, we perform a constrained blast-wave analysis in which the spectral-shape differences are parametrized by the transverse-flow profile exponent (n_i) in (beta _T(r)=beta _{0T}(r/R)^{n_i}), where (r) is the transverse radial coordinate, (R) is the transverse geometric radius, (beta _{0T}) is the surface transverse velocity, and (n_i) is the species-dependent transverse-flow profile exponent. The common kinetic freeze-out condition is analyzed using the original (pi p) extraction, the conventional (pi Kp) bulk-hadron fit, and a global all-species constrained fit. The latter gives (T_textrm{com}=155pm 3~textrm{MeV}), (beta _{0T,textrm{com}}=0.85pm 0.03), and (chi ^2_textrm{tot}/textrm{dof}simeq 0.40), where (T_textrm{com}) denotes the common kinetic freeze-out temperature extracted from the global constrained fit and (T_textrm{kin}) denotes the kinetic freeze-out temperature used in the blast-wave description, with (T_textrm{kin}) and (beta _{0T}) common to all species and (n_i) fitted separately. A stable hierarchy is obtained: light mesons favor large (n_i), the proton lies in an intermediate region, and (phi ,Lambda ,Xi ,Omega ) occupy the small-(n_i) region. The hierarchy persists under variations of the common freeze-out condition and under fully free species-by-species correlation checks. We therefore interpret the extracted (n_i) pattern as a model-dependent spectral-shape signal compatible with species-dependent kinetic decoupling, rather than as a direct reconstruction of separate freeze-out hypersurfaces for different hadrons.

We investigate Physics-Informed Neural Networks (PINNs) for computing the s-wave bound states of the hypernucleus (_{Lambda }^{208})Pb, modeled as a two-body system of a (Lambda ) hyperon and a (^{207})Pb core, with a Woods–Saxon potential without spin-orbit coupling. The radial bound-state wave function is represented by a neural network ansatz; eigenenergies are obtained from the Rayleigh–Ritz variational quotient. Because PINN eigenvalue calculations depend on the residual-loss formulation and random-seed initialization, two residual losses are compared over four independent random seeds. Performance is assessed via eigenvalue accuracy, coefficient of variation, signal-to-noise ratio, bias-variance decomposition, and Hermitian spectral-ordering consistency. The normalized residual loss yields the most stable and physically consistent bound-state spectrum across the seeds. With this loss, computed bound-state energies and root-mean-square radii agree very well with the corresponding theoretical values. The resulting wave functions are then used to construct Jost functions through the Wronskian of incoming and outgoing Riccati-Hankel functions. From these Jost functions, the residue of the partial-wave S-matrix at the bound-state pole, the Asymptotic Normalization Constants (ANC), and the Nuclear Vertex Constants (NVC) are extracted. These quantities show reasonable agreement with theoretical values, albeit with larger standard deviations than for the eigenenergies and radii. The results indicate that the Rayleigh–Ritz formulation combined with a seed-robust normalized residual loss provides a stable PINN framework for bound-state and Jost-function-based calculations in hypernuclear two-body systems. To our knowledge, this is the first PINN-based study to construct Jost functions from neural-network bound-state wave functions and to extract associated ANC, NVC, and S-matrix residue.

The cross sections of the ¹¹⁶Cd(n,2n)^115m,gCd, ^natCd(n,xn)^109,107Cd, and ^natCd(n,pxn)^{113,112,111g,,110m}Ag reactions were measured at average neutron energies ranging from 20.1 to 32.7 MeV using the activation method combined with off-line γ-ray spectrometry. Fast neutrons were produced via the ⁹Be(p, n) reaction using 35 and 45 MeV proton beams delivered by the MC-50 Cyclotron at the Korea Institute of Radiological and Medical Sciences (KIRAMS). The neutron energy spectra were simulated using the MCNPX 2.6.0 code, while the neutron flux was experimentally determined using the ²⁷Al(n, α)²⁴Na monitor reaction. The present results, together with literature data at lower energies, were compared with theoretical calculations from TENDL-2021 library and evaluated data from the JEFF-4.0 library. Overall, good agreement was observed in most of the cases.

We report new experimental cross sections for the (^text {183})W(n, n’ (gamma )) and (^text {183})W(n, 2n (gamma )) reactions. This work aims to expand the experimental knowledge on neutron scattering reactions on tungsten isotopes, which are relevant for nuclear applications, including fusion reactor design. The results presented here were obtained using the GRAPhEME setup, located at the JRC-Geel GELINA facility. The measurement relies on prompt (gamma )-ray spectroscopy combined with neutron energy determination by time-of-flight. A full Monte Carlo analysis was employed, for the first time for a GRAPhEME data set, to obtain comprehensive uncertainties and covariance matrices. We compare the experimental cross sections with theoretical predictions from reaction model calculations. The data set presented here is significant for the understanding of nuclear reactions, and completes a previous similar study on (^{182,184,186})W.

Nucleus–nucleus reaction cross sections are a key component of radiation transport simulations, with applications from particle beam cancer therapies to radiation shielding for space. For use in Monte Carlo codes, universal, reliable and highly efficient models are required. Here we describe an Glauber-based analytic density-folding model for nucleus–nucleus reaction cross sections, applicable to projectiles and targets with mass number (Age 12). The model uses spherical, Gaussian-shaped matter densities that are optimised to describe the surface of density distributions from spherical Hartree–Fock calculations (surface-optimised Gaussian approximation, SGA). A phenomenological reaction barrier correction ((1-V_B/E_{cm})) is included to improve performance of the model at low energies. Whilst the Gaussian densities are not normalised, the good description of the density near the nuclear surface results in reaction cross sections that match those from numerical density folding calculations with Hartree–Fock densities typically to within 2% between 10 and 2000 MeV/nucleon for colliding nuclides from (^{12})C to (^{238})U. Comparisons are made to experimental data for stable nuclides at (E=30) to 2000 MeV/nucleon and show good agreement for a wide range of systems. For chains of neon, sodium and magnesium isotopes interacting with carbon at 240 and 950 MeV/nucleon, the general trend with proton-neutron asymmetry is reasonably described, but specific effects of nuclear structure such as deformation and neutron skins lead to experimental measurements being underestimated. The assumption of spherical symmetry and the use of matter densities may therefore limit the accuracy of the model for exotic nuclides. Calculations for (^{12})C+(^{16})O and (^{12})C+(^{48})Ti show the model performs reasonably well at energies near (V_B), but further work is required to benchmark the parameterization of (V_B) used and to extend the parameterization of the nucleon–nucleon cross sections and ranges used within the model.

We consider the axial-vector form factor of the nucleon in a finite box. Starting from the chiral Lagrangian with nucleon and (Delta )-isobar degrees of freedom, we address, at the one-loop level, the impact of two types of finite-volume effects. On the one hand, there are the implicit effects from the in-box values of the nucleon and (Delta )-isobar masses. On the other hand, there are the explicit effects caused by computing the in-box loop integrals with the values of the nucleon and (Delta )-isobar masses obtained in the infinite-volume limit. Selected numerical results are shown for three lattice ensembles. We show that the implicit effects dominate the in-box form factor. Our results are presented in terms of a set of basis functions that generalize the Passarino–Veltman reduction scheme to the finite-box case, such that only scalar loop integrals have to be performed. The techniques we developed are more generally relevant for lattice studies of hadronic quantities.

The dineutron is a spatially compact two-neutron cluster, which is expected to appear in a low-density part of nuclei. In recent years, there has been rapid progress in experimental and theoretical research on dineutron clusters, particularly on neutron-rich rare isotopes. Experimentally, evidence for dineutron in two-neutron halo nuclei, such as (^{11})Li, has been obtained using Coulomb breakup, measurements of charge radii, and quasi-free proton scattering. Specific unbound nuclei just beyond the neutron drip line, which decay by emitting two neutrons, are also candidates for having a dineutron correlation. For instance, the dineutron structure has recently been investigated for (^{16})Be, focusing on its decay into the core and the two neutrons. Theoretically, it is shown that the dineutron is partially due to the admixture of different-parity configurations for the two valence neutrons. Few-body theories, including dynamical effects of the decay process, play important roles in interpreting three-body decays. We also discuss the four-neutron clusters, showing the experimental results of recent tetraneutron experiments and observation of (^{28})O. Possible relevance of these states to dineutron correlation is discussed. Finally, we discuss future perspectives on dineutron clusters in neutron-rich nuclei and their relation to the universal features in few-body physics.

Symmetry-based models, such as the pseudo-SU(3) scheme, have proved to be highly useful tools for describing the low-energy structure of nuclei in the rare-earth region. This model is employed to study the evolution of the collective deformation variables (beta ) and (gamma ) in the ground state ((0^+)) along the isotopic chain (^{164-188})Hf. The truncation is carried out by considering the irreducible representations (irreps) with high spatial symmetry and pseudo-spin 0 and 1, so that both the most and less symmetric relevant irreps are included, the latter being of particular importance for the description of low-energy properties, especially the shape transition. The Hamiltonian includes spherical Nilsson single-particle energies, the quadrupole–quadrupole interaction, and pairing correlations. It is parameterised in a systematic manner, so that the description is obtained without free parameters. In agreement with experimental data, the maximum deformation (beta ) occurs at (N = 100), although the model predicts values that are about 20% smaller. As in other theoretical studies, a prolate deformation ((gamma sim 8^{circ })) is predicted for almost all nuclei in the shell, with a clear transition towards triaxial shapes for (N ge 112). An analysis of the effects of the pairing and Nilsson terms on the values of (beta ) and (gamma ) indicates that it is the latter that determine the prolate–oblate transition, with the pairing term playing only a marginal role. The absence of nucleons in the intruder sector is the most significant limitation of the model.

The weak s-process in massive stars plays a crucial role in the nucleosynthesis of heavy elements between Fe and Sr. It is traditionally viewed as occurring primarily during the pre-supernova (pre-SN) phase, with minimal alteration from the ensuing core-collapse supernova (CCSN) explosion. In this study, we utilize a grid of 53 CCSN models spanning a wide range of progenitor masses and explosion energies and setups, to investigate the interplay between pre-SN s-process production and post-explosion modifications. We show that explosive contributions (without considering any contribution from neutrino-winds nucleosynthesis) can strongly alter the pre-SN isotopic abundance patterns of s-process nuclei. Also the impact of nuclear reaction rate uncertainties may vary depending on the CCSN explosion setup. We discuss the case of the C-fusion rate as example. We propose a revised framework where the weak s-process component clearly encompasses both direct production in stellar interiors and its indirect role as seeds for explosive nucleosynthesis. This dual contribution should be taken into account when comparing model predictions with observed galactic chemical evolution abundances and solar isotopic ratios, with direct implications also for understanding the origin of heavy isotopic abundances not made by the (s) process.

Working with a symmetry-preserving treatment of a vector  (otimes )  vector contact interaction (SCI), a largely algebraic three-body Faddeev equation treatment of the nucleon bound state problem is introduced and used to deliver results for all nucleon charge and magnetisation distributions and their flavour separation. A strength of the SCI treatment is that it provides for a transparent understanding of this three-body approach to developing predictions for baryon observables. Comparisons of SCI results with predictions obtained in realistic-interaction Faddeev equation studies reveal the sensitivities of a given observable to the pointwise behaviour of the quark–quark interaction and phenomena associated with the emergence of hadron mass.