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Physics Nuclear Experiment

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Tuesday 29 September

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

Development and Performance Study of a Capillary Liquid Scintillator Neutron Detector

Guang Luo, Jian Yu, Dikai Li et al. (+9 more)

Capillary liquid scintillator detectors are promising for high-resolution neutron imaging, yet experimental data on their light spread mechanism and spatial performance remain limited. Here, we report a neutron detector based on a hexagonal capillary array filled with EJ-309 liquid scintillator, with an inner diameter of about 50 um and a camera readout of 9 um pixels. Laser experiments show that the FWHM of the full light spot decreases from 260 um to 90 um with a metal light absorber, confirming effective suppression of lateral light spread. Using an AmBe neutron source, an effective field of view with a 5-sigma threshold was established from background frames. For single-capillary events, the pulse height spectrum follows a Landau distribution with a most probable value of 0.133 +/- 0.001 (stat.), and the intrinsic detection efficiency is 10.07% +/- 1.26% (stat.) +/- 1.43% (syst.), corresponding to about 13.55% when normalized to the active liquid scintillator area. The point spread function core yields a radial FWHM of 12.8 um and a centroid positioning precision of approximately 5.5 um (1 sigma), while the intrinsic position resolution is limited by the capillary pitch to 54 um. Linearity is good for 1 to 2 capillaries, with deviation appearing for 2 to 3 capillaries due to additional capture of spread light. These results provide experimental basis and physical understanding for imaging applications of capillary liquid scintillator neutron detectors.
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All authors Guang Luo, Jian Yu, Dikai Li, Yanmeng Dai, Meiling Chen, Jiaqiang Zou, Ke Yan, Shaoxuan Cui, Ge Jin, Zhao Xu, Chunhui Zhang, Leifeng Cao

Monday 28 September

Nuclear Experiment · Cross-listed from hep-ph

Full-event anomaly detection for new physics searches at the Electron-Ion Collider

Dimitrios Athanasakos, Sebastian Grieninger, Hongkai Liu et al. (+3 more)

The future Electron-Ion Collider (EIC) will offer new opportunities to search for physics beyond the Standard Model. We study resonant anomaly detection using machine learning and the full particle content of an event. We consider a new neutral gauge boson and a heavy neutral lepton as illustrative signals with different electron-jet topologies. Weakly supervised learning uses this event information to enhance the sensitivity of an invariant-mass search without identifying individual signal events during training. Comparisons with high-level observables show that the electron kinematics account for an important part of the separation, while correlations among the particles provide further sensitivity. We also construct a conditional full-event generator by adapting a model pretrained on LHC jets to produce EIC background events. A scan over signal fractions demonstrates substantial signal enhancement using the learned background reference, providing a proof of concept for this approach at the EIC. Finally, we consider a fully unsupervised graph autoencoder that provides modest signal enhancement but retains sensitivity at signal fractions too small for effective weak supervision. Our results motivate full-event anomaly detection as part of the EIC physics program and identify directions for developing methods suited to its distinct kinematics.
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All authors Dimitrios Athanasakos, Sebastian Grieninger, Hongkai Liu, Tymothy Mangan, Felix Ringer, Robert Szafron

Nuclear Experiment · Cross-listed from hep-ph

Vector Meson Dominance and Vector Meson Production

Craig D. Roberts

Against a background supported by the three pillars of emergent mass, this contribution challenges the fidelity of vector meson dominance as an instrument for relating the electromagnetic vector-meson (V) production reaction $e + p \to e^\prime + V + p$ to the hadronic process $V + p \to V + p$. It also describes a viable reaction model for exclusive photoproduction of light and heavy vector mesons from the proton, which exposes the $q\bar q$ content of the photon. That model's successes reveal that it is premature to link extant $V + p \to V + p$ data with, for instance, in-proton gluon distributions, the QCD trace anomaly, or pentaquark production. Improved reaction theory and more precise data are required before the validity of such links can objectively be assessed.
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Nuclear Experiment · Cross-listed from physics.ins-det

A portable neutron scatter camera with isotropic sensitivity

S. G. Yoon, L. Larizgoitia, C. M. Lewis et al. (+2 more)

We describe the design and characterization of a neutron scatter camera specifically developed for the study of neutron fields (flux, energy, direction) in experimental areas of spallation facilities, where multiple neutron sources can simultaneously contribute. A combination of hardware and logic triggers provides the isotropic response required for this application. Neutron source locations are accurately reconstructed on images from a built-in 360$^\circ$ panoramic camera. The full understanding of neutron fields that the device provides can be used for site selection and abatement of neutron backgrounds affecting sensitive instruments such as coherent elastic neutrino-nucleus scattering (CE$\nu$NS) detectors to be located at the upcoming European Spallation Source.
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All authors S. G. Yoon, L. Larizgoitia, C. M. Lewis, F. Monrabal, J. I. Collar

Nuclear Experiment · Cross-listed from hep-lat

A parameter independent analysis of the QCD chiral phase transition and its universal critical behaviour

Jishnu Goswami, Frithjof Karsch, Sabarnya Mitra et al. (+1 more)

We make use of unique properties of scaling functions to estimate the chiral phase transition temperature and corresponding universal critical parameters of this phase transition directly from (2+1)-flavor QCD simulations with highly improved staggered fermions on lattices with temporal extent $N_\tau=8$. Working with an improved chiral order parameter for quantifying chiral symmetry breaking, we analyze the finite-volume dependence of this observable for a wide range of lattice volumes and light quark masses, and quantitatively estimate the deviations from the expected universal scaling behaviour as a function of the light-to-strange quark mass ratio.
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All authors Jishnu Goswami, Frithjof Karsch, Sabarnya Mitra, Christian Schmidt

Nuclear Experiment · Cross-listed from hep-ph

Infrared Subtraction with Artificial Intelligence

Wenjie He, Xiaohui Liu, Yandong Liu et al. (+1 more)

We present AI-developed local infrared subtraction, building on projection to Born and EFT matching. The framework separates an integrable radiation term from a finite contribution at Born kinematics, referred to as the Born contact. The contact is determined using the EFT singular distribution in a resolution observable such as N-jettiness $\tau_N$. Under human physics guidance, an LLM develops two implementations. One uses a neural network for phase space projection and fits the contact by matching to EFT cumulants. The other uses an analytic construction that keeps the Born momenta fixed while integrating over radiation. It combines the EFT $\delta(\tau_N)$ coefficient with finite 4-dimensional radiation integrals to calculate the contact term directly. This gives a local subtraction formula without a slicing parameter, while reusing existing lower-order radiation calculations and EFT singular predictions. As a demonstration, we reconstruct the full NLO correction for massless 3- and 4-jet production in electron-positron annihilation. The attempt to the NNLO dijet production is also made by recursively using the NLO P2B construction with the LLM designing machine-learning controls to reduce the variance of the contact integral. The tested predictions are in good agreement with EERAD3. The numerical calculation and projection-network training use a 2020 Apple M1 MacBook, without GPU acceleration, illustrating the feasibility of the construction with modest computing resources. The appendices develop an extension of the local subtraction to 3-jet NNLO, giving explicit radiation maps and a proposed contact formula. We also show how to integrate over NNLO radiation while keeping the Born momenta fixed, for any number of massless final-state jets. Our results demonstrate how AI can help higher-order calculations by constructing infrared subtraction and improving its numerical integration.
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All authors Wenjie He, Xiaohui Liu, Yandong Liu, Zhan Wang

2609.36007 · 28 Sep · 31 pages, 11 figs. References and text updated, including the analytic NNLO di-jet contact term calculated by the LLM directly within the P2B+EFT subtraction in 4 dimensions. Prompts and pseudocode for LLM-based agents to reproduce the figs are available in the Ancillary Files section. Prompts for reproducing the analytic contact term can be provided upon request

Abstract PDF

Nuclear Experiment · Cross-listed from hep-ph

Meson photoproduction at Jefferson Lab: from two-meson final states to meson-baryon spin-density matrices

Vincent Mathieu

Recent progress in the understanding of meson photoproduction, obtained from the joint effort of the Joint Physics Analysis Center (JPAC) and the GlueX and CLAS experiments at Jefferson Lab, is reviewed. The photoproduction of the $\eta\pi$ system is now well understood, from the $a_2(1320)$ resonance region to the high-mass region dominated by double Regge exchanges. Since the lightest hybrid meson, the $\pi_1(1600)$, is expected to decay predominantly into $b_1\pi$, reactions with a recoiling $\Delta^{++}$ are promising channels for exotic searches. As a first step towards $\gamma p \to b_1 \pi \Delta^{++}$, the complete angular distribution of $\gamma p \to \rho^-\Delta^{++}$ with a linearly polarized photon beam is derived. It involves 56 double-index spin-density matrix elements, which describe the correlations between the $\rho$ and the $\Delta$ decays. When the production amplitudes factorize, as is the case for the exchange of a single Regge pole, the intensity reduces to the product of the standard $\rho$ and $\Delta$ decay distributions and depends on only 14 parameters.
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Nuclear Experiment

Toward FAIR and AI-Ready Data: An Assessment of the GlueX Experiment's Data Ecosystem at Jefferson Lab

Anil Panta, Brad Sawatzky, Casey Morean et al. (+2 more)

Department of Energy programs increasingly require that experimental data be not only preserved but usable by artificial intelligence (AI) systems, yet no accepted standard defines when a dataset is AI-ready. We argue that data must be FAIR (Findable, Accessible, Interoperable, Reusable) before they can be AI-ready, and that AI readiness is a distinct property requiring its own assessment. Using the GlueX experiment in Hall D at Jefferson Lab as a pilot, we map the data ecosystem, assess it against FAIR, and define an AI-readiness framework whose criteria are backed by deterministic metrics. We also evaluate existing validation software to separate what can be assessed with off-the-shelf tools from what requires domain-specific development. The assessment yields a set of findings, each paired with a recommendation, some of which are already in production or prototyped and others planned as next steps.
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All authors Anil Panta, Brad Sawatzky, Casey Morean, Dmitry Romanov, Douglas Higinbotham

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

EXO-200 Public Data Release for AI/ML Applications

S. Al Kharusi, G. Anton, I. Badhrees et al. (+103 more)

We present a public release of a subset of calibration data from the EXO-200 experiment, a liquid xenon time projection chamber designed to search for neutrinoless double-beta decay in $^{136}$Xe. The released dataset consists of approximately one million events collected during $^{228}$Th calibration campaigns performed near the end of Phase-II operations between February 26 and March 2, 2018. For each event, the dataset includes raw detector waveforms from the U-wire, V-wire, and avalanche photodiode (APD) readout channels together with reconstructed event quantities including charge energy, light energy, rotated energy, and charge-cluster information. The dataset is distributed in HDF5 format and is intended to support data preservation, educational activities, and the development of modern machine-learning techniques for rare-event physics. This paper describes the detector, dataset contents, file structure, and public access mechanism.
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All authors S. Al Kharusi, G. Anton, I. Badhrees, P. S. Barbeau, V. Belov, T. Bhatta, M. Breidenbach, T. Brunner, G. F. Cao, W. R. Cen, C. Chambers, B. Cleveland, M. Coon, A. Craycraft, T. Daniels, L. Darroch, S. J. Daugherty, J. Davis, S. Delaquis, A. Der Mesrobian-Kabakian, R. DeVoe, A. Dolgolenko, M. J. Dolinski, J. Echevers, B. Eckert, W. Fairbank Jr., D. Fairbank, J. Farine, S. Feyzbakhsh, P. Fierlinger, Y. S. Fu, D. Fudenberg, P. Gautam, R. Gornea, G. Gratta, C. Hall, E. V. Hansen, J. Hoessl, P. Hufschmidt, M. Hughes, A. Iverson, A. Jamil, C. Jessiman, M. J. Jewell, A. Johnson, A. Karelin, L. J. Kaufman, T. Koffas, R. Krücken, A. Kuchenkov, K. S. Kumar, Y. Lan, A. Larson, B. G. Lenardo, D. S. Leonard, G. S. Li, S. Li, Z. Li, C. Licciardi, Y. H. Lin, R. MacLellan, T. McElroy, T. Michel, B. Mong, D. C. Moore, K. Murray, O. Njoya, O. Nusair, A. Odian, I. Ostrovskiy, H. Peltz Smalley, A. Perna, A. Piepke, A. Pocar, F. Retière, A. L. Robinson, P. C. Rowson, S. Schmidt, D. Sinclair, K. Skarpaas, A. K. Soma, V. Stekhanov, M. Tarka, S. Thibado, J. Todd, T. Tolba, T. I. Totev, R. Tsang, B. Veenstra, V. Veeraraghavan, P. Vogel, J.-L. Vuilleumier, M. Wagenpfeil, J. Watkins, M. Weber, L. J. Wen, U. Wichoski, G. Wrede, S. X. Wu, Q. Xia, H. Xu, D. R. Yahne, L. Yang, Y.-R. Yen, O. Ya. Zeldovich, T. Ziegler

Saturday 26 September

Nuclear Experiment · Cross-listed from nucl-th

$\beta$ Recoil spectroscopy as a Beyond Standard Model laboratory

Leendert Hayen

We consider the nuclear recoil spectrum following allowed $\beta$ decay as a laboratory for Beyond Standard Model searches, and perform an exhaustive treatment of the Standard Model prediction. We consider final state interactions, nuclear structure corrections, kinematic corrections and radiative corrections, derive new results and show that the nuclear recoil spectrum is theoretically exceptionally clean. We construct a clean statistical framework and analyze the Fisher information for extracting exotic current constraints and testing Cabibbo-Kobayashi-Maskawa top-row unitarity, and consider a number of sterile neutrino scenarios. In addition, we find that for select isotopes separate measurement of the $\beta$-asymmetry and recoil spectrum can achieve an increase in the statistical power of up to a factor 40.
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Nuclear Experiment · Cross-listed from physics.soc-ph

Hydrogen mon amour

Christophe Grojean and Patrick Janot

The FCC's projected average electricity consumption is 1.3 TWh per year. If supplied entirely by nuclear power, this would represent about 10% of the annual output of a large third-generation nuclear reactor, together with a corresponding share of its radioactive waste. By 2050, however, renewable sources could provide up to 80% of this electricity on a substantially decarbonised European grid, supported by long-term power-purchase agreements and flexible operation. This could reduce the residual nuclear requirement, and its associated waste, by up to a factor of five. This essay asks whether hydrogen could help bridge the remaining periods of low wind and solar generation. It examines production from renewable electricity, transport as hydrogen or ammonia, storage and conversion back into electricity, together with their efficiency losses and carbon footprints. It then considers the still uncertain prospect of naturally occurring hydrogen. None of these routes offers a ready-made solution. But the decades before the FCC begins operation leave time to develop one–and CERN could help accelerate that development by becoming a credible long-term customer.
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Friday 25 September

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

Quantitative characterization of superconducting qubits as particle detectors

Francesco De Dominicis, Raja Yasir Mehmood Khan, Dounia L Helis et al. (+22 more)

Ionizing radiation is a major source of correlated errors in superconducting quantum processors, yet the mechanisms responsible for the qubit response to particle interactions remain only partially understood. In this work, we operate superconducting qubits as particle detectors while simultaneously monitoring the deposited energy with an independent semiconductor cryogenic sensor. This complementary measurement provides an absolute determination of the particle interaction rate in the chip, enabling the first direct measurement of the detection efficiency of superconducting qubits exposed to environmental radiation. We measure individual qubit detection efficiencies of about 30-40$\%$, increasing to approximately 50$\%$ when combining the response of two qubits. Under the conservative assumption that the efficiency loss is entirely determined by a finite detection threshold, we derive an upper limit on the effective energy threshold of the detector of $70\pm20~\mathrm{(stat)}\pm30~\mathrm{(syst)}~\mathrm{keV}$. Measurements with radioactive sources producing different deposited-energy spectra further show that the detection efficiency decreases for lower-energy interactions. We further investigate the origin of the qubit response by injecting controlled thermal pulses with a resistive heater. Although these pulses deposit energies comparable to those released by particle interactions, they do not reproduce the radiation-induced signatures, demonstrating that the qubit response to radiation cannot be explained by a transient increase in substrate temperature alone. Our results establish an experimental framework for quantitatively connecting particle energy deposition to radiation-induced responses in superconducting quantum circuits.
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All authors Francesco De Dominicis, Raja Yasir Mehmood Khan, Dounia L Helis, Ambra Mariani, Letizia Tirabasso, Alberto Ressa, Mustafa Bal, Fabio Bellini, Camilla Bonomo, Nicola Casali, Gianluigi Catelani, Ivan Colantoni, Francesco Crisa, Angelo Cruciani, Sabrina Garattoni, Luca Gironi, Andrea Melchiorre, Lorenzo Pagnanini, Valerio Pettinacci, Stefano Pirro, Andrei Puiu, Tanay Roy, Shaojiang Zhu, Anna Grassellino, Laura Cardani

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

Transition Radiation Detector Upgrade for the GlueX-III Charmonium Program

Lauren Kasper, Alexander Austregesilo, Cody Dickover et al. (+9 more)

The GlueX-III experiment at Jefferson Lab, planned to run in 2027-2029, will enhance the laboratory's capability to explore charmonium production near threshold and related aspects of QCD in the non-perturbative regime. A central upgrade for GlueX-III is a large-scale triple-GEM Transition Radiation Detector (TRD) optimized for electron identification and pion suppression in the hadron-rich environment of fixed-target photoproduction. This document describes the motivation for and efforts related to such an upgrade, including the design, construction, and performance of a 720x528mm$^{2}$ triple-GEM-TRD prototype that was tested in the existing GlueX-II experimental acceptance during the 2025 run. Results validate the prototype's integration, timing performance, and electron identification capability. Its projected impact in the GlueX-III setting is discussed, with background reduction in a $J/\psi$ candidate sample demonstrated. The development and use of a modern TRD technology in a high-background environment at Jefferson Lab may inform detector design choices as a future upgrade path for the EIC.
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All authors Lauren Kasper, Alexander Austregesilo, Cody Dickover, Sean Dobbs, Sergey Furletov, Yulia Furletova, Ilya Larin, Lubomir Pentchev, Saheli Rakshit, Nizar Septian, Simon Taylor, Julia Velkovska

Nuclear Experiment · Cross-listed from hep-ex

Strangeness Production at GlueX

Hao Li

The GlueX experiment at Jefferson Lab is well suited for exclusive studies of strangeness production, combining a linearly polarized photon beam at $8.0 < E_\gamma < 8.8$ GeV with a large-acceptance detector that reconstructs weakly decaying hyperons. We outline a research program built on three aspects: (i) spectroscopy of strange mesons, where many excited $K^*$ states remain unestablished and crypto-exotic strange hybrids must be identified from combined spectrum and decay information, anchored by the $K^*(892)$ as a standard candle; (ii) spin dynamics, where the first precise measurements of the complete spin-density matrix elements in the photoproduced $K^*(892)\Lambda$ system beyond the Schilling formalism constrain the $t$-channel strange production mechanism; and (iii) hadronization, probed through the newly published $p\bar{p}$, $\Lambda\bar{\Lambda}$, and $p\bar{\Lambda}$ photoproduction cross sections and emerging $\Lambda\bar{\Lambda}$ spin-correlation measurements. We place these efforts in the context of the broader GlueX strangeness program and give an outlook toward the high-statistics GlueX-II era.
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Nuclear Experiment · Cross-listed from nucl-th

A new type of skin thickness in high-spin isomers to constrain equation of state of spin-polarized nuclear matter

Toi Tachibana, Kouichi Hagino, Kenichi Yoshida et al. (+1 more)

We explore experimental probes for constraining the equation of state (EOS) of spin-polarized nuclear matter, where spins of nucleons are aligned along a particular direction. For this purpose, we calculate the $12^+$ isomeric state of the \ce{^{52}Fe} nucleus with the relativistic point-coupling model. We argue that the spin skin thickness of this high-spin state, that is, the difference between the radius of the spin-up density and that of the spin-down density, strongly correlates with the spin slope parameter of the EOS. This is in analogy to the well known linear correlation between the slope parameter of the symmetry energy and the neutron skin thickness of finite nuclei. We show that this correlation is retained even when one considers the difference of the radii between the $12^+$ and the ground states, even though the correlation is much weaker than in the case of the difference between the spin-up and the spin-down radii. We also discuss the mean-square charge radii of the $12^+$ state. We find that by taking the square of the radii the dependence on the spin slope parameter becomes much stronger, and thus it can serve as a good probe of the spin slope parameter given a high resolution of laser-spectroscopy experiments.
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All authors Toi Tachibana, Kouichi Hagino, Kenichi Yoshida, Qiang Zhao

Thursday 24 September

Nuclear Experiment · Cross-listed from hep-ex

Separating coherent and incoherent photoproduction at an Electron-Ion Collider: Comparing lead, gold and silver beams

Spencer R. Klein and Mathias C. Labonte

Exclusive photoproduction is an important probe of nuclear parton distributions at low Bjorken-$x$. The Good-Walker paradigm relates coherent photoproduction to the average nuclear configuration, giving access to the transverse distribution of gluons in a target, while incoherent photoproduction is sensitive to fluctuations such as gluonic hotspots. Efficiently separating coherent and incoherent interactions is a key challenge for experiments at the future Electron-Ion Collider (EIC). In this article, we study nuclear de-excitation via photon emission, and see how the finite photon detection efficiency leads to misidentification of incoherent emission. We compare the detection efficiency for incoherent $J/\psi$ production using the BeAGLE event generator for Ag-107, Au-197, and Pb-208 targets, for two different forward photon energy thresholds: 50 MeV and 200 MeV. The shell structures of the three species exhibit different incoherent tagging efficiencies due to differences in the lifetimes and energy levels of their excited states. Some of the low-lying states live long enough so that they decay outside the EIC detectors. Especially for the lower photon energy threshold, lead allows a higher tagging efficiency than gold, due to its lack of low-lying and/or long-lived excited states.
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Nuclear Experiment

Quarkonium production in light-ion collisions with the ALICE experiment

Rebecca Cerri

Quarkonium production has long been considered as one of the golden probes to study the quark-gluon plasma (QGP). In fact, the early production of heavy quarks (ccbar) and (bbbar) makes quarkonia an ideal tool to investigate the evolution of the hot and dense medium produced in ultra-relativistic heavy-ion collisions. In such a medium, quarkonium production is expected to be suppressed due to the screening of the binding potential between the heavy quark and antiquark and/or through in-medium interactions. Moreover, at LHC energies the recombination of uncorrelated charm quarks pairs, namely regeneration, was found to significantly affect charmonium observables, in contraposition to the suppression mechanism. In addition, measurements in smaller collision systems as p-Pb have highlighted the possibility to observe QGP-like effects. In this context, the study of charmonium production in intermediate collision systems, as light-ion collisions, becomes more and more interesting, representing an ideal test ground for the state-of-the art theoretical models. In this contribution the new measurements of charmonium production will be shown using the light-ion collisions data collected for the first time at the LHC in 2025 (oxygen-oxygen (OO), proton-oxygen (pO)). The results will be shown exploiting the forward ALICE rapidity coverage (2.5 < y < 4). Finally, the measurements will be compared with the existing theoretical models.
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Nuclear Experiment · Cross-listed from nucl-th

Measuring short-range correlations using relativistic heavy-ion collisions

Lu-Meng Liu, Jun Xu and Xu-Guang Huang

We propose a novel method to measure the strength and isospin dependence of short-range correlations (SRCs) in nuclei with their collisions at relativistic energies. Since nucleons in the high-momentum tail (HMT) induced by SRCs have large transverse velocities, we find that measuring the yield ratio of free spectator neutrons at large to small transverse distances detected by Zero-Degree Calorimeter (ZDC) array may probe the fraction of nucleons in the HMT. In addition, measuring the yield ratio of ZDC neutrons in central $^{96}$Zr+$^{96}$Zr to $^{96}$Ru+$^{96}$Ru collisions at large transverse distances may probe the isospin dependence of the HMT and SRCs. Compared to traditional scattering experiments, our study illustrates that relativistic heavy-ion collisions may serve as an alternative way of measuring SRCs in colliding nuclei with less final-state interactions.
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Wednesday 23 September

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

Performance of the MPD experiment in dielectron measurements at NICA

Sudhir Pandurang Rode, Itzhak Tserruya, Victor Riabov et al. (+2 more)

The Multi-Purpose Detector (MPD) experiment at NICA is designed to investigate strongly interacting matter at high net-baryon density through a broad program of heavy-ion measurements. Dielectrons constitute one of the key probes in this program, with contributions emitted throughout the entire space-time evolution of the collision. Their experimental measurement is, however, challenged by a large combinatorial background arising primarily from incompletely reconstructed photon conversions and Dalitz decays of light neutral mesons. In this work, we study the performance and capabilities of the MPD experiment for dielectron measurements using simulated minimum-bias $^{209}$Bi+$^{209}$Bi collisions at $\sqrt{s_{NN}}$ = 9.2 GeV. Electron identification is performed using the combined information from the TPC, the TOF detector and the ECal. A multilayer-perceptron classifier is used to optimize electron identification, leading to a substantial increase in electron detection efficiency relative to sequential one-dimensional selections while preserving an electron-sample purity close to unity over a broad momentum range. To address the dominant sources of combinatorial background, a pair-analysis strategy is developed that exploits partially reconstructed electron tracks. The method combines the pair opening angle, the TPC dE/dx signal, and an approximate reconstruction of the pair invariant mass to tag tracks from photon conversions and $\pi^0$ Dalitz decays at the pair level. In the mass interval 0.2 $< m_{ee}<0.7 $ GeV/$c^2$, the method improves the signal-to-background ratio by a factor of about 3.5 with the current track reconstruction algorithm. The study demonstrates the strong potential of the MPD experiment for dielectron measurements at NICA energies and highlights the importance of further improvements in low-$p_{\rm T}$ track reconstruction.
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All authors Sudhir Pandurang Rode, Itzhak Tserruya, Victor Riabov, Yonghong Wang, Chi Yang

Nuclear Experiment · Cross-listed from cs.LG

Physics-Informed Self-Supervised Learning for Joint Wire Calibration and Interaction Position Reconstruction in Multi-Wire Parallel Plate Avalanche Counters

Antoine Lemasson and Maurycy Rejmund

Scientific instruments require accurate calibration to convert detector signals into reliable physical observables. Conventional calibration procedures typically rely on dedicated calibration measurements, analytical response models or labelled reference data, limiting their ability to adapt to changing operating conditions and detector aging. We present a physics-informed self-supervised learning framework that jointly performs wire calibration and interaction position reconstruction in Multi-Wire Parallel Plate Avalanche Counters (MWPPACs) without requiring labelled position measurements or dedicated calibration runs. The method formulates detector calibration as a latent optimization problem in which global wire gains and event-wise interaction positions are estimated simultaneously using supervision derived exclusively from detector geometry and charge-energy consistency constraints. A detector-independent neural network reconstructs sub-wire interaction positions from local charge distributions, eliminating the need to assume analytical induction profiles by learning the detector response directly from experimental data. The end-to-end differentiable framework enables continuous detector self-calibration while improving the uniformity and accuracy of position reconstruction. Experimental evaluation on the entrance MWPPAC tracking detectors of the VAMOS++ magnetic spectrometer demonstrates stable convergence, improved spatial homogeneity and enhanced position resolution. Beyond the detector studied, the method establishes a general framework for physics-informed self-supervised calibration of scientific instruments and is a step toward autonomous intelligent instrumentation capable of continuous adaptation during operation. In this paradigm, detector calibration is no longer a prerequisite for an experiment but an integral part of the measurement process itself.
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Nuclear Experiment · Cross-listed from hep-ph

Simulating the emission source function in very peripheral relativistic heavy-ion collisions

Angel Reina Ramírez, Volodymyr Magas and Juan M. Torres-Rincon

We present a microscopic femtoscopic investigation of the space-time emission source in low-multiplicity (80–90% centrality) $\text{Pb}-\text{Pb}$ collisions at $\sqrt{s_{NN}} = 5.02~\text{TeV}$, using a hybrid transport framework coupling SMASH initial conditions, 3+1D viscous hydrodynamics (vHLLE), and a SMASH hadronic cascade afterburner. Access to the full space-time evolution of the produced particles allows for the direct reconstruction of emission source functions in both the Longitudinally Comoving System and the Pair Rest Frame. We study identical pairs of mesons ($\pi\pi$, $KK$) and baryons ($pp$), as well as cross-species combinations, while explicitly isolating the contributions from primordial particles, hadronic rescattering, and long-lived resonance decays. Our analysis shows that simple Gaussian fits are inadequate for precision source analyses, whereas a combined Gaussian plus exponential parametrization better captures the compact core and the extended tail. Finally, the extracted Gaussian core radii, $R_{\text{core}}$, for our very peripheral collisions demonstrate an approximate $m_T$-scaling behavior rather similar to the one observed in pp reactions.
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Nuclear Experiment · Cross-listed from physics.ins-det

Study of the properties of sustainable materials for shielding against ionizing radiations

Julien Faivre

The SuShi project aims at determining how sustainable materials can be used to shield against ionizing radiations. This contribution presents a comparison of the effect of concrete and rammed raw earth on photons. For energies around the MeV, where interactions by Compton scattering dominate, changes in the material composition have virtually no effect. The density difference results in 20% more thickness needed for earth to achieve the same flux attenuation as concrete. The same value is found for higher energies, where photons produce electromagnetic showers. Below 0.1 MeV, material composition and earth moisture content matter but the attenuation is much larger.
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Nuclear Experiment · Cross-listed from physics.ins-det

CBM T0 Detector Performance Study with Light Ions (4He, 12C) and the DOGMA Readout System

Yevhen Kozymka, Thomas Bergauer, Maximilian von Buelow et al. (+14 more)

This paper presents the realization and performance of the CBM T0 detector system. Built upon an approximately 70 {\mu}m thin polycrystalline CVD (pcCVD) diamond sensor with pad metallization, the detector is mounted on a flexible vacuum manipulator and operates entirely under passive cooling. Interfaced with the DOGMA readout architecture, the system successfully meets all operational requirements for CBM. It demonstrates a high detection efficiency (near 100%) and a timing precision below 50 ps RMS across a broad range of beam species, from light ions (such as Carbon) to heavy ions (such as Gold). The DOGMA readout features two distinct data paths: a high-precision TDC path routing data directly to the global CBM DAQ, and a secondary path deliver in real-time rate measurements crucial for online beam quality monitoring and fast beam abort logic. Finally, detailed performance studies conducted with light-ion beams at EBG MedAustron are discussed.
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All authors Yevhen Kozymka, Thomas Bergauer, Maximilian von Buelow, Henrik Flörsheimer, Jochen Frühauf, Tetyana Galatyuk, Harald Handerkas, Henning Heggen, Mladen Kis, Sergey Linev, Jerzy Pietraszko, Christian Joachim Schmidt, Luca Schramm, Michael Traxler, Michael Träger, Felix Ulrich-Pur, Robert Visinka

Nuclear Experiment

Mean-$p_T$ fluctuations in Au+Au collisions at $\sqrt{s_{\rm NN}}=3.0$–$19.6$ GeV within JAM2

Yaqi Liu, Liuyao Zhang, Chunjian Zhang et al. (+2 more)

Event-by-event mean-$p_T$ fluctuations probe initial-state fluctuations and their evolution through the dynamics of heavy-ion collisions. We study second-order mean-$p_T$ fluctuations in Au+Au collisions at $\sqrt{s_{\rm NN}}=3.0$–$19.6$ GeV using JAM2 in the RQMDv mean-field mode with the MH2 parameterization. The model qualitatively reproduces the measured identified-particle $p_T$ spectra, providing a single-particle baseline for the fluctuation analysis. The scaled fluctuation $k_2$ decreases with increasing $\langle N_{\rm part}\rangle$ and shows broad agreement with the available measurements at 7.7–19.6 GeV, whereas its calculated centrality dependence is stronger than that in the data at 3.0–4.5 GeV. For the combined proton-plus-antiproton sample, the unnormalized correlator $\langle c_2\rangle$ is positive and larger than that for charged pions. The charged-pion correlator $\langle c_2\rangle$ is negative or consistent with zero over most centrality intervals at 3.0 and 3.5 GeV, becomes weakly positive at 4.5 GeV, and remains positive at higher energies. Its energy evolution resembles the change in the reaction-plane elliptic flow, but this comparison does not establish a common microscopic origin. These calculations provide species-dependent predictions within a transport model without an explicit partonic stage. Isolating the contributions of mean fields, rescattering, and spectator interactions requires controlled variations of the transport dynamics.
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All authors Yaqi Liu, Liuyao Zhang, Chunjian Zhang, Jinhui Chen, Chunwang Ma

Nuclear Experiment · Cross-listed from nucl-th

Shell structure and spontaneous decay of superheavy $Z=124$ isotopes with the deformed relativistic Hartree-Bogoliubov theory in continuum

Yumeng Wang, Lang Liu and Cong Pan

Shell structure and spontaneous decay of $Z = 124$ isotopes are systematically investigated using the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) with the PC-PK1 density functional. By accounting for deformation and continuum effects, the neutron drip line is predicted to be located at $N = 320$, and eight potential multi-neutron emitters beyond the neutron drip line are identified. The results, compared with the spherically constrained case, highlight the critical role of deformation effects in determining the ground-state properties of superheavy nuclei. In addition, potential neutron shell closures emerge at $N = 258$ and $350$, alongside subshell closures at $N = 232$ and $320$. The results disfavor $Z = 124$ as a possible proton magic number and suggest $Z = 120$ and $138$ as more favorable candidates for proton shell closures in the superheavy region. Finally, the competition between $\alpha$ decay, $\beta$ decay, and spontaneous fission is analyzed by calculating half-lives within various semi-empirical formulas. The results indicate that $\alpha$ decay is the predominant mode on the proton-rich side, whereas spontaneous fission and $\beta^-$ decay gradually become dominant with increasing neutron number.
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Nuclear Experiment · Cross-listed from nucl-th

Multi-Model Analysis of the Astrophysical $S(E)$ Factor for the $^{9}\mathrm{Be}(p,\alpha)^{6}\mathrm{Li}$ Reaction and Its Impact on Astrophysical Reaction Rates

Xue-Jian Wang, Wei-Ke Nan, Qing Wang et al. (+5 more)

The $^{9}\mathrm{Be}(p,\alpha)^{6}\mathrm{Li}$ reaction is a destruction process for $^{9}\text{Be}$ in stars and the Big Bang. The Trojan Horse Method (THM) is a well-established indirect technique that enables the determination of reaction cross sections within the Gamow energy region while avoiding the uncertainties associated with low-energy extrapolations of the $S(E)$ factor and electron-screening effects. In this work, the bare-nucleus THM data reported by Wen et al. are systematically analyzed using polynomial fitting, a double Breit–Wigner model, and the $R$-matrix formalism. The applicability and physical implications of these theoretical approaches in describing the low-energy $S(E)$ factor of the $^{9}\mathrm{Be}(p,\alpha)^{6}\mathrm{Li}$ reaction are investigated and compared. Since the THM data have been incorporated into the NACRE II reaction-rate compilation, leading to improved accuracy in reaction-rate evaluations, the refined theoretical analysis presented here provides further insight into the underlying reaction dynamics and establishes a more reliable foundation for stellar reaction-rate calculations. The results obtained in this work offer valuable reference for future high-precision experimental investigations and the development of theoretical models in nuclear astrophysics.
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All authors Xue-Jian Wang, Wei-Ke Nan, Qing Wang, Tian-Yu Tao, Qun-Gang Wen, Jian-You Guo, Cheng-Bo Li, Hui-Ming Jia

Nuclear Experiment

Probing the $^{12}$C+$^{12}$C fusion reaction via zero-degree spectator measurement in the $^{12}$C($^{14}$N,$\alpha d$)$^{20}$Ne quasi-free reaction

Xue-Jian Wang, Qun-Gang Wen, Cheng-Bo Li et al. (+14 more)

The 12C+12C fusion reaction is a key physical process in stellar evolution and supernova explosions. It not only determines the late evolutionary fate of massive stars but also directly influences the critical conditions for triggering Type Ia supernovae in accreting white dwarfs. In this work, the THM was employed to investigate the 12C(12C,a0)20Ne reaction channel of the 12C+12C fusion process, using 14N as the Trojan horse nucleus. Telescope detectors were placed at 0 and 15 deg. to design two experimental configurations covering the forward-angle regions where spectator particles are most likely to emerge. By applying the DWBA, two sets of astrophysical S*(E) factors for the two-body reaction 12C(12C,a0)20Ne were extracted from the three-body reaction 12C(14N,da0)20Ne and normalized to existing experimental data. The results show that, limited by the overall experimental resolution, the present study cannot resolve fine resonance structures. Within the astrophysical energy region of 0.5-2 MeV, the extracted S*(E) factor exhibits an increasing trend toward lower energies. The S*(E) factor obtained with the 0-deg configuration shows a flatter trend than that obtained with the 15-deg configuration. Supported by the quasi-free reaction simulation results, the divergence between the two data sets may reflect a combination of experimental acceptance effects, finite detector resolution, and possible differences in the relative contributions of reaction mechanisms. This study provides a systematic examination of the experimental design, quasi-free event selection strategy, and interpretation of the underlying physical mechanisms, serving as a useful reference for understanding the role of the 12C+12C fusion reaction in astrophysical processes.
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All authors Xue-Jian Wang, Qun-Gang Wen, Cheng-Bo Li, Hui-Ming Jia, Jian-You Guo, Cheng-jian Lin, Lei Yang, Feng Yang, Nan-ru Ma, Pei-wei Wen, Tian-peng Luo, Chang Chang, Xue-peng Sun, Hai-rui Duan, Zhi-jie Huang, Cheng Yin, Jiong-he Yang

Tuesday 22 September

Nuclear Experiment

Non-Monotonicity of $p_{\rm T}$ Correlations in Au + Au Collisions at RHIC

Rutik Manikandhan

We report the first measurements of two-particle transverse momentum correlations for mid-rapidity charged particles in Au+Au collisions at $\sqrt{s_{\rm NN}} =$ 3.0, 3.2, 3.5, 3.9, 4.5, 5.2 and 7.7 GeV recorded by the STAR experiment. The results are compared with previous STAR measurements from the Beam Energy Scan Phase I (BES-I) and with transport model calculations. The measured two-particle $p_{\rm T}$ correlators exhibit an approximate power-law scaling with the number of participating nucleons ($N_{\rm part}$), consistent with expectations from an independent-source scenario. This scaling is least well described at the lowest collision energy, $\sqrt{s_{\rm NN}} = 3.0$~GeV. Furthermore, a non-monotonic energy dependence of the $p_{\rm T}$ correlations is observed in central collisions, representing the first systematic observation of such behavior as a function of collision energy.
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Nuclear Experiment · Cross-listed from physics.med-ph

Towards real-time ion range verification via hybrid Compton-PET 3D imaging at isochronous cyclotrons

Javier Balibrea-Correa, V. Babiano-Suarez, J. Lerendegui-Marco et al. (+8 more)

Range uncertainties remain a major limitation to the full clinical exploitation of proton therapy, motivating reliable in-vivo range-verification techniques. This work presents an experimental investigation of a hybrid Prompt-Gamma Imaging (PGI)–Positron-Emission Tomography (PET) concept at the isochronous cyclotron of the West German Proton Therapy Centre under clinically representative pencil-beam-scanning conditions. Because this accelerator delivers a quasi-continuous beam, a pulsed shoot-and-step structure was imposed to mimic the interruptions associated with clinical energy-layer switching. This enabled PGI during irradiation and PET and delayed Compton imaging during beam-off intervals within the same sequence. Four two-plane Compton cameras were arranged in a co-planar cross-shaped geometry around the beam isocenter. Polyethylene phantoms were irradiated with 100~MeV protons at known positions along the beam axis. Their positions were estimated from reconstructed one-dimensional profiles using supervised machine-learning models trained exclusively on Monte Carlo simulations. PET achieved the best performance, with a root-mean-square deviation of 0.8~mm, followed by PGI with 1.6~mm. Delayed Compton imaging based on e$^{+}$ annihilation photons and $^{10}$C$^{*}$ decays yielded 2.4~mm and 3.8~mm, respectively. PET retained good performance down to 1% of the original event statistics, whereas PGI became increasingly statistics-limited. These results demonstrate the complementary strengths of hybrid PGI–PET and support its development towards millimetre-scale proton-range verification under clinically relevant irradiation conditions.
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All authors Javier Balibrea-Correa, V. Babiano-Suarez, J. Lerendegui-Marco, P. Torres-Sánchez, I. Ladarescu, M. Pallàs, B. Brusasco, J. Wulff, C. Bäumer, A. Tarifeño-Saldivia, C. Domingo-Pardo

Nuclear Experiment

Photoneutron reactions on $^{165}$Ho and $^{169}$Tm in the giant dipole resonance region

I. Gheorghe, S. Goriely, K. Stopani et al. (+19 more)

Photoneutron reactions were investigated for the deformed $^{165}$Ho and $^{169}$Tm nuclei from the vicinity of the neutron emission threshold up to $\sim$40~MeV, well above the giant dipole resonance (GDR) region, using quasimonochromatic laser Compton scattering $\gamma$-ray beams provided at the NewSUBARU facility, Japan. A high-and-flat efficiency moderated array of $^3$He counters was used for the neutron detection and an associated neutron multiplicity sorting method for extracting the $(\gamma,\,1nX)$, $(\gamma,\,2nX)$, $(\gamma,\,3nX)$ and $(\gamma,\,4nX)$ reaction cross sections and average neutron emission energies. The present $^{165}$Ho cross sections were compared to existing data, revealing discrepancies with the Saclay multiplicity sorting results and an overall 10$\%$ strength difference with the Livermore ones. There are no other data for $^{169}$Tm. GDR parameters based on phenomenological Lorentzian models were extracted by fitting the present $\sigma(\gamma,\,Sn)$ data with adjustments for the missing contribution of charged-particle-only reactions not observed experimentally. For both nuclei we observed high energy structures at 20-25~MeV, matching giant quadrupole resonance KMFR predictions. Based on the present centroid energies of the first and second GDR peaks, hydrodynamic model predictions gave intrinsic electric quadrupole moments of +7.00(34)~b and +7.38(28)~b for the ground states of $^{165}$Ho and $^{169}$Tm, respectively. The present experimental excitation functions and photoneutron energies were compared to statistical model calculations. Using the EMPIRE code, we performed a sensitivity test to phenomenological models of photon strength functions and nuclear level densities. The TALYS code was used to reproduce the present experimental $(\gamma,\,inX)$ cross sections and average neutron energies using microscopic nuclear level density models.
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All authors I. Gheorghe, S. Goriely, K. Stopani, S. Belyshev, M. Krzysiek, D. Filipescu, H. Wang, G. Fan, L. Liu, H. Scheit, D. Symochko, T. Aumann, T. Renstrøm, G.M. Tveten, F. Furmyr, A. Görgen, A.C. Larsen, S. Siem, V. Orlin, T. Ari-izumi, S. Miyamoto, H. Utsunomiya