Tue·Dec 23, 2025Tuesday·December 23, 2025

1. 01*

   First experimental determination of the ${}^{40}$Ar($n,2n$)${}^{39}$Ar reaction cross section and ${}^{39}$Ar production in Earth's atmosphere

   S. Bhattacharya🇭🇺 · M. Paul · R. N. Sahoo · R. Purtschert · H.F.R. Hoffmann🇩🇪 · M. Pichotta🇩🇪 · K. Zuber🇩🇪 · D. Bemmerer🇩🇪 · T. Döring🇩🇪 · R. Schwengner🇩🇪 · M.L. Avila🇺🇸 · E. Lopez-Saavedra🇺🇸 and 19 other authors

   The cosmogenic ${}^{39}$Ar(t${}_{1/2}$= 268 years) isotope of argon is used for geophysical dating and tracing owing to its appropriate half-life and chemical inertness as a noble gas; ${}^{39}$Ar serves also in nuclear weapon test monitoring. We measured for the first time the total cross section of the main ${}^{39}$Ar cosmogenic production reaction in the atmosphere, namely ${}^{40}$Ar$(n,2n{)}^{39}$Ar, using 14.8$\pm 0.3$ MeV neutrons. The neutrons, produced by a deuterium-tritium generator, impinged on a stainless steel sphere filled with Ar gas highly enriched in the ${}^{40}$Ar isotope. The reaction yield was measured by atom counting of ${}^{39}$Ar with noble gas accelerator mass spectrometry and, independently, by decay counting relative to atmospheric argon. A total ${}^{40}$Ar$(n,2n{)}^{39}$Ar cross section of 610$\pm 100$ mb was determined. This result serves as a benchmark for recent theoretical calculations and evaluations, found to reproduce well the experimental total cross section. We use these energy-dependent theoretical cross sections together with experimental spectra of cosmogenic neutrons at different altitudes to calculate the global average rate of neutron-induced ${}^{39}$Ar atmospheric production, resulting in $770\pm 240$ ${}^{39}$Ar atoms/cm${}^2$/day. The secular equilibrium between the ${}^{39}$Ar calculated production rate and radioactive decay rate leads to a partial isotopic abundance ${}^{39}$Ar/Ar$=(5.9\pm 1.8)\times 10^{-16}$, showing that $\approx$73% of atmospheric ${}^{39}$Ar is produced by cosmogenic neutrons. The ${}^{40}$Ar($n,2n$)${}^{39}$Ar cross section at 14 MeV is also a key parameter for quantifying the anthropogenic contribution to atmospheric ${}^{39}$Ar produced during the thermonuclear tests of the 1960s. We estimate that anthropogenic ${}^{39}$Ar accounts for roughly 20% of the present atmospheric inventory.

   nucl-exGeochim.Cosmochim.Acta(2026)·1 citation
2. 02*

   Nuclear Physics Mid Term Plan at LNGS

   R. Buompane🇮🇹 · F. Cavanna🇮🇹 · C. Curceanu🇮🇹 · A. D'Onofrio🇮🇹 · A. Di Leva🇮🇹 · A. Formicola🇮🇹 · L. Gialanella🇮🇹 · C. Gustavino🇮🇹 · G. Imbriani🇮🇹 · M. Junker🇮🇹 · A. Marcianò🇨🇳 · F. Marzaioli🇮🇹 and 50 other authors

   The Istituto Nazionale di Fisica Nucleare-Laboratori Nazionali del Gran Sasso (LNGS) is one of the largest underground physics laboratory, a very peculiar environment suited for experiments in Astroparticle Physics, Nuclear Physics and Fundamental Symmetries. The newly established Bellotti Ion Beam facility represents a major advance in the possibilities of studying nuclear processes in an underground environment. A workshop was organized at LNGS in the framework of the Nuclear Physics Mid Term Plan in Italy, an initiative of the Nuclear Physics Division of the Instituto Nazionale di Fisica Nucleare to discuss the opportunities that will be possible to study in the near future by employing state-of-the-art detection systems. In this report, a detailed discussion of the outcome of the workshop is presented.

   nucl-exEur.Phys.J.Plus(2024)·3 citations
3. 03*

   Measurement of Fifth- and Sixth-Order Fluctuations of (Net-)proton Number in Au+Au Collisions from Phase II of the Beam Energy Scan Program at RHIC

   The STAR Collaboration

   We report high-statistics measurements of fifth- and sixth-order factorial cumulants and cumulant ratios of (net-)proton multiplicity distributions in Au+Au collisions at $\sqrt{s_{NN}}=7.7$--27 GeV, using data from the STAR experiment collected during the Beam Energy Scan Phase~II at RHIC. Protons and antiprotons are identified at midrapidity ($|y|<0.5$) with transverse momentum $0.4<p_T<2.0$ GeV/$c$. The proton factorial cumulants ${\kappa }_4$, ${\kappa }_5$, and ${\kappa }_6$ increase with order but exhibit no sign alternation within current uncertainties, offering no evidence for a two-component structure in the proton multiplicity distribution, as might be expected near a first-order phase transition. The cumulant ratios $C_5/C_1$ and $C_6/C_2$ fluctuate around zero in collisions at 0--40\% centrality. The results are consistent with both the negative predictions from lattice QCD (LQCD) and the positive trends obtained from the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model. At $\sqrt{s_{NN}}\gtrsim 27$ GeV, the $C_4/C_2$ and $C_5/C_1$ results are compatible with predictions from lattice QCD, functional renormalization group (FRG), and hadron resonance gas (HRG) models, while UrQMD describes the data better at lower energies. These measurements place constraints on baryon number fluctuations and offer valuable insights into the QCD phase structure.

   nucl-exhep-exhep-lathep-ph+1PRC(2026)·2 citations
4. 04*

   Dissociation-driven quarkonium spin alignment in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV

   Bhagyarathi Sahoo🇮🇳 · Captain R. Singh🇮🇳 · Raghunath Sahoo🇮🇳

   The observation of spin alignment of quarkonia in ultra-relativistic heavy-ion collisions provides deep insight into the possible formation of the quark-gluon plasma (QGP). The present study investigates the spin alignment of quarkonia induced by dissociation mechanisms arising from medium effects imposed on quarkonia. We implement an effective Hamiltonian with a medium-modified color-singlet potential to incorporate the coupling of quarkonium spin with medium vorticity. This coupling gives rise to spin-dependent dissociation, which we identify as a plausible mechanism contributing to quarkonium spin alignment. Within the ambit of second-order relativistic viscous hydrodynamics, we calculate the spin-dependent decay widths of charmonium ($J/\psi$, $\psi$(2S)) and bottomonium (${\rm Y}$(1S), ${\rm Y}$(2S)) in a rotating thermal medium, including collisional damping and gluonic dissociation effects. We evaluate the observable ${\rho }_{00}$ for Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV as a function of transverse momentum of the quarkonia, charged particle multiplicity, and medium rotation. The results demonstrate that medium vorticity modifies the quarkonia net decay width and, as a consequence, quarkonia spin alignment gets modified. These findings suggest new directions for understanding spin transport and the microscopic dynamics of vortical QGP.

   ↳ nucl-thhep-exhep-phhep-th+1PRD(2026)·1 citation
5. 05*

   Multi-neutron correlations in light nuclei via ab-initio lattice simulations

   Shuang Zhang🇩🇪 · Serdar Elhatisari🇸🇦 · Ulf-G. Meißner🇩🇪

   The quest to understand multi-neutron systems has a long history, and recent experimental efforts aim to probe candidate four-neutron configurations in neutron-rich light nuclei such as ${}^8$He and ${}^7$H via quasi-free knockout reactions. However, the ground-state energies of the hydrogen isotopes ${}^6$H and ${}^7$H are not yet well constrained, with substantial discrepancies across experimental analyses and theoretical predictions. Using ab initio nuclear lattice effective field theory with an ensemble of 282 chiral two- and three-nucleon forces, we perform a Bayesian uncertainty-quantified analysis of the ground-state energies of ${}^6$H and ${}^7$H. The marginal posteriors suggest single-neutron separation energy $S_n({}^7\mathrm{H})=0.35_{-0.32}^{+0.32}$ MeV, which kinematically disfavors sequential decay via ${}^6\mathrm{H}+n$ and thereby makes multi-neutron emission channels comparatively more relevant. Intrinsic densities indicate triton- and $\alpha$-like clusters in ${}^7$H and ${}^8$He, respectively. By computing two-body and reduced four-body correlation functions, we find that the valence neutrons in the surface region of these systems form compact dineutrons that predominantly organize into approximately symmetric dineutron-dineutron configurations, with only a small but non-negligible fraction assembling into more compact tetraneutron-like substructures. In ${}^7$H, these components account for roughly 95\% and 5\% of the sampled four-neutron configurations, respectively, and ${}^8$He exhibits a similar hierarchy. For these configurations, we also extract the corresponding spatial and angular correlation patterns among the nucleons. These results provide nuclear-structure insights into the debate surrounding four-neutron clusters and complement ongoing experimental searches for tetraneutron signatures in light nuclei.

   ↳ nucl-thhep-lathep-phnucl-ex4 citations
6. 06*

   Nuclear collectivity and the harmonic spectrum of two-body correlations

   Jean-Paul Blaizot🇫🇷 · Giuliano Giacalone🇨🇭 · Alessandro Lovato🇺🇸

   High-energy nuclear collisions have opened a new experimental method to reveal collective behavior in nuclear ground states through the lens of many-body correlations of nucleons. Using ab initio lattice and variational calculations of ${}^{20}$Ne and ${}^{16}$O, we study how emergent phenomena such as deformation or clustering can be identified in these systems from the dependence of their two-body density distributions on the relative azimuthal angle of nucleon pairs. A harmonic analysis of the correlation functions reveals in particular a dominant quadrupole component in ${}^{20}$Ne, consistent with a bowling-pin picture, and a prominent triangular modulation in ${}^{16}$O, possibly indicative of alpha-cluster correlations. Given that such structures can be accurately identified in high-energy collider experiments, these findings open a new paradigm for analyzing emergent collective behavior in atomic nuclei, relating their intrinsic shapes to the harmonic spectrum of microscopic correlations.

   ↳ nucl-thhep-exhep-phnucl-ex9 citations
7. 07*

   Hydrodynamic Short-Range Correlations from Boltzmann-Langevin Equation

   Li Yan🇨🇳 · Derek Teaney🇺🇸

   We investigate hydrodynamic contributions to short-range two-particle correlations in relativistic heavy-ion collisions using the Boltzmann-Langevin equation. We derive and solve the transport equation for equal-time two-point correlations, obtaining both local and non-local contributions that scale with transport coefficients. The non-local correlations emerging from 2-to-2 scattering dynamics provide a hydrodynamic signature in short-range correlation measurements.

   ↳ hep-phnucl-exnucl-thEPJ Web Conf.(2026)·0 citations
8. 08*

   Neutron star crust and outer core equation of state from chiral effective field theory with quantified uncertainties

   H. Göttling🇩🇪 · L. Hoff🇩🇪 · K. Hebeler🇩🇪 · A. Schwenk🇩🇪

   We study the order-by-order expansion of the energy per particle of asymmetric nuclear matter up to twice saturation density in chiral effective field theory (EFT) within a Bayesian framework. For this, we develop a two-dimensional Gaussian process (2D GP) that is trained using many-body perturbation theory results based on chiral two- and three-nucleon interactions from leading to next-to-next-to-next-to-leading order (N${}^3$LO). This allows for an efficient evaluation of the equation of state (EOS) and thermodynamic derivatives with EFT truncation uncertainties. After benchmarking our 2D GP against Bayesian uncertainties for pure neutron matter and symmetric matter, we study the energy per particle, pressure, and chemical potentials of neutron star matter in $\beta$-equilibrium including EFT uncertainties. We investigate the phase diagram of neutron-rich matter from neutron- to proton-drip and to the uniform phase, including surface and Coulomb corrections. Based on this, we construct EOSs for the inner crust of neutron stars that are consistent with the chiral EFT results for uniform matter at N${}^3$LO.

   ↳ nucl-thastro-ph.HEnucl-exPRC(2026)·4 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.