The European Physical Journal A最新文献

We assess the prospects for inclusive heavy-quark-pair electroproduction in electron–proton (ep) and electron–nucleus (eA) collisions, alongside double-charm-pair ((D^0 bar{D}^0) and (D^0D^0)) electroproduction in ep collisions, during the early operational phase of the Electron-Ion Collider (EIC). Based on the anticipated beam energies and luminosities of the EIC, we estimate the total cross sections and differential distributions for photon virtuality (Q^2), heavy-quark transverse momentum, and rapidity. This analysis evaluates different Bjorken-x ((x_textrm{Bj})) intervals across a range of (Q^2) values. Expected event yields are estimated from the projected integrated luminosities of the early science programme, demonstrating the substantial improvement in statistical precision over previous HERA measurements at moderate and large (x_{textrm{Bj}}). For electron–nucleus collisions, we compute the nuclear modification ratio (R^{etext {A}}) within collinear factorisation using nuclear parton distribution functions, and identify the kinematic regimes in which shadowing, anti-shadowing, and EMC-like suppression are accessible with early EIC data. These results are intended to serve as a parton-level baseline to support feasibility studies and to provide a reference for future higher-order theoretical and experimental investigations at the EIC.

A machine learning ensemble model is constructed, comprising twenty stacked Bayesian Neural Networks and an XGBoost model. The physics-informed ensemble model enhances the prediction accuracy of nuclear binding energies, achieving a training accuracy of 46 keV and an overall accuracy of 60 keV for the data of AME2020. The testing accuracy of 97 keV crosses the 100 keV threshold required for nuclear astrophysical r-processes. Extrapolation performance is further validated on nuclei first newly measured after AME2020, yielding an accuracy of 175 keV. An Explanation–Causal Analysis–Threshold multi-scale analysis framework is employed to enhance model interpretability. The proposed approach, with its superior ability to both interpret and extrapolate, can be extended to other research fields.

Femtoscopic measurements of two-pion Bose–Einstein correlations have established that particle-emitting sources in heavy-ion collisions are well described by Lévy (alpha )-stable distributions, motivating systematic studies across a wide range of collision energies. In this work, we present a three-dimensional femtoscopic analysis of pion pairs in Au + Au collisions simulated with the UrQMD model for collision energies (sqrt{s_{NN}}=3)–(27,textrm{GeV}), taking the RHIC BES-II range of collider and fixed target experiment energies for reference. Using Lévy-type source parameterisations, we extract the Lévy index (alpha ), the three-dimensional radii (R_textrm{out}), (R_textrm{side}), (R_textrm{long}), and the pair multiplicity parameter (lambda ^{*}) (related to the correlation strength (lambda )). We investigate their dependence on the transverse mass ((m_T)) and collision energy, along with derived quantities such as the radius difference (R_{textrm{diff}}^2=R_{textrm{out}}^2-R_textrm{side}^2) and the ratio (R_textrm{out}/R_textrm{side}). We find that (R_textrm{out,side,long}) all decrease with increasing (m_T) and increase with collision energy, consistent with collective expansion, (R_textrm{long}) showing the strongest and (R_textrm{side}) the weakest energy dependence. The Lévy index (alpha ) decreases with collision energy, with a larger (m_T)-dependence towards higher energies. The (lambda ^{*}) parameter is consistent with a constant close to unity in the absence of pions from long-lived resonances. These results provide a baseline for future comparisons with experimental measurements from the STAR Collaboration, contributing to constraints on the QCD phase diagram.

We present a systematic study of nuclear ground-state properties obtained with the Skyrme quark–meson coupling (SQMC) energy density functional and compare them with results from the SLy4d Skyrme parameterisation. The SQMC functional is constructed using the quark–meson coupling (QMC) model, which incorporates the internal quark structure of the nucleon and results in a significant reduction in the number of free parameters. We investigate binding energies, two-nucleon separation energies, charge radii, and quadrupole deformations across a broad range of nuclei. Particular attention is devoted to the isovector dependence of the spin–orbit interaction derived within the QMC model, and its impact on the binding energies of neutron-rich nuclei relevant to the r-process. We find that the SQMC functional provides a reasonable description of nuclear ground-state properties in comparison with SLy4d.

The Generalized Variable-Moment-of-Inertia (GVMI) model, based on a nonlinear phenomenological rotational energy expression, is applied to investigate the negative-parity (Delta I=2) Antimagnetic Rotation (AMR) bands in (^{105}textrm{Cd}) and (^{101}textrm{Pd}) nuclei. The model provides a satisfactory description of the observed excitation energies and reproduces the corresponding trend of the rotational frequency (hbar omega ). The semiclassical geometrical interpretation of the angular-momentum composition of the band is based on the gradual alignment of the relevant angular momentum vectors of proton-holes toward the neutron angular-momentum vector. This phenomenological description is consistent with the characteristic closing of the twin shears in AMR. The resulting evolution of the shears geometry is further used to examine the observed decrease of the electric quadrupole transition probabilities B(E2) with increasing spin. Thus, the GVMI approach offers a simple and transparent phenomenological framework for correlating the rotational energies, rotational frequencies, angular-momentum geometry, and B(E2) systematics of the band. Complementary microscopic insight is also provided by Cranked Shell Model (CSM) calculations, which include pairing correlations, for both (^{105}textrm{Cd}) and (^{101}textrm{Pd}) spectra with appropriate configurations before and after the backbending. The CSM results are found to be consistent with the observed rotational behavior associated with the AMR band. The comparison between the phenomenological GVMI analysis and the CSM results indicates that the simple GVMI parametrization captures important empirical features of the observed band while providing a complementary geometrical interpretation of its angular-momentum evolution. The present study therefore does not aim to replace microscopic descriptions of AMR, but demonstrates the usefulness of the GVMI model as a phenomenological tool for obtaining first-order structural information on such rotational bands.

The recently reported K(1690) provides an opportunity to examine whether color recoupling can modify the spectral scale selected by local four-quark currents in the light-strange sector. In this work, we investigate the K(1690) channel using a color-octet–color-octet local current basis with flavor content (udbar{d}bar{s}) and quantum numbers (J^P=0^-). Each quark bilinear transforms as a color octet, while the complete four-quark operator is a color singlet. We construct currents covering scalar-pseudoscalar, vector-axial-vector, and tensor Dirac structures, and evaluate their two-point correlation functions within QCD sum rules, including vacuum condensates up to dimension eight. The currents exhibiting acceptable OPE convergence, sufficient pole dominance, and stable Borel behavior yield masses around (2.4~textrm{GeV}) for the scalar-pseudoscalar structures and 2.8–(2.9~textrm{GeV}) for the vector-axial-vector structures, whereas the tensor current does not produce a reliable Borel window. These results show that color recoupling alone does not generate a low-lying pole compatible with the K(1690), indicating that the specific local octet–octet currents considered here are unlikely to provide its dominant coupling.

Presolar silicon carbide (SiC) grains found in primitive meteorites can help constrain circumstellar condensation processes and nucleosynthesis in C-rich low-mass asymptotic giant branch stars and core collapse supernovae. We performed the first presolar grain chemical separation procedure on primitive CO3 meteorite Northwest Africa 7892 and identified 45 presolar SiC grains. These grains fit into the previously defined presolar SiC groups in similar proportions. We used a new secondary ion mass spectrometer (NanoSIMS XR prototype) to obtain high spatial resolution images of the grains. Three of the grains have isotopically distinct hotspots: regions 150–500 nm in diameter whose (^{12})C/(^{13})C ratios differ from that of the host grain by (>5sigma .) Though the origin of the hotspots is unclear, these nanoscale features demonstrate the potential for new discoveries with the ultrabright (mathrm{Cs^+}) make it superscript source in the NanoSIMS XR prototype.

This work presents new experimental data for the elastic scattering, the inelastic excitations and one-neutron (1n) transfer angular distributions of (^{13})C on (^{64})Zn, at energies around the Coulomb barrier ((V_{B}) (approx ) 30 MeV). Data were obtained at four bombarding energies: (E_text {lab}) = 28, 30, 33 and 36 MeV. The corresponding optical model (OM) analysis, based on the São Paulo Optical Model Protocol (SP-OMP), and the microscopic coupled-channels calculations are also presented. We determine the best-fit ((chi _text {red}^2)) optical potentials (OPs), which are then applied to the CC/CRC calculations. The OM and CC/CRC calculations are compared to the experimental elastic and non-elastic angular distributions obtained for the (^{13})C+(^{64})Zn system. The SP-OMP effectively describes the elastic scattering cross sections of (^{13})C+(^{64})Zn. The CC/CRC calculations corroborate the OM analysis, reproducing non-elastic nuclear reaction data. These calculations highlight the main importance of taking into account the excited states of the (^{64})Zn target along the energy range, in addition to coupling the excited states and the one neutron stripping of the (^{13})C projectile, as the bombarding energy increases. Comparisons between (^{12,13})C+(^{64})Zn are also proposed. Differences due to the (^{13})C extra neutron could be inferred.

We compute the thermal conductivity and thermoelectric power (thermopower) of the inner crust of compact stars across a broad temperature–density domain relevant for proto–neutron stars, binary neutron-star mergers, and accreting neutron stars. The analysis covers the transition from a semi-degenerate to a highly degenerate electron gas and assumes temperatures above the melting threshold of the nuclear lattice, such that nuclei form a liquid. The nuclear composition is prescribed by selected zero-temperature inner-crust models and is kept fixed when the temperature is varied. The transport coefficients are obtained by solving the Boltzmann kinetic equation in the relaxation-time approximation, fully incorporating the anisotropies generated by non-quantizing magnetic fields. Electron scattering rates include (i) dynamical screening of the electron–ion interaction in the hard-thermal-loop approximation of QED, (ii) ion-ion correlations within a one-component plasma, and (iii) finite nuclear-size effects. As an additional refinement, we evaluate electron-neutron scattering induced by the coupling of electrons to the anomalous magnetic moment of free neutrons; this contribution is found to be subdominant throughout the parameter range explored. To assess the sensitivity of transport coefficients to the underlying microphysics, we perform calculations for several inner-crust compositions obtained from different nuclear interactions and many-body methods. Across most of the crust, variations in relaxation times and in the components of the anisotropic thermal-conductivity and thermopower tensors reach up to factors 3 to 4 and 1.5 to 2, respectively, with the exception of the region where pasta phases are expected. Within the adopted single-component, fixed-composition approximation, these results provide a reference set of composition-dependent microphysical inputs for dissipative magneto-hydrodynamic simulations of warm neutron stars and post-merger remnants, where anisotropic heat and charge transport are of critical importance.