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Physics Nuclear Experiment

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Tuesday 22 September

Nuclear Experiment

Observation of a magnetic shift in neutron whispering-gallery states

K. Schreiner, J. A. Pioquinto, S. Baeßler et al. (+19 more)

We developed experimental and theoretical methods to create and describe high-resolution whispering-gallery interference patterns and show the feasibility of measuring their small shifts by external interactions. Such experiments can be used to search for extra fundamental interactions, time parity violations, nonzero electric charges, precisely measuring the gravitational properties of (anti)matter, parity violations, neutron polarizability, quantum reflection, surface state effects, etc. Here, we measure a magnetic shift of such a neutron pattern $\delta g/g\sim (6.5 \pm 0.8_{st} \pm 1.2_{sys}) \cdot 10^{-4}$, and our sensitivity to spin-dependent differences between the scattering lengths was $\delta b_n/b_n \sim 10^{-4}$.
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All authors K. Schreiner, J. A. Pioquinto, S. Baeßler, V. V. Nesvizhevsky, P. Clade, P. Crivelli, R. Cubitt, J. Guyomard, C. Killian, U. Miniotaite, F. Nez, E. Perry, S. Reynaud, T. Saerbeck, L. Shen, K. Stinson, J. Vivier, A. Vorobiev, J. Walsh, E. Widmann, P. Yzombard, A. Zhao

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

Scalable Terbium-149 Production from Highly Enriched Gadolinium-150 Targets

J. F. Parisi and A. Rutkowski

We propose a two-stage production method to overcome existing supply-constraints for the alpha-emitter $^{149\mathrm{g}}$Tb, a promising candidate for Targeted Alpha Therapy (TAT) with no existing globally scalable production pathway. Although awaiting experimental measurement of the $^{150}$Gd(p,2n)$^{149\mathrm{g}}$Tb cross section, the proposed method could produce $^{149\mathrm{g}}$Tb at clinical scale and beyond on readily available proton cyclotrons, enabled by production of the extinct but long-lived isotope $^{150}$Gd, a pure alpha emitter with a 1.79 million year half-life. Stage one generates $^{150}$Gd feedstock by irradiating natural Eu or enriched $^{151}$Eu with $\gtrsim$10 MeV protons, neutrons or photons. Stage two produces $^{149\mathrm{g}}$Tb from fabricated $^{150}$Gd targets by driving the $^{150}$Gd(p,2n)$^{149\mathrm{g}}$Tb reaction with $\gtrsim$14 MeV protons, accessible on over 700 reported cyclotrons worldwide. Fast fusion neutrons appear to offer the most scalable pathway for $^{150}$Gd production: even with a large $^{149 \mathrm{g}}$Tb dose size of 1 GBq and 40 million administered doses/yr, we estimate this would require neutrons produced by only 6.8 megawatts of steady-state deuterium-tritium power to produce the required $^{150}$Gd, far below expected capacity in the next decade. The route described here, if validated, would enable $^{149\mathrm{g}}$Tb supply at the scale needed to support clinical development of $^{149\mathrm{g}}$Tb-based TAT.
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Monday 21 September

Nuclear Experiment · Cross-listed from hep-ph

System-size dependence of bottomonium suppression from Pb-Pb to light-ion collisions

Nora Brambilla, Tom Magorsch and Antonio Vairo

We test the system-size dependence of bottomonium suppression using the same open-quantum-system transport framework for Pb-Pb, O-O, and Ne-Ne collisions. The microscopic transport coefficients are retained from previous Pb-Pb analyses. Using QTraj, we solve the next-to-leading-order pNRQCD Lindblad equation in anisotropic hydrodynamic backgrounds and calculate integrated $\Upsilon$ double ratios. The QGP-induced evolution reproduces the observed sequential hierarchy and overall magnitude of the O-O suppression measured by CMS and LHCb. We quantify the sensitivity to both transport coefficients and to the termination temperature of the in-medium evolution. The Ne-Ne measurement favors somewhat stronger suppression than predicted, although the present experimental uncertainty is large. The extension from Pb-Pb to light ions supports, at least for observables less sensitive to cold nuclear matter effects, a common microscopic origin of bottomonium suppression in deconfined matter, characterized by the same temperature-dependent transport coefficients despite the large change in collision-system size.
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Nuclear Experiment · Cross-listed from physics.ins-det

Pulse-shape discrimination with machine learning for CZT detectors at the DA$\Phi$NE beam test facility

Simone Manti, Francesco Artibani, Leonardo Abbene et al. (+36 more)

Cadmium zinc telluride (CZT) detectors offer versatility, operational simplicity, and room-temperature X- and gamma-ray spectroscopy, making them attractive for collider applications, yet their use under high-flux conditions remains limited. Here, we present a preliminary feature-based pulse-shape analysis employing machine learning, on data acquired with a quasi-hemispherical CZT detector at the DA$\\Phi$NE beam test facility of the National Laboratory of Frascati of INFN. A 300-MeV electron beam impinging on a lead target produced characteristic Pb X-rays together with a broad background extending up to the electron-positron annihilation region. Physically motivated temporal and morphological features were extracted from the recorded waveforms and used to distinguish nominal photon-like pulses from anomalous events. An XGBoost classifier trained and validated on 10,000 labeled waveforms achieved an accuracy of approximately 97%, with most of its classification performance reached using only a few hundred labeled examples. The trained model was applied to more than 700,000 events, substantially reducing the spectral continuum and coincidence peaks, while preserving the characteristic Pb X-ray lines up to the 511-keV annihilation peak. These preliminary results demonstrate the potential of machine-learning-assisted pulse-shape discrimination for improving CZT spectroscopy in collider environments.
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All authors Simone Manti, Francesco Artibani, Leonardo Abbene, Massimiliano Bazzi, Manuele Bettelli, Giacomo Borghi, Damir Bosnar, Mario Bragadireanu, Antonino Buttacavoli, Mario Carminati, Alberto Clozza, Francesco Clozza, Luca De Paolis, Raffaele Del Grande, Kamil Dulski, Carlo Fiorini, Ivica Friščić, Gaetano Gerardi, Carlo Guaraldo, Mihai Iliescu, Masa Iwasaki, Alexander Khreptak, Johan Marton, Pawel Moskal, Hiroaki Ohnishi, Kristian Piscicchia, Fabio Principato, Alessandro Scordo, Francesco Sgaramella, Michał Silarski, Diana Sirghi, Florin Sirghi, Magdalena Skurzok, Antonio Spallone, Kairo Toho, Oton Vazquez Doce, Andrea Zappettini, Johann Zmeskal, Catalina Curceanu

Nuclear Experiment · Cross-listed from nucl-th

Accessing zero-point fluctuations in high-energy nuclear collisions

Jean-Paul Blaizot and Jean-Yves Ollitrault

Ultracentral high-energy collisions between identical nuclei are very sensitive to the size and shape of the frozen configuration of nucleons at the instant of the collision, an information that is encoded in the ground state wave functions of the colliding nuclei. The relative standard deviation of the size of the colliding system soon after the collision has recently been inferred from event-by-event fluctuations of the momentum per particle in collisions of $^{208}$Pb nuclei at the LHC, and since a single collision event produces thousands of particles, this information is very precise. We connect this measurement to the magnitude of the zero-point fluctuations of the radius of the lead nucleus. The value that is extracted from the data is compatible with predictions from nuclear-structure calculations, but is overestimated by classical Glauber-type modeling of high-energy collisions. The role of the Pauli principle in suppressing the fluctuations is underlined. It leads to a distinctive $A$ dependence that could be checked in collisions of smaller systems.
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Nuclear Experiment · Cross-listed from nucl-th

Ruling out nucleonic direct Urca cooling in low-mass neutron stars using nuclear data

Gabriele Montefusco, Pietro Klausner, Marco Antonelli et al. (+3 more)

Connecting nuclear experiments to neutron star composition requires controlling the extrapolation of experimental information beyond the densities probed in the laboratory. We combine a broad set of nuclear structure observables and INDRA-FAZIA isospin-transport data within a Bayesian inference of the dense matter equation of state (EoS). To limit uncontrolled extrapolation to high density, we employ a flexible asymptotically causal metamodel whose neutron star posteriors are comparable to those obtained with agnostic EoS models. The nuclear structure information is propagated through its full multidimensional distribution of correlated nuclear matter parameters, while the density-dependent INDRA-FAZIA likelihood is evaluated directly along each sampled metamodel symmetry energy curve. These two sources of laboratory information give compatible constraints on the symmetry energy, and their combination preserves agreement with finite nuclear observables. When combined with ab initio chiral effective field theory calculations and astrophysical observations, all these constraints substantially improve the determination of central proton fractions in low-mass neutron stars, while leaving larger uncertainties for massive stars. Within the adopted nucleonic metamodel, the reduced probability of large proton fractions strongly disfavors electronic direct-Urca onset at or below $1.4\,M_\odot$: its posterior probability falls from $\sim20\%$ with chiral and astrophysical constraints alone to below $1\%$ when the laboratory information is included.
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All authors Gabriele Montefusco, Pietro Klausner, Marco Antonelli, Caterina Ciampi, Diego Gruyer, Francesca Gulminelli

Nuclear Experiment · Cross-listed from hep-ph

Comparative Study of Color Glass Condensate and Collinear Frameworks for Large-Transverse-Momentum Semi-Inclusive Deep Inelastic Scattering

Swagato Mukherjee, Björn Schenke and Shaswat Tiwari

We study the Semi-Inclusive Deep Inelastic Scattering (SIDIS) cross-section at large values of hadron transverse momentum $P_t \gtrsim Q$, with $Q^2$ being the photon virtuality. This kinematic regime of SIDIS allows for a collinear factorization in terms of parton distribution functions (PDFs) and collinear fragmentation functions (FFs). On the other hand, at high energies, i.e., at small Bjorken $x$, the same SIDIS process can also be factorized within the Color Glass Condensate (CGC) framework in terms of eikonal dipole amplitudes. In this work, we perform a systematic comparison of the leading-order (LO) and next-to-leading-order (NLO) collinear and the LO CGC factorizations of this process based on the COMPASS and HERA data. We further provide comparisons of these two factorization frameworks for nucleon and nuclear large-$P_t$ SIDIS in the expected Electron Ion Collider (EIC) kinematics. We find, within the present theoretical uncertainties, that it might be difficult to distinguish between these two factorization schemes for nuclear SIDIS at the EIC. We also observe a significant dependence of the LO eikonal CGC predictions on the choice of longitudinal momentum fraction $x_g$, suggesting significant beyond-eikonal corrections for the EIC kinematics.
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Nuclear Experiment · Cross-listed from nucl-th

Flow plus coalescence explain hadron nuclear modification and high-$p_T$ anisotropy

Wilke van der Schee and Isobel Kolbé

It has long been a puzzle why the nuclear modification factor in relativistic $p$Pb collisions is consistent with unity, while the high-$p_T$ elliptic flow is significantly positive. The latter is traditionally interpreted as path-length-dependent energy loss, whereas the former is consistent with zero energy loss. In this Letter, we propose that even at high $p_T$ a hard parton coalesces with a boosted thermal medium parton whose energy is correlated with the angle-dependent radial flow. We compare this flow for $pp$, $p$Pb, $p$O, OO and PbPb collision systems and conclude in particular that the $p$Pb flow is large and anisotropic. The collective medium pushes out the hard partons, and more so in $p$Pb, or in-plane, than in $pp$ collisions, or out-of-plane. The mechanism qualitatively agrees with experiment and predicts a significantly smaller elliptic flow signal for jets than for hadrons.
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Nuclear Experiment

Jet-like di-hadron correlations in pO, OO, and Ne–Ne collisions

Suraj Prasad for the ALICE Collaboration

Heavy-ion collisions are primarily studied to investigate the properties of hot and dense nuclear matter, known as the quark–gluon plasma (QGP). However, recent observations of hydrodynamic flow-like behaviour in pp and p–Pb collisions at the LHC suggest the possible formation of QGP droplets even in small collision systems. To bridge the multiplicity gap between small and large systems and to examine the applicability of hydrodynamic descriptions, light-ion collisions were performed for the first time at the LHC in 2025. This contribution presents measurements of the near-side peak width of di-hadron correlations in pO, OO, and Ne–Ne collisions with ALICE, used to search for medium effects. The width of the near-side correlation peak is studied as a function of the average charged-particle multiplicity at midrapidity. At low transverse momentum ($p_{\rm T}$), the near-side peak is broader in OO and Ne–Ne collisions than in pp and pO collisions, and in central collisions its width approaches that measured in Pb–Pb collisions. At higher $p_{\rm T}$ the peak narrows modestly with increasing multiplicity. The results are compared with PYTHIA, AMPT, and JETSCAPE calculations, none of which reproduces the measured widths over the full kinematic range.
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Sunday 20 September

Nuclear Experiment · Cross-listed from physics.data-an

$\beta$-Oslo and Shape analyses with unresolved parent-state mixtures

Yangping Shen

An unresolved mixture of beta-decaying ground and isomeric states populates a common daughter nucleus through different excitation-energy and spin-parity distributions. A framework is developed to determine when such data admit conventional $\beta$-Oslo and Shape analyses and which quantities remain identifiable. The physical primary-$\gamma$ distribution is an average of separately normalized branching kernels; the global parent fraction does not, in general, equal the fraction in an excitation-energy bin or an accepted primary-$\gamma$ sample. Population invariance, Oslo factorization, and recovery of the total nuclear level density are separated. An exact log-linear compatibility test and a lower-cascade replacement identity isolate factorization and first-generation-subtraction effects. For Shape analysis, matched final-state spins and parities remove common angular-momentum factors but can retain excitation-dependent E1/M1 weights. A graph representation gives consistency conditions and exposes the information lost when only one fixed final-state separation is measured. Deterministic spin-parity-resolved cascade benchmarks reproduce the population-invariant limit and exhibit both exact factorization with an effective, rather than total, level density and small matrix residuals accompanied by appreciable shape errors. Evaluated $\rb\rightarrow\sr$ properties specify a relevant application, including two $2^+$ candidate final states and time-dependent parent mixing. The numerical examples are controlled synthetic tests, not an extraction from $^{90}$Rb data. The results provide criteria for interpreting unresolved-parent measurements and for identifying the additional observations required for population-aware inference.
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Nuclear Experiment

Electromagnetic transition strength in $^{53}$Ca: the lifetime of the $5/2^{-}$ state

S. Chen, M. Petri, S. Paschalis et al. (+36 more)

High-resolution in-beam ${\gamma}$-ray spectroscopy of $^{53}$Ca was performed at the Radioactive Isotope Beam Factory (RIBF) at RIKEN. Excited states in $^{53}$Ca were populated via one-neutron and one-proton removal reactions from a $^{55}$Sc radioactive beam, and the emitted ${\gamma}$ rays were detected using the HiCARI hybrid germanium detector array. The lifetime of the first excited $5/2^{-}$ state in $^{53}$Ca was measured for the first time through an analysis of Doppler-roadened ${\gamma}$-ray line shapes arising from relativistic recoil velocities. A lifetime of ${\tau} = 11.3_{-11.3}^{+5.3(stat)+3(sys)}$ ps was deduced, corresponding to a reduced transition probability of $B(E2;5/2^{-}{\rightarrow}1/2^{-}) > 2.6 e^{2}fm^{4}$ at the 1${\sigma}$ level, with a best-fit value of $4.5 e^{2}fm^{4}$. The measured transition strength is compared with state-of-the-art shell-model and ab initio calculations, providing a stringent benchmark for shell-model Hamiltonians and effective charges and modern ab initio descriptions of the neutron-rich calcium isotopes approaching the potential $N$ = 40 shell closure.
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All authors S. Chen, M. Petri, S. Paschalis, H. L. Crawford, P. Doornenbal, R. Taniuchi, K. Wimmer, B. A. Brown, J. D. Holt, B. S. Hu, T. Miyagi, T. Otsuka, Y. Tsunoda, N. Aoi, H. Baba, M. Bentley, F. Browne, C. Campbell, Z. Chen, R. Crane, H. de Witte, P. Fallon, C. Fransen, H. Hess, E. Ideguchi, S. Iwazaki, J. Kim, A. Kohda, T. Koiwai, W. Marshall, B. Mauss, B. Moon, T. Parry, P. Reiter, H. Sakurai, D. Suzuki, L. Tetley, S. Thiel, Y. Yamamoto

Nuclear Experiment · Cross-listed from nucl-th

Dynamical Coulomb effects on charged-pion HBT-radius splitting in central Au+Au collisions at few-GeV energies

Pengcheng Li, Yongjia Wang and Qingfeng Li

The pair transverse momentum ($k_T$) and collision-energy ($\sqrt{s_{NN}}$) dependent difference between $\pi^{+}\pi^{+}$ and $\pi^{-}\pi^{-}$ femtoscopic correlations was observed by the HADES and STAR Collaborations. We investigate how much of the observed splitting can be accounted for by Coulomb dynamics in 0-10% central Au+Au collisions at $\sqrt{s_{NN}}=2.42$-5.2 GeV. Using the UrQMD model and the CRAB programme, three transport scenarios that successively include baryon-baryon, baryon-meson, and meson-meson Coulomb interactions are considered. In a separate calculation based on the baryon-baryon reference, we reconstruct the time-dependent effective charge $Z_{\rm{eff}}(t)$ and radius $R_{\rm{eff}}(t)$ of the residual charged source and propagate each pion from its individual last strong-interaction point through the evolving field. The calculations reproduce the main $k_{T}$ and $\sqrt{s_{NN}}$ dependences of the radii. Baryon–meson Coulomb interactions generate most of the additional charge splitting in the microscopic calculation. The residual-source treatment also enhances the longitudinal and sideward radius ratios relative to the reference, whereas the outward ratio changes little, and the enhancement generally decreases with increasing $\sqrt{s_{NN}}$. Within the present framework, this contribution does not fully account for the data, motivating further investigation of the charged-source geometry and its interplay with strong-interaction dynamics.
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Saturday 19 September

Nuclear Experiment · Cross-listed from hep-lat

Gradient Flow for the Jet Transport Coefficient: A Quenched Lattice Benchmark

Hai-Tao Shu and Cheng Zhang

We apply the gradient-flow framework to determine the nonperturbative medium contribution to the jet transport coefficient $\hat q$ using quenched lattice QCD in the temperature range $0.76T_c \leq T \leq 2.25T_c$. The calculation focuses on the leading-twist contribution at leading order for an asymptotically energetic quark propagating through a thermal pure-gluon plasma. In the infinite-energy limit, the operator-product expansion expresses $\hat q/T^3$ in pure gauge theory as the product of a perturbative short-distance coefficient and the entropy density $s/T^3$. The latter is determined from the gradient-flow energy-momentum tensor at three lattice spacings for each temperature and the former is estimated perturbatively at one-loop order. We find that $\hat q/T^3$ is strongly suppressed below $T_c$, rises rapidly across the deconfinement transition, and remains approximately constant at $\hat q/T^3\simeq1.1$ throughout the deconfined temperature range studied. This is statistically consistent with the previous quenched lattice determination based on a different renormalization procedure, providing a nontrivial validation of the gradient-flow framework for the jet transport coefficient. The systematic treatment of operator renormalization and matching provided by gradient flow becomes particularly important in full QCD, because the need to renormalize quark operators and account for their mixing with the gluonic sector can likewise be addressed within the same framework.
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Nuclear Experiment · Cross-listed from hep-ex

Benchmarking Nucleon Production in Hadron Interactions Relevant for GeV-scale Neutrino Experiments

Richard Diurba, Steve Dytman, Matthew King et al. (+1 more)

In neutrino scattering experiments, the emitted final state particles are essential for identifying interaction channels and reconstructing neutrino energies. During intranuclear propagation, neutrino-induced hadrons can interact with surrounding nucleons, altering both the number of final state particles and detectable energy depositions. As a result, neutrino experiments rely on hadron-nucleus scattering models to simulate these nuclear effects. This paper explores nucleon production predicted by hadron scattering models for common hadrons in neutrino experiments, specifically nucleons and pions. We investigate these models with simulations from the GENIE neutrino event generator, which includes implementations of Geant4 Bertini Cascade and INCL++. For popular target nuclei, we find that the number of emitted nucleons for mesonless hadron interactions can be parameterized by simple Gaussian and exponential decay functions. We present these relationships and provide reweighting tools for addressing the hadron scattering model spread in both visible energy and final state nucleon multiplicities.
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All authors Richard Diurba, Steve Dytman, Matthew King, Yinrui Liu

Friday 18 September

Nuclear Experiment · Cross-listed from hep-ph

Machine Learning for Invisible Dark Boson Searches at the Electron-Ion Collider

Rojae Mighty and Ankush Reddy Kanuganti

We investigate whether adding $t$, the positive magnitude of the squared nuclear four-momentum transfer, enables boosted decision trees (BDTs) to improve invisible-dark-boson selection relative to optimized rectangular cuts at the Electron-Ion Collider. We model coherent exclusive scalar and vector production at generator level in electron-gold collisions at 18 GeV by 100 GeV per nucleon. Both methods use identical weighted samples, inputs, preselection, and optimization objectives. Using only electron information, the BDT provided no consistent advantage over optimized cuts for signal selection across 11 masses for each boson type. When both methods also use $t$, the BDT distinguishes signal from background slightly better than optimized cuts at 10 GeV for both boson types. These results motivate further investigation of machine learning in EIC dark-boson searches through exclusive processes where $t$ can be reconstructed.
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Nuclear Experiment · Cross-listed from nucl-th

Probing the nucleon axial form factor via the $\vec{e}^{\,+} + {}^2\text{H} \rightarrow \bar{\nu}_e + p + p$ reaction below the pion-production threshold

A. M. Ankowski, J. Golak, E. Pérez del Rio et al. (+7 more)

The nucleon axial form factor $F_A(Q^2)$ is a primary source of systematic uncertainty in charged-current quasielastic interactions, of critical importance for long-baseline neutrino-oscillation studies. Its low-$Q^2$ behavior is particularly problematic to pin down in neutrino measurements. To address this limitation, we investigate the weak process of polarized positron capture on the deuteron, $\vec{e}^{\,+} + {}^2\text{H} \rightarrow \bar{\nu}_e + p + p$. Employing a relativistic momentum-space formalism, we present predictions for the total cross section. Focusing on the kinematic regime free from pion-production backgrounds, we analyze various differential cross sections and their sensitivity to the $F_A(Q^2)$ variation. Our results demonstrate that thanks to the positron upgrade, Jefferson Lab will gain a unique position to make inroads into determining the low-$Q^2$ behavior of the axial form factor.
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All authors A. M. Ankowski, J. Golak, E. Pérez del Rio, S. Sharma, R. Skibiński, K. Topolnicki, H. Witała, W. N. Polyzou, H. Kamada, D. Dutta

Nuclear Experiment · Cross-listed from hep-ph

Coherent deeply virtual Compton scattering on helium-4 beyond the leading twist approximation

V.Martínez-Fernández, B.Pire, P.Sznajder et al. (+1 more)

Coherent hard exclusive reactions on light nuclei offer access to their quark and gluon structure and provide a framework for three-dimensional nuclear tomography. We analyze deeply virtual Compton scattering on a helium-4 target, including leading-twist contributions as well as kinematical twist-3 and twist-4 effects. We present numerical estimates of cross sections and asymmetries for kinematic regimes relevant to JLab experiments. We emphasize the importance of next to leading order (NLO) and kinematical twist 3 and 4 contributions to interpret data in the JLab kinematics. We deduce a first tomographic image of quarks and gluons in the helium-4 nucleus.
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All authors V.Martínez-Fernández, B.Pire, P.Sznajder, J.Wagner

Nuclear Experiment

First observation of the fine structure of the Pygmy Dipole Resonance in a nucleus away from stability via the $\beta^-$ decay of $^{92}$Rb to $^{92}$Sr

P. Spagnoletti, M. Ramalho, S. Tahtela et al. (+52 more)

A comprehensive $\gamma$-ray spectroscopy study of excited states in $^{92}$Sr populated via $\beta^-$ decay of $^{92}$Rb ($J^{\pi}=0^-$, $Q_{\beta}=8095(6)$~keV) was performed with the GRIFFIN spectrometer at the Isotope Separator and Accelerator (ISAC) radioactive ion beam facility at TRIUMF. The high $\gamma$-ray efficiency of the GRIFFIN spectrometer combined with the intense rubidium beams produced allowed for 864 $\gamma$-ray transitions to be placed in the level scheme with 190 excited levels populated, most of them identified for the first time. The excitation energies of low-spin states in $^{92}$Sr are well reproduced by large-scale Shell Model calculations up to 5~MeV. The $\beta$-feeding intensities are in very good agreement with results from a recent study employing Modular Total Absorption Spectroscopy, indicating a significant suppression of the Pandemonium effect. The experimental picture reveals the energy level dependence of log~$ft$ values in unprecedented detail. These log~$ft$ values are well reproduced by Multiple-Commutator Model calculations that identify the features in the excited levels' wavefunctions that enable the population of high-lying levels with a low effective Q-value that belong to the Pygmy Dipole Resonance.
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All authors P. Spagnoletti, M. Ramalho, S. Tahtela, E. Kauppinen, J. Suhonen, C. Andreoiu, M. Scheck, V. Vedia, Z. Ahmed, D. Annen, G.C. Ball, G. Benzoni, S.S. Bhattacharjee, H. Bidaman, V. Bildstein, S. Buck, R. Caballero-Folch, R.J. Coleman, S. Devinyak, I. Dillmann, I. Djianto, F.H. Garcia, A.B. Garnsworthy, P.E. Garrett, B. Greaves, C.J. Griffin, G.F. Grinyer, E.G. Fuakye, G. Hackman, D. Hymers, D. Kalaydjieva, R. Kanungo, K. Kapoor, E. Kasanda, W. Korten, N. Marchini, K. Mashtakov, A. Nannini, K. Ortner, B. Olaizola, C. Natzke, C.M. Petrache, M. Polettini, A. Radich, M. Rocchini, N. Saei, M. Satrazani, M. Siciliano, M. Singh, C.E. Svensson, D.A. Torres, R. Umashankar, E. Wadge, T. Zidar, M. Zielinska

Nuclear Experiment

Direct measurement of Enhanced octupole collectivity in 148Dy

P. Spagnoletti, V. Vedia, E. Yuksel et al. (+36 more)

Excited states in $^{148}_{~66}$Dy were populated via $\beta^+/EC$ decay of $^{148m}$Ho using the GRIFFIN spectrometer at the TRIUMF ISAC-I facility. A combined measurement of the mean lifetime of the $3_1^-$ level using the Generalized Centroid Difference (GCD) method and branching fraction of the $3_1^-\rightarrow0_1^+$ $\gamma$-ray decay has been performed. From these results, an enhanced electric octupole $B(E3;3_1^-\rightarrow0_1^+)$ transition strength of 46(3)~W.u. has been determined in $^{148}_{~66}$Dy. This is the largest measured value across the closed neutron shell at $N=82$ and provides direct evidence of enhanced octupole collectivity beyond $Z=64$. The evolution of the $B(E3; 3^-_1 \rightarrow 0^+_1)$ strength along the $N=82$ isotonic chain is compared with quasiparticle random-phase approximation (QRPA) calculations using the SkI3 and SkM$^*$ Skyrme energy-density functionals, as well as with large-scale shell-model (SM) calculations. This result extends the boundaries of enhanced octupole collectivity far from the so-called `octupole magic numbers' $Z=56$ and $N=88$.
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All authors P. Spagnoletti, V. Vedia, E. Yuksel, Y. X. Yu, G. J. Fu, R. Umashankar, G. Andreetta, C. Andreoiu, A.A. Avaa, G.C. Ball, V. Bildstein, S. Buck, E. Cantacuzene, G. Colombi, I. Dillmann, L. P. Gaffney, A.B. Garnsworthy, P.E. Garrett, G.F. Grinyer, G. Hackman, J. Liu, A. Ludlam, L.L. Luperi, Madhu, T. La Marca, D. Movilla-Quintero, S. Murillo Morales, R. Nicolas del Alamo, M.M. Rajabali, P.H. Regan, M. Rocchini, M. Scheck, J. Seger, S. Sekal, D. Stramaccioni, C.E. Svensson, A. Tsantiri, J. Williams, F. Wu

Thursday 17 September

Nuclear Experiment · Cross-listed from hep-ph

Jet transport coefficients associated with fermionic two-point correlators in a weakly-coupled plasma

Shay Duddy, Lukas Opitz, Amit Kumar et al. (+1 more)

A new set of jet-medium transport coefficients stemming from jet-medium exchanges involving Glauber quarks encoded in $\hat{\mathcal{F}}_i$ [Phys. Rev. C 111, 054913 (2025), Phys. Rev. C 113, 055207] are obtained by computing the tree-level leading-order $2\to2$ scattering rates and their moments using the approach developed in Refs. [arxiv 2608.17160, arxiv 2608.17161]. Sizeable deviations away from the leading logarithmic dependence of jet-medium transport coefficients and scattering rate are observed here, as previously mentioned in Refs.[arxiv 2608.17160, arxiv 2608.17161]. A closed-form expression for $\hat{\mathcal{F}}_i$ accurate to $\lesssim 10$% or better is obtained, enabling our approach to be used within Monte Carlo simulations of jet-medium interactions. Monte Carlo simulations incorporating $\hat{\mathcal{F}}_i$ are sensitive to flavor hydrodynamization dynamics as the medium created in nucleus-nucleus collisions transitions from the early-time Glasma dynamics to the quark-gluon plasma fluid.
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All authors Shay Duddy, Lukas Opitz, Amit Kumar, Gojko Vujanovic

Nuclear Experiment · Cross-listed from nucl-th

A comprehensive theory framework for perturbative calculations of $\delta_C$ in superallowed beta decays

Chien-Yeah Seng

The present high precision determination of $|V_{ud}|$ from superallowed beta decays of $J^P=0^+$, $T=1$ nuclei is largely built on top of the “standard” calculation of the isospin breaking correction $\delta_C$ to the Fermi matrix element, which assumes the splitting $\delta_C=\delta_{C1}+\delta_{C2}$, where $\delta_{C1}$ and $\delta_{C2}$ represent the “isospin mixing” correction and the “radial mismatch” correction, respectively. In this paper I show that this formalism violates the rule of nucleon basis independence, similar to the gauge invariance requirement in quantum field theory, therefore its outcome is inevitably subject to uncontrolled systematic errors. I further argue that the perturbative formalism is the only approach that allows the computation of $\delta_C$ at the precision level required for the test of the Cabibbo unitarity. Advancing from existing literature, I develop the full “generating function approach” to compute $\delta_C$ perturbatively, with connections to nuclear mass splittings and the isospin breaking in nuclear charge radii as theory benchmarks.
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Nuclear Experiment · Cross-listed from nucl-th

Gaussian characterization of two-neutron halo nuclei

A. Deltuva, M. Gattobigio, D. Jurčiukonis et al. (+1 more)

The halo nucleon-core system is, by definition, a shallow state nucleus. The nucleon, in most cases a neutron, is loosely bound to the other nucleons forming the core. Accordingly, the system is located inside the universal window; the halo nucleon most likely resides far from the rest of the nucleons, showing a remarkable insensitivity to details of the interaction with the core. The system can be described using a simple nucleon-core interaction, and this description can be extended to the nucleon-nucleon-core system. Specifically, treating the neutron-core and the neutron-neutron-core systems with a Gaussian interaction as a reference, we show trajectories inside the universal window governed by interaction parameters determined from low-energy observables, such as the neutron-core binding energy, scattering length, and effective range. In this way, we can relate properties of different halo nuclei that might seem uncorrelated. In particular, we determine the three-body parameter, the binding momentum at the unitary limit, and show that the two-neutron halo nuclei emerge from that limit following a linear trajectory depending on the neutron-core range.
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All authors A. Deltuva, M. Gattobigio, D. Jurčiukonis, A. Kievsky

Nuclear Experiment · Cross-listed from hep-ph

Generalized parton distributions: Theory meets experiment

Yuxun Guo, Xiangdong Ji, Yao Ji et al. (+1 more)

Over the past three decades, generalized parton distributions (GPDs) have emerged as one of the most active and important areas of research in nucleon structure and quantum chromodynamics (QCD). Since the last comprehensive review two decades ago, substantial progress has been made in experimental measurements of hard exclusive processes, such as deeply virtual Compton scattering and near-threshold $J/\psi$ production, as well as in increasingly sophisticated phenomenological analyses of GPDs that enable three-dimensional nucleon tomography. Theoretical advances in perturbative coefficient functions, scale evolutions, and kinematic and power corrections have considerably improved the precision of GPD phenomenology, while new hard exclusive processes for probing GPDs have been explored. More interestingly, lattice QCD can now directly access GPDs at fixed parton momentum fractions $x$ and skewness $\xi$ through large-momentum expansions, in addition to the traditional calculations of their moments, or generalized form factors. Significant progress has also been made in exploring the QCD energy-momentum tensor that encodes fundamental information on the nucleon's mass distribution, complete spin structure, and spatial distributions of momentum current and color-Lorentz forces acting on quarks and gluons.
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All authors Yuxun Guo, Xiangdong Ji, Yao Ji, Jialu Zhang

Wednesday 16 September

Nuclear Experiment

Measurements of $\gamma_v p \to \pi^+ \pi^-p'$ Cross Sections with the CLAS12 Detector for $Q^2$ from 2.4-8.0 GeV$^2$ and $W$ from 1.4-2.1 GeV

K. Neupane, R.W. Gothe, D.S. Carman et al. (+145 more)

This paper reports exclusive cross sections for the $ep \to e'\pi^+\pi^-p'$ reaction using the CLAS12 detector at Jefferson Laboratory. The extractions of fully integrated and nine single-differential cross sections are presented for the first time for photon virtualities $Q^2$ from 2.4 to 8.0 GeV$^2$ and center-of-mass energies $W$ from 1.4 to 2.1 GeV, which covers a large part of the nucleon resonance region. These data considerably extend the kinematic reach of previous measurements from CLAS that covered $Q^2$ up to 5.0 GeV$^2$. Exclusive $\gamma_v p \to \pi^+ \pi^-p'$ cross section measurements are of particular importance for the extraction of $\gamma_vpN^*$ resonance electrocouplings across the $N^*$ spectrum, especially in the mass range above 1.6 GeV where several resonances decay preferentially to the $\pi\pi N$ final states. The electrocouplings with extended $Q^2$ coverage expected from these new data will enable an improved understanding of the emergence of $N^*$ mass and structure in the transition from the strongly coupled toward the perturbative QCD regime.
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All authors K. Neupane, R.W. Gothe, D.S. Carman, V.I. Mokeev, A.G. Acar, P. Achenbach, J.S. Alvarado, W.R. Armstrong, H. Avakian, N.A. Baltzell, L. Barion, M. Bashkanov, M. Battaglieri, F. Benmokhtar, A. Bianconi, A.S. Biselli, A. Biswas, F. Bossù, S. Boiarinov, M. Bondi, K.-Th. Brinkmann, W.J. Briscoe, W.K. Brooks, J. Bryce, N.L. Bucuru R., V.D. Burkert, T. Cao, A. Celentano, P. Chatagnon, V. Chesnokov, H. Chinchay, G. Ciullo, E.W. Cline, P.L. Cole, M. Contalbrigo, A. D'Angelo, N. Dashyan, R. De Vita, A. Deur, S. Diehl, C. Dilks, C. Djalali, R. Dupre, H. Egiyan, M. Ehrhart, A. El Alaoui, L. El Fassi, L. Elouadrhiri, C. Fanelli, M. Farooq, S. Fegan, I.P. Fernando, E. Ferrand, A. Filippi, M. Filippini, C. Fogler, S. Frantzen, K. Gates, G.P. Gilfoyle, D.I. Glazier, Y. Gotra, S. Gramigna, B. Gualtieri, K. Hafidi, F. Hauenstein, T.B. Hayward, D. Heddle, T. Hellstern, M. Hoballah, M. Holtrop, Y. Ilieva, D.G. Ireland, E.L. Isupov, H.S. Jo, T. Kageya, M. Kerr, V. Klimenko, A. Kripko, V. Kubarovsky, C. Lama, L. Lanza, S. Lee, P. Lenisa, X. Li, D. Martiryan, V. Mascagna, M. Masud, B. McKinnon, A. Mehta, R.G. Milner, R. Milton, M. Mirazita, E.F. Molina Cardenas, C. Munoz Camacho, P. Nadel-Turonski, T. Nagorna, S. Niccolai, G. Niculescu, M. Osipenko, A. Osmond, P. Pandey, M. Paolone, L.L. Pappalardo, R. Paremuzyan, E. Pasyuk, C. Paudel, S.J. Paul, N. Pilleux, L. Polizzi, J. Poudel, Y. Prok, A. Radic, K. Ramage, B.A. Raue, M. Ripani, M. Ronayette, P. Rossi, A.A. Rusova, C. Salgado, S. Schadmand, A. Schmidt, Y.G. Sharabian, S. Shrestha, U. Shrestha, E. Sidoretti, Iu.A. Skorodumina, N. Sparveris, S. Stepanyan, I.I. Strakovsky, S. Strauch, M. Tenorio, F. Touchte Codjo, N. Tyler, R. Tyson, M. Ungaro, S. Vallarino, C. Velasquez, L. Venturelli, H. Voskanyan, E. Voutier, Y. Wang, D.P. Watts, U. Weerasinghe, X. Wei, N. Wuerfel, Z. Xu, Z.W. Zhao, M. Zurek

Nuclear Experiment · Cross-listed from nucl-th

Three-State Mixing as a Phenomenological Framework for Multiple Shape Coexistence

Marco Siciliano

Shape coexistence represents one of the most striking manifestations of competing collective and single-particle degrees of freedom in atomic nuclei. While the coexistence and mixing of two configurations can be described within the well-established Two-State Mixing framework, the observation of three or more competing structures requires a more general treatment. In this work, we introduce a Three-State Mixing (3SM) model in which three intrinsic configurations are related to the physical states through an $SO(3)$ rotation. The framework establishes a direct connection between experimental observables, configuration-mixing amplitudes, and intrinsic properties, while the experimentally known excitation energies allow the corresponding effective Hamiltonian and interaction strengths to be reconstructed. The model is applied to the low-lying structure of $^{116}$Sn using electromagnetic matrix elements recently determined through a comprehensive Coulomb-excitation measurement. The analysis identifies three intrinsic configurations characterized by spherical, weakly oblate, and strongly deformed triaxial shapes, together with substantial configuration mixing among the physical $0^+$ states. The present formulation provides a general phenomenological framework for investigating systems in which multiple configurations coexist and strongly interact.
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Nuclear Experiment · Cross-listed from stat.ME

Binning-Independent Bayesian Analysis of Time-Dependent Perturbed Angular Distribution data

Franziskus von Spee

We propose a new approach for analyzing Time-Dependent Perturbed Angular Distribution data. In this, a likelihood is constructed with the help of conditional probabilities of single events and binning of time data is avoided. This likelihood is used in a Bayesian framework to calculate the posterior probability density function for the $g$ factor of interest. This approach is compared to more traditional approaches that use binned data by analyzing simulated datasets. In many cases the resulting posterior probability densities are observed to be multimodal and the results can thus often not be summarized with a single Gaussian approximation. We find that results from the new approach are more reliable for low-statistics datasets.
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Nuclear Experiment · Cross-listed from nucl-th

From Nuclear Many-Body Correlations to Energy Detector Correlators

João Barata and Giuliano Giacalone

Relativistic nuclear collisions have opened an experimental arena for studying many-body correlations in nuclear ground states. However, the connection between initial-state correlations and final-state multi-particle observables measured at colliders is not yet formulated as a systematically improvable matching problem. We show that detector correlators built from asymptotic energy flows provide a natural framework for realizing such a construction. In particular, we express the asymptotic energy flow as a functional of the early-time stress tensor, and expand it in suitable modes to recover the familiar linear hydrodynamic relations at leading order. Then, motivated by small-$x$ QCD, we map angular projections of detector correlators to multipole-operator correlators computed in the colliding nuclei. We thus establish a systematic formalism for matching long-wavelength correlations between incoming and outgoing QCD states in high-energy hadronic collisions.
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Nuclear Experiment · Cross-listed from physics.ins-det

On the importance of cosmic-ray background in the Atomki anomaly

Hicham Benmansour, Gianluigi Boca, Gianluca Cavoto et al. (+8 more)

We report Geant4-based simulations of cosmic-ray muon backgrounds in models reproducing the geometries of the five-arm and six-arm e+e- pair spectrometers operated by the Atomki group at Debrecen. Full detector geometries are implemented for both setups, including position-sensitive detectors and plastic scintillators. In both configurations, cosmic muons generating two-arm coincidences produce statistically significant excesses in the opening-angle distribution whose positions are determined by the discrete azimuthal arrangement of detector arms and the plastic scintillators dimensions: in the six-arm spectrometer a peak appears near 140 degrees when the scintillator energy sum is selected in the 8Be transition window (16-20 MeV) and is suppressed for energy-asymmetric pairs, while a distinct peak near 120 degrees emerges in the 4He window (18-22 MeV), with no comparable enhancement in the respective background energy region. These angles, asymmetry dependences, and background characteristics show behaviours similar to those reported by the Atomki group as evidence for a 17 MeV boson. For the five-arm setup, a 140-degree excess is also reproduced at 8Be energies, and normalizing internal pair conversion events and cosmic coincidences to typical Atomki running conditions yields a cosmic-to-IPC ratio above unity in the signal window, indicating that the cosmic background is a leading contribution to the event rate at the energies and angles of interest. While they do not settle the question of the origin of the Atomki excesses, these results highlight the critical importance of a robust cosmic-ray treatment in this type of measurements, and call for a detailed description of the beam-off studies supporting the search for anomalies in the opening-angle vs. energy-sum distribution around the signal region.
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All authors Hicham Benmansour, Gianluigi Boca, Gianluca Cavoto, Marco Chiappini, Elia G. Grandoni, Luca Galli, Giovanni Gallucci, Angela Papa, Francesco Renga, Antoine Venturini, Cecilia Voena

Nuclear Experiment · Cross-listed from hep-ph

Internal structure of exotic hadron candidate $f_0$(980) by using fragmentation functions

S. Kumano

High-energy hadron reactions could be appropriate to find exotic evidences in exotic hadron candidates instead of global observables such as masses, spins, parities, and decay widths, because quarks and gluons are explicit degrees of freedom. One of possible methods is to use fragmentation functions (FFs) by taking advantage of properties on favored and disfavored functions, which corresponds to valence-quark and sea-quark distributions in parton distribution functions. Looking at these FFs, we should be able to find the exotic nature as the valence-quark distributions reflect the nature of valence constituents as shown in the pion and the proton. Recent accurate measurements of the $f_0$(980) FFs by the Belle collaboration made it possible to find its internal configuration by looking at their second moments and functional forms. Global analysis results of the $f_0$(980) FFs indicate that its internal configuration looks like $s\bar s$, which is different from a tetraquark or $K\bar K$-molecule like configuration suggested from low-energy studies. This fact indicates that the internal configuration looks different depending on the energy. At low energies, it looks like a tetraquark ($K\bar K$ molecule) hadron, but it looks like a $q\bar q$ hadron at high energies. In the similar way, some exotic hadron candidates could become ordinary $q\bar q$ or $qqq$ hadrons at high energies, although they are interpreted as exotic at low energies. This kind of new idea should be tested by future experiments especially by looking at energy or momentum dependencies in high energy hadron reactions.
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Nuclear Experiment · Cross-listed from hep-ph

Nuclear modifications on longitudinal-transverse structure-function ratio $R$ in the deuteron

S. Kumano

In lepton scattering from nuclei, it has been taken for granted that nuclear modifications do not exist for the longitudinal-transverse structure-function ratio $R$, although nuclear effects in $F_2$ have been investigated for a long time. In fact, experimental data of lepton-nucleus scattering have been analyzed with this assumption. It is obviously not appropriate because nuclear modifications exist in the function $R$ theoretically as shown in this work. In this work, we explain nucleon's Fermi motion's effects by using a convolution description for nuclear structure functions, especially on the deuteron. The longitudinal and transverse structure functions are defined by taking the virtual photon momentum direction along the $z$ axis. However, nucleons in a nucleus could move in any direction, so that nucleon's longitudinal and transverse structure functions could mix with each other in the nuclear medium. Such mixing effects could be of the order of $\vec p_\perp^{\,2}/Q^2$, where $\vec p_\perp$ is the nucleon's transverse momentum and $Q^2$ is given by $Q^2=-q^2$ with the virtual-photon momentum $q$, because the transverse Fermi-motion is the source of such a mixture. In addition, nuclear effects are different between the longitudinal and transverse structure functions in the convolution model because their $x$-dependent functional forms are different. Convolution integrals have different results between the longitudinal and transverse structure functions for nuclei. Because the experiment is in progress at the Thomas Jefferson National Accelerator Facility to measure the function $R$ for the deuteron, the numerical results are shown on the nuclear effects of $R$ in the deuteron. Hopefully, such nuclear effects are found experimentally by future experiments including heavy nuclear targets.
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