arXane › Physics
Wednesday, 4 November 2026: 2 new papers, 6 cross-lists and 4 replacements in Nuclear Experiment (nucl-ex), in arXiv's order, with full abstracts. The same papers as arXiv's own listing, set as a newspaper; every title links to arXiv.
Nuclear electric quadrupole moments of unstable isotopes are commonly extracted from laser spectroscopy of the atomic hyperfine structure, where the accuracy is limited to the several-percent level by the available electric-field-gradient (EFG) calculations. In this study, we determine the spectroscopic quadrupole moment of $^{223}$Ra (half-life $t_{1/2} = 11.4$ d) from hyperfine-resolved collinear resonance ionization spectroscopy of the radioactive molecule $^{223}$Ra$^{19}$F. The $X\,^2\Sigma^+$ electronic ground state of RaF provides a large axial EFG at the radium nucleus that can be calculated with relativistic coupled-cluster theory to sub-percent accuracy. Together with a three-fold improvement in spectral resolution over previous fast-beam measurements of radioactive molecules, this yields $Q_s = +1.211(7)_\mathrm{stat}(2)_\mathrm{syst}(5)_\mathrm{theo}\,e\mathrm{b}$ for $^{223}$Ra with a total uncertainty of 0.73%, approximately three times better than atomic and ionic determinations. This result demonstrates that molecular spectroscopy can provide access to the electromagnetic structure of unstable nuclei with a precision competitive with, and in favorable cases better than, atomic spectroscopy, and may thus be envisioned for studies beyond the limitations of current radioactive-atom experiments.
One of the important research objectives of the FRAGM experiment operating at the TWAC heavy-ion accelerator-storage complex was the study of particle production in the cumulative region. Differential cross sections were measured for the production of pions - resulting from the fragmentation of carbon nuclei at an energy of 3.2 GeV/nucleon, as well as protons with energy range from 300 to 2000 MeV/nucleon at an angle of 3.5 degrees relative to the incident ion beam. The parameterization of cumulative effect used in experiments investigating nucleus-nucleus interactions is discussed. It is shown, that the energy dependencies of these parameters are analogous to those observed in nucleon-nucleus interactions and indicate the presence of nuclear scaling behavior.
Coherent elastic neutrino--nucleus scattering (CE$\nu$NS) offers a low-energy probe of the weak mixing angle, $\sin^2\theta_W$, and possible new physics in the neutrino sector. Its reliable interpretation, however, requires independent constraints on the neutron distributions of the target nuclei. We exploit correlations across nuclei within an extended Skyrme energy-density-functional framework to propagate constraints from the CREX and PREX-II parity-violating electron-scattering (PVES) measurements to CE$\nu$NS targets. This yields neutron form factors and radii, with relative radius uncertainties below $1\%$. Using these inferred neutron form factors, we jointly analyze the COHERENT CsI, Ge, and Ar data and obtain $\sin^2\theta_W=0.231^{+0.016}_{-0.015}$, consistent with the Standard Model prediction. These results provide the first electroweak-experimentally constrained benchmarks for nuclear-structure studies, neutrino-sector electroweak tests, and CE$\nu$NS signal predictions in dark-matter detectors.
Project 8, a neutrino mass experiment, employs the novel frequency technique of cyclotron radiation emission spectroscopy (CRES) to perform a model independent measurement of neutrino mass via tritium beta decay. Our pioneering experiment will consist of a beamline that dissociates molecular tritium, surface cools atoms through accommodation, evaporatively cools and slows atoms, and traps them in a CRES resonant cavity to advance towards our sensitivity goal of 40 meV/c^2 for our final electron-weighted neutrino mass measurement. We are prototyping an electron cyclotron resonance (ECR) dissociator that uses a tunable 1 kW 2.45 GHz RF generator and electromagnets to ignite a hydrogen plasma in an aluminum resonant cavity. Our ECR source is designed to produce a high atom flux (~10^19 atoms/second) near room temperature. We present the engineering development, gas diagnostics, and spectroscopy data from our hydrogen plasma.
Reaction-amplitude reconstruction in the inverse scattering problem is limited by the bilinear form of all reaction observables. At fixed kinematics, N complex amplitudes contain 2N real quantities, whereas complete measurements determine at most 2N-1 parameters. Uniqueness therefore depends on whether additional physical constraints, such as unitarity, supply the missing information. We examine the consequences for resonance identification, focusing on angular-momentum assignments. Building on published results showing how truncation redistributes pole-bearing contributions among effective partial waves, we examine exact and practical ambiguities associated with imposing coupled-channel unitarity. A 4 x 4 counterexample shows that different on-shell unitary amplitudes can produce identical measurable bilinears. Practical unitary descriptions can also yield different pole content while remaining compatible with experimental uncertainties. We update Hoehler's clustering using the thirteen four-star N* resonances in PDG 2026 and Bonn-Gatchina results published in 2025. Nearby poles with different partial-wave assignments occur both in the PDG compilation and within Bonn-Gatchina, so their proximity is not solely a consequence of PDG averaging. Some groupings persist, while others change appreciably. We discuss a conditional interpretation in which truncation redistributes a common pole-bearing contribution among effective partial waves, with additional reconstruction uncertainties potentially accounting for departures from coincident pole positions. These considerations allow, but do not establish, a common origin for cluster members. The necessity of separate states and the stability of their angular-momentum assignments remain questions for further investigation.
The zero-energy antiproton absorption in light nuclei is considered. The ratios $R_{n/p}$ of antiproton-neutron versus antiproton-proton capture rates in the lightest nuclei $^2$H, $^3$He and $^4$He are analyzed, both from the experimental results and from some selected theoretical models. These models are used as key input in determining the level shifts and widths of the lowest states. We establish the capture orbit in $^3$He to be states of angular momentum $L=2$. Several N-\={N} optical potentials are used to compute the $R_{n/p}$ values for several heavy nuclei and the results are found to be consistent with the data. However, the old chamber experiments studying pionization in Helium, are not consistent with models. Only the Paris potential is likely to succeed provided baryonia states predicted by this model are better understood.
Collective flow emerging from spatially anisotropic many-body systems is a fundamental manifestation of strongly interacting quantum matter, from ultracold quantum gases to the quark-gluon plasma created in relativistic heavy-ion collisions. Yet how collective flow emerges across different spatial harmonics and how dissipation modifies its evolution remain largely unexplored. Here we investigate the nonequilibrium expansion of a unitary Fermi gas initially confined in nearly homogeneous potentials with engineered angular deformations. By suddenly releasing the confinement, we resolve anisotropic flow harmonics up to the seventh order. Remarkably, after normalization and rescaling by the characteristic expansion timescale, the different harmonics and system sizes exhibit a universal early-time evolution. At longer times, this universality breaks down and we observe an approximately quadratic dependence of the harmonic attenuation on harmonic order, consistent with viscous acoustic scaling. Furthermore, temperature-dependent measurements reveal the role of shear viscosity in the dissipative evolution of higher-order flow. Our results open a new route to exploring the interplay between universal hydrodynamic expansion and dissipative transport, connecting collective dynamics in ultracold quantum gases with anisotropic flow in strongly interacting nuclear matter.
Recent light-ion collisions at the Large Hadron Collider provide an opportunity to investigate the system-size dependence of hydrodynamization and whether the structure of light nuclei can be extracted from collective flow data. Both objectives require an accurate understanding of how the collision dynamics converts initial-state geometry into final-state momentum anisotropies. To this end, and to assess the impact of the experimental results, we compare simulations of O+O and Ne+Ne collisions in hydrodynamic and kinetic theory simulations across opacities. In both ultracentral and peripheral collisions, Ne+Ne-to-O+O elliptic flow ratios are robust against changes in dynamical description, supporting interpretations of data based on nuclear-geometry-driven effects. Triangular-flow ratios instead show substantially stronger sensitivity to nonequilibrium dynamics.