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Physics Nuclear Experiment

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Thursday 10 September

Nuclear Experiment · Cross-listed from hep-ph

Radiative corrections to weak interaction processes

Chien-Yeah Seng

The search for physics beyond the Standard Model in low-energy weak interaction processes requires a precise knowledge of the Standard Model background at tree- and loop-level. In many such cases, radiative corrections represent one of the major sources of theory uncertainty due to the non-perturbative structures of nucleon or nuclei. In this review, I discuss several modern strategies based on dispersion relation, lattice gauge theory and nuclear many-body calculations to pin down the hadronic and nuclear uncertainties in the radiative corrections to low-energy weak interaction processes such as beta decays and parity-violating electron-nucleus scattering.
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Nuclear Experiment · Cross-listed from nucl-th

Nuclear-physics-guided Gaussian Processes

Javier Rozalén Sarmiento, Hristijan Kochankovski, Arnau Rios et al. (+1 more)

Gaussian Process Regression is a powerful nonparametric Bayesian method that provides both predictions and principled uncertainty estimates in closed form. The majority of past applications have relied on agnostic priors, but physics knowledge can be systematically encoded into Gaussian Processes through physically-motivated mean functions and kernels. We exploit this capability in the context of nuclear physics, applying physics-guided Gaussian Process Regression to three problems: nucleon-nucleon scattering phase shifts, mass excesses, and the finite-temperature equation of state of dense matter. In each case, we demonstrate that encoding known theoretical structures yields substantial and systematic improvements in interpolation accuracy, uncertainty calibration, and extrapolation reliability over agnostic baselines. Our results highlight that the design of the prior, and in particular the mean function, is key for obtaining a reliable and well-calibrated Gaussian Process Regression.
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All authors Javier Rozalén Sarmiento, Hristijan Kochankovski, Arnau Rios, Àngels Ramos

Nuclear Experiment · Cross-listed from hep-ph

Collinear fragmentation of pseudoscalar quarkonia from NLO NRQCD

Francesco Giovanni Celiberto and Francesca Lonigro

We discuss a new family of publicly available collinear fragmentation functions (FFs) for pseudoscalar quarkonia, the NRFF1.0 set. It builds upon the Heavy-Flavor Non-Relativistic evolution (HF-NRevo) scheme, designed to describe heavy-hadron formation through leading-power fragmentation at moderate and large transverse momentum. Heavy-quarkonium production naturally involves both perturbative and non-perturbative QCD dynamics, from the production of the heavy $Q\bar{Q}$ pair to its formation into a physical bound state. Within NRFF1.0, Non-Relativistic Quantum Chromodynamics (NRQCD) provides the theoretical framework for calculating the FF inputs at the initial scale, which are subsequently evolved through the HF-NRevo scheme. This setup provides a precision baseline for investigating the underlying partonic hierarchy and jet structure across the moderate- to high-transverse-momentum regime. The explicit treatment of partonic channels and heavy-flavor thresholds makes this framework particularly suitable for exploring quarkonium-in-jet fragmentation, jet-quenching sensitivity, energy-loss mechanisms, and the emergence of medium-modified fragmentation patterns in the quark-gluon plasma.
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Nuclear Experiment · Cross-listed from nucl-th

Study of the multiplicity dependence of non-flow correlations in pp collisions at $\sqrt{s}=200$ GeV using PYTHIA

Milan Stojanovic and Joern Putschke

The observation of a near-side enhancement in long-range correlations within high-multiplicity pA and pp collisions, commonly referred to as the ridge, has motivated significant efforts to quantify possible collective effects in small systems. Estimation of non-flow contributions in two-particle correlation measurements in small systems at the LHC typically relies on the assumption that jet-induced non-flow correlations are independent of event multiplicity. Consequently, this assumption allows the high-multiplicity non-flow to be estimated and accounted for by directly using low-multiplicity events. In this paper, the validity of this assumption is studied examining the multiplicity dependence of non-flow contributions estimated via two-particle correlation functions in pp collisions at RHIC energies $\sqrt{s} = 200$~GeV using the PYTHIA event generator. It is observed that selecting any specific multiplicity range inherently biases jet production dynamics. These biases introduce a non-trivial multiplicity dependence of the non-flow contribution at RHIC energies. The dependence of jet fragmentation and $p_{\text{T}}$-differential cross sections on event multiplicity is studied using a variety of commonly used multiplicity estimators, including mid-rapidity charged-particle multiplicity, forward multiplicity, and underlying-event activity. The results indicate that non-flow contributions do not exhibit simple multiplicity scaling and challenge the applicability of standard subtraction procedures utilized at LHC energies at lower RHIC collision energies.
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Nuclear Experiment · Cross-listed from hep-ph

Qubit-Qutrit Quantum Tomography of hadronic $\Lambda\phi$ and $\Lambda K^{\ast 0}$ systems

Veronica Kanachova, Feng Liu and Zhoudunming Tu

Quantum-information observables have emerged in recent years as new tools in nuclear and particle physics, from entanglement in top-quark pairs to spin correlations in $\Lambda\bar{\Lambda}$ production. Extending these studies to unequal-spin hadronic final states poses a fundamental challenge: the $6\times6$ density matrix of a qubit-qutrit system contains 35 independent spin parameters, but the decays of $\Lambda V$ pairs, with $V=\phi$ or $K^{*0}$, provide access to only 23 due to the hidden vector polarization from the strong decay. In this Letter, we formulate a qubit-qutrit quantum tomography (QQQT) technique for these spin-$\tfrac{1}{2}\otimes1$ systems and establish exact criteria for entanglement certification from the incomplete density matrix. Compared with the $\Lambda\bar{\Lambda}$ system, QQQT of $\Lambda\phi$ and $\Lambda K^{*0}$ provides a new probe of nonperturbative QCD hadronization, enabling a direct comparison of the spin evolution of entangled quark pairs produced from the vacuum as they hadronize into a baryon or a vector meson.
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Nuclear Experiment · Cross-listed from hep-ex

Production of Light Nuclei and Hypernuclei in Heavy-Ion Collisions

Guannan Xie and Yue-Hang Leung

We review recent STAR and ALICE measurements of light-nucleus and hypernucleus yields, femtoscopic correlations, and collective flow presented at SQM 2026. Statistical-hadronization calculations provide a useful baseline for integrated yields but do not simultaneously describe all measured light-nucleus ratios across collision energies and system sizes. For bound states with mass number $A<4$, current coalescence calculations provide a broadly consistent description of yields, femtoscopic correlations, and collective flow, although the quantitative hypertriton comparison depends on the assumed few-body wave function. The suppressed production of resonant $^{4}$Li relative to compact $^{4}$He indicates an effect of nuclear structure and late-stage dynamics. However, the quantitative model comparison also depends on the treatment of feed-down from unstable states. In high-multiplicity $p$+$p$ collisions, pion-deuteron femtoscopy further indicates that most observed (anti)deuterons are formed through nucleon fusion after strong decays of short-lived resonances. Taken together, these measurements show that production chronology and internal nuclear structure leave measurable imprints on the physics observables.
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Wednesday 9 September

Nuclear Experiment

A detailed view at magnetic dipole strengths: The case of semi-magic $^{50}$Ti

B. Kelly, M. Spieker, U. Friman-Gayer et al. (+14 more)

Magnetic dipole, $M1$, strengths were studied in semi-magic $^{50}$Ti up to the neutron-separation threshold by combining data from $(d,p)$ one-neutron transfer, $(\gamma,\gamma')$ real-photon scattering, $(e,e')$ inelastic scattering at extreme backward angles, and $(p,p')$ at $E_p = 210$ MeV and extreme forward angles. The combination of all probes provided unique access to the neutron spin-flip contribution and the possibility to evaluate its role in generating the spin-flip $M1$ strengths. The small contribution of the neutron $(1f_{7/2})^{-1}(1f_{5/2})^{+1}$ spin-flip transitions, which were probed with the $(d,p)$ reaction, to the overall strength in $^{50}$Ti questions the standard picture for the microscopic origin of spin-flip strength in the $fp$ shell. For $^{50}$Ti, this letter shows that $J^{\pi} = 1^+$ states with larger neutron $(1f_{7/2})^{-1}(1f_{5/2})^{+1}$ spectroscopic factors do not correspond to the ones with the largest $B(M1;0^+_1 \rightarrow 1^+_i)$ strengths.
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All authors B. Kelly, M. Spieker, U. Friman-Gayer, L. T. Baby, T. Beck, A. L. Conley, S. W. Finch, J. Isaak, Krishichayan, E. Litvinova, H. Pai, N. Pietralla, D. Savran, W. Tornow, N. Tsoneva, A. Volya, V. Werner

Nuclear Experiment

Island of Inversion in neutron-rich cobalt isotopes revealed from mass measurements

M. Flayol, P. Ascher, D.D. Dao et al. (+19 more)

Mass measurements of the ground and isomeric states of $^{68-70}$Co have been performed using the JYFLTRAP Penning-trap mass spectrometer at the IGISOL facility. The masses were measured, either for the first time for the isomeric states of $^{68}$Co and $^{70}$Co, or with greatly improved precision for the others, removing ambiguities in the mass surface beyond $N=40$. The ordering of the low and high-spin states in $^{68}$Co and $^{70}$Co has also been established. The results, supported by Large-Scale Shell Model and Discrete Non-Orthogonal Shell-Model calculations, show a gradual lowering of intruder states with increasing neutron number, eventually leading to an inversion in $^{70}$Co. These findings clarify previously proposed contradictory interpretations. Finally, we demonstrate the importance of including induced effective 3N forces for a consistent description of binding energies in the island of inversion near $N=40$.
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All authors M. Flayol, P. Ascher, D.D. Dao, M. Gerbaux, S. Grévy, F. Nowacki, A. de Roubin, D. Atanasov, B. Blank, L. Canete, Q. Délignac, T. Eronen, Z. Ge, M. Hukkanen, A. Jaries, A. Kankainen, I.D. Moore, M. Mougeot, A. Raggio, J. Ruotsalainen, M. Stryjczyk, V. Virtanen

Nuclear Experiment · Cross-listed from nucl-th

Systematic study of E2 matrix elements in the framework of the Triaxial Projected Shell Model

Stefan Frauendorf, Syed Rouoof, Gowhar Bhat et al. (+5 more)

Nuclides for which extended sets of E2 matrix elements have been measured by means of COULEX experiments are studied in the framework of the triaxial projected shell model (TPSM). The studies encompass: 70,72,74,76Ge, 76,78,80,82Se, 100Mo, 104Ru, 110Pd, 168Er, 186,188,190Os, 184Pt. The experimental energies of the ground band, of the quasi gamma band and of some excited 0+ bands as well as their individual intra and inter band matrix E2 matrix elements are systematically accounted for by the microscopic TPSM calculations.
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All authors Stefan Frauendorf, Syed Rouoof, Gowhar Bhat, Sheikh Jehangir, Nazira Nazir, Kouser Qureshie, Niyaz Rather, Javid Sheikh

Nuclear Experiment · Cross-listed from nucl-th

Development of the {\gamma} strength function with the neutron number

Stefan Frauendorf, Ronald Schwengner, Gowhar Bhat et al. (+1 more)

The M1 and E2 {\gamma} strength functions ({\gamma}sf) have been calculated for extended series of the Mo, Fe, Sn, Ge and Gd isotopes using the conventional spherical shell model (SSM) and, as a new tool, the triaxial projected shell model (TPSM). For almost all cases the strong enhancement of the M1 {\gamma}sf (low energy magnetic radiation-LEMAR) is found. In the mid-shell region, a bimodal structure of the LEMAR spike and a bump around 3 MeV, interpreted as the scissors resonance (SR), develops. The combination of LEMAR and the SR is generated by the splitting of the spherical single particle multiplets of given j caused by deformation and their fragmentation over nearby quasiparticle configurations.
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All authors Stefan Frauendorf, Ronald Schwengner, Gowhar Bhat, Javid Sheikh

Nuclear Experiment

Search for neutrinoless quadruple beta decay of $^{136}$Xe in PandaX-4T detector

PandaX Collaboration: Zhiyuan Li, Peiyuan Chen, Wei Chen et al. (+102 more)

The observation of neutrinoless quadruple beta decay (0$\nu$4$\beta$) in the absence of neutrinoless double beta decay (0$\nu$2$\beta$) has been argued to provide a strong indication that neutrinos are Dirac particles. We report a search for 0$\nu$4$\beta$ decay of $^{136}\text{Xe}$ using a total $^{136}\text{Xe}$ exposure of 148.4 kg$\cdot$yr, collected during the commissioning and the first science runs of the PandaX-4T experiment. No significant excess of events over the background is observed. A lower limit on the 0$\nu$4$\beta$ decay half-life of $^{136}\text{Xe}$ is set at 6.01 x $10^{24}$ yr at the 90% confidence level. This result establishes the most stringent constraint on this process in xenon, demonstrating the unique capability of the PandaX-4T detector in probing lepton number violation and shedding light on the fundamental nature of neutrinos.
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All authors PandaX Collaboration: Zhiyuan Li, Peiyuan Chen, Wei Chen, Xiaohua Chen, Xun Chen, Yunhua Chen, Chen Cheng, Xiangyi Cui, Yuxin Cui, Manna Deng, Roni Dey, Yingjie Fan, Deqing Fang, Xuanye Fu, Zhixing Gao, Yujie Ge, Lisheng Geng, Xunan Guo, Xuyuan Guo, Zichao Guo, Chencheng Han, Ke Han, Changda He, Jinrong He, Ruquan Hou, Houqi Huang, Junting Huang, Yule Huang, Xiangdong Ji, Yonglin Ju, Xiaorun Lan, Chenxiang Li, Mingchuan Li, Peiyuan Li, Shuaijie Li, Tao Li, Yangdong Li, Yuan Li, Qing Lin, Jianglai Liu, Yuanchun Liu, Yunyang Luo, Yugang Ma, Yajun Mao, Yue Meng, Binyu Pang, Ningchun Qi, Xiangxiang Ren, Dong Shan, Xiyuan Shao, Manbin Shen, Xuyan Sun, Yi Tao, Yueqiang Tian, Yuxin Tian, Anqing Wang, Guanbo Wang, Hao Wang, Haoyu Wang, Jiamin Wang, Lei Wang, Meng Wang, Qiuhong Wang, Shaobo Wang, Shibo Wang, Siguang Wang, Wei Wang, Xu Wang, Zhou Wang, Yuehuan Wei, Weihao Wu, Yuan Wu, Mengjiao Xiao, Xiang Xiao, Yuhan Xie, Kaizhi Xiong, Jianqin Xu, Yifan Xu, Binbin Yan, Xiyu Yan, Yong Yang, Shunyu Yao, Peihua Ye, Chunxu Yu, Zhe Yuan, Youhui Yun, Minzhen Zhang, Peng Zhang, Shibo Zhang, Shu Zhang, Siyuan Zhang, Tao Zhang, Wei Zhang, Yang Zhang, Yingxin Zhang, Yuanyuan Zhang, Kangkang Zhao, Li Zhao, Jiaxu Zhou, Jiayi Zhou, Jifang Zhou, Ning Zhou, Xiaopeng Zhou, Zhizhen Zhou, Chenhui Zhu

Nuclear Experiment

Reinvestigation of the Yield of the Trinity Device

Eric B. Norman, Keenan J. Thomas and Pedro V. Guillaumon

Previous published analyses of trinitite to determine the yield of the Trinity nuclear explosion used various estimates of the fraction of fission products that became incorporated in trinitite. Furthermore, these studies utilized nuclear data that has subsequently been revised. Utilizing a planar germanium detector, we observed gamma rays produced by the decays of both 137Cs and 239Pu from four samples of trinitite. From the observed 137Cs/239Pu ratios of and a simple analysis method based on current nuclear data and weapons debris studies, we find an average yield of 9.1+-4.5 kilotons from our four samples. While this result is substantially lower than the established total yield of 21 kilotons, it is in reasonable agreement that attributable to fissions in the 239Pu core alone.
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Nuclear Experiment · Cross-listed from physics.ins-det

Spectral Discrimination of Deposited Gamma-Ray Energies in a Simulated CeBr$_3$ Scintillator

Andrey Elagin

We show that wavelength measurements of individual detected optical photons may provide additional information about gamma-ray energy deposited in a CeBr$_3$ crystal when the detected-photon-count distributions overlap for nearby gamma-ray energies. Monoenergetic 662 and 629 keV gammas are used in a Geant4 simulation of a $25\times25\times20~\mathrm{mm^3}$ CeBr$_3$ crystal. Assuming a light yield of $6.0\times10^4$ photons/MeV, a wavelength-independent photon-detection efficiency of 30%, and a wavelength resolution of $\sigma_{\lambda}=40$ nm, we find that the fraction of photons reconstructed above 385 nm gives an event-level separation of $\sim$ 2 standard deviations between the 662 and 629 keV event populations selected within the same $\sim$ 1%-wide detected-photon-count interval. No timing or reconstructed interaction-position information is used. The result demonstrates, within the present simulation model, that event-dependent optical spectra can retain energy information beyond an undifferentiated photon count.
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Tuesday 8 September

Nuclear Experiment

Detailed experimental study of excited states in $^{50}$Ti via the $(d,p)$ and $(d,p\gamma)$ reactions

B. Kelly, M. Spieker, L. T. Baby et al. (+7 more)

Excited states of semi-magic $^{50}$Ti were studied up to the neutron-separation energy via the $(d,p)$ and $(d,p\gamma)$ reactions. In total, 82 excited states were identified based on the measurement of angular distributions with the Super-Enge Split-Pole Spectrograph (SE-SPS) at Florida State University. From the experimental data, sum rules related to vacancies were calculated for the $2p_{3/2}$, $2p_{1/2}$, $1f_{5/2}$, $1g_{9/2}$, and $2d_{5/2}$ neutron single-particle orbitals and compared to predictions obtained with the time-dependent continuum shell model (TDCSM), the quasiparticle-phonon model (QPM), and the relativistic equation of motion theory (REOM$^3$). A comparison for the $(d,p)$ data obtained for $^{51}$Ti and $^{50}$Ti is also presented, focusing on differences of the single-particle strength fragmentation in even-$A$ and odd-$A$ nuclei.
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All authors B. Kelly, M. Spieker, L. T. Baby, S. Baker, A. L. Conley, D. Houlihan, K. W. Kemper, E. Litvinova, N. Tsoneva, A. Volya

Nuclear Experiment · Cross-listed from hep-ph

Bottomonium suppression with a machine-learning-informed Debye mass

Ajaharul Islam, Shibo Chen, Fu-Peng Li et al. (+2 more)

Motivated by recent progress in data-driven approaches, we introduce a machine-learning (ML)-informed Debye mass, extracted from lattice-informed inputs, exclusively in the complex-valued heavy-quark Kent State University (KSU) potential. The resulting complex potential is used to solve the real-time Schrödinger equation within the quantum trajectories (QTraj) framework for the evolution of bottomonium in the quark-gluon plasma. We then compute the nuclear modification factors and double ratios for bottomonium $\Upsilon(1S)$, $\Upsilon(2S)$, and $\Upsilon(3S)$ states in Pb-Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV. We compare our ML-induced results with those from the original KSU model and with experimental measurements from ALICE, ATLAS, and CMS collaborations. We find that the machine-learned Debye mass leads to improved agreement with data, particularly for excited states, highlighting the utility of machine learning in modeling in-medium QCD effects.
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All authors Ajaharul Islam, Shibo Chen, Fu-Peng Li, Long-Gang Pang, Guang-You Qin

Nuclear Experiment · Cross-listed from hep-ex

A virtual reality extension for the Geant4 toolkit

Benjamin Jobilal, Muhammad Ansar Iqbal and Jay Hauser

Geant4 is a toolkit for simulating particle interactions in matter that is widely used in particle physics, nuclear physics, medical imaging, and astrophysics. At present, Geant4 visualizations are generally viewed on a conventional, two-dimensional computer display. To enhance immersion, we have developed G4VR, a virtual reality (VR) application that extends Geant4 with VR capabilities, providing a more intuitive and comprehensive way to understand these interactions. The user running G4VR in a headset can get detailed information about individual tracks, interactions, and energy depositions by selecting them with the hand controllers. G4VR also allows the user to examine the chronology of interactions, and includes animations of entire events as immersive movies. G4VR includes built-in event displays of several types that allow a first-time user to easily explore its various functionalities. To interface with Geant4, we have developed a new visualization driver called G4XR that allows direct integration with the Geant4 source code. This enables any Geant4 experiment to be loaded and experienced in VR seamlessly.
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Nuclear Experiment

Indirect Measurement of the $\rm S^*(E)$ Factor for $\rm {}^{12}C({}^{12}C,\mathit{p}){}^{23}Na$ at Gamow Energies via the Trojan Horse Method with Near-0 degree Spectator Detection

Chengbo Li, Huiming Jia, Qungang Wen et al. (+8 more)

The astrophysical S*(E) factor for the 12C+12C reaction within the Gamow window plays a pivotal role in modeling stellar carbon burning and explosive nucleosynthesis scenarios. However, direct measurements or even simple extrapolations at these energies are severely hindered by Coulomb suppression and the possible presence of narrow resonances. To address this challenge, we performed an indirect measurement of the 12C(16O,ap)23Na reaction at the HI-13 Tandem Accelerator, employing 16O=(12C+a) as the Trojan Horse nucleus. A key innovation of this Trojan Horse Method (THM) study is the implementation of a copper beam-stopper foil, which enabled the detection of spectator particles near 0, the angular region where their yield is maximized under quasi-free kinematics. The S*(E) factor for the 12C(12C,p)23Na reaction in the astrophysically relevant energy range was extracted using the THM formalism based on the DWBA. Our results confirm the presence of resonant structures within the Gamow window around 1.5 MeV in both the p0 and p1 proton channels. No evidence of a hindrance effect is observed in the measured energy range. Without considering the resonance details, the overall trend of our results is qualitatively in reasonable agreement with the THM-Tumino2018 and TTIK2025 data, but differs significantly from the trend of the Modified-THM-Muk2019 data.
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All authors Chengbo Li, Huiming Jia, Qungang Wen, Chengjian Lin, Lei Yang, Feng Yang, Nanru Ma, Tianpeng Luo, Xuepeng Sun, Shangkun Shao, Xuejian Wang

Nuclear Experiment

$\rm S^*(E)$ measurement of the $\rm {}^{12}C({}^{12}C,\alpha){}^{20}Ne$ reaction at astrophysical energies via the Trojan horse method with $\rm ^{16}O$ quasi-free breakup

Chengbo Li, Huiming Jia, Qungang Wen et al. (+9 more)

The 12C(12C,a)20Ne reaction at astrophysical energies is crucial for understanding the carbon burning process in massive star and explosive astrophysical scenarios like Type Ia supernovae and X-ray bursts. However, directly measuring or simply extrapolating its S*(E) factor is extremely challenging due to Coulomb suppression and potential complex resonance structures near the Gamow window (1.5+-0.3 MeV). The THM can circumvent the Coulomb barrier, providing data within the Gamow window without extrapolation. Strong resonances near 1.5 MeV were previously reported by Tumino et al. using THM with 14N=(12C+d), a result that generated significant interest and debate, underscoring the need for further experimental verification. In this work, we selected 16O=(12C+a) as the Trojan-horse nucleus due to its lower binding energy, which favors quasi-free reactions. We performed an indirect measurement of 12C(16O,aa)20Ne at the HI-13 Tandem Accelerator at CIAE. Employing a copper beam-stopper foil, we measured the spectator a-particle within a small angular range around 0, where the quasi-free mechanism predicts its highest concentration. The S*(E) factor of 12C(12C,a)20Ne in the astrophysical energy region was extracted from the measured three-body reaction using THM based on DWBA. Our results confirm the existence of resonances within the Gamow window around 1.5 MeV in both the a0 and a1 channels. Without considering the details of the resonance structures, the overall trend of our results is qualitatively in reasonable agreement with the THM-Tumino2018 and TTIK2025 data, but differs significantly from the trend of the Modified-THM-Muk2019 data. We observe no evidence for hindrance effect in our results.
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All authors Chengbo Li, Huiming Jia, Qungang Wen, Chengjian Lin, Lei Yang, Feng Yang, Nanru Ma, Peiwei Wen, Tianpeng Luo, Chang Chang, Xuepeng Sun, Xuejian Wang

Nuclear Experiment

News from NA61/SHINE

Antoni Marcinek for the NA61/SHINE Collaboration

NA61/SHINE is a multi-purpose, fixed-target hadron spectrometer at the CERN SPS. Its research program includes studies of strong interactions, as well as reference measurements for neutrino and cosmic-ray physics. A significant advantage of NA61/SHINE over collider experiments is its extended coverage of phase space available for particle production. This contribution summarizes recent selected results from our strong interaction program. These include rapidity spectra of $K^+$ and $\pi^-$ mesons in Xe+La reactions compared to other collision systems, energy dependence of the scaled $\pi^-$ total yield (the `kink` plot) in Xe+La compared to other collision systems and models, $\phi$(1020) rapidity spectra in Ar+Sc collisions compared to models, $\Lambda$ transverse polarization in p+p reactions, energy dependence of intensive quantities of net-electric charge distribution in Ar+Sc collisions compared to p+p results, as well as an update on the evidence of large violation of isospin symmetry in kaon production — the excess of charged over neutral kaons.
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Nuclear Experiment · Cross-listed from hep-ph

Inclusive electron-nucleus cross section models from domain adaptation

Krzysztof M. Graczyk, Beata E. Kowal, Rwik Dharmapal Banerjee et al. (+3 more)

We apply transfer learning (TL) to construct data-driven models of inclusive electron-nucleus cross sections. Starting from an ensemble of deep neural networks pretrained on \(^{12}\)C data, we fine-tune the models separately for \(^{3}\)He, \(^{6}\)Li, \(^{16}\)O, \(^{27}\)Al, \(^{40}\)Ca, and \(^{56}\)Fe. The resulting models improve for all targets, marginally so for oxygen, where the carbon baseline is already adequate, although their predictive robustness depends on the amount, coverage, and precision of the available target data. We systematically study how model performance depends on the number of fine-tuned layers, on the fraction and selection of the training data, and on the overlap between the source and target kinematic domains. The layer-wise analysis shows that oxygen requires only shallow adaptation, whereas helium, calcium, and iron require substantially deeper fine-tuning. Lithium represents the least robust case because of its limited dataset, while aluminum demonstrates a strong sensitivity to a small subset of highly constraining measurements. For selected kinematic configurations outside the coverage of the carbon training data, the adapted models remain consistent with the measurements within their estimated uncertainties. Finally, we compare the resulting predictions with those of the phenomenological F1F2 model.
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All authors Krzysztof M. Graczyk, Beata E. Kowal, Rwik Dharmapal Banerjee, Jose Luis Bonilla, Hemant Prasad, Jan T. Sobczyk

Monday 7 September

Nuclear Experiment

Precision $\beta$-delayed charged-particle emission spectroscopy at FRIB: Proof of principle with the $\beta$-decay of $^{25}\mathrm{Si}$

E. A. M. Jensen, J. M. Eder, P. H. Pedersen et al. (+16 more)

We report on the $\beta$-delayed proton and $\gamma$-ray emission from $^{25}\mathrm{Si}$, measured at the Facility for Rare Isotope Beams (FRIB). Low-energy $^{25}\mathrm{Si}$ ions extracted from the Advanced Cryogenic Gas Stopper were implanted into a thin carbon foil surrounded by a compact, highly segmented array of silicon detector telescopes and two high-purity germanium detectors. This setup provides high-resolution charged-particle spectroscopy, establishing a proof of principle for precision stopped-beam decay studies at FRIB. We reconstruct the $^{25}\mathrm{Si}$ decay scheme, resolving new high-energy proton transitions and determining the feeding to excited states in $^{24}\mathrm{Mg}$. The observation of spectral interference patterns enables firm spin and parity assignments for highly excited states in $^{25}\mathrm{Al}$. The $^{25}\mathrm{Si}$ $\beta$-strength distribution is extracted and compared with large-scale shell-model calculations.
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All authors E. A. M. Jensen, J. M. Eder, P. H. Pedersen, A. Adams, M. J. G. Borge, B. A. Brown, J. Dopfer, H. O. U. Fynbo, B. S. O. Johansson, B. Jonson, M. Madurga, J. S. Nielsen, K. Riisager, C. S. Sumithrarachchi, L. J. Sun, O. Tengblad, L. E. Weghorn, T. Wheeler, C. Wrede

Nuclear Experiment

Independent Validation of Octupole Collectivity in radium-224 through lifetime measurements of low-lying negative-parity states

D. White, D. O'Donnell, A. Avaa et al. (+30 more)

The nucleus $^{224}$Ra is a key benchmark for octupole deformation and for theoretical descriptions of enhanced Schiff moments in reflection-asymmetric nuclei. While Coulomb-excitation measurements have established strong octupole collectivity in $^{224}$Ra, theoretical models predict that its intrinsic electric-dipole moment should be strongly quenched by a cancellation between macroscopic and microscopic contributions. Direct fast-timing measurements of the low-lying $J^\pi = 1^-_1$ and $3^-_1$ states populated following the $\beta$-decay of $^{224}$Fr at TRIUMF-ISAC were performed. Using the LaBr$_3$(Ce) detectors of the GRIFFIN array, mean lifetimes of $\tau(1^-_1) = 444(6)$~ps and $\tau(3^-_1) = 460(18)$~ps were obtained. The corresponding reduced transition probabilities agree with values inferred from Coulomb excitation, but are determined with substantially improved precision. These results provide an independent validation of the electromagnetic matrix elements associated with octupole collectivity in $^{224}$Ra and confirm a strongly-quenched intrinsic dipole moment of $D_0 \simeq 0.032~e\mathrm{fm}$. The present measurements therefore provide a stringent experimental benchmark for nuclear-structure models used in the interpretation of Schiff moments and future searches for non-zero electric dipole moments.
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All authors D. White, D. O'Donnell, A. Avaa, J. R. Murias, S. Murillo Morales, R. Umashankar, V. Vedia, C. Andreoiu, D. W. Annen, A. D. Ayangeakaa, G. C. Ball, V. Bildstein, M. Bowry, I. Dillmann, E. G. Fuakye, L. P. Gaffney, A. B. Garnsworthy, P. E. Garret, E. D. Geerlof, S. Georges, A. L. Grimes, G. F. Grinyer, G. Hackman, P. M. Jones, J. Liu, B. Olaizola, S. D. Olorunfunmi, F. Rowntree, N. K. Syeda, D. Shah, P. Spagnoletti, C. E. Svensson, F. Wu

Nuclear Experiment

Precision Neutron Skins of $^{208}$Pb and $^{48}$Ca from Parity-Violating Electron Scattering

PREX Collaboration: D. Adhikari, H. Albataineh, D. Androić et al. (+99 more)

We have measured the parity-violating elastic electron scattering asymmetry in the PREX and CREX experiments on ${}^{208}$Pb and ${}^{48}$Ca respectively; these are both doubly-magic nuclei whose excited states can be discriminated from the ground state by the high resolution spectrometers in Hall A at Jefferson Lab. This asymmetry provides a precise determination of the weak charge form factor at one $Q^2$ and pins down the neutron radius in these two nuclei in a relatively clean and model-independent way. This is because the $Z^0$ boson of the weak interaction couples primarily to neutrons. The heavier lead nucleus, with a neutron excess, provides an interpretation of the neutron skin thickness in terms of properties of bulk neutron matter. For the lighter ${}^{48}$Ca nucleus, which is also rich in neutrons, comparisons to microscopic nuclear theory calculations are sensitive to poorly constrained 3-neutron forces. The weak neutral form factors $F_W(Q^2)$ were extracted to be $0.368 \pm 0.013$ at $Q = 0.3977 {\rm\ fm}^{-1}$ for $^{208}$Pb from PREX-2 and $0.1304 \pm 0.0055$ at $Q = 0.8733 {\rm\ fm}^{-1}$ for $^{48}$Ca. The form factor differences $(F_{ch}-F_W)(Q^2)$ were calculated to be $0.041 \pm 0.013$ at $Q = 0.3977 {\rm fm}^{-1}$ for $^{208}$Pb from PREX-2 and $0.0277 \pm 0.0055$ at $Q = 0.8733 {\rm fm}^{-1}$ for $^{48}$Ca. Correcting for Coulomb distortions and using nuclear model information, we find the neutron skin thicknesses to be $R^{208}_{\rm skin} = 0.283 \pm 0.071$ fm combining PREX-1 and PREX-2 and $R^{48}_{\rm skin} = 0.121 \pm 0.035$ fm. This paper provides a full description of the special experimental and data analysis techniques employed for precisely measuring these small asymmetries.
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All authors PREX Collaboration: D. Adhikari, H. Albataineh, D. Androić, K.A. Aniol, D.S. Armstrong, T.D. Averett, C. Ayerbe Gayoso, S.K. Barcus, V. Bellini, R.S. Beminiwattha, J.F. Benesch, H. Bhatt, D. Bhatta Pathak, D. Bhetuwal, B. Blaikie, J.A. Boyd III, Q. Campagna, A. Camsonne, G.D. Cates, Y. Chen, C. Clarke, J.C. Cornejo, S. Covrig Dusa, M. M. Dalton, P. Datta, A. Deshpande, D. Dutta, E. Fuchey, C. Gal, D. Gaskell, M. Gericke, C. Ghosh, I. Halilovic, J.-O. Hansen, O. Hassan, F. Hauenstein, W. Henry, C.J. Horowitz, C. Jantzi, S. Jian, S. Johnston, D.C. Jones, S. Kakkar, B. Karki, S. Katugampola, C. Keppel, P.M. King, D.E. King, K.S. Kumar, T. Kutz, N. Lashley-Colthirst, G. Leverick, H. Liu, N. Liyanage, S. Malace, J. Mammei, R. Mammei, M. McCaughan, D. McNulty, D. Meekins, C. Metts, R. Michaels, M. Mihovilovic, M.M. Mondal, J. Napolitano, A. Narayan, D. Nikolaev, V.F. Owen, C. Palatchi, J. Pan, B. Pandey, S. Park, K.D. Paschke, M. Petrusky, M.L. Pitt, S. Premathilake, A.J.R. Puckett, B. Quinn, R. Radloff, S. Rahman, A. Rathnayake, B.T. Reed, P.E. Reimer, R. Richards, S. Riordan, Y.R. Roblin, S. Seeds, A. Shahinyan, P. Souder, L. Tang, M. Thiel, Y. Tian, G.M. Urciuoli, E.W. Wertz, B. Wojtsekhowski, T. Ye, A. Yoon, W. Xiong, A.J. Zec, W. Zhang, J. Zhang, X. Zheng

Nuclear Experiment

Evolution of Spectroscopic Factors in Neutron-deficient $p$-shell Nuclei in connection with Short-Range Correlations

S. Koyama, D. Suzuki, O. Sorlin et al. (+31 more)

We report an uncertainty-controlled determination of neutron-removal spectroscopic factors in the neutron-deficient $p$-shell nuclei $^{12}\mathrm{C}$, $^{10}\mathrm{C}$, $^{9}\mathrm{C}$, and $^{8}\mathrm{B}$, all measured under uniform conditions through exclusive ground-state-to-ground-state $(p,d)$ reactions at about 50 MeV/nucleon in a liquid hydrogen target at the GANIL/LISE facility. The deuterons were detected in the highly-segmented MUST2 detector placed at forward angles and the excitation energy was reconstructed by the missing mass method. Several transitions, including a new state in $^7\mathrm{B}$, were observed. Differential cross sections, which display an $L=1$ pattern for all nuclei, were fitted with 416 sets of uncertainty-quantified optical-model potential parameters and considering various single-particle bound-state wavefunctions to derive $C^2S$ values. The ratio between experimental and shell-model calculated values, $R_S$, is found to be slightly decreasing as a function of increasing proton to neutron separation energy asymmetry $\Delta S$, with a slope of $-0.0049(36)_{\rm stat}(13)_{\rm omp}(8)_{\rm s.p.}$. The observed trend is compatible with the phenomenological expectation that the short-range correlation effect on $C^2S$ increases with the degree of nucleon minority. The present data set delivers a high-precision benchmark that will tightly constrain future microscopic descriptions of short-range correlations in asymmetric nuclei.
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All authors S. Koyama, D. Suzuki, O. Sorlin, C. Hebborn, M. Assié, L. Lalanne, T. Abe, D. Beaumel, Y. Blumenfeld, L. Caceres, F. De Oliveira Santos, F. Delaunay, F. Flavigny, S. Franchoo, J. Gibelin, V. Girard-Alcindor, J. Guillot, F. Hammache, O. Kamalou, A. Kamenyero, N. Kitamura, V. Lapoux, A. Lemasson, A. Matta, B. Mauss, P. Morfouace, M. Niikura, H. Otsu, J. Pancin, T. Roger, T. Y. Saito, H. Sakurai, C. Stodel, J-C. Thomas

Sunday 6 September

Nuclear Experiment · Cross-listed from nucl-th

The role of strangeness in baryon and electric charge stoppings

Zi-Wei Lin and Mason Alexander Ross

Recently it has been proposed that comparing the net-baryon ($B$) stopping with net-electric charge ($Q$) stopping can help studies of the baryon stopping mechanism in nuclear collisions. Here we find the $B/Q\times Z/A$ ratio to be very sensitive to the difference between $s$ and $\bar s$ quark rapidity distributions. For mid-rapidity of isobar collisions at 200A GeV, a multi-phase transport (AMPT) model gives slightly more $\bar s$ than $s$, which leads to $B/Q\times Z/A<1$, while the model without the $s-\bar s$ asymmetry gives $B/Q\times Z/A \geq 1$. Comparing Ru+Ru and Zr+Zr isobar collisions, the AMPT (and UrQMD) model gives $B/\Delta Q\times \Delta Z/A<1$ at mid-rapidity at all centralities, which strongly contradicts the recent STAR data. We also find that the $B/\Delta Q\times \Delta Z/A$ ratio is very sensitive to the net-light quark ($u,d$) stoppings, but it is less sensitive to the $s-\bar s$ asymmetry than the $B/Q\times Z/A$ ratio by a factor of 3. These results are expected to help us resolve the stopping puzzle and better understand the baryon stopping mechanism in the future.
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Nuclear Experiment · Cross-listed from nucl-th

Microscopic study of baryon stopping in low-energy heavy-ion collisions within UrQMD model

Sudhir Pandurang Rode

In low-energy heavy-ion collisions, baryon stopping is an important process, in which protons from the initial colliding nuclei are stopped at mid-rapidity region. Quantifying such stopping can reveal information on the properties of the nuclear medium, such as net-baryon density. Though experimental measurement of net-proton rapidity spectra provides constraints, microscopic origin of such protons is not fully accessible. Transport model studies can therefore provide deeper insight into the microscopic origin of protons transported from initial nuclei, complementing experimental measurements. This article presents an investigation of baryon stopping in minimum-bias Au+Au collisions over a wide range of beam energies, $\sqrt{s_{NN}} = 2.4-17.3$ GeV ($E_{\rm lab} = 1.23A-158A$ GeV). Final-state protons are classified based on their origin by analyzing their interaction history in the UrQMD model. A significant fraction of transported protons at mid-rapidity originates from initial neutrons rather than initial protons, referred to as isospin-converted protons, and their contribution as a function of collision energy and centrality is quantified. Anisotropic flow coefficients of different proton categories are estimated and compared with experimental measurements. Furthermore, a comparison between the $\pi^{-}/\pi^{+}$ ratio and isospin conversion rate is performed. The latter is further compared with the $\alpha$ parameters of the Kitazawa-Asakawa formalism, revealing a significant deviation from the chemical equilibrium assumption $\alpha_N = \alpha_\pi$ below $\sqrt{s_{NN}} \lesssim$ 10~GeV. Finally, the saturation of the isospin conversion rate is found to coincide with the onset of nuclear transparency, demonstrating that isospin randomization and baryon stopping are coupled phenomena in hadronic transport across the NICA/FAIR energy range.
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Saturday 5 September

Nuclear Experiment

Direct measurement of $^{18}$F($\alpha,p$)$^{21}$Ne cross sections with ANASEN

K. S. Davis, J. C. Blackmon, C. M. Deibel et al. (+21 more)

The $^{18}$F($\alpha,p$)$^{21}$Ne reaction may impact Asymptotic Giant Branch nucleosynthesis and helium burning on accreting white dwarfs. This reaction has never been directly measured, and constraints from a previous time-inverse measurement leave large uncertainties in the reaction rate. We measured $^{18}$F($\alpha,p$)$^{21}$Ne cross sections directly for the first time covering from $2 \leq E_{cm} \leq 4$ MeV. Combining these results with previous work and comparisons to statistical model calculations results in a substantial improvement in uncertainties in the reaction rate. Cross sections were measured in inverse kinematics at TRIUMF-ISAC using a radioactive $^{18}$F beam and ANASEN with an extended $^{4}$He gas target. Protons were detected in arrays of silicon-strip detectors with the measured trajectories and energies allowing reconstruction of the center-of-mass energy and final state in $^{21}$Ne populated. We found the total cross section is in good agreement with statistical calculations, though population of the second excited state in $^{21}$Ne is greater than predicted. This direct measurement is combined with the previous time-inverse measurement and a new reaction rate is calculated for 0.1–3 GK. The uncertainties in the $^{18}$F($\alpha,p$)$^{21}$Ne reaction rate have been reduced to a sufficient level to allow robust predictions from AGB models. The new recommended rate leads to a 45% increase in $^{19}$F production compared to the previous rate.
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All authors K. S. Davis, J. C. Blackmon, C. M. Deibel, G. L. Wilson, M. Alcorta, L. T. Baby, D. W. Bardayan, S. Carmichael, S. Chakraborty, C. Esparza, J. Glorius, A. I. Karakas, A. Lennarz, B. Kay, J. Henning, G. W. McCann, S. Pain, C. Ruiz, R. Russell, V. Sitaraman, B. Sudarsan, I. Tolstukhin, L. Wagner, I. Wiedenhöver

Nuclear Experiment · Cross-listed from nucl-th

Nucleon Correlations in Unstable Nuclei via Knockout Reactions

C.A. Bertulani

We review the physical ideas and reaction theory underlying one- and two-nucleon removal from fast projectiles, quasi-free proton-induced reactions such as $(p,2p)$ and $(p,pn)$, and the use of exclusive momentum and coincidence observables to diagnose correlations. Particular emphasis is placed on the distinction between independent-particle occupancy, long-range collective and pairing correlations, tensor-driven neutron-proton correlations, and short-range correlations generated by the repulsive core and noncentral components of the nuclear interaction. The discussion develops the overlap-function language, spectroscopic factors, eikonal stripping and diffraction, distorted-wave impulse approximation, factorization and spectral functions, center-of-mass and recoil effects, two-nucleon amplitudes, pair densities, and the relation between measured cross sections and ab initio or shell-model structure. The well-known reduction of experimental single-particle strength relative to simple shell-model expectations, its dependence on separation-energy asymmetry, and the continuing debate over reaction-model systematics are treated in detail.
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Nuclear Experiment · Cross-listed from physics.ins-det

EBS and in-beam $\gamma$-ray investigation of FCVA-prepared Cr$_2$O$_3$ targets for low-energy $^{16}$O+$^{16}$O fusion experiments

C. Wen, X. Chen, L. Wang et al. (+22 more)

The Cr$_2$O$_3$ solid target for low-energy $^{16}$O+$^{16}$O fusion experiments was fabricated using filtered cathodic vacuum arc (FCVA) deposition. Its composition, oxygen areal density and impurity content were characterized by elastic backscattering spectrometry (EBS), and the impurity-induced background contributions were investigated by in-beam $\gamma$-ray spectroscopy. EBS results indicate that the Cr$_2$O$_3$ film exhibits good stoichiometry and uniformity, with $^{16}$O areal densities ranging from $(3.24-3.25)\times10^{17}$ atoms/cm$^2$. The EBS analysis reveals a carbon atomic fraction of approximately 1.25-1.29% in the Cr$_2$O$_3$ layer, while a large amount of carbon impurities are also identified on the surface of Cr substrate. In-beam $\gamma$-ray spectra reveal prominent transitions associated with $^{27}$Al and $^{24}$Mg at 844, 1015, and 1369 keV, mainly originating from $^{12}$C+$^{16}$O fusion reactions induced by carbon impurities under $^{16}$O irradiation. Meanwhile, characteristic $\gamma$-rays emissions from evaporation channels of the $^{16}$O+$^{16}$O reaction, including $^{31}$S, $^{31}$P, and $^{28}$Si, were also observed and can be used to extract the $^{16}$O+$^{16}$O fusion cross sections. This work provides an experimental basis for the development of high-purity oxide targets and the optimization of target configurations for future low-background $^{16}$O+$^{16}$O fusion cross section measurements.
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All authors C. Wen, X. Chen, L. Wang, Z. An, F. Bai, Y. Chen, X. Fang, Y.X. Fan, B.S. Gao, Z.Y. Guo, J.F. Han, H.T. Hu, W.P. Lin, B. Liao, S. Lin, G. Liu, X.Q. Liu, P.P. Ren, J. Su, J.H. Tan, X.D. Tang, P. Wang, S. Wang, D.H. Xie, N.T. Zhang

Nuclear Experiment · Cross-listed from nucl-th

Theoretical Review on Bulk Properties and Light/Strange Hadron Production in Heavy-Ion Collisions

Yuuka Kanakubo

Since the discovery of large elliptic flow at RHIC in the early 2000s, relativistic hydrodynamics has become a central framework for quantitative studies of the quark–gluon plasma (QGP). In parallel, increasingly sophisticated analyses have improved constraints on the initial state and the transport properties of the QGP. In this contribution, I overview the recent progress on bulk-property of QGP and light/strange hadron production.
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