Wed·Oct 1, 2025Wednesday·October 1, 2025

1. 01*

   Measurement of directed flow of $K^{\ast 0}$ and $\varphi$ resonances in Au+Au collisions at RHIC BES energies

   Md Nasim (for the STAR Collaboration)🇮🇳

   We report measurements of the directed flow ($v_1$) for charged kaons, $\varphi$ mesons, and $K^{\ast 0}$ resonances in Au+Au collisions at $\sqrt{s_{NN}}$ = 14.5, 19.6, and 27 GeV. This analysis includes the first-ever $v_1$ measurement for the $K^{\ast 0}$ resonance in heavy-ion collisions. Our results reveal a centrality-dependent difference in directed flow between charged kaons and $K^{\ast 0}$ resonances, with the difference increasing toward more central collisions.In contrast, the $v_1$ difference between kaons and $\varphi$ mesons remains nearly constant across centralities. The observed kaon-$K^{\ast 0}$ difference can be qualitatively understood within a hydrodynamic framework that incorporates a hadronic afterburner and an asymmetric loss of $K^{\ast 0}$ yields in momentum-space. Since hadronic rescattering depends strongly on the system size and scattering cross sections among hadrons, the measured $K^{\ast 0}$ $v_1$ offers valuable constraints on phase-space-dependent rescattering effects in heavy-ion collisions, thereby providing important input for transport-based models of QCD matter.

   nucl-exhep-ex0 citations
2. 02*

   Search for spontaneous fission of plutonium and americium nuclides using gamma spectrometry

   I.S.Klyuyev · D.V.Kasperovych🇺🇦 · V.V.Kobychev🇺🇦

   Spontaneous fission in americium and plutonium isotopes was investigated using high-resolution gamma spectrometry. This process was investigated through analysis of a certified PuO2 sample spectrum obtained from the IAEA database of reference spectra. Measurements were carried out with a HPGe detector, and detection efficiency calibration was performed by Monte Carlo simulations using GEANT4. There are no peaks observed that can be ascribed to beta decay of expected spontaneous-fission daughters. Thus, lower experimental limits on the partial half-lives for some spontaneous fission channels in 238-242Pu and 241Am were established. In many cases these limits have exceeded current theoretical predictions for cold fission done by S.B. Duarte et al., indicating the need to refine current models for the description of this process.

   nucl-exNucl.Phys.Atom.Energy(2025)·0 citations
3. 03*

   Precision measurement and modelling of the threshold-free 210Pb {\beta} spectrum

   Shuo Zhang · Hao-Ran Liu · Ke Han · Xavier Mougeot · Paul-Antoine Hervieux · Tao Sun · Wen-Tao Wu · Robin Cantor · Jing-Kai Xia · Zhi Liu · Jun-Cheng Liang · Fu-You Fan and 4 other authors

   Beta decay is a fundamental process that governs nuclear stability and serves as a sensitive probe of the weak interaction and possible physics beyond the Standard Model of particle physics. However, precise measurements of complete $\beta$ decay spectra, particularly at low energies, remain experimentally and theoretically challenging. Here we report a high-precision, threshold-free measurement of the full $\beta$ decay spectrum of 210Pb to excited states of 210Bi, using a transition-edge sensor (TES)-based micro-calorimeter. This approach enables the detection of $\beta$ particle energies from 0 keV up to their endpoint by coincidence summing with subsequent de-excitation energy, thereby eliminating reconstruction artifacts near zero energy that have traditionally limited low-energy spectral accuracy. To our knowledge, this is the first complete, high-precision $\beta$ decay spectrum from 0 keV. The data resolve theoretical uncertainties associated with the atomic quantum exchange (AQE) effect. An accompanying ab initio theoretical framework, incorporating atomic, leptonic, and nuclear components, predicts a statistically significant (7.2 {$\sigma$}) enhancement in $\beta$ emission probability near zero energy, in agreement with the measurement and in contrast to models that omit AQE corrections. These results provide a new benchmark for $\beta$ decay theory at low energies, deepen our understanding of the weak interaction, and establish a critical foundation for searches for new physics, including dark matter interactions and precision studies of neutrinos.

   nucl-exnucl-thphysics.ins-det1 citation
4. 04*

   Experimental overview of electromagnetic radiation in heavy-ion collisions

   Sebastian Scheid🇨🇭

   Electromagnetic (EM) probes such as photons and dileptons provide direct insight into the space-time evolution of the hot and dense matter formed in heavy-ion collisions. Being unaffected by strong interactions, they serve as penetrating messengers from all collision stages, from pre-equilibrium dynamics to the quark-gluon plasma (QGP) and hadronic phases. This contribution summarises recent experimental results on direct-photon and dilepton production from RHIC and LHC experiments, as well as at lower energies. Particular emphasis is given to the ongoing 'direct-photon puzzle', the study of universal scaling of direct-photon production over a large range of collision systems and energies. Recent dielectron measurements from ALICE, STAR, and HADES, as well as new experimental developments at the LHC, are presented, along with perspectives for future facilities.

   nucl-exnucl-thEPJ Web Conf.(2026)·4 citations
5. 05*

   Shape polarization and coexistence of high-$K$ three-quasiparticle states in odd-mass $N=106$ isotones

   Runyan Dong · Changfeng Jiao🇨🇳

   Three-quasiparticle $K$-isomeric states in odd-mass $N=106$ isotones within the $A\sim 180$ mass region are systematically investigated using configuration-constrained potential energy surface calculations. The calculations successfully reproduce the excitation energies and deformations of known high-$K$ isomers in the nuclei from ${}^{175}$Tm to ${}^{181}$Re. For the nuclei closer to the $Z=82$ shell closure (${}^{183}$Ir, ${}^{185}$Au, and ${}^{187}$Tl), predictions for the configurations of observed and yet-to-be-observed isomers are provided. The results reveal strong shape polarization, where the three-quasiparticle states are driven to larger deformations compared to the often shape-soft or spherical ground states. A particularly rich spectrum of shape coexistence is predicted in ${}^{187}$Tl, where several high-$K$ three-quasiparticle configurations with distinct prolate, oblate, and triaxial shapes are found to coexist at similar excitation energies. Notably, the oblate-deformed $K^{\pi }=29/2^{+}$ configuration at $E_x=1839$ keV is proposed to be responsible for a long-lived isomer. This study provides a comprehensive picture of shape evolution and coexistence in high-$K$ multi-quasiparticle states, offering valuable insights for future experimental research.

   ↳ nucl-thnucl-ex0 citations
6. 06*

   BABY 1L: First Tritium Breeding Campaign Results

   Rémi Delaporte-Mathurin · Nikola Goles · Collin Dunn · Emily Edwards · Sara Ferry · Ross MacDonald · Ethan Peterson🇺🇸 · Davide Pettinari · Stefano Segantin · Weiyue Zhou · Kevin B. Woller

   Achieving tritium self-sufficiency is a critical challenge for future fusion power plants. The BABY 1L experiment, part of the LIBRA project at MIT, aims to benchmark tritium breeding and release in molten salt breeder systems under deuterium-tritium (DT) neutron irradiation. Building on the initial \SI{100}{mL} campaign, BABY 1L introduces a tenfold increase in breeder volume, improved thermal and gas handling systems, and enhanced neutron diagnostics, including a proton recoil telescope. We report on results from four irradiation experiments using sealed-tube DT neutron generators, with tritium collected by water bubblers measured via liquid scintillation counting. Experimentally determined Tritium Breeding Ratios (TBRs) were compared to OpenMC neutronics simulations, showing very good agreement. The measured TBR values demonstrate a six-fold improvement over the \SI{100}{mL} experiments, largely attributed to the increased solid angle and improved measurement fidelity. We also investigate tritium release dynamics and identify diffusion-limited transport as the dominant regime in the salt volume in the temperature range 630-750 \si{\celsius}. Additionally, we observe that the introduction of hydrogen in the helium carrier gas significantly accelerates tritium release, consistent with an isotopic exchange mechanism. All analysis is conducted through the open-source \texttt{libra-toolbox} \cite{libra-toolbox}, which streamlines simulation, data processing, and validation across experimental campaigns. These results provide critical insights into the design and operation of future liquid breeder systems and demonstrate the maturity of the BABY platform as a testbed for tritium breeding studies.

   ↳ physics.ins-detnucl-exphysics.plasm-phNucl.Fusion(2026)·0 citations
7. 07*

   Initial spin fluctuations in heavy-ion collisions and where to find them

   Giuliano Giacalone🇨🇭 · Enrico Speranza🇮🇹

   Collective spin phenomena in the final states of heavy-ion collisions are typically understood to originate from vorticity and shear in the quark-gluon plasma. Here, we ask whether spin could already be present in the initial condition of the collisions. In particular, we argue that if a spin density exists at the beginning of the QGP expansion, it should experience event-by-event fluctuations due to the finite number of participant nucleons. In this contribution, we propose a simple model of fluctuating spin initial conditions for event-by-event spin hydrodynamics based on the Glauber Monte Carlo paradigm. We postulate that, if the net spin of the events is conserved from the initial to the final state, then initial state fluctuations of spin should manifest in specific spin correlations of $\Lambda$ hyperons. Within our picture, we predict that this signal is much larger in central O+O collisions than in central Pb+Pb collisions.

   ↳ nucl-thhep-exhep-phnucl-exEPJ Web Conf.(2026)·0 citations
8. 08*

   QCD in strong magnetic fields: fluctuations of conserved charges and EoS

   Heng-Tong Ding🇨🇳 · Jin-Biao Gu🇨🇳 · Arpith Kumar🇨🇳 · Sheng-Tai Li🇨🇳

   Strong magnetic fields can profoundly affect the equilibrium properties, characterized by the equation of state and bulk thermodynamics of strongly interacting matter. Although such fields are expected in off-central heavy-ion collisions, directly measuring their experimental imprints remains extremely challenging. To address this, we propose the baryon-electric charge correlations ${\chi }_{11}^{\mathrm{BQ}}$ and the chemical potential ratio ${\mu }_{\mathrm{Q}}/{\mu }_{\mathrm{B}}$ as magnetic-field-sensitive probes, based on (2+1)-flavor QCD lattice simulations at physical pion masses. Along the transition line, ${\chi }_{11}^{\mathrm{BQ}}$ and $({\mu }_{\mathrm{Q}}/{\mu }_{\mathrm{B}}{)}_{\mathrm{LO}}$ in Pb-Pb collisions increase by factors of 2.1 and 2.4 at $eB\simeq 8M_{\pi }^2$, respectively. To bridge theoretical predictions and experimental observations, we construct HRG-based proxies and apply systematic kinematic cuts to emulate STAR and ALICE detector acceptances. Furthermore, we extend this investigation to the QCD equation of state, and examine the leading-order thermodynamic coefficients for strangeness-neutral scenarios up to $eB\simeq 0.8{\mathrm{GeV}}^2\sim 45m_{\pi }^2$, revealing intriguing non-monotonic structures.

   ↳ hep-lathep-phnucl-exnucl-thJ.Subatomic Part.Cosmol.(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.