The European Physical Journal A最新文献

The question of why quantum matter exhibits hierarchical structures—from quarks, hadrons, and nuclei to atoms and molecules—is one of the fundamental problems in modern physics, yet it has not been widely discussed in a unified manner. One reason may be that each hierarchical level has traditionally been studied independently, and apparent connections between different scales were not clearly recognized. On the other hand, the concept of “clusters” may provide a common framework linking these hierarchical regimes. Namely, a cluster formed within one hierarchy can itself become a constituent particle in the next hierarchy, as nucleons in the hadronic hierarchy form atomic nuclei.

We present a gate-based quantum computing solution of the homogeneous Bethe–Salpeter equation (hBSE) for the bound state of two massive relativistic scalar particles interacting via ladder-approximation scalar exchange. After Wick rotation to Euclidean space and O(4) S-wave partial-wave projection, the hBSE is reduced to a symmetric matrix eigenvalue problem of dimension (N = 2^n). We decompose the resulting Hamiltonian into a sum of n-qubit Pauli operators and solve it with the Variational Quantum Eigensolver (VQE) using a Matrix Product State (MPS) tensor-network ansatz. For (N=16) ((n=4) qubits), the VQE recovers the maximum eigenvalue – which encodes the minimum coupling constant for binding – to better than (1%) mean relative error compared to classical diagonalization. Entanglement analysis of the BSE amplitude shows low, area-law-like entanglement over the tested sizes, which motivates the MPS ansatz. A critical analysis of three independent barriers – exponential Pauli overhead, approximately size-independent low entanglement, and decreasing VQE gradient scales for the tested ansatz, consistent with generic barren-plateau concerns at larger n – reveals that the specific problem studied here lies in a classically tractable regime: over the tested range it is well described by low-bond-dimension tensor networks and efficiently handled by MPS/Lanczos methods. This negative result provides, to our knowledge, the first entanglement quantification of the BSE amplitude in qubit encoding, establishes the Pauli Hamiltonian framework for future BSE variants, and identifies 2D Minkowski-space BSE, N-body bound states, and non-ladder kernels as physically motivated extensions where genuine quantum advantage may become plausible.

The double differential thick target neutron yields (TTNY) for 500 MeV/u (^9)Be ions incident on a lead target were measured at emission angles from (0^{circ }) to (75^{circ }) using the time-of-flight (TOF) method with organic liquid scintillators. The angular distribution of neutron yields was obtained by integrating the neutron energy spectrum above the detection threshold. The experimental data were then compared with results calculated using the Monte Carlo simulation codes GEANT4, PHITS, and FLUKA with different physics models. The results show that the neutron energy spectrum in the forward direction exhibits a broad peak centered around 60–70% of the incident particle energy per nucleon and spread up to nearly twice the projectile energy per nucleon. All calculations overestimate the neutron yields near this broad peak except at (0^{circ },) and overestimate the neutron energy corresponding to the peak center at all angles. The GEANT4 results show good agreement with the experimental data from a few tens of MeV to around 100 MeV at angles from (5^{circ }) to (60^{circ },) while PHITS and FLUKA results slightly overestimate the yields. Regarding the angular distribution, the predictions from GEANT4, PHITS, and FLUKA differ from the experimental data by less than a factor of 2 except at (75^{circ }.)

The study of t+t cluster states in (^{6})He provides valuable insights into exotic nuclear structures and the behavior of fermionic cluster systems. This study shows rich cluster resonant structures above the threshold, observed experimentally and investigated theoretically. The excitation energy spectrum above the t+t threshold in (^{6})He is measured via the fragmentation excitation process during the breakup reaction of (^{9})Li on a (^{208})Pb target at an incident energy of 32.7 MeV/nucleon. The resonant states are reconstructed from the final state coincident particles t+t using the invariant mass method, while the non-resonant background is estimated using the event mixing method. Two structures are observed at excitation energies of (E_x=14.0pm 0.3) and (15.0pm 0.3) MeV, both located above the (t+t) threshold at (E_xsimeq 12.31) MeV. Microscopic cluster model calculations exploring the (t+t) resonant states in (^6textrm{He}) yield theoretical energy spectra which are then compared with the current experimental results. The calculated reduced width amplitudes (RWA) of the (t+t) channels further support the presence of (t+t) clustering in the observed resonant structures.

The response of the (^3)He neutron long counter TETRA was investigated through detailed Monte Carlo simulations. Two analysis methods, based on the positive correlation between neutron-energy and penetration depth in the moderator, were developed to extract coarse spectral information from (^3)He long counters, although such detectors are not designed for neutron spectroscopy. The methods were first benchmarked offline using a (^{252})Cf spontaneous-fission source, and then applied to online data collected at the ALTO facility. For the beta-delayed neutron precursor (^{82})Ga, TETRA-based analyses result in a mean neutron-energy in the range 0.43–0.49 MeV and indicate that a significant fraction of the strength lies below a few hundred keV. In a second ALTO experiment, the time-of-flight spectrometer MONSTER was used to perform (beta )-delayed neutron spectroscopy of (^{82})Ga for the first time, providing an independent experimental reference above its detection threshold. The overall consistency between the TETRA-based results and the ToF measurement supports the use of these methods as a practical complementary tool for (beta )-delayed neutron spectroscopy, in particular in the low-energy region where ToF techniques are intrinsically limited by thresholds and geometrical efficiency.

In the interest of exploring resonant contributions to the radiative capture reaction (^{45})V(p,(gamma ))(^{46})Cr, which is identified to impact the (^{44})Ti nucleosynthesis in Core Collapse Supernovae at astrophysical energies, we performed a spectroscopic study of (^{46})Cr through the (beta )-decay of the progenitor (^{46})Mn. We present new results on the decay scheme of the proton-rich exotic nucleus (^{46})Mn based on a new approach at the level of the experimental data analysis. (^{46})Mn was produced among other nuclei at the LISE3 fragment separator operated in GANIL using the fragmentation technique. The novel approach is compared with a traditional data analysis, and validated using the known decay scheme of (^{45})Cr. The observed level scheme of the nucleus (^{46})Cr is compared with previous works. This work confirms former experimental results, while presenting better statistics and revealing new transitions in the decay scheme.

This letter reports on the identification of a new isomeric state of (^{164})Tb ((Z=65), (N=99)), which was measured with the DESPEC setup at the GSI Helmholtzzentrum für Schwerionenforschung GmbH following the first relativistic fragmentation of an (^{170})Er primary beam. From the time distribution and coincidences of the emitted (gamma ) rays, the isomer is tentatively assigned to a state with spin-parity ((7^{-})) at an excitation energy of (283.3(2)~textrm{keV}) with a half-life of (159(11)~textrm{ns}). The isomer is interpreted as the (pi 7/2^{-}[523]otimes nu 7/2^{+}[633]) configuration from the Nilsson orbital systematics. These results represent the first report of (gamma )-ray spectroscopy of (^{164})Tb, providing insight into the ground-state and low-lying level structure.

The SPES facility at the Legnaro National Laboratories is one of the most promising ISOL facilities currently under construction in Europe. Dedicated to basic nuclear science and nuclear-physics-based applications, it will deliver high-intensity, high-quality beams of unstable, mainly neutron-rich, isotopes at energies around the Coulomb barrier, enabling a wide range of projectile–target combinations. The technical solutions developed for SPES define it as an intermediate step towards a potential future European ISOL facility (EURISOL). SPES is based on a high-intensity production cyclotron, BEST-70p, which serves as the primary accelerator. The high-intensity proton beam is used to induce fission in a uranium carbide (UCx) direct target capable of sustaining a maximum power of 8 kW. The project aims to achieve a fission rate in the target of the order of 10(^{13}) fissions per second. Exotic nuclei, after thermal extraction from the target, ionization, and isotopic separation, are re-accelerated by the ALPI superconducting linear accelerator. Secondary beams with energies of about 10 MeV/A, for mass numbers up to A=200, will be provided, with expected intensities of the order of 10(^{7})–10(^9) particles per second for the most prolific species. This article presents a brief outline of the facility, describing the technical solutions adopted, followed by a concise description of the superconducting linac and an overview of the foreseen scientific program. In November 2024, the first SPES secondary beam of (^{28})Al was successfully extracted from the ISOL source. The radioactive ions were laser-ionized, selected, and their decay characterized by (beta )-decay.

Event-by-event fluctuations of conserved quantities provide sensitive information on the microscopic dynamics of strongly interacting matter created in relativistic heavy-ion collisions. In this work, we investigate the fluctuation measure D for net-charge, net-pion, net-kaon, and net-proton multiplicities in central Au+Au collisions at FAIR energies within the hadron–string dynamics (HSD) and parton–hadron–string dynamics (PHSD) transport approaches. The study covers beam energies (E_{textrm{lab}} = 4A)–12A GeV in the SIS100 range, together with 15A and 25A GeV. The dependence of the fluctuation strength on the pseudorapidity window (Delta eta ) is analyzed for each particle species. For all observables, the D measure decreases with increasing (Delta eta ), indicating a strong acceptance dependence. Over the FAIR energy range considered here, the beam-energy dependence remains comparatively weak, whereas the particle-species dependence is pronounced. Among the observables studied, net-kaon fluctuations exhibit a pronounced HSD–PHSD separation, indicating an enhanced sensitivity to strangeness-related dynamics; however, the magnitude of the separation is energy- and acceptance-dependent. The present results provide a transport-model baseline for future measurements of identified-particle fluctuations at FAIR.

Proton-boron-11 (p-(^{11})B) fusion is a highly attractive aneutronic pathway for clean energy production, offering abundant fuel, negligible neutron activation, and the potential for direct energy conversion of charged (alpha ) particles. However, its practical implementation is severely hindered by the extremely high Coulomb barrier, necessitating ignition temperatures far beyond those of conventional deuterium-tritium reactions. In this work, we propose a novel approach to enhance the low-energy fusion cross-section by introducing a negative muon ((mu )). Instead of relying on the thermal equilibrium formation of a muonic molecule, we investigate a kinetic scenario in which a muonic hydrogen atom (p(mu )) is formed first and subsequently bombarded with a (^{11})B nucleus. We quantitatively characterize the dynamic screening of the proton’s Coulomb field by the tightly bound (mu ) cloud, the resulting modified Coulomb potential substantially lowers the effective barrier at intermediate separations. We also evaluate the penetrability, reaction cross-section, and reactivity of the p(mu )-(^{11})B system, the results indicate that the inclusion of (mu ) enhances the tunneling probability by several orders of magnitude at incident energies below 100 keV, thereby significantly reducing the threshold for the nuclear reaction. This mechanism offers a promising alternative perspective for catalyzing p-(^{11})B fusion, and also suggests a potential ignition pathway.