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Physics Nuclear Experiment

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Friday 28 August

Nuclear Experiment

Doppler-shift attenuation method (DSAM) lifetimes in $^{54}$Cr - a re-evaluation

Andrew E. Stuchbery

Background: Contemporary stopping powers for fp-shell nuclei slowing in tantalum can differ by a factor of two from the 1963 Lindhard, Scharff and Schiøtt (LSS) theory [Mat. Fys. Medd. Dan. Vid. Selsk. 33 no. 14, (1963)] used in Doppler-shift attenuation method (DSAM) lifetime measurements dating back to the 1970s. In recent work [Phys. Rev. C 113, 044306 (2026)], it was found that anomalously high collectivity in the $4^+_1 \rightarrow 2^+_1$ transition of 58Fe given in the literature [Nucl. Data Sheets 111, 897 (2010)] could be traced back as due to the use of these historical stopping powers in the Doppler-shift lifetime measurements. Satisfactory agreement with shell-model calculations was obtained from a re-analysis of the measurement of Bolotin et al. [Nucl. Phys. A 311, 75 (1978)] once the stopping powers were replaced by up-to-date values. Purpose: The DSAM measurement on 54Cr by the same group [Nucl. Phys. A 337, 1 (1980)], which used the same experimental methods and procedures, is re-examined. Method: The computer code used in the original DSAM analysis has been rebuilt and upgraded with the capacity to use contemporary stopping powers. E2 transition strengths derived from the revised lifetimes are compared with shell-model calculations. Results: The lifetimes increase by 16% to 27%, with the larger increase generally corresponding to shorter lifetimes where electronic stopping dominates. Conclusions: Revised lifetimes, based on current stopping powers, imply E2 transition rates between states up to the 6$^+_1$ state in 54Cr that compare well with shell-model calculations. The lifetime data together with branching ratios and the shell-model calculations strongly suggest revision of the spins assigned to the levels at 3.786 (currently (4)$^+$) and 4.043 MeV (currently 5$^+$). These levels are suggested to be the 5$^+_1$ and 6$^+_2$ states, respectively.
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Nuclear Experiment · Cross-listed from hep-ph

Magnetic Moments and Radiative Transitions of the $T_{cc}(3875)^+$ and its partner states

Jing Wu, Yi-Kun Wang, Kai-Bao Chen et al. (+3 more)

We systematically investigate the magnetic moments (MMs) and radiative decay widths of S-wave doubly heavy tetraquark states based on chromomagnetic interaction (CMI). They provide a complementary probe to distinguish compact from molecule structures in addition to the mass spectrum and strong decay properties. Using the CMI eigenvectors, we compute the MMs and M1 transition rates for the tetraquarks in the compact configuration. We predict the MM of the observed $T_{cc}(3875)^+$ with $I(J^P)=0(1^+)$ to be 0.45 $\mu_N$ when treating it as a compact tetraquark state, whereas the MM of the $0(1^+)$ $DD^*$ molecule is about $-0.07\,\mu_N$. Five radiative transition channels related to the $T_{cc}(3875)^+$ are identified with widths ranging from $6.07$ keV to $306.37$ keV. Our results show that the MMs of the $J^P=1^+$ $bc\bar{q}\bar{q}^\prime$ ($q/q^\prime=u,d,s$) and $J^P=1^+$ $QQ\bar{n}\bar{s}$ ($Q=b,c; n=u,d$) states are influenced by the diquark-spin mixing. Through the analyses of radiative transitions between different tetraquark states, we find that such processes in the $QQ\bar{n}\bar{n}^\prime$, $QQ\bar{s}\bar{s}$, and $bc\bar{n}\bar{s}$ cases may serve to reveal the tetraquark structures of the initial or final states. We also define the magnetic coupling matrices characterizing the MMs of the tetraquark system with $J^P=1^+$, with which the range of MM can be constrained. The present study provides a valuable reference point for the search of exotic states in future particle physics experiments.
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All authors Jing Wu, Yi-Kun Wang, Kai-Bao Chen, Yan-Rui Liu, Jian-Bo Cheng, Wei-Hua Yang

Nuclear Experiment · Cross-listed from nucl-th

Microscopic Realization of Topologically Quantized Alignment in Fast-Rotating Nuclei

Ganlong Ding, Sibo Wang, Hiroyuki Tajima et al. (+3 more)

We present the first quantitative microscopic realization of topologically quantized alignment in a finite nuclear system. The realization is obtained by exact diagonalization of a cranking seniority model, with the first Chern number evaluated over the sphere of cranking-axis orientations and analyzed together with the orientation-averaged alignment and cranking-frame configuration probabilities. The Chern number changes in integer steps as the system evolves from initially paired configurations to increasingly aligned configurations. A new intermediate phase is found in which the Chern number is already nonzero while the alignment continues to evolve toward its quantized value. We show that this deviation originates from the competition among pairing, axial quadrupole splitting, and Coriolis mixing. Thus, our microscopic approach reveals a more nuanced emergence of topologically quantized alignment in realistic nuclei, providing a quantitative stepping stone toward experimental investigations.
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All authors Ganlong Ding, Sibo Wang, Hiroyuki Tajima, Daisuke Suzuki, Jing Peng, Haozhao Liang

Thursday 27 August

Nuclear Experiment · Cross-listed from physics.ins-det

The efficiency of moderating neutron detector: Monte Carlo simulation, experimental validation, and angular dependence

Carl R. Brune

This paper describes the Monte Carlo simulation and experimental validation of the neutron detection efficiency in a 4pi polyethylene moderating detector. The experimental validation was performed using several sources providing neutron energies from 10s of keV up to 14 MeV. The Monte Carlo simulations employed the MCNP6 code are believed to be accurate within 3% for neutron energies below 6 MeV. A new method for parametrizing the dependence of the efficiency on the neutron angular distribution for in-beam experiments is also presented. This approach utilizes a Legendre decomposition of the efficiency and allows all of the needed information to be extracted from a single simulation.
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Nuclear Experiment

Direct Bayesian Inference of Helicity Amplitudes from Detector-Level Scattering Data

Bhawani Singh, Harut Avakian, Shohini Bhattacharya et al. (+8 more)

Helicity amplitudes give the most complete description of a variety of scattering reactions used in studies of strong interactions, but they cannot be measured directly: experiments record bilinear combinations of them folded through a detector response, and conventional analyses recover them through multiple stages that introduce discrete ambiguities and require a separate extraction of the absolute cross sections. Here we replace that chain with a single Bayesian inference that determines the experimentally identifiable amplitude parameters directly from detector-level measurements. A score-based diffusion model, trained on a forward simulator, provides the full posterior in each kinematic bin, with the detector response carried by the forward model and positivity of the spin-density matrix guaranteed by the parameterization. The observable amplitude content in electroproduction of final particles grows with polarization of beams and targets, providing additional sensitivity to underlying phases. In simulation, the posterior achieves empirical coverage at or above the nominal level and delivers the angular observables and the separated contributions from longitudinal and transverse photons with their correlations retained. It transfers without retraining to a realistic detector response absent from training and remains reliable in the weakly constrained nucleon-helicity-flip sector, where per-bin likelihood maximization degrades. The result is a general framework for a broad class of inverse problems, phase retrieval, quantum-state tomography, and partial-wave analysis are further instances. Its core requires only a forward simulation of the complete measurement process, instrumental effects are handled within one statistically consistent posterior, applicable across exclusive vector-meson programs at Jefferson Lab, COMPASS, HERMES, and the future Electron-Ion Collider.
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All authors Bhawani Singh, Harut Avakian, Shohini Bhattacharya, Volker D. Burkert, Latifa Elouadrhiri, Derek I. Glazier, Valery Kubarovsky, Dillon Leahy, Yaohang Li, Richard G. Milner, Yijie Wang

Wednesday 26 August

Nuclear Experiment · Cross-listed from nucl-th

Frontier Questions and Emerging Directions in Nuclear Science and Technology

Yu-Gang Ma

Recent advances in nuclear science and technology are being driven simultaneously by fundamental questions on strong interactions and many-body emergence, by the rapid expansion of rare-isotope capabilities and multimessenger astronomy, and by growing societal demand for clean energy, precision medicine, and strategic technologies. This review reorganizes the "ten frontier questions" for nuclear science and technology, offering a scholarly roadmap accessible to a broad audience. We first discuss the fundamental frontiers, including the nonperturbative origin of hadronic mass, the properties of QCD matter under extreme conditions, the multiscale evolution of nuclear structure from light nuclei to the superheavy region, the physics of exotic nuclei and open quantum systems near the driplines, and the nuclear-astrophysical origin of the elements. We then emphasize enabling methodologies, especially modern ab initio and continuum-coupled theories, advanced accelerator and detector platforms, precision mass spectrometry, and the emerging role of data-driven and artificial-intelligence-assisted methodologies. Finally, we review translational and strategic directions, including advanced fission and fusion energy systems, cross-disciplinary nuclear technologies such as radiomedicine, isotope science, and nuclear clocks, as well as the long-term challenges of fuel cycles, waste management, and international cooperation. Rather than serving as an exhaustive bibliography of each subfield, this article aims to provide an integrative research framework that connects frontier scientific problems with enabling infrastructure, application scenarios, and long-range strategic planning.
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Nuclear Experiment · Cross-listed from nucl-th

Evidence for Quartet Binding of Valence Neutrons in $^8$He

Young-Ho Song, Yuan-Zhuo Ma and Dean Lee

Multimodal neutron superfluidity predicts quartets formed as bound states of two spin-singlet $s$-wave neutron pairs. We present evidence that the four valence neutrons of $^8$He realize the finite-system analogue. Quartet binding depends not only on the strength of neutron-neutron attraction but also on the number and symmetry of sufficiently strong attractive pair modes. Pauli blocking limits reuse of the same pair structure, while additional modes can provide extra binding. A partial-wave analysis of the neutron-neutron interaction in Daejeon16 no-core shell-model calculations identifies cooperative $^1S_0$ pairing and additional $^3P_2$ attraction as the dominant neutron-neutron contributions to this nonadditive binding, while density cumulants reveal connected four-neutron correlations.
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Nuclear Experiment · Cross-listed from nucl-th

Directional correlations in nuclear charge-radius model residuals enable extrapolation with calibrated uncertainties

Debodyuti Kar, Soumya Bagchi, Timo Dickel et al. (+1 more)

We identify a pronounced directional anisotropy in the residuals between measured nuclear charge radii and two structurally distinct global models: the phenomenological Weizsäcker–Skyrme formula (WS*) and the microscopic Hartree–Fock–Bogoliubov model (HFB-25). In both cases, the residuals remain correlated over several neutron steps along isotopic chains but decorrelate almost completely after a single proton step along isotonic chains. This common pattern, reinforced by a strong correlation between the two residual fields ($r\simeq0.73$), points to a shared deficiency of both global descriptions rather than a model-specific artefact. Motivated by this geometry, we introduce ARCUS (Anisotropic Residual Calibration with Uncertainty Scaling), which applies an anisotropic kernel-regression correction with empirically calibrated prediction intervals. In out-of-fold cross-validation, ARCUS reduces the root-mean-square errors of both WS* and HFB-25 by approximately a factor of two. On an independent, temporally blind test set of 129 nuclei, its prediction intervals retain coverage close to nominal under extrapolation. An isotropic kernel matched to the same cross-validation coverage instead substantially overestimates uncertainties on the blind set, showing that reliable calibration transfer depends on encoding the directional residual structure. In regions with anomalous structure, such as around $^{52}$Ca, ARCUS keeps its prediction intervals wide enough to cover the increased errors, rather than yielding overconfident point predictions. We also extend these calibrated predictions to 1008 unmeasured nuclei near known isotopic chains, ranked by uncertainty to support the future charge-radius measurements.
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All authors Debodyuti Kar, Soumya Bagchi, Timo Dickel, Rituparna Kanungo

Nuclear Experiment · Cross-listed from physics.ins-det

Development and Commissioning of the Cryogenic Target Detectors for the Technical Run of the NUCLEUS Experiment

N. Schermer, H. Abele, G. Angloher et al. (+57 more)

The NUCLEUS experiment aims to study coherent elastic neutrino-nucleus scattering (CE$\nu$NS) of reactor electron antineutrinos at the Chooz nuclear power plant in France. In this work, the cryogenic target-detector module for the NUCLEUS Technical Run was developed and commissioned at the Technical University of Munich. The module comprises four gram-scale CaWO$_4$ detectors, each equipped with two Transition Edge Sensors (TES), providing a total target mass of 6.96 g. We present the design, integration, detector characterization, and X-ray-based energy calibration of these detectors. Across six characterized detectors, a mean baseline resolution of $\overline{\sigma}_{\mathrm{BL}} = (2.79 \pm 0.60)\,\mathrm{eV}$ was achieved. The best-performing detector reached $\sigma_{\mathrm{BL}} = (2.16 \pm 0.02_{\mathrm{stat}})\,\mathrm{eV}$, surpassing the design goal by a factor of two and representing a state-of-the-art result for a cryogenic CaWO$_4$ detector. The target detector module was successfully operated simultaneously with the surrounding Cryogenic Outer Veto, which consists of six kg-scale Ge detectors for background discrimination, showing no measurable cross-talk. These results demonstrate the readiness of the target-detector system for the NUCLEUS Technical Run at Chooz and mark a key milestone in the development of cryogenic detectors for reactor-CE$\nu$NS measurements.
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All authors N. Schermer, H. Abele, G. Angloher, B. Arnold, M. Atzori Corona, A. Bento, E. Bossio, F. Buchsteiner, J. Burkhart, F. Cappella, M. Cappelli, N. Casali, R. Cerulli, A. Cruciani, G. Del Castello, S. Dorer, A. Erhart, M. Friedl, S. Fichtinger, V.M. Ghete, M. Giammei, J. Hakenmüller, D. Hauff, M. Hock, F. Jeanneau, E. Jericha, M. Kaznacheeva, H. Kluck, A. Langenkämper, T. Lasserre, D. Lhuillier, M. Mancuso, B. Mauri, A. Mazzolari, L. McCallin, H. Neyrial, C. Nones, L. Oberauer, L. Peters, F. Petricca, W. Potzel, F. Pröbst, F. Reindl, M. Romagnoni, J. Rothe, J. Schieck, S. Schönert, C. Schwertner, L. Scola, L. Stodolsky, A. Schröder, R. Strauss, R. Thalmeier, C. Tomei, L. Valla, M. Vignati, M. Vivier, A. Wallach, P. Wasser, L. Wienke

Nuclear Experiment · Cross-listed from physics.acc-ph

Feasibility demonstration of a high-momentum, high-purity muon beamline at the J-PARC Hadron Experimental Facility

Kotaro Shirotori, Takaya Akaishi, Kazuya Aoki et al. (+16 more)

We have established and characterized a novel high-purity muon beam delivery scheme, designated as $\mu$20, at the high-momentum hadron beamline (B-line) of the J-PARC Hadron Experimental Facility. This scheme delivers tertiary muons produced via the in-flight backward decays of secondary pions in the straight section of the beamline, inherently suppressing parent hadron contamination. In a systematic performance evaluation, the muon beam achieved a standalone intensity of $1.7\times10{^3}$ particles/spill with a spatial spread (standard deviation, $\sigma$) of approximately 15 mm at the downstream detector position. A systematic attenuation analysis utilizing an iron absorber verified a high muon purity of 98.0$\pm$0.6% for the 3 GeV/$c$ muon beam mode. Crucially, this work marks the first successful feasibility study of a high-momentum and high-purity muon beamline operation at an experimental facility in Japan.
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All authors Kotaro Shirotori, Takaya Akaishi, Kazuya Aoki, Wen-Chen Chang, Ryotaro Honda, Yusuke Hori, Takatsugu Ishikawa, Nobuyuki Kobayashi, Ruri Kurasaki, Che-Sheng Lin, Yuhei Morino, Megumi Naruki, Hiroyuki Noumi, Kyoichiro Ozawa, Shinya Sawada, Ken Suzuki, Hitoshi Takahashi, Taiga Toda, Natsuki Tomida

Tuesday 25 August

Nuclear Experiment · Cross-listed from quant-ph

Femtoscopic Correlation Functions in Density Operator Representation

Hao-Nan Liu, Duo-Lun Ge, Zhi-Wei Liu et al. (+2 more)

Femtoscopic correlation functions (CFs) have been increasingly used to extract strong interactions between pairs of unstable particles, but their physical soundness has recently been questioned. To answer this, we formulate CFs at the operator level, with the observed subsystem described by a reduced density operator and subsequent dynamics absorbed into an effective measurement operator. The Koonin-Pratt form is recovered under four well-motivated reductions. The formulation makes explicit that the source-side and interaction-side representations must be consistently matched, and motivates an operational convention in which a measured reference correlation establishes a compatible source–interaction pairing that can be extended to other pairs for CF-to-CF predictions.
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All authors Hao-Nan Liu, Duo-Lun Ge, Zhi-Wei Liu, Jun-Xu Lu, Li-Sheng Geng

Nuclear Experiment

Direct measurement of the in-medium $\eta^{\prime}$ mass spectrum through the $\gamma\gamma$ decay channel

Y. Matsumura, N. Muramatsu, T.A. Hashimoto et al. (+58 more)

We measured the invariant mass of the $\eta^{\prime}(958)$ meson through the $\eta^{\prime}\to\gamma\gamma$ decay channel to search for possible character change of $\eta^{\prime}$ in a nuclear medium. The measured invariant-mass spectra were analyzed by fitting realistic spectral functions. An enhancement was observed in the lower tail of the $\eta^{\prime}$ mass peak for low-momentum ($P_{\gamma\gamma} < 1$~$\mathrm{GeV/c}$) events. Three statistical methods were applied to assess the significance of the enhancement. All methods yield a statistical significance above 3.7$\sigma$. The spectral fitting indicates a mass reduction of $57.5^{+~5.7}_{-27.8}$~$\mathrm{MeV/c}^{2}$. Our result provides the first evidence for an in-medium spectral modification of the $\eta^{\prime}$ meson obtained through a direct measurement of its invariant mass.
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All authors Y. Matsumura, N. Muramatsu, T.A. Hashimoto, M. Miyabe, H. Shimizu, A.O. Tokiyasu, J.K. Ahn, W.C. Chang, J.Y. Chen, M.L. Chu, S. Daté, T. Gogami, H. Hamano, Q.H. He, K. Hicks, T. Hiraiwa, Y. Honda, T. Hotta, Y. Inoue, T. Ishikawa, I. Jaegle, Y. Kasamatsu, H. Katsuragawa, S. Kido, R. Kobayakawa, Y. Kon, S. Masumoto, K. Mizutani, T.Z. Mo, T. Nakamura, T. Nakano, T. Nam, M. Niiyama, Y. Nozawa, Y. Ohashi, H. Ohnishi, T. Ohta, M. Okabe, K. Ozawa, C. Rangacharyulu, S.Y. Ryu, Y. Sada, T. Shibukawa, R. Shirai, K. Shiraishi, E.A. Strokovsky, Y. Sugaya, M. Sumihama, S. Suzuki, S. Tanaka, Y. Taniguchi, N. Tomida, Y. Tsuchikawa, T. Ueda, T.F. Wang, H. Yamazaki, R. Yamazaki, Y. Yanai, T. Yorita, C. Yoshida, M. Yosoi

Nuclear Experiment · Cross-listed from hep-ph

Resonant Induced Orbital Electron Capture: Novel method for low-energy $\bar{\nu}_e$ detection

Evgeny Akhmedov, Thierry Lasserre and Leonardo Maturi

We propose a novel approach to detecting low-energy electron antineutrinos based on the induced capture of orbital electrons by nuclei. This process is resonant, requiring the antineutrino energy to precisely match the energy difference between the final and initial atomic systems. For continuous-spectrum sources, the resonance conditions can be satisfied without fine-tuning, and the effective cross sections depend on the spectral intensity of the $\bar{\nu}_e$ flux at the resonance rather than on the neutrino energy itself. This opens the possibility of detecting neutrinos of never previously probed low energies. We identify a number of candidate nuclides that allow transitions to excited states of the daughter nuclei corresponding to resonant $\bar{\nu}_e$ energies below the inverse $\beta$ decay threshold of 1.8 MeV, and we consider a distinctive atomic-nuclear coincidence signature for background rejection. We discuss implications of the proposed method for detecting low-energy reactor neutrinos, geoneutrinos, and keV-scale thermal solar neutrinos. Applications to neutrino oscillation experiments and to reactor monitoring are also briefly discussed.
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Nuclear Experiment

STAR Highlights II: Study of Small Systems and the Search for New, Exotic Physics

Jiangyong Jia

Twenty-five years of RHIC operation have produced a uniquely diverse dataset, which enables a broad physics program. This contribution highlights recent STAR results in four areas: exotic-state searches and ultra-peripheral collisions; the onset of quark–gluon plasma (QGP) signatures in small systems; radial flow and its fluctuations; and polarization and spin correlations.
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Nuclear Experiment · Cross-listed from hep-ph

Resummed Power Corrections in Nuclear DVCS

John Terry

Generalized Parton Distributions (GPDs) encode the three-dimensional structure of hadrons, yet their modification in nuclear matter remains largely unconstrained. We report the first derivation of resummed QCD power corrections to deeply virtual Compton scattering on nuclei. Extending techniques from inclusive deep inelastic scattering, we identify the nuclear-enhanced higher-twist contributions generated by coherent final-state scattering of the struck quark in the medium and resum them to all orders. The corrections are enhanced by an effective nuclear size $A_{\rm eff}^{1/3}$ and result in an exclusive analogue of dynamical nuclear shadowing. The shift is controlled by a parameter already fixed by inclusive nuclear data, so no new nonperturbative input enters. We present quantitative predictions for nuclear modifications of beam-spin observables at the Electron–Ion Collider.
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Nuclear Experiment

Cluster emission and its impact on the r-process nucleosynthesis

Natalia Thomas, Silvia Bara, Thomas Elias Cocolios et al. (+20 more)

Cluster emission is an exotic decay mode between alpha-decay and fission, in which a parent nucleus emits a cluster of nucleons heavier than an alpha-particle, but lighter than what is usually considered a fission fragment. The properties of cluster emission were investigated by analyzing five high-energy events detected in a spectrum of a mass A = 230 beam produced at ISOLDE (CERN). Under the assumption that these events were caused by cluster emission, the most likely parent-cluster pair responsible for the five high-energy events, was found to be $^{230}Ra$ emitting $^{22}O$, with a branching ratio of $(4.3$ +\- $1.9) \times 10^{-9}$. Four analytical formulas were used to estimate the partial half-lives of cluster emission for a group of neutron-rich nuclei. The decay rate was calculated for a selection of cluster nuclei for each parent isotope. The rates of all decay channels of cluster emission per parent nucleus were then included in calculations of the r-process nucleosynthesis in a neutron star merger in order to study the possible impact of cluster emission on the r-process nuclear production. The resulting isotopic abundance distributions were compared to those calculated for a case in which cluster emission was not considered. It was found that the inclusion of cluster emission decay rates from the simple analytical formulas available nowadays does not influence the results of the r-process nucleosynthesis.
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All authors Natalia Thomas, Silvia Bara, Thomas Elias Cocolios, Stephane Goriely, Boris Andel, Andrei N. Andreyev, Alberto Camaiani, James G. Cubiss, Hilde De Witte, Zoe Favier, Michael Heines, Fedor Ivandikov, Jake D. Johnson, Jozef Klimo, Razvan Lica, Jozef Mišt, Chris Page, Riccardo Raabe, Adam Sitarčík, Viktor Van Den Bergh, Piet Van Duppen, Zixuan Yue, Ahmed Youssef

Monday 24 August

Nuclear Experiment · Cross-listed from nucl-th

Spectroscopy of 211,213,215Pb isotopes and seniority properties

Larry Zamick and Praveen Srivastava

We first consider lead isotopes with valence neutrons in the g9/2shell. We especially compare 211Pb (n=3), 213Pb (n=5) and 215Pb (n=7), 213Pb being at mid-shell. Motivated by the fact the J = 21/2+ and J =3/2+ states are pure seniority v=3 states for both n=3 and n=5, we compare the energy splitting E(J=21/2+)-E(J=3/2+) for various interactions. We then discuss the position of the lowest J=3/2+ state in both n=3 and n=5, although, this state has not been found experimentally. Calculations with configurations beyond g9/2 are also considered. We next address the fact that the J=21/2+ state is isomeric for both n=3 and n=5.
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Nuclear Experiment

Core Breaking at Low Spin in $^{68}$Zn from Nuclear Resonance Fluorescence

S. R. Johnson, R. V. F. Janssens, B. A. Brown et al. (+11 more)

Low-spin excited states in $^{68}$Zn have been studied at the High Intensity Gamma-Ray Source (HI$\gamma$S) from the ground state up to the particle emission threshold using the nuclear resonance fluorescence technique (NRF) and the newly developed Clover Array. Low-spin levels were excited by linearly-polarized, $2.90 - 9.79$ MeV photon beams. Spin-parity quantum numbers as well as associated $M1$ and $E1$ decay strengths were determined for a large fraction of the 158 states observed. In addition, long-duration coincidence measurements at 9.46 and 9.79 MeV enabled the investigation of the level scheme near the ground state. The results have been interpreted with shell-model calculations using two different model spaces and several effective interactions often used to describe nuclei in this mass region. While the structure near the ground state can be understood in terms of excitations involving solely valence nucleons, core breaking is required to account for the evolution of the total $M1$ strength at excitation energies above $\sim5$ MeV.
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All authors S. R. Johnson, R. V. F. Janssens, B. A. Brown, A. D. Ayangeakaa, S. S. Bhattacharjee, E. Churchman, S. W. Finch, U. Friman-Gayer, S. Frye, M. Fulghieri, D. Gribble, X. H. -K. James, R. Longland, C. Wegner

Nuclear Experiment · Cross-listed from physics.ins-det

Performance Evaluation of a High-Granularity LYSO-SiPM-Based Position-Sensitive Detector for a One-Shot Gamma-Scanning System with Sub-Millimeter Spatial Resolution

Katyayni Tiwari, Arzoo Sharma, Jürgen Gerl et al. (+5 more)

A compact position-sensitive {\gamma}-detector based on a thin monolithic LYSO crystal and a 96-channel SiPM array is developed for the spatial characterization and calibration of segmented {\gamma}-ray detector systems used in nuclear-physics experiments. The detector is designed to provide localized irradiation and rapid two-dimensional response mapping. A 7 cm diameter and 3 mm thick LYSO crystal is optically coupled to the SiPM array, and the position of the incident {\gamma}-ray interaction is reconstructed from the relative scintillation-light signals collected by neighboring SiPM channels. An asymmetry-based charge-sharing method is employed to determine the interaction position from the spatial distribution of the detected scintillation light. Detailed GEANT4 simulations, including optical photon transport, were performed to investigate the detector response and estimate its intrinsic spatial resolution. The simulations predict a spatial resolution of approximately 0.5 mm for 60 keV and 511 keV {\gamma}-rays under idealized conditions. A prototype detector was developed and experimentally characterized using coincidence measurements with the {\gamma}-scanning facility at GSI, Germany. The experimental measurements demonstrate a spatial resolution better than 1 mm in the central detector region, while the position-dependent response and degradation near the detector boundaries are investigated. The experimental results are compared with GEANT4 predictions to identify the contributions of optical photon transport, charge sharing, and detector geometry to the measured spatial resolution. The developed detector provides a compact solution for the three-dimensional characterization of highly segmented {\gamma}-ray detector arrays in nuclear physics experiments.
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All authors Katyayni Tiwari, Arzoo Sharma, Jürgen Gerl, Ivan Kojouharov, P. Herrmann, H. Schaffner, G. Aggez, Pushpendra P. Singh

Nuclear Experiment · Cross-listed from hep-ph

Radiative decays of the isoscalar $S$-wave $D\bar D$ molecule

Yuan-Jun Gao, Gang Li, Shi-Dong Liu et al. (+1 more)

In the hadronic molecular picture, an isoscalar $S$-wave $D\bar{D}$ molecule is naturally expected as the spin-0 partner of $X(3872)$. Assuming this state, denoted by $X_0$, to be a pure $D\bar D$ molecule with quantum numbers $J^{PC}=0^{++}$, we investigate its radiative decays $X_0\to\gamma V (V=\rho^0,\omega)$ within an effective Lagrangian framework. The decay amplitudes are generated by intermediate charmed-meson loops, with electromagnetic gauge invariance consistently maintained throughout the calculation. We evaluate the partial decay widths and examine their dependence on the $X_0$ mass and the cutoff. Although the individual decay widths exhibit a sizable dependence on the cutoff, their ratio is remarkably stable. In particular, we obtain that the ratio for the decays $X_0\to\gamma\rho^0$ and $X_0\to\gamma\omega$ is approximately 2.26, which is insensitive to the variation of the cutoff. This robust ratio provides a useful model-insensitive signature of the molecular structure of $X_0$.
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All authors Yuan-Jun Gao, Gang Li, Shi-Dong Liu, Pan-Pan Shi

Nuclear Experiment · Cross-listed from hep-ph

$\Delta$ resonance contributions to QED radiative corrections in neutron and inverse beta decay

Oleksandr Tomalak and Yi-Bo Yang

We incorporate the $\Delta(1232)$ resonance into pion-induced QED radiative corrections to neutron decay and inverse beta decay (IBD). Within the framework of heavy-baryon chiral perturbation theory with explicit $\Delta$ degrees of freedom, we compute additional contributions and study their impact on IBD cross sections and on the renormalization of the nucleon isovector vector and axial-vector charges. $\Delta$ resonance does not renormalize the vector charge. For the axial-vector charge, including the $\Delta$ resonance improves convergence and reduces the QED radiative correction to the experiment-over-lattice-QCD ratio $g_A/\left(g^\mathrm{QCD}_A g_V\right)$. $\Delta$ resonance increases the pion-induced QED radiative corrections to IBD by a factor $1.2$-$1.3$.
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Nuclear Experiment · Cross-listed from nucl-th

Ab initio anatomy of quadrupole correlations in $^{16}$O and $^{20}$Ne

Chenrong Ding, Benjamin Bally, Stavros Bofos et al. (+3 more)

Azimuthal hadronic flow measured in ultra-relativistic ion–ion collisions provides a new means of imaging multipole correlations in the ground state of atomic nuclei. Early interpretations largely relied on a classical-rotor picture, in which the measured mean-square elliptic flow is directly related to an intrinsic quadrupole deformation. Atomic nuclei, however, contain additional many-body correlations generated by the Pauli exclusion principle, collective shape fluctuations and non-collective dynamical processes, whose impact on this correspondence has not yet been elucidated. Here, we resolve this issue through an ab initio analysis of $^{16}$O and $^{20}$Ne based on chiral nuclear interactions, combining the in-medium similarity renormalization group with the quantum-number-projected generator coordinate method. By successively isolating antisymmetrization, collective rotational and vibrational, and non-collective dynamical correlations, we determine, for the first time, how each component contributes to the mean-square quadrupole eccentricity. We uncover an unexpected compensation among these distinct correlation mechanisms: despite sizable individual contributions, the squared effective quadrupole deformation inferred from the elliptic flow remains close to the square intrinsic deformation of the nucleus. This result provides a microscopic explanation for the surprising success of the classical-rotor approximation and establishes a quantitative foundation for interpreting $^{16}$O+$^{16}$O and $^{20}$Ne+$^{20}$Ne collision data recently collected at the Large Hadron Collider.
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All authors Chenrong Ding, Benjamin Bally, Stavros Bofos, Thomas Duguet, Yi Li, Jiangming Yao

Sunday 23 August

Nuclear Experiment · Cross-listed from physics.ins-det

Impact of Environmental Stress on Low Gain Avalanche Diode Sensors Response

Mohamed Hijas Mohamed Farook, Gaetano Barone, Diallo Boye et al. (+9 more)

Low Gain Avalanche Diodes or LGADs are silicon sensors capable of achieving excellent timing resolution due to their characteristic internal gain. Detectors based on LGAD technology play a crucial role in High Energy and Nuclear Physics experiments, among other applications. However, their performance is affected by environmental factors such as temperature, humidity, and storage conditions. A systematic evaluation of the response of LGAD sensors as a function of these environmental parameters is therefore of essential importance for any application. LGAD sensors fabricated at the Brookhaven National Laboratory are characterized and stress-tested against various operating conditions, such as rapid temperature and humidity changes. Dedicated and detailed simulations are used to interpret the experimental results.
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All authors Mohamed Hijas Mohamed Farook, Gaetano Barone, Diallo Boye, Gabriele D'Amen, Gabriele Giacomini, Timo Peltola, Jennifer Roloff, Enrico Rossi, Trevor Russell, Sally Seidel, Alessandro Tricoli, Lixing Wang

Saturday 22 August

Nuclear Experiment

Isoscalar Giant Resonances in the even-A Pd Isotopes

J. Arroyo, U. Garg, T. Furuno et al. (+39 more)

Studies of the isoscalar giant monopole resonance (ISGMR) across the chart of nuclides provide insight into the incompressibility of nuclear matter near saturation density, K(infinity). Such studies had revealed a discrepancy between theoretical approaches: quasiparticle random phase approximation (QRPA) derived from Skyrme interactions reproduce the strength distributions of the ISGMR in the doubly-closed-shell nuclei 90Zr and 208Pb, but their descriptions of strength distributions in open-shell medium-heavy nuclei suggest higher centroid energies should be experimentally observed. The latter nuclei required a smaller K(infinity) and were thus deemed softer. The present work serves to add to this softness discourse by extracting ISGMR strength distributions for 104,106,108,110Pd via 386-MeV inelastic alpha-scattering. The extracted giant resonance strength distributions are consistent with expectations in this isotopic range. Additional Quasiparticle Vibration Coupling (QPVC) effects are included with the QRPA approach and compared to aforementioned ISGMR strength distributions.
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All authors J. Arroyo, U. Garg, T. Furuno, M. Itoh, H. Shimojo, S. Adachi, H. Akimune, J. Cai, G. Colo, M. Dozono, F. Endo, M. Fujiwara, F. Furukawa, M.N. Harakeh, Y. Hijikata, Y. Honda, G. Hosoya, N. Itakura, K. Kawata, T. Kawabata, N. Kobayashi, Z.Z. Li, Y. Lin, Y. Matsuda, T. Morishita, K. Nakano, Y.F. Niu, T. Okamura, S. Ota, F. Saito, R. Saito, S. Sakajo, K. Sakanashi, H. Shibakita, R. Tsuji, G. Umemoto, A. Yamasaki, S. Yamazaki, T. Yano, K. Yasumura, S. Yonekura, J. Zenihiro

Nuclear Experiment · Cross-listed from physics.atom-ph

Bound and Resonant Spectra of Few-Lepton Coulomb Systems

Liang-Zhen Wen, Yao Ma, Zhi-He Shen et al. (+1 more)

We present a unified calculation of bound and resonant states in purely leptonic Coulomb systems: $e^-e^-e^+$ ($\mathrm{Ps}^-$), $\mu^+e^-e^-$ ($\mathrm{Mu}^-$), $\mu^+\mu^+e^-$ ($\mathrm{Mu}_2^+$), $e^+e^+e^-e^-$ ($\mathrm{Ps}_2$), and $\mu^+\mu^+e^-e^-$ ($\mathrm{Mu}_2$). Using an extended stochastic variational method combined with the complex scaling method, we resolve the natural-parity $S$- and $P$-wave spectra. Near their respective $n=2$ thresholds, all three trilepton systems exhibit Gailitis–Damburg sequences generated by $2S$ and $2P$ Stark mixing and the resulting inverse-square attraction. Although microscopically distinct from the Efimov effect, this mechanism produces the same inverse-square asymptotics and geometric scaling. The $\mathrm{Ps}^-$ and $\mathrm{Mu}^-$ systems exhibit resonance sequences of comparable density, whereas the $\mathrm{Mu}_2^+$ produces a much denser spectrum, with 20 resolved members in the $^3P^o$ channel. In $\mathrm{Mu}_2^+$, the deeper states follow molecular Born–Oppenheimer configurations, while the near-threshold spectrum is governed by the atomic $\mathrm{Mu}(2)+\mu^+$ structure. In $\mathrm{Ps}_2$, coupling between threshold-degenerate configurations is essential for a near-threshold bound state. In $\mathrm{Mu}_2$, the Born–Oppenheimer organization of the resonance spectrum is channel dependent.
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All authors Liang-Zhen Wen, Yao Ma, Zhi-He Shen, Shi-Lin Zhu

Nuclear Experiment · Cross-listed from cs.LG

How Architecture and Training Affect TPC Representations Across Experiments

Tyler Wheeler, Michelle P. Kuchera, Raghuram Ramanujan et al. (+12 more)

Deep-learning efforts have increasingly shifted toward foundation model approaches. In experimental physics, this allows models and learned representations to be reused beyond the experiments in which they were developed. This work evaluates the reusability of representations across experiments and detector systems using probes on frozen encoders. These probes reveal task-relevant structure before downstream adaptation, complementing fine-tuning. Together with random-weight controls, they distinguish contributions from architecture and encoder training that downstream performance alone cannot resolve. Time projection chamber (TPC) data provide a useful testbed because events from TPC systems can be represented as variable-length sparse tensors, while detector geometries, event topologies, and scientific tasks can differ substantially. We investigate whether fixed-dimensional TPC event representations can be reused across classification tasks, experiments, and detector systems. Sparse ResNet and PointNet-style encoders produce 512-dimensional embeddings for four datasets from the GADGET II TPC and AT-TPC. Randomly initialized encoders isolate the contribution from architecture before supervised training. We then train each encoder on a classification task, freeze its parameters, and train a linear or nonlinear probe for each downstream task. We find that this architecture-induced structure remains useful across experiments and detector systems. The randomly initialized PointNet-style representation is highly informative on several tasks. The two architectures organize their embedding spaces differently, but neither exhibits a large, systematic loss of utility cross-detector. These results show that architecture is a major source of task-relevant structure in TPC embeddings and should be treated explicitly when assessing representation learning and developing reusable detector models.
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All authors Tyler Wheeler, Michelle P. Kuchera, Raghuram Ramanujan, William Sieland, Ryan Krupp, Yassid Ayyad, Daniel Bazin, Connor L. Cross, Hoi Yan Ian Heung, Andrew J. Jones, Ruchi Mahajan, Saiprasad Ravishankar, Pranjal Singh, Benjamin Votaw, Chris Wrede

Friday 21 August

Nuclear Experiment · Cross-listed from hep-ph

Photon production from gluon splitting and fusion induced by a magnetic field of arbitrary strength in relativistic heavy-ion collisions

Alejandro Ayala, Santiago Bernal-Langarica, José Jorge Medina-Serna et al. (+1 more)

We compute the yield and elliptic flow coefficient for photons produced during the pre-equilibrium stage of semi-central relativistic heavy-ion collisions from the gluon fusion and splitting processes induced by the presence of a magnetic field. The calculation is performed for arbitrary values of the field strength. The pre-equilibrium gluon distribution is modeled with a glasma-inspired Bose-Einstein occupation factor, as well as with an anisotropic distribution that accounts for the rapid initial expansion along the beam axis. In both cases, we find a very good agreement between the calculation and the experimental data from PHENIX. Most notably, the shape and strength of the elliptic flow coefficient are described quite well, representing a step towards solving the outstanding photon puzzle.
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All authors Alejandro Ayala, Santiago Bernal-Langarica, José Jorge Medina-Serna, Ana Julia Mizher

Nuclear Experiment

Efficient production of $^{229m,g}$Th via neutron capture in VUV-transparent crystals

Zhong-yi Chen, Hao-yang Lan, Di Wu et al. (+14 more)

The low-lying isomeric state of $^{229m}$Th, owing to its unique nuclear energy structure, has been widely regarded as one of the most promising candidates for the development of a nuclear clock. However, the limited availability of suitable $^{229}$Th sources with sufficiently high activity remains a major challenge for experimental investigations of the $^{229m}$Th isomer. We propose a neutron-capture-based approach for the in-situ production of $^{229m,g}$Th by doping $^{228}$Ra into crystal hosts, where $^{229m,g}$Th is generated through neutron-capture reactions followed by a sequence of radioactive decay processes. We systematically investigate the background contributions associated with the three doped crystal hosts, namely CaF$_2$, SrF$_2$, and LiF, and evaluate their impact on the detection and identification of $^{229m}$Th. Under a neutron flux of $10^{15}\ \mathrm{n/cm^{2}/s}$ and a $^{228}$Ra doping concentration of $10^{19}\ \mathrm{cm^{-3}}$, the proposed method is capable of producing on the order of $10^{12}$ $^{229}$Th and $^{229m}$Th nuclei within only 1 s of irradiation, with a signal-to-noise ratios as high as $10^5$. In addition, the influences of detector wavelength resolution and post-irradiation measurement time on the detectability of the $^{229m}$Th signal are systematically analyzed, and the corresponding optimal measurement conditions are identified. Furthermore, the spatial distribution of neutron-produced $^{229}$Th within the crystal is investigated, providing practical guidance for optimizing crystal geometry and illumination configuration in future continuous-wave VUV absorption spectroscopy experiments. These results suggest that the proposed scheme provides a promising alternative pathway for the production and detection of $^{229\mathrm{m,g}}$Th, which may facilitate future studies toward the realization of nuclear-clock-based technologies.
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All authors Zhong-yi Chen, Hao-yang Lan, Di Wu, Mei-zhi Wang, Ze Chen, Li-pan Qin, Mei-qi Sun, Yu-peng Chen, Yan Tian, Jin Yan, Yan Wang, Xun-jie Ma, Xun Zhu, Yu-Meng Dong, Xin-Lu Xu, Xue-qing Yan, Yun-liang Wang

Thursday 20 August

Nuclear Experiment · Cross-listed from physics.ins-det

Demonstration of inkjet-printed targets for activation cross-section measurements: deuteron-induced reactions on strontium up to 24 MeV

Akihiro Nambu, Masayuki Aikawa, Yudai Shigekawa et al. (+4 more)

Excitation functions for the $^{nat}$Sr($d,x$) reactions producing $^{86m,g}$Y, $^{87m,g}$Y, and $^{88}$Y were measured up to 24-MeV deuteron energy using the stacked-foil technique and gamma-ray spectrometry. The $^{nat}$Sr targets were prepared using an inkjet printing method to ensure sufficient uniformity. To the best of our knowledge, this is the first experimental report of excitation functions measured using inkjet-printed targets, demonstrating the applicability of this technique to cross-section measurements. The measured cross sections were discussed in comparison with literature data and TENDL-2023 predictions. Our cross sections were generally consistent with those reported in the previous study, but were slightly higher in the threshold energy region. The TENDL-2023 library generally overestimates the experimental values. We report the experimental cross sections for the $^{nat}$Sr($d,x$)$^{86m}$Y reaction for the first time. These measured cross sections contribute to the refinement of nuclear reaction databases for practical applications.
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All authors Akihiro Nambu, Masayuki Aikawa, Yudai Shigekawa, Yousuke Kanayama, Tomohiro Tomitsuka, Sayantani Mitra, Hiromitsu Haba

Nuclear Experiment

Multi-Differential DVCS Cross Section Measurement on the Proton in the Valence Region with CLAS12

S. Lee, T.B. Hayward, L. Elouadrhiri et al. (+138 more)

We report the measurement of the four-fold differential cross section of deeply virtual Compton scattering (DVCS) on the proton using a longitudinally polarized 10.6 GeV CEBAF electron beam incident on a liquid-hydrogen target with the CLAS12 detector. The analysis provides 1312 data points, expanding the measured phase space in the valence quark region, 0.06 < $x_B$ < 0.58, 1.00 < $Q^2$ < 5.76 GeV$^2$, and 0.11 < $|t|$ < 1.00 GeV$^2$. DVCS cross section measurements directly constrain the real part of the DVCS amplitude through its interference with the Bethe-Heitler process, making them essential inputs to global extractions of the Compton Form Factors (CFFs), particularly the dominant CFF $H$. These data improve sensitivity to these observables and can contribute to future determinations of the proton's internal mechanical structure.
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All authors S. Lee, T.B. Hayward, L. Elouadrhiri, R.G. Milner, P. Achenbach, J. S. Alvarado, M.J. Amaryan, W.R. Armstrong, H. Avakian, N.A. Baltzell, M. Bashkanov, M. Battaglieri, F. Benmokhtar, A. Bianconi, A.S. Biselli, M. Bondi, S. Boiarinov, F. Bossù, K.-Th. Brinkmann, W.J. Briscoe, N. L. Bucuru Rodriguez, S. Bueltmann, V.D. Burkert, T. Cao, D.S. Carman, A. Celentano, P. Chatagnon, V. Chesnokov, H. Chinchay, G. Ciullo, E.W. Cline, P.L. Cole, M. Contalbrigo, A. D'Angelo, N. Dashyan, R. De Vita, S. Diehl, C. Dilks, C. Djalali, R. Dupre, H. Egiyan, M. Ehrhart, A. El Alaoui, L. El Fassi, C. Fanelli, M. Farooq, S. Fegan, I. P. Fernando, E. Ferrand, A. Filippi, C. Fogler, S. Frantzen, K. Gates, D.I. Glazier, R.W. Gothe, Y. Gotra, B. Gualtieri, K. Hafidi, H. Hakobyan, D. Heddle, M. Hoballah, D. Holmberg, M. Holtrop, Y. Ilieva, D.G. Ireland, E.L. Isupov, H.S. Jo, S. Joosten, M. Kerr, A. Kim, V. Klimenko, I. Korover, A. Kripko, V. Kubarovsky, S.E. Kuhn, C. Lama, L. Lanza, P. Lenisa, X. Li, D. Martiryan, V. Mascagna, B. McKinnon, A. Mehta, Z.E. Meziani, R. Milton, M. Mirazita, V. Mokeev, E. F. Molina Cardenas, P. Moran, S. Muduganti, C. Munoz Camacho, P. Nadel-Turonski, T. Nagorna, K. Neupane, G. Niculescu, M. Osipenko, P. Pandey, M. Paolone, L.L. Pappalardo, R. Paremuzyan, E. Pasyuk, C. Paudel, S.J. Paul, W. Phelps, N. Pilleux, L. Polizzi, J. Poudel, Y. Prok, A. Radic, K. Ramage, M. Ripani, M. Ronayette, P. Rossi, A.A. Rusova, S. Schadmand, A. Schmidt, Y.G. Sharabian, E.V. Shirokov, S. Shrestha, E. Sidoretti, B. Singh, N. Sparveris, S. Stepanyan, I.I. Strakovsky, S. Strauch, J.A. Tan, M. Tenorio, F. Touchte Codjo, R. Tyson, M. Ungaro, D.W. Upton, S. Vallarino, C. Velasquez, L. Venturelli, H. Voskanyan, Y. Wang, U. Weerasinghe, X. Wei, N. Wuerfel, Z. Xu, M. Zurek